Abstract:
A transmission apparatus includes a frame configuration determiner that determines a modulation system from among a plurality of modulation systems on a communication situation. A first symbol generator modulates a digital transmission signal according to the modulation system determined by the frame configuration determiner and generates a first symbol, the first symbol comprising a first quadrature baseband signal. A second symbol generator modulates the digital transmission signal according to a predetermined modulation system and generates a second symbol, the second symbol comprising a second quadrature baseband signal.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation of U.S. patent application Ser. No. 09/627,070, filed on 27, 2000, the content of which is hereby incorporated herein by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a transmission apparatus, reception apparatus and digital radio communication method, which is used for digital radio communications.  
           [0004]    2. Description of the Related Art  
           [0005]    As a conventional digital modulation system, a technology described in the Unexamined Japanese Patent Publication No. HEI 1-196924 is known. This is the technology which the transmitting side configures a frame by inserting  1  known pilot symbol for every N data symbols and the receiving side estimates a frequency offset and amount of amplitude distortion by using the pilot symbol, and removes these frequency offset and amplitude distortion and demodulates.  
           [0006]    Here, in the case of a radio communication, fluctuations in the transmission path occur due to fading and in terrestrial mobile communication in particular, fluctuations in the transmission path are not uniform. When fluctuations in the transmission path are intense, the interval of inserting a pilot symbol must be shorter to prevent deterioration of the data demodulation error rate. On the contrary, when fluctuations in the transmission path are gentle, extending the interval of inserting a pilot symbol does not deteriorate the data demodulation error rate so much.  
           [0007]    On the other hand, when the level of a reception signal on the receiving side is small, a modulation system used must be highly resistant to errors for information symbols. On the contrary, when the level of a reception signal on the receiving side is large, higher priority can be given to a modulation system of high transmission efficiency for information symbols.  
           [0008]    However, in the conventional digital modulation system above, the pilot symbol insertion interval and the information symbol modulation system are fixed. Therefore, when fluctuations in the transmission path are intense or the level of the reception signal of the receiver is small, error resistance during data demodulation reduces and the quality of data deteriorates. On the other hand, when fluctuations in the transmission path are gentle or the level of the reception signal on the receiving side is large, the data transmission efficiency cannot be improved despite the excessive data quality.  
         SUMMARY OF THE INVENTION  
         [0009]    It is an object of the present invention to provide a transmission apparatus, reception apparatus and digital radio communication method capable of flexibly improving the data transmission efficiency and the quality of data.  
           [0010]    The present invention attains the above object by changing the interval of inserting a known pilot symbol, binary phase (BPSK: Binary Phase Shift Keying) modulation symbols or quadrature phase (QPSK: Quadrature Phase Shift Keying) modulation symbols and the modulation system of information symbols according to the communication situation such as fluctuations in the transmission path and the level of a reception signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The above and other objects and features of the invention will appear more fully hereinafter from a consideration of the following description taken in connection with the accompanying drawing wherein one example is illustrated by way of example, in which;  
         [0012]    [0012]FIG. 1 is a block diagram showing a configuration of a transmission apparatus according to Embodiment 1 of the present invention;  
         [0013]    [0013]FIG. 2 illustrates examples of a frame configuration of a signal transmitted from the transmission apparatus of Embodiment 1 of the present invention;  
         [0014]    [0014]FIG. 3 is a layout of signal points of 16 QAM and a known pilot symbol on an in-phase I-quadrature Q plane;  
         [0015]    [0015]FIG. 4 is a layout of signal points of 8 PSK modulation and a known pilot symbol on an in-phase I-quadrature Q plane;  
         [0016]    [0016]FIG. 5 is a block diagram showing a configuration of a reception apparatus according to Embodiment 1 of the present invention;  
         [0017]    [0017]FIG. 6 is a block diagram showing a configuration of a transmission apparatus according to Embodiment 2 of the present invention;  
         [0018]    [0018]FIG. 7 illustrates examples of a frame configuration of a signal transmitted from the transmission apparatus of Embodiment 2 of the present invention;  
         [0019]    [0019]FIG. 8 is a layout of signal points of 16 QAM and BPSK modulation on an in-phase I-quadrature Q plane;  
         [0020]    [0020]FIG. 9 is a layout of signal points of 8 PSK modulation and BPSK modulation on an in-phase I-quadrature Q plane;  
         [0021]    [0021]FIG. 10 is a block diagram showing a configuration of a reception apparatus according to Embodiment 2 of the present invention;  
         [0022]    [0022]FIG. 11 is a block diagram showing a configuration of a transmission apparatus according to Embodiment 3 of the present invention;  
         [0023]    [0023]FIG. 12 illustrates examples of a frame configuration of a signal transmitted from the transmission apparatus of Embodiment 3 of the present invention;  
         [0024]    [0024]FIG. 13 is a layout of signal points of 16 QAM and QPSK modulation on an in-phase I-quadrature Q plane;  
         [0025]    [0025]FIG. 14 is a layout of signal points of 8 PSK modulation and QPSK modulation on an in-phase I-quadrature Q plane;  
         [0026]    [0026]FIG. 15 is a block diagram showing a configuration of a reception apparatus according to Embodiment 3 of the present invention;  
         [0027]    [0027]FIG. 16 is a block diagram showing a configuration of a transmission apparatus according to Embodiment 4 of the present invention;  
         [0028]    [0028]FIG. 17 illustrates examples of a frame configuration of a signal transmitted from the transmission apparatus of Embodiment 4 of the present invention;  
         [0029]    [0029]FIG. 18 is a layout of signal points of BPSK modulation on an in-phase I-quadrature Q plane;  
         [0030]    [0030]FIG. 19 is a layout of signal points of QPSK modulation on an in-phase I-quadrature Q plane;  
         [0031]    [0031]FIG. 20 is a block diagram showing a configuration of a reception apparatus according to Embodiment 4 of the present invention;  
         [0032]    [0032]FIG. 21 is a block diagram showing a configuration of a transmission apparatus according to Embodiment 5 of the present invention;  
         [0033]    [0033]FIG. 22 illustrates examples of a frame configuration of a signal transmitted from the transmission apparatus of the Embodiment 5 of the present invention;  
         [0034]    [0034]FIG. 23 is a layout of signal points of 16 QAM, a known pilot symbol and symbols before and after the pilot symbol on an in-phase I-quadrature Q plane;  
         [0035]    [0035]FIG. 24 is a layout of signal points of 8 PSK modulation, a known pilot symbol and symbols before and after the pilot symbol on an in-phase I-quadrature Q plane; and  
         [0036]    [0036]FIG. 25 is a block diagram showing a configuration of a reception apparatus according to Embodiment 5 of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0037]    With reference now to the attached drawings, embodiments of the present invention will be explained in detail below.  
