JP2011119845A - Radio communication system, transmitter, receiver, radio communication method, transmission method, reception method and spectrum arrangement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately demodulate and decode reception signals at a reception side without increasing the number of antennas in a radio superimposed transmission system to which an error correction code is applied. <P>SOLUTION: In the superimposed transmission system of arranging spectra so that a plurality of signals are overlapped on a frequency axis and transmitting them in the transmitter and repeating successive demodulation/decoding processing procedures of the overlapped signals while using interference suppression processing and interference elimination processing in the receiver at the transmitter side, the nulling processing of a data subcarrier is performed so as not to superimpose other signals on a pilot subcarrier used for transmission line estimation among the respective signals. At the receiver side, the successive demodulation/decoding processing is performed by applying the interference suppression processing to the subcarrier to which the nulling processing is performed, the transmission line estimation is performed using the pilot subcarrier to which superimposition is not performed, and replica signals used for interference elimination are generated by estimated transmission line characteristics. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radio communication system, a transmission apparatus, a reception apparatus, a radio communication method, a transmission method, a reception method, and a spectrum arrangement method that perform multicarrier transmission using an error correction code.

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. .
In addition, studies on superposition transmission techniques that improve frequency utilization efficiency by sharing frequencies without increasing the number of antennas are underway.

  For example, FIG. 13 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 whose center frequency is fa. On the other hand, the wireless LAN base station 2b communicates using the frequency band of CH5 whose center frequency is 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. Receive signals that partially interfere with each other. As another example of sharing the frequency band, there may be a case where systems of different communication methods share a frequency such as a combination of a wireless LAN system, Bluetooth (registered trademark), and WiMAX (registered trademark).

  As described above, when the receiver 1a shown in FIG. 13 targets the wireless LAN base station 2a as a communication target, the transmission frequency band of the desired wave having the center frequency fa and the transmission from the wireless LAN base station 2b having the center frequency fb. In the frequency sharing type wireless communication in which the frequency band partially overlaps (superimposes), it is essential that the receiver 1a accurately receives the desired wave. In general, when there is interference due to superposition of such frequency bands, the communication characteristics are significantly degraded.

  Therefore, Non-Patent Document 2 describes a technology for realizing transmission by decoding FEC (Forward Error Correction) blocks distributed and arranged while suppressing the influence of this interference. In this Non-Patent Document 2, after the signal of the transmission frequency band to which the desired wave is assigned is demodulated, the reliability of the likelihood information obtained from the signal in the frequency band (interference band) affected by the interference wave is lowered. By performing the FEC likelihood mask, the likelihood information affected by the interference wave is suppressed, and then error correction decoding is performed, so that a desired signal in an environment where an interference band exists with another transmission frequency band Transmission is possible.

Satoshi Kurosaki, Yusuke Sakurai, Takatoshi Sugiyama, Masahiro Umehira, “Proposal of SDM-COFDM System for Broadband Mobile Communication Realizing 100Mbit / s with MIMO Channel”, IEICE Technical Report, RCS2001-135, pp. 37-41, October 2001 Satoshi Masuno and 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

  However, in the multiple antenna technology, it is necessary to increase the number of antennas in order to improve the characteristics by improving the number of spatial multiplexing or generating multiple null patterns. Implementation in transceivers where miniaturization is important was not realistic. On the other hand, in Non-Patent Document 2 in which interference suppression processing is performed, demodulation decoding is performed in order from a signal having a center frequency arranged in the outermost band, and a replica signal of the corresponding signal is generated from the decoding result and subtracted from the received signal Thus, the successive demodulation and decoding method enables superposition transmission at a superposition rate exceeding the limit value of the overlap bandwidth ratio resulting from the interference suppression method. However, since interference cancellation is cascaded, if a highly accurate replica signal based on the propagation path state on the superimposed band cannot be generated, error propagation occurs in the received signal after replica signal removal, and the signal is accurately demodulated and decoded. It becomes difficult to do. In order to avoid such error propagation, it is required to accurately generate a replica signal to be subtracted from the received signal. For this purpose, it is necessary to accurately estimate the transmission path state of the superposed band. However, in general multicarrier superposition transmission, a pilot signal used for transmission path estimation is also superimposed with other signals, so that the transmission path estimation accuracy, and thus the accuracy of replica signal subtraction processing, decreases.

  The present invention has been made in view of the above problems, and an object of the present invention is to accurately decode and decode a received signal on the receiving side without increasing the number of antennas in a wireless superposition transmission system to which an error correction code is applied. An object of the present invention is to provide a wireless communication system, a transmission device, a reception device, a wireless communication method, a transmission method, a reception method, and a spectrum allocation method.

  In order to solve the above-described problem, the present invention provides a wireless communication system including a multicarrier signal transmission apparatus and a reception apparatus that receives a superimposed signal on which the multicarrier signal is superimposed, the transmission apparatus comprising: , A data subcarrier that is a subcarrier that is obtained by modulating a data signal that is encoded by applying an error correction code, and a pilot subcarrier that is a subcarrier of a pilot signal are combined with pilot subcarriers of other multicarrier signals. A spectrum arrangement unit that performs spectrum arrangement so as not to be superposed, and a multicarrier signal generation unit that generates the multicarrier signal from the data subcarrier and the pilot subcarrier according to the spectrum arrangement by the spectrum arrangement unit; Was generated by the transmitter A transmission path for performing transmission path estimation using a pilot subcarrier included in the processing target signal, using the superimposed signal on which the multicarrier signal is superimposed or a signal obtained by removing a replica signal from the superimposed signal as a processing target signal The estimation unit and the highest frequency band or the lowest frequency band among the frequency bands of the multicarrier signal included in the processing target signal are set as demodulation decoding targets, and the overlapping band is suppressed for the processing target signal in the demodulation decoding target An interference suppression demodulation unit that obtains the demodulated value, a decoding unit that performs error correction decoding using the demodulated value obtained by the interference suppression demodulation unit, data obtained as a result of error correction decoding by the decoding unit, A replica generation unit that generates a multicarrier signal of a replica based on a transmission path estimation value by the transmission path estimation unit , And a subtractor for the multi-carrier signal of the replica generated by the replica generation unit is removed from the processed signal to generate a new processing object signal is a wireless communication system, characterized in that.

  Further, the present invention is the above-described wireless communication system, wherein the spectrum allocation unit assigns a predetermined subcarrier position for a data subcarrier to the data subcarrier and is predetermined for the pilot subcarrier. Nulling the data subcarrier or the pilot subcarrier to which the subcarrier position transmitted by the same frequency as that of the pilot subcarrier of another multicarrier signal is allocated. Features.

  Further, the present invention is the above-described wireless communication system, wherein the interference suppression demodulation unit includes: a demodulation unit that obtains a demodulation value of the processing target signal in the demodulation decoding target; and a superimposed band of the demodulation decoding target. A weighting factor generating unit that generates a weighting factor for reducing reliability of the demodulated value obtained by the demodulating unit, and the weighting factor generated by the weighting factor generating unit to the demodulated value obtained by the demodulating unit. And a decoding unit that performs error correction decoding using the demodulated value to which the weight coefficient is applied by the weight calculation unit.

  Further, the present invention is the above-described wireless communication system, wherein the interference suppression demodulation unit is extracted from the processing target signal by a filter unit that extracts a non-overlapping band to be demodulated and decoded, and the filter unit And a demodulator that obtains a demodulated value for the non-superimposed band to be demodulated and decoded.

  The present invention is also a transmitting apparatus that transmits the multicarrier signal to a receiving apparatus that receives a superimposed signal on which a multicarrier signal is superimposed, and modulates a data signal that has been encoded by applying an error correction code. A spectrum arrangement unit that performs spectrum arrangement so that a data subcarrier that is a subcarrier and a pilot subcarrier that is a subcarrier of a pilot signal are not superimposed on pilot subcarriers of other multicarrier signals, and the spectrum arrangement unit And a multicarrier signal generation unit that generates and outputs the multicarrier signal from the data subcarrier and the pilot subcarrier according to the spectrum arrangement according to.

  In addition, the present invention superimposes a multicarrier signal composed of a data subcarrier that is a subcarrier obtained by modulating a data signal that has been encoded using an error correction code, and a pilot subcarrier that is a subcarrier of the pilot signal. A reception device for receiving the superimposed signal, wherein the signal to be processed is a signal obtained by removing the replica signal from the superimposed signal or the superimposed signal spectrum-arranged so that pilot subcarriers are not superimposed; A transmission path estimation unit that performs transmission path estimation using pilot subcarriers included in the signal, and the highest frequency band or the lowest frequency band among the frequency bands of the multicarrier signal included in the processing target signal. And the processing target signal in the demodulation decoding target An interference suppression demodulator that obtains a demodulated value in which the signal is suppressed, a decoder that performs error correction decoding using the demodulated value obtained by the interference suppression demodulator, and data obtained as a result of error correction decoding by the decoder A replica generation unit that generates a replica multicarrier signal based on the transmission path estimation value by the transmission path estimation unit, and the replica multicarrier signal generated by the replica generation unit is removed from the processing target signal And a subtractor that generates a new signal to be processed.

  The present invention is also a wireless communication method used in a wireless communication system including a multicarrier signal transmission device and a reception device that receives a superimposed signal on which the multicarrier signal is superimposed, the transmission device comprising: A data subcarrier that is a subcarrier obtained by modulating a data signal that is encoded by applying an error correction code and a pilot subcarrier that is a subcarrier of a pilot signal are superimposed on pilot subcarriers of other multicarrier signals. A spectrum arrangement step for performing spectrum arrangement so as not to be performed, and a multicarrier signal generation step for generating the multicarrier signal from the data subcarrier and the pilot subcarrier according to the spectrum arrangement by the spectrum arrangement step, Is the transmitter A signal to be processed is the superimposed signal on which the multi-carrier signal generated by the signal is superimposed or a signal obtained by removing a replica signal from the received superimposed signal, and is transmitted using pilot subcarriers included in the signal to be processed A transmission path estimation step for performing path estimation, and the highest frequency band or the lowest frequency band among the frequency bands of the multicarrier signal included in the processing target signal, and the processing target in the demodulation decoding target An interference suppression demodulation step for obtaining a demodulated value in which a superimposed band is suppressed for the signal; a decoding step for performing error correction decoding using the demodulated value obtained in the interference suppression demodulation step; and a result of error correction decoding in the decoding step The obtained data and the transmission obtained by the transmission path estimation step. A replica generation step of generating a replica multicarrier signal based on the path estimation value, and generating a new processing target signal by removing the replica multicarrier signal generated in the replica generation step from the processing target signal And a subtracting step, wherein the processing from the transmission path estimating step is repeated using the processing target signal generated in the subtracting step.

