JP4105659B2 - Receiver and receiver circuit - Google Patents

Description

  The present invention relates to a receiving apparatus that receives a signal modulated by an OFDM (Orthogonal Frequency Division Multiplex) scheme.

  As is well known, a conventional receiver that receives a signal modulated by the OFDM method receives a synchronization symbol having a known constant pattern, and performs symbol processing to perform FFT processing on the received sample signal based on the received synchronization symbol. Had decided. Specifically, an autocorrelation value is obtained by multiplying the received sample signal by a signal obtained by delaying the sample signal by the time interval of the synchronization symbol, and the timing at which this value becomes maximum is set as the symbol timing.

  In addition to this, there is also a method of obtaining a cross-correlation value by filtering the received sample signal using a time waveform of a synchronization symbol as a coefficient, and setting a timing at which this value becomes the maximum as a symbol timing (for example, Non-patent document 1). The filter used here is called a matched filter.

  Also, in the case of a reception diversity apparatus that has a plurality of reception systems and combines the reception results to improve the reception S / N ratio, an autocorrelation value is used for each reception system with respect to the synchronization symbol of the OFDM signal. There is a method in which symbol timing is detected, and a symbol having a large reception level is used as timing for performing FFT processing (see, for example, Patent Document 1).

  However, since the conventional symbol synchronization method using the autocorrelation value has low accuracy, it is necessary to accumulate the correlation values of a large number of synchronization symbols, and there are many delay paths with similar reception levels in a multipath environment. However, there is a high possibility that it will be erroneously detected.

  On the other hand, conventionally, detection accuracy is improved by performing correlation processing on a large number of symbols. However, such a method has a drawback in that the time required for processing increases, so that the time available for data transmission decreases and the transmission capacity of the entire system decreases.

  On the other hand, the conventional symbol synchronization method using the cross-correlation value can be detected with fewer synchronization symbols than the autocorrelation value, and the accuracy of delay path detection is high even in a multipath environment. However, when the S / N ratio is low, that is, when the noise is large, there is a problem that the possibility of erroneous detection increases. The symbol synchronization method described above assumes a receiving apparatus having only one receiving system, and cannot be applied to a receiving apparatus having a plurality of receiving systems.

  In Patent Document 1, although it is a receiving apparatus having a plurality of receiving systems, since it is a receiving diversity that finally combines signals of each receiving system, the timing of FFT must be the same in all receiving systems. There is a constraint.

  Also, the symbol timing detection method can detect only the time of the maximum peak power detected in each receiving system, but in the case of an actually complex multipath model, it is close to that other than the timing having the maximum peak power. There are many timing paths having power values, and the time having the maximum peak power is not necessarily the optimum symbol timing.

  In addition, since autocorrelation is used, the number of synchronization symbols is small when performing packet communication such as wireless LAN. For this reason, in the case of a wireless communication system in which the synchronization timing must be determined in a short time, problems such as insufficient detection accuracy occur.

  By the way, recently, a MIMO (Multi Input Multi Output) system has been attracting attention. In a MIMO wireless system, a transmitter uses a plurality of transmit antennas to simultaneously transmit OFDM modulated signals in the same frequency band, while a receiver receives signals using a plurality of receive antennas and separates them. By doing so, the transmission throughput is improved.

However, since the conventional symbol synchronization method has the above-described problems, when the conventional symbol synchronization method is applied to a MIMO receiver, not only sufficient demodulation accuracy cannot be exhibited, but also the circuit scale increases. There was a problem to do.
JP 2000-143105 A "802.11 high-speed wireless LAN textbook", IDG Japan, March 29, 2003.

When applied to a MIMO receiver, the conventional symbol synchronization method has a problem that not only sufficient demodulation accuracy cannot be exhibited, but also the circuit scale increases.
The present invention has been made to solve the above problem, and an object of the present invention is to provide a MIMO receiver and a receiver that can perform demodulation with high accuracy and can be realized with a relatively small circuit scale.

