Abstract:
A multiple-input and multiple-output (MIMO) transmission apparatus includes a modulation signal generating section and a MIMO transmitting section. The modulation signal generating section generates: (i) a first OFDM modulation signal, in which a plurality of subcarriers include a subcarrier carrying a pilot symbol and a subcarrier carrying a data symbol, in both a first time period and a second time period; and (ii) a second OFDM modulation signal, in which the plurality of subcarriers include a subcarrier carrying a pilot symbol and a subcarrier carrying a data symbol in the first time period, while in the second time period an in-phase component and a quadrature-phase component of every subcarrier included in the plurality of subcarriers are zero. The MIMO transmitting section transmits the first OFDM modulation signal from a first antenna and transmits the second OFDM modulation signal from a second antenna.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 10/486,896, filed Feb. 17, 2004, which application is incorporated herein by reference in its entirety and which is a U.S. National Phase Application of PCT International Application PCT/JP02/11825, filed Nov. 13, 2002. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a transmission method for multiplexing modulation signals of a plurality of channels to the same frequency band, a transmission apparatus and a reception apparatus. 
     BACKGROUND ART 
     This kind of transmission method and reception method have been available such as the ones disclosed in Japanese Patent Application Non-Examined Publication No. 2002-44051.  FIG. 87  illustrates the transmission method and the reception method disclosed in the foregoing publication. 
     In  FIG. 87 , first space-time encoder STE 1  ( 8705 ) receives first data block b 1  [n, k], and second space-time encoder STE 2  ( 8707 ) receives second data block b 2  [n, k], and two signals coded by encoders STE 1  and STE  2  respectively are modulated by inverse fast Fourier transformers IFFT ( 8708 - 8711 ). Then the modulated signals are transmitted as OFDM (orthogonal frequency division multiplexing) signals by four transmitting antennas TA 1  ( 8712 )-TA 4  ( 8715 ). 
     A plurality of receiving antennas RA 1  ( 8701 )-RAP ( 8703 ) receive those signals transmitted by antennas TA 1  ( 8712 )-TA 4  ( 8715 ). Reception signals r 1  [n, k] ( 8716 )-rp ( 8718 ) are transformed by fast Fourier transformation (FET) sub-systems FFT 1  ( 8719 )-FFTp ( 8721 ) respectively, and supplied to space-time processor STP ( 8722 ). Processor STP ( 8722 ) detects signal information and supplies it to first and second space-time decoders STD 1  ( 8723 ) and STD 2  ( 8724 ). Channel parameter estimation unit CPE ( 8725 ) receives the transformed signal, and determines channel-parameter information, then supplies the information to the space-time processor STP ( 8722 ) for demodulating the signals. 
     However, the foregoing conventional structure gives no thought to the synchronization between channels in the same frequency band as well as a frequency offset. As a result, this structure encounters the difficulty of achieving the most important factor in order to demultiplex a multiplexed signal, namely, obtaining an accuracy of estimating channels. 
     DISCLOSURE OF THE INVENTION 
     The present invention aims to provide a communication method and a radio communication apparatus which allow estimating a channel accurately and with ease from a multiplexed modulation signal. 
     The radio communication apparatus of the present invention includes a plurality of antennas, receives modulation signals transmitted by a communication partner, estimates a radio-wave propagation environment of each one of the antennas, and transmits the information of the estimated environment to the communication partner. 
     The modulation signal transmitted by the communication partner and received by the radio communication apparatus of the present invention is transmitted from only one of the plurality of antennas at a plurality of times. 
     A radio communication apparatus of the present invention comprises the following elements: 
     a plurality of antennas for receiving modulation signals of a plurality of channels available in the same frequency band and transmitted from a plurality of antennas; and 
     a received signal strength intensity estimation unit for estimating a radio wave propagation environment of the modulation signals corresponding to each one of the antennas. The communication apparatus then transmits the information of the estimated environment to a communication partner. 
     The radio communication apparatus of the present invention receives the modulation signals when a communication starts, then transmits the information of the estimated environment to the communication partner. 
     A radio communication apparatus of the present invention transmits or receives modulation signals of a plurality of channels available in the same frequency band from a plurality of antennas. The apparatus includes a transmission method determining unit that selects one of the following transmission methods based on information about a radio-wave propagation environment of each one of the antennas of the communication partner: 
     a method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas; or 
     a method of transmitting a modulation signal of one channel from one antenna. 
     The radio-wave propagation information of the radio communication apparatus of the present invention is estimated from a modulation signal transmitted when a communication starts. 
     A radio communication apparatus of the present invention comprises the following elements: 
     a plurality of antennas for receiving modulation signals of a plurality of channels available in the same frequency band and transmitted from a plurality of antennas; 
     a received signal strength intensity estimation unit for estimating a radio wave propagation environment of the modulation signals corresponding to each one of the antennas and transmitting information of the estimated environment to a communication partner; and 
     a transmission method determining unit for determining, based on the information of the radio wave propagation environment, a transmission method by which the communication partner transmits signals. The communication apparatus then transmits the information about a transmission method to the communication partner. 
     A modulation signal received by the radio communication apparatus of the present invention is transmitted by a communication partner from only one antenna out of a plurality of antennas at a plurality of times. 
     A radio communication apparatus of the present invention comprises the following elements: 
     a plurality of antennas for transmitting or receiving modulation signals of a plurality of channels available in the same frequency band and in accordance with a spread-spectrum communication method; and 
     a received signal strength intensity estimation unit for estimating a radio-wave propagation environment of the modulation signal corresponding to each one of the antennas using a component of a control channel. The communication apparatus then transmits information of the estimated environment to a communication partner. 
     The radio communication apparatus of the present invention receives the modulation signal when a communication starts, and transmits the information of the estimated radio-wave propagation environment to the communication partner. 
     A radio communication apparatus of the present invention transmits or receives modulation signals of a plurality of channels, available in the same frequency band and in accordance with a spread-spectrum communication method, from a plurality of antennas. The apparatus includes a transmission method determining unit that selects one of the following transmission methods based on radio-wave propagation environment of each one of the antennas of the communication partner: 
     a method of transmitting modulation signals of data channels of a plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas; or 
     a method of transmitting a modulation signal of a data channel of one spread-spectrum communication method from one antenna. 
     The radio-wave propagation information of the radio communication apparatus of the present invention is estimated from the modulation signal transmitted when the communication starts. 
     A communication method of the present invention transmits or receives modulation signals of a plurality of channels available in the same frequency band from a plurality of antennas. The communication method comprises the steps of: 
     transmitting a modulation signal; 
     a communication partner receiving the modulation signals, estimating a radio-wave propagation environment corresponding to each one of the antennas based on the modulation signal, then transmitting information of the estimated environment; and based on the information; 
     selecting one of transmission methods below: 
     a method of transmitting the modulation signals of the plurality of channels to the same frequency band from the plurality of antennas, or 
     a method of transmitting a modulation signal of one channel from one antenna. 
     The communication method of the present invention transmits the modulation signal when the communication starts. 
     A communication method of the present invention transmits or receives modulation signals of a plurality of channels, available in the same frequency band and in accordance with a spread-spectrum communication method, from a plurality of antennas. The communication method comprising the steps of: 
     transmitting a modulation signal; 
     a communication partner receiving the modulation signal, estimating a radio-wave propagation environment corresponding to each one of the antennas based on the modulation signal, then transmitting the information of the estimated environment; and based on the information, 
     selecting one of the transmission methods below: 
     a method of transmitting the modulation signals of data channels of a plurality of spread-spectrum communication methods to the same frequency band from the plurality of antennas, or 
     a method of transmitting a modulation signal of a data channel of one spread-spectrum communication methods from one antenna. 
     The communication method of the present invention transmits the modulation signal when the communication starts. 
     A communication method of the present invention transmits or receives modulation signals of a plurality of channels, available in the same frequency band and in accordance with a spread-spectrum communication method, from a plurality of antennas. The communication method comprising the steps of: 
     transmitting a modulation signal; 
     a communication partner receiving the modulation signal, estimating a radio-wave propagation environment corresponding to each one of the antennas based on a reception signal of a control channel; and based on the information, 
     transmitting information which requires one of transmission methods below: 
     a method of transmitting the modulation signal of data channels of a plurality of spread-spectrum communication methods to the same frequency band from the plurality of antennas, or 
     a method of transmitting the modulation signal of a data channel of one spread-spectrum communication method from one antenna; and based on the requiring information, 
     selecting one of the foregoing transmission methods. 
     The communication method of the present invention transmits the modulation signal when the communication starts. 
     The foregoing communication method allows multiplexing modulation signals of a plurality of channels to the same frequency band, thereby increasing the data transmission rate. At the same time, a transmission method is switched from/to transmitting the signals from one antenna to/from transmitting the signals from a plurality of antennas depending on a radio-wave propagation environment, thereby improving the quality of data transmission as well as the transmission rate of data. If this procedure is prepared at the time when a communication starts, an optimum communication method can be selected at the beginning. 
     A communication method of the present invention switches between the method of transmitting modulation signals of a plurality of channels from a plurality of antennas and the method of transmitting a modulation signal of a channel from an antenna. 
     The foregoing communication method allows multiplexing modulation signals of a plurality of channels to the same frequency band, thereby increasing the data transmission rate. At the same time, in the case of a bad radio-wave propagation environment, the modulation signals are transmitted through one channel, and in the case of a fine environment, a plurality of channels are used. The transmission method can be thus switched depending on the radio-wave propagation environment, so that the quality of data transmission is improved and the data transmission rate is increased. 
     At the beginning of starting a communication, the communication method of the present invention selects a transmission method of transmitting a modulation signal of one channel from one antenna. 
     The foregoing communication method can thus switch the case of transmitting the signals from a plurality of antennas to/from the case of transmitting the signals from one antenna, thereby improving the quality of data transmission as well as increasing the data transmission rate. 
     A reception apparatus of the present invention receives signals transmitted by the transmission method of the present invention, and has a function to select one of the following cases: 
     a case of receiving modulation signals of a plurality of channels transmitted from a plurality of antennas to the same frequency band; or 
     a case of receiving modulation signals of one channel transmitted from one antenna. 
     The foregoing reception apparatus allows multiplexing modulation signals of a plurality of channels to the same frequency band, thereby increasing the data transmission rate. At the same time, in the case of a bad radio-wave propagation environment, the modulation signals are transmitted through one channel, and in the case of a fine environment, a plurality of channels are used. The reception apparatus thus switches between the foregoing two transmission methods depending on the radio-wave propagation environment, so that the quality of data transmission is improved and the data transmission rate is increased. 
     As discussed above, according to the present invention, when the communication method is used, which multiplexes modulation signals of a plurality of channels to the same frequency band, a receiver transmits the information of an estimated radio-wave propagation environment to a transmitter. The transmitter then selects a communication method based on the information. Multiplexing modulation signals of a plurality of channels to the same frequency band by using the foregoing method can increase the data transmission rate. At the same time, a radio communication apparatus of the present invention can advantageously demultiplex the multiplexed modulation signals received with ease. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows frame structures of channel A and channel B in accordance with a first exemplary embodiment of the present invention. 
         FIG. 2  shows a structure of a transmission apparatus in accordance with the first exemplary embodiment of the present invention. 
         FIG. 3  shows a structure of a modulation signal generator in accordance with the first exemplary embodiment of the present invention. 
         FIG. 4  shows a point mapping of signals in in-phase-quadrature plane in accordance with the first exemplary embodiment of the present invention. 
         FIG. 5  shows a structure of a reception apparatus in accordance with the first exemplary embodiment of the present invention. 
         FIG. 6  shows relations between symbols, transmission path variations and reception quadrature baseband signals in accordance with the first exemplary embodiment of the present invention. 
         FIG. 7  shows frame structures of channel A and channel B in accordance with the first exemplary embodiment of the present invention. 
         FIG. 8  shows a structure of a reception apparatus in accordance with a second exemplary embodiment of the present invention. 
         FIG. 9  shows a structure of a reception apparatus in accordance with the second exemplary embodiment of the present invention. 
         FIG. 10  shows a transmission path variation estimation signal in accordance with the second exemplary embodiment of the present invention. 
         FIG. 11  shows frame structures of signals in accordance with a third exemplary embodiment of the present invention. 
         FIG. 12  shows a structure of a transmission apparatus in accordance with the third exemplary embodiment of the present invention. 
         FIG. 13  shows a structure of a modulation signal generator in accordance with the third exemplary embodiment of the present invention. 
         FIG. 14  shows relations between pilot symbols and codes to multiply in accordance with the third exemplary embodiment of the present invention. 
         FIG. 15  shows a structure of a reception apparatus in accordance with the third exemplary embodiment of the present invention. 
         FIG. 16  shows a structure of a transmission path variation estimation unit in accordance with the third exemplary embodiment of the present invention. 
         FIG. 17  shows amounts of fluctuation in a transmission path along the timing axis in accordance with the third exemplary embodiment of the present invention. 
         FIG. 18  shows a structure of a reception apparatus in accordance with a fourth exemplary embodiment of the present invention. 
         FIG. 19  shows a structure of a reception apparatus in accordance with the fourth exemplary embodiment of the present invention. 
         FIG. 20  shows a frame structure of a signal in accordance with a fifth exemplary embodiment of the present invention. 
         FIG. 21  shows a point mapping of signals in in-phase-quadrature (I-Q) plane in accordance with the fifth exemplary embodiment of the present invention. 
         FIG. 22  shows a structure of a modulation signal generator in accordance with the fifth exemplary embodiment of the present invention. 
         FIG. 23  shows a structure of a transmission path variation estimation unit in accordance with the fifth exemplary embodiment of the present invention. 
         FIG. 24  shows frame structures of channel A and channel B in accordance with the fifth exemplary embodiment of the present invention. 
         FIG. 25  shows a structure of a transmission apparatus in accordance with a sixth exemplary embodiment of the present invention. 
         FIG. 26  shows a structure of a reception apparatus in accordance with the sixth exemplary embodiment of the present invention. 
         FIG. 27  shows distortions in transmission paths in accordance with the sixth exemplary embodiment of the present invention. 
         FIG. 28  shows structures of a transmission path variation estimation unit and a signal processor in accordance with the sixth exemplary embodiment of the present invention. 
         FIG. 29  shows frame structures of signals in accordance with a seventh exemplary embodiment of the present invention. 
         FIG. 30  shows frame structures of signals in accordance with the seventh exemplary embodiment of the present invention. 
         FIG. 31  shows a transmission apparatus at a base station in accordance with the seventh exemplary embodiment of the present invention. 
         FIG. 32  shows a structure of a reception apparatus at a terminal in accordance with the seventh exemplary embodiment of the present invention. 
         FIG. 33  shows a frame structure along a time axis in accordance with an eighth exemplary embodiment of the present invention. 
         FIG. 34  shows a frame structure along a time axis in accordance with the eighth exemplary embodiment of the present invention. 
         FIG. 35  shows a structure of a modulation signal generator in accordance with the eighth exemplary embodiment of the present invention. 
         FIG. 36  shows a structure of a modulation signal generator in accordance with the eighth exemplary embodiment of the present invention. 
         FIG. 37  shows a structure of a reception apparatus in accordance with the eighth exemplary embodiment of the present invention. 
         FIG. 38  shows a structure of a reception apparatus in accordance with the eighth exemplary embodiment of the present invention. 
         FIG. 39  shows a structure of a reception apparatus in accordance with the eighth exemplary embodiment of the present invention. 
         FIG. 40  shows a structure of a reception apparatus in accordance with the eighth exemplary embodiment of the present invention. 
         FIG. 41  shows a structure of a reception apparatus in accordance with the eighth exemplary embodiment of the present invention. 
         FIG. 42  shows a structure of a reception apparatus in accordance with the eighth exemplary embodiment of the present invention. 
         FIG. 43  shows a frame structure along a time axis in accordance with a ninth exemplary embodiment of the present invention. 
         FIG. 44  shows a frame structure along a time axis in accordance with the ninth exemplary embodiment of the present invention. 
         FIG. 45  shows a frame structure along a time axis in accordance with the ninth exemplary embodiment of the present invention. 
         FIG. 46  shows a structure of a modulation signal generator in accordance with the ninth exemplary embodiment of the present invention. 
         FIG. 47  shows a structure of a modulation signal generator in accordance with the ninth exemplary embodiment of the present invention. 
         FIG. 48  shows a structure of a modulation signal generator in accordance with the ninth exemplary embodiment of the present invention. 
         FIG. 49  shows a structure of a modulation signal generator in accordance with the ninth exemplary embodiment of the present invention. 
         FIG. 50  shows a frame structure along a time axis and a frequency axis in accordance with a tenth exemplary embodiment of the present invention. 
         FIG. 51  shows a frame structure along a time axis and a frequency axis in accordance with the tenth exemplary embodiment of the present invention. 
         FIG. 52  shows a structure of a reception apparatus in accordance with the tenth exemplary embodiment of the present invention. 
         FIG. 53  shows a structure of a reception apparatus in accordance with the tenth exemplary embodiment of the present invention. 
         FIG. 54  shows a structure of a reception apparatus in accordance with the tenth exemplary embodiment of the present invention. 
         FIG. 55  shows a structure of a reception apparatus in accordance with the tenth exemplary embodiment of the present invention. 
         FIG. 56  shows a structure of a reception apparatus in accordance with the tenth exemplary embodiment of the present invention. 
         FIG. 57  shows a structure of a reception apparatus in accordance with the tenth exemplary embodiment of the present invention. 
         FIG. 58  shows a structure of a reception apparatus in accordance with an eleventh exemplary embodiment of the present invention. 
         FIG. 59  shows a structure of a reception apparatus in accordance with the eleventh exemplary embodiment of the present invention. 
         FIG. 60  shows a structure of a reception apparatus in accordance with the eleventh exemplary embodiment of the present invention. 
         FIG. 61  shows a structure of a reception apparatus in accordance with the eleventh exemplary embodiment of the present invention. 
         FIG. 62  shows a structure of a reception apparatus in accordance with the eleventh exemplary embodiment of the present invention. 
         FIG. 63  shows a structure of a reception apparatus in accordance with the eleventh exemplary embodiment of the present invention. 
         FIG. 64  shows a structure of a reception apparatus in accordance with the eleventh exemplary embodiment of the present invention. 
         FIG. 65  shows a structure of a reception apparatus in accordance with the eleventh exemplary embodiment of the present invention. 
         FIG. 66  shows a structure of a reception apparatus in accordance with the eleventh exemplary embodiment of the present invention. 
         FIG. 67  shows a structure of a reception apparatus in accordance with the eleventh exemplary embodiment of the present invention. 
         FIG. 68  shows a structure of a reception apparatus in accordance with the eleventh exemplary embodiment of the present invention. 
         FIG. 69  shows a structure of a reception apparatus in accordance with the eleventh exemplary embodiment of the present invention. 
         FIG. 70  shows a frame structure in accordance with a twelfth exemplary embodiment of the present invention. 
         FIG. 71  shows a structure of an information symbol in accordance with the twelfth exemplary embodiment of the present invention. 
         FIG. 72  shows a structure of an information symbol in accordance with the twelfth exemplary embodiment of the present invention. 
         FIG. 73  shows a structure of an information symbol in accordance with the twelfth exemplary embodiment of the present invention. 
         FIG. 74  shows a structure of a transmission apparatus in accordance with the twelfth exemplary embodiment of the present invention. 
         FIG. 75  shows a structure of a reception apparatus in accordance with the twelfth exemplary embodiment of the present invention. 
         FIG. 76  shows a structure of a transmission apparatus in accordance with the twelfth exemplary embodiment of the present invention. 
         FIG. 77  shows a structure of a reception apparatus in accordance with the twelfth exemplary embodiment of the present invention. 
         FIG. 78  shows a structure of a transmission apparatus in accordance with the twelfth exemplary embodiment of the present invention. 
         FIG. 79  shows a frame structure in accordance with a thirteenth exemplary embodiment of the present invention. 
         FIG. 80  shows a structure of a transmission apparatus in accordance with the thirteenth exemplary embodiment of the present invention. 
         FIG. 81  shows a structure of a control symbol in accordance with the thirteenth exemplary embodiment of the present invention. 
         FIG. 82  shows a structure of a reception apparatus in accordance with the thirteenth exemplary embodiment of the present invention. 
         FIG. 83  shows a frame structure in accordance with the thirteenth exemplary embodiment of the present invention. 
         FIG. 84A  shows a frame structure of a transmission signal from a base station in accordance with the twelfth exemplary embodiment of the present invention. 
         FIG. 84B  shows a frame structure of the transmission signal from a terminal in accordance with the twelfth exemplary embodiment of the present invention. 
         FIG. 85  shows a structure of a control symbol in accordance with the thirteenth exemplary embodiment of the present invention. 
         FIG. 86  shows a structure of a control symbol in accordance with the thirteenth exemplary embodiment of the present invention. 
         FIG. 87  shows a block diagram illustrating parts of a conventional MIMO-OFDM system. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present invention are demonstrated hereinafter with reference to the accompanying drawings. In the following descriptions, “antenna” does not always mean a single antenna, but “antenna” means an antenna unit which is formed of a plurality of antennas. 
     Exemplary Embodiment 1 
     In a transmission method where modulation signals of a plurality of channels are multiplexed to the same frequency band, at the time when a demodulation symbol is inserted in a channel, in another channel symbol, the same phase and quadrature signals in the in-phase-quadrature plane are made to be zero signals. The foregoing method and a transmission apparatus as well as a reception apparatus employed in the method are described in this first embodiment. 
       FIG. 1  shows frame structure  120  of channel A and frame structure  130  of channel B along a time axis. Channel A has pilot symbols  101 ,  104 ,  107 , guard symbols  102 ,  105 ,  108 , and data symbol  103 ,  106 . Data symbols, for instance, have undergone QPSK (quadrature phase shift keying) modulation. Channel B has guard symbols  109 ,  112 ,  115 , pilot symbols  110 ,  113 ,  116 , and data symbols  111 ,  114 . Data symbols, for instance, have undergone QPSK modulation. 
     Pilot symbol  101  of channel A and guard symbol  109  of channel B are placed at an identical time, and the following combinations are placed at an identical time respectively: 
     guard symbol  102  of channel A and pilot symbol  110  of channel B; 
     data symbol  103  of channel A and data symbol  111  of channel B; 
     pilot symbol  104  of channel A and guard symbol  112  of channel B; 
     guard symbol  105  of channel A and pilot symbol  113  of channel B; 
     data symbol  106  of channel A and data symbol  114  of channel B; 
     pilot symbol  107  of channel A and guard symbol  115  of channel B; 
     guard symbol  108  of channel A and pilot symbol  116  of channel B. 
       FIG. 2  shows a structure of a transmission apparatus of this first embodiment, and the apparatus is formed of channel A transmitter  220 , channel B transmitter  230 , and frame structure signal generator  209 . Channel A transmitter  220  is formed of modulation signal generator  202 , radio unit  204 , power amplifier  206 , and antenna  208 . Channel B transmitter  230  is formed of modulation signal generator  212 , radio unit  214 , power amplifier  216 , and antenna  218 . 
     Modulation signal generator  202  of channel A receives frame structure signal  210  and transmission digital signal  201  of channel A, and outputs modulation signal  203  in accordance with the frame structure. 
     Radio unit  204  of channel A receives modulation signal  203  of channel A, and outputs transmission signal  205  of channel A. 
     Power amplifier  206  of channel A receives transmission signal  205  of channel A, amplifies signal  205 , and outputs transmission signal  207  of channel A as radio wave from antenna  208  of channel A. 
     Frame structure signal generator  209  outputs frame structure signal  210 . 
     Modulation signal generator  212  of channel B receives frame structure signal  210  and transmission digital signal  211  of channel B, and outputs modulation signal  213  in accordance with the frame structure. 
     Radio unit  214  of channel B receives modulation signal  213  of channel B, and outputs transmission signal  215  of channel B. 
     Power amplifier  216  of channel B receives transmission signal  215  of channel B, amplifies signal  215 , and outputs transmission signal  217  of channel B as radio wave from antenna  218  of channel B. 
       FIG. 3  shows a detailed structure of modulation signal generators  202 ,  212  shown in  FIG. 2 . Data symbol modulation signal generator  302  receives transmission digital signal  301  and frame structure signal  311 . When frame structure signal  311  indicates a data symbol, generator  302  provides signals  301  with QPSK modulation, and outputs in-phase component  303  and quadrature-phase component  304  of a transmission quadrature baseband signal of the data symbol. 
     Pilot symbol modulation signal generator  305  receives frame structure signal  311 . When signal  311  indicates a pilot symbol, generator  305  outputs in-phase component  306  and quadrature-phase component  307  of a transmission quadrature baseband signal of the pilot symbol. 
     Guard symbol modulation generator  308  receives frame structure signal  311 . When signal  311  indicates a guard symbol, generator  308  outputs in-phase component  309  and quadrature-phase component  310  of a transmission quadrature baseband signal of the guard symbol. 
     In-phase component switcher  312  receives in-phase components  303 ,  306 ,  309  and frame structure signal  311 , then selects the in-phase component of transmission quadrature baseband signal corresponding to a symbol indicated by frame structure signal  311 , and outputs the selected one as in-phase component  313  of the selected transmission quadrature baseband signal. 
     Quadrature-phase component switcher  314  receives quadrature-phase components  304 ,  307 ,  310 , and frame structure signal  311 , then selects a quadrature-phase component of a transmission quadrature baseband signal corresponding to a symbol indicated by frame structure signal  311 , and outputs the selected one as quadrature-phase component  315  of the selected transmission quadrature baseband signal. 
     Orthogonal modulator  316  receives in-phase component  313  selected, quadrature-phase component  315  selected, then provides those components  313 ,  315  with orthogonal modulation, and outputs modulation signal  317 . 
       FIG. 4  shows point-placement of signals of QPSK (data symbol), pilot symbol, guard symbol, such as QPSK signal-point  401 , pilot symbol signal-point  402 , and guard symbol signal-point  403 . 
       FIG. 5  shows a structure of a reception apparatus in accordance with the first embodiment. Radio unit  503  receives signal  502  received by antenna  501 , and outputs in-phase component  504  and quadrature-phase component  505  of reception quadrature baseband signal. 
     Transmission path variation estimation unit  506  of channel A receives reception quadrature baseband signals  504 ,  505 , then estimates a transmission path variation of channel A, and outputs transmission path variation estimation signal  507  of channel A. 
     Transmission path variation estimation unit  508  of channel B receives reception quadrature baseband signals  504 ,  505 , then estimates a transmission path variation of channel B, and outputs transmission path variation estimation signal  509  of channel B. 
     Delay unit  510  receives in-phase component  504  and quadrature-phase component  505  of the reception quadrature baseband signal, and outputs in-phase component  511  and quadrature-phase component  512  of the reception quadrature baseband signal which delays by the time needed for obtaining transmission path variation estimation signals  507  and  509  of channel A and channel B. 
     Radio unit  515  receives signal  514  received by antenna  513 , and outputs in-phase component  516  and quadrature-phase component  517  of the reception quadrature baseband signal. 
     Transmission path variation estimation unit  518  of channel A receives reception quadrature baseband signals  516  and  517 , then estimates a transmission path variation of channel A, and outputs transmission path variation estimation signal  519  of channel A. 
     Transmission path variation estimation unit  520  of channel B receives reception quadrature baseband signals  516  and  517 , then estimates a transmission path variation of channel B, and outputs transmission path variation estimation signal  521  of channel B. 
     Delay unit  522  receives in-phase component  516  and quadrature-phase component  517  of the reception quadrature baseband signal, and outputs in-phase component  523  and quadrature-phase component  524  of the reception quadrature baseband signal which delays by the time needed for obtaining transmission path variation estimation signals  519  and  521  of channel A and channel B. 
     Signal processor  525  receives the following signals: 
     transmission path variation estimation signal  507  of channel A; 
     transmission path variation estimation signal  509  of channel B; 
     in-phase component  511  and quadrature-phase component  512  of delayed reception quadrature baseband signal; 
     transmission path variation estimation signal  519  of channel A; 
     transmission path variation estimation signal  521  of channel B; and 
     in-phase component  523  and quadrature-phase component  524  of delayed reception quadrature baseband signal. 
     Then signal processor  525  outputs the following signals: 
     in-phase component  526  and quadrature-phase component  527  of reception quadrature baseband signal of channel A; and 
     in-phase component  530  and quadrature-phase component  531  of reception quadrature baseband signal of channel B. 
     Demodulator  528  receives in-phase component  526  and quadrature-phase component  527  of reception quadrature baseband signal of channel A, then demodulates those components, and outputs reception digital signal  529  of channel A. 
     Demodulator  532  receives in-phase component  530  and quadrature-phase component  531  of reception quadrature baseband signal of channel B, then demodulates those components, and outputs reception digital signal  533  of channel B. 
       FIG. 6  shows relation between a frame structure  620  of channel A and a frame structure  630  of channel B, symbols  601 - 616  of each channel at certain times, transmission path variations  621  and  631  of channels A and B, and reception quadrature baseband signal  632 . Channel A has the following symbols: pilot symbols  601 ,  607 ; guard symbols  602 ,  608 ; data symbols  603 ,  604 ,  605 , and  606 . Channel B has the following symbols: guard symbols  609 ,  615 ; pilot symbols  610 ,  616 ; data symbols  611 ,  612 ,  613 , and  614 . 
     Pilot symbol  601  of channel A and guard symbol  609  of channel B occur at time  0 , and the following combinations occur at time  1 , time  2 , time  3 , time  4 , time  5 , time  6 , and time  7  respectively: 
     guard symbol  602  of channel A and pilot symbol  610  of channel B; 
     data symbol  603  of channel A and data symbol  611  of channel B; 
     data symbol  604  of channel A and data symbol  612  of channel B; 
     data symbol  605  of channel A and data symbol  613  of channel B; 
     data symbol  606  of channel A and data symbol  614  of channel B; 
     pilot symbol  607  of channel A and guard symbol  615  of channel B; 
     guard symbol  608  of channel A and pilot symbol  616  of channel B. 
       FIG. 7  shows a structure of channel A frame  720  and a structure of channel B frame  730  along a time axis. Channel A has the following symbols: pilot symbols  701 ,  702 ,  706 ,  707 ; guard symbols  703 ,  704 ,  708 ,  709 ; and data symbol  705 . Channel B has the following symbols: guard symbols  710 ,  711 ,  715 ,  716 ; pilot symbols  712 ,  713 ,  717 ,  718 ; and data symbol  714 . Data symbol  705  of channel A and data symbol  714  of channel B have undergone QPSK modulation. 
     Pilot symbol  701  of channel A and guard symbol  710  of channel B occur at an identical time, and the following combinations occur at an identical time respectively: 
     pilot symbol  702  of channel A and guard symbol  711  of channel B; 
     guard symbol  703  of channel A and pilot symbol  712  of channel B; 
     guard symbol  704  of channel A and pilot symbol  713  of channel B; 
     data symbol  705  of channel A and data symbol  714  of channel B; 
     pilot symbol  706  of channel A and guard symbol  715  of channel B; 
     pilot symbol  707  of channel A and guard symbol  716  of channel B; 
     guard symbol  708  of channel A and pilot symbol  717  of channel B; 
     guard symbol  709  of channel A and pilot symbol  718  of channel B. 
     An operation of the transmission apparatus is demonstrated hereinafter with reference to  FIG. 1  through  FIG. 4 . In  FIG. 2 , frame structure signal generator  209  outputs the information of the frame structure shown in  FIG. 1  as frame structure signal  210 . Modulation signal generator  202  of channel A receives frame structure signal  210  and transmission digital signal  201  of channel A, then outputs modulation signal  203  of channel A in accordance with the frame structure. Modulation signal generator  212  of channel B receives frame structure signal  210  and transmission digital signal  211  of channel B, then outputs modulation signal  213  of channel B in accordance with the frame structure. 
     An operation of modulation signal generators  202  and  212  in the process discussed above is described using transmitter  220  of channel A as an example with reference to  FIG. 3 . 
     Data symbol modulation signal generator  302  receives transmission digital signal  301 , i.e. transmission digital signal  201  of channel A in  FIG. 2 , and frame structure signal  311 , i.e. frame structure signal  210  in  FIG. 2 . When frame structure signal  311  indicates a data symbol, generator  302  provides signal  201  with QPSK modulation, and outputs in-phase component  303  and quadrature-phase component  304  of a transmission quadrature baseband signal of the data symbol. 