  The present invention is also a transmission method used in a transmitting apparatus that transmits the multicarrier signal to a receiving apparatus that receives a superimposed signal on which a multicarrier signal is superimposed, and performs encoding by applying an error correction code. A spectrum arrangement step for performing spectrum arrangement so that a data subcarrier that is a modulated subcarrier of a data signal and a pilot subcarrier that is a subcarrier of a pilot signal are not superimposed on pilot subcarriers of other multicarrier signals; And a multicarrier signal generation step of generating the multicarrier signal from the data subcarrier and the pilot subcarrier according to the spectrum allocation by the spectrum allocation step.

  In addition, the present invention superimposes a multicarrier signal composed of a data subcarrier that is a subcarrier obtained by modulating a data signal that has been encoded using an error correction code, and a pilot subcarrier that is a subcarrier of the pilot signal. A reception method used for a receiving apparatus that receives the superimposed signal, and the signal to be processed is the superimposed signal that is spectrally arranged so that pilot subcarriers are not superimposed, or a signal obtained by removing a replica signal from the superimposed signal A transmission path estimation step for performing transmission path estimation using pilot subcarriers included in the processing target signal, and a highest frequency band or a lowest frequency among the frequency bands of the multicarrier signal included in the processing target signal A band is a demodulation decoding target, and the demodulation decoding target An interference suppression demodulation step for obtaining a demodulated value in which a superposition band is suppressed for the target signal, a decoding step for performing error correction decoding using the demodulated value obtained in the interference suppression demodulation step, and an error correction decoding in the decoding step A replica generation step of generating a replica multi-carrier signal based on the data obtained as a result of the above and the transmission path estimation value obtained by the transmission path estimation step; and the replica multi-path generated in the replica generation step A subtraction step of generating a new processing target signal by removing a carrier signal from the processing target signal, and repeating the processing from the transmission path estimation step using the processing target signal generated in the subtraction step The receiving method is characterized by the above.

  The present invention also relates to a method for arranging a spectrum of a superimposed signal on which a multicarrier signal is superimposed, a data subcarrier that is a subcarrier obtained by modulating a data signal encoded by applying an error correction code, and a pilot. In a transmission apparatus that transmits the multicarrier signal including pilot subcarriers that are signal subcarriers, the data subcarrier and the pilot subcarrier included in the transmitted multicarrier signal are pilots of other multicarrier signals. A spectrum allocation method is characterized in that spectrum allocation is performed so as not to be superposed on subcarriers.

  According to the present invention, a transmitter arranges and transmits a spectrum such that a plurality of multicarrier signals overlap on the frequency axis, and the receiver uses the interference suppression process and the interference removal process together. In the superposition transmission scheme that repeats the sequential demodulation / decoding processing procedure of the wrapped multicarrier signal, the transmitting apparatus side does not superimpose other signals on the pilot subcarriers used for channel estimation in each multicarrier signal. In addition, subcarrier nulling is performed, and on the receiving device side, interference suppression processing is applied to the subcarriers subjected to nulling to perform sequential demodulation and decoding, and a replica signal used for interference removal is superimposed. It is generated using the channel characteristics estimated using the pilot subcarriers that are not used. Thereby, the transmission path estimation accuracy is improved, the interference removal process is appropriately performed, and the reception characteristics are improved. In addition, when multicarrier signals to be superimposed are transmitted from the same transmitter, it is possible to perform transmission path estimation by sharing pilot subcarriers between the superimposed signals.

It is a figure explaining superposition transmission. It is a figure which shows the superimposition signal using a multicarrier signal. It is a figure which shows the outline | summary of the signal reception process in the receiver by embodiment of this invention. It is a figure explaining the demodulation decoding by a FEC likelihood mask. It is a functional block diagram of the transmitter by 1st Embodiment. It is a functional block diagram of the receiver by 1st Embodiment. It is a figure which shows the relationship between the frequency | count of the demodulation decoding process in the receiver by 1st Embodiment, the demodulation decoding object, and a weighting coefficient. It is a functional block diagram of the transmitter by 2nd Embodiment. It is a functional block diagram of the receiver by 2nd Embodiment. It is a figure which shows the relationship of the frequency | count of the demodulation decoding process in the receiver by 2nd Embodiment, a demodulation decoding object, and a weighting coefficient. It is a functional block diagram of a filtering process part. It is a flowchart which shows the filter control procedure of the filtering process part shown in FIG. It is a figure which shows the interference in two radio | wireless communications systems from which a frequency channel differs.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
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. In this way, since frequency resources are partially shared by a plurality of signals, superposition transmission is used rather than the band f _all that is necessary for transmitting the plurality of signals when the conventional spectrum arrangement is used. In this case, the band f ′ _all necessary for transmitting a plurality of signals becomes smaller, and the frequency utilization 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 illustrating a superimposed signal using a multicarrier signal. FIG. 2A is a superimposed signal received by the receiving apparatus in the wireless communication system according to the present embodiment, and FIG. Superposition signal.
In the wireless communication system of the present embodiment, the reception device receives a superimposed signal on which a plurality of signals R1 to Rn (n ≧ 2, n is an integer) are superimposed. Each of the signals R1 to Rn is a multicarrier signal such as OFDM (Orthogonal Frequency Division Multiplexing), and FEC (Forward Error Correction) code is used as error code correction. Each signal R1 to Rn includes a data subcarrier that is a subcarrier used for a data signal and a pilot subcarrier used for a pilot signal.
Here, it is assumed that each of the five signals R1 to R5 is partially overlapped with the superimposed signal received by the receiving apparatus according to the present embodiment, and the signal R1 is sequentially from the signal having the lowest center frequency in the frequency band to be used. , R2, R3, R4, R5.

  As shown in FIG. 2 (b), when signals R1a to R5a, which are conventional multicarrier signals, are transmitted with being superimposed, the same in the overlapping band regardless of whether they are data subcarriers or pilot subcarriers. Subcarriers using frequencies were superimposed. On the other hand, as shown in FIG. 2A, the transmission apparatus of the wireless communication system according to the present embodiment nulls data subcarriers that use the same frequency as pilot subcarriers of other signals in the superimposed band, that is, null ( Replace with zero).

  Specifically, as shown in FIG. 2A, the data subcarrier of signal R1 is nulled for the frequency at which the pilot subcarrier of signal R2 is arranged in the overlapping band of signal R1 and signal R2. Further, for the frequency at which the pilot subcarrier of signal R3 is arranged in the overlapping band of signal R3 and signal R2, the data subcarrier of signal R2 is nulled, and the pilot of signal R3 is overlapped in the overlapping band of signal R3 and signal R4. For the frequency at which the subcarrier is arranged, the data subcarrier of the signal R4 is nulled. Further, in the overlapping band of signal R4 and signal R5, the data subcarrier of signal R5 is nulled for the frequency at which the pilot subcarrier of signal R4 is arranged.

As described above, in the frequency band where the signal Ri and the signal R (i + 1) (1 ≦ i ≦ (n−1), i is an integer) overlap, the same frequency is used so that the pilot subcarriers of the signal Ri are not superimposed. Null the data subcarriers of the signal R (i + 1) transmitted using the same, and similarly, the data subcarriers of the signal Ri transmitted using the same frequency so that the pilot subcarriers of the signal R (i + 1) are not superimposed. Nulling.
Thereby, even when signals R1 to Rn are transmitted in a spectrum arrangement so as to overlap on the frequency axis, only the pilot subcarriers are always transmitted without being superimposed.

FIG. 3 is a diagram showing an outline of signal reception processing in the receiving apparatus according to the present embodiment.
Here, a description will be given assuming that a superimposed signal on which signals R1 to R5 shown in FIG.
Hereinafter, the frequency band used by the 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 referred to as an outer band. For example, in the case of the processing target signal A1 shown in FIG. 3, the frequency bands f1 and f5 of the 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. 3, the receiving apparatus of the present embodiment first demodulates and decodes a signal R1 that 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”). Details will be described later with reference to FIG. When the receiving device decodes the signal R1, the receiving device generates a replica signal R1 'of the signal R1 from the bit stream obtained by 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 signals R2 to R5 are superimposed is generated. When demodulating the signal R1, when generating the replica signal R1 ', the transmission path characteristic estimated using the pilot signal is used.

Subsequently, the receiving apparatus performs demodulation decoding of the 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 receiving device decodes the signal R2, the receiving device generates a replica signal R2 ′ of the signal R2 from the bit stream obtained by 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 signals R3 to R5 are superimposed is generated. When demodulating the signal R2, when generating the replica signal R2 ′, the transmission path characteristic estimated using the pilot signal is used.
By repeating the above, the receiving apparatus performs demodulation decoding of the signals R3 and R4 by the FEC likelihood mask and FEC decoding, and removes the replica signals R3 ′ and R4 ′ to obtain the processing target signal A5 including only the signal R5. . 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 signal R5.

  As described above, when receiving the signal transmitted by the superposition transmission method, the receiving apparatus according to the present embodiment estimates the channel characteristic of the outer band signal using the non-superimposed pilot signal, and the estimated channel characteristic. The signal demodulated by using the likelihood mask is subjected to interference suppression by the likelihood mask, then FEC decoding is performed, and the replica signal is generated from the demodulated signal using the estimated transmission path characteristics, and the generated replica signal is received signal By subtracting from the signal, successive demodulation and decoding of the superimposed signal is performed while removing interference.

