JP3809180B2 - Wireless transmission method - Google Patents

Description

  The present invention relates to a wireless transmission method, and is particularly applicable to a case where a modulated signal is transmitted using a plurality of antennas.

  Conventionally, for example, as in a transmission method called MIMO (MultiInput Multi Output) described in Non-Patent Document 1, different modulated signals are transmitted from a plurality of antennas, and modulated signals transmitted simultaneously from the respective antennas on the receiving side are transmitted. A method of increasing the amount of transmission information by separating and demodulating has been proposed.

  This method will be briefly described. As shown in FIG. 36, consider a case in which modulated signals A and B are simultaneously transmitted from two antennas T1 and T2, respectively, and modulated signals A and B are received by two antennas R1 and R2. In this case, it is necessary to estimate four channel fluctuations h11 (t), h12 (t), h21 (t), and h22 (t) on the receiving side.

Therefore, as shown in FIG. 37, pilot symbols (for radio wave propagation environment estimation) for estimating channel fluctuations h11 (t), h12 (t), h21 (t), and h22 (t) in modulated signals A and B. Symbols) 01, 02, 03, 04 are arranged. The known signal here the pilot symbols 01, 03 are transmitted simultaneously C, and the known signal of -C Pilot symbol 02 ^*, and sends a known signal of the pilot symbol 04 ^{C *.} Incidentally, * indicates a conjugate complex number. In addition, data symbols other than pilot symbols 01, 02, 03, and 04 are arranged for each modulation signal A and modulation signal B.

  In this way, in a conventional wireless transmission device that transmits different modulation signals from multiple antennas simultaneously, the modulation signal synthesized from the antenna is embedded on the modulation signal transmitted from each antenna so that the modulation signal synthesized on the propagation path is good on the receiving side. Can be separated and demodulated.

Conventionally, a method has been proposed in which the number of antennas that transmit a modulated signal is changed according to a radio wave propagation environment or the like, based on the above-described technique. For example, when four antennas are provided on the transmission side, four different modulation signals are transmitted simultaneously using all four antennas when the radio wave propagation environment is good, while 2 when the radio wave propagation environment is bad. Two different modulation signals are transmitted simultaneously using only one antenna.
"Proposal of SDM-COFDM system for wideband mobile communication realizing 100Mbit / s with MIMO channel" IEICE, IEICE Technical Report RCS-2001-135, October 2001

  However, in the method of changing the number of modulation signals transmitted simultaneously according to the radio wave propagation environment and the like, the level of the reception signal also changes according to the change in the number of transmission antennas (that is, the number of transmission modulation signals). • The quantization error in the digital converter may become large. This quantization error greatly affects the accuracy of channel estimation and the error rate of the information data, so that the reception quality of the modulated signal is degraded.

  The present invention has been made in view of the above points, and in a method of changing the number of modulated signals to be transmitted simultaneously in accordance with a propagation environment or the like, the reception quality is reduced by reducing the quantization error of pilot symbols and data symbols. An object of the present invention is to provide a wireless transmission method capable of improving the performance.

A radio transmission method according to the present invention is a radio transmission method for transmitting a data symbol and switching the number of antennas for transmitting a preamble, wherein the signal point amplitude is the largest among signal point amplitudes of signal points at which the data symbols are arranged. Transmitting the first preamble arranged at a signal point having a larger signal point amplitude, and arranging the first preamble by using more antennas than the number of antennas to which the first preamble is transmitted. Transmitting a second preamble arranged at a signal point having a signal point amplitude smaller than the signal point amplitude of the signal point to be processed .

  According to the present invention, even when the number of transmission antennas is changed, the PAPR of the preamble can be reduced. As a result, the quantization error of the preamble at the time of reception can be reduced, and the reception quality can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The essence of the present invention is that, in a wireless transmission device that can change the number of modulation signals transmitted simultaneously, the number of modulation signals transmitted from each antenna according to the number of antennas transmitting modulation signals simultaneously (that is, the number of modulation signals). It is to change the transmission power. That is, as shown in the basic configuration diagram of FIG. 1, the wireless transmission device 10 transmits a plurality of antennas T1 to Tn and modulated signals (modulated signals 1 to n) transmitted using the plurality of antennas T1 to Tn. There are provided modulation signal number setting means 11 for setting the number and transmission power changing means 12 for changing the transmission power of the modulation signals (modulation signal 1 to modulation signal n) according to the number of transmission modulation signals.

(Embodiment 1)
A feature of the present embodiment is that the transmission power of pilot symbols included in a modulation signal is changed according to the number of antennas (that is, the number of modulation signals) that simultaneously transmit modulation signals. Thereby, the quantization error of the pilot symbol in the receiving apparatus can be reduced.

  Specifically, if the number of modulated signals to be transmitted simultaneously is changed, the combined power (that is, dynamic range) of data symbols included in each modulated signal changes on the receiving side. The pilot symbol transmission power is changed to suit the range. Actually, the signal point arrangement when forming the pilot symbols is changed so that the ratio of the transmission power of the data symbols and the transmission power of the pilot symbols changes according to the number of transmission modulation signals.

(1) Principle First, the principle of the present embodiment will be described.

  As shown in FIG. 2, the modulated signals A and B are simultaneously transmitted from the two antennas T1 and T2, respectively, and the signals obtained by combining the modulated signals A and B by the two antennas R1 and R2 are received. A case where a signal is separated and demodulated will be described.

  In this case, the receiving side needs to demodulate each modulation signal by estimating four channel fluctuations h11 (t), h12 (t), h21 (t), and h22 (t) [where t indicates time]. is there. Therefore, it is necessary to provide pilot symbols such as symbols for signal detection, frequency offset estimation, control symbols for time synchronization, transmission method information symbols, radio wave propagation environment estimation symbols, etc. in modulated signals A and B.

  Incidentally, symbols necessary for demodulation, such as signal detection symbols, control symbols, and radio wave propagation environment symbols, can be collectively referred to as pilot symbols, unique words, preambles, etc. These are all called pilot symbols. The channel fluctuations h11 (t), h12 (t), h21 (t), and h22 (t) are estimated using radio wave propagation environment symbols.

  FIG. 3 shows a frame configuration example of the modulation signal A and the modulation signal B. FIG. 3 shows a frame configuration on the time-frequency axis when the modulation signals A and B are OFDM (Orthogonal Frequency Division Multiplexing) signals as an example. In FIG. 3, 101 is a symbol for signal detection, 102 is a frequency offset estimation, control symbol for time synchronization, 103 is a transmission method information symbol, 104 is a radio wave propagation environment estimation symbol, and 105 is a data symbol. .

  FIG. 4 shows signal point arrangement in the in-phase I-orthogonal Q plane of each symbol of FIG. In the figure, 201 indicates a signal point of the signal detection symbol 101, which is (I, Q) = (2.0, 0) or (−2.0, 0). Reference numeral 202 denotes signal points of the control symbol 102 and the radio wave propagation environment estimation symbol 104, and (I, Q) = (1.0, 1.0) or (−1.0, −1.0). . Reference numeral 203 denotes a signal point when the data symbol is QPSK (Quadrature Phase Shift Keying), and (I, Q) = (0.707, 0.707) or (0.707, −0.707) or ( −0.707, 0.707) or (−0.707, −0.707).

  FIGS. 5A and 5B show the signal point positions on the IQ plane of the modulation signal A and the modulation signal B having the frame configuration of FIG. 3 in a table. Here, the reason why different sequences are used in (a) and (b) at time i + 1 in FIG. 5 (corresponding to the control symbol 102 in FIG. 3) will be described. If the same sequence is used for each transmitting antenna, the PAPR (Peak-to-Average Power Ratio) increases when the signal is combined in phase on the receiving side, and the signal input to the receiver The dynamic range becomes unstable. Therefore, different sequences are used so as to reduce the PAPR. Here, the method of creating different sequences is not limited to the method of creating shown in FIG. For time i + 3 (corresponding to the radio wave propagation environment estimation symbol 104 in FIG. 3), a different series is used for the same reason.

  Next, as shown in FIG. 6, the modulation signal A, the modulation signal B, the modulation signal C, and the modulation signal D are simultaneously transmitted from the four antennas T1, T2, T3, and T4, respectively, and the four antennas R1, R2, and R3 are transmitted. , R4, a signal obtained by synthesizing modulated signals A, B, C, and D will be described, and these signals will be separated and demodulated.

  In this case, 4 × 4 = 16 channel fluctuations h11 (t), h21 (t), h31 (t), h41 (t),..., H44 (t) need to be estimated and demodulated on the receiving side. There is. Therefore, as in the case of the two antennas described above, modulation signals A, B, C, and D include symbols for signal detection, frequency offset estimation, control symbols for time synchronization, transmission method information symbols, and radio wave propagation. It is necessary to provide pilot symbols such as environment estimation symbols.

  FIG. 7 in which the same reference numerals are assigned to the parts corresponding to those in FIG. 3 shows the frame configuration of the modulated signal A, modulated signal B, modulated signal C, and modulated signal D.