     Pilot symbol modulation signal generator  305  receives frame structure signal  311 . When signal  311  indicates a pilot symbol, generator  305  outputs in-phase component  306  and quadrature-phase component  307  of a transmission quadrature baseband signal of the pilot symbol. 
     Guard symbol modulation signal generator  308  receives frame structure signal  311 . When signal  311  indicates a guard symbol, generator  308  outputs in-phase component  309  and quadrature-phase component  310  of a transmission quadrature baseband signal of the guard symbol. 
       FIG. 4  shows signal-point placement of the respective symbols in an in-phase-quadrature plane of the foregoing operation. Points  401  in  FIG. 4  indicate the signal-points of in-phase component  303  and quadrature-phase component  304  of the transmission quadrature baseband signal of the data symbol. Points  402  indicate the signal-points of in-phase component  306  and quadrature-phase component  307  of the transmission quadrature baseband signal of the pilot symbol. Point  403  indicates the signal-points of in-phase component  309  and quadrature-phase component  310  of the transmission quadrature baseband signal of the guard symbol. 
     In-phase component switcher  312  receives the following signals: in-phase component  303  of data symbol transmission quadrature baseband signal; 
     in-phase component  306  of pilot symbol transmission quadrature baseband signal; 
     in-phase component  309  of guard symbol transmission quadrature baseband signal; and 
     frame structure signal  311 . 
     Switcher  312  then selects an in-phase component of a transmission quadrature baseband signal corresponding to the symbol indicated by frame structure signal  311 , and outputs the selected one as in-phase component  313  of the selected transmission quadrature baseband signal. 
     Quadrature-phase component switcher  314  receives the following signals: 
     quadrature-phase component  304  of data symbol transmission quadrature baseband signal; 
     quadrature-phase component  307  of pilot symbol transmission quadrature baseband signal; 
     quadrature-phase component  310  of guard symbol transmission quadrature baseband signal; and 
     frame structure signal  311 . 
     Switcher  314  then selects a quadrature-phase component of a transmission quadrature baseband signal corresponding to the symbol indicated by frame structure signal  311 , and outputs the selected one as quadrature-phase component  315  of the selected transmission quadrature baseband signal. 
     Orthogonal modulator  316  receives in-phase component  313  and quadrature-phase component  315  discussed above, then provides those components with an orthogonal modulation, and outputs modulation signal  317 , i.e. signal  203  shown in  FIG. 2 . 
     An operation of the reception apparatus, in particular, of transmission path variation estimation unit  506  of channel A, transmission path variation estimation unit  508  of channel B, and signal processor  525 , with reference to  FIG. 5  and  FIG. 6 . 
     In-phase component  504  and quadrature-phase component  505  of reception quadrature baseband signal of the signal received by antenna  501  shown in  FIG. 5  are taken as examples for description with reference to  FIG. 6 . 
     In  FIG. 6 , at time  0  (zero), pilot symbol  601  of channel A and guard symbol  609  of channel B are multiplexed together. Assume that in-phase component  504  and quadrature-phase component  505  of the reception quadrature baseband signal are I 0  and Q 0  respectively, and the transmission path variation of channel A and that of channel B are (Ia 0 , Qa 0 ) and (Ib 0 , Qb 0 ) respectively. Since the transmission apparatus transmits 0 (zero) at the guard symbol of channel B, in-phase component  504  and quadrature-phase component  505  of the reception quadrature baseband signal, namely, I 0  and Q 0 , are formed of the component of pilot symbol  601  of channel A. Therefore, the transmission path variation of channel A, namely, (Ia 0 , Qa 0 ) can be estimated as (I′ 0 , Q′ 0 ) based on in-phase component  504  and quadrature-phase component  505 , namely, I 0  and Q 0 . 
     However, the estimation of the transmission path variation of channel A, namely, (Ia 0 , Qa 0 ), is not limited to the case discussed above, but a pilot symbol of channel A at another time can be used for finding (Ia 0 , Qa 0 ) of channel A at time  0 . 
     In a similar manner to what is discussed above, at time  1 , guard symbol  602  of channel A and pilot symbol  610  of channel B are multiplexed together. Assume that in-phase component  504  and quadrature-phase component  505  of the reception quadrature baseband signal are I 1  and Q 1  respectively, and the transmission path variation of channel A and that of channel B are (Ia 1 , Qa 1 ) and (Ib 1 , Qb 1 ) respectively. Since the transmission apparatus transmits 0 (zero) at the guard symbol of channel A, in-phase component  504  and quadrature-phase component  505  of the reception quadrature baseband signal, namely, I 1  and Q 1 , are formed of the component of pilot symbol  610  of channel B. Therefore, the transmission path variation of channel B, namely, (Ib 1 , Qb 1 ) can be estimated as (I′ 1 , Q′ 1 ) based on in-phase component  504  and quadrature-phase component  505 , namely, I 1  and Q 1 . However, the estimation of the transmission path variation of channel B, namely, (Ib 1 , Qb 1 ), is not limited to the case discussed above, but a pilot symbol of channel B at another time can be used for finding (Ib 1 , Qb 1 ) of channel B at time  1 . 
     In a similar manner to what is discussed above, at time  6 , pilot symbol  607  of channel A and guard symbol  615  of channel B are multiplexed together. Assume that in-phase component  504  and quadrature-phase component  505  of the reception quadrature baseband signal are I 6  and Q 6  respectively, and the transmission path variation of channel A and that of channel B are (Ia 6 , Qa 6 ) and (Ib 6 , Qb 6 ). Since the transmission apparatus transmits 0 at the guard symbol of channel B, in-phase component  504  and quadrature-phase component  505  of the reception quadrature baseband signal, namely, I 6  and Q 6 , are formed of the component of pilot symbol  607  of channel A. 
     Therefore, the transmission path variation of channel A, namely, (Ia 6 , Qa 6 ) can be estimated as (I′ 6 , Q′ 6 ) based on in-phase component  504  and quadrature-phase component  505 , namely, I 6  and Q 6 . However, the estimation of the transmission path variation of channel A, namely, (Ia 6 , Qa 6 ), is not limited to the case discussed above, but a pilot symbol of channel A at another time can be used for finding (Ia 6 , Qa 6 ) of channel A at time  6 . 
     In a similar manner to what is discussed above, at time  7 , guard symbol  608  of channel A and pilot symbol  616  of channel B are multiplexed together. Assume that in-phase component  504  and quadrature-phase component  505  of the reception quadrature baseband signal are I 7  and Q 7  respectively, and the transmission path variation of channel A and that of channel B are (Ia 7 , Qa 7 ) and (Ib 7 , Qb 7 ). Since the transmission apparatus transmits 0 (zero) at the guard symbol of channel A, in-phase component  504  and quadrature-phase component  505  of the reception quadrature baseband signal, namely, I 7  and Q 7 , are formed of the component of pilot symbol  610  of channel B. 
     Therefore, the transmission path variation of channel B, namely, (Ib 7 , Qb 7 ) can be estimated as (I′ 7 , Q′ 7 ) based on in-phase component  504  and quadrature-phase component  505 , namely, I 7  and Q 7 . However, the estimation of the transmission path variation of channel B, namely, (Ib 7 , Qb 7 ), is not limited to the case discussed above, but a pilot symbol of channel B at another time can be used for finding (Ib 7 , Qb 7 ) of channel B at time  7 . 
     Assume that the transmission path variations at time  2 , time  3 , time  4 , and time  5  are (Ia 2 , Qa 2 ), (Ia 3 , Qa 3 ), (Ia 4 , Qa 4 ), (Ia 5 , Qa 5 ). Those values can be found using the estimations discussed above, i.e. (Ia 0 , Qa 0 )=(I′ 0 , Q′ 0 ), (Ia 6 , Qa 6 )=(I′ 6 , Q′ 6 ), by, e.g. calculation. However, in order to find (Ia 2 , Qa 2 ), (Ia 3 , Qa 3 ), (Ia 4 , Qa 4 ), and (Ia 5 , Qa 5 ), pilot symbols at another time of channel A can be used other than (Ia 0 , Qa 0 ) and (Ia 6 , Qa 6 ). 
     In a similar way to what is discussed above, assume the transmission path variation at time  2 , time  3 , time  4 , and time  5  are (Ib 2 , Qb 2 ), (Ib 3 , Qb 3 ), (Ib 4 , Qb 4 ), (Ib 5 , Qb 5 ). Those values can be found using the estimations previously discussed, i.e. (Ib 1 , Qb 1 )=(I′ 1 , Q′ 1 ), (Ib 7 , Qb 7 )=(I′ 7 , Q′ 7 ), by, e.g. calculation. However, to find (Ib 2 , Qb 2 ), (Ib 3 , Qb 3 ), (Ib 4 , Qb 4 ), and (Ib 5 , Qb 5 ), pilot symbols at another time of channel B can be used other than (Ib 1 , Qb 1 ) and (Ib 7 , Qb 7 ). 
     The preparation discussed above allows transmission path variation estimation unit  506  of channel A to output, e.g. the foregoing (Ia 0 , Qa 0 ), (Ia 1 , Qa 1 ), (Ia 2 , Qa 2 ), (Ia 3 , Qa 3 ), (Ia 4 , Qa 4 ), (Ia 5 , Qa 5 ), (Ia 6 , Qa 6 ), and (Ia 7 , Qa 7 ) as transmission path variation estimation signals  507  of channel A. 
     In a similar way to the case of channel A, transmission path variation estimation unit  508  of channel B outputs, e.g. the foregoing (Ib 0 , Qb 0 ), (Ib 1 , Qb 1 ), (Ib 2 , Qb 2 ), (Ib 3 , Qb 3 ), (Ib 4 , Qb 4 ), (Ib 5 , Qb 5 ), (Ib 6 , Qb 6 ), and (Ib 7 , Qb 7 ) as transmission path variation estimation signals  509  of channel B. 
     The foregoing description expresses the transmission path variation in (I, Q); however, the distortion can be expressed in power and phase, so that estimation signals  507  and  509  can be expressed in power and phase. 
     In a similar way to what is discussed above, transmission path variation estimation unit  518  of channel A receives in-phase component  516  and quadrature-phase component  517  of a reception quadrature baseband signal of a signal received by antenna  513  shown in  FIG. 5 . Then estimation unit  518  outputs estimation signal  519  of channel A. Estimation unit  520  of channel B outputs estimation signal  521  of channel B. 
     Signal processor  525  receives the following signals: 
     transmission path variation estimation signal  507  of channel A; 
     transmission path variation estimation signal  509  of channel B; 
     transmission path variation estimation signal  519  of channel A; 
     transmission path variation estimation signal  521  of channel B; 
     in-phase component  511  and quadrature-phase component  512  of delayed reception quadrature baseband signal; and 
     in-phase component  523  and quadrature-phase component  524  of delayed reception quadrature baseband signal. 
     Signal processor  525  carries out matrix calculations with those known signals, so that unknown signals such as a reception quadrature baseband signal of channel A and that of channel B can be found. Signal processor  525  thus outputs those unknown signals as in-phase component  526  and quadrature-phase component  527  of the reception quadrature baseband signal of channel A, and in-phase component  530  and quadrature-phase component  531  of that of channel B. As a result, modulation signals of channels A and B can be demultiplexed from each other, which allows demodulation. 
     In this embodiment, an accuracy of demultiplexing the modulation signals between channel A and channel B at the reception apparatus depends on a quality of the pilot symbol received. Thus stronger resistance of the pilot symbol to noise increases the accuracy of demultiplexing between the modulation signals of channel A and channel B. As a result, the quality of data received can be improved. The way of achieving this goal is described hereinafter. 
     In  FIG. 4 , assume that the pilot symbol has amplitude Ap from the origin, and QPSK has the greatest signal-point amplitude Aq from the origin. In this status, the relation of Ap&gt;Aq increases the resistance to noise of the pilot symbol, so that the accuracy of demultiplexing the modulation signals of channel A from those of channel B. As a result, the quality of data received can be improved. 
     As shown in  FIG. 7 , the frame of channel A includes pilot symbols  701 ,  702 , and  706 ,  707 . The frame of channel B includes pilot symbol  712 ,  713 , and  717 ,  718 . Those pilot symbols are placed in series along the time axis, so that the pilot symbols become stronger to noises. Thus the accuracy of the demultiplexing the modulation signals between channel A and channel B. As a result, the quality of data received is improved. This is not limited to two symbols in series as shown in  FIG. 7 . 
     In this embodiment, the number of channels to be multiplexed are two; however, other numbers can be applicable to the embodiment. The frame structure is not limited to what is shown in  FIG. 1 ,  FIG. 6  or  FIG. 7 . The pilot symbol is taken as an example for demultiplexing the channels; however, other symbols as long as they are used for demodulation can be also applicable. In this case, the symbols for demodulation include, e.g. pilot symbol, unique word, synchronous symbol, preamble symbol, control symbol, tail symbol, control symbol, known PSK (phase shift keying) modulation symbol, and PSK modulation symbol added with data. 
     A modulation method of the data symbol is not limited to QPSK modulation, but respective channels can undergo different modulations. On the other hand, all the channels can use the spread spectrum communication method. The spread spectrum communication method can coexist with the other methods. 
     The structure of the transmission apparatus of this embodiment is not limited to what is shown in  FIG. 2  or  FIG. 3 , and when the number of channels increase, elements  201  through  208  shown in  FIG. 2  are added accordingly. 
     The structure of the reception apparatus of this embodiment is not limited to what is shown in  FIG. 5 , and when the number of channels increase, the number of channel estimation units increases accordingly. 
     The expression of “antenna” in the previous description does not always mean a single antenna, but “antenna” can mean an antenna unit which is formed of a plurality of antennas. 
     In this embodiment, the transmission path variation estimation unit of each channel estimates the transmission path variation; however, an estimation of transmission path fluctuation instead of distortion can achieve a similar advantage to what is discussed in this embodiment. In this case, a transmission path fluctuation estimation unit for estimating fluctuations of the transmission path is used instead of the distortion estimation unit. The output signal should be a fluctuation estimation signal accordingly. 
     According to the first embodiment discussed above, in a transmission method for transmitting modulation signals of a plurality of channels to the same frequency band, at the time when a demodulation symbol is inserted in a channel, in another channel symbol, both of the same phase signal and a quadrature signal in the in-phase-quadrature plane are made to be zero signals. Use of this method, a transmission apparatus and a reception apparatus to which this method is applicable, allows the transmission rate of data to increase, and allows the reception apparatus to demultiplex the multiplexed modulation signal with ease. 
     Exemplary Embodiment 2 
     In this second embodiment, a reception apparatus is described. The reception apparatus comprising the following elements: 
     a received signal strength intensity estimation unit for estimating a reception received signal strength intensity of a signal received by respective antennas and outputting an estimation signal of the reception received signal strength intensity of the reception signal; 
     a phase difference estimation unit for receiving a transmission path variation estimation signal of a channel of the respective antennas, finding a phase difference of the transmission path variation estimation signal between the respective antennas, and outputting a phase difference signal; and 
     a signal selection unit for receiving a reception quadrature baseband signal of the respective antennas, a transmission path variation estimation signal of each channel of the respective antennas, a reception electric field estimation signal of the reception signal, the phase difference signal, then selecting the reception quadrature baseband signal and the transmission path variation estimation signal for isolating signals of the respective channels from the reception signal, and outputting the signals selected. 
     The description refers to the case as an example where the transmission apparatus shown in  FIG. 2  transmits the modulation signals of the frame structure shown in  FIG. 1  demonstrated in the first embodiment. 
       FIG. 8  shows a structure of the reception apparatus in accordance with the second embodiment. Radio unit  803  of this apparatus receives signal  802  received by antenna  801 , and outputs in-phase component  804  and quadrature-phase component  805  of the reception quadrature baseband signal. 
     Transmission path variation estimation unit  806  of channel A receives in-phase component  804  and quadrature-phase component  805  of the reception quadrature baseband signal. Then estimation unit  806  operates, e.g. in a similar way to estimation unit  506  of channel A shown in  FIG. 5  of the first embodiment, and outputs transmission path variation estimation signal  807  of channel A. 
     Transmission path variation estimation unit  808  of channel B receives in-phase component  804  and quadrature-phase component  805  of the reception quadrature baseband signal. Then estimation unit  808  operates, e.g. in a similar way to estimation unit  506  of channel A shown in  FIG. 5  of the first embodiment, and outputs transmission path variation estimation signal  809  of channel B. 
     Delay unit  810  receives in-phase component  804  and quadrature-phase component  805  of the reception quadrature baseband signal, and outputs in-phase component  811  and quadrature-phase component  812  of the reception quadrature baseband signal which delays by the time needed for obtaining transmission path variation estimation signals  807  and  809  of channel A and channel B. 
     Radio unit  815  receives signal  814  received by antenna  813 , and outputs in-phase component  816  and quadrature-phase component  817  of the reception quadrature baseband signal. 
     Transmission path variation estimation unit  818  of channel A receives in-phase component  816  and quadrature-phase component  817  of the reception quadrature baseband signal. Then estimation unit  818  operates, e.g. in a similar way to estimation unit  506  of channel A shown in  FIG. 5  of the first embodiment, and outputs transmission path variation estimation signal  819  of channel A. 
     Transmission path variation estimation unit  820  of channel B receives in-phase component  816  and quadrature-phase component  817  of the reception quadrature baseband signal. Then estimation unit  820  operates, e.g. in a similar way to estimation unit  506  of channel A shown in  FIG. 5  of the first embodiment, and outputs transmission path variation estimation signal  821  of channel B. 
     Delay unit  822  receives in-phase component  816  and quadrature-phase component  817  of the reception quadrature baseband signal, and outputs in-phase component  823  and quadrature-phase component  824  of the reception quadrature baseband signal which delays by the time needed for obtaining transmission path variation estimation signals  819  and  821  of channel A and channel B. 
     Radio unit  827  receives signal  826  received by antenna  825 , and outputs in-phase component  828  and quadrature-phase component  829  of reception quadrature baseband signal. 
     Transmission path variation estimation unit  830  of channel A receives in-phase component  828  and quadrature-phase component  829  of the reception quadrature baseband signal. Then estimation unit  830  operates, e.g. in a similar way to estimation unit  506  of channel A shown in  FIG. 5  of the first embodiment, and outputs transmission path variation estimation signal  831  of channel A. 
     Transmission path variation estimation unit  832  of channel B receives in-phase component  828  and quadrature-phase component  829  of the reception quadrature baseband signal. Then estimation unit  832  operates, e.g. in a similar way to estimation unit  506  of channel A shown in  FIG. 5  of the first embodiment, and outputs transmission path variation estimation signal  833  of channel B. 
     Delay unit  834  receives in-phase component  828  and quadrature-phase component  829  of the reception quadrature baseband signal, and outputs in-phase component  835  and quadrature-phase component  836  of the reception quadrature baseband signal which delays by the time needed for obtaining transmission path variation estimation signals  831  and  833  of channel A and channel B. 
     Radio unit  839  receives signal  838  received by antenna  837 , and outputs in-phase component  840  and quadrature-phase component  841  of reception quadrature baseband signal. 
     Transmission path variation estimation unit  842  of channel A receives in-phase component  840  and quadrature-phase component  841  of the reception quadrature baseband signal. Then estimation unit  842  operates, e.g. in a similar way to estimation unit  506  of channel A shown in  FIG. 5  of the first embodiment, and outputs transmission path variation estimation signal  843  of channel A. 
     Transmission path variation estimation unit  844  of channel B receives in-phase component  840  and quadrature-phase component  841  of the reception quadrature baseband signal. Then estimation unit  844  operates, e.g. in a similar way to estimation unit  506  of channel A shown in  FIG. 5  of the first embodiment, and outputs transmission path variation estimation signal  845  of channel B. 
     Delay unit  846  receives in-phase component  840  and quadrature-phase component  841  of the reception quadrature baseband signal, and outputs in-phase component  847  and quadrature-phase component  848  of the reception quadrature baseband signal which delays by the time needed for obtaining transmission path variation estimation signals  843  and  845  of channel A and channel B. 
     Received signal strength intensity estimation unit  849  receives reception signals  802 ,  814 ,  826 ,  838 , then estimates the reception received signal strength intensity of the foregoing respective signals, and outputs the estimated values as reception received signal strength intensity estimation signal  850 . 
     Phase difference estimation unit  851  receives transmission path variation estimation signals  807 ,  819 ,  831 ,  843  of channel A, then finds respective phase differences such as a phase difference between signals  807  and  819  in the in-phase-quadrature plane, and outputs the phase difference as phase difference estimation signal  852  of channel A. 
     In a similar way to what is done by estimation unit  851 , phase difference estimation unit  853  receives transmission path variation estimation signals  809 ,  821 ,  833 ,  845  of channel B, then finds respective phase differences such as a phase difference between signals  809  and  821  in the in-phase-quadrature plane, and outputs the phase difference as phase difference estimation signal  854  of channel B. 
     Signal selection unit  855  receives the following signals: 
     transmission path variation estimation signal  807  of channel A; 
     transmission path variation estimation signal  809  of channel B; 
     in-phase component  811  and quadrature-phase component  812  of delayed reception quadrature baseband signal; 
     transmission path variation estimation signal  819  of channel A; 
     transmission path variation estimation signal  821  of channel B; 
     in-phase component  823  and quadrature-phase component  824  of delayed 
     reception quadrature baseband signal; 
     transmission path variation estimation signal  831  of channel A; 
     transmission path variation estimation signal  833  of channel B; 
     in-phase component  835  and quadrature-phase component  836  of delayed reception quadrature baseband signal; 
     transmission path variation estimation signal  843  of channel A; 
     transmission path variation estimation signal  845  of channel B; 
     in-phase component  847  and quadrature-phase component  848  of delayed reception quadrature baseband signal; 
     received signal strength intensity estimation signal  850 ; 
     phase difference estimation signal  852  of channel A; and 
     phase difference estimation signal  854  of channel B; 
     Then signal selection unit  855  selects a group of signals supplied from the antenna, which can most accurately demultiplex channel A signals from channel B signals, out of received signal strength intensity estimation signal  850 , phase difference estimation signal  852  of channel A, and phase difference estimation signal  854  of channel B. Signal selection unit  855  outputs signal groups  856  and  857 . 
     The signal group here refers to, e.g. transmission path variation estimation signal  807  and estimation signal  809  of channel B estimated from the signal received by antenna  801 , in-phase component  811  and quadrature-phase component  812  of the delayed reception quadrature baseband signal. 
     Signal processor  858  receives signal groups  856 ,  857 , and operates in a similar way to signal processor  525  shown in  FIG. 5  of the first embodiment. Signal processor  858  outputs in-phase component  859 , quadrature-phase component  860  of the reception quadrature baseband signal of channel A as well as in-phase component  861 , quadrature-phase component of the reception quadrature baseband signal  862  of channel B. 
     Demodulator  863  receives in-phase component  859  and quadrature-phase component  860  of the reception quadrature baseband signal of channel A, and outputs reception digital signal  864  of channel A. 
     Demodulator  865  receives in-phase component  861  and quadrature-phase component  862  of the reception quadrature baseband signal of channel B, and outputs reception digital signal  866  of channel B. 
       FIG. 9  shows a structure of the reception apparatus in accordance with the second embodiment, and the elements operating in a similar way to those shown in  FIG. 8  have the same reference marks. 
     Received signal strength intensity estimation unit  901  receives the following signals: 
     in-phase component  804  and quadrature-phase component  805  of the reception quadrature baseband signal; 
     in-phase component  816  and quadrature-phase component  817  of the reception quadrature baseband signal: 
     in-phase component  828  and quadrature-phase component  829  of the reception quadrature baseband signal; and 
     in-phase component  840  and quadrature-phase component  841  of the reception quadrature baseband signal. 
     Then estimation unit  901  estimates the reception received signal strength intensity of the foregoing respective components, and outputs reception received signal strength intensity estimation signal  850 . 
       FIG. 10  shows transmission path variation estimation signals of a channel in accordance with the second embodiment. The following four signals are mapped in  FIG. 10 : 
     transmission path variation estimation signal  1001  of a channel of a signal received by antenna  801 , and expressed in (I 801 , Q 801 ); 
     transmission path variation estimation signal  1002  of a channel of a signal received by antenna  813 , and expressed in (I 813 , Q 813 ); 
     transmission path variation estimation signal  1003  of a channel of a signal received by antenna  825 , and expressed in (I 825 , Q 825 ); transmission path variation estimation signal  1004  of a channel of a signal received by antenna  837 , and expressed in (I 837 , Q 837 ); 
     Next, an operation of the reception apparatus, in particular of phase difference estimation unit  851  and signal selection unit  855 , is demonstrated hereinafter with reference to  FIGS. 8 and 10 . 
     Assume that phase difference estimation unit  851  receives signal  1001 , signal  1002 , signal  1003  and signal  1004  in  FIG. 10  as transmission path variation estimation signals  807 ,  819 ,  831 , and  843  of channel A respectively. In this case, find the phase difference between (I 801 , Q 801 ) and (I 813 , Q 813 ) in I-Q plane. In a similar way to this, find the phase difference between the following combinations in I-Q plane: (I 801 , Q 801 ) and (I 825 , Q 825 ); (I 801 , Q 801 ) and (I 837 , Q 837 ); (I 813 , Q 813 ) and (I 825 , Q 825 ); (I 813 , Q 813 ) and (I 837 , Q 837 ). Then phase difference estimation unit  851  outputs phase difference estimation signal  852  of channel A. Phase difference estimation unit  853  outputs phase difference estimation signal  854  of channel B in a similar way to what is discussed above. 
     Next, an operation of signal selection unit  855  is demonstrated: Phase difference estimation signal  852  of channel A takes a value ranging from 0 to pi (π). In other words, the foregoing respective phase differences between (I 801 , Q 801 ) and (I 813 , Q 813 ); (I 801 , Q 801 ) and (I 825 , Q 825 ); (I 801 , Q 801 ) and (I 837 , Q 837 ); (I 813 , Q 813 ) and (I 825 , Q 825 ); (I 813 , Q 813 ) and (I 837 , Q 837 ) take a value ranging from 0 to pi (π). For instance, assume that the phase difference between (I 801 , Q 801 ) and (I 813 , Q 813 ) is θ, find an absolute value of θ, and find absolute values of each one of the phase differences. 
     In a similar way, determine whether or not phase difference estimation signal  854  of channel B has correlation. 
     Signal selection unit  855  selects an optimum antenna  2  system out of phase difference estimation signals  852 ,  854  of channels A, B supplied. A method of this selection is demonstrated hereinafter. 
     For instance, assume that a phase difference of channel A of signals received by antenna  801  and antenna  813  is 0 (zero) and that of channel B is also 0. At this time, it is prepared that the signals received by antennas  801  and  813  should not be selected as signal groups  856 ,  857 . On the other hand, assume that a phase difference of channel A of signals received by antenna  801  and antenna  813  is 0 (zero) and that of channel B is pi (π). At this time, it is prepared that the signals received by antennas  801  and  813  should be selected as signal groups  856 ,  857 . 
     Place signal  802  received by antenna  801 , signal  814  by antenna  813 , signal  826  by antenna  825 , and signal  838  by antenna  837  in descending order of reception received signal strength intensity with received signal strength intensity estimation signal  850 . Then select the signals having stronger electric field intensities as signal groups  856 ,  857 . 
     As such, optimum signal groups are selected on a priority base using a phase difference or a reception received signal strength intensity, then the selected ones are output as signal groups  856 ,  857 . For instance, the phase difference between a transmission path variation of channel A of antenna  801  and that of antenna  813  does not correlate with the phase difference between a transmission path variation of channel B of antenna  801  and that of antenna  813 . The reception received signal strength intensity of antenna  801  and that of antenna  813  are stronger than those of other antennas. Then transmission path variation estimation signal  807  of channel A, variation estimation signal  809  of channel B, in-phase component  811  and quadrature-phase component  812  of the delayed reception orthogonal are output as signal group  856 . Transmission path variation estimation signal  819  of channel A, variation estimation signal  821  of channel B, in-phase component  823  and quadrature-phase component  824  of the delayed reception orthogonal are output as signal group  857 . 
       FIG. 9  has a structure of the received signal strength intensity estimation unit different from that shown in  FIG. 8 . Reception electric field estimation unit  901  of  FIG. 9  differs from that of  FIG. 8  in the following point: Estimation unit  901  finds reception received signal strength intensity from in-phase component  804  and quadrature-phase component  805  of the reception quadrature baseband signal. In a similar manner, estimation unit  901  finds the respective field intensity from in-phase component  816  and quadrature-phase component  817 , from in-phase component  828  and quadrature-phase component  829 , and from in-phase component  840  and quadrature-phase component  841 . 
     In the descriptions discussed above, the frame structure of the transmission signal shown in  FIG. 1  is taken as an example; however, this second embodiment is not limited to the example. Use of two channels as the number of channels in the descriptions does not limit this embodiment, and an increase of channels will increase the number of transmission path variation estimation units. Each channel can undergo a different modulation method from each other. On the other hand, all the channels can use the spread spectrum communication method. The spread spectrum communication method can coexist with the other methods. 
     Not less than four antennas installed in the reception apparatus can assure the better reception sensitivity. The expression of “antenna” in the previous description does not always mean a single antenna, but “antenna” can mean an antenna unit which is formed of a plurality of antennas. 
     According to the second embodiment discussed above, the reception apparatus comprises the following elements: 
     a received signal strength intensity estimation unit for estimating a reception received signal strength intensity of a signal received by respective antennas and outputting an estimation signal of the reception received signal strength intensity of the reception signal; 
     a phase difference estimation unit for receiving a transmission path variation estimation signal of a channel of the respective antennas, finding a phase difference of the transmission path variation estimation signal, and outputting a phase difference signal; and 
     a signal selection unit for receiving a reception quadrature baseband signal of the respective antennas, a transmission path variation estimation signal of each channel of the respective antennas, a reception electric field estimation signal of the reception signal, the phase difference signal, then selecting the reception quadrature baseband signal and the transmission path variation estimation signal for demultiplexing signals of the respective channels from the reception signal, and outputting the signals selected. The foregoing structure allows the reception apparatus to demultiplex the multiplexed signals with accuracy. 
     Exemplary Embodiment 3 
     The third embodiment describes a transmission method, which handles the following frame structure of signals transmitted from respective antennas: 
     a symbol for estimating transmission path variation is inserted into the frame; 
     the symbols are multiplied by a code; 
     the symbols of the respective antennas are placed at an identical time; and 
     the codes of the respective antennas are orthogonal to each other. 
     The third embodiment also describes a transmission apparatus and a reception apparatus both used in the foregoing transmission method. 
       FIG. 11  shows frame structure  1120  in accordance with spread spectrum communication method A, and frame structure  1130  in accordance with spread spectrum communication method B. Pilot symbols  1101 ,  1103 ,  1105  of spread spectrum communication method A are multiplied by a code. Data symbols  1102 ,  1104  of spread spectrum communication method A are multiplied by a code. 
     Pilot symbols  1106 ,  1108 ,  1110  of spread spectrum communication method B are multiplied by a code. Data symbols  1107 ,  1109  of spread spectrum communication method B are multiplied by a code. 
     Pilot symbol  1101  of communication method A and pilot symbol  1106  of communication method B occur at an identical time. In the same manner, the following combinations occur at an identical time: 
     data symbol  1102  of method A and data symbol  1107  of method B; 
     pilot symbol  1103  of method A and pilot symbol  1108  of method B; 
     data symbol  1104  of method A and data symbol  1109  of method B; and 
     pilot symbol  1105  of method A and pilot symbol  1110  of method B. 
       FIG. 12  shows a structure of the transmission apparatus in accordance with this third embodiment, and the apparatus comprises transmission unit  1220  of spread spectrum communication method A, transmission unit  1230  of spread spectrum communication method B, and frame structure signal generator  1217 . 
     Transmission unit  1220  of method A is formed of modulation signal generator  1202 , radio unit  1204 , power amplifier  1206 , and antenna  1208 . Transmission unit  1230  of method B is formed of modulation signal generator  1210 , radio unit  1212 , power amplifier  1214 , and antenna  1216 . Frame structure signal generator  1217  outputs the information about the frame structure shown in  FIG. 11  as frame structure signal  1218 . 
