JP6264207B2 - Receiver - Google Patents

Description

  The present invention relates to a technique for demodulating a signal subjected to interference.

  2. Description of the Related Art Conventionally, in a packet communication device that transmits and receives an OFDM (Orthogonal Frequency Division Multiplexing) signal, when two packets A and B interfere with each other, a technique for demodulating both packets without discarding them is known. Specifically, first, one of the packets A is demodulated, and a replica signal having the same waveform as the transmission waveform of the packet A is generated by remodulating the data string obtained by the demodulation, and the received signal that has received the interference The received signal of the packet B is extracted by subtracting (cancelling) the replica signal from the received signal and demodulated (see Patent Document 1).

JP 2011-109278 A

  In the conventional apparatus, the interference in the frequency domain is dealt with, but the same measures can be taken for the interference in the time domain. In particular, in the case of time domain interference, in order to improve the extraction accuracy of the packet B, the timing of cancellation by the replica signal is important. When this timing is shifted, there is a problem that a large cancellation error remains in the signal after cancellation, and the demodulation accuracy of the packet B is lowered.

  Here, the cause of the cancellation error will be described with reference to FIG. It is assumed that the OFDM symbol is composed of 80 samples including, for example, data of 64 samples (bits) per symbol and a guard interval of 16 samples. However, in the figure, it is shown on a ¼ scale for easy viewing. That is, the illustrated OFDM symbol is composed of 20 samples including 16 samples of data and 4 samples of guard intervals.

  In the processing on the transmission side, among the 16-sample data (Ai to Pi, i = 1, 2,...) Obtained as a result of the inverse Fourier transform (IFFT), 4 samples (Mi to Pi) at the rear end are used as guard intervals. , Added to the head of the symbol.

  In the processing on the reception side, the timing that becomes the boundary of the OFDM symbol is extracted from the short preamble added to the head of the packet, and based on the extracted timing, the timing at the center of the guard interval (between samples Ni and Gi) Let it be the starting point of FFT to be executed during demodulation. The FFT is performed using 16 samples following this starting point. Then, reception data is generated by performing interleaving processing and decoding of an error correction code on the data string obtained from the FFT result. A replica signal is generated by remodulating the received data in the same manner as the processing on the transmission side.

  At that time, of the 16-sample data (Oi to Ni) obtained by IFFT, the rearmost two samples (Mi, Ni) are added to the head of the symbol, and the frontmost two samples (Oi, Pi) are added after the symbol. By adding to the end, an OFDM symbol consisting of 20 samples is generated.

  Then, in the processing on the receiving side, when the synchronization by the short preamble is correctly performed and the timing for starting the FFT coincides with the center of the guard interval as shown in FIG. Since the boundary of the OFDM symbol matches the signal, the cancellation is performed well.

  On the other hand, in the processing on the receiving side, synchronization by the short preamble is not correctly performed, and the timing for starting the FFT does not coincide with the center of the guard interval as shown in FIG. 18B (one sample earlier in the figure). In this case, since the replica signal is reproduced as being correctly synchronized, there is a deviation at the OFDM symbol boundary between the received signal and the replica signal. As a result, cancellation is performed between different OFDM symbols (see the timing of the symbol L2 of the replica signal) at the OFDM symbol boundary. Usually, since the signal waveform is greatly different for each OFDM symbol, a large noise (cancellation error) occurs in a portion (sample) where cancellation across OFDM symbols is executed.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a technique for improving the demodulation accuracy of a received signal that has received interference by suppressing a cancellation error due to a replica signal.

The receiving apparatus of the present invention includes first demodulating means, replica signal generating means, interference wave removing means, second demodulating means, and canceller control means.
The first demodulating means demodulates the received signal modulated by the OFDM method. The replica signal generation unit generates a replica signal by remodulating the demodulation result of the first demodulation unit. The interference wave removal means generates an interference wave removal signal by subtracting the replica signal from the received signal. The second demodulation means demodulates the interference wave removal signal. The canceller control means detects a cancellation error included in the interference wave removal signal, and when an evaluation value based on the cancellation error exceeds a preset allowable value, a replica signal for reducing the cancellation error is regenerated. The replica signal generating means is controlled so that

  According to such a configuration, when two packets that interfere with each other on the time axis are received, a packet (previous packet) that has been received first is demodulated based on the received signal. Packets that are subsequently received based on the interference wave cancellation signal that is the result of canceling the signal component based on the preceding packet from the received signal using the replica signal generated based on the demodulation result (following packet) Is decrypted.