         [0038]    (Embodiment 1)  
         [0039]    Embodiment 1 describes a digital radio communication method by which the interval of inserting a known pilot symbol and the modulation system of information symbols are changed according to the communication situation.  
         [0040]    [0040]FIG. 1 is a block diagram showing a configuration of a transmission apparatus according to this embodiment. As shown in FIG. 1, the transmission apparatus according to this embodiment mainly consists of frame configuration determination section  101 , quadrature baseband modulation section  102 , pilot symbol generation section  103 , frame configuration section  104 , and LPFs (Low Pass Filters)  105  and  106 , transmission radio section  107  and transmission antenna  108 .  
         [0041]    Frame configuration determination section  101  judges the communication situation based on transmission path information which shows the degree of fluctuations of the transmission path due to fading and data transmission speed information which shows the transmission speed of transmission data based on the level of a reception signal and decides the interval of inserting a known pilot symbol and the modulation system of a transmission digital signal. Then, frame configuration determination section  101  outputs a signal indicating the determined modulation system to quadrature baseband modulation section  102  and outputs a signal indicating the determined interval of inserting the known pilot symbol to frame configuration section  104 . By the way, details of the method of determining a frame configuration by frame configuration determination section  101  will be described later.  
         [0042]    Here, when an identical frequency band is used for the uplink and the downlink, the situation of fluctuations in the transmission path due to fading can be estimated from a transition in the result of measuring the reception level of the modulated signal transmitted from the other end of communication on the receiving side, which is not shown in the figure, of the communication apparatus in which the transmission apparatus shown in FIG. 1 is mounted. Furthermore, the transmission apparatus shown in FIG. 1 can recognize the situation of fluctuations in the transmission path due to fading, by the reception apparatus, which is the other end of communication of the transmission apparatus shown in FIG. 1, measuring the reception level of the modulated signal transmitted from the other end of communication, estimating the situation of fluctuations in the transmission path due to fading based on the transition of the measurement result.  
         [0043]    Then, when an identical frequency band is used for the uplink and the downlink, the transmission speed of the transmission data can be determined from a result of measuring the reception level of the modulated signal transmitted from the other end of communication on the receiving side, which is not shown in the figure, of the communication apparatus in which the transmission apparatus shown in FIG. 1 is mounted. Furthermore, the transmission apparatus shown in FIG. 1 can recognize the transmission speed of the transmission data by the reception apparatus, which is the other end of communication of the transmission apparatus shown in FIG. 1, measuring the reception level of the pilot symbol transmitted from the other end of communication and determining the transmission speed of the transmission data based on the measurement result.  
         [0044]    Quadrature baseband modulation section  102  modulates a transmission digital signal to a quadrature baseband signal with the modulation system indicated from frame configuration determination section  101  and outputs the in-phase component and the quadrature component of the quadrature baseband signal to frame configuration section  104 .  
         [0045]    Pilot symbol generation section  103  generates a pilot symbol known between the transmitting and receiving sides and outputs the in-phase component and the quadrature component of the known pilot symbol to frame configuration section  104 .  
         [0046]    Frame configuration section  104  inserts the known pilot symbol output from pilot symbol generation section  103  into the output signal of quadrature baseband modulation section  102  at the insertion interval instructed from frame configuration determination section  101  and composes a frame.  
         [0047]    LPF  105  lets pass only a predetermined frequency band section of the in-phase component output from frame configuration section  104 . LPF  106  lets pass only a predetermined frequency band section of the quadrature component output from frame configuration section  104 .  
         [0048]    Transmission radio section  107  transmits a radio frequency signal as the electric wave from transmission antenna  108  after performing radio processing on the output signals of LPF  105  and LPF  106 .  
         [0049]    Next, examples of the method of determining a frame configuration by frame configuration determination section  101  of the transmission apparatus shown in FIG. ! above will be explained.  
         [0050]    [0050]FIG. 2 illustrates examples of a frame configuration of a signal transmitted from the transmission apparatus of this embodiment and shows a time-symbol relationship. ( 201 ) is a frame configuration when the modulation system of information symbols is 16-value quadrature amplitude modulation (16 QAM: 16 Quadrature Amplitude Modulation) and a known pilot symbol interval is N symbols. ( 202 ) is a frame configuration when the modulation system of information symbols is 16 QAM and a known pilot symbol interval is M symbols. ( 203 ) is a frame configuration when the modulation system of information symbols is 8 phases (8 PSK: 8 Phase Shift Keying) modulation and a known pilot symbol interval is N symbols. ( 204 ) is a frame configuration when the modulation system of information symbols is 8 PSK modulation and a known pilot symbol interval is M symbols. Suppose N&lt;M at this time.  
         [0051]    Frame configuration determination section  101  selects one of ( 201 ), ( 202 ), ( 203 ) or ( 204 ) in FIG. 2 as the optimal frame configuration based on the transmission path information and the request data transmission speed information.  