     Modulation signal generator  1202  of method A receives transmission digital signal  1201  of spread spectrum transmission method A and frame structure signal  1218 , then outputs modulation signal  1203  of method A in accordance with the frame structure. 
     Radio unit  1204  of method A receives modulation signal  1203 , then outputs transmission signal  1205  of method A. 
     Power amplifier  1206  of method A receives transmission signal  1205 , amplifies it, then outputs the amplified signal as transmission signal  1207  from antenna  1208  in the form of radio wave. 
     Modulation signal generator  1210  of method B receives transmission digital signal  1209  of spread spectrum transmission method B and frame structure signal  1218 , then outputs modulation signal  1211  of method B in accordance with the frame structure. 
     Radio unit  1212  of method B receives modulation signal  1211 , then outputs transmission signal  1213  of method B. 
     Power amplifier  1214  of method B receives transmission signal  1213 , amplifies it, then outputs the amplified signal as transmission signal  1215  from antenna  1216  in the form of radio wave. 
       FIG. 13  shows a structure of modulation signal generators  1202 ,  1210  shown in  FIG. 12  of the third embodiment. Pilot symbol modulation signal generator  1301  receives code Cpa(t)  1302  for a pilot symbol, and multiplies the pilot symbol by code Cpa(t)  1302 , then outputs in-phase component  1303  and quadrature-phase component  1304  of a transmission quadrature baseband signal of the pilot symbol. 
     Primary modulation unit  1306  receives transmission digital signal  1305 , then outputs in-phase component  1307  and quadrature-phase component  1308  of the quadrature baseband signal of channel  0  undergone the primary modulation. 
     Spread unit  1309  receives in-phase component  1307  and quadrature-phase component  1308  of the quadrature baseband signal of channel  0  undergone the primary modulation, code C 0   a (t)  1310  for channel  0 , frame structure signal  1320 , then multiplies in-phase component  1307 , quadrature-phase component  1308  and code C 0   a (t)  1310  based on the information about frame structure in the frame structure signal  1320 , and outputs in-phase component  1311  and quadrature-phase component  1312  of a transmission quadrature baseband signal of channel  0 . 
     Primary modulation unit  1313  receives transmission digital signal  1305 , then outputs in-phase component  1314  and quadrature-phase component  1315  of the quadrature baseband signal of channel  1  undergone the primary modulation. 
     Spread unit  1316  receives in-phase component  1314  and quadrature-phase component  1315  of the quadrature baseband signal of channel  1  undergone the primary modulation, code C 1   a (t)  1317  for channel  1 , frame structure signal  1320 , then multiplies in-phase component  1314 , quadrature-phase component  1315  and code C 1   a (t)  1317  based on the information about the frame structure in the frame structure signal  1320 , and outputs in-phase component  1318  and quadrature-phase component  1319  of a transmission quadrature baseband signal of channel  1 . 
     Adding unit  1321  receives in-phase component  1311  of the transmission quadrature baseband signal of channel  0  and in-phase component  1318  of that of channel  1 , and adds component  1311  and component  1318  together, then outputs the added in-phase component  1322 . 
     Adding unit  1323  receives quadrature-phase component  1312  of the transmission quadrature baseband signal of channel  0  and in-phase component  1319  of that of channel  1 , and adds component  1312  and component  1319  together, then outputs the added quadrature-phase component  1324 . 
     In-phase component switcher  1325  receives in-phase component  1303  of the pilot symbol transmission quadrature baseband signal  1303 , added in-phase component  1322  and frame structure signal  1320 , then selects in-phase component  1303  and added in-phase component  1322  based on the information about frame structure in the frame structure signal  1320 , and outputs in-phase component  1326  of the selected transmission quadrature baseband signal. 
     Quadrature-phase component switcher  1327  receives quadrature-phase component  1304  of the pilot symbol transmission quadrature baseband signal, added quadrature-phase component  1324  and frame structure signal  1320 , then selects quadrature-phase component  1304  and added quadrature-phase component  1324  based on the information about frame structure in the frame structure signal  1320 , and outputs quadrature-phase component  1328  of the selected transmission quadrature baseband signal. 
     Orthogonal modulation unit  1329  receives in-phase component  1326  and quadrature-phase component  1328  of the selected transmission quadrature baseband signal, then provides the input with orthogonal modulation, and outputs modulation signal  1330 . 
       FIG. 14  shows a relation between a pilot symbol and a code to be multiplied to the pilot symbols in pilot-symbol structure  1420  of spread-spectrum communication method A and in pilot-symbol structure  1430  of method B. Spread code  1401  of method A at time  0  is expressed as Cpa( 0 ), and spread code  1402  of method A at time  1  is expressed as Cpa( 1 ). The following codes are expressed in the same manner: 
     code  1403  of method A at time  2  as Cpa( 2 ); 
     code  1404  of method A at time  3  as Cpa( 3 ); 
     code  1405  of method A at time  4  as Cpa( 4 ); code  1406  of method A at time  5  as Cpa( 5 ); 
     code  1407  of method A at time  6  as Cpa( 6 ); and 
     code  1408  of method A at time  7  as Cpa( 7 ). 
     Time  0 -time  7  form one cycle of spread code Cpa. 
     In a similar manner to the spread codes of method A, spread codes of method B are expressed as follows: 
     code  1409  of method B at time  0  as Cpb( 0 ); 
     code  1410  of method B at time  1  as Cpb( 1 ); 
     code  1411  of method B at time  2  as Cpb( 2 ); 
     code  1412  of method B at time  3  as Cpb( 3 ); 
     code  1413  of method B at time  4  as Cpb( 4 ); 
     code  1414  of method B at time  5  as Cpb( 5 ); 
     code  1415  of method B at time  6  as Cpb( 6 ); and 
     code  1416  of method B at time  7  as Cpb( 7 ). 
     Time  0 -time  7  form one cycle of spread code Cpb. 
       FIG. 15  shows a structure of the reception apparatus in accordance with the third embodiment. The elements operating in the same way as those in  FIG. 5  have the same reference marks. 
     Transmission path variation estimation unit  1501  of spread-spectrum communication method A receives in-phase component  504  and quadrature-phase component  505  of the reception quadrature baseband signal. Then estimation unit  1501  estimates transmission-path distortion of method A, and outputs transmission path estimation signal  1502  of method A. 
     Transmission path variation estimation unit  1503  of spread-spectrum communication method B receives in-phase component  504  and quadrature-phase component  505  of the reception quadrature baseband signal. Then estimation unit  1503  estimates transmission-path distortion of method B, and outputs transmission path estimation signal  1504  of method B. 
     Transmission path variation estimation unit  1505  of spread-spectrum communication method A receives in-phase component  516  and quadrature-phase component  517  of the reception quadrature baseband signal. Then estimation unit  1505  estimates transmission-path distortion of method A, and outputs transmission path estimation signal  1506  of method A. 
     Transmission path variation estimation unit  1507  of spread-spectrum communication method B receives in-phase component  516  and quadrature-phase component  517  of the reception quadrature baseband signal. Then estimation unit  1507  estimates transmission-path distortion of method B, and outputs transmission path estimation signal  1508  of method B. 
     Signal processor  1509  receives the following signals: 
     transmission path variation estimation signal  1502  of method A; 
     transmission path variation estimation signal  1504  of method B; 
     in-phase component  511  and quadrature-phase component  512  of delayed reception quadrature baseband signal; 
     transmission path variation estimation signal  1506  of method A; 
     transmission path variation estimation signal  1508  of method B; and 
     in-phase component  523  and quadrature-phase component  524  of delayed reception quadrature baseband signal. 
     Then signal processor  1509  outputs the following signals: 
     in-phase component  1510  and quadrature-phase component  1511  of reception quadrature baseband signal of method A; and 
     in-phase component  1512  and quadrature-phase component  1513  of reception quadrature baseband signal of method B. 
     Demodulator  1514  of spread spectrum communication method A receives in-phase component  1510  and quadrature-phase component  1511  of reception quadrature baseband signal of method A, and outputs reception-digital signal group  1515  of method A. 
     Demodulator  1516  of spread spectrum communication method B receives in-phase component  1512  and quadrature-phase component  1513  of reception quadrature baseband signal of method B, and outputs reception-digital signal group  1517  of method B. 
       FIG. 16  shows a structure of transmission path variation estimation units  1501 ,  1505  of spread-spectrum communication method A and distortion estimation units  1503 ,  1507  of method B, both shown in  FIG. 15 . 
     Pilot-symbol inverse spread unit  1603  receives in-phase component  1601  and quadrature-phase component  1602  of the reception quadrature baseband signal, and spread-code  1604 , and outputs in-phase component  1605  and quadrature-phase component  1606  of the pilot symbol of the reception quadrature baseband signal undergone the inverse spread. 
     Transmission path variation estimation unit  1607  receives in-phase component  1605  and quadrature-phase component  1606 , and outputs transmission path variation estimation signal  1608 . 
       FIG. 17  shows frame structure  1710  and transmission path variation amount  1720  along a time axis. Pilot symbol  1701  and transmission path variation (I 0 , Q 0 ) occur at time  0  (zero). In the same manner, following combinations occur at respective times: 
     pilot symbol  1702  and transmission path variation (I 1 , Q 1 ) at time  1 ; 
     pilot symbol  1703  and transmission path variation (I 2 , Q 2 ) at time  2 ; 
     pilot symbol  1704  and transmission path variation (I 3 , Q 3 ) at time  3 ; 
     pilot symbol  1705  and transmission path variation (I 4 , Q 4 ) at time  4 ; 
     pilot symbol  1706  and transmission path variation (I 5 , Q 5 ) at time  5 ; 
     pilot symbol  1707  and transmission path variation (I 6 , Q 6 ) at time  6 . 
     An operation of the transmission apparatus is demonstrated hereinafter with reference to  FIG. 11-FIG .  14 . Structures of pilot symbol  1101  of communication method A and pilot symbol  1106  of method B, both occurring at the same time, are described with reference to  FIG. 14 . 
       FIG. 14  shows a structure of one pilot symbol. Pilot symbol  1101  of spread-spectrum communication method A shown in  FIG. 11  is multiplied by code Cpa, and formed of, e.g. spread codes  1401 ,  1402 ,  1403 ,  1404 ,  1405 ,  1406 ,  1407 , and  1408 . In a similar way, pilot symbol  1106  of spread-spectrum communication method B shown in  FIG. 11  is multiplied by code Cpb, and formed of, e.g. spread codes  1409 ,  1410 ,  1411 ,  1412 ,  1413 ,  1414 ,  1415 , and  1416 . Spread code Cpa multiplied to the pilot symbol of method A is orthogonal to spread code Cpb multiplied to the pilot symbol of method B. 
     Next, the operation of the transmission apparatus is demonstrated. In  FIG. 12 , frame structure signal generator  1217  outputs the information about the frame structure shown in  FIG. 11  as frame structure signal  1218 . Modulation signal generator  1202  of method A receives transmission digital signal  1201  of spread spectrum transmission method A and frame structure signal  1218 , then outputs modulation signal  1203  of method A in accordance with the frame structure. Modulation signal generator  1210  of method B receives transmission digital signal  1209  of spread spectrum transmission method B and frame structure signal  1218 , then outputs modulation signal  1211  of method B in accordance with the frame structure. 
     Operations of modulation signal generators  1202  and  1210  are demonstrated with reference to  FIG. 13 . At a transmitter of spread-spectrum communication method A, pilot-symbol transmission signal generator  1301  shown in  FIG. 13  receives code  1302  for the pilot symbol and frame structure signal  1320 . Then generator  1301  outputs, e.g. in-phase component  1303  and quadrature-phase component  1304  of a pilot symbol transmission quadrature baseband signal in accordance with the structure of the pilot symbol of communication method A shown in  FIG. 14 . 
     In a similar way to the foregoing transmitter, at a transmitter of spread-spectrum communication method B, pilot-symbol transmission signal generator  1301  shown in  FIG. 13  receives code  1302  for the pilot symbol and frame structure signal  1320 . Then generator  1301  outputs, e.g. in-phase component  1303  and quadrature-phase component  1304  of a pilot symbol transmission quadrature baseband signal in accordance with the structure of the pilot symbol of communication method B shown in  FIG. 14 . 
     As such, the pilot symbol of communication method A is orthogonal to the spread code of the pilot symbol of communication method B. 
     Next, an operation of the reception apparatus is demonstrated with reference to  FIG. 15-FIG .  17 . Antenna  501  shown in  FIG. 15  receives signal  502  in which spread-spectrum communication methods A and Bare mixed, and radio unit  503  outputs in-phase component  504  and quadrature-phase component  505 , in which methods A and B are mixed, of a reception quadrature baseband signal. 
     Operations of transmission path variation estimation unit  1501  of method A and estimation unit  1503  of method B are demonstrated with reference to  FIG. 16 . Estimation unit  1501  of method A operates as follows: Pilot-symbol inverse-spread unit  1603  in  FIG. 16  receives in-phase component  1601  and quadrature-phase component  1602  of the reception quadrature baseband signal, in which methods A and B are mixed, and spread code  1604  for the pilot symbol of method A. Then inverse-spread unit  1603  detects pilot symbols in in-phase component  1601  and quadrature-phase component  1602 , and provides the detected pilot symbols with the inverse-spread using spread-code  1604 . Finally, inverse-spread unit  1603  outputs in-phase component  1605  and quadrature-phase component  1606  undergone the inverse spread. 
     In the foregoing operation, the component of method B in the pilot symbol of in-phase component  1601  and quadrature-phase component  1602  can be removed by the inverse-spread because the code of method A is orthogonal to the code of method B. 
     Transmission path variation estimation unit  1607  is described with reference to  FIG. 17 . Transmission path variations (I 0 , Q 0 ) and (I 6 , Q 6 ) of the pilot symbol in  FIG. 17  are found using in-phase component  1605  and quadrature-phase component  1606  of the reception quadrature baseband signal of the pilot symbol undergone the inverse-spread. Then transmission path variations (I 1 , Q 1 ), (I 2 , Q 2 ), (I 3 , Q 3 ), (I 4 , Q 4 ), and (I 5 , Q 5 ) of data symbol are found using distortions (I 0 , Q 0 ) and (I 6 , Q 6 ) of the pilot symbol. Those distortions are output as transmission path variation estimation signal  1608 . 
     In a similar way to what is discussed above, transmission path variation estimation unit  1503  of method B outputs estimation signal  1504  from reception signal  502  in which methods A and B are mixed. Distortion estimation unit  1505  of method A and estimation unit  1507  of method B output transmission variation estimation signal  1506  of method A and estimation signal  1508  of method B respectively from reception signal  514  in which methods A and B are mixed. 
     In the foregoing descriptions, the transmission path variation is expressed in (I, Q); however the distortion can be expressed in power or phase, so that the distortions expressed in power and phase can be output as variation estimation signals  1502 ,  1506  of method A, and signals  1506 ,  1508  of method B. 
     The structures and operations discussed above allow demultiplexing the modulation signals of spread-spectrum communication method A from those of method B, so that the signals can be demodulated. 
     In this embodiment, an accuracy of demultiplexing the modulation signals between channel A and channel B at the reception apparatus depends on a quality of the pilot symbol received. Thus stronger resistance of the pilot symbol to noise increases the accuracy of demultiplexing the modulation signals of channel A from channel B. As a result, the quality of data received can be improved. A greater transmission power to the pilot symbols than that to the data symbols increases the noise resistance of the pilot symbols, so that the accuracy of demultiplexing the modulation signals of spread-spectrum communication method A from method B increases. As a result, the quality of reception data can be improved. 
     In this third embodiment, two methods of spread-spectrum communication methods are multiplexed; however, the present invention is not limited to two methods. The present invention is not limited to the frame structures shown in  FIGS. 11 ,  14 , and  16 . The transmission path variation can be estimated using the pilot symbol as an example; however other symbols can be used for this purpose as long as they can estimate distortions. Spread-spectrum communication methods A and B use two channels for multiplexing; however, it is not limited to two channels only. 
     The structure of the transmission apparatus in accordance with the third embodiment is not limited to what is shown in  FIG. 12  or  FIG. 13 , and when the number of spread-spectrum communication methods increases, the number of sections formed of elements  1201 - 1208  shown in  FIG. 12  increases accordingly. When the number of channels increases, the number of sections formed of elements  1306  and  1309  shown in  FIG. 13  increases accordingly. 
     The structure of the reception apparatus in accordance with the third embodiment is not limited to what is shown in  FIG. 15 , and when the number of spread-spectrum communication methods increases, the number of distortion estimation units increases accordingly. 
     The expression of “antenna” in the previous description does not always mean a single antenna, but “antenna” can mean an antenna unit which is formed of a plurality of antennas. 
     According to the third embodiment discussed above, the transmission method handles the following frame structure of a signal transmitted from respective antenna: 
     a symbol for estimating transmission path variation is inserted into the frame; 
     the symbol is multiplied by a code; 
     the symbols of the respective antennas are arranged at an identical time; and 
     the codes of the respective antennas are orthogonal to each other. 
     The third embodiment also uses the transmission apparatus and the reception apparatus in the foregoing transmission method. In this system, multiplexing modulation signals of a plurality of channels to the same frequency band increases the data transmission rate, and allows the reception apparatus to demultiplex the multiplexed modulation signal with ease. 
     Exemplary Embodiment 4 
     The fourth exemplary embodiment demonstrates a reception apparatus comprising the following elements: 
     a received signal strength intensity estimation unit for receiving a modulation signal of a spread-spectrum communication method transmitted to the same frequency band from respective transmission antennas, then estimating a reception received signal strength intensity of the signal received by respective antennas, and outputting an estimation signal of the reception received signal strength intensity of the reception signal; 
     a phase difference estimation unit for receiving a transmission path variation estimation signal of a spread-spectrum communication method of the respective antennas, finding a phase difference of the transmission path variation estimation signals of the spread-spectrum communication method between the respective antennas, and outputting a phase difference signal; and 
     a signal selection unit for receiving a reception quadrature baseband signal of the respective antennas, the transmission path variation estimation signals of respective spread-spectrum communication methods of the respective antennas, the reception received signal strength intensity estimation signal of the reception signal, the phase difference signal, then selecting the reception quadrature baseband signal and the transmission path variation estimation signal for isolating signals of the respective methods from the reception signal, and outputting the signals selected. 
     The description of this fourth embodiment takes the case as an example, where the modulation signal having the frame structure shown in  FIG. 11  is transmitted by the transmission apparatus shown in  FIG. 12  and used in the third exemplary embodiment. 
       FIG. 18  shows a structure of a reception apparatus in accordance with the fourth embodiment. The elements operating in a similar way to those in  FIG. 8  have the same reference marks. 
     Transmission path variation estimation unit  1801  of spread-spectrum communication method A receives in-phase component  804  and quadrature-phase component  805  of the reception quadrature baseband signal. Then estimation unit  1801  operates, e.g. in a similar way to estimation unit  1501  of method A shown in  FIG. 15  of the third embodiment, and outputs transmission path variation estimation signal  1802  of method A. 
     Transmission path variation estimation unit  1803  of spread-spectrum communication method B receives in-phase component  804  and quadrature-phase component  805  of the reception quadrature baseband signal. Then estimation unit  1803  operates, e.g. in a similar way to estimation unit  1501  of method A shown in  FIG. 15  of the third embodiment, and outputs transmission path variation estimation signal  1804  of method B. 
     Delay unit  1805  receives in-phase component  804  and quadrature-phase component  805  of the reception quadrature baseband signal, and outputs in-phase component  1806  and quadrature-phase component  1807  of the reception quadrature baseband signal which delays by the time needed for obtaining transmission path variation estimation signals  1802  and  1804  of method A and method B. 
     Transmission distortion estimation unit  1808  of method A receives in-phase component  816  and quadrature-phase component  817  of the reception quadrature baseband signal. Then estimation unit  1808  operates, e.g. in a similar way to estimation unit  1501  of the same method A shown in  FIG. 15  of the third embodiment, and outputs transmission path variation estimation signal  1809  of method A. 
     Transmission path variation estimation unit  1810  of method B receives in-phase component  816  and quadrature-phase component  817  of the reception quadrature baseband signal. Then estimation unit  1810  operates, e.g. in a similar way to estimation unit  1501  of method A shown in  FIG. 15  of the third embodiment, and outputs transmission path variation estimation signal  1811  of method B. 
     Delay unit  1812  receives in-phase component  816  and quadrature-phase component  817  of the reception quadrature baseband signal, and outputs in-phase component  1813  and quadrature-phase component  1814  of the reception quadrature baseband signal which delays by the time needed for obtaining transmission path variation estimation signals  1809  and  1811  of method A and method B. 
     Transmission distortion estimation unit  1815  of method A receives in-phase component  828  and quadrature-phase component  829  of the reception quadrature baseband signal. Then estimation unit  1815  operates, e.g. in a similar way to estimation unit  1501  of channel A shown in  FIG. 15  of the third embodiment, and outputs transmission path variation estimation signal  1816  of method A. 
     Transmission path variation estimation unit  1817  of method B receives in-phase component  828  and quadrature-phase component  829  of the reception quadrature baseband signal. Then estimation unit  1817  operates, e.g. in a similar way to estimation unit  1501  of method A shown in  FIG. 15  of the third embodiment, and outputs transmission path variation estimation signal  1818  of method B. 
     Delay unit  1819  receives in-phase component  828  and quadrature-phase component  829  of the reception quadrature baseband signal, and outputs in-phase, component  1820  and quadrature-phase component  1821  of the reception quadrature baseband signal which delays by the time needed for obtaining transmission path variation estimation signals  1816  and  1818  of method A and method B. 
     Transmission distortion estimation unit  1822  of method A receives in-phase component  840  and quadrature-phase component  841  of the reception quadrature baseband signal. Then estimation unit  1822  operates, e.g. in a similar way to estimation unit  1501  of method A shown in  FIG. 15  of the third embodiment, and outputs transmission path variation estimation signal  1823  of method A. 
     Transmission path variation estimation unit  1824  of method B receives in-phase component  840  and quadrature-phase component  841  of the reception quadrature baseband signal. Then estimation unit  1824  operates, e.g. in a similar way to estimation unit  1501  of channel A shown in  FIG. 15  of the third embodiment, and outputs transmission path variation estimation signal  1825  of method B. 
     Delay unit  1826  receives in-phase component  804  and quadrature-phase component  805  of the reception quadrature baseband signal, and outputs in-phase component  1827  and quadrature-phase component  1828  of the reception quadrature baseband signal which delays by the time needed for obtaining transmission path variation estimation signals  1823  and  1825  of method A and method B. 
     Phase difference estimation unit  1829  receives transmission path variation estimation signals  1802 ,  1809 ,  1816 ,  1823  of method A, then finds respective phase differences such as a phase difference between signals  1802  and  1809  in the in-phase-quadrature plane, and outputs the phase difference as phase difference estimation signal  1830  of method A. 
     In a similar way to what is done by estimation unit  1829 , phase difference estimation unit  1831  receives transmission path variation estimation signals  1804 ,  1811 ,  1818 ,  1825  of method B, then finds respective phase differences such as a phase difference between signals  1804  and  1811  in the in-phase-quadrature plane, and outputs the phase differences as phase difference estimation signal  1832  of method B. 
     Signal selection unit  1833  receives the following signals: 
     transmission path variation estimation signal  1802  of method A; 
     transmission path variation estimation signal  1804  of method B; 
     in-phase component  1806  and quadrature-phase component  1807  of delayed reception quadrature baseband signal; 
     transmission path variation estimation signal  1809  of method A; 
     transmission path variation estimation signal  1811  of method B; 
     in-phase component  1813  and quadrature-phase component  1814  of delayed reception quadrature baseband signal; 
     transmission path variation estimation signal  1816  of method A; 
     transmission path variation estimation signal  1818  of method B; 
     in-phase component  1820  and quadrature-phase component  1821  of delayed reception quadrature baseband signal; 
     transmission path variation estimation signal  1823  of method A; 
     transmission path variation estimation signal  1825  of method B; 
     in-phase component  1827  and quadrature-phase component  1828  of delayed reception quadrature baseband signal; 
     received signal strength intensity estimation signal  850 ; 
     phase difference estimation signal  1830  of method A; and 
     phase difference estimation signal  1832  of method B. 
     Then signal selection unit  1833  selects a group of signals supplied from the antenna, which can most accurately isolate method A signals from method B signals, out of received signal strength intensity estimation signal  850 , phase difference estimation signal  1830  of method A, and phase difference estimation signal  1832  of method B. Signal selection unit  1833  then outputs signal groups  1834  and  1835 . 
     The signal group here refers to, e.g. transmission path variation estimation signal  1802  of method A, estimation signal  1804  of method B, in-phase component  1806  and quadrature-phase component  1807  of the delayed reception quadrature baseband signal of the signal received by antenna  801 . 
     Signal processor  1836  receives signal groups  1834 ,  1835 , and operates in a similar way to signal processor  1509  shown in  FIG. 15  of the third embodiment. Signal processor  1836  outputs in-phase component  1837 , quadrature-phase component  1838  of the reception quadrature baseband signal of method A as well as in-phase component  1839 , quadrature-phase component of the reception quadrature baseband signal  1840  of method B. 
     Demodulator  1841  of spread-spectrum communication method A receives in-phase component  1837  and quadrature-phase component  1838  of the reception quadrature baseband signal of method A, and outputs reception digital signal  1842  of method A. 
     Demodulator  865  of spread-spectrum communication method B receives in-phase component  1839  and quadrature-phase component  1840  of the reception quadrature baseband signal of method B, and outputs reception digital signal  1844  of method B. 
       FIG. 19  shows a structure of the reception apparatus in accordance with this exemplary embodiment, and the elements operating in a similar way to those shown in  FIGS. 8 ,  18  have the same reference marks. 
       FIG. 10  shows transmission path variation estimation signals of a spread-spectrum communication method in accordance with the fourth embodiment. The following four signals are mapped in  FIG. 10 : 
     transmission path variation estimation signal  1001  of a signal of a spread-spectrum communication method received by antenna  801 , and expressed in (I 801 , Q 801 ); 
     transmission path variation estimation signal  1002  of a signal of a spread-spectrum communication method received by antenna  813 , and expressed in (I 813 , Q 813 ); 
     transmission path variation estimation signal  1003  of a signal of a spread-spectrum communication method received by antenna  825 , and expressed in (I 825 , Q 825 ); 
     transmission path variation estimation signal  1004  of a signal of a spread-spectrum method received by antenna  837 , and expressed in (I 837 , Q 837 ); 
     Next, an operation of the reception apparatus, in particular operations of phase difference estimation unit  1829  and signal selection unit  1831 , is demonstrated hereinafter with reference to  FIGS. 1 and 18 . 
     Assume that phase difference estimation unit  1829  receives signal  1001 , signal  1002 , signal  1003  and signal  1004  shown in  FIG. 10  as transmission path variation estimation signals  1802 ,  1809 ,  1816 , and  1823  of method A respectively. In this case, find the phase difference between (I 801 , Q 801 ) and (I 813 , Q 813 ) in I-Q plane. In a similar way to this, find the phase difference between the following combinations in I-Q plane: (I 801 , Q 801 ) and (I 825 , Q 825 ); (I 801 , Q 801 ) and (I 837 , Q 837 ); (I 813 , Q 813 ) and (I 825 , Q 825 ); (I 813 , Q 813 ) and (I 837 , Q 837 ). Then phase difference estimation unit  851  outputs phase difference estimation signal  852  of method A. Phase difference estimation unit  1831  outputs phase difference estimation signal  1832  of method B in a similar way to what is discussed above. 
     Next, an operation of signal selection unit  1833  is demonstrated: Phase difference estimation signal  1830  of method A takes a value ranging from 0 to pi (π). In other words, the foregoing respective phase differences between (I 801 , Q 801 ) and (I 813 , Q 813 ); (I 801 , Q 801 ) and (I 825 , Q 825 ); (I 801 , Q 801 ) and (I 837 , Q 837 ); (I 813 , Q 813 ) and (I 825 , Q 825 ); (I 813 , Q 813 ) and (I 837 , Q 837 ) take a value ranging from 0 to pi (π). For instance, assume that the phase difference between (I 801 , Q 801 ) and (I 813 , Q 813 ) is θ, find an absolute value of θ, and find absolute values of each one of the phase differences. 
     In a similar way, determine whether or not phase difference estimation signal  1832  of method B has correlation. 
     Signal selection unit  1833  selects optimum antenna system  2  based on phase difference estimation signals  1830 ,  1832  of spread-spectrum communication methods A, B supplied. A method of this selection is demonstrated hereinafter. 
     For instance, assume that a phase difference of method A of signals received by antenna  801  and antenna  813  is 0 (zero) and that of method B is also 0. At this time, it is prepared that the signals received by antennas  801  and  813  should not be selected as signal groups  856 ,  857 . On the other hand, assume that a phase difference of method A of signals received by antenna  801  and antenna  813  is 0 (zero) and that of method B is pi (π). At this time, it is prepared that the signals received by antennas  801  and  813  should be selected as signal groups  1834 ,  1835 . 
     Place signal  802  received by antenna  801 , signal  814  by antenna  813 , signal  826  by antenna  825 , and signal  838  by antenna  837  in descending order of reception received signal strength intensity with electric field estimation signal  850 , then select the signals having stronger received signal strength intensity as signal groups  856 ,  857 . 
     As such, optimum signal groups are selected on a priority base using a phase difference or a reception received signal strength intensity, then the selected ones are output as signal groups  1834 ,  1835 . For instance, the phase difference between a transmission path variation of method A of antenna  801  and that of antenna  813  does not correlate with the phase difference between a transmission path variation of method B of antenna  801  and that of antenna  813 . The reception received signal strength intensity of antenna  801  and that of antenna  813  are stronger than those of other antennas. Then transmission path variation estimation signal  1802  of method A, variation estimation signal  1804  of method B, in-phase component  1806  and quadrature-phase component  1807  of the delayed reception orthogonal are output as signal group  1834 . Transmission path variation estimation signal  1809  of method A, variation estimation signal  1811  of method B, in-phase component  1813  and quadrature-phase component  1814  of the delayed reception orthogonal are output as signal group  1835 . 
       FIG. 19  shows a structure of the received signal strength intensity estimation unit different from that shown in  FIG. 18 . Reception received signal strength intensity estimation unit  901  of  FIG. 19  differs from that of  FIG. 18  in the following point: Estimation unit  901  finds reception received signal strength intensity from in-phase component  804  and quadrature-phase component  805  of the reception quadrature baseband signal. In a similar manner, estimation unit  901  finds the respective field intensity from in-phase component  816  and quadrature-phase component  817 , from in-phase component  828  and quadrature-phase component  829 , and from in-phase component  840  and quadrature-phase component  841 . 
     In the descriptions discussed above, the frame structure of the transmission signal shown in  FIG. 11  is taken as an example; however, this embodiment is not limited to the example. Use of two spread-spectrum communication methods as the number of communication methods in the descriptions does not limit this embodiment, and an increase of the methods will increase the number of transmission path variation estimation units. Method A and method B undergo multiplexing of two channels; however, the present invention is not limited to two-channels. 
     Not less than four antennas installed in the reception apparatus assure the better reception sensitivity. The expression of “antenna” in the previous description does not always mean a single antenna, but “antenna” can mean an antenna unit which is formed of a plurality of antennas. 
     As discussed above, the fourth exemplary embodiment has referred to the reception apparatus comprising the following elements: 
     a received signal strength intensity estimation unit for receiving a modulation signal of a spread-spectrum communication method transmitted to the same frequency band from respective transmission antennas, then estimating a reception received signal strength intensity of the signal received by respective antennas, and outputting an estimation signal of the reception received signal strength intensity of the reception signal; 
     a phase difference estimation unit for receiving a transmission path variation estimation signal of a spread-spectrum communication method of the respective antennas, finding a phase difference of the transmission path variation estimation signal of the spread-spectrum communication method between the respective antennas, and outputting a phase difference signal; and 
     a signal selection unit for receiving a reception quadrature baseband signal of the respective antennas, a transmission path variation estimation signal of respective spread-spectrum communication methods of the respective antennas, a reception electric field estimation signal of the reception signal, and the phase difference signal, then selecting the reception quadrature baseband signal and the transmission path variation estimation signal for isolating signals of the respective methods from the reception signal, and outputting the signals selected. 
     The foregoing structure allows the reception apparatus to demultiplex a multiplexed signal with accuracy. 