  When the synchronization timing of the OFDM signal extracted from the received signal deviates from the actual one, the cancellation timing by the replica signal is deviated, and a large cancellation error is detected in the interference wave removal signal. In this case, a replica signal whose timing is adjusted is regenerated, and cancellation is executed by the reproduction replica signal. Therefore, finally, an interference wave removal signal in which the cancellation error is sufficiently suppressed is obtained, and the reception signal based on the two packets subjected to interference can be demodulated with high accuracy.

  In addition, the code | symbol in the parenthesis described in the claim shows the correspondence with the specific means as described in embodiment mentioned later as one aspect, Comprising: The technical scope of this invention is limited is not.

  In addition to the above-described receiving apparatus, the present invention can be realized in various forms such as a communication system including the receiving apparatus as a component, a program for causing a computer to function as the receiving apparatus, and a receiving method.

It is a block diagram which shows the whole structure of an OFDM receiver. It is a block diagram which shows the structure of the demodulation part in 1st Embodiment. It is a block diagram which shows the structure of the 1st and 2nd demodulator in a demodulation part. It is a block diagram which shows the structure of the remodulator in a demodulation part. It is a flowchart of the process which the canceller controller of 1st Embodiment performs. It is a timing diagram which shows the effect of cancellation control in 1st Embodiment. It is a block diagram which shows the structure of the demodulation part in 2nd Embodiment. It is a flowchart of the process which the canceller controller of 2nd Embodiment performs. It is a flowchart of the replacement control generation / output process in the second embodiment. It is a timing diagram which shows the effect of cancellation control in 2nd Embodiment. 12 is a flowchart of replacement control generation / output processing in the third embodiment. It is a timing diagram which shows the effect of cancellation control in 3rd Embodiment. It is a block diagram which shows the structure of the demodulation part in 4th Embodiment. It is explanatory drawing which illustrates the content of the conversion table used at the time of calculation of the number of replacement samples by cancellation control in 4th Embodiment. It is a block diagram which shows the structure of the demodulation part in 5th Embodiment. It is a block diagram which shows the structure of the delay device in 6th Embodiment. It is a flowchart of the process which the canceller controller of 6th Embodiment performs. It is explanatory drawing which shows the outline | summary of the process which cancels a replica signal from a received signal, and its problem.

Embodiments to which the present invention is applied will be described below with reference to the drawings.
[First Embodiment]
An OFDM receiver 1 to which the present invention is applied is shown in FIG. The OFDM receiver 1 receives radio waves from an OFDM transmitter that wirelessly transmits an OFDM signal as packet data, and demodulates the received signal to restore transmission data. The OFDM receiver 1 may constitute an OFDM communication device together with the OFDM transmitter, and is used for, for example, vehicle-to-vehicle communication and road-to-vehicle communication.

<OFDM signal>
An OFDM signal is composed of a plurality of subcarriers that are orthogonal to each other. Each subcarrier is modulated by transmission data divided by a predetermined number of bits by a predetermined digital modulation method such as QPSK (Quadrature Phase Shit Keying), 16QAM (Quadrature Amplitude Modulation), or 64QAM. The OFDM signal is composed of a short preamble, a long preamble, and a data symbol. The short preamble is an unmodulated signal having a predetermined pattern, and is used for synchronizing symbol timing and sample timing. Long preambles and data symbols are also referred to as OFDM symbols. In the OFDM symbol, a guard interval (GI) is added to each head portion. The guard interval is a copy of a part of the OFDM symbol (usually the rear end part).

<Overall configuration>
The OFDM receiver 1 includes an RF receiver 2, a quadrature detector 3, an ADC unit 4, and a demodulator 5.

  An RF (Radio Frequency) receiving unit 2 down-converts the received signal from the antenna AR into a received signal in a frequency band suitable for signal processing, and removes unnecessary frequency components using a filter. Further, the RF receiver 2 automatically amplifies the gain of the filter output while automatically adjusting the gain so that the average power of the amplified received signal matches a preset target value. Control (AGC: Auto Gain Control) is executed.

