JP4448454B2 - Symbol synchronization circuit - Google Patents

Description

  The present invention generally relates to a symbol synchronization circuit for a received signal, and more particularly to a symbol synchronization circuit for an OFDM received signal.

  In OFDM (Orthogonal Frequency Division Multiplex) transmission, each of a plurality of orthogonal carriers arranged at fixed frequency intervals is digitally modulated with a symbol frequency and data is allocated. The modulation and demodulation in OFDM is realized by executing IFFT processing on a plurality of symbol data on the transmission side and executing FFT processing on the reception signal on the reception side. At this time, the receiving apparatus needs to detect the window timing for applying the FFT processing to the received signal. For this reason, it is required to detect the symbol timing of the OFDM symbol with high accuracy.

FIG. 1 is a diagram showing a format of a preamble portion of an OFDM signal according to IEEE802.1a. As shown in FIG. 1, 10, identical short training symbols t ₁ ~t ₁₀ a predetermined period at the beginning of the frame: provided by (16 data samples long hereinafter called symbol sample interval), thereafter 32 data sample length of the guard interval GI2,64 data sample length of the same long training symbols _{T 1} and _{T 2} is followed. To detect the symbol timing of the OFDM symbols as described above, the timing of the end of the short training symbol portion, i.e. may be detected timing of the end of t _10.

  FIG. 2 is a diagram showing a conventional apparatus configuration for symbol timing detection. The configuration in FIG. 2 is disclosed in Non-Patent Document 1, and includes a symbol timing detection unit 10, an A / D converter 11, and a signal detection unit 12. The symbol timing detection unit 10 includes a matched filter 13, an autocorrelation power calculation unit 14, a synchronous addition unit 15, a moving average unit 16, and a symbol start detection unit 17. The received OFDM signal is A / D converted by the A / D converter 11 and supplied to the signal detector 12, the matched filter 13, and the autocorrelation power calculator 14. The matched filter 13 performs matched filter processing on the signal supplied from the A / D converter 11 with the signal waveform supplied from the known signal storage circuit storing the same signal waveform as the short training symbol. As a result, the output of the matched filter 13 becomes a signal having a peak at the boundary portion of the short training symbol. This output signal is synchronously added at a symbol sample interval by a synchronous adder 15 and a moving average is calculated by a moving averager 16 in another path. The synchronous addition value and the moving average value are respectively supplied to the symbol start detection unit 17. The autocorrelation power calculation unit 14 calculates the autocorrelation power of the signal supplied from the A / D converter 11 and supplies it to the symbol start detection unit 17.

The symbol start detection unit 17 determines a provisional start point from the synchronous addition value, and detects the end position of the short training symbol portion based on the level determination between the autocorrelation power and the moving average value. Thereby, the symbol timing of the OFDM symbol can be detected with high accuracy.
JP-A-11-168446 Tomoya Hanshiro, Kazumi Sato, Satoshi Nogata, “Examination of IEEE802.11a time synchronization method”, Proceedings of 2002 IEICE General Conference, IEICE, March 7, 2002, Communication 1, P704

  However, the conventional configuration shown in FIG. 2 has a drawback that it is vulnerable to noise because the threshold values used for level determination of synchronous addition, autocorrelation power, and moving average value are fixed. In particular, in the case of a multipath configuration instead of a single path, the received power fluctuates greatly by superimposing a multipath delay wave on the received signal, so that accuracy is considerably degraded in the case of symbol synchronization detection using a fixed threshold. There is a problem. In the field of wireless communication, since a multipath configuration is naturally required, the performance of the receiving apparatus will be greatly degraded unless some measures are taken.

  As a countermeasure when the level of the received signal fluctuates in a multipath environment, when determining the null section in the synchronization symbol group from the magnitude of the received signal power value, the threshold used for the determination is set to the average value of the received signal power value. There is a technique of changing based on (Patent Document 1). However, this technique only discloses threshold determination of the signal power value, and there is no suggestion about synchronization detection based on other signals. That is, the threshold value of the signal power value at the time of null section determination is only adjusted based on the signal power value of itself, and there is no suggestion about threshold determination for other signals, and the OFDM format as shown in FIG. It is not applicable to.

  In view of the above, an object of the present invention is to provide an OFDM symbol synchronization circuit having high accuracy in threshold determination of a plurality of signals in OFDM symbol synchronization detection.

