JP2011119826A - Transmitter and transmission method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmitter and a transmission method for improving the efficiency of frequency utilization. <P>SOLUTION: The transmitter includes: a control part for setting transmission power when transmitting a plurality of transmission signals which are superimposed with the transmission signals adjacent to one another in a frequency domain at ends and to which an error correction code is applied corresponding to the order of decoding the plurality of transmission signals by a receiver; and an amplification part for amplifying the transmission signals corresponding to the transmission power set by the control part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a transmission device and a transmission method.

In recent years, depletion of frequency resources has become a problem due to the spread of various wireless communication systems.
Thus, as a technique for improving the frequency utilization efficiency, a technique using a plurality of antennas has been actively studied. For example, Non-Patent Document 1 MIMO (Multi-Input Multi Output) antenna technology uses a plurality of transmission / reception antennas and performs spatial multiplexing utilizing the independence of a plurality of spatial paths due to a scattering environment. .
However, in the multiple antenna technology, in order to improve the characteristics by increasing the number of spatial multiplexing and generating multiple null patterns, it is necessary to increase the number of antennas in either method, as in a portable terminal Mounting on a transceiver that places importance on the small size of the housing was not practical.

On the other hand, studies are being made on a superposition transmission technique that improves frequency utilization efficiency by superimposing the spectrum of a plurality of signals and sharing the frequency without increasing the number of antennas. For example, FIG. 10 is a conceptual diagram showing the entire two wireless LAN (Local Area Network) systems having different frequency channels as an example of a combination of wireless communication systems sharing a frequency band.
In the figure, the wireless communication system includes wireless LAN base stations 2a and 2b and a receiver 1a. The wireless LAN base station 2a communicates using the frequency band of CH1, which is the center frequency fa. On the other hand, the wireless LAN base station 2b communicates using the frequency band of CH5 having the center frequency fb (fa <fb). The receiver 1a is arranged at a position where wireless signals of both the wireless LAN base station 2a and the wireless LAN base station 2b reach, and two wireless signals of a wireless signal with a center frequency fa and a wireless signal with a center frequency fb are received. A radio signal including signals that partially interfere with each other is received. As another example of sharing the frequency band, there may be a case where systems of different communication systems share a frequency such as a combination of a wireless LAN system, Bluetooth (registered trademark), and WiMAX (registered trademark).

In this way, for example, when the receiver 1a shown in FIG. 10 targets the wireless LAN base station 2a as a communication target, the transmission frequency band of the desired wave that is the center frequency fa and the wireless LAN base station 2b that is the center frequency fb. In the frequency sharing type wireless communication in which the transmission frequency band of the interference wave partially overlaps (superimposes), it is essential that the receiver 1a accurately receives the desired wave. In general, when such an interference wave exists, the communication characteristics are significantly deteriorated. However, the FEC (Forward Error Correction) block distributed in a distributed manner is decoded while suppressing the influence of the interference, so that accurate transmission is performed. There is an interference suppression technique disclosed in Non-Patent Document 2. In the interference suppression technique described in Non-Patent Document 2, after the desired wave is demodulated, the influence of the interference wave is suppressed and error correction decoding is performed by weighting in a direction that reduces the reliability of the likelihood of the interference band. Thus, accurate transmission can be realized even in the presence of strong interference waves.
In Non-Patent Document 3, partial overlap of frequency allocation resources of a plurality of users is allowed for the purpose of acquiring frequency diversity.

Satoshi Kurosaki, Yusuke Sakurai, Takatoshi Sugiyama, Masahiro Umehira, “Proposal of SDM-COFDM System for Broadband Mobile Communication Realizing 100 Mbit / s Using MIMO Channel”, IEICE Tech. RCS 2001-135, pp. 37-41, October 2001 Satoshi Masuno, Takatoshi Sugiyama, “Effect of frequency utilization improvement by multi-carrier superposition transmission”, IEICE Technical Report, vol. 108, no. 188, RCS2008-67, pp. 85-90, August 2008. Yokomakura Kazunari, Takahashi Hiroki, Nakamura Osamu, Goto Yasuhiro, Hamaguchi Yasuhiro, “Performance Evaluation when Multi-level Modulation is Applied to Single Carrier Using Spectral Overlap Resource Management”, IEICE Tech. 145-150, May 2009

However, in the technique described in Non-Patent Document 3, when multi-level modulation in which constellation points are close to each other is used in a high overlap ratio environment, interference between multiple signals is collectively removed by turbo equalization processing on the receiver side. Therefore, an error floor occurs due to error propagation.
On the other hand, in the interference suppression method described in Non-Patent Document 2, decoding is performed by reducing the reliability of the likelihood information obtained from the interference band with the adjacent transmission frequency band in the transmission frequency band, that is, in the transmission frequency band. The signal is decoded based on the likelihood information of the bandwidth that is not superimposed on the adjacent transmission frequency band. For this reason, if the bandwidth of the portion to be superimposed is widened, the likelihood information used for decoding is reduced and decoding cannot be performed correctly by FEC, so that the bandwidth to be superposed cannot be increased beyond a certain bandwidth. There is.

  The present invention has been made in view of the above problems, and in a communication method for transmitting information using a plurality of signals, the bandwidth to be superimposed in the frequency domain is increased to further improve the frequency utilization efficiency. An object of the present invention is to provide a transmission device and a transmission method.

  (1) In order to solve the above-described problem, the present invention receives a plurality of transmission signals whose ends are superimposed on an adjacent transmission signal in the frequency domain and to which an error correction code is applied as a superimposed signal. The process of demodulating and decoding the transmission signal of the highest frequency or the lowest frequency band and generating a replica signal of the demodulated and decoded transmission signal and removing it from the superimposed signal is repeated, and the transmission signal included in the received superimposed signal A transmission device that transmits the plurality of transmission signals to a reception device that performs demodulation and decoding, and sets the transmission power of each of the plurality of transmission signals according to the order in which the reception device decodes the plurality of transmission signals A transmission unit comprising: a control unit configured to perform amplification; and an amplification unit configured to amplify a transmission signal in accordance with transmission power set by the control unit.

  (2) Further, the present invention is characterized in that, in the above-described invention, the control unit increases the transmission power of the transmission signal in the order from the earliest decoding order of the plurality of transmission signals by the reception device. .

  (3) Further, according to the present invention, in the above-described invention, the control unit lowers the transmission power of the superposed band of the transmission signals that are early in the order of decoding by the receiving apparatus among the transmission signals having a common superposed band. It is characterized by doing.

  (4) Moreover, the present invention provides an encoder for performing error correction coding on data to be transmitted, a modulator for modulating data encoded by the encoder, A frequency converter that frequency-converts the data modulated by the modulator and converts the data into a plurality of transmission signals, and the control unit, among the plurality of transmission signals, in order of early decoding order of the receiving device, The coding rate in the encoder is lowered, or the number of bits per symbol in the modulator is reduced.

  (5) Further, the present invention receives a plurality of transmission signals that are overlapped with an adjacent transmission signal in the frequency domain and to which an error correction code is applied as a superimposed signal, and the highest frequency or the lowest of the superimposed signals. Receiving device for demodulating and decoding a transmission signal included in the received superimposed signal by repeating a process of demodulating and decoding a transmission signal in the frequency band and generating a replica signal of the demodulated and decoded transmission signal and removing it from the superimposed signal A transmission method for transmitting the plurality of transmission signals to the transmission apparatus, wherein the reception apparatus sets the transmission power of each of the transmission signals according to the order in which the plurality of transmission signals are decoded; A transmission method comprising: an amplification step of amplifying a transmission signal in accordance with the transmission power set in the control step.

  According to the present invention, in a communication system that transmits information using a plurality of signals, frequency utilization efficiency can be improved by increasing the overlapping region between adjacent signals.

It is a figure explaining superposition transmission. It is a figure which shows the outline | summary of the signal reception process which the receiver of the radio | wireless communications system in each embodiment of this invention performs. It is a figure explaining the demodulation decoding by a FEC likelihood mask. It is a schematic block diagram which shows the structure of the transmitter 100 of the radio | wireless communications system of 1st Embodiment. It is a schematic block diagram which shows the structure of the receiver 500 in the radio | wireless communications system of 1st Embodiment. It is a schematic block diagram which shows the structure of the transmitter 200 in the radio | wireless communications system of 2nd Embodiment. It is a schematic diagram which shows the transmission signal (superimposed signal) which the transmitter 200 of this embodiment transmits. It is a schematic block diagram which shows the structure of the transmitter 300 in the radio | wireless communications system of 3rd Embodiment. It is the schematic block diagram which shows the structure of the transmitters 400-1 to 400-N of the radio | wireless communications system of 4th Embodiment, and the figure which showed an example of arrangement | positioning in the frequency band of the signal which each transmits. FIG. 2 is a conceptual diagram showing the entire two wireless LAN systems having different frequency channels as an example of a combination of wireless communication systems sharing a frequency band.

