Abstract:
A communication apparatus based on the multi-carrier modulation system may be included in a mobile station or a base station for simultaneous transmission and reception with a simplified structure between the mobile station and base station using in common the same frequency band. A communication apparatus based on a multi-carrier modulation system for simultaneous communications with a plurality of sub-carriers using a plurality of sub-carriers modulated with data respectively, comprising a transmitting unit operable to transmit data with a plurality of sub-carriers by modulating a sub-carrier among the plurality of sub-carriers with data, and operable to use the other sub-carriers a receiving band without modulation with the data.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a communication apparatus based on multi-carrier modulation system for two-way communication using a plurality of sub-carriers and more specifically to a communication apparatus based on a multi-carrier modulation system for enabling simultaneous transmission and reception by avoiding interference from the other communication apparatuses, for example, base stations or mobile stations or preventing diffusion of the transmitting signal of a station to the receiving side of that station. 
         [0003]    2. Background of the Prior Art 
         [0004]    Conventional mobile communications where various kinds of mobile communications with mobile stations, such as portable phones or the like, have been put into practical use in recent years have basically used the same communication system as that used for communications with fixed stations. 
         [0005]    For example,  FIG. 1  illustrates an application example where there is no problem in the frequency domain and the time domain for transmission and reception between a plurality of mobile stations and a fixed station.  FIG. 1(   a ) illustrates the example where a mobile station is capable of realizing data communication with the other mobile stations and fixed stations with single transmissions using all frequency bands. Frequency is plotted on the horizontal axis f, while power of each sub-carrier is on the vertical axis Pow.  FIG. 1(   b ) illustrates an example for shifting the transmission timings in order to eliminate overlap thereof within the time domain in each mobile station or fixed station. The horizontal axis t indicates the time and the vertical axis Pow, the power of each sub-carrier. 
         [0006]    In summary,  FIG. 1(   b ) illustrates the case where if data is transmitted simultaneously from a plurality of mobile stations and a fixed station, data reception is disabled because the transmitting data are mixed with each other and therefore a certain mobile station transmits the data in the timing A as the transmission timing and the other mobile station or fixed station shifts the transmission timing to transmit the data in the other timing B by detecting that a certain mobile station transmits the data in the transmission timing A. 
         [0007]      FIG. 2  illustrates an application example where there is a problem in the time domain for transmission and reception between a plurality of mobile stations and a fixed station using the frequency domain explained in regard to  FIG. 1 . Description of  FIG. 2(   a ) is omitted because the application example of the other mobile station is same as that of  FIG. 1(   a ).  FIG. 2(   b ) illustrates an example where the other mobile station or fixed station cannot sense the carrier of transmission in the transmission timing A from a certain mobile station and transmits data in the transmission timing B the same as the transmission timing A and thereby the transmission timing B is matched with the timing A. Accordingly, a certain mobile station cannot receive the important data from the other mobile station or fixed station. 
         [0008]    Moreover, JP-A 2001-285236 proposes a transmitting circuit for multi-carrier modulation system for eliminating interference by transmission from the other mobile station or fixed station like that in  FIG. 2  explained above. 
         [0009]    The transmitting circuit described in JP-A 2001-285236 will be explained with regard to  FIG. 3 . 
         [0010]    In  FIG. 3 , an input signal s 101  is input to a 16 QAM modulating circuit  101  and thereby the modulated signal s 102  is obtained. The modulated signal s 102  is then input to a serial-to-parallel converting circuit  102  and thereby a sub-carrier modulated signal s 103  is output. A null signal generating circuit  103  outputs the null signal s 104  having the value 0 for both Ich and Qch. The sub-carrier modulated signal s 103  divided for each sub-carrier and the null signal s 104  are input to an IFFT circuit  104  and thereby the OFDM signal s 105  can be output through the OFDM modulation. Here, the null signal is input to the IFFT point corresponding to both end edges of the transmission frequency band and to the point corresponding to the frequency band of the other system provided for common use in view of eliminating returning of the transmitting spectrum in the circuit stages higher than the IF stage. 
         [0011]    As explained above, the IFFT circuit  104  corresponds to a multi-carrier modulating means. The OFDM signal s 105  is input to the parallel-to-serial converting circuit  105 . Here, the control signal s 106 , which is an output signal of a guard interval addition control circuit  130  provided to control the read sequence of the parallel-to-serial converting circuit  105  is also input to control the read sequence of the parallel-to-serial converting circuit  105 . Accordingly, the guard interval read out by repeating a part of the output signal of the IFFT circuit  104  is added to the OFDM signal to generate the OFDM symbol and thereby it is output as the transmitting signal s 107 . 
