JP2012124694A - Communication apparatus, transmitting device, and receiving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication apparatus, a transmitting device and receiving device which can reduce a PAPR in a simple structure without executing complicated processing.SOLUTION: A communication system, designed to transmit signals using a multicarrier, comprises a transmitting device which includes a transmit side phase rotator which rotates, by 180°, the phase of a rule-conforming half of a plurality of first mapping signals mapped on coordinate axes to generate a plurality of second mapping signals and an IFFT circuit which modulates a plurality of subcarrier signals whose frequencies have orthogonal relations based on the plurality of second mapping signals; a receiving device which includes an FFT circuit which performs FFT processing on a received time domain signal to output the plurality of second mapping signals of a plurality of subcarrier signals and a receive side phase rotator which rotates, by 180°, the phase of half the plurality of second mapping signals conforming to the same rule as for the transmit side to generate the plurality of first mapping signals.

Description

  The present invention relates to a communication device, a transmission device, and a reception device.

  In a communication system using OFDM (Orthogonal Frequency Division Multiplexing) or OFDMA (Orthogonal Frequency Division Multiple Access), a transmission apparatus has a plurality of sub-channels having frequencies whose phases are orthogonal to each other. The modulated component is modulated by the carrier, IFFT is performed on a plurality of subcarriers, and the signal is upconverted to the carrier frequency and transmitted. On the other hand, the receiving apparatus down-converts the received signal, performs FFT, and demodulates the modulated components of a plurality of subcarriers.

  In a communication system that handles multi-carriers such as OFDM and OFDMA, the ratio between the low signal level and the high signal level is often increased by multiplexing the modulation signal. In such a case, PAPR (Peak to Average Power Ratio increases. When the PAPR becomes high, the nonlinearity of the power amplifier in the transmitter is affected, and the OFDM signal is radiated out of the band, which has a serious effect on adjacent channels and other communication systems.

  For example, if the average power of the transmission signal is set as the operating point, the peak value will exceed the dynamic range of the power amplifier, the output will be distorted spurious due to the operation in the saturation region, and this will cause interference to other adjacent communication channels. Become.

  In order to prevent the PAPR from becoming high in this way, the transmission signal is mapped and spread with a known pattern, the data is rearranged, and the peak of the OFDM time domain signal with a known characteristic is determined. For example, it has been proposed to perform amplitude compensation to be suppressed before the power amplifier.

JP 2008-199405 A JP 2009-147637 A

  However, in the above method, it is necessary to transmit information on mapping and data rearrangement performed on the transmitting device side to the receiving device side, and a channel band for transmitting the information is required, thereby reducing transmission efficiency. . In addition, it is necessary for the receiving apparatus to restore the original signal by applying an inverse characteristic to the amplitude-compensated transmission signal, which causes signal degradation.

  Therefore, an object of the present invention is to provide a communication device, a transmission device, and a reception device that can reduce PAPR with a simple structure without performing complicated processing.

A first aspect of the communication system is a communication system that transmits and receives signals using multicarriers.
A transmission-side phase rotator that generates a plurality of second mapping signals by rotating a half of the plurality of first mapping signals mapped on the coordinate axis by 180 ° in phase according to a predetermined rule; and the plurality of second mapping signals A transmitter having an IFFT circuit that modulates a plurality of subcarrier signals having orthogonal frequencies based on the mapping signal, and generates a time domain signal by performing IFFT processing on the modulated subcarrier signals;
An FFT circuit that performs FFT processing on the received time-domain signal and outputs the plurality of second mapping signals of a plurality of subcarrier signals, and a half of the plurality of second mapping signals that follows the same rules as the transmission side And a reception-side phase rotator that generates the plurality of first mapping signals by rotating the phase by 180 °.

  According to the first aspect, PAPR can be reduced.

It is a block diagram of the communication apparatus which concerns on this Embodiment. It is a block diagram of the mapping circuit 11 and the IFFT circuit 12 in the transmission apparatus in this Embodiment. It is a timing chart figure which shows the operation | movement of the transmitter of this Embodiment. It is a figure which shows the example of the signal S11 after the mapping corresponding to 16 subcarriers. It is the figure which multiplexed the signal corresponding to 16 mapped subcarriers of FIG. In the case of the example of FIG. 5, it is a figure which shows the case where the phase of the even-numbered subcarrier is rotated 180 degrees (phase inversion) with respect to 16 subcarriers in the same symbol period by the transmission apparatus of this Embodiment. . It is a block diagram of the FFT circuit 23 and the demapping circuit 24 in the receiver in this Embodiment.