     Exemplary Embodiment 5 
     The fifth exemplary embodiment describes the transmission method of transmitting modulation signals of a plurality of channels from a plurality of antennas to the same frequency band. More particularly, a demodulation symbol to be inserted into a channel is formed of a plurality of sequential symbols, and each one of demodulation symbols of respective channels is placed at the same time and orthogonal to each other. The fifth embodiment also describes a transmission apparatus and a reception apparatus to be used in the foregoing transmission method. 
       FIG. 20  shows frame structure  2020  of channel A and frame structure  2030  of channel B along a time axis. Frame structure  2020  includes pilot symbols  2001 ,  2002 ,  2003 ,  2004 ,  2006 ,  2007 ,  2008 ,  2009 , and data symbol  2005 . Frame structure  2030  includes pilot symbols  2010 ,  2011 ,  2012 ,  2013 ,  2015 ,  2016 ,  2017 ,  2018 , and data symbol  2014 . 
       FIG. 21  shows a placement of signal points of the pilot symbols of channels A and B in in-phase-quadrature (I-Q) plane, and signal points  2101  and  2102  indicate the pilot symbols. 
       FIG. 2  shows a structure of the transmission apparatus in accordance with the fifth embodiment. 
       FIG. 22  shows a detailed structure of modulation signal generators  202 ,  212 . Data-symbol modulation signal generator  2202  receives transmission digital signal  2201 , frame structure signal  2208 . When frame structure signal  2208  indicates a data symbol, generator  2202  provides signals  2201  with, e.g. QPSK modulation, and outputs in-phase component  2203  and quadrature-phase component  2204  of a transmission quadrature baseband signal of the data symbol. 
     Pilot symbol modulation signal generator  2205  receives frame structure signal  2208 . When signal  2208  indicates a pilot symbol, generator  2205  outputs in-phase component  2206  and quadrature-phase component  2207  of a transmission quadrature baseband signal of the pilot symbol. 
     In-phase component switcher  2209  receives in-phase components  2203 ,  2206  and frame structure signal  2208 , then selects the in-phase component of transmission quadrature baseband signal corresponding to a symbol indicated by frame structure signal  2208 , and outputs the selected one as in-phase component  2210  of the selected transmission quadrature baseband signal. 
     Quadrature-phase component switcher  2211  receives quadrature-phase components  2204 ,  2207  and frame structure signal  2208 , then selects a quadrature-phase component of a transmission quadrature baseband signal corresponding to a symbol indicated by frame structure signal  2208 , and outputs the selected one as quadrature-phase component  2212  of the selected transmission quadrature baseband signal. 
     Orthogonal modulator  2213  receives in-phase component  2210  selected, quadrature-phase component  2212  selected, then provides those components  2210 ,  2212  with orthogonal modulation, and outputs modulation signal  2214 . 
       FIG. 5  shows a structure of the reception apparatus in accordance with this fifth embodiment. 
       FIG. 17  shows amounts of transmission path variation along a time axis. Transmission path variation (I 0 , Q 0 )  1701  at time  0  (zero) is found by correlation calculation. In the same manner, following combinations are found at respective times by correlation calculations: 
     data symbol  1702  and transmission path variation (I 1 , Q 1 ) at time  1 ; 
     data symbol  1703  and transmission path variation (I 2 , Q 2 ) at time  2 ; 
     data symbol  1704  and transmission path variation (I 3 , Q 3 ) at time  3 ; 
     data symbol  1705  and transmission path variation (I 4 , Q 4 ) at time  4 ; 
     data symbol  1706  and transmission path variation (I 5 , Q 5 ) at time  5 ; 
     data symbol  1707  and transmission path variation (I 6 , Q 6 ) at time  6 . 
       FIG. 23  shows a structure of transmission path variation estimation units  506 ,  518  of channel A and estimation units  508 ,  520  of channel B shown in  FIG. 5 . 
     Pilot symbol correlation calculation unit  2303  receives in-phase component  2301 , quadrature-phase component  2302  of a reception quadrature baseband signal, and pilot-symbol series  2304 , then outputs in-phase component  2305 , quadrature-phase component  2306  of the reception quadrature baseband signal of the pilot symbols undergone the correlation calculations. 
     Transmission path variation estimation unit  2307  receives in-phase component  2305  and quadrature-phase component  2306 , and outputs transmission-path variation estimation signal  2308 . 
     The transmission method in accordance with this fifth embodiment is demonstrated hereinafter with reference to  FIGS. 20 and 21 . 
     The signal point of pilot symbol  2001  of channel A at time  0  is placed at point  2101  (1, 1) in  FIG. 21 . The signal point of pilot symbol  2002  of channel A at time  1  is placed at point  2101  (1, 1) in  FIG. 21 . The signal point of pilot symbol  2003  of channel A at time  2  is placed at point  2101  (1, 1) in  FIG. 21 . The signal point of pilot symbol  2004  of channel A at time  3  is placed at point  2101  (1, 1) in  FIG. 21 . 
     The signal point of pilot symbol  2010  of channel B at time  0  is placed at point  2101  (1, 1) in  FIG. 21 . The signal point of pilot symbol  2011  of channel B at time  1  is placed at point  2101  (1, 1) in  FIG. 21 . The signal point of pilot symbol  2012  of channel B at time  2  is placed at point  2102  (−1, −1) in  FIG. 21 . The signal point of pilot symbol  2013  of channel B at time  3  is placed at point  2102  (−1, −1) in  FIG. 21 . 
     In a similar way to what is discussed above, the signal point of pilot symbol  2006  is placed at the same place as that of pilot symbol  2001 . The signal points of pilot symbols  2007 ,  2008 ,  2009  are placed at the same places of pilot symbols  2002 ,  2003 ,  2004  respectively. In the same manner, the signal points of pilot symbols  2015 ,  2016 ,  2017 ,  2018  are placed at the same places of pilot symbols  2010 ,  2011 ,  2012 ,  2013  respectively. 
     As such, sequential pilot symbols  2001 ,  2002 ,  2003 ,  2004  of channel A has correlation of 0 (zero) with sequential pilot symbols  2010 ,  2011 ,  2012 ,  2013  of channel B. 
     Next, an operation of the transmission apparatus is demonstrated hereinafter with reference to  FIG. 2  and  FIG. 22 . 
     In  FIG. 2 , frame structure signal generator  209  outputs the information of the frame structure shown in  FIG. 20  as frame structure signal  210 . Modulation signal generator  202  of channel A receives frame structure signal  210  and transmission digital signal  201  of channel A, then outputs modulation signal  203  of channel A in accordance with the frame structure. Modulation signal generator  212  of channel B receives frame structure signal  210  and transmission digital signal  211  of channel B, then outputs modulation signal  213  of channel B in accordance with the frame structure. 
     An operation of modulation signal generators  202  and  212  at the process discussed above is described using transmitter  220  of channel A as an example with reference to  FIG. 22 . 
     Data symbol modulation signal generator  2202  receives transmission digital signal  2201 , i.e. transmission digital signal  201  of channel A in  FIG. 2 , and frame structure signal  2208 , i.e. frame structure signal  210  in  FIG. 2 . When frame structure signal  2208  indicates a data symbol, generator  2202  provides signal  2201  with QPSK modulation, and outputs in-phase component  2203  and quadrature-phase component  2204  of a transmission quadrature baseband signal of the data symbol. 
     Pilot symbol modulation signal generator  2205  receives frame structure signal  2208 . When signal  2208  indicates a pilot symbol, generator  2205  outputs in-phase component  2206  and quadrature-phase component  2207  of a transmission quadrature baseband signal of the pilot symbol. 
     In-phase component switcher  312  receives the following signals: 
     in-phase component  2203  of a data symbol transmission quadrature baseband signal; 
     in-phase component  2206  of a pilot symbol transmission quadrature baseband signal; and 
     frame structure signal  2208 . 
     Switcher  312  then selects an in-phase component of the transmission quadrature baseband signal corresponding to the symbol indicated by frame structure signal  2208 , and outputs the selected one as in-phase component  2210  of the selected transmission quadrature baseband signal. 
     Quadrature-phase component switcher  2211  receives the following signals: 
     quadrature-phase component  2204  of data symbol transmission quadrature baseband signal; 
     quadrature-phase component  2207  of pilot symbol transmission quadrature baseband signal; and 
     frame structure signal  2208 . 
     Switcher  2211  then selects a quadrature-phase component of a transmission quadrature baseband signal corresponding to the symbol indicated by frame structure signal  2208 , and outputs the selected one as quadrature-phase component  2212  of the selected transmission orthogonal base-band. 
     Orthogonal modulator  2213  receives in-phase component  2210  and quadrature-phase component  2212  discussed above, then provides those components with an orthogonal modulation, and outputs modulation signal  2214 , i.e. signal  203  shown in  FIG. 2 . 
     Next, an operation of the reception apparatus, in particular, operations of transmission path variation estimation unit  506  of channel A, transmission path variation estimation unit  508  of channel B, and signal processor  525 , with reference to  FIG. 5  and  FIG. 23 . Estimation unit  506  of channel A is taken as an example for the description purpose. 
     Pilot correlation calculation unit  2303  shown in  FIG. 23  receives in-phase component  2301 , quadrature-phase component  2302  of a reception quadrature signal, in which channel A and channel B are mixed with each other, received by antenna  501 , and pilot symbol series  2304  of channel A, then detects pilot symbols in in-phase component  2301  and quadrature-phase component  2302 . Calculation unit  2303  then calculates correlation between the pilot symbol section detected and pilot-symbol series  2304 , and outputs in-phase component  2305 , quadrature-phase component  2306  undergone the correlation calculation. 
     The pilot-symbol series of channel A can be formed of the in-phase component and the quadrature-phase component. In such a case, channel B component of the pilot symbol in in-phase component  2301  and quadrature-phase component  2302  of the reception quadrature baseband signal can be removed by the correlation calculation because the pilot symbol series of channel A is orthogonal to the pilot symbols series of channel B. 
     Transmission path variation estimation unit  2307  is described with reference to  FIG. 17 . Distortions (I 0 , Q 0 ) and (I 6 , Q 6 ) in  FIG. 17  are found by pilot-symbol correlation calculation unit  2303 . Data-symbol transmission path variations (I 1 , Q 1 ), (I 2 , Q 2 ), (I 3 , Q 3 ), (I 4 , Q 4 ), (I 5 , Q 5 ) are found from distortions (I 0 , Q 0 ) and (I 6 , Q 6 ), then estimation unit  2307  outputs those distortions as transmission path variation estimation signal  2308 . 
     In a similar way to estimation unit  506  of channel A, transmission path variation estimation unit  508  of channel B outputs transmission path variation estimation signal  509  of reception signal  502  in which channel A and channel B are mixed with each other. Estimation unit  518  of channel A and estimation unit  520  of channel B output variation estimation signal  519  of channel A and variation estimation signal  521  of channel B respectively from reception signal  514  where channel A and channel B are mixed. 
     The foregoing description expresses the transmission path variation in (I, Q); however, the distortion can be expressed in power and phase, so that estimation signals  507 ,  519  of channel A and estimation signal  509 ,  521  of channel B can be expressed in power and phase. 
     The foregoing structure and operation allow the reception apparatus to demultiplex the modulation signals of channel A from those of channel B, so that the signals can be demodulated. 
     In this fifth embodiment, the number of channels to be multiplexed is two, however, the embodiment is not limited to two channels, and not limited to the frame structure shown in  FIG. 20 . The transmission path variation can be estimated using the pilot symbol as an example, and other symbols can be used for this purpose as long as they can estimate the distortion. 
     The expression of “antenna” in the previous description does not always mean a single antenna, but “antenna” can mean an antenna unit which is formed of a plurality of antennas. 
     The structure of the transmission apparatus of this embodiment is not limited to what is shown in  FIG. 2  or  FIG. 22 , and when the number of channels increase, the structure formed of elements  201  through  208  shown in  FIG. 2  is added accordingly. 
     The structure of the reception apparatus of this embodiment is not limited to what is shown in  FIG. 5  or  FIG. 23 , and when the number of channels increase, the number of channel estimation units increases accordingly. 
     As discussed above, the fifth exemplary embodiment describes the transmission method of transmitting modulation signals of a plurality of channels from a plurality of antennas to the same frequency band. More particularly, a demodulation symbol to be inserted into a channel is formed of a plurality of sequential symbols, and each one of demodulation symbols of respective channels is placed at the same time and orthogonal to each other. The fifth embodiment also describes the transmission apparatus and the reception apparatus to be used in the foregoing transmission method. The foregoing transmission method, transmission apparatus and reception apparatus allow multiplexing modulation signals of a plurality of channels to the same frequency band. Through this operation, the transmission rate of data can be increased, at the same time, the demodulation symbol has resistance to noises, so that an accuracy of channel estimation in the reception apparatus is increased. As a result, transmission quality of data is improved. 
     Exemplary Embodiment 6 
     The sixth exemplary embodiment describes the transmission method which transmits modulation signals of a plurality of channels to the same frequency band from a plurality of antennas. More particularly, in this method, at the same time and sub-carrier(s) at which a demodulation symbol is inserted in a channel having a frame structure in accordance with OFDM method, in a symbol that is inserted in other such channel(s) both of an in-phase signal and a quadrature signal in the in-phase-quadrature plane are made to be zero signals. The sixth embodiment also describes a transmission apparatus and a reception apparatus to be used in the foregoing transmission method. 
       FIG. 4  shows a placement of signal points in in-phase-quadrature (I-Q) plane.  FIG. 24  shows examples of frame structure  2410  of channel A and frame structure  2420  of channel B along a frequency axis. Frame structure  2410  includes pilot symbol  2401  and data symbol  2402 . As shown in  FIG. 24 , at time  0  of channel A, sub-carrier  2  is assigned as pilot symbol. At this time, assume that channel B has a symbol of (I, Q)=(0, 0). As such, assume that at a certain time and a certain frequency, when channel A shows a pilot symbol, channel B has a symbol of (I, Q)=(0, 0). On the contrary, when channel B shows a pilot symbol, channel A has a symbol of (I, Q)=(0, 0). 
       FIG. 25  shows a structure of the transmission apparatus in accordance with the sixth embodiment, and the transmission apparatus is formed of channel A transmitter  2530 , channel B transmitter  2540  and frame structure signal generator  2521 . 
     Transmitter  2530  of channel A comprises serial-parallel converter  2502 , inverse discrete Fourier transformer  2504 , radio unit  2506 , power amplifier  2508 , and antenna  2510 . 
     Transmitter  2540  of channel B comprises serial-parallel converter  2512 , inverse discrete Fourier transformer  2514 , radio unit  2516 , power amplifier  2518 , and antenna  2520 . 
     Frame structure signal generator  2521  outputs the information of the frame structure as frame structure signal  2522 . 
     Serial-parallel converter  2502  of channel A receives transmission digital signal  2501  of channel A and frame structure signal  2522 , and outputs parallel signal  2503  of channel A in accordance with the frame structure. 
     Inverse discrete Fourier transformer  2504  of channel A receives parallel signal  2503 , and outputs signal  2505  undergone the inverse discrete Fourier transformation of channel A. 
     Radio unit  2506  of channel A receives signal  2505 , and outputs transmission signal  2507  of channel A. 
     Power amplifier  2508  of channel A receives and amplifies transmission signal  2507 , and outputs transmission signal  2509  as radio-wave from antenna  2510  of channel A. 
     Serial-parallel converter  2512  of channel B receives transmission digital signal  2511  of channel B and frame structure signal  2522 , and outputs parallel signal  2513  of channel B in accordance with the frame structure. 
     Inverse discrete Fourier transformer  2514  of channel B receives parallel signal  2513 , and outputs signal  2515  undergone the inverse discrete Fourier transformation of channel B. 
     Radio unit  2516  of channel B receives signal  2515 , and outputs transmission signal  2517  of channel B. 
     Power amplifier  2518  of channel B receives and amplifies transmission signal  2517 , and outputs transmission signal  2519  as radio-wave from antenna  2520  of channel B. 
       FIG. 26  shows a structure of the reception apparatus in accordance with this embodiment, and radio unit  2603  receives signal  2602  received by antenna  2601 , then outputs a reception quadrature baseband signal  2604 . 
     Fourier transformer  2605  receives quadrature baseband signal  2604 , and outputs parallel signal  2606 . 
     Transmission path variation estimation unit  2607  of channel A receives parallel signal  2606 , and outputs transmission path variation parallel signal  2608  of channel A. 
     Transmission path variation estimation unit  2609  of channel B receives parallel signal  2606 , and outputs transmission path variation parallel signal  2610  of channel B. 
     Radio unit  2613  receives signal  2612  received by antenna  2611 , and outputs reception quadrature baseband signal  2614 . 
     Fourier transformer  2615  receives signal  2614 , and outputs parallel signal  2616 . 
     Transmission path variation estimation unit  2617  of channel A receives parallel signal  2616 , and outputs transmission path variation parallel signal  2618  of channel A. 
     Transmission path variation estimation unit  2619  of channel B receives parallel signal  2616 , and outputs transmission path variation parallel signal  2620  of channel B. 
     Signal processor  2621  receives parallel signals  2606 ,  2616 , transmission path variation parallel signals  2608 ,  2618  of channel A, and transmission path variation parallel signals  2610 ,  2620  of channel B, then demultiplexes the signals of channel A from those of channel B, and outputs parallel signal  2622  of channel A as well as parallel signal  2623  of channel B. 
     Demodulator  2624  of channel A receives parallel signal  2622  of channel A, and outputs reception digital signal  2625  of channel A. 
     Demodulator  2626  of channel B receives parallel signal  2623  of channel B, and outputs reception digital signal  2627  of channel B. 
       FIG. 27  shows a transmission path variation of a carrier along a time axis. Specifically, relations between frame structure  2720  of carrier  1  of channel A, transmission path variation  2721  of carrier  1  of channel A, frame structure  2730  of carrier  1  of channel B, transmission path variation  2731  of carrier  1  of channel B, and reception base-band signal  2732  of carrier  1 . 
     Frame structure  2720  includes symbol  2701  of a carrier of channel A at time  0 , symbol  2702  of a carrier of channel A at time  1 , symbol  2703  of a carrier of channel A at time  2 , symbol  2704  of a carrier of channel A at time  3 , symbol  2705  of a carrier of channel A at time  4 , symbol  2706  of a carrier of channel A at time  5 . Frame structure  2730  includes symbol  2707  of a carrier of channel B at time  0 , symbol  2708  of a carrier of channel B at time  1 , symbol  2709  of a carrier of channel B at time  2 , symbol  2710  of a carrier of channel B at time  3 , symbol  2711  of a carrier of channel B at time  4 , symbol  2712  of a carrier of channel B at time  5 . 
       FIG. 28  shows a structure of transmission path variation estimation units and a signal processor of carrier  1 . 
     Estimation unit  2803  of carrier  1  of channel A receives in-phase component  2801  and quadrature-phase component  2802  of carrier  1  of the parallel signal, and outputs transmission path variation estimation signal  2804  of carrier  1  of channel A. 
     Estimation unit  2805  of carrier  1  of channel B receives in-phase component  2801  and quadrature-phase component  2802  of carrier  1  of the parallel signal, and outputs transmission path variation estimation signal  2806  of carrier  1  of channel B. 
     Estimation unit  2809  of carrier  1  of channel A receives in-phase component  2807  and quadrature-phase component  2808  of carrier  1  of the parallel signal, and outputs transmission path variation estimation signal  2810  of carrier  1  of channel A. 
     Estimation unit  2811  of carrier  1  of channel B receives in-phase component  2807  and quadrature-phase component  2808  of carrier  1  of the parallel signal, and outputs transmission path variation estimation signal  2812  of carrier  1  of channel B. 
     Signal processor  2813  of carrier  1  receives the following signals: 
     in-phase component  2801  and quadrature-phase component  2802  of carrier  1  of the parallel signal; 
     transmission path variation estimation signal  2804  of carrier  1  of channel A; 
     transmission path variation estimation signal  2806  of carrier  1  of channel B; 
     in-phase component  2807  and quadrature-phase component  2808  of carrier  1  of the parallel signal; 
     transmission path variation estimation signal  2810  of carrier  1  of channel A; and 
     transmission path variation estimation signal  2812  of carrier  1  of channel B. 
     Signal processor  2813  then demultiplexes the signals of channel A from channel B, and outputs in-phase component  2814 , quadrature-phase component  2815  of carrier  1  of the parallel signal of channel A, and in-phase component  2816 , quadrature-phase component  2817  of carrier  1  of the parallel signal of channel B. 
     An operation of the transmission apparatus is demonstrated hereinafter with reference to  FIGS. 4 ,  24  and  25 . In  FIG. 24 , the signal point of pilot symbol  2401  corresponds to signal point  402  shown in  FIG. 4 . The signal point of symbol of (I, Q)=(0, 0) corresponds to signal point  403  shown in  FIG. 4 . 
     In  FIG. 25 , frame structure signal generator  2521  outputs the information about the frame structure shown in  FIG. 24  as frame structure signal  2522 . Serial-parallel converter  2502  of channel A receives transmission digital signal  2501  of channel A, frame structure signal  2522 , then outputs parallel signal  2503  of channel A in accordance with the frame structure shown in  FIG. 24 . In a similar way to converter  2502 , serial-parallel converter  2512  of channel B receives transmission digital signal  2511  of channel B, frame structure signal  2522 , then outputs parallel signal  2513  of channel B in accordance with the frame structure shown in  FIG. 24 . 
     Next, an operation of the reception apparatus is demonstrated, in particular, operations of transmission path variation estimation units  2607 ,  2617  of channel A, estimation units  2609 ,  2619  of channel B, and signal processor  2621  are demonstrated with reference to  FIGS. 26 ,  27  and  28  using carrier  1  shown in  FIG. 24  as an example. 
       FIG. 28  shows a structure where only the functions of carrier  1  are extracted from estimation units  2607 ,  2617  of channel A, estimation units  2609 ,  2619  of channel B, and signal processor  2621  shown in  FIG. 26 . 
     In  FIG. 28 , in-phase component  2801  and quadrature-phase component  2802  of carrier  1  of the parallel signal correspond to the component of carrier  1  of parallel signal  2606  shown in  FIG. 26 . A structure of transmission path variation estimation unit  2803  of carrier  1  of channel A shows the function of carrier  1  in estimation unit  2607  shown in  FIG. 26 . Estimation signal  2804  of channel A is a component of carrier  1  of parallel signal  2608  shown in  FIG. 26 . A structure of transmission path variation estimation unit  2805  of carrier  1  of channel B shows the function of carrier  1  in estimation unit  2609  shown in  FIG. 26 . Estimation signal  2806  of channel B is a component of carrier  1  of parallel signal  2610  shown in  FIG. 26 . 
     In-phase component  2807  and quadrature-phase component  2808  of carrier  1  of the parallel signal correspond to the component of carrier  1  of parallel signal  2616  shown in  FIG. 26 . A structure of transmission path variation estimation unit  2809  of carrier  1  of channel A shows the function of carrier  1  in estimation unit  2617  shown in  FIG. 26 . Estimation signal  2810  of channel A is a component of carrier  1  of parallel signal  2618  in  FIG. 26 . A structure of transmission path variation estimation unit  2811  of carrier  1  of channel B shows the function of carrier  1  in estimation unit  2619  shown in  FIG. 26 . Estimation signal  2812  of channel B is a component of carrier  1  of parallel signal  2620  in  FIG. 26 . 
     Signal processor  2813  of carrier  1  shows the function of carrier  1  in signal processor  2621 . In-phase component  2814  and quadrature-phase component  2815  of carrier  1  of the parallel signal of channel A correspond to the component of carrier  1  of parallel signal  2622  of channel A shown in  FIG. 26 . In-phase component  2816  and quadrature-phase component  2817  of carrier  1  of the parallel signal of channel B correspond to the component of carrier  1  of parallel signal  2623  of channel B shown in  FIG. 26 . 
     Next, operations of transmission path variation estimation units  2803 ,  2809  of carrier  1  of channel A, and estimation units  2805 ,  2811  of carrier  1  of channel B shown in  FIG. 28  are demonstrated using units  2803  and  2805  as examples. 
     In  FIG. 27 , assume that a reception base-band signal of carrier  1  at time  0  through time  5 , i.e. in-phase component  2807  and quadrature-phase component  2808  of carrier  1  in the parallel signal, are (I 0 , Q 0 ), (I 1 , Q 1 ), (I 2 , Q 2 ), (I 3 , Q 3 ), (I 4 , Q 4 ), and (I 5 , Q 5 ). 
     Assume that the transmission path variation of carrier  1  of channel A at time  0  through time  5 , i.e. transmission variation estimation signal  2804  of carrier  1  of channel A, are (Ia 0 , Qa 0 ), (Ia 1 , Qa 1 ), (Ia 2 , Qa 2 ), (Ia 3 , Qa 3 ), (Ia 4 , Qa 4 ), and (Ia 5 , Qa 5 ). 
     Assume that the transmission path variation of channel B of carrier  1  at time  0  through time  5 , i.e. transmission variation estimation signal  2806  of channel B of carrier  1 , are (Ib 0 , Qb 0 ), (Ib 1 , Qb 1 ), (Ib 2 , Qb 2 ), (Ib 3 , Qb 3 ), (Ib 4 , Qb 4 ), and (Ib 5 , Qb 5 ). 
     In the foregoing case, since (I 0 , Q 0 ) has only a pilot component of channel B of carrier  1 , (Ib 0 , Qb 0 )=(I 0 , Q 0 ). Similarly, since (I 1 , Q 1 ) has only a pilot component of channel A of carrier  1 , (Ia 1 , Qa 1 )=(I 1 , Q 1 ). For instance, (Ia 0 , Qa 0 )=(Ia 1 , Qa 1 )=(Ia 2 , Qa 2 )=(Ia 3 , Qa 3 )=(Ia 4 , Qa 4 )=(Ia 5 , Qa 5 ), and (Ib 0 , Qb 0 )=(Ib 1 , Qb 1 )=(Ib 2 , Qb 2 )=(Ib 3 , Qb 3 )=(Ib 4 , Qb 4 )=(Ib 5 , Qb 5 ) will find transmission path variation estimation signals  2804  and  2806  of channels A and B respectively of carrier  1 . 
     A similar operation to what is discussed above will find transmission path variation estimation signals  2810  and  2812  of channels A and B respectively of carrier  1 . 
     Signal processor  2813  of carrier  1  receives the following signals: 
     variation estimation signals  2804 ,  2810  of channel A; 
     variation estimation signals  2806 ,  2812  of channel B; 
     in-phase component  2801 , quadrature-phase component  2802  of the parallel signal; and 
     in-phase component  2807 , quadrature-phase component  2808  of the parallel signal. 
     Then processor  2813  carries out matrix calculations for demultiplexing the signals of channel A from channel B, and outputs the following signals: 
     in-phase component  2814  and quadrature-phase component  2815  of carrier  1  of the parallel signal of channel A; and 
     in-phase component  2816  and quadrature-phase component  2817  of carrier  1  of the parallel signal of channel B. 
     As a result, modulation signals of channel A and channel B can be demultiplexed from each other, and the modulation signals can be demodulated. 
     The foregoing description expresses the transmission path variation in (I, Q); however, the distortion can be expressed in power and phase, so that estimation signals  2804 ,  2810  of channel A and estimation signal  2806 ,  2812  of channel B can be expressed in power and phase. 
     Signals of channel A and channel B of carriers  2 ,  3 , and  4  can be demultiplexed from each other in a similar way to what is discussed above using the structure shown in  FIG. 28 . 
     A method of estimating a transmission path of carrier  2  is demonstrated hereinafter. The reception apparatus of this embodiment can estimate a fluctuation of the transmission path from a pilot symbol of carrier  2  at time  0  shown in  FIG. 24 . Also the reception apparatus can estimate the fluctuation of the transmission path of carrier  2  at time  1  from the pilot symbols of carrier  1  and carrier  3  at time  1 . As such, the transmission path fluctuation of carrier  2  can be estimated by an estimated value of the transmission path fluctuation of carrier  2  estimated at time  0  and time  1 . As a result, the transmission path fluctuation can be estimated with accuracy. 
     A method of estimating a transmission path of, e.g. carrier  2  shown in  FIG. 24 , is demonstrated hereinafter. The reception apparatus can estimate a fluctuation of the transmission path from a pilot symbol of carrier  2  at time  0  shown in  FIG. 24 . Also the reception apparatus can estimate the fluctuation of the transmission path of carrier  2  at time  1  from the pilot symbols of carrier  1  and carrier  3  at time  1 . As such, the transmission path fluctuation of carrier  2  can be estimated by an estimated value of the transmission path fluctuation of carrier  2  estimated at time  0  and time  1 . As a result, the transmission path fluctuation can be estimated with accuracy. 
     The expression of “antenna” in the previous description does not always mean a single antenna, but “antenna” can mean an antenna unit which is formed of a plurality of antennas. 
     In this embodiment, an accuracy of demultiplexing the modulation signals between channel A and channel B at the reception apparatus depends on a quality of the pilot symbol received. Thus stronger resistance of the pilot symbol to noise increases the accuracy of isolation between the modulation signals of channel A and channel B. As a result, the quality of data received can be improved. The way how to achieve this goal is described hereinafter. 
     In  FIG. 4 , assume that the pilot symbol has amplitude Ap from the origin, and QPSK has the greatest signal-point amplitude Aq from the origin. In this status, the relation of Ap&gt;Aq increases the resistance to noise of the pilot symbol, so that the accuracy of demultiplexing the modulation signals of channel A from those of channel B. As a result, the quality of data received can be improved. 
     In this embodiment, the number of channels to be multiplexed are two; however, other numbers can be applicable to the embodiment. The frame structure is not limited to what is shown in  FIG. 24 . The pilot symbol is taken as an example for demultiplexing the channels; however, other symbols as long as they are used for demodulation can be also applicable. A modulation method of the data symbol is not limited to QPSK modulation, but respective channels can undergo different modulations. 
     The structure of the transmission apparatus of this embodiment is not limited to what is shown in  FIG. 25 , and when the number of channels increase, the structure formed of elements  2501  through  2510  shown in  FIG. 25  is added accordingly. 
     The structure of the reception apparatus of this embodiment is not limited to what is shown in  FIGS. 26 ,  28 , and when the number of channels increase, the number of channel estimation units increases accordingly. 
     As discussed above, the sixth exemplary embodiment describes the transmission method which transmits modulation signals of a plurality of channels to the same frequency band from a plurality of antennas. More particularly, in this method, at the same time and sub-carrier(s) at which a demodulation symbol is inserted in a channel having a frame structure in accordance with OFDM method, in a symbol that is inserted in other such channel(s) both of an in-phase signal and a quadrature signal in the in-phase-quadrature plane are made to be zero signals. The sixth embodiment also describes the transmission apparatus and the reception apparatus to be used in the foregoing transmission method. The foregoing method and structure allow increasing the data transmission rate, and at the same time, the reception apparatus can demultiplex the multiplexed modulation signals with ease. 
     Exemplary Embodiment 7 
     The seventh exemplary embodiment describes a transmission method that switches between a method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas and a method of transmitting a modulation signal of one channel from an antenna. The embodiment also describes a transmission apparatus and a reception apparatus to be used in the foregoing transmission method. 
       FIG. 29  shows a frame structure in accordance with the seventh embodiment, specifically, frame structure  2910  of channel A and frame structure  2920  of channel B. Frame structure  2910  includes multiplex information symbols  2901 ,  2903 , and frame symbol groups  2902 ,  2904  of frame A. Structure  2920  includes frame symbol group  2905  of channel B. 
     In this case, multiplex information symbol  2901  includes the information that indicates that the frame symbol groups of channel A and channel B are transmitted simultaneously. Symbol group  2902  of channel A and symbol group  2905  of channel B are thus transmitted simultaneously. 
     Multiplex information symbol  2903  includes the information which indicates that only the frame symbol group of channel A is transmitted, so that only frame symbol group  2904  of channel A is transmitted. 
       FIG. 30  shows a frame structure in accordance with the seventh embodiment, specifically, frame structure  3010  of channel A and frame structure  3020  of channel B. Structure  3010  includes multiplex information symbol  3001  and information symbol  3002 . 
     In this case, the multiplex information symbol at time  0  includes the information which indicates that the information symbol of channel A and that of channel B are transmitted simultaneously at time  1  through time  5 . Those symbols are thus transmitted simultaneously at time  1  through time  5 . 