         [0052]    For example, in the case of high-speed fading, frame configuration determination section  101  sacrifices data transmission efficiency on the receiving side and selects a frame configuration of either ( 201 ) or ( 203 ) in FIG. 2 so that the interval of inserting a known pilot symbol becomes narrower to prevent deterioration of the data demodulation error rate and maintain the quality of data. On the other hand, in the case of low-speed fading, frame configuration determination section  101  selects a frame configuration of either ( 202 ) or ( 204 ) in FIG. 2 to widen the interval of inserting a known pilot symbol to improve the data transmission efficiency.  
         [0053]    Also, when the level of the reception signal is large, frame configuration determination section  101  gives priority to data transmission efficiency on the receiving side and selects a frame configuration of either ( 201 ) or ( 202 ) in FIG. 2 adopting 16 QAM as the modulation system of information symbols. On the other hand, when the level of the reception signal is small, frame configuration determination section  101  gives priority to increasing error resistance while sacrificing data transmission efficiency on the receiving side and selects a frame configuration of either ( 203 ) or ( 204 ) in FIG. 2 adopting 8 PSK as the modulation system of information symbols.  
         [0054]    [0054]FIG. 3 shows a signal point layout according to the 16 QAM modulation system on the in-phase I-quadrature Q plane and signal point layout of a known pilot symbol. Signal point  301  is the signal point of a known pilot symbol and signal points  302  are the signal points of 16 QAM modulation symbols. FIG. 4 shows a signal point layout according to the 8 PSK modulation system on the in-phase I-quadrature Q plane and signal point layout of a known pilot symbol. Signal point  401  is the signal point of a known pilot symbol and signal points  402  are the signal points of 8 PSK modulation symbols.  
         [0055]    [0055]FIG. 5 is a block diagram showing a configuration of the reception apparatus according to this embodiment. As shown in FIG. 5, the reception apparatus according to this Embodiment mainly consists of reception antenna  501 , reception radio section  502 , transmission path distortion estimation section  503  and detection section  504 .  
         [0056]    Reception radio section  502  receives the radio signal received by reception antenna  501  as an input, performs predetermined radio processing and outputs the in-phase component and the quadrature component of the reception quadrature baseband signal.  
         [0057]    Transmission path distortion estimation section  503  receives the in-phase component and the quadrature component of the quadrature baseband signal as inputs, extracts the signal of the known pilot symbol shown in FIG. 3 and FIG. 4 above, estimates the amount of transmission path distortion from the reception condition of the known pilot symbol and outputs the amount of transmission path distortion to detection section  504 .  
         [0058]    Detection section  504  receives the in-phase component and the quadrature component of the quadrature baseband signal as inputs, detects information symbols based on the amount of transmission path distortion and outputs a reception digital signal.  
         [0059]    Thus, changing the interval of inserting a known pilot symbol and the modulation system of information symbols according to the communication situation such as fluctuations in the transmission path and the level of the reception signal can improve both the data transmission efficiency and the quality of data at the same time.  
         [0060]    Here, this embodiment explains two kinds of the interval of inserting a known pilot symbol, but the present invention is not limited to this. Furthermore, this embodiment explains two kinds of the modulation system of information symbols, 16 QAM and the 8 PSK modulation, but the present invention is not limited to this.  
         [0061]    Furthermore, this embodiment only explains the frame configuration of information symbols and a known pilot symbol shown in FIG. 2, but since it is also possible to consider a frame configuration in which signals such as a symbol for synchronization to adjust timing between the receiver and transmitter and a symbol to correct an error on the receiver side are inserted, the present invention is not limited to the frame configuration composed of only information symbols and known pilot symbol.  
         [0062]    (Embodiment 2)  
         [0063]    Embodiment 2 describes a digital radio communication method by which the interval of inserting a BPSK modulation symbol and the modulation system of information symbols other than the above BPSK modulation symbol are changed according to the communication situation.  
         [0064]    [0064]FIG. 6 is a block diagram showing a configuration of the transmission apparatus according to this Embodiment. Here, in the transmission apparatus shown in FIG. 6, the components common to those in the transmission apparatus shown in FIG. 1 are assigned the same reference numerals as those in FIG. 1 and their explanations will be omitted.  
         [0065]    In the transmission apparatus in FIG. 6, frame configuration determination section  601  differs in the way of operation from the frame configuration determination section  101  in FIG. 1. Also, when compared to FIG. 1, the transmission apparatus in FIG. 6 adopts the configuration with BPSK symbol modulation section  602 , instead of pilot symbol generation section  103 , added.  
         [0066]    Frame configuration determination section  601  judges the communication situation, determines the interval of inserting a BPSK modulation symbol and the modulation system of a transmission digital signal, outputs a signal indicating the determined modulation system to quadrature baseband modulation section  102  and outputs a signal indicating the interval of inserting the determined BPSK modulation symbol to quadrature baseband modulation section  102 , BPSK symbol modulation section  602  and frame configuration section  104 .  
         [0067]    BPSK symbol modulation section  602  performs BPSK-modulation on the transmission digital signal at the timing indicated from frame configuration determination section  601  and outputs the in-phase component and the quadrature component of the BPSK modulation symbol to frame configuration section  104 .  
         [0068]    [0068]FIG. 7 illustrates examples of a frame configuration of a signal transmitted from the transmission apparatus of this embodiment and shows a time-symbol relationship. ( 701 ) is a frame configuration when the modulation system of information symbols is 16 QAM and a BPSK modulation symbol interval is N symbols. ( 702 ) is a frame configuration when the modulation system of information symbols is 16 QAM and a BPSK modulation symbol interval is M symbols. ( 703 ) is a frame configuration when the modulation system of information symbols is 8 PSK modulation and a BPSK modulation symbol interval is N symbols. ( 704 ) is a frame configuration when the modulation system of information symbols is 8 PSK modulation and a BPSK modulation symbol interval is M symbols. Suppose N&lt;M at this time.  