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

[First embodiment]
FIG. 1 is a diagram illustrating superposition transmission. As shown in FIG. 1A, when transmitting a plurality of signals, in the conventional spectrum arrangement, a guard band is provided between the frequency bands used by each of these signals for transmission. On the other hand, as shown in FIG. 1B, in superimposed transmission, a part of frequency bands of adjacent spectra are partially overlapped (superposed) and transmitted. As described above, since the plurality of signals partially share the frequency resources, the superposition transmission is used rather than the band f _all necessary for transmitting the plurality of signals in the case of using the conventional spectrum arrangement. In this case, the band f ′ _all necessary for transmitting a plurality of signals becomes smaller, and the frequency use efficiency can be improved. The ratio of the interference band b to the frequency band a used for data transmission of one signal is referred to as a superposition rate (= b / a).

FIG. 2 is a diagram showing an outline of signal reception processing performed by the reception device of the wireless communication system in each embodiment of the present invention.
The receiving apparatus of this embodiment receives a superimposed signal on which a plurality of transmission signals R1 to Rn (n ≧ 2, n is an integer) are superimposed. Here, it is assumed that each of the five transmission signals R1 to R5 is partially overlapped with the superimposed signal received by the receiving apparatus, and the transmission signals R1 and R2 are sequentially from the signal having the lowest center frequency in the frequency band to be used. , R3, R4, R5. These transmission signals R1 to R5 are, for example, multicarrier signals such as OFDM (Orthogonal Frequency Division Multiplexing), and FEC (Forward Error Correction) codes are used as an error correction mechanism. . In the present embodiment, the case where the superimposed signal is a multicarrier signal will be described.

Hereinafter, the frequency band used by the transmission signal Ri (1 ≦ i ≦ n, i is an integer) is referred to as fi.
Moreover, the frequency band used for the signal with the lowest center frequency or the signal with the highest center frequency among the signals superimposed on the superimposed signal is described as an outer band. For example, in the case of the processing target signal A1 shown in FIG. 2, the frequency bands f1 and f5 of the transmission signals R1 and R5 are the outer bands. The signal in the outer band has a frequency band superimposed on only one other signal, and the signal in the band other than the outer band has a frequency band superimposed on the other two signals.

  As shown in FIG. 2, the receiving apparatus according to the present embodiment first demodulates and decodes a transmission signal R1, which is one of the signals in the outer band, from the processing target signal A1 that is the received superimposed signal. In this demodulation and decoding (hereinafter also referred to as “demodulation decoding”), FEC decoding is performed after the FEC likelihood mask processing, but FEC likelihood mask processing (hereinafter also simply referred to as “FEC likelihood mask”). The details of will be described later with reference to FIG. When the reception device decodes the transmission signal R1, the reception device generates a replica signal R1 'of the transmission signal R1 from the bit stream obtained by the decoding, and removes the generated replica signal R1' from the processing target signal A1. As a result, the processing target signal A2 on which the transmission signals R2 to R5 are superimposed is generated.

Subsequently, the receiving apparatus performs demodulation decoding of the transmission signal R2, which is one of the signals in the outer band, from the processing target signal A2 by the FEC likelihood mask and FEC decoding. When the reception device decodes the transmission signal R2, the reception device generates a replica signal R2 ′ of the transmission signal R2 from the bit stream obtained by the decoding, and removes the generated replica signal R2 ′ from the processing target signal A2. As a result, the processing target signal A3 on which the transmission signals R3 to R5 are superimposed is generated.
By repeating the above, the receiving apparatus performs demodulation decoding of the transmission signals R3 and R4 using the FEC likelihood mask and FEC decoding, removes the replica signals R3 ′ and R4 ′, and processes the signal A5 including only the transmission signal R5. Get. When the processing target signal A5 is obtained, the receiving apparatus performs only normal FEC decoding without performing FEC likelihood masking, and performs demodulation decoding of the transmission signal R5.

That is, the reception apparatus demodulates the transmission signal Ri from the processing target signal Ai on which the transmission signal Ri to the transmission signal Rn are superimposed with respect to i = 1, 2,..., (N−1) by FEC likelihood masking and FEC decoding. Decoding is performed, and the replica signal Ri ′ of the transmission signal Ri is generated from the obtained bit stream, and the replica signal Ri ′ is removed from the processing target signal Ai to generate the processing target signal A (i + 1). Since the finally processed signal An includes only the transmission signal Rn, normal demodulation and decoding are performed.
As described above, when receiving the signal transmitted by the superposition transmission method, the receiving apparatus of the present embodiment performs FEC decoding of the signal in the outer band by suppressing interference using the likelihood mask, and generates the signal from the demodulated and decoded signal. Using the replica signal, the superimposed signal is sequentially demodulated and decoded while removing the interference of the superimposed signal.

  In the above, demodulation decoding is performed in the order of the transmission signals R1, R2,..., Rn, but the order may be arbitrary by always performing demodulation decoding of the signals in the outer band of the superimposed signal. . For example, transmission signals Rn, R (n-1),..., R1 in order, R1, Rn, R2, R (n-1), R3, R (n-2),..., R1, R2,. , Rp, Rn, R (n−1),..., R (p + 1) (1 <p <n, where p is an integer) may be demodulated and decoded. However, the order in which demodulation and decoding are performed is assumed to be predetermined.

FIG. 3 is a diagram for explaining demodulation decoding using the FEC likelihood mask.
This figure shows a case where a part of the transmission signal Ri to be demodulated and decoded is superimposed on another transmission signal R (i + 1), and the transmission signal R (i + 1) can be further superimposed on another signal. . The receiving apparatus performs demodulation according to the encoding method used for the transmission signal Ri in the transmitting apparatus. Here, a case where the receiving apparatus is a soft decision positive / negative multi-level encoding method will be described as an example. In the decoding process in this soft decision positive / negative multilevel encoding method, the demodulated value of the received signal is a positive / negative multilevel output, and the magnitude of the absolute value is negative as the reliability (value indicating likelihood, likelihood). Decoding processing is performed in which the value is “+1” and the positive value is “−1”.

  FIG. 3A is a diagram illustrating an example of a result of demodulating a superimposed signal with respect to the frequency band fi used by the transmission signal Ri by the reception apparatus. By the demodulation, each subcarrier included in the frequency band fi is illustrated. Indicates that a demodulated value of positive / negative multi-value output has been obtained. In the figure, the subcarrier with the maximum positive value “+27.02” has the highest reliability for being “−1”. On the other hand, the subcarrier with the smallest negative value “−26.34” has the highest reliability for being “+1”. It should be noted that “+1” or “−1” is the most ambiguous (low reliability) is the value having the smallest absolute value, that is, the subcarrier having the demodulated value of 0.

  FIG. 3B is a diagram illustrating weighting factors used for the frequency band fi. The weighting factor corresponds to each subcarrier included in the frequency band fi, uses the demodulated value as it is for the subcarrier in the non-superimposed band, and reduces the reliability of the demodulated value for the subcarrier in the superposed band. This is a coefficient for setting the demodulated value to 0 or approaching 0. That is, the weight coefficient of each subcarrier in the non-superimposed band is “1”, and the weight coefficient of each subcarrier in the superimposed band is “k” (0 ≦ k <1). In the figure, an example in which the demodulated value of the subcarrier in the superposed band is set to 0 is shown. That is, weighting of signals when used for decoding is performed.

FIG. 3 (c) is a diagram showing a likelihood data string obtained as a result of weighting a weighting coefficient and a positive / negative multilevel demodulated value for each subcarrier. This is obtained by multiplying the positive and negative multilevel demodulated values shown in FIG. 3A by the weighting coefficient shown in FIG. 3B for each corresponding subcarrier. That is, the value obtained by multiplying the subcarrier in the non-superimposed band by the demodulated value and the weighting coefficient “1”, and the subcarrier in the superposed band is set to the demodulated value and the weighting coefficient “k” (0 ≦ k <1). A likelihood data string after weighting calculation is obtained as a multiplied value. For example, in the same figure, the demodulated value “−25.32” is multiplied by the weighting coefficient “0” for the subcarrier SC1 that is the subcarrier in the superposed band, and the multiplication result “0” is demodulated after the weighting calculation. As a value. Similarly, the demodulated value after the weighting calculation is “0” for the other subcarriers in the superimposed band. Therefore, as shown in FIG. 3 (c), the value of the likelihood data after the weighting operation corresponding to the subcarriers in the superposed band is the value “0” having the lowest reliability, and the demodulated value of the subcarrier in the non-superimposed band Does not change.
In this way, the reliability of the demodulated value of the subcarrier in the superposed band is reduced by performing the weighting calculation process for converting the demodulated value of the subcarrier in the superposed band to “0” or “a value close to 0”. It becomes possible.