  FIG. 8 shows signal point arrangement in the in-phase I-orthogonal Q plane of each symbol of FIG. In the figure, 401 indicates the signal point of the symbol 101 for signal detection, and (I, Q) = (4.0, 0) or (−4.0, 0). Reference numeral 402 denotes signal points of the control symbol 102 and the radio wave propagation environment estimation symbol 104, and (I, Q) = (2.0, 2.0) or (−2.0, −2.0). . Reference numeral 203 denotes a signal point when the data symbol is QPSK, and (I, Q) = (0.707, 0.707) or (0.707, −0.707) or (−0.707,0). .707) or (−0.707, −0.707).

  9 (a), 9 (b), 9 (c), and 9 (d) show the modulation signal A, the modulation signal B, the modulation signal C, and the modulation signal D in the frame configuration of FIG. The signal point positions in the IQ plane are shown in a table. Here, the reason why different sequences are used in (a) and (b) at time i + 1 in FIG. 9 (corresponding to the control symbol 102 in FIG. 7) will be described. When the same sequence is used for each transmission antenna, the PAPR becomes large when in-phase synthesis is performed on the receiving side, and the dynamic range of the signal input to the receiving apparatus becomes unstable. Therefore, different sequences are used so as to reduce the PAPR. Here, the method of creating the different series is not limited to the method of making shown in FIG. 9, but it is only necessary that the PAPR can be reduced. For time i + 3 (corresponding to the radio wave propagation environment estimation symbol 104 in FIG. 7), a different series is used for the same reason.

  FIG. 10 shows an example of waveforms on the time axis of the modulated signals when the modulated signals A and B are transmitted from the two antennas T1 and T2, respectively, as shown in FIGS. FIG. 10A shows the data symbol waveforms of the modulation signals A and B. FIG. FIG. 10B shows the waveform of the combined signal of the modulation signal A and the modulation signal B. FIGS. 10C and 10D show waveforms when a pilot symbol modulation signal is inserted into the combined signal of FIG. 10B.

  FIG. 11 shows an example of waveforms on the time axis of the modulation signals when the modulation signals A to D are transmitted from the four antennas T1 to T4, respectively, as shown in FIGS. FIG. 11A shows waveforms of data symbols of the modulation signals A, B, C, and D. FIG. 11B shows the waveform of the combined signal of the modulation signals A, B, C, and D. FIG. 11C and FIG. 11D are waveforms when a pilot symbol modulation signal is inserted into the combined signal of FIG. 11B.

  Next, features and effects of the wireless transmission method according to the present embodiment will be sequentially described.

  First, as is apparent from FIGS. 4 and 8, the first feature is that the maximum signal point amplitude of each pilot symbol (the amplitude at which the distance between the signal point and the origin is maximum) is the maximum signal of the modulation signal of the data symbol. That is, it is larger than the point amplitude. This makes it possible to accurately detect pilot symbols that are very important in data demodulation. This also makes it possible to bring the reception level of pilot symbols in the receiving apparatus closer to the reception level of data symbols. In other words, data symbols are generally transmitted from all antennas at the same time in order to increase the amount of data to be transmitted. However, pilot symbols place importance on the detection accuracy at the receiving apparatus, so that, for example, one data symbol is switched while switching the transmitting antenna. In many cases, each antenna is transmitted. Considering this, the reception level of the data symbol and the pilot symbol becomes closer when the maximum signal point amplitude of the pilot symbol is made larger than the maximum signal point amplitude of the data symbol as in this embodiment. Quantization error can be reduced.

  The second feature is that only the modulation signal A is transmitted (in this embodiment, only the signal detection symbol 101 is transmitted). The maximum signal point amplitude at time i is the pilot at another time. That is, it is larger than the maximum signal point amplitude of the symbol. Thereby, the reception level of only the pilot symbol of modulated signal A can be made equal to the reception level of the pilot symbol when modulated signal A and modulated signal B are multiplexed. That is, in the present embodiment, the maximum signal point amplitude of pilot symbols is increased as the number of multiplexed pilot symbols is decreased. Thereby, since the reception level of the pilot symbol can be made substantially the same, the quantization error of the pilot symbol in the receiving apparatus can be reduced. In other words, the first feature reduces the quantization error by making the reception levels of the data symbol and the pilot symbol equal, whereas the second feature makes the reception level of the pilot symbol equivalent. To reduce the quantization error.

  The third feature is that four transmission antennas T1 to T4 are used and four pilot antennas T1 to T4 are used instead of the pilot signal maximum signal point amplitude when two modulation signals A and B are transmitted using two transmission antennas T1 and T2. That is, the maximum signal point amplitude of the pilot symbol in the case of transmitting two modulated signals A to D is increased. As a result, the reception levels of the data symbol and the pilot symbol can be made closer, so that the quantization error in the receiving apparatus can be reduced.

  For example, as shown in FIGS. 4 and 8, the maximum signal point amplitude of the signal detection symbol 101 (FIGS. 3 and 7) is 2 when the number of transmitting antennas is 2 and two modulated signals are transmitted (FIG. 4). The signal point 201 of FIG. 8 is 2, whereas the number of transmission antennas is 4 and 4 signals are transmitted when 4 systems of modulated signals are transmitted (signal point 401 in FIG. 8). Similarly, the frequency offset, the control symbol 102 for synchronization, and the signal point amplitude of the radio wave propagation environment estimation symbol 104 are 2 when the number of transmitting antennas and two modulated signals are transmitted (signal point 202 in FIG. 4), 1 .414, whereas when the number of transmission antennas is 4 and four modulated signals are transmitted (signal point 402 in FIG. 8), 2.828.

  Here, when the modulation signal is transmitted from two antennas, the number of data symbols is two. However, when the modulation signal is transmitted from four antennas, the number of data symbols is four. On the other hand, as described above, considering that pilot symbols are not transmitted from all antennas (for example, transmitted from only one antenna), reception levels of data symbols and reception of pilot symbols are considered. In order to make the levels equal, it is necessary to increase the transmission power of pilot symbols as the number of antennas used increases. Focusing on this point, in the present embodiment, the larger the number of antennas used (that is, the number of modulated signals to be transmitted) is, the larger the pilot symbol transmission power is set, so that the reception levels of the data symbols and pilot symbols are combined. It is designed to reduce the error in the conversion.

  Next, operations and effects obtained from the features of the above-described embodiment will be described.

  First, a case where two modulation signals are transmitted with two transmission antennas will be described. As shown in FIG. 10A, the operation range of the data symbols of the modulated signals A and B is, for example, −128 to 128. Then, as shown in FIG. 10B, the waveform of the combined signal obtained by combining the data symbols of the two modulated signals A and B (the combined signal of the modulated signal A and the modulated signal B is received by the receiving antenna) The range is from -256 to 256. However, this value is not accurate. However, the operating range is greater than -128 to 128.

  10 (c) and 10 (d) show a signal detection symbol 101, a frequency offset, a control symbol 102 for synchronization, a transmission method information symbol 103, a radio wave propagation, and a combined signal of the data symbols in FIG. 10 (b). This shows a modulation signal when a pilot symbol modulation signal (pilot signal) such as the environment estimation symbol 104 is added. At this time, as shown in FIG. 10C, when the operation range of the combined signal of the data symbols is −256 to 256, the operation range of the pilot signal becomes −128 to 128. Since the quantization error in the analog / digital converter increases, the separation accuracy of the data symbol of the modulation signal A and the data symbol of the modulation signal B decreases, and the data symbol of the modulation signal A and the modulation signal B The demodulation accuracy of the data symbol is lowered.

  Focusing on this point, in the present embodiment, by operating the above feature points, the operating range of the combined data symbol signal and the operating range of the pilot signal are the same level as shown in FIG. Thus, the transmission power (maximum signal point amplitude) of the pilot symbols is appropriately selected according to the number of modulation signals and the like. For example, as shown in FIG. 10 (d), when the operating range of the combined data symbol signal is −256 to 256, the operating range of the pilot signal may be set to −256 to 256 to match this. .

  Next, a case where four systems of modulated signals are transmitted with four transmission antennas will be described. As shown in FIG. 11A, the operation range of the data symbols of the modulated signals A to D is set to, for example, −64 to 64. Then, as shown in FIG. 11 (b), the waveform of the synthesized signal obtained by synthesizing the data symbols of the four modulated signals A to D (received by the receiving antenna is a synthesized signal of the modulated signals A to D) has an operation range. -256 to 256. However, this value is not accurate. However, the operating range is larger than -64 to 64. Further, the ratio between the operating range of the combined signal and the operating range of each modulation signal is larger than when two modulation signals are transmitted by two transmission antennas. Here, when the ratio of the operating range of the combined signal and the operating range of each modulated signal is 2 when the modulated signal is transmitted in two systems with two transmitting antennas, the modulated signal is transmitted in four systems with four transmitting antennas. The ratio of the operation range of the combined signal to the operation range of each modulation signal is 4. In the present embodiment, paying attention to the difference in the ratio of the operation range, the operation of the third feature is performed.