  In order to achieve the above object, the present invention provides a receiving apparatus including a first demodulating unit and a second demodulating unit that respectively demodulate an OFDM-modulated radio signal. Each demodulating means is preset with a frequency converting means for converting a radio signal into a baseband signal, an A / D converting means for converting the output of the frequency converting means into a digital signal, and an output of the A / D converting means. A correlation detection unit that obtains a correlation with a symbol pattern and creates a delay profile indicating a relationship between a plurality of symbol timings and a correlation level, and a clock that generates a symbol clock at a timing based on the delay profile created by the correlation detection unit The frequency offset is corrected from the output of the A / D conversion unit based on the generation unit and the frequency offset information. And a frequency offset based on the output of the A / D conversion means provided in the first demodulating means, and the OFDM demodulating means for OFDM demodulating the output of the correcting means using the symbol clock generated by the clock generating means. The frequency offset detection means for outputting the detected frequency offset as frequency offset information to the correction means included in the first demodulation means and the second demodulation means, the first demodulation means and the second demodulation, respectively. The output of the OFDM demodulating means included in each means is used to provide MIMO demodulating means for performing MIMO demodulation.

  As described above, in the present invention, one frequency offset detection means for detecting a frequency offset is provided, and the detection result of this frequency offset detection means is shared by the first demodulation means and the second demodulation means, The first demodulator and the second demodulator generate symbol clocks by correlation detection and perform OFDM demodulation.

  Therefore, according to the present invention, since only one frequency offset detection means is mounted, the circuit scale is small, and since each demodulation means can receive a path suitable for reception, a receiving apparatus capable of performing demodulation with high accuracy. And a receiving circuit can be provided.

Embodiments of the present invention will be described below with reference to the drawings.
First, a MIMO radio system according to the present invention will be described. This wireless system has a configuration as shown in FIG. 1, for example. The transmission apparatus 100 includes OFDM modulation units 101 to 10n configured as illustrated in FIG. 2 and a switching unit 110, and performs transmission in a transmission frame format as illustrated in FIG. The receiving apparatus 200 includes OFDM demodulation units 201 to 20m and a MIMO demodulation unit 210.

  The OFDM modulation units 101 to 10n modulate a carrier wave by input data by OFDM (Orthogonal Frequency Division Multiplex) modulation, and receive independent transmission data series D1 to Dn, respectively. The transmission data series D1 to Dn may be encoded audio data or packet data. However, the OFDM modulation unit 101 selectively receives one of a synchronization symbol having a known synchronization symbol pattern in the receiving apparatus 200 and the transmission data sequence D1 through the switching unit 110.

  As a result, the OFDM modulation unit 101 transmits a transmission data sequence D1 after transmitting a plurality of synchronization symbols, as indicated by Tx1 in FIG. Further, the OFDM modulation units 102 to 10n perform OFDM modulation on the corresponding transmission data sequences D2 to Dn, respectively, as shown by Tx2 to Txn in FIG. 3 in accordance with the transmission of the transmission data sequence D1 by the OFDM modulation unit 101. To do.

  As shown in FIG. 2, the OFDM modulation unit 101 includes a serial / parallel (S / P) conversion unit 1011, a mapping unit 1012, an IFFT unit 1013, a GI addition unit 1014, a D / A conversion unit 1015, and a transmission radio unit 1016. Prepare. The OFDM modulation units 102 to 10n have the same configuration as that of the OFDM modulation unit 101, and thus description thereof is omitted.

  The serial / parallel conversion unit 1011 temporarily keeps the transmission data series D1 input in the order of time sequence in a storage area such as an internal memory, and when the predetermined number of data is reached, the serial / parallel conversion unit 1011 performs parallel processing on the mapping unit 1012. By outputting, serial data is converted into parallel data.