         [0012]    However, JP-A 2001-285236, explained above only nulls the particular sub-carriers but does not consider reception of the desired signal simultaneously with transmission of signals. Therefore, JP-A 2001-285236 explained above still includes a problem that the receiving signal to be received with the sub-carrier, where the side-lobe element of its own sub-carrier to be transmitted is nulled, is suppressed. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention has been proposed in view of solving the problem explained above and therefore it is an object of the present invention to provide a communication apparatus based on the multi-carrier modulation system to be mounted into a mobile station or a base station for simultaneously transmitting and receiving signals with a simplified structure with mobile stations and base stations using in common the same frequency band. 
         [0014]    According to a first embodiment of the present invention, in order to achieve the object explained above, a communication apparatus based on the multi-carrier modulation system for simultaneous communications with a plurality of sub-carriers attained by modulating respective sub-carriers with data is used, wherein a transmitting unit is further included to transmit data with a plurality of sub-carriers by modulating a part of sub-carriers among a plurality of sub-carriers with data and then using the other sub-carriers as the receiving band without modulation with data. 
         [0015]    According to a second embodiment of the present invention, a communication apparatus based on the multi-carrier modulation system for simultaneous communications with a communication apparatus of a distant party with a plurality of sub-carriers where respective sub-carriers are modulated with data, wherein a transmitting unit is included to modulate a plurality of said sub-carriers with data and then transmit the modulated sub-carriers when the communication apparatus is located in the area far from the communication apparatus of the distance party and to set the data from the communication apparatus of the distant party to the receiving band and to transmits the data with a plurality of sub-carriers by modulating a part of a plurality of sub-carriers with the data and without modulation of the other sub-carriers with the data when the mobile communication apparatus is located in the area near the communication apparatus of the distant party. 
         [0016]    According to a third embodiment of the present invention, a communication apparatus based on the multi-carrier modulation system further provided with an adding unit to transmit additional guard band in addition to a plurality of sub-carriers and a removing unit for removing the guard band added to the receiving signal is used as the transmitting unit. 
         [0017]    According to a fourth embodiment of the present invention, a communication apparatus based on the multi-carrier modulation system further provided with an active filter for dynamically changing the pass-band to pass only a plurality of sub-carriers to transmit the data is used as the transmitting unit. 
         [0018]    According to a fifth embodiment of the present invention, a communication apparatus based on the multi-carrier modulation system for null-modulation of the sub-carriers other than the sub-carriers modulated with the data is used. 
         [0019]    According to a sixth embodiment of the present invention, a communication apparatus based on the multi-carrier modulation system for selecting and setting a part of the sub-carriers and the other sub-carriers among a plurality of sub-carriers on the basis of the received control information is used. 
         [0020]    According to a seventh embodiment of the present invention, a communication apparatus based on the multi-carrier modulation system is used, wherein an inserting unit for inserting the null signal having the value 0 for both real numbers and imaginary numbers, a serial-to-parallel converting means for converting serial-to-parallel conversion to the transmitting data including the null signal and then outputting the parallel transmitting data, a sub-carrier modulating means for performing sub-carrier modulation to respective parallel transmitting data, a multi-carrier modulating means for performing multi-carrier modulation to the sub-carrier modulated signal input from a plurality of sub-carrier modulating means and then outputting the multi-carrier modulated signal and an adding means for adding the guard interval to the multi-carrier modulated signal are included and the inserting unit determines the number of null signals to be inserted and inserting position on the basis of the control information for assignment of frequencies from an external side and then inserts the null signal to the transmitting data. 
         [0021]    According to an eighth embodiment of the present invention, a communication apparatus based on the multi-carrier modulation system is used, wherein comprising an inserting unit for inserting the null signal having the value 0 for both real numbers and imaginary numbers into the transmitting data, a serial-to-parallel converting means for performing serial-to-parallel conversion to the transmitting data including the null signal and then outputting the parallel transmitting data, a sub-carrier modulating means for performing the sub-carrier modulation to respective parallel transmitting data, a multi-carrier modulating means for performing the multi-carrier modulation to the sub-carrier modulated signal input from a plurality of sub-carrier modulating means and then outputting the multi-carrier modulated signal, an adding means for adding the guard interval to the multi-carrier modulated signal, and a size changing means for changing the processing size to be used for modulation of the multi-carrier modulating means on the basis of the control information in regard to assignment of frequency from the external side. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is an application example in the case where there is no problem in the frequency domain and time domain in transmission and reception between a plurality of mobile stations and a fixed station. 