  FIG. 1 is a configuration diagram of a communication apparatus according to the present embodiment. The transmission device side of the communication device includes an encoding circuit (encoder) 10 that encodes transmission data Txd, a mapping circuit 11 that maps the encoded data on the I and Q coordinate axes, and mapping coordinate points. An IFFT circuit 12 that modulates the I component and the Q component with a plurality of subcarriers and performs IFFT conversion, a digital-analog conversion circuit 13, and an orthogonal modulation circuit 14 that orthogonally modulates the time domain signal of the I component and the Q component with a local frequency signal; And a high frequency (RF) circuit 15 for up-converting to a high frequency of the carrier wave. The carrier signal is transmitted from the antenna AT via the duplexer 16.

  On the other hand, on the receiving device side of the communication device, the received signal received by the antenna AT is input to the RF circuit 20 via the duplexer 16 and down-converted to the baseband. Then, the quadrature detection circuit 21 performs quadrature detection with the local frequency signal to generate a time domain signal of I component and Q component. Thereafter, the analog-to-digital conversion circuit 22 converts it into a digital signal, the FFT circuit 23 performs FFT conversion to convert the time domain signal into a frequency domain signal, the propagation path characteristic of each subcarrier is estimated from the pilot signal, and the data signal The distortion due to the propagation path is removed from the I and Q components and demodulated, and the demapping circuit 24 demaps from the coordinate points on the I and Q coordinates to reproduce the encoded data, and the decoder circuit 25 decodes it. Received data Rxd is extracted (decoded).

  In the present embodiment described below, in order to simplify the explanation, an OFDM system with an FFT size of 16, that is, the number of subcarriers is 16, and the modulation scheme of 16 subcarriers is QPSK. However, the present embodiment is not limited to them.

  FIG. 2 is a configuration diagram of the mapping circuit 11 and the IFFT circuit 12 in the transmission apparatus according to the present embodiment. In the transmitter, as described above, the mapping circuit 11 maps the transmission data Txd encoded by the encoder to the first to fourth quadrants on the I and Q coordinate axes. This mapping is performed in synchronization with the second clock CLK2 corresponding to the 16 subcarriers in the symbol.

  Further, the transmission apparatus includes any one of the phase rotator 31 that rotates the phase of the mapped signal S11 by 180 °, the rotation amount supply unit 32 that gives the phase rotation amount, and the mapped signal S11 or the signal S11X rotated by 180 °. Selector 33 for selecting or, and even / odd selection that supplies selector 33 with select signal “1” for odd-numbered subcarriers and select signal “0” for even-numbered subcarriers. Circuit 34. The even-odd selection circuit 34 synchronizes with the first clock CLK1 synchronized with the symbol period and with the second clock CLK2, and the odd-numbered selection signal S34 is “1”, and the even-numbered selection circuit is “0”. The select signal S34 is generated.

  Further, the transmitting apparatus includes a serial / parallel converter 35 that serial-parallel converts the mapping signal S33 for each subcarrier selected by the selector 33 for each subcarrier, and the subcarrier mapping signal has a frequency whose phase is orthogonal. An IFFT circuit 12 that modulates the carrier signal and outputs a time-domain signal Rx_ofdm by performing IFFT (inverse fast Fourier transform) on the subcarrier signals of a plurality of frequencies. The IFFT circuit 12 performs an IFFT operation on the subcarrier signal in the symbol in synchronization with the first clock CLK1 synchronized with the symbol period. A plurality of subcarrier signals are multiplexed by this IFFT calculation. Therefore, if this mapping is unevenly distributed at a certain coordinate point of many mapping signals S33, the amplitude of the multiplexed signal becomes excessively large and the PAPR deteriorates.

  The transmission apparatus according to the present embodiment includes a phase rotator 31, a selector 33, and an even / odd selection circuit 34 between the mapping circuit 11 and the IFFT circuit 12, and a mapping signal corresponding to a plurality of subcarriers in each symbol. The odd-numbered S11 is not rotated by 180 ° (phase inversion), and the even-numbered S11 is rotated by 180 ° (phase inversion).

  FIG. 3 is a timing chart showing the operation of the transmission apparatus of this embodiment. As shown in FIG. 3, in the transmission apparatus, the phase rotator 31, the selector 33, and the even / odd selection circuit 34 are included in the mapped signal S11 in synchronization with the first clock CLK1 synchronized with the OFDM symbol. In response to the select signal S34, a signal corresponding to the subcarrier of the second is not phase-rotated, and the even-numbered signal S33 is rotated 180 °.