  11 (c) and 11 (d) show a signal symbol 101, a frequency offset, a control symbol 102 for synchronization, a transmission method information symbol 103, a radio wave propagation, and a combined signal of the data symbols in FIG. 11 (b). This shows a modulation signal when a pilot symbol modulation signal (pilot signal) such as the environment estimation symbol 104 is added. At this time, as shown in FIG. 11C, the operation range of the combined signal of the data symbols is −256 to 256, whereas the operation range of the pilot signal becomes −64 to 64, Since the quantization error in the analog / digital converter increases, the separation accuracy of the data symbols of the modulation signals A to D decreases, and the demodulation accuracy of the data symbols of the modulation signals A to D decreases. .

  Focusing on this point, in the present embodiment, the operation of the above feature points is performed so that the operation range of the data symbol combined signal and the pilot signal becomes the same level as shown in FIG. In addition, the transmission power (maximum signal point amplitude) of the pilot symbol is appropriately selected according to the number of modulation signals and the like. For example, as shown in FIG. 11 (d), when the operating range of the combined data symbol signal is −256 to 256, the operating range of the pilot signal may be set to −256 to 256 to match this. .

  That is, in the present embodiment, by performing the operations of the first to third feature points, waveforms such as those shown in FIGS. 10 (d) and 11 (d) can be obtained. The quantization error in the analog / digital converter can be reduced. As a result, the accuracy of separating the data symbols of the modulated signals A and B or the modulated signals A to D is improved, and the reception quality of each modulated signal is improved.

  As described above, in the present embodiment, the reception quality of data at the receiving apparatus is improved by changing the pilot signal point arrangement in accordance with the change in the number of modulated signals to be transmitted. At this time, as the number of modulated signals to be transmitted increases, the effect of the pilot symbol can be further enhanced by increasing the pilot symbol signal point amplitude.

  Here, the signal detection symbol 101 has been described as an example of a pilot symbol that exists only in the modulated signal A (that is, a pilot symbol that is not multiplexed), but naturally the control symbol 102 and the radio wave propagation environment estimation symbol 104 are multiplexed. Pilot symbols that are not converted may be used. That is, the multiplexing method is not limited to that shown in FIG. 3 or FIG. 7, and is broadly effective when the number of multiplexed pilot symbols is small compared to data symbols. This specific example will be described in detail in Embodiment 3.

(2) Configuration FIG. 12 shows a configuration of radio transmitting apparatus 500 in the present embodiment.

  The data series generation unit 501 receives the transmission digital signal S1 and the frame configuration signal S2, and based on the frame configuration signal S2, transmits the transmission digital signal S3A of the modulation signal A, the transmission digital signal S3B of the modulation signal B, and the modulation signal C. The transmission digital signal S3C and the transmission digital signal S3D of the modulation signal D are output.

  Each of modulation sections 502A to 502D receives transmission digital signals S3A to S3D of modulation signals A to D and frame configuration signal S2, and outputs transmission baseband signals S4A to S4D according to frame configuration signal S2.

  Each of the serial / parallel conversion units 503A to 503D receives the transmission baseband signals S4A to S4D and outputs parallel signals S5A to S5D. Inverse Fourier transform units (idft) 504A to 504D each receive parallel signals S5A to S5D and output parallel signals S6A to S6D after inverse Fourier transform. Radio units 505A to 505D each receive parallel signals S6A to S6D after inverse Fourier transform, and output transmission signals S7A to S7D.

  The power amplifying units 506A to 506D receive the transmission signals S7A to S7D, respectively, and output amplified transmission signals S8A to S8D. The amplified transmission signals S8A to S8D are output as radio waves from the antennas T1 to T4, respectively.

  Frame configuration signal generation section 507 receives transmission method request information S10 and modulation scheme request information S11 as input, determines a transmission method and modulation scheme, and outputs information about the frame configuration including the information as frame configuration signal S2.

  FIG. 13 shows the configuration of each of the modulation units 502A to 502D. Since the modulation units 502A to 502D have the same configuration, FIG. 13 representatively shows the configuration of the modulation unit 502A.

  Data symbol mapping section 510 receives transmission digital signal S3A and frame configuration signal S2, performs mapping based on the modulation scheme of the modulation scheme information included in frame configuration signal S2, and outputs data symbol transmission baseband signal S20. .

  Transmission method information symbol mapping section 511 receives frame configuration signal S2 as input, and outputs transmission baseband signal S21 of the transmission method information symbol as a symbol indicating transmission method and modulation method information included in frame configuration signal S2.

  Pilot symbol mapping section 512 receives frame configuration signal S2 as input, performs mapping for generating a pilot signal corresponding to the transmission method based on information on the transmission method included in frame configuration signal S2, and transmits a pilot symbol transmission base. The band signal S22 is output.

  The signal selection unit 513 receives a data symbol transmission baseband signal S20, a transmission method information symbol transmission baseband signal S21, a pilot symbol transmission baseband signal S22, and a frame configuration signal S2, and is included in the frame configuration signal S2. According to the timing information, one of a data symbol transmission baseband signal S20, a transmission method information symbol transmission baseband signal S21, and a pilot symbol transmission baseband signal S22 is selected, and the selected signal is output as a transmission baseband signal S4A. To do.

  FIG. 14 shows the configuration of pilot symbol mapping section 512. The pilot symbol mapping unit 512 includes a pilot symbol generation unit 520 for the number of transmission antennas 520 and a pilot symbol generation unit 521 for the number of transmission antennas 4 and inputs the frame configuration signal S2 to each of the pilot symbol generation units 520 and 521. The pilot symbol generation unit 520 for the number of transmission antennas 2 generates a pilot symbol having a signal point arrangement such as signal points 201 and 202 in FIG. 4 according to the frame configuration signal S2, and generates this pilot symbol baseband signal S30. Output as. On the other hand, the pilot symbol generating unit 521 for the number of transmitting antennas 4 generates pilot symbols having signal point arrangements such as signal points 401 and 402 in FIG. 8 according to the frame configuration signal S2, and uses the pilot symbols as pilot symbols. Is output as a baseband signal S31. The signal selection unit 522 selects one of the pilot symbol baseband signals S30 and S31 according to the transmission modulation signal number information included in the frame configuration signal S2, and outputs it as the transmission baseband signal S22. Thereby, the transmission power of the pilot symbol can be changed according to the number of transmission modulation signals.

  FIG. 15 shows the configuration of radio receiving apparatus 600 in the present embodiment.

  The radio units 601A to 601D receive the received signals K1A to K1D and the frequency offset estimation signal K10 received by the antennas R1 to R4, respectively, and perform frequency control and analog / digital conversion processing based on the frequency offset estimation signal K10. Reception baseband signals K2A to K2D are output.

  The Fourier transform units (dft) 602A to 602D each receive the received baseband signals K2A to K2D and the timing signal K11, and output the received baseband signals K3A to K3D after the Fourier transform.

  The transmission path estimation units 603A to 603D for the modulated signals A, B, C, and D receive the received baseband signals K3A to K3D and the timing signal K11 after the Fourier transform, and output transmission path estimation signals K4A to K4D. .

  Demodulation, frequency offset estimation, and transmission method detection section 604 receives received baseband signals K3A to K3D and transmission path estimation signals K4A to K4D after Fourier transform, estimates a frequency offset, and uses frequency offset estimation signal K10 as input. In addition to outputting, the transmission method is identified, and the data is demodulated to output received digital signals K5A to K5D corresponding to the modulated signals A to D, respectively.

  The transmission method / modulation method determination unit 605 receives the received digital signals K5A to K5D corresponding to the modulation signals A to D, calculates a frame error rate, a packet loss rate, a bit error rate, and the like, and based on the calculation results The transmission method and modulation method requested to the communication partner are determined and output as request information K12. That is, the request information K12 includes the transmission method request information S10 and the modulation scheme request information S11 described above with reference to FIG. 12, and the transmission method request information S10 indicates whether the modulation signals A and B are transmitted from the two antennas T1 and T2. This is information for instructing whether to transmit modulated signals A to D from the antennas T1 to T4. The modulation scheme request information S11 is information indicating whether the data symbol is modulated by a QPSK (Quadrature Phase Shift Keying) scheme or a 16-value QAM (Quadrature Amplitude Modulation) scheme.

  The signal detection / synchronization unit 606 receives the received baseband signal K2A, performs signal detection based on the signal detection symbol 101 (FIGS. 3 and 7) included in the received baseband signal K2A, performs time synchronization, The timing signal K11 is output.

  FIG. 16 shows the configuration of each of the wireless units 601A to 601D. Since each of the wireless units 601A to 601D has the same configuration, FIG. 16 representatively shows the configuration of the wireless unit 601A.

  Gain control section 610 receives reception signal K1A and outputs reception signal K20 after gain control. The quadrature demodulator 611 receives the received signal K20 after gain control, and outputs the in-phase component K21 and the quadrature component K22 of the received quadrature baseband signal.

  The analog / digital conversion unit 612 receives the in-phase component K21 of the received quadrature baseband signal and outputs the in-phase component digital signal K23 of the received quadrature baseband signal. The analog / digital conversion unit 613 receives the quadrature component K22 of the received quadrature baseband signal and outputs the quadrature component digital signal K24 of the received quadrature baseband signal.