           [0023]      FIG. 2  is an application example in the case where there is a problem in the frequency domain and time domain in transmission and reception between a plurality of mobile stations and a fixed station. 
           [0024]      FIG. 3  is an exemplary block diagram showing a structure of the existing transmitting circuit for multi-carrier modulation system. 
           [0025]      FIG. 4  is an exemplary diagram showing the principle of the communication system of the present invention. 
           [0026]      FIG. 5  is a structure example of the communication apparatus based on the multi-carrier modulation system illustrating a first embodiment of the present invention. 
           [0027]      FIG. 6  is an exemplary diagram showing an example of receiving a command. 
           [0028]      FIG. 7  is an exemplary diagram showing a detail structure example of the BB decoding and null control unit. 
           [0029]      FIG. 8  is an exemplary diagram showing a detail structure example of the active filter and band control unit. 
           [0030]      FIG. 9  is an exemplary diagram showing a structure example of the communication apparatus based on the multi-carrier modulation system illustrating a second embodiment of the present invention. 
           [0031]      FIG. 10  is an exemplary diagram showing a detail structure example of the IFFT/FFT size control unit of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    The communication apparatus of the present invention is capable of obtaining, with introduction of the structure explained above, excellent receiving characteristics in its own station and in other stations without any suppression of the desired receiving signal to its own station or to the other stations with the side-lobe element of the sub-carriers due to the transmission by simultaneously performing transmission and reception in the multi-carrier modulation system. 
         [0033]    The preferred embodiments of the present invention will be explained with reference to the accompanying drawings. However, the preferred embodiment do not restrict the technical scope of the present invention. 
         [0034]    In the preferred embodiments of the present invention, a communication apparatus based on the multi-carrier modulation system will be explained below. 
         [0035]      FIG. 4  illustrates the principle of the communication system of the present invention. 
         [0036]    Letter C in  FIG. 4(   a ) indicates the frequency band used for transmission in the frequency domain of the communication apparatus based on the multi-carrier modulation system of the present invention. Letter D in  FIG. 4(   a ) indicates the receiving frequency band. Letter A in  FIG. 4(   b ) indicates the transmission timing in the time domain of the communication apparatus based on the multi-carrier modulation system of the present invention. Letter B in  FIG. 4(   b ) indicates the transmission timing from the other mobile station or base station. This communication apparatus is characterized in that diffusion of the transmitting signal to the receiving unit by the apparatus itself can be prevented and transmission can be realized without consideration of the transmission timing of the other communication apparatus, because the frequency band is assigned to sub-carriers for transmission and reception. 
         [0037]    Next, a detailed structural example of the communication apparatus based on the multi-carrier modulation system utilizing the communication system of the present invention will be explained below. 
         [0038]      FIG. 5  illustrates a structural example of the communication apparatus based on the multi-carrier modulation system as the first embodiment of the present invention. The communication apparatus is roughly formed of a transmitting unit  1 , a common unit  2 , and a receiving unit  3 . The transmitting unit  1  includes a BB coding unit  11 , a serial-to-parallel S/P converting unit  12 , a modulating unit (MOD)  13 , an IFFT  14 , a guard interval adding unit  15  (+G 1 ), an active filter  16 , a frequency converting circuit  17 , a local oscillator  18  and a band-pass filter (BPF)  19 . 
         [0039]    The common unit  2  includes a null control unit  21 , a band control unit  22 , a circulator  23 , and an antenna  24 . 
         [0040]    The receiving unit  3  includes, in the sequence of transfer of the receiving signal, a band-pass filter  39 , a local oscillator  38 , a frequency converting circuit  37 , an active filter  36 , a guard interval removing unit (−GI)  35 , an FFT  34 , a demodulating unit  33 , a parallel-to-serial P/S converting unit  32 , and a BB decoding unit  31 . 
         [0041]    Operation of each unit in the communication apparatus explained above will be explained below. 