         [0069]    Frame configuration determination section  601  selects one of ( 701 ), ( 702 ), ( 703 ) or ( 704 ) in FIG. 7 as the optimal frame configuration based on the transmission path information and the request data transmission speed information.  
         [0070]    For example, in the case of high-speed fading, frame configuration determination section  601  sacrifices data transmission efficiency on the receiving side and selects a frame configuration of either ( 701 ) or ( 703 ) in FIG. 7 so that the interval of inserting a BPSK modulation symbol becomes narrower to prevent deterioration of the data demodulation error rate and maintain the quality of data. On the other hand, in the case of low-speed fading, frame configuration determination section  601  selects a frame configuration of either ( 702 ) or ( 704 ) in FIG. 7 to widen the interval of inserting a BPSK modulation symbol to improve the data transmission efficiency.  
         [0071]    Furthermore, when the level of the reception signal is large, frame configuration determination section  601  gives priority to data transmission efficiency on the receiving side and selects a frame configuration of either ( 701 ) or ( 702 ) in the FIG. 7 adopting 16 QAM as the modulation system of information symbols. On the other hand, when the level of the reception signal is small, frame configuration determination section  601  gives priority to increasing error resistance while sacrificing data transmission efficiency on the receiving side and selects a frame configuration of either ( 703 ) or ( 704 ) in FIG. 7 adopting 8 PSK as the modulation system of information symbols.  
         [0072]    [0072]FIG. 8 shows a signal point layout according to the 16 QAM modulation system on the in-phase I-quadrature Q plane and signal point layout of BPSK modulation symbols. Signal points  801  are the signal points of BPSK modulation symbols and signal points  802  are the signal points of 16 QAM modulation symbols. FIG. 9 shows a signal point layout according to the 8 PSK modulation system on the in-phase I-quadrature Q plane and signal point layout of BPSK modulation symbols. Signal points  901  are the signal points of BPSK modulation symbols and signal points  902  are the signal points of 8 PSK modulation symbols.  
         [0073]    [0073]FIG. 10 is a block diagram showing a configuration of the reception apparatus according to this Embodiment. In the reception apparatus shown in FIG. 10, the components common to the reception apparatus shown in FIG. 5 are assigned the same reference numerals as those in FIG. 5 and their explanations will be omitted.  
         [0074]    In the reception apparatus in FIG. 10, transmission path distortion estimation section  1001  differs in the way of operation from transmission path distortion estimation section  503  in FIG. 5 and detection section  1002  differs in the way of operation from detection section  504  in FIG. 5.  
         [0075]    Transmission path distortion estimation section  1001  receives the in-phase component and the quadrature component of the quadrature baseband signal as inputs, extracts the signals of the BPSK modulation symbols shown in FIG. 8 and FIG. 9 above, estimates the amount of transmission path distortion from the reception condition of the BPSK modulation symbols and outputs the amount of transmission path distortion to detection section  1002 .  
         [0076]    Detection section  1002  receives the in-phase component and the quadrature component of the quadrature baseband signal as inputs, detects information symbols and BPSK modulation symbols based on the amount of transmission path distortion and outputs a reception digital signal.  
         [0077]    Thus, in this embodiment, by sending information with BPSK modulation symbols, instead of a known pilot symbol, inserted, it is possible to improve the transmission speed compared with Embodiment 1.  
         [0078]    Here, this embodiment describes two kinds of the interval of inserting BPSK modulation symbols but the present invention is not limited to this. Also, this embodiment describes two kinds of the modulation system of information symbols, 16 QAM and 8 PSK modulation, but the present invention is not limited to this.  
         [0079]    Furthermore, this embodiment describes the frame configuration of only information symbols and BPSK modulation symbols shown in FIG. 7 but the present invention is not limited to this frame configuration.  
         [0080]    (Embodiment 3)  
         [0081]    Embodiment 3 describes a digital radio communication method by which the interval of inserting QPSK modulation symbols and the modulation system of information symbols other than the above QPSK modulation symbols are changed according to the communication situation.  
         [0082]    [0082]FIG. 11 is a block diagram showing a configuration of the transmission apparatus according to this Embodiment. In the transmission apparatus shown in FIG. 11, the components common to those in the transmission apparatus shown in FIG. 1 are assigned the same reference numerals as those in FIG. 1 and their explanations will be omitted.  
         [0083]    In the transmission apparatus in FIG. 11, frame configuration determination section  1101  differs in the way of operation from the frame configuration determination section  101  in FIG. 1. Also, when compared to FIG. 1, the transmission apparatus in FIG. 11 adopts a configuration with QPSK symbol modulation section  1102 , instead of pilot symbol generation section  103 , added.  
         [0084]    Frame configuration determination section  1101  judges the communication situation, determines the interval of inserting QPSK modulation symbols and the modulation system of a transmission digital signal, outputs a signal indicating the determined modulation system to quadrature baseband modulation section  102  and outputs a signal indicating the determined interval of inserting QPSK modulation symbols to quadrature baseband modulation section  102 , QPSK symbol modulation section  1102  and frame configuration section  104 .  
         [0085]    QPSK symbol modulation section  1102  performs QPSK-modulation on a transmission digital signal at the timing indicated from frame configuration determination section  1101  and outputs the in-phase component and the quadrature component of the QPSK modulation symbol to frame configuration section  104 .  
         [0086]    [0086]FIG. 12 illustrates examples of a frame configuration of a signal transmitted from the transmission apparatus of this embodiment and shows a time-symbol relationship. ( 1201 ) is a frame configuration when the modulation system of information symbols is 16 QAM and a QPSK modulation symbol interval is N symbols. ( 1202 ) is a frame configuration when the modulation system of information symbols is 16 QAM and a QPSK modulation symbol interval is M symbols. ( 1203 ) is a frame configuration when the modulation system of information symbols is 8 PSK modulation and a QPSK modulation symbol interval is N symbols. ( 1204 ) is a frame configuration when the modulation system of information symbols is 8 PSK modulation and a QPSK modulation symbol interval is M symbols. Suppose N&lt;M at this time.  