The quadrature detection unit 3 generates an I (in-phase component) signal and a Q (quadrature component) signal that are 90 ° different from each other based on the reception signal supplied from the RF reception unit 2.
An ADC (AD Converter) unit 4 samples the I signal and the Q signal generated by the quadrature detection unit 3 to generate two systems of digital data strings. Hereinafter, these two digital data strings are referred to as an I signal and a Q signal, and when both are collectively referred to as a received signal.

The demodulator 5 demodulates the I signal and Q signal sampled by the ADC unit 4 to generate reception data.
<Demodulation unit>
As shown in FIG. 2, the demodulator 5 includes a first demodulator 11, a remodulator 12, a delay unit 13, a subtracter 14, a canceller controller 15, a second demodulator 16, and a data extractor / rearranger 17. Prepare.

  The demodulating unit 5 is composed of a microcomputer, and the processing of each unit constituting the demodulating unit 5 is realized by executing software. However, it is not always necessary to implement all of them by software, and the whole or a part of the demodulator 5 may be realized by hardware such as a logic circuit.

  As shown in FIG. 3, the first demodulator 11 includes a GI removal unit 111, an FFT unit 112, a channel equalization unit 113, a subcarrier demodulation unit 114, a deinterleaving unit 115, and a Viterbi decoding unit 116. It is. The GI removal unit 111 removes the guard interval from the received signal (I signal / Q signal) according to the timing signal (symbol synchronization signal, sample synchronization signal) extracted from the short preamble. An FFT (Fast Fourier Transform) unit 112 performs fast Fourier transform (FFT) on the received signal from which the guard interval is removed for each OFDM symbol, and separates the received signal into signals (primary modulated signals) for each subcarrier constituting the OFDM signal. . However, a section to be subjected to FFT (hereinafter referred to as “FFT section”) is set to an area corresponding to the number of samples included in one OFDM symbol, starting from the center of the guard interval (see FIG. 18). The channel equalization unit 113 estimates the phase and amplitude distorted in the communication path (channel) for each subcarrier, and based on the estimation result, for each primary modulation signal separated by the FFT unit 112, that is, for each subcarrier. Perform channel equalization to correct phase and amplitude. The subcarrier demodulating unit 114 demodulates the primary modulation signal for each channel equalized subcarrier to generate a code string having a predetermined number of bits. Deinterleaving section 115 rearranges the order of the code strings output from subcarrier demodulation section 114 in the original order according to a preset rule. The Viterbi decoding unit 116 performs Viterbi decoding that decodes the output of the deinterleaving unit 115 while correcting an error to generate first demodulated data.

  As shown in FIG. 4, the remodulator 12 includes a convolutional encoding unit 121, an interleaving unit 122, a subcarrier modulation unit 123, a channel adding unit 124, an IFFT (Inverse Fast Fourier Transform) unit 125, a GI adding unit 126, a symbol. This is a well-known device including a shaping unit 127. The convolutional encoding unit 121 encodes the first demodulated data output from the first demodulator 11 into a convolutional code that is an error correction code. The interleaving unit 122 performs interleaving for rearranging the order of the code string output from the convolutional coding unit 121 according to a preset rule. Subcarrier modulation section 123 divides the output of interleaving section 122 into predetermined bits to generate primary modulation symbols, and sequentially assigns the generated primary modulation symbols to each subcarrier. The channel addition unit 124 adds phase / amplitude distortion in the communication path using the channel correction value in the channel equalization unit 113 of the first demodulator 11. The IFFT unit 125 performs two inverse Fourier transforms (IFFT) on the output of the subcarrier modulation unit 123 to generate two data sequences representing the waveform of the OFDM symbol. The GI adding unit 126 adds a guard interval to each of the two data strings generated by the IFFT unit 125. However, the guard interval is defined by adding the samples of the front end area immediately after the IFFT section, with the areas located at the front end and rear end of the section subject to IFFT (hereinafter referred to as “IFFT section”) as the front end area and the rear end area. This is set by adding the sample in the rear end area immediately before the IFFT target area (see FIG. 18). The number of samples included in the front end region and the rear end region is normally set to half of the number of samples included in the guard interval, but according to the correction information from the canceller controller 15, samples included in both regions It is configured so that it can be increased or decreased in units of samples, provided that the total number is constant. The GI adding unit 126 also outputs synchronization information indicating the boundary timing of the OFDM symbol to the canceller control unit 15. The symbol shaping unit 127 performs waveform shaping for alleviating waveform discontinuity between symbols. As a result, a replica signal (IR signal and QR signal) obtained by reproducing the I signal and the Q signal used on the transmission side of the OFDM signal is generated.