  An OFDM reception signal symbol synchronization circuit according to the present invention includes a cross-correlation detection processing unit that detects a cross-correlation value of a reception signal, a synchronous addition unit that synchronously adds the cross-correlation values at predetermined intervals, and a reception power of the reception signal A received power calculation unit that calculates the autocorrelation power of the received signal, a threshold calculation unit that calculates a synchronization addition threshold corresponding to the received power, and a peak value of the synchronously added value In response to the determination that the autocorrelation power is less than or equal to the value obtained by multiplying the received power by a predetermined coefficient at the timing, and the value obtained by the synchronization addition is greater than or equal to the synchronization addition threshold, the timing of the peak is used as the symbol timing. A symbol timing detection unit for detection is included.

  According to another aspect of the present invention, a symbol synchronization circuit for an OFDM reception signal includes a cross-correlation detection processing unit that detects a cross-correlation value of the reception signal, and a synchronization addition unit that synchronously adds the cross-correlation value at a predetermined interval. A moving average unit for calculating a moving average of the cross-correlation values, a received power calculating unit for calculating the received power of the received signal, a threshold calculating unit for calculating a synchronization addition threshold and a moving average threshold according to the received power, The timing of the peak is symbolized in response to the determination that the moving average is less than or equal to the moving average threshold and the synchronized addition value is greater than or equal to the synchronization addition threshold at the timing of the peak of the synchronized addition value. A symbol timing detection unit that detects the timing is included.

  According to at least one embodiment of the present invention, when OFDM symbol timing is detected, a threshold value is determined in at least one of a threshold value determination of a synchronous addition value, a threshold value determination of a moving average value, and a threshold value determination of an autocorrelation power. Is appropriately changed according to the received power. By applying the threshold that is dynamically adjusted according to the received power in this way to the signal level determination different from the received power, the received power fluctuates due to the presence of noise due to multipath effects, etc. Even in such a case, it is possible to detect the symbol timing with high accuracy.

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

  FIG. 3 is a diagram showing a first embodiment of an apparatus configuration for symbol timing detection according to the present invention. The configuration in FIG. 3 includes a symbol timing detection unit 20, an A / D converter 21, and a signal detection unit 22. The symbol timing detection unit 20 includes a matched filter 23, a power generation unit 24, a synchronous addition unit 25, a moving average unit 26, a symbol start detection unit 27, a delay circuit 28, a conjugate complex signal generation unit 29, a complex multiplication unit 30, and an integrator. Unit 31, power generation unit 32, correlation determination unit 33, power generation unit 34, integrator unit 35, square calculation unit 36, coefficient multiplication unit 37, and threshold value table 38. The received OFDM signal is A / D converted by the A / D converter 21 and supplied to the signal detection unit 22, the matched filter 23, the delay circuit 28, the conjugate complex signal generation unit 29, the complex multiplication unit 30, and the powerization unit 34. The The signal detection unit 22 detects a packet based on the supplied signal and sends a signal notifying the arrival of the packet.

  The matched filter 23 performs matched filter processing (cross-correlation) on the signal supplied from the A / D converter 21 based on the signal waveform supplied from the known signal storage circuit storing the same signal waveform as the short training symbol. Detection process). The power generation unit 24 converts the signal after the matched filter processing into power (square of the envelope). As a result, the output of the power conversion unit 24 becomes a signal having a peak that rises sharply at the boundary of the short training symbol. This output signal is synchronously added at a symbol sample interval by a synchronous adder 25, and a moving average is calculated by a moving averager 26 in another path. The synchronous addition value and the moving average value are supplied to the symbol start detection unit 27, respectively.

  The delay circuit 28 delays the signal from the A / D converter 21 by a symbol sample interval. The conjugate complex signal generation unit 29 obtains a complex conjugate signal of the delayed signal and outputs the complex conjugate signal to the complex multiplication unit 30. The complex multiplier 30 multiplies the delayed complex conjugate signal by the signal without delay from the A / D converter 21 to generate an autocorrelation signal. The autocorrelation signal is integrated for a predetermined time interval by the integrator unit 31 and further converted into electric power by the power generation unit 32. Thereby, autocorrelation signal power is obtained.

  The power generation unit 34 converts the signal supplied from the A / D converter 21 into power. The powerized signal is integrated by the integrator unit 35 for the same interval as the integrator unit 31 and is squared by the square calculation unit 36. Since the received signal is squared twice in the above autocorrelation power calculation path, the square calculation unit 36 squares the power after the power generation unit 34 converts the power to the dimension. As a result, the received power is obtained.