         [0087]    Frame configuration determination section  1101  selects one of ( 1201 ), ( 1202 ), ( 1203 ) or ( 1204 ) in FIG. 12 as the optimal frame configuration based on the transmission path information and the request data transmission speed information.  
         [0088]    For example, in the case of high-speed fading, frame configuration determination section  1101  sacrifices data transmission efficiency on the receiving side and selects a frame configuration of either ( 1201 ) or ( 1203 ) in FIG. 12 so that the QPSK modulation symbol insertion interval becomes narrower to prevent deterioration of the data demodulation error rate and maintain the quality of data. On the other hand, in the case of low-speed fading, frame configuration determination section  1101  selects a frame configuration of either ( 1202 ) or ( 1204 ) in FIG. 12 to widen the interval of inserting QPSK modulation symbols to improve the data transmission efficiency.  
         [0089]    Furthermore, when the level of the reception signal is large, frame configuration determination section  1101  gives priority to data transmission efficiency on the receiving side and selects a frame configuration of either ( 1201 ) or ( 1202 ) in FIG. 12 adopting 16 QAM as the modulation system of information symbols. On the other hand, when the level of the reception signal is small, frame configuration determination section  1101  gives priority to increasing error resistance while sacrificing data transmission efficiency on the receiving side and selects a frame configuration of either ( 1203 ) or ( 1204 ) in FIG. 12 adopting 8 PSK as the modulation system of information symbols.  
         [0090]    [0090]FIG. 13 shows a signal point layout according to the 16 QAM modulation system on the in-phase I-quadrature Q plane and signal point layout of QPSK modulation symbols. Signal points  1301  are the signal points of QPSK modulation symbols and signal points  1302  are the signal points of 16 QAM modulation symbols. FIG. 14 shows a signal point layout according to the 8 PSK modulation system on the in-phase I-quadrature Q plane and signal point layout of QPSK modulation symbols. Signal points  1401  are the signal points of QPSK modulation symbols and signal points  1402  are the signal points of 8 PSK modulation symbols.  
         [0091]    [0091]FIG. 15 is a block diagram showing a configuration of the reception apparatus according to this embodiment. In the reception apparatus shown in FIG. 15, the components common to the reception apparatus shown in FIG. 5 are assigned the same reference numerals as those in FIG. 5 and their explanations will be omitted.  
         [0092]    In the reception apparatus in FIG. 15, transmission path distortion estimation section  1501  differs in the way of operation from transmission path distortion estimation section  503  in FIG. 5 and detection section  1502  differs in the way of operation from detection section  504  in FIG. 5.  
         [0093]    Transmission path distortion estimation section  1501  receives the in-phase component and the quadrature component of the quadrature baseband signal as inputs, extracts the signals of the QPSK modulation symbols shown in FIG. 13 and FIG. 14 above, estimates the amount of transmission path distortion from the reception condition of the QPSK modulation symbols and outputs the amount of transmission path distortion to detection section  1502 .  
         [0094]    Detection section  1502  receives the in-phase component and the quadrature component of the quadrature baseband signal as inputs, detects information symbols and QPSK modulation symbols based on the amount of transmission path distortion and outputs a reception digital signal.  
         [0095]    Thus, in this embodiment, by sending information with QPSK modulation symbols, instead of a known pilot symbol, inserted, it is possible to improve the transmission speed compared with Embodiment 1 and Embodiment 2.  
         [0096]    Here, this embodiment describes two kinds of the interval of inserting QPSK modulation symbols but the present invention is not limited to this. Also, this embodiment describes two kinds of the modulation system of information symbols, 16 QAM and 8 PSK modulation, but the present invention is not limited to this.  
         [0097]    Furthermore, this embodiment describes the frame configuration of only information symbols and QPSK modulation symbols shown in FIG. 12 but the present invention is not limited to this frame configuration.  
         [0098]    (Embodiment 4)  
         [0099]    Embodiment 4 describes a digital radio communication method by which the modulation system of information symbols is changed according to the communication situation and when the modulation system of information symbols uses 8 or more values, a known pilot symbol is inserted with the insertion interval changed according to the communication situation.  
         [0100]    [0100]FIG. 16 is a block diagram showing a configuration of the transmission apparatus according to this Embodiment. In the transmission apparatus shown in FIG. 16, the components common to those in the transmission apparatus shown in FIG. 1 are assigned the same reference numerals as those in FIG. 1 and their explanations will be omitted.  
         [0101]    In the transmission apparatus in FIG. 16, frame configuration determination section  1601  differs in the way of operation from the frame configuration determination section  101  in FIG. 1.  
         [0102]    Frame configuration determination section  1601  determines the modulation system of a transmission digital signal based on the communication situation and outputs a signal indicating the determined modulation system to quadrature baseband modulation section  102 . Also, when the determined modulation system uses 8 or more values, frame configuration determination section  1601  determines the interval of inserting a pilot symbol based on the communication situation and outputs a signal indicating the determined interval of inserting the pilot symbol to frame configuration section  104 . Also, when the determined modulation system uses 8 fewer values, frame configuration determination section  1601  outputs a signal giving an instruction for stopping the generation of pilot symbols to pilot symbol generation section  103 .  
         [0103]    Pilot symbol generation section  103  generates a pilot symbol known between the transmitting and receiving sides and outputs the in-phase component and the quadrature component of the known pilot symbol to frame configuration section  104 . However, when instructed to stop the generation of pilot symbols from frame configuration determination section  1601 , pilot symbol generation section  103  stops operation.  
         [0104]    [0104]FIG. 17 illustrates examples of a frame configuration of a signal transmitted from the transmission apparatus of this embodiment and shows a time-symbol relationship. ( 1701 ) is a frame configuration when the modulation system of information symbols is BPSK. ( 1702 ) is a frame configuration when the modulation system of information symbols is QPSK.  