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

FIG. 4 is a diagram for explaining demodulation decoding using the FEC likelihood mask.
This figure shows a case where a part of the signal Ri to be demodulated and decoded is superimposed on another signal R (i + 1), and the signal R (i + 1) can be further superimposed on another signal. The receiving apparatus performs demodulation according to the encoding method used for the 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. 4A is a diagram illustrating an example of a result of the demodulation of the superimposed signal in the frequency band fi used by the signal Ri performed by the reception apparatus. For each subcarrier at the data subcarrier position of the signal Ri, positive and negative are illustrated. Indicates that a demodulated value of multi-level output has been obtained. Since the pilot subcarrier of the signal Ri is not subject to demodulation, a demodulated value cannot be obtained. The data subcarrier of the signal Ri that is nulled so as not to be superimposed on the pilot subcarrier of the signal R (i + 1) is a demodulation target, but the obtained demodulated value is a meaningless value. The pilot subcarrier is used for transmission path estimation.
In the frequency band fi shown 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. 4B is a diagram illustrating weighting factors used for the likelihood mask of the frequency band fi. The weighting coefficient corresponds to each subcarrier at the data subcarrier position included in the signal Ri, uses the demodulated value as it is for the data subcarrier in the non-superimposed band, and the data subcarrier of the signal R (i + 1) in the superimposed band. The demodulated value is set to 0 for the superimposed data subcarriers, or the demodulated value is set to 0 for the data subcarriers nulled in the superimposed band, that is, the pilot subcarriers of the signal R (i + 1). Is a coefficient for That is, the weighting factor of each data subcarrier in the non-superimposed band is “1”, the weighting factor of each data subcarrier that is not nulled in the superimposed band is “k” (0 ≦ k <1), and the superposed band is nulled. The weight coefficient of the data subcarrier is “0”.

  FIG. 4 (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. 4A by the weighting factor shown in FIG. 4B for each corresponding subcarrier. That is, for the data subcarriers in the non-superimposed band, a value obtained by multiplying the demodulated value and the weighting coefficient “1”, and for the data subcarriers in the superimposed band that are not nulled, the demodulated value and the weighting coefficient “k” (0 ≦ k <1), the nulled data subcarrier, that is, the pilot subcarrier of the signal R (i + 1) in the superposed band, is weighted as a value obtained by multiplying the demodulated value and the weighting coefficient “0”. A later likelihood data string is obtained. Accordingly, as shown in FIG. 4C, the likelihood data value of the data subcarriers that are nulled in the superposed band has a value “0” that has the lowest reliability, and the data subcarriers that are not nulled in the superposed band. The value of the likelihood data after the corresponding weight calculation has a reliability of “0” or “a value close to 0”, and the demodulated value of the subcarrier in the non-superimposed band does not change.

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 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 of each subcarrier, masks data subcarriers in a superimposed band with low reliability, and pilot subcarriers of other signals whose demodulated values do not mean, and reliability By decoding a received signal using a demodulated value of a high data subcarrier, it is possible to improve 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.

In wireless communication, a reflected wave is received in addition to a direct wave, and a valley may occur in the frequency response of the propagation path according to the number of reflection paths, so that a subcarrier existing in the equal frequency band may not be received. Therefore, there is a method for dealing with these unforeseen situations by performing encoding with redundancy such as FEC code (for example, 32 bits are consumed to transmit 16 bits). . When an error correction code is combined with a multi-carrier transmission scheme such as OFDM, it is combined with a bit interleaver or subcarrier interleaver, and each bit of 32-bit FEC encoded data having redundancy as described above is a completely different subcarrier. In general, the data is transmitted in a distributed manner. This makes it possible to avoid data burst errors due to missing specific subcarriers.
In the embodiment of the present invention, by utilizing some of these redundancy and error correction effects, even if some data is lost by nulling on the transmission side, the error correction capability of FEC Since it is relieved by other received data that can be received, data transmission can be performed accurately. Furthermore, in this embodiment, since the pilot signal transmission and reception are prioritized, the generation accuracy of the received replica signal can be dramatically improved, so that it is possible to prevent the occurrence of error propagation in the successive demodulation / decoding process. It becomes.

[First Embodiment]
A radio communication system according to a first embodiment of the present invention will be described. In the first embodiment, one transmission device divides and superimposes one transmission data signal into N signals R1 to Rn and transmits the signals to the reception device.

FIG. 5 is a schematic block diagram illustrating a configuration of the transmission device 100 in the wireless communication system according to the first embodiment of this invention.
In the figure, a transmission apparatus 100 includes a serial / parallel converter (hereinafter referred to as “S / P converter”) 110, encoders 120-1 to 120-n (2 ≦ n, n is an integer), modulation. Units 130-1 to 130-n, pilot signal inserters 140-1 to 140-n, a superimposing signal generator 150, and an OFDM signal generator 160. In the figure, a case where n = 3 is shown as an example.

  The S / P converter 110 converts the input input bit stream from a serial signal sequence to a parallel signal sequence and divides it into N bit streams, and each of the divided bit streams is encoded by an encoder 120-1. To 120-n.

  The encoder 120-i (1 ≦ i ≦ n) performs predetermined error correction encoding on the bit stream input from the S / P converter 110, and outputs it to the modulator 130-i. The modulator 130-i (1 ≦ i ≦ n) is a predetermined modulation scheme for the error correction encoded bitstream input from the encoder 120-i, for example, BPSK (Binary phase-shift keying; A data signal is generated by performing modulation in units of subcarriers using 2 phase shift keying), 16 QAM (16 Quadrature amplitude modulation), or the like. That is, the generated data signal is composed of data subcarriers. The pilot signal inserter 140-i (1 ≦ i ≦ n) inserts the pilot signal at a predetermined position of the data signal generated by the modulation by the modulator 130-i, and generates a frequency domain signal. As a result, a frequency domain signal in which pilot subcarriers are inserted into data subcarriers is generated.

  Superimposition signal generator 150 includes null permuters 152-1 to 152-n and combiners 154-1 to 154-m (m is the number of subcarriers in the superimposition band), and includes pilot signal inserters 140-1 to 140-1. The data subcarrier assigned with the same subcarrier position as the pilot subcarrier is nulled with respect to the frequency domain signal generated by 140-n, and then the subcarrier in the superposed band is superposed to the OFDM signal generator 160. Output.

The null replacer 152-i (1 ≦ i ≦ n) assigns a subcarrier position to each subcarrier of the frequency band signal output from the pilot signal inserter 140-i, and another null replacer 152-k (1 Null data subcarriers at subcarrier positions assigned to pilot subcarriers in ≦ k ≦ n, k ≠ i). Null permuters 152-1 to 152-n output non-superimposed band subcarriers to OFDM signal generator 160, and for superimposed band subcarriers, combiners 154-1 to 154 corresponding to subcarrier positions. Output to -m.
The combiners 154-1 to 154-m correspond to the respective subcarrier positions in the superimposed band, and the subcarriers output from the null replacers 152-1 to 152-n as being the subcarrier positions corresponding to the combiners 154-1 to 154-m. Synthesize a carrier.

  The OFDM signal generator 160 performs an inverse Fourier transform by IFFT (Inverse Fast Fourier Transform) or IDFT (Inverse Discrete Fourier Transformation) on the subcarrier output from the superimposed signal generator 150 to generate an OFDM time signal, and transmits a transmission signal. Is output wirelessly.

Next, the operation of the transmission device 100 of this embodiment will be described.
Here, a case will be described in which transmitting apparatus 100 generates a superimposed signal in which signals R1 to R3 each consisting of 6 subcarriers are superimposed. The subcarrier positions of the subcarriers included in this superimposed signal are SC1 to SC12 in order of frequency, signal R1 is subcarrier positions SC1 to 6, signal R2 is subcarrier positions SC4 to 9, and signal R2 is subcarrier positions SC7 to SC7. 12 is used. For simplicity, four subcarriers among the six subcarriers of the signals R1 to R3 will be described as data subcarriers. However, the ratio of data subcarriers is usually higher than this.

  (Process 1-1): The S / P converter 110 converts the input bit stream from a serial signal sequence to a low-speed parallel signal sequence and divides the input bit stream into three sequence bit streams. Are output to encoders 120-1 to 120-3, respectively.

  (Processing 1-2): The encoder 120-i (1 ≦ i ≦ 3) performs error correction coding on the bit stream input from the S / P converter 110, and sends it to the modulator 130-i. Output.

  (Process 1-3): The modulator 130-i (1 ≦ i ≦ 3) converts the error correction encoded bit stream output from the encoder 120-i into subcarriers according to a predetermined modulation scheme. The data signal modulated in units is output to the pilot signal inserter 140-i. The generated data signal is composed of four data subcarriers.

  (Processing 1-4): Pilot signal inserter 140-i (1 ≦ i ≦ 3) sets two pilot subcarriers at predetermined positions of the data subsubcarriers in the data signal output from modulator 130-i. The frequency domain signal consisting of 6 subcarriers is generated and output to the null replacer 152-i.

  (Processing 1-5) The null permuters 152-1 to 152-3 assign subcarrier positions to the subcarriers output from the pilot signal inserter 140-i. Here, null replacer 152-1 has subcarrier positions SC1-6, pilot signal inserter 140-2 has subcarrier positions SC4-9, and pilot signal inserter 140-3 has subcarrier positions SC7-12. assign. Since null replacer 152-2 has assigned subcarrier positions SC5 and SC5 to pilot subcarriers in the overlapping region, null replacer 152-1 nulls the data subcarrier at subcarrier position SC5, and null replacer 152-3 Null the data subcarrier at subcarrier position SC9. Since null replacer 152-1 assigns subcarrier position SC6 to the pilot subcarrier in the overlap region, and null replacer 152-3 assigns subcarrier position SC8 to the pilot subcarrier in the overlap region, null replacer 152-2 has a subcarrier position SC6. Nulling data subcarriers at carrier positions SC6 and SC8.

  (Processing 1-6) The null permuters 152-1 to 152-3 output the non-overlapping band subcarriers to the OFDM signal generator 160, and combine the superimposing band subcarriers with the subcarrier positions. -1 to 154-6. Specifically, null replacer 152-1 outputs subcarriers at subcarrier positions SC1 to SC3, and null replacer 152-3 outputs subcarriers at subcarrier positions SC10 to SC12 to OFDM signal generator 160. Also, null replacer 152-1 outputs the subcarriers at subcarrier positions SC4 to SC4-6 to combiners 154-1 to 154-3, respectively, and null replacer 152-2 receives subcarriers at subcarrier positions SC4 to SC9. The carriers are output to combiners 154-1 to 154-6, respectively, and null replacer 152-3 outputs the subcarriers at subcarrier positions SC7 to SC9 to combiners 154-4 to 154-6, respectively. The combiners 154-1 to 154-6 combine the input subcarriers and output the combined subcarriers to the OFDM signal generator 160.