The receiving device performs the FEC decoding process based on the likelihood data string obtained by the weighting calculation. This FEC decoding corresponds to the FEC encoding method applied in the transmission apparatus that has transmitted the transmission signal Ri. Applicable FEC coding methods for error correction include, for example, a method based on convolutional coding, a method based on a combination of iterative decoding and turbo code, and the like.
As described above, the receiving apparatus performs a weighting operation on the demodulated value according to the reliability of the received signal for each subcarrier, masks the subcarriers in the overlapping band with low reliability, and demodulates the subcarrier with high reliability. By decoding the received signal using the value, it is possible to improve the reception error correction capability.

In the above description, the soft decision positive / negative multivalue is described as an example, but a positive multivalue output may be used. In the soft decision output type, the bit value is decoded as “−1” as the demodulated value of the positive multivalued output is closer to 0, and the bit value is decoded as “1” as the demodulated value is closer to the maximum value. Therefore, as a weighting factor, a weighting factor that replaces the demodulated value of the subcarrier in the superposed band with the median of the output candidate values (for example, the median value 3 or 4 if the output candidate value is 0 to 7). Can be used.
Further, a hard decision output type may be used. For example, when the hard decision output type is a binary output type of “−1” and “+1”, a weighting factor that replaces the demodulated value of the subcarrier in the superposed band with “0” can be used.

FIG. 4 is a schematic block diagram illustrating a configuration of the transmission device 100 of the wireless communication system according to the first embodiment. Here, a case where transmitting apparatus 100 transmits N transmission signals R1 to Rn will be described.
In the figure, a transmission apparatus 100 includes a serial / parallel converter (S / P converter) 120, N transmission units 130-1 to 130-N (N is a natural number of n = N and 2 or more), and And a synthesizer 191. The serial / parallel converter 120 performs serial / parallel conversion on an input bit stream representing information to be transmitted and divides the input bit stream into N bit streams, and the divided bit streams are respectively transmitted to the transmission units 130-1 to 130-N. Output to. The transmission units 130-1 to 130 -N generate transmission signals R 1 to RN corresponding to the bit streams input from the serial / parallel converter 120, respectively, and output them to the combiner 191. The combiner 191 generates a superimposed signal by combining the transmission signals R1 to RN input from the transmission units 130-1 to 130-N, and transmits the generated superimposed signal to the receiving device via the antenna.
Since each of the transmission units 130-1 to 130-N has the same configuration, the transmission unit 130-1 will be described, and the description of the transmission units 130-2 to 130-N will be omitted.

  The transmission unit 130-1 includes an encoder 140, a modulator 150, and a frequency converter 170. The encoder 140 performs a predetermined error correction encoding on the bit stream input from the serial / parallel converter 120 and outputs the error corrected encoded bit stream to the modulator 150. Modulator 150 outputs, to frequency converter 170, a signal obtained by modulating subcarriers using a bitstream that has been subjected to error correction coding and input from encoder 140 using a predetermined modulation scheme. The frequency converter 170 converts the frequency of the signal modulated by the modulator 150 and outputs a transmission signal R1 (radio signal) in a predetermined carrier frequency band.

The predetermined error correction code used in the encoder 140 is, for example, a Reed-Solomon code, a turbo code, a low density parity check code, or the like. The predetermined modulation method used in the modulator 150 includes BPSK (Binary phase-shift keying), 16QAM (16 Quadrature amplitude modulation), and the like. In addition, the predetermined carrier frequency is different for each frequency converter 170 so that the frequency bands of the transmission signals R1 to RN output from each frequency converter 170 are superimposed on the frequency bands of adjacent signals. It is a defined frequency.
For example, as shown in FIG. 2, the transmission signal is superimposed on both sides of the frequency band with another transmission signal having adjacent carrier frequencies. At this time, the transmission signal is determined according to transmission quality and communication quality (Quality of Service: QoS) required for the input bit stream.

FIG. 5 is a schematic block diagram illustrating a configuration of the reception device 500 in the wireless communication system according to the first embodiment.
As shown in the figure, the receiving apparatus 500 includes a decoding number counter 510, a switch 515, a subtracter 520, a delay unit 525, a processing band determining unit 530, a local signal generator 535, a mixer 540, a band pass filter 545, a transmission path. An estimator 550, a demodulator 555, a weight coefficient generator 560, a first weight calculator 565, a decoder 570, a data buffer 575, a replica generator 580, and a data extractor / reorderer 590 are provided.

  The decoding number counter 510 sequentially counts the number of times decoding is performed after receiving a new superimposed signal from the transmission apparatus 100, and stores the counted value. The switch 515 switches the connection source of the subtracter 520 to either the reception signal side or the delay device 525 side according to the value of the decoding number counter 510. Specifically, the switch 515 selects and outputs a received signal input from the outside when the number of decoding is the initial value, and selects the signal output from the delay unit 525 when the number of decoding is larger than the initial value. Output.

  The subtractor 520 removes the replica signal from the received superimposed signal or the processing target signal stored in the delay unit 525 to generate a new processing target signal. Here, the replica signal is generated in the replica generation unit 580 based on the decoded signal. However, in the case of the first processing after receiving a new superimposed signal, the replica signal is not generated, so the initial value of the replica signal is zero. The delay unit 525 stores the signal to be processed output from the subtracter 520 and adds a time delay.

The processing band determiner 530 determines the frequency bandwidth and center frequency of the demodulation target signal based on the value of the decoding number counter 510, and instructs the local signal generator 535 to generate a local signal of the determined center frequency. The determined center frequency and frequency bandwidth are output to the bandpass filter 545, and an instruction is given to remove components other than the frequency components to be demodulated and decoded.
The processing frequency determiner 530 has a table in which the value of the decoding counter 510, the center frequency and the band frequency width of the demodulation decoding target signal are stored, and the counter value is read from the decoding counter 510. The transmission frequency and bandwidth to be demodulated and decoded are read out and output to the local signal generator 535.
Further, the processing band determining unit 530 outputs the association between the number of decoding times and the frequency band to the data extracting / rearranging unit 590.

  The local signal generator 535 generates a local signal having a center frequency specified by the processing band determiner 530. The mixer 540 down-converts the processing target signal output from the subtracter 520 with the local signal generated by the local signal generator 535. The band pass filter 545 removes components other than the frequency components of the center frequency and frequency bandwidth instructed by the processing band determiner 530 from the processing target signal down-converted by the mixer 540, and only the signal in the frequency band to be demodulated and decoded. To extract. Transmission path estimator 550 estimates transmission path characteristics from a pilot signal or the like included in a signal to be demodulated and decoded extracted by bandpass filter 545. The demodulator 555 demodulates the demodulation target signal extracted by the band pass filter 545 using the transmission path characteristic estimated by the transmission path estimator 550 to calculate the likelihood.

  The weighting coefficient generator 560 uses the likelihood obtained by demodulation by the demodulator 555 for the frequency band to be demodulated based on the value of the decoding number counter 510 as it is for the non-superimposed band, and for the superposed band. A weighting factor that reduces the reliability is generated. The first weight calculator 565 decodes the likelihood data sequence obtained by multiplying the likelihood obtained by the demodulation by the demodulator 555 by the weight coefficient generated by the weight coefficient generator 560, that is, the likelihood masked likelihood data string. To the device 570. The decoder 570 performs error correction processing and decoding processing based on the likelihood data sequence masked by the first weight calculator 565 to obtain a bit stream.

  The data buffer 575 stores the bit stream decoded by the decoder 570. The data extractor / rearranger 590 generates a bit stream of a desired signal from the bit stream stored in the data buffer 575 based on the information indicating the correspondence between the number of decoding times received from the processing band determiner 530 and the frequency band. Extracting or rearranging the order of the bitstreams stored in the data buffer 575 to generate and output a correct bitstream. Here, the rearrangement of the order of the bitstreams performed by the data extraction / rearranger 590 is a rearrangement for restoring the order of the input bitstream sequence input to the serial / parallel converter 120 of the transmission apparatus 100.