         [0105]    The ranking of the frame configurations shown in FIG. 2 and FIG. 17 in descending order of resistance to fading speed is ( 1701 ), ( 1702 ), ( 203 ), ( 201 ), ( 204 ) and ( 202 ). Furthermore, the ranking in descending order of error resistance is ( 1701 ), ( 1702 ), ( 203 ), ( 204 ), ( 201 ) and ( 202 ). On the other hand, the ranking in descending order of data transmission efficiency on the receiving side is ( 202 ), ( 201 ), ( 204 ), ( 203 ), ( 1702 ) and ( 1701 ).  
         [0106]    Frame configuration determination section  1601  selects one of ( 201 ), ( 202 ), ( 203 ) or ( 204 ) in FIG. 2 or ( 1701 ) or ( 1702 ) in FIG. 17 above as the optimal frame configuration based on the transmission path information and the request data transmission speed information.  
         [0107]    [0107]FIG. 18 shows a signal point layout according to the BPSK modulation method on the in-phase I-quadrature Q plane and signal points  1801  are the signal points of BPSK symbols.  
         [0108]    [0108]FIG. 19 shows a signal point layout according to the QPSK modulation method on the in-phase I-quadrature Q plane and signal points  1901  are the signal points of QPSK symbols.  
         [0109]    [0109]FIG. 20 is a block diagram showing a configuration of the reception apparatus according to this embodiment. In the reception apparatus shown in FIG. 20, the components common to those in the reception apparatus shown in FIG. 5 are assigned the same reference numerals as those in FIG. 5 and their explanations will be omitted.  
         [0110]    In the reception apparatus in FIG. 20, transmission path distortion estimation section  2001  differs in the way of operation from transmission path estimation section  503  in FIG. 5 and detection section  2002  differs in the way of operation from-detection section  504  in FIG. 5.  
         [0111]    Transmission-path distortion estimation section  2001  receives the in-phase component and the quadrature component of the quadrature baseband signal as inputs, estimates the amount of transmission path distortion from the reception condition of the BPSK modulation symbol shown in FIG. 18 or the QPSK modulation symbol shown in FIG. 19 and outputs the amount of transmission path distortion to detection section  2002 .  
         [0112]    Detection section  2002  receives the in-phase component and the quadrature component of the quadrature baseband signal as inputs, detects information symbols based on the amount of transmission path distortion and outputs a reception digital signal.  
         [0113]    In this way, by changing the modulation system of information symbols according to the communication situation such as fluctuations in the transmission path and the level of the reception signal, inserting a known pilot symbol when the information symbol modulation system is a multi-value modulation system with 8 or more values and changing the interval of inserting the above known pilot symbol according to the communication situation, it is possible to improve both the data transmission efficiency and the quality of data at the same time.  
         [0114]    Here, in this embodiment, the transmission apparatus in FIG. 16 can also have a configuration equipped with BPSK symbol modulation section  602  shown in FIG. 6 instead of pilot symbol generation section  103 .  
         [0115]    In this case, frame configuration determination section  1601  determines the modulation system of the transmission digital signal based on the communication situation. For example, frame configuration determination section  1601  selects one of ( 701 ), ( 702 ), ( 703 ) or ( 704 ) in FIG. 7 above or ( 1701 ) or ( 1702 ) in FIG. 17 as the optimal frame configuration.  
         [0116]    Then, frame configuration determination section  1601  outputs the signals indicating the determined modulation system to quadrature baseband modulation section  102 . Also, when the determined modulation system uses 8 or more values, frame configuration determination section  1601  determines the interval of inserting BPSK modulation symbols based on the communication situation and outputs a signal indicating the determined interval of inserting the BPSK modulation symbols to BPSK symbol modulation section  602  and frame configuration section  104 . Furthermore, when the determined modulation system is 8 fewer values, frame configuration determination section  1601  outputs a signal giving an instruction for stopping the generation of BPSK modulation symbols to BPSK symbol modulation section  602 .  
         [0117]    BPSK symbol modulation section  602  performs BPSK-modulation on a transmission digital signal at the timing indicated from frame configuration determination section  1601  and outputs the in-phase component and the quadrature component of the. BPSK modulation symbols to frame configuration section  104 . However, when instructed to stop the generation of BPSK modulation symbols from frame configuration determination section  1601 , BPSK symbol modulation section  602  stops operation.  
         [0118]    Transmission path distortion estimation section  2001  receives the in-phase component and the quadrature component of the quadrature baseband signal as inputs, estimates the amount of transmission path distortion from the reception condition of the BPSK modulation symbols shown in FIG. 8 and FIG. 9 above, the BPSK modulation symbols shown in FIG. 18 or the QPSK modulation symbols shown in FIG. 19 and outputs the amount of transmission path distortion to detection section  2002 .  
         [0119]    Furthermore, in this embodiment, the transmission apparatus in FIG. 16 can also have a configuration equipped with QPSK symbol modulation section  1102  shown in FIG. 11 instead of pilot symbol generation section  103 .  
         [0120]    In this case, frame configuration determination section  1601  determines the modulation system of the transmission digital signal based on the communication situation. For example, frame configuration determination section  1601  selects one of ( 1201 ), ( 1202 ), ( 1203 ) or ( 1204 ) in FIG. 12 above or ( 1701 ) or ( 1702 ) in FIG. 17 as the optimal frame configuration.  
         [0121]    Then, frame configuration determination section  1601  outputs a signal indicating the determined modulation system to quadrature baseband modulation section  102 . Also, when the determined modulation system uses 8 or more values, frame configuration determination section  1601  determines the interval of inserting QPSK modulation symbols based on the communication situation and outputs a signal indicating the determined interval of inserting the QPSK symbols to QPSK symbol modulation section  1102  and frame configuration section  104 . Also, when the determined modulation system is 8 fewer values, frame configuration determination section  1601  outputs a signal giving an instruction for stopping the generation of QPSK modulation symbols to QPSK symbol modulation section  1102 .  