  (Processing 1-7) The OFDM signal generator 160 receives the subcarriers of the subcarrier positions SC1 to SC12 output from the null permuters 152-1 to 152-1 and the combiners 154-1 to 154-6. Then, these subcarriers are subjected to inverse Fourier transform to generate an OFDM time signal, and transmitted as a transmission signal to the receiving apparatus by radio.

  Transmission in which the signal R1 composed of subcarriers at subcarrier positions SC1 to SC6, the signal R2 composed of subcarriers at subcarrier positions SC4 to SC9, and the signal R3 composed of subcarriers at subcarrier positions SC7 to SC12 are superimposed as described above. A signal is transmitted from the transmitter 100. In the transmission signal shown in FIG. 5, the length of each subcarrier represents the signal power, and the subcarriers at subcarrier positions SC4 and SC7 on which data subcarriers are superimposed are more than the other subcarriers on which data subcarriers are not superimposed. Signal power is strong. Although the subcarrier positions SC5, 6, 8, and 9 are superposed bands, but are pilot signals that are not superposed, the power level is the same as the subcarriers in the non-superimposed band.

FIG. 6 is a functional block diagram of the receiving device 500 in the wireless communication system according to the first embodiment.
In the figure, a receiving apparatus 500 includes a decoding number counter 510, a switch 515, a subtracter 520, a delay unit 525, a transmission path estimator 550, an OFDM demodulator 552, a processing band determining unit 556, a band extracting unit 557, and a demodulator 558. , 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 / rearranger 590.

  The decoding number counter 510 counts the number of times decoding has been performed after receiving a new superimposed signal, and stores the counted value. The switch 515 switches the connection source of the subtracter 520 to the reception signal side or the delay device 525 side according to the value of the decoding number counter 510. That is, when the number of decoding is the initial value, switching is made to the reception signal side, and when it is larger than the initial value, switching is made to the delay unit 525 side.

  The subtracter 520 removes the replica signal generated by the replica generator 580 from the received superimposed signal or the processing target signal stored in the delay unit 525 to generate a new processing target 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 transmission path estimator 550 estimates transmission path characteristics from the pilot signal included in the processing target signal output from the subtracter 520. The OFDM demodulator 552 uses the transmission path characteristics estimated by the transmission path estimator 550 to perform OFDM demodulation on the processing target signal output from the subtractor 520. Specifically, after equalization processing is performed on the signal to be processed using transmission path characteristics, the signal to be processed is serial-parallel converted, and is subjected to FFT (Fast Fourier Transform) or DFT (Discrete Fourier Transformation) for each subcarrier. Fourier transform is performed to obtain an OFDM demodulated value that is a signal in the frequency domain of each subcarrier.

  The processing band determiner 556 determines the frequency bandwidth and center frequency to be demodulated and decoded based on the value of the decoding number counter 510, and outputs the determined center frequency and frequency bandwidth to the band extractor 557 to be demodulated and decoded. Instruct to remove OFDM demodulated values other than the frequency components of. The band extractor 557 outputs the OFDM demodulated value of the center frequency and frequency bandwidth to be demodulated and decoded instructed by the processing band determiner 556 from the OFDM demodulated value obtained by the OFDM demodulator 552.

  The demodulator 558 determines a demodulation target with reference to the counter value of the decoding number counter 510, and among the OFDM demodulated values output from the band extractor 557, QPSK, QAM, etc. for subcarriers determined to be demodulated The symbol demapping operation corresponding to the modulation executed by the transmitting apparatus 100, that is, demodulation is performed to obtain the likelihood that is the demodulated value. At this time, what is determined as a demodulation target is a subcarrier having a frequency corresponding to the data subcarrier position of the demodulation / decoding target signal.

  Weight coefficient generator 560 generates a weight coefficient based on the frequency band to be demodulated and decoded corresponding to the value of decoding number counter 510. The weighting factor generator 560 uses the likelihood obtained by the demodulation by the OFDM demodulator 552 as it is for the data subcarriers in the non-overlapping area, and reduces the reliability of the data subcarriers not nulled in the overlapping area, For the data subcarriers in which the superposed band is nulled, a weighting coefficient that reduces the reliability most is generated. The first weight calculator 565 decodes a likelihood data string obtained by multiplying the likelihood obtained by the demodulation by the demodulator 558 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 / reorderer 590 rearranges the order of the bitstreams stored in the data buffer 575 to generate a correct bitstream and outputs it, or outputs a desired signal from the bitstream stored in the data buffer 575. Extract the bitstream.

The replica generator 580 includes a re-encoder 582, a re-modulator 584, a null permuter 585, a second weight calculator 586, and an OFDM re-modulator 588, and the replica generator 580 generates a replica from the bit stream obtained by the decoder 570. Generate a signal.
The re-encoder 582 performs encoding similar to the encoding used in the transmission apparatus 100 that has transmitted the bit stream to the bit stream decoded by the decoder 570. The remodulator 584 performs modulation similar to the modulation used in the transmission apparatus 100 on the signal encoded by the reencoder 582. The null replacer 585 assigns the subcarrier position to the data subcarrier modulated by the remodulator 584 and performs nulling similar to that of the transmission apparatus 100, and outputs the result to the second weight calculator 586. Second weight calculator 586 multiplies each subcarrier signal output from null replacer 585 by the estimated value of the transmission path characteristic for each subcarrier estimated by transmission path estimator 550. The OFDM remodulator 588 generates a replica signal by performing inverse Fourier transform on each subcarrier output from the second weight calculator 586 by IFFT or IDFT, and outputs the replica signal to the subtractor 520.

Subsequently, the operation of the receiving apparatus 500 of this embodiment will be described.
Here, it is assumed that receiving apparatus 500 receives a transmission signal on which signals R1, R2, and R3 are transmitted and transmitted by transmitting apparatus 100 described above, and performs demodulation decoding in the order of signals R1, R3, and R2. Further, the receiving device 500 measures and detects the signal R1 to R3 use frequency bands f1 to f3, the center frequency, the superposition band, and the like by individually receiving the signals R1 to R3 when the receiving device 500 is installed. Suppose you are. 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. The position of the pilot subcarrier in each of the signals R1 to R3 is determined in advance between the transmission device 100 and the reception device 500, or is notified from the transmission device 100 to the reception device 500 by a control signal.
FIG. 7 is a diagram illustrating the relationship between the number of demodulation / decoding processes in the receiving apparatus 500, the demodulation / decoding target, and the weighting coefficient generated by the weighting coefficient generator 560. FIG. 7A shows the first demodulation / decoding process, FIG. 7B shows the second demodulation / decoding process, and FIG. 7C shows the third demodulation / decoding process.

(Processing 2-1): The receiving device 500 receives a signal on which the signals R1 to R3 are superimposed from the transmitting device 100 by an antenna (not shown).
(Process 2-2): 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 2-3): 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 is output to the transmission path estimator 550 and the OFDM demodulator 552.

(Process 2-4): The transmission path estimator 550 is based on the pilot signals of the subcarrier positions SC2, 5, 6 included in the frequency domain fi of the demodulation target signal R1 in the target signal A1. The transmission line characteristics between are estimated.
(Processing 2-5): The OFDM demodulator 552 uses the transmission path characteristic estimated by the transmission path estimator 550 to perform OFDM demodulation on the processing target signal A1 output from the subtractor 520, and performs subcarrier positions SC1 to SC1. An OFDM demodulated value for each of the 12 subcarriers is calculated.

  (Processing 2-6): The processing band determining unit 556 stores in advance the association between the number of decoding times and the frequency band of the signal to be demodulated and decoded, and demodulates based on the value “1” of the decoding number counter 510. When it is determined that the decoding target frequency is the frequency band f1 of the signal R1, the center frequency of the frequency band f1 and its frequency bandwidth are obtained. The processing band determiner 556 outputs the center frequency and frequency bandwidth of the frequency band f1 to the band extractor 557, and instructs to extract the OFDM demodulated value of the subcarrier of the frequency band f1.

(Processing 2-7): The band extractor 557 uses the OFDM demodulated value of each subcarrier of the entire processing target signal A1 output from the OFDM demodulator 552, and the center frequency and frequency band indicated by the processing band determiner 556. That is, the OFDM demodulated value of each subcarrier in the frequency band f1 is extracted.
(Process 2-8): The demodulator 558 stores the number of times of decoding and information on the frequency used for the data subcarrier to be demodulated in association with each other. As shown in FIG. 7A, the demodulator 558 determines that the demodulation target is the frequency of the data subcarrier positions SC1, 3, 4, 5 of the signal R1 based on the value “1” of the decoding number counter 510. to decide. The demodulator 558 demodulates the subcarrier of the frequency to be demodulated using the OFDM demodulated value of the subcarrier output from the band extractor 557, and calculates the likelihood.

  (Process 2-9): The weighting factor generator 560 associates the superimposition band information indicating the frequency band and the superposition band of the demodulation decoding target signal with the number of decoding, and the data subcarrier and pilot subcarrier of each signal. And the frequency of use are stored in advance. The weighting factor generator 560, based on the value “1” of the decoding number counter 510, the frequency band f1 of the signal R1, the superimposed band in which the signals R1 and R2 are superimposed, and the pilot subcarriers of the signal R1 and the signal R2 When the frequency information is obtained, a weighting coefficient as shown in FIG. 7A is generated. That is, for the subcarrier positions SC1 and SC3 of the data subcarriers in the non-overlapping band of the frequency band f1, the weighting factor is set to “1”, and the superpositions assigned to the data subcarriers of the signal R1 and R2 are assigned. For the subcarrier position SC4 in the band, the weighting factor is “k” (0 ≦ k <1), and the subcarrier position SC5 in the superposed band allocated to the data subcarrier of the signal R1 and the pilot subcarrier of the signal R2. For, a sequence of weighting factors with a weighting factor of “0” is generated. Note that no weighting coefficient is generated for the subcarrier positions SC2 and SC6 of the pilot subcarrier of the signal R1 that has not been demodulated and the subcarrier positions SC7 to SC12 that are not extracted by the band extractor 557.