  The reception power is supplied to the correlation determination unit 33 after being multiplied by a predetermined coefficient β (greater than 0 and less than 1) by the coefficient multiplication unit 37. The correlation determination unit 33 compares the autocorrelation power from the power generation unit 32 with the received power multiplied by the coefficient β, and supplies a signal indicating the magnitude relationship between the two to the symbol start detection unit 27. Further, the threshold value table 38 stores a synchronous addition threshold value and a moving average threshold value corresponding to each level of received power in a table format. The threshold value table 38 reads the synchronous addition threshold value and the moving average threshold value corresponding to the supplied received power from the table and supplies them to the symbol start detection unit 27. The symbol start detection unit 27 is supplied from the synchronization addition value supplied from the synchronization addition unit 25, the moving average value supplied from the moving average unit 26, the autocorrelation power determination value supplied from the correlation determination unit 33, and the threshold value table 38. The end of the short training symbol sequence is detected as a symbol timing based on the synchronized addition threshold and the moving average threshold.

  FIG. 4 is a flowchart showing a symbol timing detection operation by the symbol start detection unit 27. In step S1, a symbol start operation is started. In step S2, it is determined whether or not the synchronous addition value has reached a peak. As described above, the synchronous addition value is obtained by synchronously adding a signal having a peak that rises steeply at the boundary portion of the short training symbol at the symbol sample interval. Therefore, the peak value of the waveform that rises sharply increases with time. Signal. This peak value is detected in step S2.

  In step S3, a synchronous addition threshold value and a moving average threshold value are determined from the threshold value table based on the power value at the peak position. Specifically, since the synchronous addition threshold and the moving average threshold corresponding to the received power value at that time are supplied from the threshold table 38, the synchronous addition threshold and the moving average threshold supplied at the peak position timing can be used. That's fine.

  In step S4, the power value and the autocorrelation value are compared at the peak position of the synchronous addition. Specifically, since the determination result of the magnitude relationship between the autocorrelation power at that time and β × received power is supplied from the correlation determination unit 33, the determination result supplied at the timing of the peak position may be used.

  In step S5, it is determined whether or not the condition that the synchronous addition value is equal to or larger than the obtained synchronous addition threshold value, the moving average value is equal to or smaller than the obtained moving average threshold value, and the autocorrelation power is smaller than β × received power is satisfied. To do. If all of these conditions are satisfied, it is determined that the peak position is the symbol timing, and the symbol timing detection operation is completed in step S6. If the above condition is not satisfied, the process returns to step S2 and the same process is repeated.

  As described above, in the first embodiment of the present invention, when detecting the OFDM symbol timing, the threshold value is determined in the threshold determination of the synchronous addition value, the threshold determination of the moving average value, and the threshold determination of the autocorrelation power. Is appropriately changed according to the received power. This makes it possible to detect the symbol timing with high accuracy even when there is noise due to the influence of multipath and the received power fluctuates.

  FIG. 5 is a diagram illustrating an example of the threshold value table. As shown in FIG. 5, the threshold value table stores a synchronous addition threshold value and a moving average threshold value corresponding to each range of the received power value P. As the received power increases, the synchronization addition threshold value and the moving average threshold value are configured to increase. FIG. 5 is an example, and the range of the received power value P and the value of each threshold may be changed as appropriate according to the actual implementation conditions.

  FIG. 6 is a diagram showing a modification of the first embodiment of the symbol timing detection apparatus according to the present invention. In FIG. 6, the same components as those of FIG. 3 are referred to by the same numerals, and a description thereof will be omitted.

  In the configuration of the first embodiment shown in FIG. 3, for each of the synchronous addition value, the moving average value, and the autocorrelation power value, a threshold value corresponding to the reception power is set and a determination for symbol timing detection is performed. It was. On the other hand, in the modification shown in FIG. 6, only the synchronous addition value and the moving average value are used for the determination for detecting the symbol timing.

  The symbol timing detection unit 20A illustrated in FIG. 6 includes a delay circuit 28, a conjugate complex signal generation unit 29, a complex multiplication unit 30, an integrator unit 31, a power generation unit 32, and a correlation determination unit 33 from the symbol timing detection unit 20 illustrated in FIG. , And the coefficient multiplier 37 are removed. The symbol start detection unit 27A is short-circuited based on the synchronous addition value supplied from the synchronous addition unit 25, the moving average value supplied from the moving average unit 26, the synchronous addition threshold and the moving average threshold supplied from the threshold table 38. The end of the training symbol sequence is detected as a symbol timing.