  The mapping unit 1012 performs mapping on the IQ plane according to a predetermined modulation method for each subcarrier for the data input in parallel from the serial / parallel conversion unit 1011, and outputs this to the IFFT unit 1013. . The IFFT unit 1013 performs an IFFT (Inverse Fast Fourier Transform) process on the data input from the mapping unit 1012 to convert the data on the frequency axis into the data on the time axis.

  The GI adding unit 1014 is a functional block that uses a signal obtained by copying the latter half of the signal sequence converted into the time domain by the IFFT unit 1013 as a guard interval, and adds this to the head of the output from the IFFT unit 1013. Here, the length of the guard interval is specified by the communication system, and is set to a time range in which a multipath delayed wave exists. For example, in IEEE801.11a, the guard interval length is set to 0.8 μsec with respect to the OFDM symbol length of 3.2 μsec.

  The D / A conversion unit 1015 converts the data input from the GI addition unit 1014 into an analog signal. The transmission radio unit 1016 converts the analog signal into a predetermined frequency, amplifies the power, and performs band limitation. The radio signal generated in this way is radiated into space through the corresponding transmitting antenna.

  Note that the OFDM modulation units 101 to 10n generate the radio signal using the same frequency carrier. As a result, the radio signals transmitted from the n transmitting antennas are multiplexed in space and reach the receiving apparatus 200. Since the receiving device 200 includes m receiving antennas, there are n × m transmission paths between the transmitting device 100 and the receiving device 200.

  The receiving apparatus 200 estimates each of the transmission paths and separates each signal. In the case of communication using an OFDM modulated signal for each transmission path, different independent transmission paths are generated for each OFDM subcarrier, so that the transmission path estimation and the MIMO demodulation separation are performed after the subcarrier separation. The MIMO demodulation method includes a spatial filtering method, an MLD (maximum likelihood estimation) method, an ordered sequential decoding method, and the like.

  Next, a first embodiment of the receiving apparatus 200 shown in FIG. 1 is shown as a receiving apparatus 400 in FIG. This receiving apparatus 400 includes m antennas, OFDM demodulation units 401 to 40m corresponding to the respective antennas, and a MIMO demodulation unit 410.

  The OFDM demodulation unit 401 includes a reception radio unit 4011, a cross-correlation unit 4012, a symbol clock generation unit 4013, an AFC (Auto Frequency Control) unit 4014, a multiplier 4015, a GI (Guard Interval) removal unit 4016, and an FFT (Fast Fourier). Transform) section 4017 is provided. The OFDM demodulating units 402 to 40m are not provided with the AFC unit 4014 and have the same configuration as that of the OFDM demodulating unit 401, and thus description thereof is omitted.

  The reception radio unit 4011 performs a filtering process on a signal input from a corresponding antenna to limit the signal to a predetermined band, performs frequency conversion, performs a low noise power amplification, and then performs an orthogonal demodulation process. The baseband signal thus obtained is converted into a digital signal having a predetermined sampling frequency by A / D conversion. This digital signal is output to cross-correlation section 4012, AFC section 4014 and multiplier 4015.

  The cross-correlation unit 4012 performs a matched filter process on the digital signal to create a delay profile. In this matched filter processing, a time waveform of a synchronization symbol signal obtained by OFDM-modulating the synchronization symbol pattern used in the transmission apparatus 100 is used as a tap coefficient. A configuration example of the cross-correlation unit 4012 is shown in FIG.

  As shown in this figure, the cross-correlation unit 4012 includes shift registers 501 to 50j, multipliers 511 to 51j, an adder 520, adders 531 to 53k, and memories 541 to 54k, and is output from the reception radio unit 4011. Digital signals are sequentially input from the shift register 501 for each sample.

  The values of the shift registers 501 to 50j are output from the shift registers 501 to 50j to the corresponding multipliers 511 to 51j in synchronization with the sample data being input and shifted. The multipliers 511 to 51j multiply the input sample data by the tap coefficient, and the multiplication results are added by the adder 520.