  (Process 2-10): 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 558 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 number of decoding times.

  (Processing 2-11): 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 transmission apparatus 100 on the bit stream decoded by the decoder 570, and the re-modulator 584 transmits the signal encoded by the re-encoder 582 to Modulation similar to that of apparatus 100 is performed to generate data subcarriers. Null replacer 585 assigns subcarrier positions SC1, 3, 4, 5 to the data subcarriers of remodulator 584, and then pilot subcarrier positions SC2, 6 of signal R1 and pilot subcarriers of signal R2. The subcarrier at the position SC5 is nulled and output to the second weight calculator 586. Second weight calculator 586 multiplies each subcarrier signal modulated by remodulator 584 by the estimated value of the channel characteristics estimated by channel estimator 550 for each subcarrier at subcarrier positions SC1 to SC6. The OFDM remodulator 588 generates a replica signal R1 'by performing inverse Fourier transform on each subcarrier output from the second weight calculator 586. When the replica signal R1 'is generated, 1 is added to the value of the decoding number counter 510.

  (Process 2-12): 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. Since the replica signal does not include the pilot signal, the pilot subcarrier is not attenuated or removed even if the replica signal is removed. The processing target signal A2 is stored in the delay unit 525 and is output to the transmission path estimator 550 and the OFDM demodulator 552.

(Process 2-13): The receiving apparatus 500 sets the counter value “1” to the counter value “2”, the counter value “2” to the counter value “3”, the processing target signal A1 to the processing target signal A2, and the processing target signal A2. Is processed signal A3, signal R1 is signal R3, frequency band f1 is frequency band f3, and replica signal R1 ′ is replaced with replica signal R3 ′, and processes (process 2-4) to (process 2-12) are performed. .
However, in (Processing 2-4), the transmission path estimator 550 estimates transmission path characteristics based on the pilot signals of the subcarrier positions SC8, 9, 12 included in the frequency band f3 of the demodulation decoding target signal R3. .
Further, in (Process 2-8), as shown in FIG. 7B, the demodulator 558, based on the value “2” of the decoding number counter 510, demodulates the data subcarrier position SC7 of the signal R3, It is determined that the frequencies are 9, 10, and 11.
In (Process 2-9), as shown in FIG. 7B, the weighting factor generator 560 uses the weighting factor for the subcarrier positions SC10 and SC11 of the data subcarriers in the non-superimposed band of the frequency band f3. For the subcarrier position SC7 in the superposed band assigned to the data subcarrier of the signal R3 and the data subcarrier of the signal R2, the weighting factor is “k” (0 ≦ k <1), For the subcarrier position SC9 in the superposed band allocated to the data subcarrier of the signal R3 and the pilot subcarrier of the signal R2, a weight coefficient sequence with a weight coefficient of “0” is generated. For the subcarrier positions SC9 and SC12 of the pilot subcarrier of the signal R3 that has not been demodulated, and the subcarrier positions SC1 to SC6 that are not extracted by the band extractor 557, no weighting coefficient is generated. In the figure, the power of the data subcarrier in the frequency band f1 is decreased because the replica signal R1 ′ is subtracted.
Further, in (Process 2-11), the null replacer 585 assigns the subcarrier positions SC7, 9, 10, and 11 to the data subcarriers of the remodulator 584, and then the pilot subcarrier position SC8 of the signal R3, 12. Null the subcarrier at pilot subcarrier position SC9 of signal R2 and output it to second weight calculator 586. Second weight calculator 586 multiplies each subcarrier signal modulated by remodulator 584 by the estimated value of the channel characteristics estimated by channel estimator 550 for each subcarrier at subcarrier positions SC7 to SC12.

(Process 2-14): Reception apparatus 500 reads counter value “1” as counter value “3”, process target signal A1 as process target signal A3, signal R1 as signal R2, and frequency band f1 as frequency band f2. , (Process 2-4) to (Process 2-10) are performed.
However, in (Process 2-4), the transmission path estimator 550 estimates transmission path characteristics based on the pilot signals of the subcarrier positions SC5, SC6, and 10 included in the frequency band f2 of the demodulation decoding target signal R2. .
Further, in (Process 2-8), as shown in FIG. 7C, the demodulator 558, based on the value “3” of the decoding number counter 510, demodulates the data subcarrier position SC4 of the signal R2, It is determined that the frequencies are 6, 7, and 8.
In (Process 2-9), as shown in FIG. 7C, the weighting coefficient generator 560 applies the weighting coefficient for the subcarrier positions SC4 and SC7 of the data subcarriers in the non-superimposed band of the frequency band f2. Is set to “1”, the subcarrier position SC6 assigned to the data subcarrier of the signal R2 and the pilot subcarrier of the signal R1, and the subcarrier position assigned to the data subcarrier of the signal R2 and the pilot subcarrier of the signal R3. For the carrier position SC8, a sequence of weighting factors with a weighting factor of “0” is generated. Coefficients are not generated for the subcarrier positions SC5 and SC9 of the pilot subcarrier of the signal R2 that has not been demodulated, and the subcarrier positions SC1 to SC3 and 9 to 12 that are not extracted by the band extractor 557. In the figure, the power of the data subcarriers in the frequency bands f1 and f3 is decreased because the replica signals R1 ′ and R3 ′ are subtracted.

  (Process 2-15): When the decoded bit stream is written in the data buffer 575, the data extraction / reorder unit 590 changes the order of the bit streams stored in the data buffer 575 to the signals R1, R2, and R3. Are rearranged in the order of the bitstreams obtained from

[Second Embodiment]
Next, a radio communication system according to the second embodiment will be described. In the second embodiment, the receiving device receives a superimposed signal on which N signals R1 to Rn transmitted from each of the N transmitting devices are superimposed.

FIG. 8 is a schematic block diagram showing the configuration of the transmission apparatus 200 of the wireless communication system according to the second embodiment of the present invention.
In the figure, a transmission apparatus 200 includes an S / P converter 210, an encoder 220, a modulator 230, a pilot signal inserter 240, a null replacer 250, an OFDM signal generator 260, a frequency converter 270, an antenna 280, In addition, a pilot position detector 290 is provided.

  The S / P converter 210 converts the inputted input bit stream from a serial signal sequence to a parallel signal sequence, and outputs the converted signal to the encoder 220. The encoder 220 performs predetermined error correction encoding on the bit stream input from the S / P converter 210 and outputs the result to the modulator 230. The modulator 230 modulates the error correction encoded bit stream input from the encoder 220 in units of subcarriers using a predetermined modulation scheme, for example, BPSK, 16QAM, etc., and generates a data signal. . That is, the generated data signal is composed of data subcarriers. The pilot signal inserter 240 inserts a pilot signal at a predetermined position of the data signal generated by the modulation by the modulator 230 to generate a frequency domain signal. As a result, a frequency domain signal in which pilot subcarriers are inserted into data subcarriers is generated.

  Pilot position detector 290 detects pilot subcarrier arrangement information indicating a frequency used for a pilot subcarrier of a signal transmitted by another transmitting apparatus 200, and detects a subcarrier position using a frequency indicated by the pilot subcarrier arrangement information. Instructs null replacer 250 to null data subcarriers.

  Null permuter 250 assigns a subcarrier position to each subcarrier output from pilot signal inserter 240, and then, in accordance with an instruction from pilot position detector 290, the same as the pilot subcarrier transmitted by other transmitting apparatus 200 Data subcarriers at subcarrier positions using frequencies are nulled and output to OFDM signal generator 260. The OFDM signal generator 260 generates an OFDM time signal by performing inverse Fourier transform on each subcarrier output from the null replacer 250 by IFFT or IDFT, and outputs the OFDM time signal to the frequency converter 270. The frequency converter 270 modulates the frequency of the signal output from the OFDM signal generator 260 and outputs it from the antenna 280 by radio.

Subsequently, the operation of the transmission apparatus 200 of the present embodiment will be described.
Here, there are N transmission apparatuses 200, which are referred to as transmission apparatuses 200-1 to 200-n, respectively. Hereinafter, there will be described an example in which there are three transmission apparatuses 200, the transmission apparatus 200-1 transmits the signal R1, the transmission apparatus 200-2 transmits the signal R2, and the transmission apparatus 200-3 transmits the signal R3. When the subcarriers when the signals R1 to R3 are superimposed are the subcarrier positions SC1 to SC12 from the lowest frequency, the signal R1 is the subcarrier positions SC1 to SC6, the signal R2 is the subcarrier positions SC4 to SC9, Signal R3 uses subcarrier positions SC7-12. Further, it is assumed that the pilot subcarrier position of the signal R1 is SC2 and 6, the pilot subcarrier position of the signal R2 is SC5 and 9, and the pilot subcarrier position of the signal R3 is SC8 and 12.

Pilot position detectors 290 of transmitting apparatuses 200-1 to 200-3 detect pilot subcarrier positions of other transmitting apparatuses 200 by an arbitrary method. For example, the pilot position detector 290 can identify the pilot subcarrier position of the other transmitting apparatus 200 from the received signal received from the other transmitting apparatus 200 in the time slot zone in which no signal is transmitted or received in the own apparatus. Alternatively, the pilot subcarrier position of the other transmission apparatus 200 may be acquired in advance by an input unit (not shown) or read from a recording medium.
Since the processing of the transmission devices 200-1 to 200-3 is the same, the processing of the transmission device 200-1 will be described as an example.

(Processing 3-1): The S / P converter 210 converts the input bit stream from a serial signal sequence into a parallel signal sequence and outputs the parallel signal sequence to the encoder 220.
(Processing 3-2): The encoder 220 performs error correction coding on the bit stream input from the S / P converter 210 and outputs the result to the modulator 230.

  (Process 3-3): The modulator 230 modulates the error correction encoded bit stream output from the encoder 220 in units of subcarriers according to a predetermined modulation method, and pilots the generated data signal. Output to the signal inserter 240. The generated data signal is composed of four data subcarriers.

  (Process 3-4): The pilot signal inserter 240 inserts two pilot subcarriers at predetermined positions of the data subsubcarriers in the data signal output from the modulator 230, and a frequency domain signal composed of six subcarriers. And output to the null replacer 250.