The replica generator 580 includes a re-encoder 582, a re-modulator 584, and a second weight calculator 586, and generates a replica signal from the bit stream obtained by the decoder 570.
The re-encoder 582 performs the same encoding on the bit stream decoded by the decoder 570 as the encoding used in the transmission apparatus 100 that has transmitted the bit stream. That is, the re-encoder 582 performs the same encoding as the encoder 140 (FIG. 4).
The remodulator 584 uses the signal encoded by the reencoder 582 to perform modulation using the same modulation method as that used in the transmission apparatus 100 that has transmitted the bitstream.
That is, remodulator 584 performs modulation using the same modulation scheme as modulator 150 (FIG. 4).
Second weight calculator 586 multiplies the signal modulated by remodulator 584 by the estimated value of the channel characteristic estimated by channel estimator 550 and receives the signal transmitted from transmitting apparatus 100 at its own receiving apparatus. A replica signal that is an estimated signal is generated.

Subsequently, operations of the transmission device 100 and the reception device 500 of the present embodiment will be described.
In the transmission apparatus 100, the serial / parallel converter 120 performs serial / parallel conversion in which the input bit stream is divided into N bit streams, and the N bit streams obtained by the conversion are transmitted to different transmission units 130, respectively. Output to −1 to 130-N.
In the transmission units 130-1 to 130-N, the encoder 140 and the modulator 150 perform error correction coding and modulation on the input bit stream to generate a baseband signal. The generated baseband signal is input to the frequency converter 170, and the frequency converter 170 performs frequency conversion (up-conversion) to a predetermined carrier frequency, and the transmission signal Ri (i is 1 ≦ i ≦ n). = N natural number). The combiner 191 generates a superimposed signal obtained by superimposing the transmission signals R1, R2,..., RN output from the transmitting units 130-1 to 130-N, and receives the generated superimposed signal from the antenna. Sent to 500.

The receiving apparatus 500 receives a superimposed signal on which transmission signals R1, R2,..., Rn are superimposed from the transmitting apparatus 100, and performs demodulation decoding in the order of the transmission signals R1, R2,. In addition, before receiving the bit stream from the transmission device 100, the reception device 500 uses the use frequency bands f1 to fn of the transmission signals R1 to Rn at a timing where there is no desired wave or a frequency band of a subcarrier where there is no desired wave. It is assumed that the center frequency, the superimposed band, etc. are measured, detected, or determined in advance. That is, the receiving apparatus 500 uses the frequency bands 170 to fn of the frequency converters 170 included in the transmitting units 130-1 to 130 -N of the transmitting apparatus 100, the center frequency of the carrier wave, the overlapping band with adjacent signals, and the like. Are pre-measured, detected, or predetermined before transmission by superimposition transmission.
Alternatively, these pieces of information may be acquired from control information transmitted / received to / from the transmission apparatus 100, and these pieces of information may be acquired in advance by an input unit (not shown) or read from a recording medium.

(Process 1-1): The receiving device 500 receives a signal on which transmission signals R1 to Rn are superimposed.
(Processing 1-2): The switch 515 switches the connection source of the subtracter 520 to the reception signal side because the value of the decoding number counter 510 is an initial value. Here, the initial value is “1”.

  (Processing 1-3): The subtracter 520 generates a processing target signal A1 by removing the replica signal from the received superimposed signal. However, the replica signal is 0 for the first processing after receiving the superimposed signal, and the received superimposed signal becomes the processing target signal A1 as it is. The processing target signal A1 is stored in the delay unit 525 and output to the mixer 540.

  (Processing 1-4): The processing band determining unit 530 stores a correspondence between the number of decoding times and the frequency band of the demodulation target signal in advance, and performs demodulation based on the value “1” of the decoding number counter 510. If it is determined that the decoding target is the frequency band f1 of the transmission signal R1, the center frequency of the frequency band f1 and its frequency bandwidth are obtained. The processing band determiner 530 instructs the local signal generator 535 to generate a local signal of the center frequency of the frequency band f1, and removes components other than the center frequency and frequency bandwidth components of the frequency band f1 to the bandpass filter 545. Instruct them to do so.

(Process 1-5): The local signal generator 535 generates a local signal having a center frequency designated by the processing band determiner 530, and the mixer 540 generates the processing target signal A1 by the local signal generator 535. Down-converted by the local signal.
(Process 1-6): The band-pass filter 545 removes the frequency other than the frequency components of the center frequency and the frequency bandwidth indicated by the processing band determiner 530 from the processing target signal A1 down-converted by the mixer 540. When the signal of the band f1 is extracted, the extracted signal is output as a signal to be demodulated and decoded.

(Process 1-7): The transmission path estimator 550 estimates transmission path characteristics from the signal to be demodulated and decoded extracted by the bandpass filter 545. The estimation of transmission path characteristics is performed based on a pilot signal included in a signal to be demodulated and decoded.
(Process 1-8): Demodulator 555 demodulates the signal to be demodulated and decoded extracted by bandpass filter 545 using the channel characteristics estimated by channel estimator 550, and calculates the likelihood (demodulated value). ) Is calculated.

  (Processing 1-9): The weighting factor generator 560 stores in advance a correspondence between superimposition band information indicating the frequency band and superposition band of the demodulation decoding target signal and the number of decoding times, and the value of the decoding number counter 510 When information on the frequency band f1 of the transmission signal R1 and the superposed band on which the transmission signal R1 and the transmission signal R2 are superimposed is obtained based on “1”, for each subcarrier of the transmission signal R1 included in the frequency band f1 Generate a weighting factor for. That is, the weight coefficient is “1” for the subcarriers in the non-superimposed band excluding the superposed band from the frequency band f1, and the coefficient is “k” (0 ≦ k <1) for the subcarriers in the superposed band. Generate a sequence of weighting factors.

  (Process 1-10): The first weight calculator 565 is a likelihood data string calculated as a result of multiplying the likelihood obtained by the demodulation by the demodulator 555 by the weight coefficient generated by the weight coefficient generator 560. Is output to the decoder 570. When the decoder 570 performs error correction decoding processing based on the likelihood data sequence masked by the first weight calculator 565 and obtains a bit stream, the decoder 570 writes the obtained bit stream in the data buffer 575. For example, the bit stream may be written in association with the decoding counter value, or may be written in a storage area corresponding to the decoding counter value.

  (Process 1-11): The replica generator 580 generates a replica signal R1 'from the bit stream obtained by the decoder 570. That is, the re-encoder 582 performs encoding similar to the encoder 140 on the bit stream decoded by the decoder 570, and the re-modulator 584 converts the signal encoded by the re-encoder 582 into The same modulation as that of the modulator 150 is performed. The second weight calculator 586 multiplies the signal modulated by the remodulator 584 by the estimated value of the transmission line characteristic between the transmission signal R1 estimated by the transmission line estimator 550 and the transmission apparatus 100 and the replica signal. R1 ′ is generated. When the replica signal R1 'is generated, 1 is added to the value of the decoding number counter 510.

  (Process 1-12): Since the value of the decoding number counter 510 is 2, the switch 515 switches the connection source of the subtracter 520 to the delay unit 525 side. The subtracter 520 removes the replica signal R1 'generated by the replica generator 580 from the processing target signal A1 stored in the delay unit 525, and generates the processing target signal A2. The processing target signal A2 is stored in the delay unit 525 and output to the mixer 540.

  (Processing 1-13): Thereafter, the counter value “1” is the counter value “i”, the processing target signal A1 is the processing target signal Ai, the processing target signal A2 is the processing target signal A (i + 1), and the transmission signal R1 is transmitted. The processing of (processing 1-4) to (processing 1-12) is performed by replacing the signal Ri, the transmission signal R2 with the transmission signal R (i + 1), the frequency band f1 with the frequency band fi, and the replica signal R1 ′ with the replica signal Ri ′. Is performed when i is 2, 3,..., (N−1).

(Processing 1-14): When i is n, the processes of (Processing 1-4) to (Processing 1-10) are performed. In (Process 1-9), since there is no overlapping band, the weighting coefficient generator 560 generates weighting coefficients whose coefficients are all 1.
(Processing 1-15): When the decoded bitstream is written in the data buffer 575 by (Processing 1-14), the data extraction / rearranger 590 receives the number of decodings input from the processing band determining unit 530 and Based on the data indicating the association with the frequency band, the order of the bit streams stored in the data buffer 575 is rearranged in the order of the bit streams obtained from the transmission signals R1, R2,. As described above, when demodulation decoding is performed in the order of the transmission signals R1, R2,..., Rn, the original data is obtained by arranging the data in the order in which the bitstreams are obtained. When decoding is performed in the order of transmission signals R1, Rn, R2, R (n-1),..., Replacement is necessary.