(3) Operation Next, operations of the wireless transmission device 500 configured as shown in FIGS. 12 to 14 and the wireless reception device 600 configured as shown in FIGS. 15 and 16 will be described.

  The wireless transmission device 500 responds to the transmission method request information S10 requested from the wireless reception device 600 (the wireless transmission device 500 receives the transmission method request information S10 and the modulation method request information S11 from a not-shown receiving unit). Switching is made between transmitting two modulation signals A and B using the two antennas T1 and T2 or transmitting four modulation signals A to D using the four antennas T1 to T4. Specifically, when the transmission method of the wireless reception device 600, the frame error rate, the packet loss rate, the bit error rate, etc. at the modulation scheme determination unit 605 are bad, the two antennas T1 and T2 are set according to the transmission method request information S10. It is required to transmit two modulated signals A and B, and in a good case, it is required to transmit four modulated signals A to D using four antennas T1 to T4.

  The number of transmission modulation signals corresponding to the transmission method request information S10 is set by the frame configuration signal generation unit 507 and the modulation units 502A to 502D as the modulation signal number setting unit 11 (FIG. 1). Specifically, when transmitting two modulation signals A and B using two antennas T1 and T2 based on the frame configuration signal S2 generated by the frame configuration signal generation unit 507, the modulation unit 502A, 502B operates, and the modulation units 502C and 502D stop operating. On the other hand, when the four modulation signals A to D are transmitted using the four antennas T1 to T4, all the modulation units 502A to 502D operate.

  In addition, when two modulated signals A and B are transmitted using two antennas T1 and T2, pilot symbol mapping section 512 as transmission power changing means 12 (FIG. 1) generates pilot symbols for two transmission antennas. The pilot symbol baseband signal S30 obtained by the unit 520 is selected. On the other hand, when transmitting four modulation signals A to D using four antennas T1 to T4, the pilot symbol mapping unit 512 is the pilot obtained by the pilot symbol generation unit 521 for the number of transmission antennas 4. A symbol baseband signal S31 is selected. In this way, radio transmitting apparatus 500 changes the transmission power of pilot symbols according to the number of transmission modulation signals.

  As a result, as shown in FIG. 10 (d) and FIG. 11 (d), radio receiving apparatus 600 receives a received signal in which the operating range of the combined data symbol signal and the operating range of the pilot signal are substantially the same. be able to. As a result, it is possible to reduce the quantization error when the quantization is performed in the analog / digital conversion units 612 and 613 (FIG. 16).

  Here, the operation of the radio units 601A to 601D will be described in detail. As shown in FIG. 16, each radio unit 601A (601B to 601D) adjusts the gain of the reception signal K1A (K1B to K1D) by the gain control unit 610. However, at this time, it is difficult to perform gain control in units of one symbol or one frame (for example, one frame of 100 symbols).

  For example, as shown in FIG. 10B, it is assumed that gain control is performed so that the operation range of the combined signal of the modulation signal A and the modulation signal B is −256 to 256. Then, when a pilot signal having an operation range of −128 to 128 is input as shown in FIG. 10C, the operation range of this pilot signal is instantaneously changed from −256 to 256 as shown in FIG. It is difficult to control the gain.

  However, in the present embodiment, as described above, when the operating range of the combined signal is −256 to 256, the pilot signal signal point is arranged and transmitted so that the operating range of the pilot signal becomes the same level as this. Therefore, it is possible to receive pilot symbols whose operation range is almost the same as the operation range of data symbols. The same applies to the case where four modulation signals A to D are transmitted by four transmission antennas.

  Incidentally, if the level of the signal input to the analog / digital conversion units 612 and 613 is small, generally the quantization error becomes large. For example, if the operating range of the pilot signal is small as shown in FIGS. 10C and 11C, the pilot signal quantization error becomes large. Then, since each of the transmission path estimation units 603A to 603D (FIG. 15) performs transmission path estimation using the pilot signal and outputs the transmission path estimation signals K4A to K4D, the estimation accuracy deteriorates due to the quantization error. become. Similarly, demodulation, frequency offset estimation, and transmission method detection section 604 (FIG. 15) estimates the frequency offset using the pilot signal and outputs frequency offset estimation signal K10, so that the estimation accuracy is the quantization error. Will deteriorate. As a result of the above-described deterioration in estimation accuracy, the accuracy of data demodulation deteriorates, resulting in a deterioration in reception quality.

  In radio transmitting apparatus 500 of the present embodiment, the maximum signal point amplitude of each pilot symbol is made larger than the maximum signal point amplitude of data symbols in order to suppress this deterioration. In addition, the maximum signal point amplitude at time i during which only modulated signal A is transmitted is made larger than the maximum signal point amplitude of pilot symbols at other times. Furthermore, the pilot signal point arrangement when transmitting four modulation signals from four transmission antennas and the pilot signal point arrangement when transmitting two modulation signals from two transmission antennas are changed. .

  Here, changing the pilot symbol signal point arrangement means changing the ratio of the pilot symbol signal point amplitude to the QPSK signal point amplitude when the data symbol modulation method is QPSK or the pilot symbol signal. This corresponds to changing the ratio between the point amplitude and the maximum signal point amplitude of the modulation system. As a result, the ratio between the transmission power of the data symbols and the transmission power of the pilot symbols can be changed according to the number of transmission modulation signals.

  Incidentally, the signal point amplitude means the distance between the origin and the signal point in the in-phase I-orthogonal Q plane. Increasing the pilot symbol signal point amplitude means increasing the ratio of the pilot symbol signal point amplitude to the modulation method maximum signal point amplitude.

(4) Effect Thus, according to the present embodiment, in the method of changing the number of modulated signals to be transmitted simultaneously, the signal of the pilot symbol is adapted to the combined signal level of the data symbols according to the number of modulated signals to be transmitted. By adjusting the level, the pilot symbol quantization error on the receiving side can be reduced. As a result, estimation accuracy of radio wave propagation environment estimation using pilot symbols, time synchronization accuracy, and frequency offset estimation accuracy are improved, so that data reception quality is improved.

(Embodiment 2)
The feature of this embodiment is that the average transmission power of each modulated signal is changed when the number of antennas that transmit modulated signals (that is, the number of modulated signals) changes. Thereby, especially the quantization error of each modulated signal immediately after switching the number of transmitting antennas can be reduced.

(1) Principle First, the principle of the present embodiment will be described.

  FIG. 17 and FIG. 18 show changes in a general received waveform when the number of modulated signals transmitted from a plurality of antennas is switched. FIG. 17 shows a case where the number of modulation signals to be transmitted (that is, the number of transmission antennas) is switched from 2 to 4, and FIG. 18 shows a case where the number of modulation signals to be transmitted (the number of transmission antennas) is switched from 4 to 2. As is apparent from FIG. 17, when switching is performed so that the number of modulation signals is increased, the number of modulation signals to be combined is also increased, so that the operating range of received signals is increased after switching the number of antennas. On the contrary, as can be seen from FIG. 18, when the number of modulation signals is switched to be small, the number of modulation signals to be synthesized is also small, so the operating range of the received signal is small after switching the number of antennas. .

  In this embodiment, paying attention to this point, transmission power control is performed so that the combined signal level of the modulated signal immediately after switching the number of antennas is substantially equal to the combined signal level of the modulated signal before switching the number of antennas. To do. Here, in general, the radio transmission apparatus performs closed-loop transmission power control for controlling transmission power using a TPC (Transmit Power Control) bit transmitted from a partner station, so the number of transmission antennas is switched. When the combined signal level of the modulated signal changes, the transmission power of the modulated signal is controlled so that the combined signal level fluctuates the desired operating range. The gain control unit on the receiving side adjusts the gain so that the combined signal level fluctuates within a desired operating range. However, the transmission power control and the received signal gain control require a certain response time until the received signal level is converged to a desired operating range.

  Therefore, in the present embodiment, the combined signal level of the modulated signal immediately after switching the number of antennas is forcibly changed immediately after switching the number of antennas so that it becomes substantially equal to the combined signal level of the modulated signal before switching the number of antennas.

  In FIG. 19, four modulation signals A to D are transmitted using four transmission antennas T1 to T4 from a state where two modulation signals A and B are transmitted using two transmission antennas T1 and T2. An outline of transmission power control of each modulation signal A to D in the present embodiment when switching to a state to be performed will be shown. First, as shown in FIG. 19A, it is assumed that a modulated signal A having an average transmission power of 1.0 W is transmitted from the antenna T1, and a modulated signal B having an average transmission power of 1.0 W is transmitted from the antenna T2. . Then, switching from the transmission method of transmitting the two modulation signals A and B by the two transmission antennas T1 and T2 to the transmission method of transmitting the four modulation signals A to D using the four transmission antennas T1 to T4. Suppose. At this time, modulated signals A to D having an average transmission power of 0.5 W are transmitted from antennas T1 to T4, respectively. As a result, as shown in FIG. 20, the combined signal level of modulated signals A to D immediately after switching the number of antennas can be made equal to the combined signal level of modulated signals A and B before switching the number of antennas.