  (Processing 3-5) The null permuter 250 assigns a subcarrier position to each subcarrier output from the pilot signal inserter 240. Null permuter 250 nulls data subcarriers having the same subcarrier position SC5 as the pilot subcarrier of signal R2 after frequency conversion in accordance with an instruction from pilot position detector 290, and outputs each subcarrier to OFDM signal generator 260 To do.

  (Processing 3-7) When receiving the subcarriers output from the null permutation unit 250, the OFDM signal generator 260 performs an inverse Fourier transform on these subcarriers to generate an OFDM time signal. The frequency converter 270 converts the frequency of the OFDM time signal generated by the OFDM signal generator 260 and outputs it from the antenna 280 by radio.

  In the above, the processing of the transmission apparatus 200-1 has been described. In the case of the transmission apparatus 200-2, in (Processing 3-5), the null permutation unit 250 applies each subcarrier output from the pilot signal inserter 240. After assigning subcarrier positions, an OFDM signal is generated by nulling data subcarriers having the same subcarrier positions SC6 and SC8 as the pilot subcarriers of other signals R1 and R3 after frequency conversion according to instructions from pilot position detector 290 Output to the device 260. Further, in the case of transmitting apparatus 200-3, in (Process 3-5), null replacer 250 assigns a subcarrier position to each subcarrier output from pilot signal inserter 240, and then performs pilot position detector 290's. According to the instruction, data subcarriers having the same subcarrier position SC9 as the pilot subcarriers of other signals R2 after frequency conversion are nulled and output to OFDM signal generator 260.

  As described above, the receiving apparatus has a signal R1 composed of subcarriers at subcarrier positions SC1 to SC6 transmitted by the transmitting apparatus 200-1, a signal R2 composed of subcarriers at subcarrier positions SC4 to 9 transmitted by the transmitting apparatus 200-2, And the superimposition signal with which signal R3 which consists of the subcarrier of subcarrier position SC7-12 transmitted by the transmitter 200-3 was superimposed is received. In this superimposed signal, subcarrier positions SC5, 6, 8, and 9 are pilot subcarriers that are included in the superimposed band but are not superimposed.

FIG. 9 is a functional block diagram of the receiving device 500a in the wireless communication system according to the second embodiment. In the figure, the same components as those of the receiving apparatus 500 of the first embodiment are denoted by the same reference numerals and description thereof is omitted.
In the figure, a receiving apparatus 500a 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, and a transmission path estimator 550a. , 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 / rearranger 590a.

  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 sine wave 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. 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 590a.

  The local signal generator 535 generates a sine wave having a center frequency indicated by the processing band determiner 530. The mixer 540 down-converts the processing target signal output from the subtracter 520 with the sine wave 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. The transmission path estimator 550a estimates transmission path characteristics from a pilot signal included in a signal to be demodulated and decoded extracted by the bandpass filter 545.

  Demodulator 555 demodulates the signal to be demodulated and decoded extracted by bandpass filter 545 using the channel characteristics estimated by channel estimator 550a, and calculates the likelihood that is the demodulated value of each subcarrier. . Specifically, demodulator 555 performs equalization processing on a signal to be demodulated and decoded using transmission path characteristics, and then serial-parallel converts the signal to be demodulated and decoded, and performs Fourier transform by IFT or DFT for each subcarrier. OFDM demodulation to be converted is performed, and further, a symbol demapping operation corresponding to the modulation performed by the transmission apparatus 200 such as QPSK and QAM is performed from the OFDM demodulation result obtained by Fourier transform, that is, the demodulated value is obtained by performing demodulation. Get likelihood.

  The data extractor / rearranger 590a obtains the bit stream of the 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.

Next, the operation of the receiving device 500a according to this embodiment will be described.
Here, receiving apparatus 500a receives a superimposed signal on which signals R1, R2, and R3 transmitted from transmitting apparatuses 200-1 to 200-3 described above are superimposed, and performs demodulation and decoding in the order of signals R1, R3, and R2. Shall be done. Further, the receiving device 500a, when the receiving device 500a is installed, uses the frequency bands f1 to f3 of the signals R1 to R3, the center frequency, and the superposition at the timing when there is no desired wave and the frequency band of the subcarrier where there is no desired wave. Assume that the band is measured and detected. Alternatively, these pieces of information may be acquired from control information transmitted / received to / from the transmission apparatuses 200-1 to 200-3. These pieces of information may be acquired in advance by an input unit (not shown) or read from a recording medium. May be. The positions of the pilot subcarriers in the signals R1 to R3 are determined in advance between the transmission devices 200-1 to 200-3 and the reception device 500a, or from the transmission devices 200-1 to 200-3 to the reception device 500a by a control signal. To be notified.
FIG. 10 is a diagram illustrating the relationship between the number of demodulation / decoding processes in the receiving apparatus 500a, the demodulation / decoding target, and the weighting coefficient generated by the weighting coefficient generator 560. 10A shows the first demodulation / decoding process, FIG. 10B shows the second demodulation / decoding process, and FIG. 10C shows the third demodulation / decoding process.

  (Processing 4-1): The receiving apparatus 500a performs the same processes as (Processing 2-1) to (Processing 2-3) in the receiving apparatus 500 of the first embodiment. The processing target signal A1 generated by the subtracter 520 is stored in the delay unit 525 and output to the mixer 540.

  (Process 4-2): The processing band determiner 530 stores in advance the association between the number of decoding times and the frequency band of the demodulation target signal, and demodulates 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 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 sine wave 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 4-3): The local signal generator 535 generates a sine wave having a center frequency specified by the processing band determiner 530, and the mixer 540 generates the processing target signal A1 by the local signal generator 535. Down-converted with a sine wave.
(Process 4-4): The band pass filter 545 removes the frequency other than the frequency component of the center frequency and the frequency bandwidth instructed 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 4-5): The transmission path estimator 550a estimates the transmission path characteristics from the demodulation and decoding target signal extracted by the bandpass filter 545. The estimation of the transmission path characteristics is performed based on the pilot signals of the subcarrier positions SC2 and SC6 received from the transmission device 200-1 that is the transmission source of the demodulation decoding target signal R1.
(Process 4-6): The demodulator 555 demodulates the signal to be demodulated and decoded extracted by the bandpass filter 545 using the transmission path characteristic estimated by the transmission path estimator 550a, and the data sub-signal of the signal R1. The likelihood of subcarriers at carrier positions SC1, 3, 4, 5 is calculated.

(Process 4-7): Processes similar to (Process 2-9) to (Process 2-12) of the first embodiment are performed. In (Processing 2-9), the weighting factor generator 560 determines the frequency band f1 of the demodulation target signal R1 for each subcarrier as shown in FIG. 10A based on the value “1” of the decoding number counter 510. Generate a weighting factor for. That is, for the subcarrier positions SC1 and SC3 of the data subcarriers in the non-overlapping band of the frequency band f1, the weighting factor is set to “1”, and the superpositions assigned to the data subcarriers of the signal R1 and R2 are assigned. For the subcarrier position SC4 in the band, the weighting factor is “k” (0 ≦ k <1), and the subcarrier position SC5 in the superposed band allocated to the data subcarrier of the signal R1 and the pilot subcarrier of the signal R2. For, a sequence of weighting factors with a weighting factor of “0” is generated.
In (Process 2-11), the second weight calculator 586 uses the remodulator 584 to estimate the channel characteristics estimated by the channel estimator 550a for each subcarrier at the subcarrier positions SC1 to SC6. Multiply each modulated subcarrier signal.
In (Process 2-12), the signal A2 to be processed is stored in the delay unit 525 and output to the mixer 540.

(Process 4-8): The receiving apparatus 500a sets the counter value “1” to the counter value “2”, the counter value “2” to the counter value “3”, the processing target signal A1 to the processing target signal A2, and the processing target signal A2. Are processed signal A3, signal R1 is signal R3, frequency band f1 is frequency band f3, and replica signal R1 ′ is replaced with replica signal R3 ′, and processes (Process 4-2) to (Process 4-7) are performed. .
However, in (Process 4-5), the transmission path estimator 550a transmits the transmission path characteristics based on the pilot signals of the subcarrier positions SC8 and SC12 received from the transmission apparatus 200-3 that is the transmission source of the demodulation decoding target signal R3. Is estimated.
In (Process 2-9), the weighting factor generator 560 generates a weighting factor for each subcarrier as shown in FIG. 10B for the frequency band f3 of the demodulation target signal R3. That is, for the subcarrier positions SC10 and SC11 of the data subcarriers in the non-overlapping band of the frequency band f3, the weighting factor is set to “1” and assigned to the data subcarrier of the signal R3 and the data subcarrier of the signal R2. For the subcarrier position SC7 in the superposition band, the weighting factor is “k” (0 ≦ k <1), and the subcarrier position in the superposition band assigned to the data subcarrier of the signal R3 and the pilot subcarrier of the signal R2 For SC9, a sequence of weighting factors with a weighting factor of “0” is generated.
Also, in (Process 2-11), when null substituting unit 585 assigns subcarrier positions SC7, 9, 10, and 11 to the data subcarriers of remodulator 584, pilot subcarrier positions SC8 and SC12 of signal R3 are assigned. Then, the subcarrier at the pilot subcarrier position SC9 of the signal R2 is nulled and output to the second weight calculator 586. Second weight calculator 586 multiplies each subcarrier signal modulated by remodulator 584 by the estimated value of the channel characteristics estimated by channel estimator 550 for each subcarrier at subcarrier positions SC7 to SC12.
In (Process 2-12), the signal A3 to be processed is stored in the delay unit 525 and output to the mixer 540.

(Processing 4-9): The receiving apparatus 500a reads the counter value “1” as the counter value “3”, the processing target signal A1 as the processing target signal A3, the signal R1 as the signal R2, and the frequency band f1 as the frequency band f2. The processes of (Process 4-2) to (Process 4-7) are performed, and (Process 4-7) is the same as (Process 2-9) to (Process 2-10) of the first embodiment. Perform the following process.
In (Process 4-5), the transmission path estimator 550a transmits the transmission path characteristics based on the pilot signals of the subcarrier positions SC5 and SC9 received from the transmission apparatus 200-2 that is the transmission source of the demodulation decoding target signal R2. Is estimated.
In (Process 2-9), the weight coefficient generator 560 generates a weight coefficient for each subcarrier as shown in FIG. 10C for the frequency band f2 of the demodulation target signal R2. That is, for the subcarrier positions SC4 and SC7 of the data subcarriers in the non-superimposed band of the frequency band f2, the weighting factor is set to “1” and assigned to the data subcarrier of the signal R2 and the pilot subcarrier of the signal R1. For the subcarrier position SC6, the subcarrier position SC8 assigned to the data subcarrier of the signal R2 and the pilot subcarrier of the signal R3, a sequence of weighting coefficients with a weighting coefficient of “0” is generated.