  Returning to FIG. 2, the delay unit 13 includes a first delay unit 131, a second delay unit 132, and a changeover switch 133. The first delay unit 131 delays the received signal by a predetermined time required for remodulating the first modulated data by the remodulator 12 and outputs the delayed signal. The second delay unit 132 delays the delayed reception signal output from the first delay unit 131 by a predetermined time required to remodulate the first modulation data and outputs the delayed reception signal. The changeover switch 133 selects either the output of the first delay unit 131 or the output of the second delay unit 132 according to the switching signal from the canceller controller 15 and supplies the selected output to the subtractor 14 as the output of the delay unit 13. . Note that the selector switch 133 is set to select the output of the first delay device 131 in the initial state.

  The subtractor 14 generates an interference wave removal signal (I-IR signal and Q-QR signal) by subtracting the output (replica signal) of the remodulator 12 from the output (delayed received signal) of the delay unit 13. To do.

The second demodulator 16 is configured in the same manner as the first demodulator 11 and outputs second demodulated data obtained by demodulating the interference wave removal signal output from the subtractor 14.
The data extractor / rearranger 17 rearranges the first demodulated data supplied from the first demodulator 11 and the second demodulated data supplied from the second demodulator 16 into parallel data having a predetermined bit width, Output sequentially as received data.

  The canceller controller 15 generates correction information and a switching signal based on the interference wave removal signal output from the subtractor 14, the synchronization information from the remodulator 12, and the state information from the second demodulator 16. Then, control for canceling the interference wave from the received signal is executed. The synchronization information represents the position of the symbol boundary of the replica signal, and the status information represents whether or not the second demodulator 16 is receiving a packet (during demodulation).

<Cancel control>
Details of the cancel control executed by the canceller controller 15 will be described with reference to FIG.
This process is activated every time the remodulator 12 generates the first replica signal based on the first demodulated data. When this process is started, the canceller controller 15 first measures the power and time width of the cancellation error based on the interference wave removal signal in S110, and obtains the accumulated value of the cancellation error through the packet as the evaluation value E. . The cancellation error is an error region that is a region in which the reception level of the interference wave removal signal is larger than a preset threshold (see FIG. 6) in a period corresponding to the long preamble after the replica signal. Then, based on the result of counting the number of samples included in each error region, the sum of the count results in all error regions is set as the cancellation error evaluation value E, and the average value of the count results in each error region or The maximum value is the time width W of the cancellation error. Further, at this time, based on the synchronization information from the remodulator 12, it is also determined whether the error region occurs before or after the boundary of the OFDM symbol. Hereinafter, the case where it is determined that the error region occurs before the symbol boundary is referred to as “timing delay”, and the case where it is determined that the error region occurs later is referred to as “timing advance”.

  In subsequent S120, it is determined whether or not the evaluation value E of the cancellation error is greater than or equal to a preset specified value. If the evaluation value E has not reached the specified value (S120: NO), it is assumed that the cancellation has been performed satisfactorily, and this process ends. On the other hand, if the evaluation value E is equal to or greater than the specified value (S120: YES), it is determined that the cancellation is insufficient and the process proceeds to S130.

  In S130, correction information for adjusting the addition status of the guard interval in the remodulator 12 is generated based on the time width W of the cancellation error obtained in S110 and the determination result of timing delay / advance. Specifically, in the case of timing delay, the correction information is such that the guard interval added in front of the IFFT interval is increased by the time width W and the guard interval added behind the IFFT interval is decreased by the time width W. Is generated. In the case of timing advance, conversely, the guard interval added in front of the IFFT interval is decreased by the time width W, and the correction information is generated to increase the guard interval added behind the IFFT interval by the time width W. To do. For example, in the case of FIG. 18B, three samples (N1 to P1) at the front end of the IFFT interval of the replica signal are added after the IFFT interval, and one sample (M1) at the rear end of the IFFT interval is added before the IFFT interval. Will be added.

  In subsequent S140, the output of the delayed received signal is started by switching the selector switch 133 so as to select the output of the second delay device 132, and the remodulator 12 is started to generate the replica signal.