  The values added by the adder 520 are selectively output to the memories 541, 542,..., 54k at each timing of input of sample data to the shift registers 501 to 50j. The adders 531 to 53k and the memories 541 to 54k are paired, and the adders 531 to 53k correspond by adding the output of the adder 520 and the values stored in the corresponding memories 541 to 54k. Accumulated addition is performed by outputting to the memories 541 to 54k.

  The number of pairs of adders 531 to 53k and memories 541 to 54k corresponding to the number of synchronization symbols shown in FIG. 3 is provided, and the above cumulative addition is repeated for the number of times the OFDM modulation unit 101 transmits the synchronization symbols. Is called. The value cumulatively added to the memories 541 to 54k in this way indicates a delay profile and is output to the symbol clock generation unit 4013.

  Here, as shown in FIG. 6, in a multipath environment in which an obstacle such as a building exists between the transmission device 100 and the reception device 400, for example, two delayed waves a, b arrives at the receiving apparatus 400. In this case, the synchronization symbol arrives at the receiving apparatus 400 with a direct wave and two delayed waves a and b delayed from the direct wave, and the delay profile is as shown in FIG.

  A symbol clock generation unit 4013 generates a symbol clock at an optimal timing for OFDM demodulation based on the delay profile generated by the cross-correlation unit 4012. The symbol clock generated here is output to GI removal section 4016.

  The AFC unit 4014 detects a frequency offset from the digital signal input from the reception radio unit 4011. The frequency offset detected here is output not only to the multiplier 4015 of the OFDM demodulator 401 but also to the multiplier 4015 of the OFDM demodulator 402 to 40m.

  The multiplier 4015 multiplies the digital signal input from the reception radio unit 4011 by the frequency offset detected by the AFC unit 4014, thereby correcting the frequency offset included in the digital signal. The digital signal whose frequency offset is corrected in this way is output to the GI removal unit 4016.

  GI removal section 4016 removes the guard interval from the digital signal input from multiplier 4015 based on the symbol clock generated by symbol clock generation section 4013, and outputs a data symbol. The data symbols extracted in this way are output to the FFT unit 4017.

  The FFT unit 4017 performs FFT processing on the data symbols input from the GI removal unit 4016, thereby converting the data on the time axis into the data on the frequency axis, and divides it into symbol data corresponding to the subcarrier. To do. The symbol data obtained in this way is output to the MIMO demodulator 410. Similarly, in OFDM demodulation sections 402 to 40m, symbol data corresponding to subcarriers is obtained and output to MIMO demodulation section 410.

  The MIMO demodulator 410 estimates and separates a transmission path for each subcarrier from the symbol data input from the OFDM demodulators 401 to 40m, and performs demapping. Then, the MIMO demodulator 410 performs a hard decision on the demapping result and decodes the original data D1 to Dn. Depending on the modulation method, the original data D1 to Dn are decoded by error correction decoding using soft decision or the like.

  As described above, the receiving apparatus 400 having the above configuration includes one AFC unit 4014, and each OFDM demodulator 401 to 40m uses the frequency offset obtained thereby to remove the frequency offset and each OFDM demodulator. 401 to 40m include a cross-correlation unit 4012 to detect a correlation level, thereby generating a symbol clock for receiving a path suitable for reception and performing OFDM demodulation.

  Therefore, according to the receiving apparatus having the above configuration, the circuit scale is small because only one AFC unit 4014 is mounted, and each OFDM demodulating unit 401 to 40m can receive a path suitable for reception, so that demodulation is performed with high accuracy. be able to.

  Since the frequency offset is caused by the local frequency on the transmitting apparatus 100 side and the local frequency on the receiving apparatus 400 side, the same frequency offset value is used even in a plurality of receiving systems such as the receiving apparatus 400. Therefore, even if the detection result of one AFC unit 4014 is also used, a sufficient effect can be exhibited.

  Next, a second embodiment of the receiving apparatus 200 shown in FIG. 1 is shown as a receiving apparatus 800 in FIG. The receiving apparatus 800 includes m antennas, OFDM demodulation units 801 to 80m corresponding to the respective antennas, a timing likelihood calculation unit 810, a symbol clock generation unit 820, and a MIMO demodulation unit 830.