  In FIG. 21, four modulation signals A to D are transmitted using four transmission antennas T1 to T4, and two modulation signals A and B are transmitted using two transmission antennas T1 and T2. An outline of transmission power control of each modulation signal A to D in the present embodiment when switching to a state to be performed will be shown. First, as shown in FIG. 21A, it is assumed that modulated signals A to D having an average transmission power of 0.5 W are transmitted from the antennas T1 to T4, respectively. Then, switching from a transmission method of transmitting four modulation signals A to D by four transmission antennas T1 to T4 to a transmission method of transmitting two modulation signals A and B using two transmission antennas T1 and T2 Suppose. At this time, modulated signals A and B with an average transmission power of 1.0 W are transmitted from the antennas T1 and T2, respectively. As a result, as shown in FIG. 22, the combined signal level of modulated signals A and B immediately after switching the number of antennas can be made equal to the combined signal level of modulated signals A to D before switching the number of antennas.

  Furthermore, in this embodiment, immediately after switching the number of antennas, the transmission power of the modulation signal is set so that the combined signal level of the modulation signal to be transmitted is equivalent to the combined signal level of the modulation signal transmitted before the number of antennas is switched. In addition, the transmission level of each modulation signal is gradually returned to the transmission level of each modulation signal before switching the number of antennas after switching the number of antennas. Thereby, the demodulation accuracy of the modulation signal can be further improved.

  This transmission power control will be described with reference to FIGS. In FIG. 23, four modulation signals A to D are transmitted using four transmission antennas T1 to T4 from a state where two modulation signals A and B are transmitted using two transmission antennas T1 and T2. An example of transmission power control of each modulation signal A to D when switching to a state to perform is shown. As shown in FIG. 23, immediately after switching the number of antennas, the average transmission power of the modulated signal transmitted from each antenna T1 to T4 is changed to 0.5W. Then, with the passage of time, the average transmission power is changed to 0.75 W and 1.0 W.

  Incidentally, even if the average transmission power of each modulation signal A to D is 1 W as a power amplifier that amplifies the average transmission power of each modulation signal A to D, the frequency spectrum is not distorted as shown in FIG. Assume that such a transmission power amplifier is used. Then, even if the number of modulated signals to be transmitted is 2 systems or 4 systems, even if the average transmission power is 1 W, the frequency spectrum in which distortion is generated as shown in FIG. A frequency spectrum without distortion as shown in FIG. 25A can be obtained.

  In FIG. 24, two modulation signals A and B are transmitted using two transmission antennas T1 and T2 from a state where four modulation signals A to D are transmitted using four transmission antennas T1 to T4. An example of transmission power control of each modulation signal A to D when switching to a state to perform is shown. As shown in FIG. 24, immediately after switching the number of antennas, the average transmission power of the modulation signals transmitted from the antennas T1 and T2 is changed to 1.0 W. Then, with the passage of time, the average transmission power is changed to 0.75 W and 0.5 W.

  Here, as shown in FIG. 23, immediately after the number of transmission antennas increases, the average transmission power of each modulation signal is sharply reduced, and thereafter the average transmission power of each modulation signal is returned to before switching as time passes. The average transmission power is controlled so that a good SIR (Signal to Interference Ratio) can be obtained at the receiver, and the reception quality of each modulated signal is improved by returning to the original average transmission power. is there. In consideration of the power consumption and distortion of the power amplifier, it is better to set to an appropriate average power. Therefore, it is better to return the average transmission power to the original average transmission power. For the same reason, the average transmission power of each modulated signal is suddenly increased immediately after the number of transmission antennas is decreased as shown in FIG. 24, and then the average transmission power of each modulated signal is returned to the level before switching as time passes. is there.

  In addition, when restoring the average transmission power of each modulation signal that has been drastically lowered in this way, the gain control unit of the receiving apparatus follows the gain control by gradually returning it over a period of time. It becomes possible to fit the signal within the operating range of the analog / digital converter. Also, when restoring the average transmission power of each modulation signal that has been suddenly increased, it gradually returns over a period of time so that the gain control unit of the receiver follows this and the signal after gain control is converted to analog. -It can be raised to the extent that no quantization error occurs in the digital converter. That is, the speed at which the average transmission power of each modulation signal that has been suddenly lowered or suddenly increased simultaneously with the switching of the analog number may be selected according to the operating speed of the gain control unit.

(2) Configuration FIG. 26, in which parts corresponding to those in FIG. 12 are assigned the same reference numerals, shows the configuration of radio transmitting apparatus 700 in the present embodiment. Here, the description of the part corresponding to FIG. 12 is omitted.

  The gain control units 701A to 701D receive the transmission signals S7A to S7D and the frame configuration signal S2, respectively, detect information indicating that the transmission method is switched from the transmission method information included in the frame configuration signal S2, and switch the transmission method. At this time, the gain control is performed, and the transmission signals S10A to S10D after the gain control are output.

  That is, in this embodiment, the gain control units 701A to 701D function as the transmission power changing unit 12 in FIG. 1, and change the average transmission power of each modulation signal according to the number of transmission modulation signals. . Actually, as described above, the average transmission power of each modulation signal is rapidly decreased simultaneously with the increase in the number of transmission modulation signals, while the average transmission power of each modulation signal is rapidly increased while the number of transmission modulation signals is decreased. It has become.

(3) Operation Next, the operation of the wireless transmission device 700 configured as shown in FIG. 26 will be described.

  The radio receiving apparatus 600 shown in FIG. 15 requests the radio transmitting apparatus 700 in FIG. 26 to change the transmission method, and the radio transmitting apparatus 700 in FIG. It is the same as that of description.

  Gain control sections 701A to 701D receive transmission signals S7A to S7D and frame configuration signal S2, respectively, detect information indicating that the transmission method is switched from the transmission method information included in frame configuration signal S2, and switch the transmission method. The gain control is performed, and the transmission signals S10A to S10D after the gain control are output.

  At this time, the gain to be amplified is a coefficient such that the average transmission power is as shown in FIGS. Further, as shown in FIGS. 23 and 24, gain control may be performed so that the average transmission power is gradually restored after the transmission method is switched.

  Here, the operation range of the radio units 601A to 601D in the radio receiving apparatus 600 of FIG. 15, more specifically, the analog / digital conversion units 612 and 613 of FIG. 16, is, for example, an analog / digital converter of 14 bits. Assuming that the digital conversion units 612 and 613 are using it, −8192 to 8192. The gain control unit 610 controls the gain of the received signal so that the level of the received signal K20 after gain control falls within this operating range. This is why the operating range of the combined signal of the modulated signal before switching the number of transmitting antennas shown in FIGS. 17 and 18 is just within the range of −8192 to 8192.

  However, immediately after switching the number of transmission antennas, the gain control unit 610 cannot follow the level fluctuation of the composite signal of the modulation signal, and performs gain control so that the operation range of the composite signal is just within the range of −8192 to 8192. It is not possible. For example, assuming that each modulation signal is transmitted with the same average transmission power before and after switching the number of transmission antennas, when the number of transmission antennas (that is, the number of transmission modulation signals) is increased from 2 to 4, shown in FIG. As described above, the operation range of the combined signal of the four modulated signals after switching the transmission antenna is from −32768 to 32768, which exceeds the operation range of the analog / digital conversion units 612 and 613 from −8192 to 8192, resulting in a quantization error. Will occur. Similarly, when the number of transmission antennas (the number of transmission modulation signals) is reduced from 4 to 2, as shown in FIG. 18, the operation range of the combined signal of the two modulation signals after switching the transmission antenna is -256 to 256. Therefore, the operation range is considerably smaller than −8192 to 8192, which is the operation range of the analog / digital conversion units 612 and 613, and a quantization error occurs.

  However, in the configuration of the present embodiment described above, the average transmission power of each modulation signal is drastically reduced at the same time as the number of transmission modulation signals increases, while the average transmission power of each modulation signal is drastically reduced at the same time as the number of transmission modulation signals decreases. 20 and FIG. 22, the combined signal level of the modulated signal immediately after switching the number of antennas is not dependent on the gain control unit 610, and the operations of the analog / digital conversion units 612 and 613 are performed. The range can be adjusted from -8192 to 8192.

  As a result, the quantization error in the analog / digital conversion units 612 and 613 immediately after switching the number of transmission modulation signals can be reduced. Accordingly, since frequency offset estimation, transmission path estimation accuracy, and demodulation accuracy can be ensured, it is possible to avoid deterioration in data reception quality immediately after switching the number of modulation signals.

(4) Effect Thus, according to the present embodiment, when the number of modulation signals transmitted simultaneously is switched in the method of changing the number of modulation signals transmitted simultaneously, the average transmission of each modulation signal according to the number of transmission modulation signals By switching the power, it is possible to reduce the quantization error that occurs during the analog-digital conversion of the received signal, so that the reception quality can be improved.

(Embodiment 3)
In the present embodiment, an actual radio system related to the method of changing the transmission power of pilot symbols and modulation signals according to the number of antennas (number of modulation signals) that simultaneously transmit modulation signals described in the first and second embodiments. A specific example in the case of applying to will be described. In particular, in the present embodiment, a method for stabilizing gain control by increasing the gain control time of automatic gain control AGC (Automatic Gain Control) in the receiving apparatus will be described.