  Specifically, as in the case of the configuration of FIG. 3, it is first determined whether or not the synchronous addition value has reached a peak, and the synchronous addition threshold value and moving average threshold value supplied at the timing of the peak position are obtained. Based on the threshold value thus obtained, it is determined whether or not the condition that the synchronous addition value is equal to or greater than the synchronous addition threshold value and the moving average value is equal to or less than the moving average threshold value is satisfied. When all of these conditions are satisfied, it is determined that the peak position is the symbol timing.

  As described above, it is possible to detect the symbol timing without using all of the synchronous addition value, the moving average value, and the autocorrelation power value, for example, using only the synchronous addition value and the moving average value. In this case, the accuracy is lowered, but there is an advantage that the circuit configuration is simplified.

  FIG. 7 is a diagram showing another modification of the first embodiment of the symbol timing detection apparatus according to the present invention. In FIG. 7, the same components as those of FIG. 3 are referred to by the same numerals, and a description thereof will be omitted. In the modification shown in FIG. 7, only the synchronous addition value and autocorrelation power value are used for determination for symbol timing detection.

  The symbol timing detection unit 20B shown in FIG. 7 is configured by removing the moving average unit 26 from the symbol timing detection unit 20 of FIG. The symbol start detection unit 27 </ b> B is based on the synchronization addition value supplied from the synchronization addition unit 25, the autocorrelation power determination value supplied from the correlation determination unit 33, and the synchronization addition threshold supplied from the threshold table 38. The end of the ning symbol sequence is detected as a symbol timing.

  Specifically, as in the case of the configuration of FIG. 3, first, it is determined whether or not the synchronous addition value has reached a peak, and the synchronous addition threshold value and autocorrelation power determination value supplied at the timing of the peak position are obtained. . Based on these, it is determined whether or not the condition that the synchronous addition value is equal to or greater than the synchronous addition threshold and the autocorrelation power is smaller than β × received power is satisfied. When all of these conditions are satisfied, it is determined that the peak position is the symbol timing.

  As described above, it is possible to detect the symbol timing without using all of the synchronous addition value, the moving average value, and the autocorrelation power value, for example, using only the synchronization addition value and the autocorrelation power value. In this case, the accuracy is lowered, but there is an advantage that the circuit configuration is simplified.

  FIG. 8 is a diagram showing a second embodiment of the device configuration for symbol timing detection according to the present invention. In FIG. 8, the same components as those of FIG. 3 are referred to by the same numerals, and a description thereof will be omitted. In the configuration of the first embodiment shown in FIG. 3, the signal detector 22 detects a packet and transmits a packet detection signal. For this packet detection processing, autocorrelation power threshold processing is used. Therefore, in the second embodiment of the present invention, the circuit scale is reduced by sharing the circuit of the signal detector (packet detector) and the symbol timing detector.

  In the configuration of FIG. 8, the symbol timing detection unit 20C includes a matched filter 23, a power generation unit 24, a synchronous addition unit 25, a moving average unit 26, a symbol start detection unit 27, a correlation determination unit 33, a coefficient multiplication unit 37, and a threshold value. A table 38 is included. The delay circuit 28, the conjugate complex signal generation unit 29, the complex multiplication unit 30, the integrator unit 31, and the power generation unit 32 that are included in the symbol timing detection unit 20 of FIG. 3 but are not included in the symbol timing detection unit 20C of FIG. The power generation unit 34, the integrator unit 35, and the square calculation unit 36 are incorporated in the signal detection unit 22. The signal detector 22 includes a coefficient multiplier 41 and a signal detection determination unit 42 in addition to these components.

  The signal detection determination unit 42 receives the autocorrelation power calculated in the same manner as in the first embodiment from the power generation unit 32. The received power calculated in the same manner as in the first embodiment is supplied to the signal detection determination unit 42 after being multiplied by a predetermined coefficient α by the coefficient multiplier 41. The signal detection determination unit 42 determines that a packet has been detected when a state where the autocorrelation power is equal to or higher than α × reception power is maintained for a predetermined time, and detects a packet detection signal. This packet detection signal is supplied to the symbol timing detection unit 20C and also to the AGC control unit 43. The AGC control unit 43 performs an AGC control operation based on the packet detection signal and the received power supplied from the square calculation unit 36.

  The symbol timing detection operation in the symbol start detection unit 27 of the symbol timing detection unit 20C is the same as that in the first embodiment.

  In this way, in the second embodiment, by sharing a circuit between the signal detection unit 22 that detects a packet and the symbol timing detection unit 20 that detects a symbol timing, the circuit scale is reduced and the power consumption is reduced. Can be reduced. The same effect can be obtained for the AGC control unit.