  The OFDM demodulation unit 801 includes a reception radio unit 8011, a cross-correlation unit 8012, an AFC (Auto Frequency Control) 8013, a multiplier 8014, a GI (Guard Interval) removal unit 8015, and an FFT (Fast Fourier Transform) unit 8016. The OFDM demodulating units 802 to 80m are not provided with the AFC unit 8013 and have the same configuration as that of the OFDM demodulating unit 801, and thus description thereof is omitted.

  The reception radio unit 8011 performs filtering processing on a signal input from the corresponding antenna to limit the signal to a predetermined band, performs frequency conversion, further performs low noise power amplification, and then performs orthogonal demodulation processing. The baseband signal thus obtained is converted into a digital signal having a predetermined sampling frequency by A / D conversion. This digital signal is output to cross-correlation section 8012, AFC section 8013 and multiplier 8014.

  The cross-correlation unit 8012 performs a matched filter process on the digital signal, creates a delay profile from this, and outputs it to the timing likelihood calculation unit 810. In this matched filter processing, a time waveform of a synchronization symbol signal obtained by OFDM-modulating the synchronization symbol pattern used in the transmission apparatus 100 is used as a tap coefficient. The cross-correlation unit 8012 is configured as shown in FIG. 5, for example.

  The timing likelihood calculation unit 810 aggregates the delay profiles created by the cross-correlation units 8012 provided in the OFDM demodulation units 801 to 80m, respectively, and creates a table as shown in FIG. 9, for example. This table is composed of m rows of reception systems and k columns of timings for storing correlation values, and each cell stores a power value indicating a correlation level.

Then, the timing likelihood calculating unit 810 obtains the timing likelihood λ according to the following equation. That is, the timing likelihood λ corresponding to the timing obtained by a plurality of correlators and the degree of the correlation level is obtained. Since the timing likelihood λ does not become an integer value as can be predicted from the following equation, the timing likelihood calculation unit 810 determines the closest integer value as the synchronization timing value. Note that a timing having an integer value that is earlier in time may be determined as the synchronization timing value.

  Here, for example, a case where a delay profile as shown in FIG. 10 is obtained by each cross-correlation unit 8012 of the OFDM demodulation units 801 to 80m will be described. In this figure, T1 to Tn indicate timing within a time window having the same width as the time interval of the synchronization symbols. P1 to Pn indicate cross-correlation values at corresponding timings T1 to Tn, respectively.

  If the result of the likelihood calculation is that λ is between T2 and T3, the timing likelihood calculation unit 810 notifies the symbol clock generation unit 820 of T2 as the synchronization timing. Note that the amount of calculation can be reduced by setting a predetermined threshold value in advance and assigning only samples that are equal to or greater than the threshold value to the above equation to obtain the likelihood.

  Symbol clock generator 820 generates a symbol clock with timing likelihood λ obtained by timing likelihood calculator 810. The symbol clock generated here is output to GI removal section 8015 provided in each of OFDM demodulation sections 801 to 80m.

  The AFC unit 8013 detects a frequency offset from the digital signal input from the reception radio unit 8011. The detected frequency offset is output not only to the multiplier 8014 of the OFDM demodulator 801 but also to the multiplier 8014 of the OFDM demodulator 802 to 80m.

  The multiplier 8014 multiplies the digital signal input from the reception radio unit 8011 by the frequency offset detected by the AFC unit 8013, thereby correcting the frequency offset included in the digital signal. The digital signal whose frequency offset is corrected in this way is output to the GI removal unit 8015.

  GI removal section 8015 removes the guard interval from the digital signal input from multiplier 8014 based on the symbol clock generated by symbol clock generation section 820, and outputs a data symbol. The data symbols extracted in this way are output to the FFT unit 8016.