In a general receiving device, when it is detected that a signal has been input to the receiving device, AGC is performed in accordance with the input signal level so that the received signal falls within the dynamic range of an A / D converter that performs analog-digital conversion. . As a method to stabilize the gain control by AGC,
(I) Stabilize the dynamic range of the signal input to the receiver. (Ii) Take longer time for gain control. Regarding (i), Embodiments 1 and 2 have shown that it can be realized by increasing the transmission power of pilot symbols included in the modulation signal or by forcibly changing the transmission power of the modulation signal. In the present embodiment, a pilot symbol transmission power changing method that can realize (i) while realizing (i) will be described.

  As a MIMO system in the present embodiment, modulated signal A, modulated signal B, modulated signal C, and modulated signal D are simultaneously transmitted from four antennas T1, T2, T3, and T4 shown in FIG. , R2, R3, and R4, a case where a signal obtained by combining modulated signals A, B, C, and D is received, and these signals are separated and demodulated will be described.

  In this embodiment, “(1) Principle of Embodiment 1” and “(4) Effect of Embodiment 1” are different from Embodiment 1, but “Embodiment 1” is different. Since (2) Configuration ”and“ (3) Operation of Embodiment 1 ”are the same as those described in Embodiment 1, (2) Configuration of Embodiment 1” and “(1) of Embodiment 1 The description of “3) Operation” is omitted.

  On the receiving side, 4 × 4 = 16 channel fluctuations h11 (t), h21 (t), h31 (t), h41 (t),..., H44 (t) shown in FIG. There is a need. Therefore, it is necessary to provide pilot symbols such as a signal detection symbol, a gain control symbol, a frequency offset estimation symbol, a transmission method information symbol, a radio wave propagation environment estimation symbol, etc. in the modulated signals A, B, C, and D. Here, the time synchronization can be obtained by using a signal detection symbol, a frequency offset estimation symbol, a correlation between guard intervals, and the like, and thus is not added to the following description.

  FIG. 27 shows a frame configuration example of the modulation signals A, B, C, and D. FIG. 27 shows a frame configuration on the time-frequency axis when the modulated signals A, B, C, and D are OFDM signals as an example. In FIG. 27, 2701 is a symbol for signal detection (corresponding to 101 in FIG. 7), 2702 is a symbol for gain control (corresponding to 102 in FIG. 7), and 2703 is a symbol for estimating frequency offset ( 2704 is a transmission method information symbol (corresponding to 103 in FIG. 7), 2705 is a radio wave propagation environment estimation symbol (corresponding to 104 in FIG. 7), and 2706 is a data symbol (corresponding to 105 in FIG. 7). ).

  Among pilot symbols, signal detection symbol 2701, gain control symbol 2702, frequency offset estimation symbol 2703, and transmission method information symbol 2704 are present only in modulated signal A (that is, symbols that are not multiplexed), thereby enabling communication. It is configured to do. The characteristics of this configuration will be described below.

  When the frequency offset is estimated by the receiving apparatus, when the frequency offset estimation symbol 2703 is transmitted from a plurality of transmitting antennas (at least two of T1, T2, T3, and T4), the four receiving antennas R1, R2, R3, and R4 are transmitted. Then, these frequency offset estimation symbols 2703 are multiplexed and received. In that case, it is necessary to accurately perform channel estimation and to separate received signals.

  On the other hand, if the frequency offset estimation symbol 2703 is transmitted from only one transmission antenna T1 as in the modulation signal A of FIG. 27, it is not necessary to separate the reception signal by the reception device. As a result, the frequency offset can be estimated more easily and more accurately.

  For the same reason, the transmission method information symbol 2704 is transmitted from only one transmission antenna T1. At this time, gain control is performed using gain control symbol 2702 to reduce the quantization error of frequency offset estimation symbol 2703 and transmission method information symbol 2704.

  In contrast, the radio wave propagation environment estimation symbol 2705 is transmitted from each of the transmission antennas T1, T2, T3, and T4. This is because, as described above, it is necessary to estimate 4 × 4 = 16 channel fluctuations shown in FIG. 6 for demodulation on the receiving side.

  Next, description of the method of “(ii) increasing the time of gain control” while using “(i) stabilizing the dynamic range of the signal input to the receiving apparatus” using pilot symbols and the effect thereof in the present embodiment To state.

  The method for increasing the pilot symbol power in order to stabilize the dynamic range of the signal input to the receiving apparatus has been described in the first embodiment. Consider applying this method to the modulation signals A, B, C, and D in FIG.

  FIG. 28 shows an example of a waveform on the time axis of the modulation signal when the modulation signals A, B, C, and D shown in FIG. 27 are transmitted. FIG. 28A shows the waveforms of pilot symbols and data symbols of modulated signals A, B, C, and D. FIG. 28B shows the waveform of the combined signal of the modulation signals A, B, C, and D. Here, the time i in FIG. 28B is a time corresponding to the time i at which each symbol is transmitted.

  As shown in FIG. 28A, the operation ranges of pilot symbols and data symbols of the modulated signals A, B, C, and D are set to, for example, −64 to 64. Then, a signal obtained by synthesizing the four modulation signals A, B, C, and D has an operation range from −64 from time i to i + 3 (time during which only the modulation signal A is transmitted) as shown in FIG. 64, from time i + 4 to i + 7 (time during which modulated signals A, B, C, and D are transmitted), the operation range is from −256 to 256. However, this value is not accurate. However, the operation range from time i + 4 to i + 7 is larger than the operation range from time i to i + 3. Here, the ratio between the operating range of the combined signal and the operating range of each modulated signal when the four transmission antennas transmit four lines of modulated signals is 4. In the present embodiment, the operation range from time i to i + 3 (time during which only modulated signal A is transmitted) and time i + 4 to i + 7 (time during which modulated signals A, B, C, and D are transmitted). Focusing on the ratio of the operating range, and bringing this ratio close to 1 realizes the above-mentioned “(ii) Take longer gain control time”.

  In the wireless communication in the configuration of FIG. 28, time i to i + 3 (time when only modulated signal A is transmitted) and time i + 4 to time i + 7 (time when modulated signals A, B, C, and D are transmitted). You can communicate independently.

  From time i to i + 3, after detecting the signal at time i, the gain control symbol 2702 (time i + 2) and the gain control symbol 2702 (time i + 3) are matched to the operating range of the frequency offset estimation symbol 2703 (time i + 2) and transmission method information symbol 2704 (time i + 3). Set the operating range of time i + 1). For example, as shown in FIG. 28, three symbols 2702, 2703, and 2704 are transmitted with the same operation range (−64 to 64).

  After time i + 4, the radio wave propagation environment estimation symbol 2705 (time i + 5) and the data symbol 2706 (time i + 6, i + 7) are combined so that the operation range of the combined signal on the receiving side is equal to the time i + 3. The operating range of the gain control symbol 2702 (time i + 4) is set in accordance with the operating range. For example, as shown in FIG. 28, the operation ranges of the modulation signals A, B, C, and D are made equal (−64 to 64). At this time, since AGC for symbols after time i + 5 is performed using gain control symbol 2702 at time i + 4, it is desired to increase the time of gain control symbol 2702 in order to perform stable AGC. However, the longer the time is allocated to the gain control symbol 2702, the lower the data transmission efficiency.

  In addition, as described with reference to FIG. 11 in the first embodiment, the synthesized signal shown in FIG. 28 (b) has a large operating range when changing from time i + 3 to i + 4. The quantization error at 1 increases, and the data symbol separation accuracy and demodulation accuracy of the modulated signals A, B, C, and D decrease. In response to the problem that “the operating range fluctuates greatly” described here, in Embodiment 1, “the signal level of the pilot symbol is adjusted to match the combined signal level of the data symbols according to the number of modulated signals to be transmitted. By doing so, the method of reducing the pilot symbol quantization error on the receiving side has been described.

  Therefore, as a method of increasing the AGC gain control time while reducing the quantization error using the method of the first embodiment, the operation range of the time during which only the modulation signal A is transmitted (from time i to i + 3) The ratio of the operation range of the time (time i + 4 to i + 7) during which the modulation signals A, B, C, and D are transmitted is made close to 1. As a result, the symbol of the time during which only the modulated signal A is transmitted can also be used for AGC gain control, and it is possible to realize the above “(ii) Take longer gain control time”.

  In FIG. 29, the transmission power of the pilot symbols during the time when only the modulated signal A is transmitted (from time i to i + 3) is shown as the time during which the modulated signals A, B, C and D are transmitted (from time i + 4 to i + 7). An example of the waveform of the modulated signal on the time axis when the transmission power of the symbol is made larger is shown.

  FIG. 29A shows waveforms of pilot symbols and data symbols of modulated signals A, B, C, and D. FIG. 29B shows the waveform of the combined signal of the modulation signals A, B, C, and D. Here, the time i in FIG. 29B is a time corresponding to the transmitted time i. As shown in FIG. 29 (a), the operation range of the pilot symbols in the time (only from time i to i + 3) during which only the modulated signal A is transmitted is set to −256 to 256, for example. In addition, the operation range of the symbols during the time when the modulation signals A, B, C, and D are transmitted (from time i + 4 to i + 7) is, for example, −64 to 64.