         [0122]    QPSK symbol modulation section  1102  performs QPSK-modulation on a transmission digital signal at the timing indicated from frame configuration determination section  1601  and outputs the in-phase component and the quadrature component of the QPSK modulation symbols to frame configuration section  104 . However, when instructed to stop generating QPSK modulation symbols from frame configuration determination section  1601 , QPSK symbol modulation section  1102  stops operation.  
         [0123]    Transmission path distortion estimation section  2001  receives the in-phase component and the quadrature component of the quadrature baseband signal as inputs, estimates the amount of transmission path distortion from the reception condition of the QPSK modulation symbols shown in FIG. 13 or FIG. 14 and the BPSK modulation symbols shown in FIG. 18 or the QPSK modulation symbol shown in FIG. 19 and outputs the amount of transmission path distortion to detection section  2002 .  
         [0124]    Here, this embodiment explains two kinds of the interval of inserting a known pilot symbol, but the present invention is not limited to this. Also, this embodiment explains two kinds of the multi-value modulation system with 8 or more values of information symbols, 16 QAM and the 8 PSK modulation, but the present invention is not limited to this.  
         [0125]    Furthermore, this embodiment describes the frame configurations in FIG. 2, FIG. 7, FIG. 12 and FIG. 17 but the present invention is not limited to these frame configurations.  
         [0126]    Furthermore, the BPSK modulation method and the QPSK modulation method of the modulation system of information symbols of the present invention are not limited to the signal point layouts shown in FIG. 18 and FIG. 19 but π/2 shift BPSK modulation or π/4 shift QPSK modulation can also be used.  
         [0127]    (Embodiment 5)  
         [0128]    Embodiment 5 describes a digital radio communication method by which the interval of inserting a known pilot symbol, the number of signal points with one symbol immediately before and after a known pilot symbol (hereinafter referred to as “symbols before and after a pilot”) and signal point layout and the modulation system of information symbols other than those symbols are changed.  
         [0129]    [0129]FIG. 21 is a block diagram showing a configuration of the transmission apparatus according to this embodiment. In the transmission apparatus shown in FIG. 21, the components common to those in the transmission apparatus shown in FIG. 1 are assigned the same reference numerals as those shown in FIG. 1 and their explanations will be omitted.  
         [0130]    In the transmission apparatus in FIG. 21, frame configuration determination section  2101  differs in the way of operation from frame configuration determination section  101  in FIG. 1. Furthermore, the transmission apparatus in FIG. 21 adopts a configuration with symbols before and after a pilot modulation section  2102  added compared to FIG. 1.  
         [0131]    Frame configuration determination section  2101  determines the interval of inserting a known pilot symbol and the modulation system of a transmission digital signal based on the communication situation. In this case, frame configuration determination section  2101  uses different modulation systems for symbols before and after a pilot and for other information symbols.  
         [0132]    Then, frame configuration determination section  2101  outputs a signal indicating the modulation system of symbols before and after a pilot to symbols before and after a pilot modulation section  2102 , outputs a signal indicating the modulation system of other information symbols to quadrature baseband modulation section  102  and outputs a signal indicating the interval of inserting the determined known pilot symbol to symbols before and after a pilot modulation section  2102  and frame configuration section  104 .  
         [0133]    Symbols before and after a pilot modulation section  2102  modulates on a transmission digital signal by predetermined modulation system at the timing indicated from frame configuration determination section  2101  and outputs the in-phase component and the quadrature component of the symbols before and after a pilot to frame configuration section  104 .  
         [0134]    [0134]FIG. 22 illustrates examples of a frame configuration of a signal transmitted from the transmission apparatus of this embodiment and shows a time-symbol relationship. ( 2201 ) is a frame configuration when the modulation system of information symbols is 16 QAM and a known pilot symbol interval is N symbols. ( 2202 ) is a frame configuration when the modulation system of information symbols is 16 QAM and a known pilot symbol interval is M symbols. ( 2203 ) is a frame configuration when the modulation system of information symbols is BPSK modulation and a known pilot symbol interval is N symbols. ( 2204 ) is a frame configuration when the modulation system of information symbols is 8 PSK modulation and a known pilot symbol interval is M symbols. Suppose N&lt;M at this time.  
         [0135]    Signal point  2211  is 1 symbol immediately before the known pilot symbol when the information symbol modulation system is 16 QAM and signal point  2212  is 1 symbol immediately after the known pilot symbol when the information symbol modulation system is 16 QAM. Signal point  2213  is 1 symbol immediately before the known pilot symbol when the information symbol modulation system is 8 PSK modulation and signal point  2214  is 1 symbol immediately after the known pilot symbol when the information symbol modulation system is 8 PSK modulation.  
         [0136]    Frame configuration determination section  2101  selects one of ( 2201 ), ( 2202 ), ( 2203 ) or ( 2204 ) in FIG. 22 as the optimal frame configuration based on the transmission path information and the request data transmission speed information.  
         [0137]    For example, in the case of high-speed fading, frame configuration determination section  2101  sacrifices data transmission efficiency on the receiving side and selects a frame configuration of either ( 2201 ) or ( 2203 ) in FIG. 22 so that the interval of inserting a known pilot symbol becomes narrower to prevent deterioration of the data demodulation error rate and maintain the quality of data. On the other hand, in the case of low-speed fading, frame configuration determination section  2101  selects a frame configuration of either ( 2202 ) or ( 2204 ) in FIG. 22 to widen the interval of inserting a known pilot symbol to improve the data transmission efficiency.  