  The transmission apparatus described above only needs to provide the phase rotator 31, the selector 33, and the even / odd selection circuit 34 for generating the select signal S34 between the mapping circuit 11 and the IFFT circuit 12, and the configuration thereof is very high. Simple. For example, the phase rotator 31 has a function of rotating the signal S11 after mapping by 180 °, but in actuality, it is only necessary to invert the signs of the I signal and the Q signal of the signal S11, and the circuit configuration is simple. is there.

  4, 5 and 6 are diagrams for explaining that the PAPR of signal Tx_ofdm after IFFT processing is reduced by the transmission apparatus according to the present embodiment. FIG. 4 is a diagram illustrating an example of the mapped signal S11 corresponding to 16 subcarriers. The mapped signal S11 corresponding to the subcarriers 1 to 16 is mapped in the first to fourth quadrants on the I and Q coordinate axes by the QPSK modulation method. In the example shown in FIG. 4, subcarriers 1, 2, 4, 11, 14, and 15 are mapped in the first quadrant, subcarriers 3, 5, 8, and 12 are mapped in the second quadrant, 6, 9 are mapped to the third quadrant, and subcarriers 7, 10, 13, 16 are mapped to the fourth quadrant.

  The IFFT circuit 12 modulates each subcarrier signal according to the mapping information, performs IFFT processing, multiplexes 16 modulated subcarrier signals, and outputs a time domain signal.

  FIG. 5 is a diagram in which signals corresponding to the 16 subcarriers mapped in FIG. 4 are multiplexed. According to FIG. 5, subcarriers 1, 2, 4, 11, 14, and 15 are multiplexed in the first quadrant signal 51, and subcarriers 3, 5, 8, and 12 in the second quadrant 52 are multiplexed. In the third quadrant signal 53, subcarriers 6 and 9 are multiplexed, and in the fourth quadrant signal 54, subcarriers 7, 10, 13, and 16 are multiplexed. As the number of multiplexed subcarriers increases, the amplitude increases and PAPR deteriorates.

  Statistically, each of the multiplexed signals 51 to 54 in each quadrant has a high probability that odd-numbered and even-numbered subcarriers are present at approximately 1: 1. Since the actual number of subcarriers is very large, such as 2048, for example, it can be said that the above statistical probability is almost correct.

  FIG. 6 shows a case where the phase of the even-numbered subcarrier is rotated by 180 ° (phase inversion) with respect to 16 subcarriers within the same symbol period by the transmission apparatus of the present embodiment in the case of FIG. FIG. In the example of FIG. 5, subcarriers 2, 4, and 14 are phase-inverted from the first quadrant signal 51, subcarriers 8 and 12 are phase-inverted from the second quadrant signal 52, and subcarriers from the third quadrant signal 53 Carrier 6 is phase-inverted, and subcarrier 10 is phase-inverted from signal 54 in the fourth quadrant.

  As a result, as shown in FIG. 6, the signal 51X in the first quadrant is multiplexed with the signals of subcarriers 1, 11, 15, and 6, and the signal 52X in the second quadrant is subcarriers 3, 5, and 12 The signal 53X in the third quadrant is multiplexed with the signals of subcarriers 6 and 9, and the signal 54X in the fourth quadrant is multiplexed with the signals of subcarriers 7, 10, 13, and 16. Will be converted. That is, the signal 51 in the first quadrant of FIG. 5 has an excessively large amplitude due to the multiplexing of six subcarriers, but in FIG. 6, the signal 51X in the first quadrant is multiplexed with four subcarrier signals. The amplitude is suppressed. Further, in FIG. 6, the multiplexed signals 51X to 54X in all quadrants have substantially the same amplitude.

  That is, since the transmission data Txd is random data, when mapped on the coordinate axis, the mapped signal S11 may have a very large amplitude and the PAPR may deteriorate. However, according to the transmission device of the present embodiment, since about half of the signals in each quadrant are statistically phase-inverted, the excessive amplitude and the excessive amplitude of the signals in each quadrant are suppressed, It will have a closer amplitude.

  The above phase inversion may be performed for about half of the plurality of subcarriers in the symbol. In the above example, the phase is inverted for the even-numbered subcarriers, but the phase may be inverted for the odd-numbered subcarriers. Alternatively, the phase of the pseudo-random half subcarriers determined in advance on the transmission side and the reception side may be inverted. By making it pseudo-random, the further effect that the confidentiality of transmission data improves can be brought about.