As described above, reception apparatus 500 performs demodulation decoding in order from the transmission signal Ri (1 ≦ i ≦ n) in the outer band of the received superimposed signal, generates a replica signal by demodulation decoding and transmission path estimation, By repeatedly removing the replica signal, the transmission signals R1,..., Rn included in the superimposed signal can be demodulated and decoded.
When the frequency bandwidth is the n number of transmitting signals R1~Rn the same width, the occupied bandwidth in the case of transmitted without superimposed without providing a guard band set to f _all, that is, of each transmitted signal R1~Rn When the frequency bandwidth is f _all / N and the limit (maximum) superimposition rate that can be decoded by interference suppression processing is α, the frequency bandwidth occupied by the superimposed signal is as follows.
When demodulated and decoded using only the FEC likelihood mask, the occupied frequency bandwidth necessary for transmitting the N transmission signals R1 to Rn is [{1- (α / 2)} + α / 2N] f _all (However, N is 3 or more).

That is, since the superposition ratio = superimposition bandwidth / occupied frequency bandwidth can be expressed, the bandwidth of the superposition band in one signal is α × f _all / N at the maximum. Here, paying attention to the transmission signals R2 to R (n-1), since the superposition bands are on the high frequency side and the low frequency side, the superposition bands on the high frequency side and the low frequency side are α × f _all / 2N. The non-overlapping band is (1 / N−α / N) × f _all . In the case of the transmission signals R1 and Rn in the outer band, since there is a superimposed band only on either the high frequency side or the low frequency side, the non-superimposed band is (1 / N−α / 2N) × f _all .
Since the number of signals in the outer band is 2, the number of signals other than the outer band is (N-2), and the number of superposed bands (N-1), the occupied frequency band when using the FEC likelihood mask The width is as follows.

(Bandwidth of outer band non-superimposed band) x (Number of signals in outer band) + (Bandwidth of non-superimposed band other than outer band) x (Number of signals excluding outer band) + (Bandwidth of superimposed band) × (Number of overlapping bands)
= (1 / N−α / 2N) × f _all × 2 + (1 / N−α / N) × f _all × (N−2) + (α × f _all / 2N) × (N−1)
= {(1-α / 2) + α / 2N)} f _all

On the other hand, when this embodiment is used, the occupied frequency bandwidth is {(1−α) + α / N)} _all . This is due to the following.
In the present embodiment, the signal is demodulated and decoded in order from the outer band of the received superimposed signal, and the replica signal is subtracted from the superimposed signal that has not been demodulated and decoded yet. For example, considering that demodulation decoding is performed in the order of the transmission signals R1, R2,..., The overlapping bandwidth of the transmission signal R1 is a bandwidth where the transmission signal R1 and the transmission signal R2 overlap. Subsequently, when the transmission signal R1 is demodulated and decoded, and the replica signal of the transmission signal R1 is removed, the superimposition bandwidth of the transmission signal R2 to be demodulated and decoded next is only the band where the transmission signal R2 and the transmission signal R3 overlap. It becomes. Since the transmission signal R3 and the like can be considered in the same manner, the transmission signal R1 and the transmission signal R2, the transmission signal R2 and the transmission signal R3,..., The transmission signal R (n−1) and the transmission signal Rn overlap with each other by α Xf _all / N.

As described above, in the case of the transmission signals R2 to R (n-1) other than the outer band, the superimposition band is on the high frequency side and the low frequency side. Since demodulation and decoding can be performed as a superposition band, superposition bands of (1 / N−α / N) × f _all can be provided on the high frequency side and the low frequency side, respectively. Thus, non-overlapping band of the transmission signal R2~R (n-1) becomes (1 / N-2α / N ) × f all. Further, the non-superimposed band of the transmission signals R1 and Rn in the outer band is (1 / N−α / N) × f _all .
Accordingly, the occupied frequency bandwidth when using the present embodiment is as follows.

(Bandwidth of outer band non-superimposed band) x (Number of signals in outer band) + (Bandwidth of non-superimposed band other than outer band) x (Number of signals excluding outer band) + (Bandwidth of superimposed band) × (Number of overlapping bands)
= (1 / N−α / N) × f _all × 2 + (1 / N−2α / N) × f _all × (N−2) + (α × f _all / N) × (N−1)
= {(1-α) + α / N)} f _all

  As described above, when α is the maximum superposition rate achievable by using interference suppression processing on the receiving side, superposition rate exceeding α is allowed for signals other than the outer band by using this embodiment. Can be done. Therefore, compared with the prior art, the occupied frequency bandwidth of the entire transmission signal can be compressed, so that the frequency utilization efficiency can be improved.

In the successive demodulation decoding for the signal transmitted by the superposition transmission method in this embodiment, in order to demodulate and decode the signal arranged inside the outer band, the demodulation and decoding are repeated while generating the replica signal and removing the interference. As a result, if an error that cannot be corrected occurs in the initial demodulation decoding of the successive demodulation decoding, the error propagates to the subsequent demodulation decoding, so that all superimposed signals cannot be correctly demodulated and decoded. .
Therefore, in the following embodiment, a transmission device that can reduce the propagation of errors to subsequent demodulation and decoding in successive demodulation and decoding of the superposition transmission method will be described.

[Second Embodiment]
FIG. 6 is a schematic block diagram illustrating a configuration of the transmission device 200 in the wireless communication system according to the second embodiment. Here, a case will be described in which the transmission apparatus 200 transmits a superimposed signal in which N transmission signals R1 to Rn are superimposed, similarly to the transmission apparatus 100 of the first embodiment. Further, the center frequency and bandwidth of each of the N transmission signals R1 to Rn included in the superimposed signal and the superimposed bandwidth of the adjacent signal are determined in advance. In addition, since the receiving device in the wireless communication system of the present embodiment has the same configuration as the receiving device 500 of the first embodiment, description thereof is omitted.
As shown in the figure, the transmission apparatus 200 includes a radio resource control unit 210, a variable serial / parallel converter 220, N intermediate signal generation units 230-1 to 230-N, a frequency converter 280, A synthesizer 290 is provided.

  The radio resource control unit 210 controls the transmission energy of each of the transmission signals R1 to Rn according to the order in which the reception device that receives the N transmission signals R1 to Rn sequentially demodulates and decodes the transmission signals R1 to Rn. Specifically, a large amount of transmission power is assigned to signals that are earlier in the order of sequential demodulation and decoding in accordance with the order of sequential demodulation and decoding. This transmission power control is performed by setting the transmission power and MCS (Modulation and Coding Scheme) level when transmitting the input bit stream, MCS (coding rate and modulation scheme), average transmission The power value and the power ratio between the superimposed band and the non-superimposed band (= (transmission power of the non-superimposed band) / (transmit power of the superimposed band)) are set as parameters.

For example, if the coding rate is lowered, 1-bit information is transmitted with redundant bits added according to the reciprocal of the coding rate, so that transmission power required for transmitting the information increases. If the modulation method is changed from 64 QAM (16 quadrature amplitude modulation) to QPSK (quadrature phase shift keying), the number of bits per symbol to be transmitted is reduced and transmission per bit is performed. Electric power increases. Further, the transmission power per bit of information increases as the transmission power increases.
Here, the control signal is a signal including a coding rate, a modulation scheme, an average transmission power value, and a power ratio between a superimposed band and a non-superimposed band. Then, radio resource control section 210 outputs the control signal to each of intermediate signal generation sections 230-1 to 230-N, so that the transmission signals R1 to Rn are demodulated and decoded in the receiving apparatus in order. The transmission power of the transmission signals R1 to Rn is controlled by comparing the power ratio accordingly.

The variable serial / parallel converter 220 receives an input bit stream to be transmitted, divides the input bit stream into N bit streams, and outputs the divided bit streams to intermediate signal generation units 230-1 to 230 -N.
Since the intermediate signal generation units 230-1 to 230-N have the same configuration, the configuration of the intermediate signal generation unit 230-1 will be described, and the description of the intermediate signal generation units 230-2 to 230-N will be omitted. To do. The intermediate signal generation unit 230-1 includes an encoder 240, a modulator 250, a weight calculator 260, and a frequency converter 270.