  In subsequent S150, it is determined whether or not the reception of the packet is confirmed based on the state information from the second demodulator 16. If the packet reception is confirmed (S150: YES), the process waits until the second demodulator 16 completes the reception of the packet in S160, and then proceeds to S170. On the other hand, when reception of the packet is not confirmed (S150: NO), S160 is skipped and the process proceeds to S170.

In S170, the selector switch 133 is switched to a setting for selecting the output of the first delay device 131, and this process is terminated.
<Operation>
In the demodulator 5 configured as described above, when the reception signal is input, the first demodulator 11 demodulates the reception signal, and outputs the first demodulated data when the demodulation is successful. The first demodulated data is output from the demodulator 5 as received data via the data extractor / rearranger 17 and supplied to the remodulator 12. The remodulator 12 remodulates the first demodulated data to generate a replica signal. This replica signal is supplied to the subtractor 14 at the same timing as the reception signal delayed by the first delay unit 131. The subtractor 14 generates an interference wave removal signal by subtracting (cancelling) the replica signal from the received signal. The second demodulator 16 demodulates the interference wave removal signal, and outputs second demodulated data when the demodulation is successful. The second demodulated data is output as received data after the first demodulated data via the data extractor / rearranger 17. The canceller controller 15 monitors the interference wave cancellation signal, and when the cancellation is not sufficiently performed, causes the remodulator 12 to generate a replica signal in which the timing of the OFDM symbol is adjusted. The interference wave cancellation signal is regenerated by controlling the delayed reception signal supplied to the subtracter 14 together with the delayed reception signal supplied via the unit 132.

<Effect>
As described above, in the OFDM receiver 1, when two packets A and B are received in a state where they partially overlap on the time axis, first, the preceding packet A is demodulated, and when demodulation is successful, The demodulated data is remodulated to generate a replica signal of packet A. Next, an interference wave cancellation signal is generated by canceling the received replica signal using the replica signal as an interference wave, and the succeeding packet B is demodulated from the interference wave cancellation signal. As a result, both packets A and B can be received, and efficient communication can be realized.

  Further, in the OFDM receiver 1, as shown in FIG. 6, when a large cancellation error (evaluation value E exceeding a specified value) occurs due to a shift in the timing of cancellation by the replica signal, correction based on the observation result of the cancellation error By adjusting the way of adding the guard interval in the remodulator 12 according to the information, a replica signal in which the boundary timing of the OFDM symbol is adjusted so as to suppress the cancellation error is regenerated. Therefore, finally, an interference wave removal signal with sufficiently suppressed cancellation error can be obtained, and both of the two packets (interference wave / desired wave) that have received interference can be accurately demodulated. it can.

[Second Embodiment]
The second embodiment is the same as the first embodiment except that the configuration of the demodulator is partially different. Therefore, the description of the common configuration is omitted, and the difference will be mainly described.

  In the first embodiment described above, the canceller controller 15 adjusts the cancellation timing. On the other hand, the second embodiment is different from the first embodiment in that the error region sample in which the cancellation error occurs is replaced when the cancellation error cannot be sufficiently removed by adjusting the cancellation timing. To do.

<Demodulation unit>
In the present embodiment, as shown in FIG. 7, the demodulator 5a has a data replacer 18 added to the configuration of the demodulator 5 in the first embodiment, and the canceller controller 15a The configuration is the same as that of the demodulator 5 except that it also controls the replacer 18.

  The data replacer 18 replaces the value of the sample designated according to the replacement control information from the canceller controller 15a with respect to the interference wave removal signal with a predetermined value (here, 0). Note that the predetermined value is not limited to 0. For example, an interpolation value obtained from the values of samples located before and after the sample to be replaced may be used.

<Cancel control>
Processing executed by the canceller controller 15a instead of the processing (FIG. 5) in the canceller controller 15 of the first embodiment will be described with reference to the flowchart of FIG. The processes other than S142 to S146 are the same as the processes in FIG.

  That is, when the cancellation process using the replica signal regenerated using the correction information is started (S140), in the subsequent S142, based on a predetermined number of error areas set in advance detected from the interference wave removal signal. The evaluation value E and the time width W of the cancellation error are calculated.

  In the subsequent S144, it is determined whether or not the cancellation error evaluation value E is equal to or greater than a specified value, as in the previous S120. If the evaluation value E has not reached the specified value (S144: NO), the process proceeds to S150, assuming that the cancellation has been performed satisfactorily. On the other hand, if the evaluation value E is equal to or greater than the specified value (S144: YES), it is determined that the cancellation is insufficient and the process proceeds to S146.