  Then, as shown in FIG. 29 (b), the synthesized signal has an operation range of −256 to 256 during the time when only the modulated signal A is transmitted (from time i to i + 3), and the modulated signals A, B, C, and D are The operation range of the transmission time (from time i + 4 to i + 7) is also −256 to 256, and the ratio of the two operation ranges is 1. However, this value is not accurate. However, as compared with the case of FIG.

  In this way, by appropriately changing the transmission power of the pilot symbols during the time when only the modulated signal A is transmitted (the time when only the single antenna is transmitted) so as to stabilize the operation range of the combined signal, The time required for AGC gain control can be lengthened, and the quantization error in the A / D converter of the receiving apparatus can be reduced. As a result, the data symbol separation accuracy and the reception quality of each modulation signal A, B, C, D are improved.

  At this time, signal detection symbol 2701 (time i), gain control symbol 2702 (time i + 1), frequency offset estimation symbol 2703 (time i + 2), and transmission method information symbol 2704 (time) transmitted from only one antenna. i + 3) includes a signal detection symbol 2701 (time i), a gain control symbol 2702 (time i + 1), a frequency offset estimation symbol 2703 (time i + 2), and a transmission method information symbol included in the modulation signal A of FIG. Since it becomes larger than the transmission power of 2704 (time i + 3), the estimation accuracy of these four symbols 2701 to 2704 can be improved, and the quantization error can be reduced.

  Thus, according to the present embodiment, in the method of changing the number of modulation signals to be transmitted simultaneously, only one modulation signal is transmitted in accordance with the number of modulation signals to be transmitted so as to match the combined signal level in the receiving apparatus. By adjusting the level of the modulation signal in this case, it is possible to increase the time required for AGC gain control, and to reduce the quantization error in the A / D converter. As a result, the radio wave propagation environment estimation accuracy is improved, and the data reception quality is improved. At this time, the transmission power of pilot symbols included in the modulation signal when only one modulation signal is transmitted also increases, so that the frequency offset estimation accuracy and transmission method information estimation accuracy using the pilot symbols are improved, and data reception Quality is improved.

(Embodiment 4)
In the present embodiment, the pilot symbols related to the method of changing the pilot symbol and the transmission power of the modulation signal according to the number of antennas (the number of modulation signals) that transmit the modulation signal at the same time described in the first, second, and third embodiments. The signal point arrangement method will be described. In particular, in the present embodiment, a method for reducing the PAPR on the receiving side and stabilizing the dynamic range on the receiving side by changing the signal point arrangement of the gain control symbols in the pilot symbols for each transmitting antenna will be described. To do.

  In the present embodiment, a new signal point arrangement method will be described with respect to the signal point arrangement of the modulation signal described in Embodiment 1 with reference to FIGS. Others are the same as those of the first, second, and third embodiments, and the description thereof is omitted.

  First, a case where there are two transmission antennas will be described. In Embodiment 1, as shown in FIG. 4, a BPSK-modulated signal is used as a pilot symbol. Here, the reason for using BPSK modulation is that the modulation method is the simplest and the error rate is low. This is an effective modulation scheme for symbols having different data for each transmission, such as the transmission method information symbol 2704 (shown in FIG. 27) described in the third embodiment.

  On the other hand, consider a case where BPSK modulation is applied to the gain control symbol 2702 (shown in FIG. 27) described in the third embodiment. Since the gain control symbol 2702 is a symbol for which gain control is intended, it is only necessary to always transmit the same pattern in every transmission. Therefore, the transmission pattern for each modulation signal should be determined so that gain control can be easily performed.

  FIG. 30 shows signal point arrangement on the in-phase I-quadrature Q plane of each symbol of subcarrier k (k = 1,..., N N: number of FFT points) when modulated signals A and B are OFDM signals. And an example of the signal point arrangement of the combined signal that received the modulated signals A and B. Here, the channel estimation is illustrated as ideally performed without considering the influence of noise.

  In FIG. 30, the modulation signals A and B use the same signal point arrangement for both amplitude and phase. Looking at the synthesized signal in FIG. 30, there are two points with large signal point amplitudes, and the amplitude is 4 (4.0, 0.0) and (−4.0, 0.0). ). In addition, there are two points with small signal point amplitudes, and the amplitude is 0 (two points overlapping at (0.0, 0.0)). Therefore, the dynamic range evaluated by the amplitude is 4.

  On the other hand, FIG. 31 shows a signal point arrangement of the modulation signal B, in which only the phase is rotated by 90 ° without changing the amplitude. Looking at the signal point arrangement of the synthesized signal at that time, it can be seen that the amplitude is 2√2 (about 2.8) at all four points, the dynamic range evaluated by the amplitude is 2.8, and the PAPR becomes small.

  Thus, by changing the signal point arrangement for each modulation signal, the PAPR can be reduced compared to the case where the signal point is not changed, and gain control can be easily performed.

  32 and 33 show the in-phase I-quadrature Q planes of each symbol of subcarrier k (k = 1,..., N N: FFT point number) when four modulation signals A to D are OFDM signals. Is a signal point arrangement of the combined signal that received the modulated signals A, B, C, and D. Here, the channel estimation is illustrated as ideally performed without considering the influence of noise.

  FIG. 32 shows a case where each modulation signal A, B, C, D is transmitted using the same signal point arrangement, and FIG. 33 shows a case where each modulation signal A, B, C, D is transmitted using a different signal point arrangement. is there. In FIG. 32, the dynamic range evaluated by the amplitude of the synthesized signal is 16, whereas in FIG. 33, the dynamic range evaluated by the amplitude of the synthesized signal is suppressed to 4√2 (about 5.6). As described above, when the method of changing the signal point arrangement for each modulation signal in the gain control symbol is employed, the effect of further stabilizing the dynamic range can be obtained as the number of modulation signals increases.

  In this embodiment, the two patterns shown in FIG. 31 have been described as modulation signal patterns. However, the present invention is not limited to this pattern, and the point is that the PAPR is reduced in the synthesized signal. The pattern may be changed for each modulation signal. Therefore, as shown in FIG. 34, it is also possible to transmit with a BPSK signal that does not have a phase difference of 180 °. Comparing the synthesized signals of FIG. 30 and FIG. 34, the point ((4.0.0.0), (−4.0.0.0)) where the amplitude is 4 is about 3.7 ((3.4 , 1.4) and (-3.4, 1.4)), it can be seen that the dynamic range can be reduced.

  In the present embodiment, the method of changing the signal point arrangement of BPSK modulation for the gain control symbol has been described. Again, since the gain control symbol is the symbol for gain control, the error rate at which the symbol is demodulated is completely irrelevant. Considering this, it can be said that the same PAPR reduction effect can be obtained and the dynamic range can be reduced by using multi-level modulation in each modulation signal and transmitting using a different transmission pattern for each modulation signal. At this time, a modulation method without amplitude fluctuation is suitable as multi-level modulation, for example, PSK modulation, and the larger the multi-level number (8 PSK → 16 PSK → 32 PSK...), The more random the phase in each modulation signal. Therefore, the dynamic range can be reduced. Therefore, the multi-value number may be selected so as to obtain a desired dynamic range.

  Thus, according to the present embodiment, in the method of changing the number of modulation signals to be transmitted simultaneously, the PAPR reduction effect can be obtained by arranging different signal point for each modulation signal with respect to the gain control symbol. And the quantization error in the A / D converter can be reduced.

(Other embodiments)
In the above-described embodiment, the case where the frame configurations of the modulation signals A to D are as shown in FIGS. 3, 7, and 27 has been described. However, the frame configuration of the modulation signals is not limited to this.

  Further, in the above-described embodiment, the case where the frame configuration signal generation unit 507 and the modulation units 502A to 502D are used as the modulation signal number setting unit 11 and the number of transmission modulation signals corresponding to the transmission method request information S10 is set is described. However, the present invention is not limited to this, and the number of transmission modulation signals may be set by the own station. For example, when the amount of data to be transmitted is large, the number of transmission modulation signals may be set large, and when the amount of data to be transmitted is small, the number of transmission modulation signals may be set small. In short, it is only necessary to set the number of modulated signals to be transmitted using a plurality of antennas.

  In the first embodiment described above, the case where pilot symbol mapping section 512 as shown in FIG. 14 is used as transmission power changing means 12 has been described. However, the transmission power changing means of the present invention is not limited to this, and is required. Is sufficient as long as the ratio between the transmission power of data symbols and the transmission power of pilot symbols can be changed in accordance with the number of transmission modulation signals.

  Moreover, in Embodiment 2 mentioned above, although the case where gain control part 701A-701D (FIG. 26) was used as the transmission power change means 12 was described, the transmission power change means of this invention is not restricted to this, The important point is It is only necessary that the transmission power of each modulation signal can be changed at the same time as the number of transmission modulation signals is switched.