  The encoder 240 performs error correction encoding on the bit stream input from the variable serial / parallel converter 220 at the encoding rate indicated by the control signal input from the radio resource control unit 210 and outputs the result. Modulator 250 is a modulation scheme indicated by the control signal input from radio resource control section 210, modulates the subcarrier using the bit stream that has been error correction encoded by encoder 240, and is obtained by modulation. The baseband signal is output to the weight calculator 260.

Based on the average transmission power value and the power ratio included in the control signal input from the radio resource control unit 210, the weight calculator 260, after the baseband signal among the baseband signals input from the modulator 250, The baseband signal that is sequentially demodulated and decoded is amplified with a different amplification factor for the signal in the frequency band to be superimposed and the signal in the other frequency band. Specifically, the weight calculator 260 has an average power value of the signal “(control signal) for a signal in a frequency band superimposed on a baseband signal that is sequentially demodulated and decoded after the input baseband signal. The average transmission power value included in the control signal) × (the power ratio between the superimposed band and the non-superimposed band included in the control signal) ”. On the other hand, the signals in other frequency bands are amplified so that the average power value of the signals becomes the average transmission power value included in the control signal.
The frequency converter 270 performs frequency conversion on the baseband signal amplified by the weight calculator 260 and outputs an intermediate signal in a predetermined intermediate frequency (IF) band.

  Note that the error correction code used in the encoder 240 is the same as that of the encoder 140 of the first embodiment. The modulation method used in the modulator 250 is the same as that of the modulator 150 of the first embodiment. Further, the intermediate frequency used in the frequency converter 270 is different for each of the intermediate signal generators 230-1 to 230-N, and is determined so that the intermediate signals output from the intermediate signals are superimposed on the adjacent intermediate signals in the frequency domain. . However, the intermediate frequency is based on the bandwidth of the intermediate signal output by the intermediate signal generators 230-1 to 230 -N so that the overlapping bandwidth of adjacent intermediate signals does not exceed the mutual limit superposition rate. Determined.

  The synthesizer 290 synthesizes all the intermediate signals output from the intermediate signal generation units 230-1 to 230 -N and outputs them to the frequency converter 280. The frequency converter 280 performs frequency conversion of the intermediate signal combined by the combiner 290 into a transmission signal having a predetermined carrier frequency band, and outputs the transmission signal obtained by the conversion to the antenna for transmission.

  With the above configuration, the radio resource control unit 210 individually outputs control signals to the intermediate signal generation units 230-1 to 230-N and has an encoder 240, a modulator 250, and a weight calculator. 260 is controlled. As a result, the radio resource control unit 210 superimposes the coding rate, the modulation scheme, the power ratio of the superimposed frequency band and the non-superimposed band, and the average transmission power for each of the N divided bit streams as parameters. The transmission power of each of the transmission signals R1 to Rn included in the signal is controlled.

FIG. 7 is a schematic diagram illustrating a transmission signal (superimposed signal) transmitted by the transmission apparatus 200 according to the present embodiment. The horizontal axis indicates the frequency, and the vertical axis indicates the power value of each signal included in the superimposed signal. Here, a case where the superimposed signal includes transmission signals R1 to R5 will be described (N = 5).
FIG. 7A shows a receiving apparatus that receives a superimposed signal sequentially demodulates and decodes transmission signals R1 to R5 from the superimposed signal while suppressing interference using a signal demodulated and decoded from the outermost side toward the inner side as a foothold. It is a figure which shows the transmission signal in the case (For example, when demodulating and decoding in order of transmission signal R1, R5, R2, R4, R3). At this time, the radio resource control unit 210 uses the average power value included in the control signal output to the weight calculator 260 of the intermediate signal generation units 230-1 to 230-N to be closer to the end of the frequency band than the transmission signal R3. More transmission power is allocated to the transmission signal R2 and the transmission signal R4 arranged at close positions than the transmission signal R3, and the transmission signal R1 and the transmission signal R5 closer to the end of the frequency band than the transmission signal R2 and the transmission signal R4 More transmission power is allocated than signal R3.

For example, the combination of (MCS, average transmission power value) is (64QAM1 / 2, +4 dB) for the transmission signal R1, (64QAM1 / 2, -2 dB) for the transmission signal R2, and for the transmission signal R3. (64QAM1 / 2, −4 dB), (64QAM1 / 2, −2 dB) for the transmission signal R4, and (64QAM1 / 2, +4 dB) for the transmission signal R5. Note that the power ratio between the superposed band and the non-superimposed band is “1.0”.
As a result, when each of the transmission signals R1 to R5 is demodulated and decoded from the superimposed signal in the reception device, the reception power value can be increased as the signal is sequentially demodulated and decoded, and the demodulation and decoding of the transmission signals R1 and R5 is performed. Can reduce the possibility of errors.

  FIG. 7B shows transmission in the case where the receiving apparatus that receives the superimposed signal sequentially demodulates and decodes in order (transmission signals R1, R2, R3, R4, and R5) from the low frequency side to the high frequency side. It is a figure which shows a signal. At this time, the radio resource control unit 210 uses the average power value included in the control signal output to the weight calculator 260 of each of the intermediate signal generation units 230-1 to 230-N to transmit the transmission power of the transmission signals R1 to R5. The transmission power is assigned so that the magnitude relationship of the values is “transmission signal R1> transmission signal R2> transmission signal R3> transmission signal R4> transmission signal R5”. At this time, the coding rate and the modulation scheme may be the same in each of the intermediate signal generation units 230-1 to 230-N. Note that the power ratio between the superimposed band and the non-superimposed band is “1”.

In FIG. 7C, the receiving apparatus that receives the superimposed signal performs successive demodulation and decoding as in FIG. 7A and sets the power ratio between the superimposed band and the non-superimposed band to a value smaller than 1. It is a figure which shows the transmission signal in a case.
As a result, in the superimposed band of adjacent signals, the power of the subcarriers in the superimposed band can be adjusted so that the reception intensity of the signal demodulated and decoded first is lower than the signal demodulated and decoded later. As a result, even if an error is included in the replica signal generated by successive demodulation and decoding, the received power value of a signal that is subsequently demodulated and decoded can be increased, compared to the case of FIG. The probability of error propagation can be further reduced. In the figure, specifically, the transmission power of the superimposition band superimposed on the transmission signal R3 that is sequentially demodulated and decoded after the transmission signal R2 in the frequency band of the transmission signal R2 is low. Even if an error occurs in the successive demodulation decoding, the possibility that the error of the transmission signal R2 propagates to the successive demodulation decoding of the transmission signal R3 can be reduced.

As illustrated in FIGS. 7A to 7C, the radio resource control unit 210 allocates a large amount of transmission power in order from the earliest order of sequential demodulation and decoding in the reception device. Further, the radio resource control unit 210 may assign a signal having a high interference tolerance in order from the earliest order of sequential demodulation and decoding in the receiving apparatus.
The signal interference tolerance is higher for QPSK1 / 2 signals than for signals with a coding rate / modulation method of 64QAM3 / 4, for example. That is, when the transmission power per data to be transmitted is increased, the interference tolerance is increased. In addition, when FEC having higher error correction capability is used, interference tolerance becomes higher. For example, when a signal to which a turbo code is applied is compared at the same coding rate compared to a signal to which an RS (Read-Solomon) code is applied. It has reception characteristics.

Also, radio resource control section 210 performs successive demodulation decoding of the receiving apparatus so that the signal having the highest interference tolerance is first sequentially demodulated and decoded in own transmission apparatus 200, and the signal having the lowest interference tolerance is finally decoded and decoded. The coding rate of each signal, the modulation method, the average power value, and the power ratio between the superposed band and the non-superimposed band may be determined according to the order.
For example, when performing sequential demodulation and decoding in the order shown in FIG. 7A, each parameter is determined as follows. The combination of (MCS, average transmission power value, power ratio of superposed band and non-superimposed band) is (QPSK3 / 4, 0 dB, 1.0) for the transmission signal R1, and (16QAM1 for the transmission signal R2 / 2, 0 dB, 1.0), (64QAM1 / 2, 0 dB, 1.0) for the transmission signal R3, (16QAM1 / 2, 0 dB, 1.0) for the transmission signal R4, and transmission Assume that (QPSK3 / 4, 0 dB, 1.0) for the signal R5.