  FIG. 9 is a diagram showing a third embodiment of the device configuration for symbol timing detection according to the present invention. 9, the same components as those of FIG. 8 are referred to by the same numerals, and a description thereof will be omitted.

  In OFDM, an autocorrelation value is used in offset estimation of a wideband carrier frequency. Therefore, in the third embodiment shown in FIG. 9, the signal detection unit 22 and the broadband carrier frequency offset estimation unit of the second embodiment share a circuit portion for calculating the autocorrelation value. In the configuration of FIG. 9, the wideband carrier frequency offset estimation unit includes a buffer 51 and a phase calculation unit 52. After the packet detection, the AGC control and the symbol timing detection operation are started, and at the same time, the autocorrelation value output from the integrator unit 31 of the signal detection unit 22 is supplied to the buffer 51. After detecting the symbol start by the symbol timing detection operation, the phase calculation unit 52 of the broadband carrier frequency offset estimation unit is activated to obtain the carrier frequency offset.

  In this manner, in the third embodiment, the circuit scale can be reduced by sharing the circuit between the signal detection unit 22 that performs packet detection and the broadband carrier frequency offset estimation unit. By proceeding in parallel with symbol timing detection and AGC control, the latency of wideband carrier frequency offset estimation can be reduced.

  FIG. 10 is a diagram showing a configuration of an OFDM transmission / reception system to which a symbol synchronization circuit for detecting symbol timing is applied according to the present invention.

  As shown in FIG. 10A, the transmission side includes a scrambler 101, an FEC (Forward Error Correction) encoding unit 102, a puncturing / interleaving mapping unit 103, an IFFT unit 104, a GI adding unit 105, D The transmission data is processed by the / A converter 106 to generate a transmission signal, and a radio signal is transmitted from the antenna. On the receiving side shown in FIG. 10 (b), the received signal received by the antenna is converted into an A / D converter 107, a packet detection unit 108, a symbol synchronization unit 109, a carrier frequency correction unit 110, an FFT window control unit 111, an FFT. Unit 112, channel estimation unit 113, synchronous detection unit 114, residual carrier frequency correction / phase noise correction / sampling frequency correction unit 115, demapping / deinterleaving / depuncturing unit 116, FEC decoding unit 117, and descrambler 118 To process the received data.

  The symbol timing detection unit according to the present invention corresponds to the symbol synchronization unit 109. The signal detection unit 22 corresponds to the packet detection unit 108. The symbol synchronization unit 109 detects the symbol timing as described in the above embodiment, and calculates a wide band carrier frequency offset. The carrier frequency correction unit 110 corrects the carrier frequency based on the calculated broadband carrier frequency offset. The FFT window control unit 111 controls the window timing of the FFT processing based on the detected symbol timing. The FFT unit 112 executes FFT processing at the controlled window timing.

  FIG. 11 is a diagram showing a comparison between the prior art of FIG. 2 by simulation and the symbol timing detection processing of the present invention of FIG. The simulation environment is assumed to have six multipaths, and the average power of each path attenuates exponentially. The data rate is 6 Mbps and the packet length is 1000 bytes. In the prior art simulation of FIG. 2, the threshold values optimized in the simulation environment are the autocorrelation power threshold value 0.03, the synchronous addition threshold value 0.06, and the moving average threshold value 0.01.

  The vertical axis of FIG. 11 shows the packet error rate PER, and the horizontal axis shows the ratio of 1-bit energy to AWGN (added white Gaussian noise) vector density. A smaller PER value indicates fewer reception errors. In the IEEE802.11a standard, there is a standard that PER is 0.1 for every 1000 bytes under AWGN. In the case of multipath, there is no particular standard, but PER = 0.1 can be considered as a temporary guide. As shown in FIG. 11, the configuration of the conventional example maintains a level of PER = 0.1 or higher regardless of the amount of noise in a multipath environment, whereas the configuration of the present invention has noise. If small, PER can be zero.

  As mentioned above, although this invention was demonstrated based on the Example, this invention is not limited to the said Example, A various deformation | transformation is possible within the range as described in a claim.