     The multiplex information symbol at time  6  includes the information which indicates that only the information of channel A is transmitted at time  7  through time  11 . 
       FIG. 31  shows a structure of, e.g. a transmission apparatus at a base station, and the apparatus comprises channel A transmitter  3120 , channel B transmitter  3130 , and frame structure signal generator  3118 . Transmitter  3120  comprises modulation signal generator  3102 , radio unit  3105 , power amplifier  3107 , and antenna  3109 . Transmitter  3130  comprises modulation signal generator  3102 , radio unit  3111 , power amplifier  3113 , and antenna  3115 . 
     Modulation signal generator  3102  receives transmission digital signal  3101 , frame structure signal  3119 , and outputs modulation signal  3103  of channel A and modulation signal  3110  of channel B in accordance with the frame structure. 
     Radio unit  3105  of channel A receives modulation signal  3103  of channel A, and outputs transmission signal  3106  of channel A. 
     Power amplifier  3107  of channel A receives transmission signal  3106  of channel A, then amplifies it, and outputs amplified transmission signal  3108  from antenna  3109  as radio wave. 
     Radio unit  3111  of channel B receives modulation signal  3110  of channel B, and outputs transmission signal  3112  of channel B. 
     Power amplifier  3113  of channel B receives transmission signal  3112  of channel B, then amplifies it, and outputs amplified transmission signal  3114  from antenna  3115  as radio wave. 
     Frame structure signal generator  3118  receives radio-wave propagation environmental information  3116 , transmission data amount information  3117 , then outputs frame structure signal  3119 . 
       FIG. 32  shows a structure of, e.g. a reception apparatus at a terminal in accordance with this embodiment. Radio unit  3203  receives signal  3202  received by antenna  3201 , and outputs reception quadrature baseband signal  3204 . 
     Multiplex information symbol demodulator  3205  receives base-band signal  3204 , and multiplex information data  3206 . 
     Transmission path variation estimation unit  3207  of channel A receives base-band signal  3204 , and outputs variation estimation signal  3208 . Transmission path variation estimation unit  3209  of channel B receives base-band signal  3204 , and outputs variation estimation signal  3210 . 
     Radio unit  3213  receives signal  3212  received by antenna  3211 , and outputs reception quadrature baseband signal  3214 . Transmission path variation estimation unit  3215  of channel A receives base-band signal  3214 , and outputs variation estimation signal  3216 . Transmission path variation estimation unit  3209  of channel B receives base-band signal  3214 , and outputs variation estimation signal  3218 . 
     Signal processor  3219  receives the following signals: 
     transmission path variation estimation signals  3208 ,  3216  of channel A; 
     transmission path variation estimation signals  3210 ,  3218  of channel B; 
     reception quadrature baseband signals  3204 ,  3214 ; and 
     multiplex information data  3206 . 
     Signal processor  3219  then outputs signal  3220  of channel A and signal  3221  of channel B based on multiplex information data  3206 . 
     Demodulator  3222  receives signals  3220 ,  3221 , data  3206 , and based on data  3206 , outputs reception digital signal  3223 . 
     Radio-wave propagation environment estimation unit  3224  receives base-band signal  3204 ,  3214 , then estimates the radio-wave propagation environment, e.g. a received signal strength intensity or a spatial correlation of the radio-wave propagation environment, and outputs radio-wave propagation environment estimation signal  3225 . 
     The transmission apparatus of, e.g. a base station, in accordance with the embodiment with reference to  FIGS. 29 ,  31  and  32 . 
     The reception apparatus shown in  FIG. 32  includes radio-wave propagation environment estimation unit  3224  which receives reception quadrature baseband signal  3204 ,  3214 . Estimation unit  3224  then estimates the radio-wave propagation environment, e.g. a received signal strength intensity or a spatial correlation of the radio-wave propagation environment, and outputs radio wave propagation environment estimation signal  3225 . The information of signal  3225  is transmitted as data from a transmitter of the terminal, and the base station receives and demodulates it for obtaining the information corresponding to signal  3225 . This information corresponds to radio-wave propagation environmental information  3116  shown in  FIG. 31 . 
     Frame structure signal generator  3118  receives information  3116 , transmission data amount information  3117 , and outputs frame structure signal  3119  that includes, e.g. the following information as shown in  FIG. 29 : 
     Multiplex information symbol  2901  indicates that the frame symbol groups of channels A and B are simultaneously transmitted; 
     Frame symbol group  2902  of channel A and frame symbol group  2905  of channel B indicate that both of them are transmitted simultaneously; 
     Multiplex information symbol  2903  of channel A indicates that only the frame symbol groups of channel A are transmitted; and 
     Multiplex information symbol  2904  of channel A indicates that only the frame symbol groups of channel A are transmitted. 
     Modulation signal generator  3102  shown in  FIG. 31  receives transmission digital signal  3101 , frame structure signal  3119 , and outputs modulation signal  3103  of channel A and modulation signal  3110  of channel B. 
     The reception apparatus of the terminal in accordance with the seventh embodiment is described with reference to  FIG. 29  and  FIG. 32 . Multiplex information symbol decoder  3205  receives reception quadrature baseband signal  3204 , then demodulates the multiplex information symbol shown in  FIG. 29 . When decoder  3205  decodes, e.g. multiplex information symbol  2901 , decoder  3205  outputs the following information as multiplex information data  3206 : the information indicating that the frame symbol groups of channels A and B are transmitted simultaneously. When decoder  3205  decodes, e.g. multiplex information symbol  2903 , decoder  3205  outputs the following information as multiplex information data  3206 : the information indicating that the frame symbol group of only channel A is transmitted. 
     Signal processor  3219  receives the following signals: 
     transmission path variation estimation signals  3208 ,  3216  of channel A; 
     transmission path variation estimation signals  3210 ,  3218  of channel B; 
     reception quadrature baseband signals  3204 ,  3214 ; and 
     multiplex information data  3206 . 
     When data  3206  indicates that the frame symbol groups of channels A and B are transmitted simultaneously, processor  3219  carries out inverse matrix calculations from estimation signals  3208 ,  3216  of channel A, estimation signals  3210 ,  3218  of channel B, base-band signals  3204 ,  3214 . Then processor  3219  demultiplexes the signals of channel A from those of channel B, and outputs signal  3220  of channel A and signal  3221  of channel B. When multiplex information data  3206  indicates that the frame symbol group of only channel A is transmitted, processor  3219  outputs only signal  3220  of channel A. 
     Demodulator  3222  receives signal  3220  of channel A, signal  32210  of channel B, and multiplex information data  3206 . When data  3206  indicates that the frame symbol groups of channels A and B are simultaneously transmitted, decoder  3222  decodes signals  3220 ,  3221 . When data  3206  indicates that the frame symbol group of only channel A is transmitted, demodulator  3222  demodulates signal  3220  of channel A. Then demodulator  3222  outputs reception digital signal  3223 . 
     In the case of orthogonal frequency multiplexing (OFDM) system, a similar way to what is discussed above is applicable. The transmitter of the base station, for instance, in accordance with the seventh embodiment is demonstrated hereinafter with reference to  FIGS. 30 ,  31 ,  32 . 
     The reception apparatus shown in  FIG. 32  includes radio-wave propagation environment estimation unit  3224  which receives reception quadrature baseband signal  3204 ,  3214 . Estimation unit  3224  then estimates the radio-wave propagation environment, e.g. received signal strength intensity or spatial correlation of the radio-wave propagation environment, and outputs radio wave propagation environment estimation signal  3225 . The information of signal  3225  is transmitted as data from a transmitter of the terminal, and the base station receives and demodulates it for obtaining the information corresponding to signal  3225 . This information corresponds to radio-wave propagation environmental information  3116  shown in  FIG. 31 . 
     Frame structure signal generator  3118  receives information  3116 , transmission data amount information  3117 , and outputs frame structure signal  3119  that includes, e.g. the following information as shown in  FIG. 30 : 
     multiplex information symbol at time  0  indicating that the information symbols of channels A and B are simultaneously transmitted at time  1 -time  5 , and showing the frame structure where both of information symbols of channel A and channel B are transmitted simultaneously at time  1 -time  5 ; 
     multiplex information symbol at time  6  indicating that only the information of channel A is transmitted at time  7 -time  11 , and showing the frame structure where the information of only channel A is transmitted at time  7 -time  11 . 
     Generator  3118  outputs the foregoing information as frame structure signal  3119 . Modulation signal generator  3102  receives transmission digital signal  3101 , frame structure signal  3119 , and outputs modulation signal  3103  of channel A and modulation signal  3110  of channel B in accordance with the frame structure. 
     Next, a reception apparatus of a terminal in accordance with the seventh embodiment is described with reference to  FIG. 30  and  FIG. 32 . 
     Multiplex information symbol demodulator  3205  receives base-band signal  3204 , and demodulates the multiplex information symbol shown in  FIG. 30 . When, for instance, demodulator  3205  demodulates the multiplex information symbol at time  0 , demodulator  3205  outputs the information indicating that the frame symbol groups of channels A and B are transmitted simultaneously. When demodulator  3205  demodulates the symbol at time  6 , demodulator  3205  outputs the information indicating that the frame symbol group of only channel A is transmitted. As such, the information of either one of the foregoing cases is output as multiplex information data  3206 . 
     Signal processor  3219  receives the following signals: 
     transmission path variation estimation signals  3208 ,  3216  of channel A; 
     transmission path variation estimation signals  3210 ,  3218  of channel B; 
     reception quadrature baseband signals  3204 ,  3214 ; and 
     multiplex information data  3206 . 
     When data  3206  indicates that the frame symbol groups of channels A and 
     B are transmitted simultaneously, processor  3219  carries out inverse matrix calculations from estimation signals  3208 ,  3216  of channel A, estimation signals  3210 ,  3218  of channel B, base-band signals  3204 ,  3214 . Then processor  3219  demultiplexes the signals of channel A from those of channel B, and outputs signal  3220  of channel A and signal  3221  of channel B. When multiplex information data  3206  indicates that the frame symbol group of only channel A is transmitted, processor  3219  outputs only signal  3220  of channel A. 
     Demodulator  3222  receives signal  3220  of channel A, signal  32210  of channel B, and multiplex information data  3206 . When data  3206  indicates that the frame symbol groups of channels A and B are simultaneously transmitted, decoder  3222  decodes signals  3220 ,  3221 . When data  3206  indicates that the frame symbol group of only channel A is transmitted, demodulator  3222  demodulates signal  3220  of channel A. Then demodulator  3222  outputs reception digital signal  3223 . 
     In this embodiment, the number of channels to be multiplexed are two; however, other numbers can be applicable to this embodiment. The frame structure is not limited to what is shown in  FIG. 29  or  FIG. 30 . 
     The structure of the transmission apparatus of this embodiment is not limited to what is shown in  FIG. 31 , and when the number of channels increase, the structure formed of elements  3103  through  3109  shown in  FIG. 31  is added accordingly. The structure of the reception apparatus of this embodiment is not limited to what is shown in  FIG. 32 . 
     The expression of “antenna” in the previous description does not always mean a single antenna, but “antenna” can mean an antenna unit which is formed of a plurality of antennas. 
     The seventh exemplary embodiment as discussed above describes the transmission method that switches between the method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas and the method of transmitting a modulation signal of one channel from an antenna. The embodiment also describes the transmission apparatus and the reception apparatus used in the foregoing transmission method. Multiplexing the transmission signals of a plurality of channels to the same frequency band allows the method and the apparatuses to increase the data transmission rate, and allows the reception apparatus to demultiplex the multiplexed modulation signals received with ease. 
     Exemplary Embodiment 8 
     The eighth exemplary embodiment describes a transmission method of multiplexing modulation signals of a plurality of channels to the same frequency band, more particularly, a method of transmitting a synchronous symbol for the foregoing transmission method. This embodiment also describes a transmission apparatus as well as a reception apparatus to be used in the foregoing transmission method. 
       FIG. 2  shows a structure of the transmission apparatus in accordance with the eighth embodiment. 
       FIG. 4  shows a placement of signal points in the in-phase-quadrature plane in accordance with this embodiment. 
       FIG. 33  shows a frame structure along a time-axis in accordance with this embodiment, and to be more specific, it shows frame structure  3310  of channel A and frame structure  3320  of channel B. Frame structures  3310 ,  3320  include synchronous symbols  3301 ,  3305 , guard symbols  3302 ,  3304 , and data symbols  3303 ,  3306 . 
       FIG. 34  shows a frame structure along a time axis in accordance with this embodiment, specifically, frame structure  3410  of channel A and frame structure  3420  of channel B. Structures  3410 ,  3420  include synchronous symbols  3401 , data symbols  3402 ,  3404 , and guard symbol  3403 . 
       FIG. 35  shows a structure of modulation signal generators  202 ,  212 , and the elements operating in a similar way to those in  FIG. 3  have the same reference marks. Synchronous symbol modulation signal generator  3501  receives frame structure signal  311 , and outputs in-phase component  3502  and quadrature-phase component  3503  of the transmission quadrature baseband signal of the synchronous symbol when frame structure signal  311  indicates the synchronous symbol. 
     In-phase component switcher  312  receives the following signals: 
     in-phase component  303  of a data symbol transmission quadrature baseband signal; 
     in-phase component  3502  of the synchronous symbol transmission quadrature baseband signal; 
     in-phase component  309  of a guard symbol transmission quadrature baseband signal, and frame structure signal  311 , 
     then switcher  312  selects the in-phase component of transmission quadrature baseband signal corresponding to a symbol indicated by frame structure signal  311 , and outputs the selected one as in-phase component  313  of the selected transmission quadrature baseband signal. 
     Quadrature-phase component switcher  314  receives the following signals: 
     quadrature-phase component  304  of a data symbol transmission quadrature baseband signal; 
     quadrature-phase component  3503  of the synchronous symbol transmission quadrature baseband signal; 
     quadrature-phase component  310  of a guard symbol transmission quadrature baseband signal, and frame structure signal  311 , 
     then selects a quadrature-phase component of a transmission quadrature baseband signal corresponding to a symbol indicated by frame structure signal  311 , and outputs the selected one as quadrature-phase component  315  of the selected transmission quadrature baseband signal. 
       FIG. 36  shows a structure of modulation signal generators  202 ,  212  shown in  FIG. 2 . Guard symbol or synchronous symbol transmission signal generator  3601  receives frame structure signal  311 , and outputs in-phase component  3602 , quadrature-phase component  3603  of the transmission quadrature baseband signal of the guard symbol or the synchronous symbol. 
       FIG. 37  shows a structure of the reception apparatus in accordance with the eighth embodiment, and its radio unit  3703  receives signal  3702  received by antenna  3701 , then outputs reception quadrature baseband signal  3704 . 
     Transmission path variation estimation unit  3705  receives base-band signal  3704  and timing signal  3719 , then outputs transmission path variation estimation signal  3706 . 
     Radio unit  3708  receives signal  3707  received by antenna  3706 , then outputs reception quadrature baseband signal  3709 . 
     Transmission path variation estimation unit  3710  receives base-band signal  3709  and timing signal  3719 , then outputs transmission path variation estimation signal  3711 . 
     Radio unit  3714  receives signal  3713  received by antenna  3712 , then outputs reception quadrature baseband signal  3715 . 
     Transmission path variation estimation unit  3716  receives base-band signal  3715  and timing signal  3719 , then outputs transmission path variation estimation signal  3717 . 
     Synchronizing unit  3717  receives base-band signal  3715 , and searches for a synchronous symbol transmitted by the transmission apparatus to synchronize with the transmission apparatus, then outputs timing signal  3719 . 
     Signal isolator  3720  receives the following signals: 
     reception quadrature baseband signals  3704 ,  3709 ,  3715 ; 
     transmission path variation estimation signals  3706 ,  3711 ,  3717 ; and timing signal  3719 . 
     Signal isolator  3720  then outputs reception quadrature baseband signal  3721  of channel A and quadrature baseband signal  3722  of channel B. 
     Demodulator  3723  receives signal  3721  of channel A, and outputs reception digital signal  3724 . Demodulator  3725  receives signal  3722  of channel B, and outputs reception digital signal  3725 . 
       FIG. 38  shows a structure of the reception apparatus in accordance with the eighth embodiment, and the elements operating in a similar way to those in  FIG. 37  have the same reference marks. 
     Synchronizing unit  3801  receives reception quadrature baseband signal  3704 , and searches for a synchronous symbol transmitted by the transmission apparatus to synchronize with the transmission apparatus, then outputs timing signal  3802 . 
     Transmission path variation estimation unit  3705  receives base-band signal  3704  and timing signal  3802 , then outputs transmission path variation estimation signal  3706 . 
     Synchronizing unit  3803  receives reception quadrature baseband signal  3709 , and searches for a synchronous symbol transmitted by the transmission apparatus to synchronize with the transmission apparatus, then outputs timing signal  3804 . 
     Transmission path variation estimation unit  3710  receives reception quadrature baseband signal  3709  and timing signal  3804 , then outputs transmission path variation estimation signal  3711 . 
     Synchronizing unit  3805  receives reception quadrature baseband signal  3715 , and searches for a synchronous symbol transmitted by the transmission apparatus to synchronize with the transmission apparatus, then outputs timing signal  3806 . 
     Transmission path variation estimation unit  3716  receives reception quadrature baseband signal  3715  and timing signal  3806 , then outputs transmission path variation estimation signal  3717 . 
       FIG. 39  shows a structure of the reception apparatus in accordance with the eighth embodiment, and the elements operating in a similar way to those in  FIG. 37  have the same reference marks. 
     Received signal strength intensity estimation unit  3901  receives signal  3702 , then estimates the received signal strength intensity, and outputs received signal strength intensity estimation signal  3902 . 
     Received signal strength intensity estimation unit  3903  receives signal  3707 , then estimates the received signal strength intensity, and outputs received signal strength intensity estimation signal  3904 . 
       FIG. 40  shows a structure of the reception apparatus in accordance with the eighth embodiment, and the elements operating in a similar way to those in  FIG. 37  or  FIG. 39  have the same reference marks. 
     Signal selection unit  4001  receives the following signals: 
     received signal strength intensity estimation signals  3902 ,  3904 ,  3906 ; and 
     reception quadrature baseband signal  3704 ,  3709 ,  3715 , 
     then unit  4001  selects, e.g. the reception quadrature baseband signal supplied from the antenna that receives the signal having the best electric field among the received signal strength intensity estimation signals, and outputs it as reception quadrature baseband signal  4002 . 
     Synchronizing unit  4003  receives reception quadrature baseband signal  4002  selected, and searches for a synchronous symbol transmitted by the transmission apparatus to synchronize with the transmission apparatus, then outputs timing signal  4004 . 
       FIG. 41  shows a structure of the reception apparatus in accordance with the eighth embodiment, and the elements operating in a similar way to those in  FIG. 39  or  FIG. 40  have the same reference marks. 
     An operation of the transmission apparatus is demonstrated hereinafter with reference to  FIGS. 2 ,  4 ,  33 ,  34 ,  35  and  36 . 
     Frame structure signal generator  209  outputs the information of the frame structure shown in  FIG. 33  or  FIG. 34  as frame structure signal  210 . Modulation signal generator  202  of channel A receives frame structure signal  210  and transmission digital signal  201  of channel A, then outputs modulation signal  203  of channel A in accordance with the frame structure. Modulation signal generator  212  of channel B receives frame structure signal  210  and transmission digital signal  211  of channel B, then outputs modulation signal  213  of channel B in accordance with the frame structure. 
     Next, an operation of modulation signal generators  202  and  212  in accordance with the frame structure shown in  FIG. 33  is described with reference to  FIG. 35  using a transmitter of channel A as an example. 
     Data symbol modulation signal generator  302  receives transmission digital signal  301 , i.e. transmission digital signal  201  of channel A in  FIG. 2 , and frame structure signal  311 , i.e. frame structure signal  210  in  FIG. 2 . When frame structure signal  311  indicates a data symbol, generator  302  outputs in-phase component  303  and quadrature-phase component  304  of a transmission quadrature baseband signal of the data symbol. 
     Synchronous symbol modulation signal generator  3501  receives frame structure signal  311 . When frame structure signal  311  indicates the synchronous symbol, generator  3501  outputs in-phase component  3502  and quadrature-phase component  3503  of the transmission quadrature baseband signal of the synchronous symbol. 
     Guard symbol modulation signal generator  308  receives frame structure signal  311 . When signal  311  indicates a guard symbol, generator  308  outputs in-phase component  309  and quadrature-phase component  310  of a transmission quadrature baseband signal of the guard symbol. 
       FIG. 4  shows the signal-point placement of the respective symbols in an in-phase-quadrature plane of the foregoing operation. Points  401  in  FIG. 4  indicate the signal-points of in-phase component  303  and quadrature-phase component  304  of the transmission quadrature baseband signal of the data symbol. Points  402  indicate the signal-points of in-phase component  3502  and quadrature-phase component  3503  of the transmission quadrature baseband signal of the synchronous symbol. Point  403  indicates the signal-points of in-phase component  309  and quadrature-phase component  310  of the transmission quadrature baseband signal of the guard symbol. 
     In-phase component switcher  312  receives the following signals: 
     in-phase component  303  of data symbol transmission quadrature baseband signal; 
     in-phase component  3502  of synchronous symbol transmission quadrature baseband signal; 
     in-phase component  309  of guard symbol transmission quadrature baseband signal; and frame structure signal  311 . 
     Switcher  312  then selects an in-phase component of a transmission quadrature baseband signal corresponding to the symbol indicated by frame structure signal  311 , and outputs the selected one as in-phase component  313  of the selected transmission quadrature baseband signal. 
     Quadrature-phase component switcher  314  receives the following signals: 
     quadrature-phase component  304  of data symbol transmission quadrature baseband signal; 
     quadrature-phase component  3503  of synchronous symbol transmission quadrature baseband signal; 
     quadrature-phase component  310  of guard symbol transmission quadrature baseband signal; and 
     frame structure signal  311 . 
     Switcher  314  then selects a quadrature-phase component of a transmission quadrature baseband signal corresponding to the symbol indicated by frame structure signal  311 , and outputs the selected one as quadrature-phase component  315  of the selected transmission quadrature baseband signal. 
     Orthogonal modulator  316  receives in-phase component  313  and quadrature-phase component  315  discussed above, then provides those components with an orthogonal modulation, and outputs modulation signal  317 , i.e. signal  203  shown in  FIG. 2 . 
     An operation of modulation signal generators  202 ,  212  at frame structure  34  is demonstrated with reference to  FIG. 36 . 
     An operation of generator  202  is demonstrated hereinafter. Data symbol modulation signal generator  302  receives transmission digital signal  301 , i.e. transmission digital signal  201  of channel A in  FIG. 2 , and frame structure signal  311 , i.e. frame structure signal  210  in  FIG. 2 . When frame structure signal  311  indicates a data symbol, generator  302  outputs in-phase component  303  and quadrature-phase component  304  of a transmission quadrature baseband signal of the data symbol. 
     Synchronous symbol modulation signal generator  3601  receives frame structure signal  311 , and outputs in-phase component  3602  and quadrature-phase component  3603  of the transmission quadrature baseband signal of the synchronous symbol when frame structure signal  311  indicates the synchronous symbol. 
       FIG. 4  shows the signal-point placement of the respective symbols in an in-phase-quadrature plane of the foregoing operation. Points  401  in  FIG. 4  indicate the signal-points of in-phase component  303  and quadrature-phase component  304  of the transmission quadrature baseband signal of the data symbol. Points  402  indicate the signal-points of in-phase component  3602  and quadrature-phase component  3603  of the transmission quadrature baseband signal of the synchronous symbol. 
     In-phase component switcher  312  receives the following signals: 
     in-phase component  303  of data symbol transmission quadrature baseband signal; 
     in-phase component  3602  of synchronous symbol transmission quadrature baseband signal, and frame structure signal  311 . 
     Switcher  312  then selects an in-phase component of a transmission quadrature baseband signal corresponding to the symbol indicated by frame structure signal  311 , and outputs the selected one as in-phase component  313  of the selected transmission quadrature baseband signal. 
     Quadrature-phase component switcher  314  receives the following signals: 
     quadrature-phase component  304  of data symbol transmission quadrature baseband signal; 
     quadrature-phase component  3603  of synchronous symbol transmission quadrature baseband signal, and frame structure signal  311 . 
     Switcher  314  then selects a quadrature-phase component of a transmission quadrature baseband signal corresponding to the symbol indicated by frame structure signal  311 , and outputs the selected one as quadrature-phase component  315  of the selected transmission quadrature baseband signal. 
     Orthogonal modulator  316  receives in-phase component  313  and quadrature-phase component  315  discussed above, then provides those components with an orthogonal modulation, and outputs modulation signal  317 , i.e. signal  203  shown in  FIG. 2 . 
     An operation of generator  212  is demonstrated hereinafter. Data symbol modulation signal generator  302  receives transmission digital signal  301 , i.e. transmission digital signal  211  of channel B in  FIG. 2 , and frame structure signal  210 , i.e. frame structure signal  311  in  FIG. 36 . When frame structure signal  210  indicates a data symbol, generator  302  outputs in-phase component  303  and quadrature-phase component  304  of a transmission quadrature baseband signal of the data symbol. 
     Guard symbol modulation signal generator  3601  receives frame structure signal  311 . When signal  311  indicates a guard symbol, generator  3601  outputs in-phase component  3602  and quadrature-phase component  3603  of a transmission quadrature baseband signal of the guard symbol. 
       FIG. 4  shows the signal-point placement of the respective symbols in an in-phase-quadrature plane of the foregoing operation. Points  401  in  FIG. 4  indicate the signal-points of in-phase component  303  and quadrature-phase component  304  of the transmission quadrature baseband signal of the data symbol. Points  403  indicate the signal-points of in-phase component  3602  and quadrature-phase component  3603  of the transmission quadrature baseband signal of the guard symbol. 
     In-phase component switcher  312  receives the following signals: 
     in-phase component  303  of the data symbol transmission quadrature baseband signal; 
     in-phase component  3602  of the guard symbol transmission quadrature baseband signal, and frame structure signal  311 . 
     Switcher  312  then selects an in-phase component of a transmission quadrature baseband signal corresponding to the symbol indicated by frame structure signal  311 , and outputs the selected one as in-phase component  313  of the selected transmission quadrature baseband signal. 
     Quadrature-phase component switcher  314  receives the following signals: 
     quadrature-phase components  304  of a data symbol transmission quadrature baseband signal; 
     quadrature-phase component  3603  of the guard symbol transmission quadrature baseband signal, and frame structure signal  311 , 
     then selects a quadrature-phase component of a transmission quadrature baseband signal corresponding to a symbol indicated by frame structure signal  311 , and outputs the selected one as quadrature-phase component  315  of the selected transmission quadrature baseband signal. 
     Orthogonal modulator  316  receives in-phase component  313  and quadrature-phase component  315  selected as discussed above, then provides those components with an orthogonal modulation, and outputs modulation signal  317 , i.e. signal  213  shown in  FIG. 2 . 
     An operation of the reception apparatus is demonstrated hereinafter with reference to  FIG. 37  through  FIG. 42 . First, the operation is demonstrated with reference to  FIG. 37 . 
     Radio unit  3714  receives signal  3713  received by antenna  3712 , then outputs reception quadrature baseband signal  3715 . 
     Synchronizing unit  3718  receives base-band signal  3715 , and detects a synchronous symbol among the signals transmitted by the transmission apparatus, then outputs timing signal  3719  which synchronizes with the transmission apparatus time-wise. Signal  3719  is used as a timing signal at the respective units in the reception apparatus. 
     Next, an operation of the reception apparatus is demonstrated with reference to  FIG. 38 . 
     Radio unit  3703  receives signal  3702  received by antenna  3701 , then outputs reception quadrature baseband signal  3704 . 
     Synchronizing unit  3801  receives base-band signal  3704 , and detects a synchronous symbol among the signals transmitted by the transmission apparatus, then outputs timing signal  3802  which synchronizes with the transmission apparatus time-wise. Signal  3802  is, e.g. supplied to transmission path variation estimation unit  3705  and signal isolator  3807 . Signal  3802  then extracts a signal from base-band signal  3704  by timing to itself for signal processing. 
     Radio unit  3708  receives signal  3707  received by antenna  3706 , then outputs reception quadrature baseband signal  3709 . 
     Synchronizing unit  3803  receives base-band signal  3709 , and detects a synchronous symbol among the signals transmitted by the transmission apparatus, then outputs timing signal  3804  which synchronizes with the transmission apparatus time-wise. Signal  3804  is, e.g. supplied to transmission path variation estimation unit  3710  and signal isolator  3807 . Signal  3802  then extracts a signal from base-band signal  3709  by timing to itself for signal processing. 
     Radio unit  3714  receives signal  3713  received by antenna  3712 , then outputs reception quadrature baseband signal  3715 . 
     Synchronizing unit  3805  receives base-band signal  3715 , and detects a synchronous symbol among the signals transmitted by the transmission apparatus, then outputs timing signal  3806  which synchronizes with the transmission apparatus time-wise. Signal  3806  is, e.g. supplied to transmission path variation estimation unit  3716  and signal isolator  3807 . Signal  3802  then extracts a signal from base-band signal  3715  by timing to itself for signal processing. 
     Next, an operation of the reception apparatus is demonstrated with reference to  FIG. 39 . 
     Received signal strength intensity estimation unit  3901  receives signal  3702  received by antenna  3701 , then estimates the reception received signal strength intensity, and outputs received signal strength intensity estimation signal  3902 . 
     In a similar way to what is discussed above, received signal strength intensity estimation unit  3903  receives signal  3707  received by antenna  3706 , then estimates the reception received signal strength intensity, and outputs received signal strength intensity estimation signal  3904 . Received signal strength intensity estimation unit  3905  receives signal  3713  received by antenna  3712 , then estimates the reception received signal strength intensity, and outputs received signal strength intensity estimation signal  3906 . 
     Synchronizing unit  3907  receives reception quadrature baseband signal  3704 , and detects a synchronous symbol among the signals transmitted by the transmission apparatus, then outputs timing signal  3908  which synchronizes with the transmission apparatus time-wise. 
     In a similar way to what is discussed above, synchronizing unit  3909  receives reception quadrature baseband signal  3709 , and detects a synchronous symbol among the signals transmitted by the transmission apparatus, then outputs timing signal  3910  which synchronizes with the transmission apparatus time-wise. Synchronizing unit  3911  receives reception quadrature baseband signal  3715 , and detects a synchronous symbol among the signals transmitted by the transmission apparatus, then outputs timing signal  3912  which synchronizes with the transmission apparatus time-wise. 
     Synchronous signal selection unit  3913  receives received signal strength intensity estimation signals  3902 ,  3904 ,  3906 , and timing signals  3908 ,  3910 ,  3912 . When the electric field of the signal received by, e.g. antenna  3701  is the strongest among others, timing signal  3908  is selected from the foregoing estimation signals. Selection unit  3913  then outputs timing signal  3908  selected as timing signal  3914 . As such, the timing signal found from the reception signal that has the best electric field is used as the timing signal of the reception apparatus. 
     Next, an operation of the reception apparatus is demonstrated with reference to  FIG. 40 . 
     Signal selection unit  4001  receives the following signals: 
     received signal strength intensity estimation signals  3902 ,  3904 ,  3906 ; and 
     reception quadrature baseband signals  3704 ,  3709 ,  3715 . 
     When the electric field of the signal received by, e.g. antenna  3701  is the strongest among others, base-band signal  3704  is selected from the foregoing base-band signals. Then unit  4001  outputs signal  3704  as reception quadrature baseband signal  4002 . 
     Synchronizing unit  4003  receives reception quadrature baseband signal  4002  selected, and searches for a synchronous symbol transmitted by the transmission apparatus, then outputs timing signal  4004  which synchronizes with the transmission apparatus. As such, the timing signal found from the reception signal that has the best electric field is used as the timing signal of the reception apparatus. 
     Next, an operation of the reception apparatus is demonstrated with reference to  FIG. 41 . The operation shown in  FIG. 41  differs from that of  FIG. 39  in finding the received signal strength intensity by using a reception quadrature baseband signal. 
     Received signal strength intensity estimation unit  3901  receives reception quadrature baseband signal  3704 , then estimates the reception received signal strength intensity, and outputs received signal strength intensity estimation signal  3902 . 