In S146, a replacement control information generation / output process is executed, and the process proceeds to S150.
Here, details of the replacement control information generation / output process will be described with reference to FIGS. 9 and 10.

First, in S210, the canceller controller 15a determines a sample located at the center of each error region as a replacement center sample based on the error region detected in the previous S110.
In the subsequent S220, the time width W obtained in the previous S142 is determined as the number of replacement samples.

In subsequent S230, the replacement level is determined. Here, 0 is used.
In subsequent S240, the information determined in S210 to S230 is output to the data replacer 18 as replacement control information, and this process is terminated.

<Operation>
The demodulator 5a configured as described above operates in the same manner as the demodulator 5 of the first embodiment until the interference wave removal signal is regenerated by adjusting the timing of the replica signal. Further, in the demodulator 5a, the canceller controller 15a monitors the regenerated interference wave cancellation signal as shown in FIG. The sample value is replaced with a predetermined value, and the second demodulator 16 demodulates the interference wave removal signal after the replacement.

<Effect>
According to this embodiment, in addition to the effects of the first embodiment described above, the following effects can be obtained. That is, even if the cancellation cannot be sufficiently performed only by adjusting the cancellation timing by the replica signal, the remaining cancellation error can be removed, so that the demodulation accuracy of the desired wave (following packet B) is further improved. be able to.

[Third Embodiment]
The third embodiment is the same as the second embodiment except that the content of the replacement control information generation / output process is partially different. Therefore, the description of the common configuration will be omitted, and the difference will be mainly described.

  In the second embodiment described above, the canceller controller 15a determines a sample to be replaced based on information obtained from the interference wave removal signal. On the other hand, the third embodiment is different from the second embodiment in that the sample to be replaced is determined based on the synchronization information obtained from the remodulator 12.

<Replacement control information generation / output processing>
Processing executed by the canceller controller 15a in place of the replacement control information generation / output processing (FIG. 9) in the second embodiment will be described with reference to FIGS. In the flowchart of FIG. 11, the processes other than S212 and S214 are the same as the processes in FIG.

That is, in S212, the replacement reference sample is determined from the synchronization information, and in subsequent S214, the replacement direction is determined from the timing delay / advance determination result in the previous S110.
That is, in this embodiment, the replacement reference sample and the replacement direction are included in the replacement control information instead of the replacement center sample.

Based on the replacement control information, the data replacement unit 18 replaces the sample value with the replacement level by the number of replacement samples in the replacement direction from each replacement reference sample.
<Effect>
According to this embodiment, in addition to the effects of the second embodiment described above, the following effects can be obtained. In other words, in the second embodiment, if the level of the cancellation error does not exceed the threshold value, it will be excluded from the replacement target (see FIG. 10). However, in this embodiment, the cancellation error regardless of the level of the cancellation error. Since the boundaries of all OFDM symbols in which the error occurs are to be replaced (see FIG. 12), the cancellation error can be eliminated without omission.

[Fourth Embodiment]
The fourth embodiment is the same as the second and third embodiments except that the configuration of the demodulator is partially different. Therefore, the description of the common configuration will be omitted, and the difference will be mainly described.

  In the second and third embodiments described above, the number of replacement samples, which is one of the replacement control information, is determined based on the time width W of the sample error. On the other hand, the fourth embodiment differs from the second and third embodiments in that it is determined according to the received power level of the received signal (interference wave).

<Demodulation unit>
As shown in FIG. 13, the demodulator 5b is different from the configuration of the demodulator 5a in the second and third embodiments in that a received power calculator 19 is added, and the canceller controller 15b The configuration is the same as that of the demodulation unit 5a except that the replacement control information is generated based on the received power information from the calculator 19.

The reception power calculator 19 is a well-known one, and calculates the reception power of the reception signal before cancellation output from the delay unit 13.
<Canceller controller>
The canceller controller 15b is different from the canceller controller 15a only in the processing content of S220 executed in the replacement control information generation / output process (FIGS. 9 and 11).

That is, the canceller controller 15b determines the number of replacement samples by referring to a conversion table prepared in advance based on the received power information from the received power calculator 19 in S220.
As shown in FIG. 14, the conversion table is set so that the number of replacement samples increases as the received power decreases.