         [0138]    Furthermore, when the level of the reception signal is large, frame configuration determination section  2101  gives priority to data transmission efficiency on the receiving side and selects a frame configuration of either ( 2201 ) or ( 2202 ) in FIG. 22 adopting 16 QAM as the modulation system of information symbols. On the other hand, when the level of the reception signal is small, frame configuration determination section  2101  gives priority to increasing error resistance while sacrificing data transmission efficiency on the receiving side and selects a frame configuration of either ( 2203 ) or ( 2204 ) in FIG. 22 adopting 8 PSK as the modulation system of information symbols.  
         [0139]    [0139]FIG. 23 shows a signal point layout according to the 16 QAM modulation method on the in-phase I-quadrature Q plane and a signal point layout according to a known pilot symbol and a signal point layout of symbols before and after a pilot. Signal point  2301  is the signal point of a known pilot symbol, signal points  2302  are the signal points of 16 QAM modulation symbols and signal points  2303  are the signal points of symbols before and after a pilot.  
         [0140]    [0140]FIG. 24 shows a signal point layout according to the 8 PSK modulation system on the in-phase I-quadrature Q plane, a signal point layout of a known pilot symbol and a signal point layout of symbols before and after a pilot. Signal points  2401 ,  2401 -A and  2401 -B are the signal points of 8 PSK modulation symbols,  2401 -A is the signal point of the known pilot symbol,  2401 -A and  2401 -B are the signal points of symbols before and after a pilot and straight line  2402  is the straight line formed by linking the signal point of the known pilot symbol and the origin on the in-phase I-quadrature Q plane.  
         [0141]    [0141]FIG. 25 is a block diagram showing a configuration of the reception apparatus according to this embodiment. In the reception apparatus shown in FIG. 25, the components common to those in the reception apparatus shown in FIG. 5 are assigned the same reference numerals as those shown in FIG. 5 and their explanations will be omitted.  
         [0142]    In the reception apparatus in FIG. 25, transmission path estimation section  2501  differs in the way of operation from transmission path estimation section  503  and detection section  2502  differs in the way of operation from detection section  504  in FIG. 5.  
         [0143]    Transmission path distortion estimation section  2501  receives the in-phase component and the quadrature component of the quadrature baseband signal as inputs, extracts the signal of the known pilot symbol shown in FIG. 23 and FIG. 24 above, estimates the amount of transmission path distortion from the reception condition of the known pilot symbol and outputs the amount of transmission path distortion to detection section  2502 .  
         [0144]    Detection section  2502  receives the in-phase component and the quadrature component of the quadrature baseband signal as inputs, detects information symbols including symbols before and after a pilot based on the amount of transmission path distortion and outputs a reception digital signal.  
         [0145]    Thus, changing the interval of inserting a known pilot symbol and the modulation system of information symbols according to the communication situation such as fluctuations in the transmission path and the level of the reception signal can improve both the data transmission efficiency and the quality of data at the same time.  
         [0146]    Furthermore, as shown in FIG. 23 and FIG. 24, by arranging two or more signal points before and after a pilot on the straight line formed by linking the origin and the signal point of the known pilot symbol on the in-phase I-quadrature Q plane, it is possible for the reception apparatus in FIG. 25 to suppress deterioration of the estimation accuracy of reference phase and the amount of frequency offset by the pilot symbol, even if symbol synchronization is not established completely when a reference phase and the amount of frequency offset is estimated from the pilot signal. When detection section  116  performs detection, this allows the bit error rate characteristic based on the carrier-to-noise ratio to be improved.  
         [0147]    Here, this embodiment can be combined with Embodiment 4 above. That is, when the determined modulation system uses 8 or more values, frame configuration determination section  2101  in FIG. 21 determines the interval of inserting a pilot symbol based on the communication situation and outputs a signal indicating the interval of inserting the determined pilot symbol to symbols before and after a pilot modulation section  2102  and frame configuration section  104 . Furthermore, when the determined modulation system uses 8 fewer values, frame configuration determination section  2101  outputs a signal giving an instruction for stopping the generation of pilot symbols to symbols before and after a pilot modulation section  2102  and pilot symbol generation section  103 .  
         [0148]    Pilot symbol generation section  103  generates a pilot symbol known between the transmitting and receiving sides and outputs the in-phase component and the quadrature component of the known pilot symbol to frame configuration section  104 . However, when instructed to stop the generation of pilot symbols from frame configuration determination section  2101 , pilot symbol generation section  103  stops operation.  
         [0149]    Symbols before and after a pilot modulation section  2102  performs BPSK-modulation or QPSK-modulation on a transmission digital signal at the timing indicated from frame configuration determination section  2101  and outputs the in-phase component and the quadrature component of the symbols before and after a pilot to frame configuration section  104 . However, when instructed to stop the generation of pilot symbols from frame configuration determination section  2101 , symbols before and after a pilot modulation section  2102  stops operation.  
         [0150]    This allows the effect of Embodiment 4 to be attained in addition to the effect of this embodiment as described above.  
         [0151]    Here, this embodiment describes two kinds of modulation system of information symbols, 16 QAM and 8 PSK modulation, but the present invention is not limited to this.  
         [0152]    Furthermore, this embodiment explains only the configuration of information symbols, a known pilot symbol, symbols before and after a pilot in FIG. 22, but the frame configuration of the present invention is not limited to the frame configuration composed of only information symbols, a known pilot symbol, symbols before and after a pilot.  
         [0153]    As described above, according to the present invention, by changing the interval of inserting a known pilot symbol, BPSK modulation symbols or QPSK modulation symbols and the modulation system of information symbols according to the communication situation of fluctuations in the transmission path and the level of the reception signal, etc., it is possible to improve both the data transmission efficiency and the quality of data at the same time.  
         [0154]    The present invention is not limited to the above described embodiments, and various variations and modifications may be possible without departing from the scope of the present invention. This application is based on the Japanese Patent Application No.HEI 11-213289 filed on Jul. 28, 1999, entire content of which is expressly incorporated by reference herein.