     In a similar way to what is discussed above, received signal strength intensity estimation unit  3903  receives reception quadrature baseband signal  3709 , then estimates the reception received signal strength intensity, and outputs received signal strength intensity estimation signal  3904 . Received signal strength intensity estimation unit  3905  receives reception quadrature baseband signal  3715 , then estimates the reception received signal strength intensity, and outputs received signal strength intensity estimation signal  3906 . 
     The operation shown in  FIG. 42  differs from that of  FIG. 40  in finding the received signal strength intensity by using a reception quadrature baseband signal. 
     In the foregoing discussion, the received signal strength intensity is used as an example of a parameter of the radio-wave propagation environment; however, this embodiment is not limited to this example, and Doppler frequency or the number of paths of multi-path can be used as the parameter. 
     The foregoing discussion proves that the transmission apparatus can be synchronized with the reception apparatus time-wise. 
     In this embodiment, the number of channels to be multiplexed are two; however, other numbers can be applicable to the embodiment. The frame structure is not limited to what is shown in  FIG. 33 , or  FIG. 34 . A modulation method of the data symbol is not limited to QPSK modulation, but respective channels can undergo different modulations. On the other hand, all the channels can use the spread spectrum communication method. The spread spectrum communication method can coexist with the other methods. 
     The synchronous symbols shown in  FIGS. 33 ,  34  are used for time-synchronizing the reception apparatus with the transmission apparatus; however, the symbols are not limited to this usage, and they can be used for, e.g. estimating a frequency offset between the reception apparatus and the transmission apparatus. 
     The structure of the transmission apparatus of this embodiment is not limited to what is shown in  FIGS. 2 ,  35 ,  36 , and when the number of channels increases, the structure formed of elements  201  through  208  shown in  FIG. 31  is added accordingly. 
     The structure of the reception apparatus of this embodiment is not limited to what is shown in  FIG. 37  through  FIG. 42 ; but the number of antennas can be increased. 
     The expression of “antenna” in the previous description does not always mean a single antenna, but “antenna” can mean an antenna unit which is formed of a plurality of antennas. 
     The eighth exemplary embodiment, as discussed above, describes the transmission method of multiplexing modulation signals of a plurality of channels to the same frequency band, more particularly, the method of transmitting a synchronous symbol in the foregoing transmission method. This embodiment also describes the transmission apparatus and the reception apparatus to be used in the foregoing transmission method. The method and the apparatuses can increase the transmission rate of data, and synchronize the transmission apparatus with the reception apparatus time-wise. 
     Exemplary Embodiment 9 
     The ninth exemplary embodiment describes a transmission method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas, more particularly, a method of transmitting a synchronous symbol in the spread-spectrum transmission method. The ninth embodiment also describes a transmission apparatus and a reception apparatus to be used in the foregoing transmission method. 
       FIG. 4  shows a placement of signal points in the in-phase-quadrature plane in accordance with this embodiment. 
       FIG. 12  shows a structure of the transmission apparatus in accordance with the eighth embodiment. 
       FIG. 43  shows a frame structure along a time-axis in accordance with this embodiment, and to be more specific, it shows frame structure  4310  of spread-spectrum communication method A and frame structure  4320  of method B. Frame structures  4310 ,  4320  include synchronous symbols  4301 ,  4305 , guard symbols  4302 ,  4304 , and data symbols  4303 ,  4306 . 
       FIG. 44  shows a frame structure along a time axis in accordance with this embodiment, specifically, frame structure  4410  of method A and frame structure  4420  of method B. Structures  4410 ,  4420  include synchronous symbols  3401 , data symbols  3402 ,  3404 , and guard symbol  4403 . 
       FIG. 45  shows a frame structure along a time axis in accordance with this embodiment, specifically, frame structure  4510  of method A and frame structure  4520  of method B. Structures  4510 ,  4520  include guard symbols  4503 ,  4505 ,  4507 , data symbols  4502 ,  4504 ,  4506 ,  4508  and synchronous symbol  4501 . 
       FIG. 46  shows a structure of modulation signal generators  1202 ,  1210 , and the elements operating in a similar way to those in  FIG. 13  have the same reference marks. 
     Guard symbol modulation signal generator  4601  receives frame structure signal  1320 . When signal  1320  indicates a guard symbol, generator  4601  outputs in-phase component  4602  and quadrature-phase component  4603  of a transmission quadrature baseband signal of the guard symbol. 
     Synchronous symbol modulation signal generator  4604  receives frame structure signal  1320 , and outputs in-phase component  4605  and quadrature-phase component  4606  of the transmission quadrature baseband signal of the synchronous symbol when frame structure signal  1320  indicates the synchronous symbol. 
       FIG. 47  shows a structure of modulation signal generators  1202 ,  1210  shown in  FIG. 12 , and the elements operating in a similar way to those in  FIG. 13  have the same reference marks. 
     Guard symbol or synchronous symbol modulation signal generator  4701  receives frame structure signal  1320 , and outputs in-phase component  4702 , quadrature-phase component  4703  of a transmission quadrature baseband signal of the guard symbol or the synchronous symbol. 
       FIG. 48  shows a structure of modulation signal generators  1202 ,  1210  shown in  FIG. 12 , and the elements operating in a similar way to those in  FIG. 13  have the same reference marks. 
     Primary modulator  4802  receives control information  4801  and frame structure signal  1320 , and outputs in-phase component  4803 , quadrature-phase component  4804  of the transmission quadrature baseband signal undergone the primary modulation. 
     Synchronous symbol transmission signal generator  4805  receives frame structure signal  1320 , and outputs in-phase component  4806 , quadrature-phase component  4807  of the transmission quadrature baseband signal of the synchronous symbol. 
     Spread unit  4808  receives the following signals: 
     in-phase component  4803  and quadrature-phase component  4804  of the transmission quadrature baseband signal undergone the primary modulation; 
     in-phase component  4806 , quadrature-phase component  4807  of the synchronous symbol transmission quadrature baseband signal; 
     spread code  1317 ; and 
     frame structure signal  1320 . 
     Spread unit  4808  then outputs in-phase component  4809  and quadrature-phase component  4810  of a transmission quadrature baseband signal corresponding to frame structure signal  1320  and undergone the spread of the symbol. 
       FIG. 49  shows a structure of modulation signal generators  1202 ,  1210  shown in  FIG. 12 , and the elements operating in a similar way to those in  FIG. 13  or  FIG. 48  have the same reference marks. 
     Guard symbol modulation signal generator  4901  receives frame structure signal  1320 , then outputs in-phase component  4902  and quadrature-phase component  4903  of a transmission quadrature baseband signal of the guard symbol. 
     Spread unit  4808  receives the following signals: 
     in-phase component  4803  and quadrature-phase component  4804  of the transmission quadrature baseband signal undergone the primary modulation; 
     in-phase component  4902 , quadrature-phase component  4903  of the synchronous symbol transmission quadrature baseband signal; 
     spread code  1317 ; and 
     frame structure signal  1320 . 
     Spread unit  4808  then outputs in-phase component  4809  and quadrature-phase component  4810  of a transmission quadrature baseband signal corresponding to frame structure signal  1320  and undergone the spread of the symbol. 
       FIG. 37  shows a structure of a reception apparatus in accordance with this exemplary embodiment. 
       FIG. 38  shows a structure of a reception apparatus in accordance with this exemplary embodiment. 
       FIG. 39  shows a structure of a reception apparatus in accordance with this exemplary embodiment. 
       FIG. 40  shows a structure of a reception apparatus in accordance with this exemplary embodiment. 
       FIG. 41  shows a structure of a reception apparatus in accordance with this exemplary embodiment. 
       FIG. 42  shows a structure of a reception apparatus in accordance with this exemplary embodiment. 
     An operation of the transmission apparatus is demonstrated with reference to  FIGS. 4 ,  12 , and  FIG. 43  through  FIG. 49 . 
     In  FIG. 12 , frame structure signal generator  1217  outputs the information about the frame structure shown in  FIG. 43 ,  FIG. 44 , or  FIG. 45  as frame structure signal  1218 . Modulation signal generator  1202  of spread-spectrum communication method A receives frame structure signal  1218  and transmission digital signal  1201  of spread spectrum transmission method A, then outputs modulation signal  1203  of method A in accordance with the frame structure. Modulation signal generator  1210  of method B receives frame structure signal  1218  and transmission digital signal  1209  of spread spectrum transmission method B, then outputs modulation signal  1211  of method B in accordance with the frame structure. 
     Operations of modulation signal generators  1202  and  1210  in the case of the frame structure shown in  FIG. 43  are demonstrated with reference to  FIG. 46 . At a transmitter of spread-spectrum communication method A, guard-symbol transmission signal generator  4601  shown in  FIG. 46  receives frame structure signal  1320 . When signal  1320  indicates the guard symbol, generator  4601  outputs in-phase component  4602  and quadrature-phase component  4603  of the guard symbol transmission quadrature baseband signal. 
     Synchronous symbol transmission signal generator  4604  receives frame structure signal  1320 . When signal  1320  indicates the synchronous symbol, generator  4604  outputs in-phase component  4605 , quadrature-phase component  4606  of the transmission quadrature baseband signal of the synchronous symbol. 
       FIG. 4  shows the signal-point placement of the respective symbols in an in-phase-quadrature plane of the foregoing operation. Points  401  in  FIG. 4  indicate the signal-points of in-phase components  1311 ,  1318  and quadrature-phase component  1312 ,  1319  of the transmission quadrature baseband signal of the data symbol. Points  402  indicate the signal-points of in-phase component  4605  and quadrature-phase component  4606  of the transmission quadrature baseband signal of the synchronous symbol. Point  403  indicates the signal-points of in-phase component  4602  and quadrature-phase component  4603  of the transmission quadrature baseband signal of the guard symbol. 
     Operations of modulation signal generators  1202 ,  1210  in the case of the frame structure shown in  FIG. 44  are demonstrated with reference to  FIG. 47  taking the transmitters of spread spectrum communication methods A and B as examples. 
       FIG. 47  shows a detailed structure of modulation signal generator  1202  at the transmitter of method A. Guard symbol or synchronous symbol modulation signal generator  4701  receives frame structure signal  1320 , and outputs in-phase component  4702 , quadrature-phase component  4703  of a transmission quadrature baseband signal of the guard symbol or the synchronous symbol when signal  1320  indicates the synchronous symbol. 
       FIG. 47  shows a detailed structure of modulation signal generator  1202  at the transmitter of method B. Guard symbol or synchronous symbol modulation signal generator  4701  receives frame structure signal  1320 , and outputs in-phase component  4702 , quadrature-phase component  4703  of a transmission quadrature baseband signal of the guard symbol or the synchronous symbol when signal  1320  indicates the guard symbol. 
       FIG. 4  shows the signal-point placement of the respective symbols in an in-phase-quadrature plane of the foregoing operation. Points  401  in  FIG. 4  indicate the signal-points of in-phase components  1311 ,  1318  and quadrature-phase component  1312 ,  1319  of the transmission quadrature baseband signal of the data symbol. Points  402  indicate the signal-points of the in-phase component and the quadrature-phase component of the transmission quadrature baseband signal of the synchronous symbol. Point  403  indicates the signal-points of the in-phase component and the quadrature-phase component of the transmission quadrature baseband signal of the guard symbol. 
     Operations of modulation signal generators  1202 ,  1210  in the case of the frame structure shown in  FIG. 45  are demonstrated with reference to  FIGS. 48 ,  49  taking the transmitters of spread spectrum communication methods A and B as examples. 
       FIG. 48  shows a detailed structure of modulation signal generator  1202  at the transmitter of method A. Primary modulator  4802  shown in  FIG. 48  receives control information  4801 , frame structure signal  1320 , and outputs in-phase component  4803 , quadrature-phase component  4804  of a transmission quadrature baseband signal of the control information. 
     Synchronous symbol transmission signal generator  4805  receives frame structure signal  1320 . When signal  1320  indicates the synchronous symbol, generator  4805  outputs in-phase component  4806 , quadrature-phase component  4807  of the transmission quadrature baseband signal of the synchronous symbol. 
     Spread unit  4808  receives in-phase component  4803  and quadrature-phase component  4804  of the quadrature baseband signal of the control information, in-phase component  4806 , quadrature-phase component  4807  of the transmission quadrature baseband signal of the synchronous symbol, spread code  1317 , frame structure signal  1320 . Spread unit  4808  then multiplies code  1317  by the transmission quadrature baseband signal of the symbol indicated by frame structure signal  1320 , and outputs in-phase component  4809  and quadrature-phase component  4810  of a transmission quadrature baseband signal of a control channel undergone the spread. 
       FIG. 49  shows a detailed structure of guard symbol modulation signal generator  1212  at the transmitter of method B. Guard symbol modulation signal generator  4901  receives frame structure signal  1320 . When signal  1320  indicates the guard symbol, generator  4901  outputs in-phase component  4902 , quadrature-phase component  4903  of a transmission quadrature baseband signal of the guard symbol. 
     Spread unit  4808  receives the following signals: 
     in-phase component  4803  and quadrature-phase component  4804  of the transmission quadrature baseband signal; 
     in-phase component  4902 , quadrature-phase component  4903  of the guard symbol transmission quadrature baseband signal; 
     spread code  1317 ; and 
     frame structure signal  1320 . 
     Spread unit  4808  then multiplies spread code  1317  by the transmission quadrature baseband signal of the symbol indicated by frame structure signal  1320 , and outputs in-phase component  4809  and quadrature-phase component  4810  of a transmission quadrature baseband signal of the control channel. 
       FIG. 4  shows the signal-point placement of the respective symbols in an in-phase-quadrature plane of the foregoing operation. Points  401  in  FIG. 4  indicate the signal-points of in-phase components and quadrature-phase components of the data symbol and the control symbol. Points  402  indicate the signal-points of the in-phase component and the quadrature-phase component of the transmission quadrature baseband signal of the synchronous symbol. Point  403  indicates the signal-points of the in-phase component and the quadrature-phase component of the transmission quadrature baseband signal of the guard symbol. 
     An operation of the reception apparatus is demonstrated with reference to  FIG. 37  through  FIG. 42 , in those drawings, demodulators  3723 ,  3725  carries out demodulation following the spread-spectrum communication method, namely, carries out inverse spread, then carries out demodulation. 
     In the foregoing discussion, the received signal strength intensity is used as an example of a parameter of the radio-wave propagation environment; however, this embodiment is not limited to this example, and Doppler frequency or the number of paths of multi-path can be used as the parameter. 
     The foregoing discussion proves that the transmission apparatus can be synchronized with the reception apparatus time-wise. 
     In this embodiment, the number of channels to be multiplexed are two; however, other numbers can be applicable to the embodiment. The frame structure is not limited to what is shown in  FIG. 43 ,  FIG. 44 , or  FIG. 45 . Both of spread-spectrum communication methods A and B use two channels multiplied; however, they are not limited to the two channels. 
     The synchronous symbols shown in  FIGS. 43 ,  44  and  45  are used for time-synchronizing the reception apparatus with the transmission apparatus; however, the symbols are not limited to this usage, and they can be used for, e.g. estimating a frequency offset between the reception apparatus and the transmission apparatus. 
     The structure of the transmission apparatus of this embodiment is not limited to what is shown in  FIGS. 12 ,  13 , and when the number of spread-spectrum communication methods increases, the structure formed of elements  1201  through  1208  shown in  FIG. 12  are added accordingly. When the number of channels increases, elements  1306 ,  1309  in  FIG. 13  increase accordingly. 
     The expression of “antenna” in the previous description does not always mean a single antenna, but “antenna” can mean an antenna unit which is formed of a plurality of antennas. 
     The ninth exemplary embodiment, as discussed above, describes the transmission method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas, more particularly, the method of transmitting the synchronous symbol in the spread-spectrum transmission method. The ninth embodiment also describes the transmission apparatus and the reception apparatus to be used in the foregoing transmission method. The foregoing structure and operation allows increasing the data transmission rate, and synchronizing the transmission apparatus with the reception apparatus time-wise. 
     Exemplary Embodiment 10 
     The tenth exemplary embodiment describes a transmission method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas, more particularly, a method of transmitting a synchronous symbol in accordance with OFDM method. The tenth embodiment also describes a transmission apparatus and a reception apparatus to be used in the foregoing method. 
       FIG. 4  shows a placement of signal points in the in-phase-quadrature plane in accordance with this embodiment. 
       FIG. 25  shows a structure of the transmission apparatus in accordance with this embodiment. 
       FIG. 50  shows a frame structure along a frequency-axis in accordance with this embodiment, and to be more specific, it shows frame structure  5010  of channel A and frame structure  5020  of channel B. Frame structures  5010 ,  5020  include synchronous symbol  5001 , data symbols  5002 . 
       FIG. 51  shows a frame structure along a frequency-axis in accordance with this embodiment, and to be more specific, it shows frame structure  5110  of channel A and frame structure  5120  of channel B. Frame structures  5110 ,  5120  include synchronous symbol  5101 , data symbols  5102 . 
       FIG. 52  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 26  have the same reference marks. 
     Synchronizing unit  5201  receives reception quadrature baseband signal  2604 , then synchronizes with the transmission apparatus time-wise, and outputs timing signal  5204 . 
     Synchronizing unit  5203  receives reception quadrature baseband signal  2614 , then synchronizes with the transmission apparatus time-wise, and outputs timing signal  5204 . 
       FIG. 53  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 26  have the same reference marks. 
     Synchronizing unit  5301  receives reception quadrature baseband signal  2604 , then synchronizes with the transmission apparatus time-wise, and outputs timing signal  5302 . 
       FIG. 54  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 37 , or  FIG. 39  have the same reference marks. 
     Discrete Fourier transformer  5401  receives reception quadrature baseband signal  3704 , timing signal  3914  selected, then outputs signal  5402  undergone the discrete Fourier transformation. 
     In a similar way, discrete Fourier transformer  5403  receives reception quadrature baseband signal  3709 , timing signal  3914  selected, then outputs signal  5404  undergone the discrete Fourier transformation. 
     Discrete Fourier transformer  5405  receives reception quadrature baseband signal  3715 , timing signal  3914  selected, then outputs signal  5406  undergone the discrete Fourier transformation. 
       FIG. 55  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 37 ,  FIG. 39 ,  FIG. 40  or  FIG. 50  have the same reference marks. 
       FIG. 56  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 37 ,  FIG. 39 , or  FIG. 54  have the same reference marks. 
       FIG. 57  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 37 ,  FIG. 39 ,  FIG. 40  or  FIG. 54  have the same reference marks. 
     An operation of the transmission apparatus is demonstrated hereinafter with reference to  FIGS. 4 ,  25 ,  50  and  51 . First, the transmission apparatus that transmits modulation signals having the frame structure shown in  FIG. 25  is described. 
     Frame structure signal generator  2521  shown in  FIG. 25  outputs the information about the frame structure shown in  FIG. 50  as frame structure signal  2522 . 
     In  FIG. 50 , a synchronous symbol is transmitted through channel A at time  0 , no signal is transmitted through channel B, in other words, the signal is indicated by signal point  403  shown in  FIG. 4 . In a similar manner, when a synchronous symbol is transmitted through channel B at time  1 , no signal is transmitted through channel A, in other words, the signal is indicated by signal point  403  shown in  FIG. 4 . 
     An operation of the transmission apparatus, which transmits a modulation signal having the frame structure shown in  FIG. 51 , is demonstrated hereinafter. Frame structure signal generator  2521  shown in  FIG. 25  outputs the information about the frame structure shown in  FIG. 51  as frame structure signal  2522 . In  FIG. 55 , a synchronous symbol is transmitted through channel A at time  0 , no signal is transmitted through channel B, in other words, the signal is indicated by signal point  403  shown in  FIG. 4 . 
     Next, an operation of the reception apparatus in accordance with this embodiment is demonstrated with reference to  FIG. 50  through  FIG. 57 . 
     In  FIG. 52 , synchronizing unit  5201  receives reception quadrature baseband signal  2604 , then detects the synchronous symbol transmitted as shown in  FIG. 50  or  FIG. 51  for synchronizing with the transmission apparatus time-wise, and outputs timing signal  5202 . 
     Discrete Fourier transformer  2605  receives reception quadrature baseband signal  2604 , timing signal  5202 , then provides base-band signal  2604  with discrete Fourier transformation based on timing signal  5202 , and outputs signal  2606  undergone the discrete Fourier transformation. 
     Synchronizing unit  5203  receives reception quadrature baseband signal  2614 , then detects the synchronous symbol transmitted as shown in  FIG. 50  or  FIG. 51  for synchronizing with the transmission apparatus time-wise, and outputs timing signal  5204 . 
     Discrete Fourier transformer  2615  receives reception quadrature baseband signal  2614 , timing signal  5204 , then provides base-band signal  2614  with discrete Fourier transformation based on timing signal  5204 , and outputs signal  2616  undergone the discrete Fourier transformation. 
     In  FIG. 53 , synchronizing unit  5301  receives reception quadrature baseband signal  2604 , then detects the synchronous symbol transmitted as shown in  FIG. 50  or  FIG. 51  for synchronizing with the transmission apparatus time-wise, and outputs timing signal  5302 . 
     Discrete Fourier transformer  2605  receives reception quadrature baseband signal  2604 , timing signal  5302 , then provides base-band signal  2604  with discrete Fourier transformation based on timing signal  5302 , and outputs signal  2606  undergone the discrete Fourier transformation. 
     Discrete Fourier transformer  2615  receives reception quadrature baseband signal  2614 , timing signal  5302 , then provides base-band signal  2614  with discrete Fourier transformation based on timing signal  5302 , and outputs signal  2616  undergone the discrete Fourier transformation. 
     In  FIG. 54 , discrete Fourier transformer  5401  receives reception quadrature baseband signal  3704 , timing signal  3914  received by the antenna having the best electric field, then provides base-band signal  3704  with discrete Fourier transformation based on timing signal  3914 , and outputs signal  5402  undergone the discrete Fourier transformation. 
     In a similar way to what is discussed above, discrete Fourier transformer  5403  receives reception quadrature baseband signal  3709 , timing signal  3914  received by the antenna having the best electric field, then provides base-band signal  3709  with discrete Fourier transformation based on timing signal  3914 , and outputs signal  5404  undergone the discrete Fourier transformation. 
     Discrete Fourier transformer  5405  receives reception quadrature baseband signal  3715 , timing signal  3914  received by the antenna having the best electric field, then provides base-band signal  3715  with discrete Fourier transformation based on timing signal  3914 , and outputs signal  5406  undergone the discrete Fourier transformation. 
     In  FIG. 55 , discrete Fourier transformer  5401  receives reception quadrature baseband signal  3704 , timing signal  4004  received by the antenna having the best electric field, then provides base-band signal  3704  with discrete Fourier transformation based on timing signal  4004 , and outputs signal  5402  undergone the discrete Fourier transformation. 
     In a similar way to what is discussed above, discrete Fourier transformer  5403  receives reception quadrature baseband signal  3709 , timing signal  4004  received by the antenna having the best electric field, then provides base-band signal  3709  with discrete Fourier transformation based on timing signal  4004 , and outputs signal  5404  undergone the discrete Fourier transformation. 
     Discrete Fourier transformer  5405  receives reception quadrature baseband signal  3715 , timing signal  4004  received by the antenna having the best electric field, then provides base-band signal  3715  with discrete Fourier transformation based on timing signal  4004 , and outputs signal  5406  undergone the discrete Fourier transformation. 
     In a similar way to what is discussed above, discrete Fourier transformer  5403  receives reception quadrature baseband signal  3709 , timing signal  3914  received by the antenna having the best electric field, then provides base-band signal  3709  with discrete Fourier transformation based on timing signal  3914 , and outputs signal  5404  undergone the discrete Fourier transformation. 
     Discrete Fourier transformer  5405  receives reception quadrature baseband signal  3715 , timing signal  3914  received by the antenna having the best electric field, then provides base-band signal  3715  with discrete Fourier transformation based on timing signal  3914 , and outputs signal  5406  undergone the discrete Fourier transformation. 
     In  FIG. 57 , discrete Fourier transformer  5401  receives reception quadrature baseband signal  3704 , timing signal  4004  received by the antenna having the best electric field, then provides base-band signal  3704  with discrete Fourier transformation based on timing signal  4004 , and outputs signal  5402  undergone the discrete Fourier transformation. 
     In a similar way to what is discussed above, discrete Fourier transformer  5403  receives reception quadrature baseband signal  3709 , timing signal  4004  received by the antenna having the best electric field, then provides base-band signal  3709  with discrete Fourier transformation based on timing signal  4004 , and outputs signal  5404  undergone the discrete Fourier transformation. 
     Discrete Fourier transformer  5405  receives reception quadrature baseband signal  3715 , timing signal  4004  received by the antenna having the best electric field, then provides base-band signal  3715  with discrete Fourier transformation based on timing signal  4004 , and outputs signal  5406  undergone the discrete Fourier transformation. 
     In the foregoing discussion, the received signal strength intensity is used as an example of a parameter of the radio-wave propagation environment; however, this embodiment is not limited to this example, and Doppler frequency or the number of paths of multi-path can be used as the parameter. 
     The foregoing discussion proves that the transmission apparatus can be synchronized with the reception apparatus time-wise. 
     In this embodiment, two transmission antennas are used for the description purpose; however, this embodiment is not limited to the two antennas, and two channels are multiplexed for the description purpose; however, this embodiment is not limited to the two channels. Frame structures are not limited to those shown in  FIG. 50  and  FIG. 51 . 
     The synchronous symbols shown in  FIGS. 50 ,  51  are used for time-synchronizing the reception apparatus with the transmission apparatus; however, the symbols are not limited to this usage, and they can be used for, e.g. estimating a frequency offset between the reception apparatus and the transmission apparatus. 
     The structure of the transmission apparatus of this embodiment is not limited to the one shown in  FIG. 25 , and the structure of the reception apparatus of this embodiment is not limited to the ones shown in  FIG. 52  through  FIG. 57 . 
     The expression of “antenna” in the previous description does not always mean a single antenna, but “antenna” can mean an antenna unit which is formed of a plurality of antennas. 
     The tenth exemplary embodiment, as discussed above, describes the transmission method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas, more particularly, the method of transmitting a synchronous symbol in accordance with OFDM method. The tenth embodiment also describes the transmission apparatus and the reception apparatus to be used in the foregoing method. The structure and the operation discussed above allows increasing the data transmission rate, and synchronizing the transmission apparatus with the reception apparatus time-wise. 
     Exemplary Embodiment 11 
     The 11th exemplary embodiment describes a transmission method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas, more particularly, a reception apparatus which is applicable to a method of transmitting a signal including a control symbol. 
       FIGS. 33 ,  34 ,  FIGS. 43-45 , and  FIGS. 50 ,  51  show a frame structure in accordance with this embodiment.  FIG. 58  shows a structure of the reception apparatus in accordance with the 11th embodiment, and the elements operating in a similar way to those in  FIG. 37  have the same reference marks. 
     Frequency offset estimation unit  5801  receives reception quadrature baseband signal  3715 , then estimates a frequency offset with respect to a transmission apparatus, and outputs frequency offset estimation signal  5802 . 
     Frequency offset estimation unit  5803  receives reception quadrature baseband signal  5802 , then provides signal  5802  with frequency control, and outputs, e.g. signal  5802  which becomes a source signal of a radio unit. 
       FIG. 59  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 37  have the same reference marks. 
     Frequency offset estimation unit  5901  receives reception quadrature baseband signal  3704 , then estimates a frequency offset, and outputs frequency offset estimation signal  5902 . 
     Frequency offset estimation unit  5903  receives reception quadrature baseband signal  3709 , then estimates a frequency offset, and outputs frequency offset estimation signal  5904 . 
     Frequency offset estimation unit  5905  receives reception quadrature baseband signal  3715 , then estimates a frequency offset, and outputs frequency offset estimation signal  5906 . 
     Calculation unit  5907  receives frequency offset signals  5902 ,  5904 ,  5906 , then, e.g. averages those signals, and outputs frequency offset estimation signal  5908  averaged. 
     Frequency controller  5909  receives averaged signal  5908 , then outputs, e.g. signal  5910  to be a source signal of the radio unit. 
       FIG. 60  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 37  or  FIG. 39  have the same reference marks. 
     Frequency offset estimation unit  6001  receives reception quadrature baseband signal  3704 , then estimates a frequency offset, and outputs frequency offset estimation signal  6002 . 
     Frequency offset estimation unit  6003  receives reception quadrature baseband signal  3709 , then estimates a frequency offset, and outputs frequency offset estimation signal  6004 . 
     Frequency offset estimation unit  6005  receives reception quadrature baseband signal  3715 , then estimates a frequency offset, and outputs frequency offset estimation signal  6006 . 
     Calculation unit  6007  receives frequency offset signals  6002 ,  6004 ,  6006 , and received signal strength intensity estimation signals  3902 ,  3904 ,  3906 , then weights those signals with the received signal strength intensity, and averages the frequency offset signals, then outputs frequency offset estimation signal  6008  averaged. 
     Frequency controller  6009  receives averaged signal  6008 , then outputs, e.g. signal  6010  to be a source signal of the radio unit. 
       FIG. 61  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 37  or  FIG. 39  have the same reference marks. 
     Frequency offset estimation unit  6101  receives a reception quadrature baseband signal selected, then estimates a frequency offset, and outputs frequency offset estimation signal  6012 . 
     Frequency controller  6103  receives frequency offset estimation signal  6102 , then outputs, e.g. signal  6104  to be a source signal of the radio unit. 
       FIG. 62  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 37 ,  FIG. 39  or  FIG. 60  have the same reference marks. 
       FIG. 63  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 37 ,  FIG. 39 ,  FIG. 40 , or  FIG. 61  have the same reference marks. 
       FIG. 64  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 26  have the same reference marks. 
     Frequency offset estimation unit  6401  receives reception quadrature baseband signal  2604 , then estimates a frequency offset, and outputs frequency offset estimation signal  6402 . 
     Frequency offset estimation unit  6403  receives reception quadrature baseband signal  2614 , then estimates a frequency offset, and outputs frequency offset estimation signal  6404 . 
     Calculation unit  6405  receives frequency offset signals  6402 ,  6404 , then e.g. averages those signals, and outputs frequency offset estimation signal  6406  averaged. 
     Frequency controller  6407  receives averaged signal  6406 , then outputs, e.g. signal  6408  to be a source signal of the radio unit. 
       FIG. 65  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 26  have the same reference marks. 
     Frequency offset estimation unit  6501  receives reception quadrature baseband signal  2604 , then estimates a frequency offset, and outputs frequency offset estimation signal  6502 . 
     Frequency controller  6503  receives frequency offset estimation signal  6502 , then outputs, e.g. signal  6504  to be a source signal of the radio unit. 
       FIG. 66  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 37 ,  FIG. 39 , or  FIG. 54  have the same reference marks. 
     Frequency offset estimation unit  6601  receives reception quadrature baseband signal  3704 , then estimates a frequency offset, and outputs frequency offset estimation signal  6602 . 
     Frequency offset estimation unit  6603  receives reception quadrature baseband signal  3709 , then estimates a frequency offset, and outputs frequency offset estimation signal  6604 . 
     Frequency offset estimation unit  6605  receives reception quadrature baseband signal  3715 , then estimates a frequency offset, and outputs frequency offset estimation signal  6606 . 
     Calculation unit  6607  receives frequency offset signals  6602 ,  6604 ,  6606 , and received signal strength intensity estimation signals  3902 ,  3904 ,  3906 , then weights those signals with the received signal strength intensity, and averages the frequency offset signals, then outputs frequency offset estimation signal  6608  averaged. 
     Frequency controller  6609  receives averaged signal  6608 , then outputs, e.g. signal  6610  to be a source signal of the radio unit. 
       FIG. 67  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 37 ,  FIG. 39 ,  FIG. 40  or  FIG. 54  have the same reference marks. 
     Frequency offset estimation unit  6701  receives reception quadrature baseband signal  4002  selected, then estimates a frequency offset, and outputs frequency offset estimation signal  6702 . 
     Frequency controller  6703  receives frequency offset estimation signal  6702 , then outputs, e.g. signal  6704  to be a source signal of the radio unit. 
       FIG. 68  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 37 ,  FIG. 39 ,  FIG. 54  or  FIG. 66  have the same reference marks. 