<Effect>
According to the present embodiment, in addition to the effects of the second and third embodiments described above, it is possible to obtain an effect that the processing load required for determining the number of replacement samples can be reduced.

[Fifth Embodiment]
The fifth embodiment is the same as the fourth embodiment except that the configuration of the demodulator is partially different. Therefore, the description of the common configuration is omitted, and the difference will be mainly described.

  In the fourth embodiment described above, the number of replacement samples, which is one of the replacement control information, is determined according to the reception power level of the interference wave. On the other hand, the fifth embodiment is different from the fourth embodiment in that it is determined according to the SNR of the interference wave.

<Demodulation unit>
As shown in FIG. 15, the demodulator 5c is different from the demodulator 5b in the fourth embodiment in that an SNR calculator 20 is added instead of the received power calculator 19, and a canceller controller 15c. However, the configuration is the same as that of the demodulator 5b except that the replacement control information is generated based on the SNR information from the SNR calculator 20.

The SNR calculator 20 is a well-known one, and calculates the SNR of the received signal output from the delay unit 13 before cancellation.
<Canceller controller>
The canceller controller 15c is different from the canceller controller 15b only in the processing content of S220 executed in the replacement control information generation / output process (FIGS. 9 and 11).

That is, in S220, the canceller controller 15c determines the number of replacement samples with reference to a conversion table prepared in advance based on the SNR information from the SNR calculator 20.
The conversion table is the same as that in FIG. 14, and is set so that the number of replacement samples increases as the SNR decreases.

<Effect>
According to this embodiment, the same effect as that of the fourth embodiment described above can be obtained.
[Sixth Embodiment]
The sixth embodiment is the same as the first embodiment except that the configuration of the delay device is partially different and the content of the processing executed by the canceller control unit is partially different. Therefore, the common configuration will be described. The description will be centered on the differences.

  In the first embodiment described above, the number of times the replica signal is regenerated is limited to one. On the other hand, the sixth embodiment is different from the first embodiment in that it can be repeated an arbitrary number of times.

<Delay device>
As shown in FIG. 16, the delay device 13 a includes a first delay device 131, a second delay device 132, and a changeover switch 133 as in the case of the delay device 13. However, the second delay device 132 is connected so that the output of the changeover switch 133 is input instead of the output of the first delay device 131.

<Cancel control>
Processing executed by the canceller controller 15 in place of the processing (FIG. 5) in the first embodiment will be described with reference to the flowchart of FIG. Note that, except that S100, S142, S144, S147, and S148 are added, the process is the same as the process in FIG.

That is, when this process is started, the canceller controller 15 first initializes the count value C of the number of times of replica signal regeneration in S100 to 0, and then executes S110 to S140.
When cancellation processing using the regenerated replica signal is started (S140), in the subsequent S142, the evaluation value E and the time width W of the cancellation error are calculated and timing delay / advance is determined in the same manner as in the previous S110. .

  In continuing S144, it is judged whether the evaluation value E calculated | required by S140 is more than a regulation value. If the evaluation value E has not reached the specified value (S144: NO), the process proceeds to S150, assuming that the cancellation has been performed satisfactorily. On the other hand, when the evaluation value E is equal to or greater than the specified value (S144: YES), it is determined that the cancellation is insufficient and the process proceeds to S147.

  In S147, the count value C of the number of times the replica signal is regenerated is incremented. In subsequent S148, it is determined whether or not the count value C exceeds the repeat threshold value N. If it is less than or equal to the repeat threshold N (S148: NO), the process returns to S130, and if it exceeds the repeat threshold N, this process ends.

<Effect>
According to the present embodiment, the adjustment of the cancellation timing by the replica signal is repeated within the range of the repetition threshold N until the cancellation error becomes sufficiently small. Therefore, the interference wave removal signal in which the interference wave is sufficiently suppressed is used. Thus, the desired wave can be demodulated with high accuracy.

[Other Embodiments]
As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention can take a various form, without being limited to the said embodiment.

  (1) In the second to fifth embodiments, the replica signal is regenerated only once, and if the cancellation is insufficient, the sample is replaced, but the replica signal is regenerated multiple times. However, sample replacement may be executed when cancellation is still insufficient.