As described above, the radio resource control unit 210 generates parameters to be transmitted (MCS (coding rate and modulation scheme), average transmission power value, superimposition value, etc.) according to the order of sequential demodulation and decoding in the receiving apparatus. The power ratio between the band and the non-superimposed band) is determined. Accordingly, it is possible to increase the transmission power used when transmitting a signal having a fast sequential demodulation decoding order to increase the interference tolerance, and it is possible to suppress the occurrence of errors at the initial stage of the sequential demodulation decoding. Further, it is possible to reduce the possibility that all signals included in the superimposed signal cannot be correctly demodulated and decoded due to error propagation.
In other words, by increasing the transmission power per bit of data to be transmitted, the interference immunity of signals that are early in the order of sequential demodulation and decoding is increased, and the possibility of occurrence of errors in the initial stage of sequential demodulation and decoding is reduced. In addition, it is possible to reduce the propagation of errors in subsequent demodulation and decoding in successive demodulation and decoding, and it is possible to improve the accuracy of successive demodulation and decoding of all signals included in the superimposed signal.

  Note that the radio resource control unit 210 performs variable serial parallel processing according to the amount of data that each of the intermediate signal generation units 230-1 to 230-N can transmit per unit time according to the selected coding rate and modulation scheme. The data amount of each of the N bit streams output from the converter 220 may be changed. Specifically, the data amount of the bit stream transmitted with the signal with the earlier sequential demodulation decoding order is made smaller than the data amount of the bit stream transmitted with the signal with the later sequential demodulation decoding order. As a result, even when the amount of data that can be transmitted is reduced by setting the coding rate and modulation method, the input bit stream can be transmitted without delay.

Radio resource control section 210 obtains a combination of MCS (coding rate and modulation scheme), transmission average power value, power ratio of superposed band and non-superimposed band, and an index indicating communication quality in the receiving apparatus. An associated table is provided, an index indicating the reception quality of the transmission signals R1 to Rn included in the superimposed signal in the reception device 500 is received, and the MCS, the transmission average power value, and the index corresponding to the index indicating the reception quality Alternatively, a combination of power ratios between the superimposed band and the non-superimposed band may be read from the table, and the transmission power may be set based on the read combination.
Thereby, the superimposed signal according to the reception quality of the transmission signals R1 to Rn in the receiving apparatus 500 can be transmitted, and the superimposed signal can be transmitted so as to prevent the deterioration of the reception quality of the transmission signals R1 to Rn. . The index representing the reception quality is, for example, a BER (Bit Error Rate) or a reception power value of the transmission signals R1 to Rn. In addition, the combinations of MCS, transmission average power value, and power ratio of superposed band and non-superimposed band, which are stored in the table, are based on simulations and actually measured values, and are predetermined. is there.

[Third embodiment]
FIG. 8 is a schematic block diagram illustrating the configuration of the transmission device 300 in the wireless communication system according to the third embodiment. Here, similarly to the transmission apparatus 100 of the first embodiment, a case will be described in which a superimposed signal in which N transmission signals R1 to Rn are superimposed is transmitted. Further, the center frequency and bandwidth of each of the N transmission signals R1 to Rn included in the superimposed signal and the superimposed bandwidth of the adjacent signal are determined in advance. In addition, since the receiving device in the wireless communication system of the present embodiment has the same configuration as the receiving device 500 of the first embodiment, description thereof is omitted.
As shown in the figure, the transmission apparatus 300 includes a radio resource control unit 310, a variable serial / parallel converter 320, baseband signal generation units 330-1 to 330-N, an OFDM signal generator 370, a frequency A converter 380 and combiners 390-1 to 390- (N-1) are provided.

  The radio resource control unit 310 has the same configuration as the radio resource control unit 210 of the second embodiment, and performs control of transmission power of each of the transmission signals R1 to Rn included in the superimposed signal transmitted by the own device. The signal is output to each of the baseband signal generation units 330-1 to 330-N. The variable serial / parallel converter 320 receives an input bit stream to be transmitted, divides the input bit stream into (N × 3) bit streams, and divides the three bit streams into a baseband signal generator. Output to 330-1 to 330-N. Three bit streams input to each of the baseband signal generation units 330-1 to 330-N are transmitted signals R (i−1) adjacent to the low frequency side in the transmission signal Ri (1 ≦ i ≦ n). Correspond to a signal arranged in the superposed band of the transmission signal R (i + 1) adjacent to the high frequency side. However, since there is no signal adjacent to the low frequency side in the transmission signal R1, and no signal adjacent to the high frequency side in the transmission signal Rn, two bit streams are arranged in the non-overlapping area, and one bit stream Are arranged in the overlapping region.

Baseband signal generators 330-1 to 330-N correspond to transmission signals R1 to Rn in order from the lowest frequency band. Further, since the baseband signal generation units 330-1 to 330-N have the same configuration, the configuration of the baseband signal generation unit 330-1 will be described, and the baseband signal generation units 330-2 to 330- Description of N is omitted. The baseband signal generation unit 330-1 includes an encoder 340, a modulator 350, and a weight calculator 360.
The encoder 340 performs error correction encoding on each of the three bit streams input from the variable serial / parallel converter 320 at the encoding rate indicated by the control signal input from the radio resource control unit 310 and outputs the result. Modulator 350 modulates a subcarrier using each of the three bitstreams error-coded by encoder 340 in a modulation scheme represented by a control signal input from radio resource control section 310, and modulates the subcarrier. The three baseband signals obtained by the above are output to the weight calculator 360.

  Based on the average transmission power value and the power ratio included in the control signal input from the radio resource control unit 310, the weight calculator 360 includes the baseband signal among the three baseband signals input from the modulator 350. The baseband signal that is sequentially demodulated and decoded later, the baseband signal to be added, and the other two baseband signals are amplified at different amplification factors. Specifically, the weight calculator 360 has an average power value of the baseband signal for a baseband signal in a frequency band superimposed on a baseband signal that is sequentially demodulated and decoded after the input baseband signal. Amplification is performed so that “(average transmission power value indicated by control signal) × (power ratio between superimposed band and non-superimposed band indicated by control signal)”. On the other hand, the other two baseband signals are amplified so that the average power value of the signal becomes the average transmission power value included in the control signal.

  The weight calculator 360 of the baseband signal generation unit 330-1 outputs the baseband signal of the superposed band on the low frequency side and the baseband signal of the non-superimposed band to the OFDM signal generator 370 and outputs the superposed band on the high frequency side. Are output to the combiner 390-1. The weight calculator 360 of the baseband signal generation unit 330-i (2 ≦ i ≦ N−1) outputs the baseband signal of the superposed band on the low frequency side to the synthesizer 390-i, and the baseband of the non-superimposed band The signal is output to the OFDM signal generator 370, and the baseband signal in the superposed band on the high frequency side is output to the synthesizer 390- (i + 1). The baseband signal generation unit 330-N outputs the baseband signal of the low frequency side superimposition band to the combiner 390- (N-1), and the baseband signal of the non-superimposition band and the superposition band of the high frequency side. The baseband signal is output to OFDM signal generator 370.

  The synthesizer 390-1 includes the baseband signal on the high frequency side superimposed band output from the baseband signal generation unit 330-1 and the frequency band on the low frequency side superimposed band output from the baseband signal generation unit 330-2. The baseband signal is synthesized by addition and output to the OFDM signal generator 370. The synthesizer 390-i (2 ≦ i ≦ N−1) includes a baseband signal on the high frequency side that is output from the baseband signal generation unit 300-i and a baseband signal generation unit 330- (i + 1). A baseband signal obtained by combining the baseband signal of the superposed band on the low frequency side output from the signal is output to the OFDM signal generator 370. The synthesizer 390- (N-1) is output from the baseband signal of the high frequency side superimposition band output from the baseband signal generation unit 330- (N-1) and the baseband signal generation unit 330-N. A baseband signal synthesized by adding the baseband signal of the superposed band on the low frequency side is output to the OFDM signal generator 370.

The OFDM signal generator 370 performs an inverse Fourier transform (Inverse Fast Transform) on the baseband signals input from the baseband signal generators 330-1 to 330 -N and the combiners 390-1 to 390-(N−1). Fourier transform (IFFT) is performed to convert the signal from the frequency domain to the time domain and output to the frequency converter 380.
The frequency converter 380 converts the frequency of the signal input from the OFDM signal generator 370 into a carrier band transmission signal, and outputs the transmission signal obtained by the conversion to the antenna for transmission.

  As described above, when OFDM modulation is used for the FEC likelihood mask and interference suppression processing, transmitting apparatus 300 performs addition processing of a plurality of signal sequences in the baseband region, and transmits only subcarriers in the frequency band to be superimposed on each other. The added subcarrier and the subcarrier in the non-superimposed band can be input to an OFDM signal generator 370 (inverse Fourier transformer) to generate a superimposed signal on which transmission signals R1 to Rn are superimposed. Thereby, it is possible to perform superimposed transmission without providing a plurality of frequency converters in order to convert a plurality of baseband signals to an intermediate frequency, and the configuration of the transmission apparatus can be simplified.