       FIG. 69  shows a structure of the reception apparatus in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 37 ,  FIG. 39 ,  FIG. 40 ,  FIG. 54  or  FIG. 67  have the same reference marks. 
     Next, in the transmission method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas, a reception apparatus, which is applicable to a method of transmitting a signal including a control symbol, is described hereinafter. 
     Examples of the frame structure in accordance with this embodiment are shown in  FIGS. 33 ,  34 ,  43 ,  44 ,  45 ,  50  and  51 . The reception apparatus uses, e.g. a synchronous symbol, for estimating a frequency offset. In this case, the transmission apparatus has only one frequency source, so that signals transmitted from the respective antennas are synchronized in frequency with each other. 
     An operation of the reception apparatus shown in  FIG. 58  is demonstrated hereinafter. Frequency offset estimation unit  5801  receives reception quadrature baseband signal  3715 , then estimates a frequency offset from the synchronous symbol, and outputs a frequency offset estimation signal. 
     Demodulators  3723 ,  3725  removes the frequency offset from frequency offset estimation signal  5802  supplied. 
     Frequency controller  5803  receives frequency offset estimation signal  5802 , then removes the frequency offset therefrom, and outputs source signal  5804  of the radio unit. 
     Next, operations of the reception apparatus shown in  FIG. 59  different from those described in  FIG. 58  are demonstrated. Calculation unit  5907  receives frequency offset estimation signals  5902 ,  5904 ,  5906 , then averages those signals, and outputs frequency offset signal  5908  averaged. This averaging of the signals can produce a more accurate estimation of the frequency offset. 
     Next, operations of the reception apparatus shown in  FIG. 60  different from those described in  FIG. 58  are demonstrated. Calculation unit  6007  receives received signal strength intensity estimation signals  3902 ,  3904 ,  3906 , and frequency offset estimation signals  6002 ,  6004 ,  6006 , then weights those signals in response to the received signal strength intensity, and outputs a frequency offset estimation signal averaged. This operation allows increasing the reliability of the frequency offset estimation signal having strong received signal strength intensity, so that more accurate estimation of the frequency offset can be expected. 
     Next, operations of the reception apparatus shown in  FIG. 61  different from those described in  FIG. 58  are demonstrated. Signal selection unit  4001  outputs a reception quadrature baseband signal having strong received signal strength intensity as signal  4002 , so that frequency offset estimation unit  6101  produces more accurate estimation of the frequency offset. 
       FIGS. 62 ,  63  differ from  FIGS. 60 ,  61  in finding the received signal strength intensity from the reception quadrature baseband signal. 
     As discussed above, in the method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas, and in the reception apparatus used in the spread-spectrum communication method, the frequency offset can be removed. 
       FIG. 64  through  FIG. 69  show structures of the reception apparatus used in OFDM transmission method, and the reception apparatus operates in a similar way to what are shown in  FIG. 58  through  FIG. 63 . 
     In the method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas, and in the reception apparatus used in the OFDM transmission method, the frequency offset can be removed according to the foregoing structure and operation. 
     As a result, the frequency offset can be removed from both of the transmission apparatus and the reception apparatus. 
     In this embodiment, the frame structure is not limited to what is shown in  FIG. 33 ,  34 ,  43 ,  44 ,  45 ,  50  or  51 . 
     In the transmission apparatus and the reception apparatus, the source signal supplied to the radio unit can be commonly used by the respective radio units equipped to the respective antennas, so that the frequency offset can be commonly estimated to the plurality of antennas. 
     Similarly, in the transmission apparatus and the reception apparatus, production of modulation signals in the transmission apparatus as well as the source signal for synchronizing in the reception apparatus can be commonly used by the respective modulation signal generators and synchronizing units equipped to the respective antennas. As a result, time-synchronization can be done commonly to the plurality of antennas. 
     The expression of “antenna” in the previous description does not always mean a single antenna, but “antenna” can mean an antenna unit which is formed of a plurality of antennas. 
     The 11th exemplary embodiment, as discussed above, describes the transmission method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas, more particularly, the reception apparatus which is used in the method of transmitting a signal including a control symbol. The structure and operation discussed above allow increasing a data transmission rate, and allow the reception apparatus to remove frequency-offset. 
     Exemplary Embodiment 12 
     The 12th exemplary embodiment describes the following method and apparatus: 
     a communication method of transmitting a modulation signal to a receiver, who receives the modulation signal then estimates radio-wave propagation environment of respective antennas, and transmits the estimated information of the radio-wave propagation environment, then the communication method selecting one of the following transmission methods based on the estimated information: 
     a method of transmitting the modulation signals of a plurality of channels to the same frequency band from the plurality of antennas; or 
     a method of transmitting the modulation signal of one channel from one antenna, and 
     a radio communication apparatus using the foregoing communication method. 
     The 12th exemplary embodiment further describes the following method and apparatus: 
     a communication method of transmitting a modulation signal to a receiver, who receives the modulation signal then estimates radio-wave propagation environment of respective antennas, then the communication method sending the information which requires one of the following transmission methods based on the estimated information of the radio-wave propagation environment: 
     a method of transmitting the modulation signals of a plurality of channels to the same frequency band from the plurality of antennas, or 
     a method of transmitting the modulation signal of one channel from one antenna; 
     then the communication method selecting, based on the requiring information, one of the foregoing two transmission methods, and 
     a radio communication apparatus using the foregoing communication method. 
       FIG. 4  shows a placement of signal points in in-phase-quadrature (I-Q) plane.  FIG. 70  shows a frame structure in accordance with this embodiment along a time axis, to be more specific, frame structure  7040  of a signal transmitted from a base station and frame structure  7050  of a signal transmitted from a terminal. As shown in  FIG. 70 , frame structure  7040  includes frame structure  7020  of channel A and frame structure  7030  of channel B. 
     Frame structure  7020  includes information symbols  7001 ,  7003 ,  7004 ,  7005 , and guard symbol  7002  of the signal of channel A transmitted from the base station. Frame structure  7030  includes information symbols  7007 ,  7009 , guard symbols  7006 ,  7008 ,  7010  of the signal of channel B transmitted from the base station. Frame structure  7050  includes information symbols  7011 ,  7012 ,  7013  of the signal transmitted from the terminal. 
       FIG. 71  shows information symbol structure  7110  of channel A signal transmitted from the base station in accordance with this embodiment. Structure  7110  includes multiplex information symbol  7101  and data symbol  7102 . 
       FIG. 72  shows information symbol structure  7210  of a signal transmitted from the terminal in accordance with this embodiment. Structure  7210  includes received signal strength intensity information symbol  7201 , transmission path variation information symbol  7202 , multi-path information symbol  7203 , disturbance information symbol  7204 , and data symbol  7205 . 
       FIG. 73  shows information symbol structure  7310  of a signal transmitted from the terminal in accordance with this embodiment. Structure  7310  includes transmission method requiring information symbol  7301 , data symbol  7302 . 
       FIG. 74  shows a structure of a transmission apparatus at the base station in accordance with this embodiment. The apparatus includes channel A transmitter  7410 , channel B transmitter  7420 , and frame structure signal generator  209 . 
     Channel A transmitter  7410  is formed of modulation signal generator  202 , radio unit  204 , power amplifier  206 , and antenna  208 . 
     Channel B transmitter  7420  is formed of modulation signal generator  212 , radio unit  214 , power amplifier  216 , and antenna  218 . 
     The elements operating in a similar way to those in  FIG. 13  have the same reference marks. 
     Modulation signal generator  202  receives transmission digital signal  7401 , multiplex information  7402 , frame structure signal  210 , and outputs modulation signal  203  in accordance with the frame structure. 
     Frame structure signal generator  209  receives transmission method determining information  7403 , and outputs frame structure signal  210 . 
     Modulation signal generator  212  receives transmission digital signal  7401  and frame structure signal  210 , then outputs modulation signal  213 . 
       FIG. 75  shows a structure of a reception apparatus at the base station, and its radio unit  7503  receives signal  7502  received by antenna  7501 , then outputs reception quadrature baseband signal  7504 . 
     Demodulator  7505  receives reception quadrature baseband signal  7504 , then outputs reception digital signal  7506 . 
     Signal isolator  7507  receives signal  7506 , and outputs radio-wave propagation environmental information or transmission method requiring information  7508  and reception data  7509 . 
     Transmission method determining unit  7510  receives radio-wave propagation environmental information or transmission method requiring information  7508 , then outputs transmission method determining information  7511  and multiplex information  7512 . 
       FIG. 76  shows a structure of a transmission apparatus at the terminal in accordance with this embodiment. Modulation signal generator  7606  receives transmission digital signal  7601 , radio-wave propagation environment estimation signals  7602 ,  7603 , and frame structure signal  7605 , then outputs transmission quadrature baseband signal  7607 . 
     Frame structure signal generator  7604  outputs frame structure signal  7605 . 
     Modulator  7608  receives transmission quadrature baseband signal  7607 , then outputs modulation signal  7609  from antenna  7610  as radio wave. 
       FIG. 77  shows a structure of a reception apparatus at the terminal in accordance with this embodiment. Radio unit  7703  receives signal  7702  received by antenna  7701 , then outputs reception quadrature baseband signal  7704 . 
     Multi-path estimation unit  7705  receives signal  7704 , and outputs multi-path estimation signal  7706 . 
     Disturbance intensity estimation unit  7707  receives reception quadrature baseband signal  7704 , then outputs disturbance intensity estimation signal  7708 . 
     Received signal strength intensity estimation unit  7709  of channel A receives reception quadrature baseband signal  7704 , then outputs received signal strength intensity estimation signal  7710  of channel A. 
     Received signal strength intensity estimation unit  7711  of channel B receives reception quadrature baseband signal  7704 , then outputs received signal strength intensity estimation signal  7712  of channel B. 
     Transmission distortion estimation unit  7713  of channel A receives reception quadrature baseband signal  7704 , then outputs transmission variation estimation signal  7714  of channel A. 
     Transmission distortion estimation unit  7715  of channel B receives reception quadrature baseband signal  7704 , then outputs transmission variation estimation signal  7716  of channel B. 
     Information generator  7717  receives the following signals: 
     multi-path estimation signal  7706 ; 
     disturbance intensity estimation signal  7708 ; 
     received signal strength intensity estimation signal  7710  of channel A; 
     received signal strength intensity estimation signal  7712  of channel B; 
     transmission path variation estimation signal  7714  of channel A; and 
     transmission path variation estimation signal  7716  of channel B, 
     then generator  7717  outputs radio wave propagation environment estimation signal  7718 . 
     Signal isolator  7719  receives the following signals: 
     reception quadrature baseband signals  7704 ,  7729 ; 
     transmission path variation estimation signals  7714 ,  7739  of channel A; and 
     transmission path variation estimation signal  7716 ,  7741  of channel B, 
     then isolator  7719  outputs reception quadrature baseband signals  7720 ,  7721  of channel A and channel B respectively. 
     Radio unit  7728  receives signal  7727  received by antenna  7726 , then outputs reception quadrature baseband signal  7729 . 
     Multi-path estimation unit  7730  receives reception quadrature baseband signal  7729 , and outputs multi-path estimation signal  7731 . 
     Disturbance intensity estimation unit  7732  receives reception quadrature baseband signal  7729 , then outputs disturbance intensity estimation signal  7733 . 
     Received signal strength intensity estimation unit  7734  of channel A receives reception quadrature baseband signal  7729 , then outputs received signal strength intensity estimation signal  7735  of channel A. 
     Received signal strength intensity estimation unit  7736  of channel B receives reception quadrature baseband signal  7729 , then outputs received signal strength intensity estimation signal  7737  of channel B. 
     Transmission distortion estimation unit  7738  of channel A receives reception quadrature baseband signal  7729 , then outputs transmission variation estimation signal  7739  of channel A. 
     Transmission distortion estimation unit  7740  of channel B receives reception quadrature baseband signal  7729 , then outputs transmission variation estimation signal  7741  of channel B. 
     Information generator  7742  receives the following signals: 
     multi-path estimation signal  7731 ; 
     disturbance intensity estimation signal  7733 ; 
     received signal strength intensity estimation signal  7735  of channel A; 
     received signal strength intensity estimation signal  7737  of channel B; 
     transmission path variation estimation signal  7739  of channel A; and 
     transmission path variation estimation signal  7741  of channel B, 
     then generator  7742  outputs radio wave propagation environment estimation signal  7743 . 
       FIG. 78  shows a structure of a transmission apparatus at the terminal in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 76  have the same reference marks. 
     Transmission method requiring information generator  7801  receives radio-wave propagation environmental information  7602 ,  7603 , then outputs transmission method requiring information  7802 . 
       FIG. 84A  shows a frame structure of a signal transmitted from the base station in accordance with this embodiment, to be more specific, frame structure  8410  of channel A and frame structure  8420  of channel B. 
       FIG. 84B  shows a frame structure of a signal transmitted from the terminal in accordance with this embodiment. 
     The base station transmits a modulation signal of OFDM method, and the frame structure includes guard symbol  8401  of the signal transmitted from the base station, information symbol  8402  of the signal transmitted from the base station, and information symbol  8403  of a signal transmitted from the terminal. 
     Next, the following communication method is demonstrated with reference to  FIG. 4 , and  FIG. 70  through  FIG. 77 : 
     a communication method where a modulation signal is transmitted to a receiver, who receives the modulation signal, estimates radio-wave propagation environment of respective antennas, and outputs the estimated information of the radio-wave propagation environment, then the communication method selects one of the following transmission methods based on the estimated information: 
     a plurality of antennas transmit the modulation signals of a plurality of channels to the same frequency band based on the information, or 
     one antenna transmits the modulation signal of one channel. 
     A radio communication apparatus using the foregoing communication method is also described hereinafter. 
       FIG. 74  shows the structure of the transmission apparatus at the base station. Frame structure signal generator  209  receives transmission method determining information  7403 . Based on information  7403 , generator  209  outputs, e.g. the information about one of the following frame structures as frame structure signal  210 : 
     a transmission method where information symbol  7004  of channel A shown in  FIG. 70  and the information symbol of channel B are multiplexed; and 
     a transmission method where information symbol  7005  of channel A shown in  FIG. 70  is transmitted; however, channel B has guard symbol  7010 , so that they are not multiplexed. 
     Transmission determining information  7403  corresponds to output signal  7511  from transmission method determining unit  7510 . 
     Modulation signal generator  202  receives transmission digital signal  7401 , multiplex information  7402 , and frame structure signal  210 , then outputs modulation signal  203  of the information symbol. At this time, the information symbol is formed of multiplex information symbol  7101  and data symbol  7102 , as shown in  FIG. 71 . Multiplex information symbol  7101  is a symbol of multiplex information  7402 , and data symbol  7102  is transmission digital signal  7401 . Multiplex information  7402  corresponds to output signal  7512  from the reception apparatus shown in  FIG. 75  at the base station. 
     Modulation signal generator  212  receives transmission digital signal  7401 , frame structure signal  210 , and outputs modulation signal  213  of the guard symbol or the information symbol in response to frame structure signal  210 , as shown in  FIG. 70 . At this time the modulation signal of the guard symbol corresponds to signal point  403  shown in  FIG. 4 . 
       FIG. 75  shows the structure of the reception apparatus at the base station. Signal isolator  7507  isolates the following signals in the frame structure shown in  FIG. 72 : 
     data symbol  7205 ; 
     received signal strength intensity information symbol  7201  corresponding to the radio-wave propagation environmental information; 
     transmission path variation information symbol  7202 ; 
     multi-path information symbol  7203 ; and 
     disturbance information symbol  7204 . 
     Signal isolator  7507  then outputs the information of data symbol  7205  as reception data  7509 , also outputs symbols  7201 ,  7202 ,  7203  and  7204  as radio-wave propagation environmental information  7508 . 
     Transmission method determining unit  7510  receives information  7508 , and based on this information  7508 , selects the communication method which selects one of the following transmission methods: 
     a method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas; or 
     a method of transmitting a modulation signal of one channel from one antenna. 
     Determining unit  7510  then outputs the information of the transmission methods as transmission method determining information  7511  and multiplex information  7512 . 
       FIG. 76  shows the transmission apparatus at the terminal. The apparatus receives transmission digital signal  7601 , radio-wave propagation environment estimation signals  7602 ,  7603 , and frame structure signal  7605 . According to the frame structure shown in  FIG. 72 , signal  7601  is treated as data symbol  7205 , signals  7602 ,  7603  are treated as received signal strength intensity information symbol  7201 , transmission path variation information symbol  7202 , multi-path information symbol  7203 , and disturbance information symbol  7204 . Then the transmission apparatus outputs modulation signal  7606 . Radio-wave propagation estimation signals  7602 ,  7603  correspond to radio-wave propagation environment estimation signals  7718 ,  7743  of the reception apparatus shown in  FIG. 77  at the terminal. 
       FIG. 77  shows the structure of the reception apparatus at the terminal. 
     Information generator  7717  receives the following signals: 
     multi-path estimation signal  7706 ; 
     disturbance intensity estimation signal  7708 ; 
     received signal strength intensity estimation signal  7710  of channel A signals; 
     received signal strength intensity estimation signal  7712  of channel B signals; 
     transmission path variation estimation signal  7714  of channel A; and 
     transmission path variation estimation signal  7716  of channel B. 
     Generator  7717  then outputs radio-wave propagation environment estimation signal  7718  corresponding to the information of received signal strength intensity information symbol  7201 , transmission path variation information symbol  7202 , multi-path information symbol  7203 , and disturbance information symbol  7204  shown in  FIG. 72 . 
     In a similar way to the foregoing operation, information generator  7742  receives the following signals: 
     multi-path estimation signal  7731 ; 
     disturbance intensity estimation signal  7733 ; 
     received signal strength intensity estimation signal  7735  of channel A signals; 
     received signal strength intensity estimation signal  7737  of channel B signals; 
     transmission path variation estimation signal  7739  of channel A; and 
     transmission path variation estimation signal  7741  of channel B. 
     Generator  7742  then outputs radio-wave propagation environment estimation signal  7743  corresponding to the information of received signal strength intensity information symbol  7201 , transmission path variation information symbol  7202 , multi-path information symbol  7203 , and disturbance information symbol  7204  shown in  FIG. 72 . 
     In conclusion, depending on a radio-wave propagation environment, the transmission method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas can be switched to/from the transmission method of transmitting modulation signals of a plurality of channels without multiplexing to the same frequency band. This operation can improve the quality of information. 
     In the foregoing operation, radio-wave propagation environment estimation signals  7718 ,  7743  correspond to signals  7602 ,  7603  of the transmission apparatus shown in  FIG. 76  at the terminal. 
     Next, an operation at starting a communication is demonstrated hereinafter. When the communication starts, the base station transmits modulation signals by the transmission method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas. At this time, if the terminal is not suitable for the foregoing transmission method, the quality of reception data is lowered. 
     In order to avoid this problem, when a communication to the terminal starts, the base station transmits modulation signals of a plurality of channels without multiplexing to the same frequency band as symbols  7001 ,  7006 , and symbols  7002 ,  7007  shown in  FIG. 70 . 
     Frame structure signal generator  209  shown in  FIG. 74  outputs frame structure signal  210  in which the following frame structure is prepared: When a communication to the terminal starts, modulations signals of a plurality of channels are transmitted, without being multiplexed, to the same frequency band as symbols  7001 ,  7006  and symbols  7002 ,  7007  shown in  FIG. 70 . 
     The reception apparatus shown in  FIG. 77  at the terminal estimates a radio-wave propagation environment from the reception signal of symbols  7001 ,  7007  transmitted from the base station, then generates radio-wave propagation environment estimation signals  7718 ,  7743 . 
     The transmission apparatus shown in  FIG. 76  at the terminal transmits estimation signals  7718 ,  7743  with information symbols  7011 ,  7012  shown in  FIG. 70 . 
     The reception apparatus shown in  FIG. 75  at the terminal selects one of the following transmission methods based on the radio-wave propagation environment estimation information included in information symbol  7011  which is a part of the signal transmitted from transmission apparatus shown in  FIG. 76  at the terminal: 
     a method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas; or 
     a method of transmitting modulation signals of a plurality of channels without being multiplexed to the same frequency band. In the case of, e.g. a fine environment for the radio-wave propagation, the modulation signals of the plurality of channels are transmitted from the plurality of antennas such as information symbols  7004 ,  7009 . 
     As discussed above, when the communication to the terminal starts, modulation signals of a plurality of channels are transmitted without being multiplexed to the same frequency band, thereby improving the information quality. 
     In the foregoing discussion, a modulation signal indicating that the terminal requires a communication to the base station can be transmitted at the beginning. When the base station uses the OFDM transmission method, what is discussed above can be also used. 
     Next, a communication method, which selects one of the following transmission methods, and a radio communication apparatus using this communication method are described hereinafter with reference to  FIGS. 4 ,  70 ,  71 ,  73 ,  74 ,  75 ,  77  and  78 . When a modulation signal is transmitted to a receiver, who receives the modulation signal and estimates radio-wave propagation environments of respective antennas, the communication method selects one of the following transmission methods based on the estimation: 
     a method of transmitting information that requires one of the following two methods, and based on the information, this method selects one of the transmission methods below: 
     a method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas; or 
     a method of transmitting a modulation signal of one channel from one antenna. 
       FIG. 74  shows the structure of the transmission apparatus at the base station. Frame structure signal generator  209  receives transmission method determining information  7403 . Based on information  7403 , generator  209  outputs, e.g. the information about one of the following frame structures as frame structure signal  210 : 
     a frame structure of a transmission method where information symbol  7004  of channel A shown in  FIG. 70  and the information symbol of channel B are multiplexed; or 
     a frame structure of a transmission method where information symbol  7005  of channel A shown in  FIG. 70  is transmitted; however, channel B has guard symbol  7010 , so that they are not multiplexed. 
     Transmission determining information  7403  corresponds to output signal  7511  from transmission method determining unit  7510 . 
     Modulation signal generator  202  receives transmission digital signal  7401 , multiplex information  7402 , and frame structure signal  210 , then outputs modulation signal  203  of the information symbol. At this time, the information symbol is formed of multiplex information symbol  7101  and data symbol  7102 , as shown in  FIG. 71 . Multiplex information symbol  7101  is a symbol of multiplex information  7402 , and data symbol  7102  is transmission digital signal  7401 . Multiplex information  7402  corresponds to output signal  7512  from the reception apparatus shown in  FIG. 75  at the base station. 
     Modulation signal generator  212  receives transmission digital signal  7401 , frame structure signal  210 , and outputs modulation signal  213  of the guard symbol or the information symbol in response to frame structure signal  210 , as shown in  FIG. 70 . At this time the modulation signal of the guard symbol corresponds to signal point  403  shown in  FIG. 4 . 
       FIG. 75  shows the structure of the reception apparatus. Signal isolator  7507  isolates data symbol  7302  from transmission method requiring information symbol  7301  in the frame structure shown in  FIG. 73 , then outputs the information of data symbol  7205  as reception data  7509 , and information symbol  7301  as transmission method requiring information  7509 . 
     Transmission method determining unit  7510  receives information  7508 , then selects a communication method which selects one of the transmission method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas, or a transmission method of transmitting a modulation signal of one channel from one antenna. Determining unit  7510  outputs the information about the transmission method selected as transmission method determining information  7511  and multiplex information  7512 . 
       FIG. 78  shows the structure of the transmission apparatus at the terminal. Transmission method requiring information generator  7801  receives radio-wave propagation environment estimation signals  7602 ,  7603 . In response to those signals generator  7801  outputs a communication method which selects one of the following two transmission methods as transmission request information  7802 : 
     in the case of, e.g. a fine environment for the radio-wave propagation, the transmission method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas. 
     in the case of, e.g. a bad environment for the radio-wave propagation, the transmission method of transmitting a modulation signal of one channel from one antenna. 
     Modulation signal generator  7606  receives transmission digital signal  7601 , frame structure signal  7605 , and transmission request information  7802 , and modulates signal  7601  and information  7802  according to the frame structure shown in  FIG. 73 , then outputs transmission quadrature baseband signal  7607 . Radio-wave propagation environment estimation signals  7602 ,  7603  correspond to radio-wave propagation environment estimation signals  7718 ,  7743  of the reception apparatus shown in  FIG. 77  at the terminal. 
       FIG. 77  shows the structure of the reception apparatus at the terminal. Information generator  7717  receives the following signals: 
     multi-path estimation signal  7706 ; 
     disturbance intensity estimation signal  7708 ; 
     received signal strength intensity estimation signal  7710  of channel A signals; 
     received signal strength intensity estimation signal  7712  of channel B signals; 
     transmission path variation estimation signal  7714  of channel A; and 
     transmission path variation estimation signal  7716  of channel B, 
     then generator  7717  outputs radio wave propagation environment estimation signal  7718 . 
     In a similar way to the foregoing operation, information generator  7742  receives the following signals: 
     multi-path estimation signal  7731 ; 
     disturbance intensity estimation signal  7733 ; 
     received signal strength intensity estimation signal  7735  of channel A signals; 
     received signal strength intensity estimation signal  7737  of channel B signals; 
     transmission path variation estimation signal  7739  of channel A; and 
     transmission path variation estimation signal  7743  of channel B, then generator  7742  outputs radio wave propagation environment estimation signal  7743 . 
     Radio wave propagation environment estimation signals  7718 ,  7743  correspond to signals  7602 ,  7603  of the transmission apparatus shown in  FIG. 78  at the terminal. 
     In conclusion, depending on a radio-wave propagation environment, the transmission method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas can be switched to/from the transmission method of transmitting modulation signals of a plurality of channels without multiplexing to the same frequency band. This operation can increase the quality of information. 
     Next, an operation at starting a communication is demonstrated hereinafter. When the communication starts, the base station transmits modulation signals by the transmission method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas. At this time, if the terminal is not suitable for the foregoing transmission method, the quality of reception data is lowered. 
     In order to avoid this problem, when a communication to the terminal starts, the base station transmits modulation signals of a plurality of channels without multiplexing to the same frequency band as symbols  7001 ,  7006 , and symbols  7002 ,  7007  shown in  FIG. 70 . 
     Frame structure signal generator  209  shown in  FIG. 74  outputs frame structure signal  210  in which the following frame structure is prepared: When a communication to the terminal starts, modulation signals of a plurality of channels are transmitted, without being multiplexed, to the same frequency band as symbols  7001 ,  7006  and symbols  7002 ,  7007  shown in  FIG. 70 . 
     The reception apparatus shown in  FIG. 77  at the terminal estimates a radio-wave propagation environment from the reception signal of symbols  7001 ,  7007  transmitted from the base station, then generates radio-wave propagation environment estimation signals  7718 ,  7743 . 
     Transmission method requiring information generator  7801  of the transmission apparatus shown in  FIG. 78  at the terminal receives radio-wave propagation environment estimation signals  7718 ,  7743  which estimate the environment from the reception signal of symbols  7001 ,  7007  transmitted from the base station. Generator  7801  then selects one of the following two transmission methods: 
     a method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas; or 
     a method of transmitting modulation signals of a plurality of channels without being multiplexed to the same frequency band. Generator  7801  outputs transmission request information  7802 , which is transmitted in the structure of the information symbol of the transmission signal shown in  FIG. 73  in accordance with, e.g. information symbol  7011  shown in  FIG. 70 . 
     The reception apparatus shown in  FIG. 75  at the terminal selects one of the following transmission methods based on the transmission method requiring information symbol included in information symbol  7011  which is a part of the signal transmitted from transmission apparatus shown in  FIG. 78  at the terminal: 
     a method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas; or 
     a method of transmitting modulation signals of a plurality of channels without being multiplexed to the same frequency band. 
     As discussed above, when the communication to the terminal starts, modulation signals of a plurality of channels are transmitted without being multiplexed to the same frequency band, thereby improving the information quality. 
     In the foregoing discussion, a modulation signal indicating that the terminal requires a communication to the base station can be transmitted at the beginning. 
     In this embodiment, what is discussed previously is applicable to any one of the following methods: single carrier method, spread-spectrum communication method, CDMA method (multiplexing method). In the case of using any one of those methods, the transmission apparatus needs a spread unit, and the reception apparatus needs an inverse-spread unit. 
     Hereinafter the case, where OFDM method among others is employed, is described.  FIG. 84  shows a frame structure when the base station transmits signals by OFDM method. The transmission apparatus at the base station transmits a modulation signal of channel A at time  0  (see the frame structure  8410 ), and a modulation signal of channel B at time  1  (see the frame structure  8420 ). The terminal receives the modulation signal transmitted by the base station at time  0  as well as the modulation signal transmitted by the base station at time  1 . The terminal then estimates a radio-wave propagation environment such as multi-path, disturbance signal electric field intensity, electric field intensities of channels A and B respectively, and transmission path variations of channels A and B respectively. The terminal then transmits such radio-wave propagation environment estimation information or transmission request information, which requests one of the following transmission methods, to the base station: 
     a method of transmitting modulation signals of a plurality of channels to the same frequency band from a plurality of antennas; or 
     a method of transmitting modulation signals of a plurality of channels without being multiplexed to the same frequency band. 
     The base station determines the transmission method based on the foregoing radio-wave propagation environment estimation information or the transmission request information. In the case of a fine environment for the radio wave propagation, channel A and channel B are multiplexed for transmission such as at time  3  and time  4  shown in  FIG. 84A . In the case of a bad environment, a modulation signal of channel A only is transmitted such as at time  5  in  FIG. 84A . In those cases, the transmission apparatus and the reception apparatus at the base station and the terminal can be structured as shown in  FIG. 74  through  FIG. 78 , which are described in reference to the frame structure shown in  FIG. 70 . What is discussed above is also applicable to the case where a signal of the spread-spectrum communication method is modulated by OFDM method. 
     This embodiment refers to the case where two channels are multiplexed, or being switched to the case where one channel is used without being multiplexed; however, this example does not limit the embodiment. For instance, in the case where three channels can be multiplexed to the same frequency band, the transmission apparatus at the base station switches the number of multiplexing between 1-3 channels. 
     The expression of “antenna” in the previous description does not always mean a single antenna, but “antenna” can mean an antenna unit which is formed of a plurality of antennas. 
     The 12th exemplary embodiment, as discussed above, proves that the following method and apparatus are achievable: 
     a communication method of transmitting a modulation signal to a receiver, which receives the modulation signal then estimates the radio-wave propagation environment of respective antennas, and transmits the estimated information of the radio-wave propagation environment, then the communication method selecting one of the following transmission methods based on the estimated information: 
     a method of transmitting the modulation signals of a plurality of channels to the same frequency band from the plurality of antennas; or 
     a method of transmitting the modulation signal of one channel from one antenna, and 
     a radio communication apparatus using the foregoing communication method. 
     This operation and apparatus allow switching between the foregoing two transmission methods depending on the radio-wave propagation environment. As a result, the information can be transmitted more accurately. 
     Exemplary Embodiment 13 
     The 13th exemplary embodiment describes the following method, by which modulation signals of a plurality of spread-spectrum communication methods can be transmitted: 
     a communication method where a modulation signal of a transmission method, by which a control channel is transmitted, is transmitted to a receiver, who receives the modulation signal, estimates radio-wave propagation environment of respective antennas from reception signals of the control channel, and transmits the estimated information of the radio-wave propagation environment, then the communication method selects one of the following transmission methods based on the estimated information: 
     a method of transmitting the modulation signals of a plurality of data channels of the plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas, or 
     a method of transmitting the modulation signal of one data channel of one spread-spectrum communication method from one antenna. The 13th embodiment also describes a radio communication apparatus using the foregoing communication method. 
     The 13th exemplary embodiment further describes the following method, by which modulation signals of a plurality of spread-spectrum communication methods can be transmitted: 
     a communication method where a modulation signal of the transmission method, by which a control channel is transmitted, is transmitted to a receiver, who receives the modulation signal, estimates radio-wave propagation environment of respective antennas from reception signals of the control channel, then the communication method sends the information which requires one of the following transmission methods based on the estimated information of the radio-wave propagation environment: 
     a method of transmitting the modulation signals of a plurality of data channels of the plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas, or 
     a method of transmitting the modulation signal of a data channel of one spread-spectrum communication method from one antenna; 
     then the communication method selects, based on the requiring information, one of the foregoing two transmission methods, and 
     a radio communication apparatus using the foregoing communication method is also described. 
       FIG. 4  shows a placement of signal points on the in-phase-quadrature (I-Q) plane. 