It is a figure which shows the format of the preamble part of an OFDM signal. It is a figure which shows the apparatus structure for the conventional symbol timing detection. It is a figure which shows the 1st Example of the apparatus structure for the symbol timing detection by this invention. It is a flowchart which shows the symbol timing detection operation | movement by a symbol start detection part. It is a figure which shows an example of a threshold value table. It is a figure which shows the modification of the 1st Example of the symbol timing detection apparatus by this invention. It is a figure which shows another modification of the 1st Example of the symbol timing detection apparatus by this invention. It is a figure which shows the 2nd Example of the apparatus structure for the symbol timing detection by this invention. It is a figure which shows the 3rd Example of the apparatus structure for the symbol timing detection by this invention. It is a figure which shows the structure of the OFDM transmission / reception system to which the symbol synchronizing circuit which detects symbol timing by this invention is applied. It is a figure which shows the comparison with the prior art of FIG. 2 and the symbol timing detection process of this invention of FIG. 3 by simulation.

Explanation of symbols

20 symbol timing detection unit 21 A / D converter 22 signal detection unit 23 matched filter 24 power generation unit 25 synchronous addition unit 26 moving average unit 27 symbol start detection unit 28 delay circuit 29 conjugate complex signal generation unit 30 complex multiplication unit 31 integration Unit 32 Power generation unit 33 Correlation determination unit 34 Power generation unit 35 Integrator unit 36 Square calculation unit 37 Coefficient multiplication unit 38 Threshold table

Claims (8)

A cross-correlation detection processing unit for detecting a cross-correlation value of the received signal;
A synchronous adder for synchronously adding the cross-correlation values at predetermined intervals;
A received power calculation unit for calculating received power of the received signal;
An autocorrelation power calculator for obtaining autocorrelation power of the received signal;
A threshold value calculation unit for obtaining a synchronous addition threshold value according to the received power;
In response to determination that the autocorrelation power is equal to or less than a value obtained by multiplying the received power by a predetermined coefficient at the peak timing of the synchronous addition value, and that the synchronous addition value is equal to or greater than the synchronization addition threshold value. And a symbol timing detection unit for detecting the timing of the peak as a symbol timing.   2. The threshold calculation unit includes a table for storing different synchronization addition threshold values corresponding to different reception powers, and obtains and outputs the synchronization addition threshold values corresponding to the reception powers from the table. Symbol synchronization circuit.   When it is detected that the autocorrelation power calculated by the autocorrelation power calculation unit is equal to or greater than a value obtained by multiplying the reception power calculated by the reception power calculation unit by a predetermined coefficient for a predetermined time or more. 2. The symbol synchronization circuit according to claim 1, further comprising a signal detection unit for outputting a packet detection signal.   4. The symbol synchronization circuit according to claim 3, further comprising an AGC control unit that performs AGC control based on the packet detection signal and the received power calculated by the received power calculation unit.   2. The symbol synchronization circuit according to claim 1, further comprising a broadband carrier frequency offset estimation unit that estimates an offset of a broadband carrier frequency based on the autocorrelation value calculated by the autocorrelation power calculation unit. A cross-correlation detection processing unit for detecting a cross-correlation value of the received signal;
A synchronous adder for synchronously adding the cross-correlation values at predetermined intervals;
A moving average unit for obtaining a moving average of the cross-correlation values;
A received power calculation unit for calculating received power of the received signal;
A threshold value calculation unit for obtaining a synchronous addition threshold value and a moving average threshold value according to the received power;
In response to the determination that the moving average is less than or equal to the moving average threshold and the synchronized addition value is greater than or equal to the synchronous addition threshold at the timing of the peak of the synchronously added value, the timing of the peak is symbol timing A symbol synchronization circuit for an OFDM reception signal, comprising:   7. The threshold calculation unit includes a table that stores different moving average thresholds corresponding to different received powers, and calculates and outputs the moving average thresholds corresponding to the received powers from the table. Symbol synchronization circuit. A cross-correlation detection processing unit for detecting a cross-correlation value of the received signal;
A synchronous adder for synchronously adding the cross-correlation values at predetermined intervals;
A moving average unit for obtaining a moving average of the cross-correlation values;
A received power calculation unit for calculating received power of the received signal;
An autocorrelation power calculator for obtaining autocorrelation power of the received signal;
A threshold value calculation unit for obtaining a synchronous addition threshold value and a moving average threshold value according to the received power;
At the timing of the peak of the synchronously added value, the autocorrelation power is less than or equal to a value obtained by multiplying the received power by a predetermined coefficient, the moving average is less than or equal to the moving average threshold, and the synchronously added value is A symbol synchronization circuit for an OFDM reception signal, comprising: a symbol timing detection unit that detects the timing of the peak as a symbol timing in response to a determination that the synchronization addition threshold value is exceeded.

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