         [0042]    The BB coding unit  11  inserts a null symbol into the transmitting data in units of symbols with the control signal from the null control unit  21  and outputs the transmitting data including the null symbol to the S/P converting unit  12  as the coded data. This null symbol indicates the null symbol formed of the signal having the value 0 for the real number element and the imaginary number element. The S/P converting unit  12  outputs the coded data to each modulating unit  13  through the parallel conversion. The converting unit  13  performs multi-level modulation on the parallel-converted data of each sub-carrier from the S/P converting unit  12  and outputs the sub-carrier modulated data to the IFFT  14 . The IFFT  14  outputs the OFDM signal OFDM-modulated through inverse Fourier&#39;s transformation of the sub-carrier modulated data. The guard interval adding unit  15  outputs, to the active filter  16 , the OFDM symbol generated with addition of the guard interval attained by repeating a part of the OFDM signal to the OFDM signal. The active filter  16  outputs, to the frequency converting circuit  17 , the OFDM symbol where the side-lobe by the sub-carrier of the OFDM symbol is cut with the control signal from the band control unit  22 . The frequency converting circuit  17  up-converts an output of the active filter  16  with the local oscillating signal of the local oscillator  18 . The band-pass filter  19  outputs an output from the frequency converting circuit  17  to the circulator  23  through filtering to the predetermined frequency band. The antenna  24  transmits an output signal from the circulator  23  as the electromagnetic wave. The band-pass filter  39  outputs the receiving signal obtained via the antenna  24  and circulator  23  to the frequency converting circuit  37  as the receiving signal of the predetermined frequency band. The frequency converting circuit  37  outputs the receiving signal to the active filter  36  through the down-conversion with the local oscillating signal from the local oscillator  38 . The active filter  36  outputs, to the guard interval-removing unit  35 , the OFDM symbol where the side-lobe due to the sub-carrier of the OFDM symbol of the receiving frequency band is cut with the control signal from the band control unit  22 . The guard interval-removing unit  35  provides an output to the FFT  35  by removing the guard interval of the OFDM symbol. The FFT  34  outputs, to the demodulating unit  33 , the sub-carrier modulated symbol frequency-converted through Fourier&#39;s transformation of the OFDM symbol from which the guard interval is removed. The demodulating unit  33  demodulates the sub-carrier modulated symbol attained through multi-level modulation and outputs this sub-carrier modulated symbol to the P/S converting unit  32  as the baseband symbol. The P/S converting unit  32  outputs, to the BB coding unit  31 , the demodulated parallel baseband symbol from a plurality of demodulating units  33  through the serial conversion. The BB coding  31  removes the inserted null symbol with the control signal from the null control unit  21  and outputs the receiving data. 
         [0043]    The null control unit  21  issues a command for designating the part for inserting and removing the null symbol with the band-share control command, while the band control unit  22  issues a command for designating the sub-carrier for transmission and reception with the band-share control command. A receiving example of such a command will be explained with reference to  FIG. 6 . First, the command receiving unit  41  outputs the band-share control signal to an encoder  42  from the receiving signal received via the antenna  40 . The band-share control signal is the source information (macro-command) in the transmitting frequencies fa and fb and in the receiving frequencies fc and fd. The encoder  42  outputs the band-share control signal as the code information of the band-share control command. The band-share control command is the encoding information (concrete command) for designating the sub-carrier numbers # 0  to # 15  for transmission and the sub-carrier numbers # 16  to # 31  for reception. 
         [0044]      FIG. 7  illustrates detailed structural examples of the BB coding, BB decoding and null control units. For example, in  FIG. 7 , the transmitting data is formed of eight symbols, one symbol corresponds to one sub-carrier, and the eight sub-carriers in maximum are provided as the transmitting/receiving frequency band. 
         [0045]    A blank symbol inserting circuit  111  within the BB coding  1  inserts the transmitting data of eight symbols, also inserts the continuous null symbols of four symbols after the symbols of the transmitting data numbers 0 to 3 based on the blank symbol position information from the blank symbol position generating unit  212  within the control unit  21 , and then outputs the coded data. The blank symbol position generating unit  212  generates the control signal to indicate the null symbol inserting position and null symbol removing position with the information obtained by decoding the band-share control command with the decoder  211  and then supplies such control signal to the blank symbol inserting circuit  111  and the blank symbol removing circuit  311 . The blank symbol removing circuit  311  within the BB decoding  31  removes the null symbol between the symbol numbers 0 to 3 and the symbol numbers 4 to 7 of the receiving data and outputs the decoded data. 
         [0046]      FIG. 8  illustrates detailed structural examples of the active filter and band control unit. 