  In the above-described embodiment, in the wireless transmission device provided with four transmission antennas T1 to T4, the number of transmission antennas (the number of transmission modulation signals) is switched between two and four, or between one and four. However, the present invention is not limited to this, and the present invention can be widely applied to devices that transmit n types of modulated signals with n transmission antennas. In addition, the number of transmission antennas and the number of modulated signals to be transmitted do not need to match, even if the number of transmission antennas is larger than the number of transmission modulated signals, a transmission antenna is selected, and a modulated signal is transmitted from the selected transmission antenna. Good. Moreover, the antenna may form one antenna part with a plurality of antennas.

  In the above-described embodiment, the radio transmission apparatus that performs OFDM has been described as an example. However, the present invention is not limited to this, and the present invention can be similarly applied to a multicarrier system and a single carrier system. A spread spectrum communication method may be used. In particular, the present invention can be similarly implemented even if it is applied to a method combining the OFDM method and the spread spectrum method.

  In the above-described embodiment, coding was not particularly mentioned, but it can be performed even when space-time coding is not performed, and the document “Space-Time Block Codes from Orthogonal Design” IEEE Transactions on Information Theory, pp. .1456-1467, vol.45, no.5, July 1999 Space-Time Block Codes, Literature “Space-Time Block Codes for High Data Rate Wireless Communication: Performance Criterion and Code Construction” IEEE Transactions on Information Theory , pp.744-765, vol.44, no.2, March 1998, can be implemented in the same way even if the space-time trellis code shown in March 1998 is applied.

  Furthermore, when an OFDM signal is transmitted from each antenna as a modulation signal, the transmission power of the modulation signal may be changed or changed by changing the transmission power of each subcarrier in changing the transmission power of the modulation signal. The transmission power may be changed by changing the number of subcarriers to be performed.

  A case where the number of subcarriers to be used is changed will be briefly described with reference to FIG. FIG. 35 shows a specific example for generating the power waveform as shown in FIG. 29 described in the third embodiment, and each modulation signal A to D is formed of 64 subcarriers. Is assumed. From time i to time i + 3, modulated signal A is transmitted from antenna T1 using all 64 subcarriers. On the other hand, from time i + 4 to time i + 7, each of the modulation signals A to D is transmitted from the antennas T1 to T4 using 16 subcarriers. Here, if the transmission power per subcarrier is the same, a power waveform as shown in FIG. 29 can be obtained. Incidentally, since the number of subcarriers used from time i to time i + 3 and the number of subcarriers used from time i + 4 to time i + 7 are both 64, the transmission power of the combined signal from time i to time i + 3, The transmission power from time i + 4 to time i + 7 is equal.

  In short, when changing the number of subcarriers used, the number of subcarriers used in each modulated signal (OFDM signal) increases as the number of antennas transmitting modulated signals increases (the number of modulated signals to be multiplexed increases). To reduce. Incidentally, the subcarrier to be used refers to a subcarrier in which a symbol whose signal point is not (0, 0) on the IQ plane is arranged. For example, in the case of BPSK, it means a subcarrier in which a symbol of (1, 0) or (-1, 0) is arranged. On the contrary, the unused subcarrier means a subcarrier in which a symbol of a signal point (0, 0) is arranged.

  In addition, when transmitting an OFDM signal from each antenna as a modulation signal, transmission is performed from multiple antennas by using both the method of changing the transmission power of each subcarrier and the method of changing the number of subcarriers to be used. The total transmission power of the modulation signal may be changed.

  The present invention relates to a wireless transmission method, and in particular, in a method of transmitting different modulation signals from a plurality of antennas and changing the number of modulation signals transmitted simultaneously, even when the number of modulation signals to be transmitted is changed, high-precision demodulation is required. It is suitable for application to a wireless communication system.

The block diagram which shows the basic composition of the wireless transmitter of this invention The figure for explanation when transmitting a modulated signal from two antennas The figure which shows the frame structural example of each modulation signal in the case of transmitting two modulation signals simultaneously. The figure which shows the example of signal point arrangement | positioning of each symbol in the case of transmitting two modulation signals simultaneously. Chart showing signal point arrangement example of each symbol when two modulated signals are transmitted simultaneously The figure which uses for description in the case of transmitting a modulation signal from four antennas The figure which shows the frame structural example of each modulation signal in the case of transmitting four modulation signals simultaneously. The figure which shows the example of signal point arrangement | positioning of each symbol in the case of transmitting four modulation signals simultaneously. Chart showing an example of signal point arrangement of each symbol when four modulated signals are transmitted simultaneously (A) is a waveform diagram of data symbols of two modulated signals, (b) is a combined waveform diagram of two data symbols, and (c) is a relationship between a general pilot symbol waveform and a combined waveform of two data symbols. FIG. 4D is a diagram showing a relationship between a pilot symbol waveform and a combined waveform of two data symbols according to the embodiment; (A) is a waveform diagram of data symbols of four modulation signals, (b) is a combined waveform diagram of four data symbols, and (c) is a relationship between a general pilot symbol waveform and a combined waveform of four data symbols. FIG. 4D is a diagram showing the relationship between the pilot symbol waveform and the combined waveform of four data symbols in the embodiment; FIG. 3 is a diagram illustrating a configuration of a wireless transmission device according to the first embodiment. Diagram showing the configuration of the modulator The figure which shows the structure of a pilot symbol mapping part FIG. 3 illustrates a configuration of a wireless reception device according to the first embodiment. The figure which shows the composition of the radio section Waveform diagram showing a change in the combined signal of the modulation signal when the number of transmission antennas is switched from two to four without performing transmission power control in the second embodiment Waveform diagram showing a change in the combined signal of the modulation signal when the number of transmission antennas is switched from four to two without performing transmission power control in the second embodiment The figure which shows the outline of the transmission power control at the time of switching the number of transmission antennas from 2 in Embodiment 2 Waveform diagram showing a change in the combined signal of the modulation signal when the transmission power control of the second embodiment is applied when the number of transmission antennas is switched from two to four The figure which shows the outline of transmission power control at the time of switching the number of transmission antennas from four to two in Embodiment 2. Waveform diagram showing a change in the combined signal of the modulation signal when the transmission power control of the second embodiment is applied when the number of transmission antennas is switched from four to two The figure which shows returning transmission power lowered by the increase in the number of transmitting antennas. The figure which shows returning transmission power which was raised by decrease of the number of transmitting antennas Diagram for explaining frequency spectrum distortion caused by power amplifier FIG. 3 is a block diagram illustrating a configuration of a wireless transmission device according to a second embodiment. The figure which shows the frame structural example of each modulation signal in the case of transmitting four modulation signals simultaneously. Waveform diagram showing an example of a transmission waveform when the ratio of the operation range of the combined signal and the operation range of each modulation signal is set to 4 when four systems of modulated signals are transmitted by four transmission antennas Waveform diagram showing an example of a transmission waveform when the ratio of the operation range of the combined signal and the operation range of each modulation signal is 1 when transmitting four systems of modulated signals with four transmission antennas Signal point arrangement of modulation signals A and B and signal point arrangement example of combined signal of modulation signals A and B Example of signal point arrangement of modulation signal A and B and combined signal of modulation signal A and B when signal point arrangement of modulation signal B is rotated by 90 ° only in phase Signal point arrangement of modulation signals A to D and signal point arrangement example of combined signal of modulation signals A to D Example of signal point arrangement of modulation signals A to D and signal point arrangement of combined signals of modulation signals A to D when each modulation signal A, B, C, D is transmitted using different signal point arrangements Example of signal point arrangement of modulation signals A to D and signal point arrangement of combined signals of modulation signals A to D when each modulation signal A, B, C, D is transmitted using different signal point arrangements The figure which shows the example which changes the transmission power of a modulation signal by changing the number of subcarriers to be used The figure for explanation when transmitting a modulated signal from two antennas The figure which shows the pilot symbol arrange | positioned at a modulation signal

Explanation of symbols

10, 500, 700 Radio transmission device 11 Modulation signal number setting means 12 Transmission power changing means 201, 401 Signal detection symbol signal point 202, 402 Control symbol, radio wave propagation environment estimation symbol signal point 203 Data symbol signal point 502A ˜502D Modulation unit 505A˜505D Radio unit 506A˜506D Power amplification unit 507 Frame configuration signal generation unit 512 Pilot symbol mapping unit 520 Transmit symbol number 2 pilot symbol generation unit 521 Transmit antenna number 4 pilot symbol generation unit 600 Wireless receiver 701A-701D Gain control part T1-Tn, R1-R4 Antenna S2 Frame constituent signal

Claims (2)

A wireless transmission method for switching the number of antennas for transmitting a data symbol and transmitting a preamble,
Transmitting a first preamble arranged at a signal point having a signal point amplitude larger than the largest signal point amplitude among signal point amplitudes of signal points at which the data symbols are arranged;
A second antenna arranged at a signal point having a signal point amplitude smaller than a signal point amplitude of a signal point at which the first preamble is arranged, using antennas larger than the number of antennas to which the first preamble is transmitted. Sending a preamble of
A wireless transmission method including: Transmitting the first and second preambles before transmitting the data symbols;
The wireless transmission method according to claim 1.

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