(2) In the above embodiment, the interference wave is the preceding wave and the desired wave is the trailing wave, but this may be reversed. This case can be dealt with by increasing the delay amount of the delay device of the embodiment.
(3) Each component of the present invention is conceptual and is not limited to the above embodiment. For example, the functions of one component may be distributed to a plurality of components, or the functions of a plurality of components may be integrated into one component. Further, at least a part of the configuration of the above embodiment may be replaced with a known configuration having the same function. In addition, at least a part of the configuration of the above embodiment may be added to or replaced with the configuration of the other embodiment.

  DESCRIPTION OF SYMBOLS 1 ... OFDM receiver 2 ... RF receiving part 3 ... Quadrature detection part 4 ... ADC part 5, 5a-5c ... Demodulator 11 ... 1st demodulator 12 ... Remodulator 13, 13a ... Delayer 14 ... Subtractor 15, 15a to 15c ... canceller controller 16 ... second demodulator 17 ... data extraction / rearranger 18 ... data replacer 19 ... received power calculator 20 ... SNR calculator

Claims (7)

First demodulation means (11) for demodulating a received signal modulated by OFDM (Orthogonal Frequency Division Multiplexing);
Replica signal generating means (12) for generating a replica signal by remodulating the demodulation result in the first demodulating means;
Interference wave removal means (13, 14) for generating an interference wave removal signal by subtracting the replica signal from the received signal;
Second demodulation means (16) for demodulating the interference wave cancellation signal;
When a cancellation error included in the interference wave removal signal is detected and an evaluation value based on the cancellation error exceeds a preset allowable value, a replica signal that reduces the cancellation error is regenerated. Canceller control means (15, 15a, 15b, 15c) for controlling the replica signal generation means;
Equipped with a,
The replica signal generation means adds a guard interval before and after the reproduced OFDM symbol,
The receiving apparatus according to claim 1, wherein the canceller control means adjusts an OFDM symbol period between the received signal and the replica signal by adjusting a ratio of the guard interval added before and after . Data replacement means (18) for replacing the value of the sample constituting the interference wave removal signal with a predetermined value set in advance;
The value of the sample in which the cancellation error is detected in the reproduced interference wave cancellation signal, which is an interference wave cancellation signal generated using the replica signal regenerated by the canceller control means, is replaced by the data replacement means. Replacement control means (15a, 15b, 15c: S146) set to
The receiving apparatus according to claim 1, further comprising:   First demodulation means (11) for demodulating a received signal modulated by OFDM (Orthogonal Frequency Division Multiplexing);
  Replica signal generating means (12) for generating a replica signal by remodulating the demodulation result in the first demodulating means;
  Interference wave removal means (13, 14) for generating an interference wave removal signal by subtracting the replica signal from the received signal;
  Second demodulation means (16) for demodulating the interference wave cancellation signal;
  When a cancellation error included in the interference wave removal signal is detected and an evaluation value based on the cancellation error exceeds a preset allowable value, a replica signal that reduces the cancellation error is regenerated. Canceller control means (15, 15a, 15b, 15c) for controlling the replica signal generation means;
  Data replacement means (18) for replacing the value of the sample constituting the interference wave removal signal with a predetermined value set in advance;
  The value of the sample in which the cancellation error is detected in the reproduced interference wave cancellation signal, which is an interference wave cancellation signal generated using the replica signal regenerated by the canceller control means, is replaced by the data replacement means. Replacement control means (15a, 15b, 15c: S146) set to
  The receiving apparatus according to claim 1, further comprising: 4. The replacement control unit according to claim 2 or 3, wherein the replacement control unit sets, as the replacement target, a sample in which the cancellation error equal to or greater than a predetermined value set in advance in the reproduction interference wave removal signal is detected. Receiver. When the evaluation value of the cancellation error obtained for the reproduced interference wave removal signal exceeds a preset allowable value, the replacement control means, according to the symbol boundary position information obtained from the replica signal generation means, 4. The receiving apparatus according to claim 2 , wherein a sample corresponding to a generation timing of a cancellation error is set as the replacement target. Receiving state information calculating means (19, 20) for obtaining at least one of received power or SNR (Signal-Noise Ratio) of the received signal as receiving state information,
The replacement control means (15b, 15c) sets the number of samples to be replaced at each occurrence timing of the cancellation error to a larger value as the reception state information is smaller. Receiver.   The canceller control means repeats the generation of a replica signal by the replica signal generation means within a preset repeat threshold range until the evaluation value of the cancellation error becomes equal to or less than the allowable value. The receiving device according to any one of claims 1 to 6.

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