         [0047]    Here, as the input signal to be input to the active filter  16 , the full frequency band of eight sub-carriers is usually used for transmission. Moreover, in the irregular case, for example, when a mobile station enters a certain area to realize transmission and reception using eight sub-carriers, it is assumed that the four sub-carriers are used for transmission and the remaining four sub-carriers are used for reception in order to realize simultaneous transmission and reception. In the usual case, a mobile station is making communication, for example, using the full frequency band with the other mobile station. In the irregular case, it is assumed that a mobile station is coming near to the base station to change the transmission mode to the transmission with a half frequency band of the full frequency band from the transmission with the full frequency band with the other mobile station and simultaneously to always receive the signal from the base station with the remaining half frequency band. 
         [0048]    The input signal to the active filter  16  (transmitting side) is used in four sub-carriers for transmission and the other four sub-carriers indicate the side-lobe or noise by the sub-carriers for transmission. In this input signal, any sub-carrier has different amplitude and the amplitude of the right side four sub-carriers indicating side-lobe or noise is smaller than that of the left side four sub-carriers used for transmission. The right side four sub-carriers indicating this side-lobe or noise is removed with the active filter  16  (transmitting side). 
         [0049]    The active filter  16  (transmitting side) equalizes waveforms of the input signal (here, eight sub-carriers) with a delay line  161 , a plurality of taps  162 , and an adder  163  and outputs the output signal with restriction to the necessary sub-carriers (here, left side four sub-carriers are necessary sub-carriers). The tap  162  is controlled with a plurality of weighting coefficient from a weighting coefficient-generating unit  222  of the band control unit  22 . 
         [0050]    The active filter  36  (receiving side) equalizes waveforms of the input signal (here, eight sub-carriers) when the full frequency band is used with a delay line  362 , a plurality of taps  361 , and an adder  363  and outputs the output signal with restriction to the necessary sub-carriers. In addition, the weighting coefficient-generating unit  222  reads the weighting coefficient values for transmission and reception stored in the table and controls the respective taps  162  and  361  on the basis of the value obtained by decoding the band-share control command with the decoder  221 . 
         [0051]    Another example other than that explained above may also be considered. Namely, the transmission and reception are performed by sharing the time in place of the common transmission and reception in the frequency band explained in above example. 
         [0052]    In this case, control is executed to set the taps  162  and  361  to the same value so that the active filters  16  and  36  do not restrict the frequency band with equalization of waveform. 
         [0053]      FIG. 9  illustrates an example of structure of the communication apparatus based on the multi-carrier modulation system as a second embodiment of the present invention. In this structure example, the like reference numbers are designated to the like structure element. Since the operating processes are similar in these elements, the similar operating processes are eliminated and only different structure elements will be explained. 
         [0054]    In the structure example of the communication apparatus as the second embodiment of the present invention, an IFFT/FFT size control unit  25 , which is not provided in the structure example of the communication apparatus as the first embodiment, is additionally provided. 
         [0055]    This IFFT/FFT size control unit  25  is capable of changing a sample size of the IFFT  14  and FFE  34  by receiving the band-share control command. For example, the 256 sample size is changed to a half sample size of 128 sample size or vice versa. 
         [0056]    A detail structure example of the IFFT/TFF size control unit of the present invention is illustrated in  FIG. 10 . Operations of the detail structure example of  FIG. 10  will be explained below. 
         [0057]    A switching signal-generating unit  252  reads the switching signal for IFFT stored in a table based on the value obtained by decoding the band-share control command with the decoder  251  and then outputs this switching signal to the IFFT  14  via the control line  253 . Simultaneously, the switching signal-generating unit  252  also reads the switching signal for FFT stored in the table on the basis of the value obtained by decoding the band-share control command with the decoder  251  and then outputs this switching signal to the FFT  34  (FFT module) via the control line  254 . In the IFFT  14 , a switch  142  is turned ON/OFF with the switching signal for IFFT and the IFFT module  141  receives the parallel input signal from the switch  142  in the ON state and outputs the OFDM signal. 
         [0058]    The FFT  34  executes the frequency conversion of the received serial signal and outputs the frequency-converted signal only to the switch  342  turned ON with the switching signal for the receiving FFT. 
         [0059]    The communication apparatus based on the multi-carrier modulation system of the present invention has been explained above but the present invention also allows various changes of modifications to the apparatus other than that explained above.