  (Processing 4-10): When the decoded bit stream is written in the data buffer 575, the data extraction / rearranger 590a receives the data indicating the correspondence between the number of decoding times received from the processing band determining unit 530 and the frequency band. Based on the above, it is determined how many times the desired signal has been decoded, and the bit stream written in the data buffer 575 at the number of times of decoding is extracted as the bit stream of the desired signal.

  Note that, in the above, the receiving device 500a extracts the bit stream of the desired signal after performing demodulation decoding of all the signals R1 to R3, but when the bit stream is obtained by demodulating and decoding the desired signal, You may make it complete | finish a process.

  Also, if the pilot subcarriers of the adjacent signal Ri and the pilot subcarrier of the signal R (i + 1) are arranged at the same subcarrier position in the superposition band, any pilot subcarrier is nulled. The transmission path estimator 550a estimates transmission path characteristics based only on pilot subcarriers set by the transmission apparatus 200 that is the transmission source of the signal in the frequency band to be demodulated and decoded.

[Interference suppression processing by filtering interference bands]
In the above, demodulation decoding using a likelihood mask is performed as interference suppression processing, but interference band filtering processing may be performed. The interference suppression process using the interference band filtering process will be described below.

FIG. 11 shows the configuration of a filtering processing unit 910 that performs interference band filtering processing. When performing interference suppression processing using interference band filtering, the OFDM demodulator 552, the processing band determiner 556, the band extractor 557, the demodulator 558, the weight coefficient generator 560 of the receiving apparatus 500 shown in FIG. Instead of the first weight calculator 565, a filtering processor 910 is provided.
As shown in the figure, the filtering processing unit 910 includes an interference information extraction unit 913, a filter control unit 914, a delay unit 915, a filter 916, and a demodulation unit 917.

  The interference information extraction unit 913 includes the center frequency and the frequency bandwidth for the frequency band of the demodulation target signal and the frequency band of the processing target signal excluding the demodulation target signal (hereinafter referred to as “suppression target signal”). Interference information is stored in association with the number of decoding times. For example, when the signal to be processed is a signal on which signals R1 to R5 are superimposed and the signal to be demodulated and decoded is signal R1, the signals to be suppressed are signals R2 to R5. Further, when the signal to be processed is a signal on which signals R2 to R5 are superimposed and the signal to be demodulated and decoded is signal R5, the signals to be suppressed are signals R2 to R4.

The filter control unit 914 stores the signal to be processed output from the subtracter 520, and satisfies the following two conditions based on the interference information obtained by the interference information extraction unit 913 based on the value of the decoding number counter 510. The filter parameter is determined, and the determined parameter is set in the filter 916.
(1) Pass a signal to be processed in a frequency band in which only a signal to be demodulated and decoded exists without a signal to be suppressed (2) Attenuate a signal to be processed in a frequency band in which a signal to be suppressed exists Filter parameters Is composed of, for example, a filter type and a cut-off frequency.

  The delay unit 915 adds a time delay corresponding to the time required for the interference information extraction unit 913 and the filter control unit 914 to end the processing after the subtracter 520 ends the processing. And output to the filter 916. The amount of delay added to the processing target signal by the delay unit 915 is set in advance by the designer.

The filter 916 filters the processing target signal to which the delay is added by the delay unit 915 based on the parameter filter set by the filter control unit 914. That is, the filter 916 filters the processing target signal referred to by the filter control unit 914 when determining the parameter based on the parameter filter set by the filter control unit 914.
Demodulation section 917 demodulates the demodulation / decoding target signal filtered by filter 916, calculates the likelihood that is the demodulated value of each subcarrier, and outputs the likelihood to decoder 570. Specifically, the demodulator 917 performs equalization processing on the signal to be demodulated and decoded using the transmission path characteristics, serially parallel-converts the signal to be demodulated and decoded, and performs Fourier transform by IFT or DFT for each subcarrier. OFDM demodulation for conversion is performed, and further, symbol demapping operation corresponding to the modulation executed by the transmission apparatus, that is, demodulation is performed from the OFDM demodulation result obtained by Fourier transform to obtain likelihood.

  In the case of the receiving apparatus 500a shown in FIG. 9, a filtering processing unit 910 is provided instead of the bandpass filter 545, the demodulator 555, the weight coefficient generator 560, and the first weight calculator 565, and the output from the mixer 540 is demodulated. 555 and the weight coefficient generator 560 may be input.

Next, details of the operation of the filter control unit 914 will be described.
Based on the interference information corresponding to the counter value, the filter control unit 914 calculates a relative position between the demodulation target signal and the suppression target signal, and determines a filter parameter to be applied to the filter 916 according to the calculation result. To do. Specifically, the filter control unit 914 selects a filter type to be applied to the filter 916 based on the interference information from a high pass filter and a low pass filter. Further, the filter control unit 914 determines a cutoff frequency. Then, the filter control unit 914 controls the filter 916 according to the determined filter type and cutoff frequency.

  Next, details of the filter control process will be described. The center frequency of the demodulation target signal is fc_d, the frequency bandwidth is bw_d, the center frequency of the suppression target signal is fc_i, and the frequency bandwidth bw_i.

  First, filter control processing when the filter control unit 914 sets a low-pass filter for the filter 916 will be described. The filter control unit 914 calculates the highest value (bmax_i), which is the highest frequency in the frequency band of the suppression target signal, based on the center frequency and frequency bandwidth of the suppression target signal, and the center frequency and frequency of the demodulation decoding target signal The highest value (bmax_d), which is the highest frequency in the frequency band of the demodulation and decoding target signal, is calculated based on the bandwidth, and when bmax_i is higher than bmax_d, a low-pass filter is applied to the filter 916.

  In this case, the filter control unit 914 calculates the lowest value (bmin_i) that is the lowest frequency in the frequency band of the suppression target signal based on the center frequency and the frequency bandwidth of the suppression target signal, and the cutoff frequency (low-pass filter) The value of the frequency at which the filter gain is −3 dB is determined to be bmin_i. Then, the filter control unit 914 sets, in the filter 916, a parameter whose filter type is a low-pass filter and whose cutoff frequency is bmin_i. The filter 916 attenuates the power of a signal having a frequency higher than the lowest value (bmin_i) of the frequency band of the suppression target signal from the processing target signal.

  Next, filter control processing when the filter control unit 914 sets a high-pass filter for the filter 916 will be described. The filter control unit 914 calculates the lowest value (bmin_i), which is the lowest frequency of the frequency band of the suppression target signal, based on the center frequency and frequency bandwidth of the suppression target signal, and the center frequency and frequency of the demodulation decoding target signal Based on the bandwidth, the lowest value (bmin_d), which is the lowest frequency in the frequency band of the signal to be demodulated and decoded, is calculated. When bmin_i is lower than bmin_d, a high-pass filter is applied to the filter 916.

  In this case, the filter control unit 914 calculates the highest value (bmax_i), which is the highest frequency in the frequency band of the suppression target signal, based on the center frequency and the frequency bandwidth of the suppression target signal, and cuts off the high-pass filter cutoff frequency (high-pass The value of the frequency at which the filter gain is −3 dB is determined as bmax_i. Then, the filter control unit 914 sets, in the filter 916, a parameter whose filter type is a high-pass filter and whose cutoff frequency is bmax_i. The filter 916 attenuates the power of a signal having a frequency lower than the maximum value (bmax_i) of the frequency band of the suppression target signal from the processing target signal.

Next, the operation and processing procedure of the filtering processing unit 910 will be described.
FIG. 15 is a flowchart illustrating a processing procedure when the filtering processing unit 910 performs filter control.
First, the interference information extraction unit 913 extracts interference information based on the value of the decoding number counter 510 (step S910). Next, the filter control unit 914 determines the type of filter applied to the filter 916 and the cutoff frequency of the filter as described above based on the interference information extracted by the interference information extraction unit 913 (step S920). ). Then, the filter control unit 914 sets the determined filter type and filter cutoff frequency in the filter 916 (step S930).

  In parallel with the processing in steps S910 to S930, the delay unit 915 adds a delay to the processing target signal (step S940). Next, the filter 916 forms a filter according to the parameters set in the processing of step S930, and filters the processing target signal to which the delay is added, so that the power in the frequency band where the suppression target signal exists in the processing target signal. Is attenuated (step S950). Next, the demodulator 917 demodulates the signal to be processed that has passed through the filter 916 to obtain a demodulated value (step S960).

[effect]
As described above, in the embodiment of the present invention, when transmitting a spectrum by arranging a spectrum such that a plurality of multicarrier signals overlap on the frequency axis, the transmission apparatus does not superimpose pilot subcarriers. Perform spectral alignment. That is, when the pilot subcarrier and the data subcarrier use the same subcarrier position between adjacent signals to be superimposed, nulling is performed on the data subcarrier side. Then, when receiving the multicarrier signal overlapped on the frequency axis, the receiving apparatus does not superimpose interference suppression processing for demodulating and decoding subcarriers that are nulled in the multicarrier signal in the outer band. Generates a replica signal of the signal demodulated and decoded by interference suppression processing using the channel characteristics estimated from the pilot subcarrier, and removes the generated replica signal from the received signal to form a new received signal. The process is repeated sequentially. Thereby, it is possible to improve the accuracy of the replica signal subtraction process by increasing the transmission path estimation accuracy in the receiving apparatus, and as a result, it is possible to improve the reception accuracy of the received signal.
Further, as in the first embodiment, when a transmission signal is divided into N by one transmission apparatus and the divided N signals are transmitted by being superimposed, the reception apparatus has the same superimposed multicarrier signal. When transmitted from the transmission apparatus, pilot subcarriers can be shared between signals superimposed, and transmission path estimation can be performed, and further, the accuracy of replica signal subtraction processing can be improved.