       FIG. 73  shows a structure of an information symbol at a terminal in accordance with this embodiment. 
       FIG. 75  shows a structure of a reception apparatus at a base station in accordance with this embodiment. 
       FIG. 76  shows a structure of a transmission apparatus at the terminal in accordance with this embodiment. 
       FIG. 78  shows a structure of a transmission apparatus at the terminal in accordance with this embodiment. 
       FIG. 79  shows a frame structure along a time axis in accordance with this embodiment, to be more specific, frame structure  7980  of a signal transmitted from the base station and frame structure  7990  of a signal transmitted from the terminal. One example of frame structure  7980  includes the following frames: 
     frame structure  7960  of spread-spectrum communication method A, where frame structure  7960  is formed of data channel  7920  and control channel  7930 , and 
     frame structure  7970  of spread-spectrum communication method B, where frame structure  7970  is formed of data channel  7940  and control channel  7950 . 
     Frame structure  7920  includes information symbols  7901 ,  7902 . Frame structure  7930  includes control symbols  7903 ,  7904 ,  7905 , and  7906  of method A. 
     Frame structure  7940  includes information symbols  7907 , guard symbol  7908 . Frame structure  7950  includes control symbols  7909 ,  7910 ,  7911 , and  7912  of method B. 
     Information symbols  7913 ,  7914 , and  7915  belong to the signal transmitted from the terminal. 
       FIG. 80  shows a structure of the transmission apparatus at the base station in accordance with this embodiment. The apparatus includes transmitters  8020  and  8030  responsible for spread-spectrum communication methods A and B respectively, and frame structure signal generator  209 . 
     Transmitter  8020  of method A includes data-channel modulation and spread unit  8002 , control-channel modulation and spread unit  8006 , adding unit  8004 , radio unit  204 , power amplifier  206 , and antenna  208 . 
     Transmitter  8030  of method B includes data-channel modulation and spread unit  8009 , control-channel modulation and spread unit  8012 , adding unit  8011 , radio unit  214 , power amplifier  216 , and antenna  218 . 
     The elements operating in a similar way to those in  FIG. 2  have the same reference marks. 
     Data-channel modulation and spread unit  8002  receives transmission digital signal  8001 , frame structure signal  210 , and outputs transmission quadrature baseband signal  8003  of the data channel of method A. 
     Control-channel modulation and spread unit  8006  receives transmission method determining information  8005 , frame structure signal  210 , and outputs transmission quadrature baseband signal  8010  of the control channel of method A. 
     Adding unit  8004  receives base-band signals  8003  of data channel and  8010  of control channel, then adds those signals together, thereby outputting transmission quadrature baseband signal  203 . 
     Data-channel modulation and spread unit  8009  receives transmission digital signal  8008 , frame structure signal  210 , then outputs transmission quadrature baseband signal  8010  of the data channel of method B. 
     Control-channel modulation and spread unit  8012  receives transmission method determining information  8005 , frame structure signal  210 , then outputs transmission quadrature baseband signal  8013  of the control channel of method B. 
     Adding unit  8011  receives base-band signals  8010  of data channel and  8013  of control channel, then adds those signals together, thereby outputting transmission quadrature baseband signal  213 . 
     Frame structure signal generator  209  receives transmission method determining information  8005 , then outputs frame structure signal  210 . 
       FIG. 81  shows a structure of control symbol  8110 , and details a structure of control symbols  7903 ,  7904 ,  7905 ,  7906 ,  7909 ,  7910 ,  7911 , and  7912  shown in  FIG. 79 . 
     Control symbol  8110  includes multiplex information  8101 , pilot symbol  8102 , and transmission power control information  8103 . 
       FIG. 82  shows a structure of a reception apparatus at the terminal in accordance with this embodiment, and the elements operating in a similar way to those in  FIG. 77  have the same reference marks. 
     Received signal strength intensity estimation unit  8201  of method A receives reception quadrature baseband signal  7704 , and outputs received signal strength intensity estimation signal  8202  of method A. 
     Received signal strength intensity estimation unit  8203  of method B receives reception quadrature baseband signal  7704 , and outputs received signal strength intensity estimation signal  8204  of method B. 
     Transmission path variation estimation unit  8205  of method A receives reception quadrature baseband signal  7704 , and outputs transmission path variation estimation signal  8206  of method A. 
     Transmission path variation estimation unit  8207  of method B receives reception quadrature baseband signal  7704 , and outputs transmission path variation estimation signal  8208  of method B. 
     Information generator  7717  receives the following signals: 
     multi-path estimation signal  7706 ; 
     disturbance intensity estimation signal  7708 ; 
     received signal strength intensity estimation signal  8202  of method A signals; 
     received signal strength intensity estimation signal  8204  of method B signals; 
     transmission path variation estimation signal  8206  of method A; and 
     transmission path variation estimation signal  8208  of method B, then generator  7717  outputs radio wave propagation environment estimation signal  7718 . 
     Received signal strength intensity estimation unit  8209  of method A receives reception quadrature baseband signal  7729 , and outputs electric field intensity estimation signal  8210  of method A. 
     Received signal strength intensity estimation unit  8211  of method B receives reception quadrature baseband signal  7729 , and outputs electric field intensity estimation signal  8212  of method B. 
     Transmission path variation estimation unit  8213  of method A receives reception quadrature baseband signal  7729 , and outputs transmission path variation estimation signal  8214  of method A. 
     Transmission path variation estimation unit  8215  of method B receives reception quadrature baseband signal  7729 , and outputs transmission path variation estimation signal  8216  of method B. 
     Information generator  7742  receives the following signals: 
     multi-path estimation signal  7731 ; 
     disturbance intensity estimation signal  7733 ; 
     received signal strength intensity estimation signal  8210  of method A signals; 
     received signal strength intensity estimation signal  8212  of method B signals; 
     transmission path variation estimation signal  8214  of method A; and 
     transmission path variation estimation signal  8216  of method B, then generator  7742  outputs radio wave propagation environment estimation signal  7743 . 
       FIG. 83  shows a frame structure in accordance with this embodiment, to be more specific, frame structure  8301  of a signal transmitted from the base station, and frame structure  8302  of a signal transmitted from the terminal. An example of frame structure  8301  includes frame structure  8303  of method A, where structure  8303  is formed of data channel  8305  and control channel  8306 , and frame structure  8304  of method B, where structure  8304  is formed only data channel  8307 . 
       FIG. 85  shows a structure of a control symbol of control channel  8510  when the base station transmits a signal of spread-spectrum communication method by OFDM method. Control channel  8510  includes control symbols  8501  through  8504  along a time axis. 
       FIG. 86  shows a structure of a control symbol of control channel  8610  when the base station transmits a signal of spread-spectrum communication method by OFDM method. Control channel  8610  includes control symbols  8601  through  8604  along a frequency axis. 
     Next, the following method, by which modulation signals of a plurality of spread-spectrum communication methods can be transmitted, is described with reference to  FIGS. 4 ,  72 ,  75 ,  76 ,  79 ,  80 ,  81 , and  82 : 
     a communication method where a modulation signal of a transmission method, which transmits a control channel, is transmitted to a receiver, who receives the modulation signal, estimates radio-wave propagation environment of respective antennas from reception signals of the control channel, and transmits the estimated information of the radio-wave propagation environment, then the communication method selects one of the following transmission methods based on the estimated information: 
     a method of transmitting the modulation signals of a plurality of data channels of the plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas, or 
     a method of transmitting the modulation signal of one data channel of one spread-spectrum communication method from one antenna. A radio communication apparatus using the foregoing communication method is also described hereinafter. 
       FIG. 80  shows a structure of the transmission apparatus at the base station. Frame structure signal generator  209  receives transmission method determining information  8005 , and based on information  8005 , outputs the following frame structure information about one of the following two transmission methods as frame structure signal  210 : 
     a method, where, e.g. information symbol  7901  of method A and information symbol  7907  of method B shown in  FIG. 79  are multiplexed together; or 
     a method, where, information symbol  7902  of method A is transmitted; however, method B has guard symbol  7908 , so that they are not multiplexed. 
     Transmission method determining information  8005  corresponds to reception apparatus  7511  shown in  FIG. 75  at the base station. 
     Data-channel modulation and spread unit  8002  receives transmission digital signal  8001 , frame structure signal  210 , then outputs transmission quadrature baseband signal  8003  of method A. 
     Data-channel modulation and spread unit  8009  receives transmission digital signal  8008 , frame structure signal  210 , then in response to frame structure signal  210 , outputs base-band signal  8010  of method B of the guard symbol or the information symbol as shown in  FIG. 79 . At this time, the modulation signal of the guard symbol is indicated by signal point  403  shown in  FIG. 4 . 
     Control channel modulation and spread unit  8006  receives transmission method determining information  8005 , then outputs transmission quadrature baseband signal  8007  containing the control information for the control channel which includes, as shown in  FIG. 81 , multiplex information  8101 , pilot symbol  8102 , and transmission power control information  8103 . 
     In a similar way to what is discussed above, control channel modulation and spread unit  8012  receives transmission method determining information  8005 , then outputs transmission quadrature baseband signal  8013  containing the control information for the control channel which includes, as shown in  FIG. 81 , multiplex information  8101 , pilot symbol  8102 , and transmission power control information  8103 . 
     Multiplex information  8101  shown in  FIG. 81  works as a symbol for notifying one of the following transmission methods to the terminal: 
     a method of multiplexing method A and method B together; or 
     a transmission method of transmitting method A only. 
       FIG. 75  shows a structure of the reception apparatus of the base station. Signal isolator  7507  isolates data symbol  7205  from the following elements corresponding to the radio-wave propagation environment information: 
     received signal strength intensity information symbol  7201 ; 
     transmission path variation information symbol  7202 ; 
     multi-path information symbol  7203 ; and 
     disturbance information symbol  7204 . 
     Isolator  7507  then outputs the information of data symbol  7205  as reception data  7509 . Isolator  7507  also outputs the information of foregoing symbols  7201  through  7204  as radio-wave propagation environment estimation information  7508 . 
     Transmission method determining unit  7510  receives radio-wave propagation environmental information, and based on this information, selects one of the following transmission methods: 
     a method of transmitting modulation signals of data channels of a plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas; or 
     a method of transmitting a modulation signal of a data channel of one spread-spectrum communication method to the same frequency band from one antenna. 
     Determining unit  7510  then outputs the information about the transmission method as transmission method determining information  7511  and multiplex information  7512 . 
       FIG. 76  shows the structure of the transmission apparatus at the terminal. The apparatus receives transmission digital signal  7601 , radio-wave propagation environment estimation signals  7602 ,  7603 , and frame structure signal  7604 . According to the frame structure shown in  FIG. 72 , signal  7601  is treated as data symbol  7205 , signals  7602 ,  7603  are treated as received signal strength intensity information symbol  7201 , transmission path variation information symbol  7202 , multi-path information symbol  7203 , and disturbance information symbol  7204 . Then the transmission apparatus outputs modulation signal  7606 . Radio-wave propagation estimation signals  7602 ,  7603  correspond to radio-wave propagation environment estimation signals  7718 ,  7743  of the reception apparatus shown in  FIG. 82  at the terminal. 
       FIG. 82  shows a structure of the reception apparatus at the terminal. Received signal strength intensity estimation unit  8201  of method A receives reception quadrature baseband signal  7704 , and estimates a received signal strength intensity from, e.g. a component of the control channel shown in  FIG. 79  of method A of reception quadrature baseband signal  7704 . Estimation unit  8201  then outputs received signal strength intensity estimation signal  8202  of method A. 
     Received signal strength intensity estimation unit  8203  of method B receives reception quadrature baseband signal  7704 , and estimates a received signal strength intensity from, e.g. a component of the control channel shown in  FIG. 79  of method B of reception quadrature baseband signal  7704 . Estimation unit  8203  then outputs received signal strength intensity estimation signal  8204  of method B. 
     Transmission path variation estimation unit  8205  of method A receives reception quadrature baseband signal  7704 , and estimates a transmission path variation from, e.g. a component of the control channel shown in  FIG. 79  of method A, then outputs transmission path variation estimation signal  8206  of method A. 
     Transmission path variation estimation unit  8207  of method B receives reception quadrature baseband signal  7704 , and estimates a transmission path variation from, e.g. a component of the control channel shown in  FIG. 79  of method B, then outputs transmission path variation estimation signal  8208  of method B. 
     Information generator  7717  receives the following signals: 
     multi-path estimation signal  7706 ; 
     disturbance intensity estimation signal  7708 ; 
     received signal strength intensity estimation signal  8202  of method A signals; 
     received signal strength intensity estimation signal  8204  of method B signals; 
     transmission path variation estimation signal  8206  of method A; and 
     transmission path variation estimation signal  8208  of method B, then generator  7717  outputs radio wave propagation environment estimation signal  7718  corresponding to the information of received signal strength intensity information symbol  7201 , transmission path variation information symbol  7202 , multi-path information symbol  7203 , and disturbance information symbol  7204  shown in  FIG. 72 . 
     Received signal strength intensity estimation unit  8209  of method A receives reception quadrature baseband signal  7729 , and estimates a received signal strength intensity from, e.g. a component of the control channel shown in  FIG. 79  of method A of reception quadrature baseband signal  7729 . Estimation unit  8209  then outputs received signal strength intensity estimation signal  8210  of method A. 
     Received signal strength intensity estimation unit  8211  of method B receives reception quadrature baseband signal  7729 , and estimates a received signal strength intensity from, e.g. a component of the control channel shown in  FIG. 79  of method B of reception quadrature baseband signal  7729 . Estimation unit  8211  then outputs received signal strength intensity estimation signal  8212  of method B. 
     Received signal strength intensity estimation unit  8213  of method A receives reception quadrature baseband signal  7729 , and estimates a received signal strength intensity from, e.g. a component of the control channel shown in  FIG. 79  of method A of reception quadrature baseband signal  7729 . Estimation unit  8213  then outputs received signal strength intensity estimation signal  8214  of method A. 
     Received signal strength intensity estimation unit  8215  of method B receives reception quadrature baseband signal  7729 , and estimates a received signal strength intensity from, e.g. a component of the control channel shown in  FIG. 79  of method B of reception quadrature baseband signal  7729 . Estimation unit  8215  then outputs received signal strength intensity estimation signal  8216  of method B. 
     Information generator  7742  receives the following signals: 
     multi-path estimation signal  7731 ; 
     disturbance intensity estimation signal  7733 ; 
     received signal strength intensity estimation signal  8210  of method A signals; 
     received signal strength intensity estimation signal  8212  of method B signals; 
     transmission path variation estimation signal  8214  of method A; and 
     transmission path variation estimation signal  8216  of method B, then generator  7742  outputs radio wave propagation environment estimation signal  7743  corresponding to the information of received signal strength intensity information symbol  7201 , transmission path variation information symbol  7202 , multi-path information symbol  7203 , and disturbance information symbol  7204  shown in  FIG. 72 . 
     The foregoing discussion proves that a switch between the following two transmission methods improves the information quality: 
     a method of transmitting modulation signals of data channels of a plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas; and 
     a method of transmitting a modulation signal of a data channel of one spread-spectrum communication method to the same frequency band from one antenna. 
     Radio-wave propagation environment estimation signals  7718 ,  7743  correspond to signals  7602 ,  7603  of the transmission apparatus shown in  FIG. 76  at the terminal. 
     Next, an operation at the start of a communication is described hereinafter. At the start of the communication, if the base station transmits modulation signals of data channels of a plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas, the terminal does not suit to this transmission method because of, e.g. a bad radio-wave propagation environment. In this case, the quality of reception data is lowered. 
     The transmission signal from the base station is then prepared such that neither information symbols of method A nor information symbols of method B shown in  FIG. 79  exist. For instance, no plural data channels exist at the same frequency band, such as the time of control symbol  7903  of method A and control symbol  7909  of method B, and the time of control symbol  7904  of method A and control symbol  7913  of method B as shown in  FIG. 79 . 
     Frame structure signal generator  209  shown in  FIG. 80  prepares a frame structure at the start of a communication with the terminal such that no plural data channels exist at the same frequency band, such as the time of control symbol  7903  of method A and control symbol  7909  of method B, and the time of control symbol  7904  of method A and control symbol  7913  of method B as shown in  FIG. 79 . Generator  209  then outputs this frame structure as frame structure signal  210 . 
     The reception apparatus shown in  FIG. 82  at the terminal estimates a radio-wave propagation environment from the following signals, then outputs radio-wave propagation estimation signals  7718 ,  7743 : 
     control symbol  7903  of method A and control symbol  7909  of method B of the transmission signal from the base station shown in  FIG. 80 ; and 
     control symbol  7904  of method A and control symbol  7913  of method B of the transmission signal from the base station shown in  FIG. 80 . 
     Transmission apparatus shown in  FIG. 76  at the terminal estimates a radio-wave propagation environment from the following signals, then outputs radio-wave propagation estimation signals  7718 ,  7743  with information symbols  7913 ,  7914  shown in  FIG. 79 : 
     control symbol  7903  of method A and control symbol  7909  of method B of the transmission signal from the base station; and 
     control symbol  7904  of method A and control symbol  7913  of method B of the transmission signal from the base station. 
     The reception apparatus shown in  FIG. 75  at the base station determines one of the following transmission methods based on the radio-wave propagation environment estimation information included in information symbol  7913 , an element of the transmission signal from the transmission apparatus shown in  FIG. 76  at the terminal: 
     a method of transmitting modulation signals of data channels of a plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas; or 
     a method of transmitting a modulation signal of a data channel of one spread-spectrum communication method to the same frequency band from one antenna. 
     Then in the case of a fine environment for radio-wave propagation, modulation signals of data channels of a plurality of spread-spectrum communication methods are transmitted to the same frequency band from a plurality of antennas such as information symbols  7901 ,  7907 . 
     The foregoing discussion proves that the preparation of no data channels of plural spread-spectrum communication methods existing at the same frequency band at the start of a communication with the terminal can improve the quality of information. 
     In the foregoing description, a modulation signal indicating that the terminal requires a communication with the base station can be transmitted at the beginning Next, the following method, by which modulation signals of a plurality of spread-spectrum communication methods can be transmitted, is described with reference to  FIGS. 4 ,  73 ,  75 ,  78 ,  79 ,  80 ,  81 , and  82 : 
     a communication method where a modulation signal of the transmission method, which transmits a control channel, is transmitted to a receiver, who receives the modulation signal then estimates radio-wave propagation environment of respective antennas from reception signals of the control channel, then the communication method sends the information which requires one of the following transmission methods based on the estimated information of the radio-wave propagation environment: 
     a method of transmitting the modulation signals of a plurality of data channels of the plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas, or 
     a method of transmitting the modulation signal of a data channel of one spread-spectrum communication method from one antenna; 
     then the communication method selects, based on the requiring information, one of the foregoing two transmission methods, and 
     a radio communication apparatus using the foregoing communication method is also described. 
       FIG. 80  shows the structure of the transmission apparatus at the base station. Frame structure signal generator  209  receives transmission method determining information  8005 , and based on information  8005 , outputs the following frame structure information about one of the following two transmission methods as frame structure signal  210 : 
     a transmission method, where, e.g. information symbol  7901  of method A and information symbol  7907  of method B shown in  FIG. 79  are multiplexed together; or 
     a transmission method, where, information symbol  7902  of method A is transmitted; however, method B has guard symbol  7908 , so that they are not multiplexed. 
     Transmission method determining information  8005  corresponds to reception apparatus  7511  shown in  FIG. 75  at the base station. 
     Data-channel modulation and spread unit  8002  receives transmission digital signal  8001 , frame structure signal  210 , then outputs transmission quadrature baseband signal  8003  of method A. 
     Data-channel modulation and spread unit  8009  receives transmission digital signal  8008 , frame structure signal  210 , then in response to frame structure signal  210 , outputs base-band signal  8010  of method B of the guard symbol or the information symbol as shown in  FIG. 79 . At this time, the modulation signal of the guard symbol corresponds to signal point  403  shown in  FIG. 4 . 
     Control channel modulation and spread unit  8006  receives transmission method determining information  8005 , then outputs transmission quadrature baseband signal  8007  containing the control information for the control channel which includes, as shown in  FIG. 81 , multiplex information  8101 , pilot symbol  8102 , and transmission power control information  8103 . 
     In a similar way to what is discussed above, control channel modulation and spread unit  8012  receives transmission method determining information  8005 , then outputs transmission quadrature baseband signal  8013  containing the control information for the control channel which includes, as shown in  FIG. 81 , multiplex information  8101 , pilot symbol  8102 , and transmission power control information  8103 . 
     Multiplex information  8101  shown in  FIG. 81  works as a symbol for notifying one of the following transmission methods to the terminal: 
     a method of multiplexing method A and method B together; or 
     a method of transmitting method A only. 
       FIG. 75  shows a structure of the reception apparatus of the base station. Signal isolator  7507  isolates data symbol  7302  from transmission method requiring information symbol  7301 , then isolator  7507  outputs the information of data symbol  7302  as reception data  7509 , and outputs also the information of transmission method requiring symbol  7301  as transmission request information  7508 . 
     Transmission method determining unit  7510  receives transmission request information  7508 , and based on this information, selects one of the following transmission methods: 
     a method of transmitting modulation signals of data channels of a plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas; or 
     a method of transmitting a modulation signal of a data channel of one spread-spectrum communication method to the same frequency band from one antenna. 
     Determining unit  7510  then outputs the information about the transmission method as transmission method determining information  7511  and multiplex information  7512 . 
       FIG. 78  shows the structure of the transmission apparatus at the terminal. Transmission method requiring information generator  7801  receives radio-wave propagation environment estimation signals  7602 ,  7603 , then outputs transmission method requiring information  7802 . Modulation signal generator  7606  receives transmission digital signal  7601 , transmission request information  7802 , and frame structure signal  7605 , and outputs modulation signal  7607  according to the frame structure shown in  FIG. 73 . Radio-wave propagation environment estimation signals  7602 ,  7603  correspond to estimation signals  7718 ,  7743  of the reception apparatus shown in  FIG. 82  at the terminal. 
       FIG. 82  shows the structure of the reception apparatus at the terminal. Received signal strength intensity estimation unit  8201  of spread-spectrum communication method A receives reception quadrature baseband signal  7704 , and estimates a received signal strength intensity from, e.g. a component of the control channel shown in  FIG. 79  of method A of reception quadrature baseband signal  7704 . Estimation unit  8201  then outputs received signal strength intensity estimation signal  8202  of method A. 
     Received signal strength intensity estimation unit  8203  of spread-spectrum communication method B receives reception quadrature baseband signal  7704 , and estimates a received signal strength intensity from, e.g. a component of the control channel shown in  FIG. 79  of method B of reception quadrature baseband signal  7704 . Estimation unit  8203  then outputs received signal strength intensity estimation signal  8204  of method B. 
     Transmission path variation estimation unit  8205  of method A receives reception quadrature baseband signal  7704 , and estimates a transmission path variation from, e.g. a component of the control channel of method A shown in  FIG. 79 , then outputs transmission path variation estimation signal  8206  of method A. 
     Transmission path variation estimation unit  8207  of method B receives reception quadrature baseband signal  7704 , and estimates a transmission path variation from, e.g. a component of the control channel of method B shown in  FIG. 79 , then outputs transmission path variation estimation signal  8208  of method B. 
     Information generator  7717  receives the following signals: 
     multi-path estimation signal  7706 ; 
     disturbance intensity estimation signal  7708 ; 
     received signal strength intensity estimation signal  8202  of method A signals; 
     received signal strength intensity estimation signal  8204  of method B signals; 
     transmission path variation estimation signal  8206  of method A; and 
     transmission path variation estimation signal  8208  of method B, then generator  7717  outputs radio wave propagation environment estimation signal  7718  corresponding to the information of received signal strength intensity information symbol  7201 , transmission path variation information symbol  7202 , multi-path information symbol  7203 , and disturbance information symbol  7204  shown in  FIG. 72 . 
     Received signal strength intensity estimation unit  8209  of method A receives reception quadrature baseband signal  7729 , and estimates a received signal strength intensity from, e.g. a component of the control channel shown in  FIG. 79  of method A of reception quadrature baseband signal  7729 . Estimation unit  8209  then outputs received signal strength intensity estimation signal  8210  of method A. 
     Received signal strength intensity estimation unit  8211  of method B receives reception quadrature baseband signal  7729 , and estimates a received signal strength intensity from, e.g. a component of the control channel shown in  FIG. 79  of method B of reception quadrature baseband signal  7729 . Estimation unit  8211  then outputs received signal strength intensity estimation signal  8212  of method B. 
     Received signal strength intensity estimation unit  8213  of method A receives reception quadrature baseband signal  7729 , and estimates a received signal strength intensity from, e.g. a component of the control channel shown in  FIG. 79  of method A of reception quadrature baseband signal  7729 . Estimation unit  8213  then outputs received signal strength intensity estimation signal  8214  of method A. 
     Received signal strength intensity estimation unit  8215  of method B receives reception quadrature baseband signal  7729 , and estimates a received signal strength intensity from, e.g. a component of the control channel shown in  FIG. 79  of method B of reception quadrature baseband signal  7729 . Estimation unit  8215  then outputs received signal strength intensity estimation signal  8216  of method B. 
     Information generator  7742  receives the following signals: 
     multi-path estimation signal  7731 ; 
     disturbance intensity estimation signal  7733 ; 
     received signal strength intensity estimation signal  8210  of method A signals; 
     received signal strength intensity estimation signal  8212  of method B signals; 
     transmission path variation estimation signal  8214  of method A; and 
     transmission path variation estimation signal  8216  of method B, then generator  7742  outputs radio wave propagation environment estimation signal  7743  corresponding to the information of received signal strength intensity information symbol  7201 , transmission path variation information symbol  7202 , multi-path information symbol  7203 , and disturbance information symbol  7204  shown in  FIG. 72 . 
     The foregoing discussion proves that a switch between the following two transmission methods improves the information quality: 
     a method of transmitting modulation signals of data channels of a plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas; and 
     a method of transmitting a modulation signal of a data channel of one spread-spectrum communication method to the same frequency band from one antenna. 
     Radio-wave propagation environment estimation signals  7718 ,  7743  correspond to signals  7602 ,  7603  of the transmission apparatus shown in  FIG. 76  at the terminal. 
     Next, an operation at the start of a communication is described hereinafter. At the start of the communication, if the base station transmits modulation signals of data channels of a plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas, the terminal does not suit to this transmission method because of, e.g. a bad radio-wave propagation environment. In this case, the quality of reception data is lowered. 
     The transmission signal from the base station is then prepared such that neither information symbols of method A nor information symbols of method B shown in  FIG. 79  exist. For instance, no plural data channels exist at the same frequency band, such as the time of control symbol  7903  of method A and control symbol  7909  of method B, and the time of control symbol  7904  of method A and control symbol  7913  of method B as shown in  FIG. 79 . 
     Frame structure signal generator  209  shown in  FIG. 80  prepares a frame structure at the start of a communication with the terminal such that no plural data channels exist at the same frequency band, such as the time of control symbol  7903  of method A and control symbol  7909  of method B, and the time of control symbol  7904  of method A and control symbol  7913  of method B as shown in  FIG. 79 . Generator  209  then outputs this frame structure as frame structure signal  210 . 
     The reception apparatus shown in  FIG. 82  at the terminal estimates a radio-wave propagation environment from the following signals, then outputs radio-wave propagation estimation signals  7718 ,  7743 : 
     control symbol  7903  of method A and control symbol  7909  of method B of the transmission signal from the base station shown in  FIG. 80 ; and 
     control symbol  7904  of method A and control symbol  7913  of method B of the transmission signal from the base station shown in  FIG. 80 . 
     Transmission method requiring information generator  7801  of the transmission apparatus shown in  FIG. 78 , based on radio-wave propagation environment estimation signals  7718  and  7743  discussed above, transmits information which requires one of the following transmission methods as the transmission request information with information symbols  7913 ,  7914  shown in  FIG. 79 : 
     a method of transmitting modulation signals of data channels of a plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas; or 
     a method of transmitting a modulation signal of a data channel of one spread-spectrum communication method to the same frequency band from one antenna. 
     The reception apparatus shown in  FIG. 75  at the base station determines one of the following transmission methods based on the radio-wave propagation environment estimation information included in information symbol  7913 , which is an element of the transmission signal from the transmission apparatus shown in  FIG. 76  at the terminal: 
     a method of transmitting modulation signals of data channels of a plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas; or 
     a method of transmitting a modulation signal of a data channel of one spread-spectrum communication method to the same frequency band from one antenna. 
     Then the modulation signals of the transmission method determined are transmitted from the antenna. 
     The foregoing discussion proves that the preparation of no data channels of plural spread-spectrum communication methods existing at the same frequency band at the start of a communication with the terminal can improve the quality of information. 
     In the foregoing description, a modulation signal indicating that the terminal requires a communication with the base station can be transmitted at the beginning. 
     In the foregoing description, as shown in  FIG. 79 , the control channel exists in both of spread-spectrum communication methods A and B; however, e.g. this embodiment is applicable to the case where the control channel exits only in method A, as shown in  FIG. 83 . In this case, the transmission apparatus in  FIG. 80  does not have control channel modulation and spread unit  8012  of method B. 
     This embodiment refers to the case where the number of spread-spectrum communication methods to be multiplexed are switched between two channels and one channel; however, this example does not limit the embodiment. For instance, in the case where three methods can be multiplexed to the same frequency band, the transmission apparatus at the base station switches the number of multiplexing between 1-3 methods. 
     This embodiment is also applicable to the case where signals of a spread-spectrum communication method is modulated by OFDM method. A structure of a control symbol of a spread-spectrum communication method transmitted from the base station in this case is shown in  FIGS. 85 and 86 . In  FIG. 85 , the control symbols are spread on the time axis, while they are spread on the frequency axis in  FIG. 86 . Information symbols are also spread either on a time axis or a frequency axis as shown in  FIGS. 85 and 86 , so that they are multiplexed to signals of the control channels. The transmission apparatus and the reception apparatus both at the base station and the terminal can be formed of elements described in  FIGS. 75 ,  76 ,  78 ,  80  and  82  which are referred to the frame structure shown in  FIG. 70 . 
     In this embodiment, one data channel per method A or method B is used for the description purpose; however, the number of data channels is not limited to one, and plural data channels are applicable to this embodiment. Codes to be used for spread or inverse-spread of spread-spectrum communication methods A and B can be identical to each other or different from each other. 
     The expression of “antenna” in the previous description does not always mean a single antenna, but “antenna” can mean an antenna unit which is formed of a plurality of antennas. 
     The previous discussion refers to the following method, by which modulation signals of a plurality of spread-spectrum communication methods can be transmitted: 
     the communication method where a modulation signal of a transmission method, which transmits a control channel, is transmitted to a receiver, who receives the modulation signal then estimates radio-wave propagation environment of respective antennas from reception signals of the control channel, and transmits the estimated information of the radio-wave propagation environment, then the communication method selects one of the following transmission methods based on the estimated information: 
     a method of transmitting the modulation signals of a plurality of data channels of the plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas, or 
     a method of transmitting the modulation signal of one data channel of one spread-spectrum communication method from one antenna. The previous discussion also refers to the radio communication apparatus using the foregoing communication method. 
     The discussion above also describes the method below, by which modulation signals of a plurality of spread-spectrum communication methods can be transmitted: 
     the communication method where a modulation signal of the transmission method, which transmits a control channel, is transmitted to a receiver, who receives the modulation signal then estimates radio-wave propagation environment of respective antennas from reception signals of the control channel, then the communication method sends the information which requires one of the transmission methods below based on the information of the estimated radio-wave propagation environment: 
     a method of transmitting the modulation signals of a plurality of data channels of the plurality of spread-spectrum communication methods to the same frequency band from a plurality of antennas, or 
     a method of transmitting the modulation signal of a data channel of one spread-spectrum communication method from one antenna; 
     then the communication method selects, based on the requiring information, one of the foregoing two transmission methods. 
     The discussion above also refers to the radio communication apparatus using the communication method. In conclusion, the methods and the apparatuses discussed above allow transmitting information more accurately. 
     INDUSTRIAL APPLICABILITY 
     The present invention is useful for a transmission and reception method by which modulation signals of a plurality of channels are multiplexed to the same frequency band. The present invention allows estimating channels accurately and with ease for demultiplexing multiplexed modulation signals received by a reception apparatus.