  FIG. 7 is a configuration diagram of the FFT circuit 23 and the demapping circuit 24 in the receiving apparatus according to the present embodiment. On the transmitter side, phase inversion is performed for even-numbered subcarriers in the symbol. Therefore, on the receiving apparatus side, it is necessary to invert the phase of the even-numbered subcarrier signal after the FFT processing and return it to the original mapping signal.

  That is, in the receiving apparatus, the FFT circuit 23 performs FFT processing on the time domain signal Rx_ofdm and converts it into a frequency domain signal S23. This signal S23 is a signal in which a plurality of subcarriers are mapped. The mapped signal S23 corresponding to the plurality of subcarriers is converted into serial data by the parallel serial circuit 42.

  The receiving apparatus includes a phase rotator 43, a rotation amount supply unit 44 that supplies a phase rotation amount of 180 ° to the phase rotator 43, and the mapped signal S 42 or 180 ° phase between the FFT circuit 23 and the demapping circuit 24. A selector 45 that selects one of the rotated (phase-inverted) signals S42X and an even / odd selection circuit 46 that supplies the selector 45 with a select signal S46 are provided.

  The FFT circuit 23 performs an FFT operation in synchronization with the first clock CLK1 synchronized with the symbol period. Further, the even / odd selection circuit 46 synchronizes with the first clock CLK1 synchronized with the symbol period and the second clock CLK2 synchronized with the subcarrier, and selects the select signal “1” with respect to the odd-numbered subcarrier. S46 is output, and a select signal S46 of “0” is output for even-numbered subcarriers. As a result, the phase-inverted mapping signal S42X is selected and output for even-numbered subcarriers. Then, the mapping circuit 24 demaps the mapping signal S45 returned to the original phase information by phase inversion in synchronization with the second clock CLK2, and outputs the reception data Rxd.

  Signals S42, S45, and S46 in the receiving apparatus of FIG. 7 are shown in FIG. In FIG. 3, the parallel-serial converted mapped signal S42 is phase-inverted even-numbered subcarriers according to the even / odd selection signal S46, and the original mapped signal S45 before phase inversion is output from the selector 45. Is done.

  Since the transmitting apparatus in FIG. 2 has inverted the phase of the mapped signal corresponding to the even-numbered subcarriers in the symbol, the receiving apparatus in FIG. 7 displays the mapped signal corresponding to the even-numbered subcarriers. The phase is inverted to restore the original mapped signal. In other words, the phase inversion is performed on the transmission device side and the reception device side according to the same rule.

  If the transmitting apparatus has inverted the phase of the signal corresponding to the odd-numbered subcarrier, the receiving apparatus will naturally invert the phase of the signal corresponding to the odd-numbered subcarrier. Furthermore, when the transmitting apparatus has inverted the phase of a signal corresponding to a predetermined pseudorandom subcarrier, the receiving apparatus also inverts the phase of the signal corresponding to the same pseudorandom subcarrier.

  In the above embodiment, the IFFT subcarrier modulation scheme has been described as an example of QPSK. However, the same applies to the case of BPSK. In this case as well, PAPR can be suppressed by rotating half of the signal mapped to the phase to the opposite phase.

  Further, the present invention can be similarly applied when the modulation method of each subcarrier of IFFT is 16QAM or 64QAM. For example, in the case of 16QAM, a signal corresponding to each subcarrier is mapped to 16 coordinate points by mapping. Therefore, among the signals mapped to the 16 coordinate points, the odd-numbered or even-numbered subcarriers or the pseudo-random-numbered subcarriers are rotated in the opposite phase to be mapped to the 16 coordinate points, respectively. It is possible to suppress the PAPR from becoming excessively poor by suppressing the number of signals that are generated.

  According to the present embodiment, the phase of the mapped signal is inverted with a probability of half for each quadrant, so that the amplitude of the signal multiplexed by the IFFT operation becomes excessively large and PAPR is deteriorated. It is suppressed. In addition, since subcarriers whose phase is inverted between the transmission device and the reception device follow a predetermined rule, information indicating which subcarrier is phase-inverted from the transmission device to the reception device is transmitted data. It is not necessary to send it in In addition, the phase rotators 31 and 43, the selectors 33 and 45, and the select signal generation circuits 34 and 46 may be simply provided, and a simple circuit configuration may be added.

  The above embodiment is summarized as follows.