100, 200... Transmitter 110, 210... Serial / parallel converter (S / P converter)
120-1 to 120-n, 220 ... encoders 130-1 to 130-n, 230 ... modulators 140-1 to 140-n, 240 ... pilot signal feeders 150, 250 ... superimposed signal generator (spectrum) Placement part)
152-1 to 152-n, 260... Null replacer (spectrum arrangement unit)
154-1 to 154-m... Synthesizer 160, 260... OFDM signal generator (multi-carrier signal generator)
270 ... Frequency converter 280 ... Antenna 290 ... Pilot position detector 500, 500a ... Receiver 510 ... Decoding counter 515 ... Switch 520 ... Subtractor (subtractor)
525 ... Delay units 530, 556 ... Processing band decision unit 535 ... Local signal generator 540 ... Mixer 545 ... Band pass filter 550, 550a ... Transmission path estimator (transmission path estimation unit)
552... OFDM demodulator (interference suppression demodulator, demodulator)
555, 558 ... demodulator (interference suppression demodulator, demodulator)
557 ... Band extractor (interference suppression demodulator, demodulator)
560 ... Weight coefficient generator (interference suppression demodulator, weight coefficient generator)
565... First weight calculator (interference suppression demodulator, weight calculator)
570: Decoder (decoding unit)
575 ... data buffer 580 ... replica generator (replica generator)
582... Re-encoder 584... Remodulator 585... Null replacer 586. 914: Filter control unit 915 ... Delay unit 916 ... Filter 917 ... Demodulation unit

Claims (10)

A wireless communication system comprising a multicarrier signal transmitter and a receiver that receives a superimposed signal on which the multicarrier signal is superimposed,
The transmitter is
A data subcarrier that is a subcarrier obtained by modulating a data signal that is encoded by applying an error correction code and a pilot subcarrier that is a subcarrier of a pilot signal are superimposed on pilot subcarriers of other multicarrier signals. A spectrum arrangement unit for performing spectrum arrangement so as not to occur,
A multi-carrier signal generation unit that generates the multi-carrier signal from the data subcarrier and the pilot subcarrier according to the spectrum allocation by the spectrum allocation unit;
The receiving device is:
A signal to be processed is a signal obtained by superimposing the multicarrier signal generated by the transmission device or a signal obtained by removing a replica signal from the superimposed signal, and using a pilot subcarrier included in the signal to be processed A transmission path estimation unit for performing transmission path estimation;
Among the frequency bands of the multicarrier signal included in the signal to be processed, the highest frequency band or the lowest frequency band is set as a demodulation decoding target, and a demodulated value obtained by suppressing a superimposition band for the processing target signal in the demodulation decoding target An interference suppression demodulation unit to obtain,
A decoding unit that performs error correction decoding using the demodulated value obtained by the interference suppression demodulation unit;
A replica generation unit that generates a multicarrier signal of a replica based on data obtained as a result of error correction decoding by the decoding unit and a transmission path estimation value by the transmission path estimation unit;
A subtractor that removes the multicarrier signal of the replica generated by the replica generation unit from the processing target signal and generates a new processing target signal;
A wireless communication system. The spectrum arrangement unit is:
A subcarrier position for a predetermined data subcarrier is allocated to the data subcarrier, and a subcarrier position for a predetermined pilot subcarrier is allocated to the pilot subcarrier, so that pilot subcarriers of other multicarrier signals are allocated. Nulling the data subcarriers or pilot subcarriers assigned subcarrier positions transmitted on the same frequency as
The wireless communication system according to claim 1. The interference suppression demodulation unit
A demodulator that obtains a demodulated value of the signal to be processed in the demodulation and decoding target;
A weighting factor generating unit that generates a weighting factor for reducing reliability of the demodulated value obtained by the demodulating unit with respect to the superimposed band to be demodulated and decoded;
A weight calculation unit that applies the weighting factor generated by the weighting factor generation unit to the demodulated value obtained by the demodulation unit;
The decoding unit performs error correction decoding using the demodulated value to which the weight coefficient is applied by the weight calculation unit.
The wireless communication system according to claim 1, wherein the wireless communication system is a wireless communication system. The interference suppression demodulation unit
A filter unit for extracting a non-superimposed band to be demodulated and decoded from the signal to be processed;
A demodulation unit that obtains a demodulation value for the non-overlapping band to be demodulated and decoded extracted by the filter unit,
The wireless communication system according to claim 1, wherein the wireless communication system is a wireless communication system. A transmission device that transmits the multicarrier signal to a reception device that receives a superimposed signal on which a multicarrier signal is superimposed,
A data subcarrier that is a subcarrier obtained by modulating a data signal that is encoded by applying an error correction code and a pilot subcarrier that is a subcarrier of a pilot signal are superimposed on pilot subcarriers of other multicarrier signals. A spectrum arrangement unit for performing spectrum arrangement so as not to occur,
A multicarrier signal generation unit that generates and outputs the multicarrier signal from the data subcarrier and the pilot subcarrier according to a spectrum arrangement by the spectrum arrangement unit;
A transmission device comprising: Receives a superimposed signal in which a multi-carrier signal composed of a data subcarrier that is a modulated subcarrier of a data signal that is encoded using an error correction code and a pilot subcarrier that is a subcarrier of a pilot signal is superimposed A receiving device,
The superposed signal in which the spectrum is arranged so that pilot subcarriers are not superposed, or the signal obtained by removing the replica signal from the superposed signal is set as a processing target signal, and transmission path estimation is performed using the pilot subcarrier included in the processing target signal. A transmission path estimator to perform,
Among the frequency bands of the multicarrier signal included in the signal to be processed, the highest frequency band or the lowest frequency band is set as a demodulation decoding target, and a demodulated value obtained by suppressing a superimposition band for the processing target signal in the demodulation decoding target An interference suppression demodulation unit to obtain,
A decoding unit that performs error correction decoding using the demodulated value obtained by the interference suppression demodulation unit;
A replica generation unit that generates a multicarrier signal of a replica based on data obtained as a result of error correction decoding by the decoding unit and a transmission path estimation value by the transmission path estimation unit;
A subtractor that removes the replica multi-carrier signal generated by the replica generation unit from the processing target signal to generate a new processing target signal;
A receiving apparatus comprising: A wireless communication method used in a wireless communication system including a multicarrier signal transmission device and a reception device that receives a superimposed signal on which the multicarrier signal is superimposed,
The transmitting device is
A data subcarrier that is a subcarrier obtained by modulating a data signal that is encoded by applying an error correction code and a pilot subcarrier that is a subcarrier of a pilot signal are superimposed on pilot subcarriers of other multicarrier signals. A spectral placement step for performing spectral placement so as not to occur,
A multicarrier signal generation step of generating the multicarrier signal from the data subcarrier and the pilot subcarrier according to the spectrum allocation by the spectrum allocation step,
The receiving device is
The superimposed signal generated by the transmission device is superimposed, or a signal obtained by removing a replica signal from the received superimposed signal is a processing target signal, and pilot subcarriers included in the processing target signal are A transmission path estimation step using the transmission path estimation,
Among the frequency bands of the multicarrier signal included in the signal to be processed, the highest frequency band or the lowest frequency band is set as a demodulation decoding target, and a demodulated value obtained by suppressing a superimposition band for the processing target signal in the demodulation decoding target Obtaining interference suppression demodulation step;
A decoding step of performing error correction decoding using the demodulated value obtained in the interference suppression demodulation step;
A replica generation step of generating a multicarrier signal of a replica based on data obtained as a result of error correction decoding in the decoding step and a transmission path estimation value obtained in the transmission path estimation step;
A subtraction step of generating a new processing target signal by removing the replica multi-carrier signal generated in the replica generation step from the processing target signal;
Repeat the processing from the transmission path estimation step using the processing target signal generated in the subtraction step,
A wireless communication method. A transmission method used in a transmission apparatus that transmits a multicarrier signal to a reception apparatus that receives a superimposed signal on which a multicarrier signal is superimposed,
A data subcarrier that is a subcarrier obtained by modulating a data signal that is encoded by applying an error correction code and a pilot subcarrier that is a subcarrier of a pilot signal are superimposed on pilot subcarriers of other multicarrier signals. A spectral placement step for performing spectral placement so as not to occur,
A multicarrier signal generating step for generating the multicarrier signal from the data subcarriers and the pilot subcarriers according to the spectrum allocation by the spectrum allocation step;
A transmission method characterized by comprising: Receives a superimposed signal in which a multi-carrier signal composed of a data subcarrier that is a modulated subcarrier of a data signal that is encoded using an error correction code and a pilot subcarrier that is a subcarrier of a pilot signal is superimposed A receiving method used for a receiving device,
The superposed signal in which the spectrum is arranged so that pilot subcarriers are not superposed, or the signal obtained by removing the replica signal from the superposed signal is set as a processing target signal, and transmission path estimation is performed using the pilot subcarrier included in the processing target signal. A transmission path estimation step to be performed;
Among the frequency bands of the multicarrier signal included in the signal to be processed, the highest frequency band or the lowest frequency band is set as a demodulation decoding target, and a demodulated value obtained by suppressing a superimposition band for the processing target signal in the demodulation decoding target Obtaining interference suppression demodulation step;
A decoding step of performing error correction decoding using the demodulated value obtained in the interference suppression demodulation step;
A replica generation step of generating a multicarrier signal of a replica based on data obtained as a result of error correction decoding in the decoding step and a transmission path estimation value obtained in the transmission path estimation step;
A subtraction step of generating a new processing target signal by removing the replica multi-carrier signal generated in the replica generation step from the processing target signal;
Repeat the processing from the transmission path estimation step using the processing target signal generated in the subtraction step,
And a receiving method. A spectrum arrangement method of a superimposed signal on which a multicarrier signal is superimposed,
In the transmission apparatus that transmits the multicarrier signal including a data subcarrier that is a subcarrier obtained by modulating a data signal that has been encoded by applying an error correction code, and a pilot subcarrier that is a subcarrier of the pilot signal, Spectrum allocation is performed so that the data subcarriers and the pilot subcarriers included in the multicarrier signal to be transmitted are not overlapped with pilot subcarriers of other multicarrier signals.
A spectral arrangement method characterized by the above.

Images