Radio resource control section 310 obtains a combination of MCS (coding rate and modulation scheme), transmission average power value, power ratio between the superimposed band and the non-superimposed band, and an index indicating the communication quality in the receiving apparatus. An associated table is provided, an index indicating the reception quality of the transmission signals R1 to Rn included in the superimposed signal in the reception device 500 is received, and the MCS, the transmission average power value, and the index corresponding to the index indicating the reception quality Alternatively, a combination of power ratios between the superimposed band and the non-superimposed band may be read from the table, and the transmission power may be set based on the read combination.
Thereby, the superimposed signal according to the reception quality of the transmission signals R1 to Rn in the receiving apparatus 500 can be transmitted, and the superimposed signal can be transmitted so as to prevent the deterioration of the reception quality of the transmission signals R1 to Rn. . The index representing the reception quality is, for example, a BER (Bit Error Rate) or a reception power value of the transmission signals R1 to Rn. In addition, the combinations of MCS, transmission average power value, and power ratio of superposed band and non-superimposed band, which are stored in the table, are based on simulations and actually measured values, and are predetermined. is there.

[Fourth embodiment]
Subsequently, a fourth embodiment of the present invention will be described. The wireless communication system according to the present embodiment includes N transmission devices and at least one reception device.
FIG. 9 is a schematic block diagram illustrating a configuration of transmission apparatuses 400-1 to 400-N (N = n is a natural number of 2 or more) of the wireless communication system according to the fourth embodiment, and frequency bands of signals transmitted by the respective apparatuses. It is the figure which showed an example of arrangement | positioning in. Here, a case will be described in which the transmission apparatus 200 transmits a superimposed signal in which N transmission signals R1 to Rn are superimposed, similarly to the transmission apparatus 100 of the first embodiment. Further, the center frequency and bandwidth of each of the N transmission signals R1 to Rn included in the superimposed signal and the superimposed bandwidth of the adjacent signal are determined in advance. In addition, since the receiving device in the present embodiment has the same configuration as that of the receiving device 500 in the first embodiment, the description of the configuration and the description of the processing are omitted.

  In the figure, transmitting apparatuses 400-1 to 400-N have the same configuration, and each includes a radio resource control unit 410, an encoder 240, a modulator 250, a weight calculator 260, and a frequency. And a converter 470. In addition, the same code | symbol (240, 250, 260) is attached | subjected to the same structure as the transmitter 200 of 2nd Embodiment, and the description is abbreviate | omitted.

The radio resource control unit 410 has the same configuration as that of the radio resource control unit 210 of the second embodiment, and a transmission signal Ri (1) transmitted by the own device according to reception quality such as a reception power value in the reception device. ≦ i ≦ n), a control signal for controlling the transmission power is output to the encoder 240, the modulator 250, and the weight calculator 260. Specifically, the radio resource control unit 410 determines the magnitude relationship between the received power value of the signal that is adjacently superimposed on the frequency axis and the received power of the signal transmitted by the own device, and the receiving device transmits the transmitted signals R1 to Rn. Parameters for the coding rate, modulation scheme, average transmission power, and power ratio between the superposed band and the non-superimposed band are set at predetermined time intervals based on the order of sequential demodulation and decoding A control signal including is output.
The frequency converter 470 converts the baseband signal input from the weight calculator 260 into a carrier frequency, and outputs the transmission signal obtained by the conversion to the antenna for transmission. As shown in FIG. 9, the signal transmitted by each of the transmission apparatuses 400-1 to 400-N has a predetermined center frequency and frequency bandwidth so that ends of adjacent signals are superimposed on the frequency axis. It has been.

With the above configuration, the transmission apparatuses 400-1 to 400-N can transmit the transmission signals R1 to Rn with transmission power corresponding to the reception quality in the reception apparatus, and are thus synthesized on the transmission path received by the reception apparatus. In addition, the received power of the transmission signals R1 to Rn included in the superimposed signal can be increased in the order of early demodulation and decoding. As a result, it is possible to increase the interference tolerance of signals that are earlier in the order of sequential demodulation and decoding, thereby reducing the possibility of errors in the initial stage of sequential demodulation and decoding, and to perform sequential demodulation and decoding of all signals included in the superimposed signal. Accuracy can be improved.
In this way, even in a wireless communication system that performs FEC likelihood masking and interference suppression processing on a signal that is superimposed and transmitted, it is possible to reduce the propagation of errors in subsequent demodulation decoding in successive demodulation decoding.

  Note that the amplifying unit described in the present invention corresponds to the weight calculator 260 and the weight calculator 360.

  The present invention can be applied to a communication apparatus and a communication system that transmit a plurality of signals by wireless communication, regardless of whether it is a mobile station or a fixed station.

DESCRIPTION OF SYMBOLS 100, 200, 300 ... Transmission apparatus 120 ... Serial / parallel converter 130-1, 130-2, 130-3, 130-N ... Transmission part 140, 240, 340 ... Encoder 150, 250, 350 ... Modulator 170, 270, 280, 380, 470 ... Frequency converter 191 ... Synthesizer 210, 310, 410 ... Radio resource control unit 220, 320 ... Variable serial / parallel converter 230-1, 230-2, 230-3, 230 -N ... intermediate signal generator 260, 360 ... weight calculator 290 ... combiner 330-1, 330-2, 330-3, 330-N ... baseband signal generator 370 ... OFDM signal generator 390-1, 390 -2, 390-3, 390- (N-1) ... Synthesizers 400-1, 400-2, 400-3, 400-N ... Transmitting device 500 ... Receiving device 5 0 ... Decoding counter 515 ... Switch 520 ... Subtractor 525 ... Delay units 530, 530a ... Processing band determiner 535 ... Local signal generator 540 ... Mixer 545 ... Band pass filters 550, 550a ... Transmission path estimators 555, 555a ... demodulator 557 ... band extractor 560 ... weight coefficient generator 565 ... first weight calculator 570 ... decoder 575 ... data buffer 580 ... replica generator 582 ... re-encoder 584 ... remodulator 586 ... second weight Arithmetic unit 590 ... Data extraction / rearranger

Claims (5)

A plurality of transmission signals whose ends are superimposed on an adjacent transmission signal in the frequency domain and to which an error correction code is applied are received as a superimposed signal, and the transmission signal of the highest frequency or the lowest frequency band among the superimposed signals is demodulated and decoded. In addition, a process of generating a replica signal of the transmission signal demodulated and decoded and removing it from the superimposed signal is repeated, and the plurality of transmission signals are transmitted to a receiving apparatus that performs demodulation decoding of the transmission signal included in the received superimposed signal A transmitting device,
A control unit configured to set transmission power of each of the plurality of transmission signals according to an order in which the reception device decodes the plurality of transmission signals;
An amplifying unit that amplifies a transmission signal according to transmission power set by the control unit. The transmission device according to claim 1, wherein the control unit increases transmission power of the transmission signal in an order from an earlier order of decoding by the reception device among the plurality of transmission signals. The transmission apparatus according to claim 2, wherein the control unit lowers the transmission power of the superimposition band of transmission signals that are received in a fast order of decoding among the transmission signals having a common superposition band. An encoder that performs error correction coding on data to be transmitted;
A modulator for modulating data encoded by the encoder;
A frequency converter that converts the frequency of the data modulated by the modulator into a plurality of transmission signals; and
With
The control unit lowers the coding rate in the encoder or decreases the number of bits per symbol in the modulator in order from the earliest decoding order of the plurality of transmission signals by the receiving device. The transmission device according to any one of claims 1 to 3, wherein the transmission device is configured as follows. A plurality of transmission signals whose ends are superimposed on an adjacent transmission signal in the frequency domain and to which an error correction code is applied are received as a superimposed signal, and the transmission signal of the highest frequency or the lowest frequency band among the superimposed signals is demodulated and decoded. In addition, a process of generating a replica signal of the transmission signal demodulated and decoded and removing it from the superimposed signal is repeated, and the plurality of transmission signals are transmitted to a receiving apparatus that performs demodulation decoding of the transmission signal included in the received superimposed signal A transmission method in a transmission device, comprising:
A control process for setting the transmission power of each of the transmission signals according to the order in which the reception device decodes the plurality of transmission signals;
An amplification process for amplifying a transmission signal according to the transmission power set in the control process.

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