(Appendix 1)
In a communication system that transmits and receives signals using multicarrier,
A transmission-side phase rotator that generates a plurality of second mapping signals by rotating a half of the plurality of first mapping signals mapped on the coordinate axis by 180 ° in phase according to a predetermined rule; and the plurality of second mapping signals A transmitter having an IFFT circuit that modulates a plurality of subcarrier signals having orthogonal frequencies based on the mapping signal, and generates a time domain signal by performing IFFT processing on the modulated subcarrier signals;
An FFT circuit that performs FFT processing on the received time-domain signal and outputs the plurality of second mapping signals of a plurality of subcarrier signals, and a half of the plurality of second mapping signals that follows the same rules as the transmission side And a receiving device having a receiving-side phase rotator that rotates the phase by 180 ° to generate the plurality of first mapping signals.

(Appendix 2)
In Appendix 1,
The communication system, wherein the predetermined rule is either an odd number or an even number.

(Appendix 3)
In Appendix 1,
The communication system wherein the predetermined rule is a pseudo-random number.

(Appendix 4)
In a transmission device that transmits signals using multicarriers,
A transmission-side phase rotator for generating a plurality of second mapping signals by rotating a half of a plurality of first mapping signals mapped on the coordinate axis by 180 ° in phase according to a predetermined rule;
An IFFT circuit that modulates a plurality of subcarrier signals having orthogonal frequencies based on the plurality of second mapping signals and generates a time domain signal by performing IFFT processing on the modulated subcarrier signals; A transmission device having.

(Appendix 5)
In Appendix 4,
The transmitted time domain signal is subjected to FFT processing on the receiving device side to generate the plurality of second mapping signals of a plurality of subcarrier signals, and the same as the transmission side among the plurality of second mapping signals A transmission device that generates the plurality of first mapping signals by rotating a half according to a rule by 180 °.

(Appendix 6)
In a receiving apparatus that receives a signal transmitted using a multicarrier,
A plurality of second mapping signals are generated by rotating half of the first mapping signals mapped on the coordinate axes by 180 ° in accordance with a predetermined rule, and the frequency based on the plurality of second mapping signals is generated. Modulates a plurality of subcarrier signals having an orthogonal relationship, receives a time domain signal generated by performing IFFT processing on the modulated subcarrier signals, and performs FFT processing on the received time domain signal. An FFT circuit for outputting the plurality of second mapping signals of the subcarrier signals of
A receiving apparatus comprising: a receiving-side phase rotator that rotates the half of the plurality of second mapping signals following the same rule as that of the transmitting side by 180 ° to generate the plurality of first mapping signals.

11: Mapping circuit 31: Phase rotator 33: Selector 12: IFFT
23: FFT 43: Phase rotator 45: Selector

Claims (5)

In a communication system that transmits signals using multicarriers,
A transmission-side phase rotator that generates a plurality of second mapping signals by rotating a half of the plurality of first mapping signals mapped on the coordinate axis by 180 ° in phase according to a predetermined rule; and the plurality of second mapping signals A transmitter having an IFFT circuit that modulates a plurality of subcarrier signals having orthogonal frequencies based on the mapping signal, and generates a time domain signal by performing IFFT processing on the modulated subcarrier signals;
An FFT circuit that performs FFT processing on the received time-domain signal and outputs the plurality of second mapping signals of a plurality of subcarrier signals, and a half of the plurality of second mapping signals that follows the same rules as the transmission side And a receiving device having a receiving-side phase rotator that rotates the phase by 180 ° to generate the plurality of first mapping signals. In claim 1,
The communication system, wherein the predetermined rule is either an odd number or an even number. In claim 1,
The communication system wherein the predetermined rule is a pseudo-random number. In a transmission device that transmits signals using multicarriers,
A transmission-side phase rotator for generating a plurality of second mapping signals by rotating a half of a plurality of first mapping signals mapped on the coordinate axis by 180 ° in phase according to a predetermined rule;
An IFFT circuit that modulates a plurality of subcarrier signals having orthogonal frequencies based on the plurality of second mapping signals and generates a time domain signal by performing IFFT processing on the modulated subcarrier signals; A transmission device having. In a receiving apparatus that receives a signal transmitted using a multicarrier,
A plurality of second mapping signals are generated by rotating half of the first mapping signals mapped on the coordinate axes by 180 ° in accordance with a predetermined rule, and the frequency based on the plurality of second mapping signals is generated. Receiving a time domain signal generated by performing IFFT processing on the plurality of modulated subcarrier signals,
An FFT circuit that performs FFT processing on the received time domain signal and outputs the plurality of second mapping signals of a plurality of subcarrier signals;
A receiving apparatus comprising: a receiving-side phase rotator that rotates the half of the plurality of second mapping signals following the same rule as that of the transmitting side by 180 ° to generate the plurality of first mapping signals.

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