  The FFT unit 8016 performs FFT processing on the data symbol input from the GI removal unit 8015, thereby converting the data on the time axis into the data on the frequency axis, and divides it into symbol data corresponding to the subcarrier. To do. The symbol data obtained in this way is output to the MIMO demodulator. In OFDM demodulating sections 802 to 80m, symbol data corresponding to subcarriers is obtained in the same manner and output to MIMO demodulating section 830.

  The MIMO demodulator 830 estimates and separates the transmission path for each subcarrier from the symbol data input from the OFDM demodulator 801 to 80m, and performs demapping. Then, the MIMO demodulator 830 performs a hard decision on the demapping result, and decodes the original data D1 to Dn. Depending on the modulation method, the original data D1 to Dn are decoded by error correction decoding using soft decision or the like.

  As described above, the receiving apparatus 800 having the above configuration includes one AFC unit 8013, and each OFDM demodulation unit 801 to 80m uses the frequency offset obtained thereby to remove the frequency offset. Each OFDM demodulator 801 to 80m includes a cross-correlator 8012 to detect a correlation level, and obtains a generation timing of a symbol clock suitable for reception using the detected correlation levels of a plurality of timings as likelihoods. OFDM demodulation is performed using the generated symbol clock.

  Therefore, according to the receiving apparatus having the above-described configuration, the circuit scale is small because only one AFC unit 8013 is mounted, and a path suitable for reception at the timing determined by a plurality of correlators and the timing considering the likelihood thereof. Since reception is possible, demodulation can be performed with high accuracy.

  Since the frequency offset is caused by the local frequency on the transmitting apparatus 100 side and the local frequency on the receiving apparatus 800 side, the same frequency offset value is used even in a plurality of receiving systems such as the receiving apparatus 800. Therefore, even if the detection result of one AFC unit 8013 is also used, a sufficient effect can be exhibited.

  Next, a third embodiment of the receiving apparatus 200 shown in FIG. 1 is shown as a receiving apparatus 1100 in FIG. The receiving apparatus 1100 includes m antennas, OFDM demodulation units 1101 to 110m corresponding to the respective antennas, a switching control unit 1110, a switching unit 1120, a cross-correlation unit 1130, a symbol clock generation unit 1140, a MIMO, A demodulator 1150.

  OFDM demodulation section 1101 includes reception radio section 11011, reception power measurement section 11012, AFC (Auto Frequency Control) 11013, multiplier 11014, GI (Guard Interval) removal section 11015, and FFT (Fast Fourier Transform) section 11016. . The OFDM demodulating units 1102 to 110m are not provided with the AFC unit 11013 and have the same configuration as that of the OFDM demodulating unit 1101, and thus the description thereof is omitted.

  Reception radio section 11011 performs filter processing on the signal input from the corresponding antenna to limit it to a predetermined band, performs frequency conversion, further performs low noise power amplification, and then performs orthogonal demodulation processing. The baseband signal thus obtained is converted into a digital signal having a predetermined sampling frequency by A / D conversion. This digital signal is output to received power measuring section 11012, AFC section 11013, multiplier 11014, and switching section 1120.

Received power measuring section 11012 measures the received power level based on the digital signal, and outputs the measured received power level to switching control section 1110.
The switching control unit 1110 receives measurement values from the received power measurement units 11012 of the OFDM demodulation units 1101 to 110m, and obtains average values of these measurement values. Then, the switching control unit 1110 detects the OFDM demodulating units 1101 to 110m from which the largest value is obtained, and performs switching control on the switching unit 1120 based on the detected OFDM demodulating units 1101 to 110m, thereby obtaining the largest received power level. A 110 m digital signal is output to the cross-correlation unit 1130.

  The cross-correlation unit 1130 performs matched filter processing on the digital signal input from the switching unit 1120 to create a delay profile, and outputs this to the symbol clock generation unit 1140. In this matched filter processing, a time waveform of a synchronization symbol signal obtained by OFDM-modulating the synchronization symbol pattern used in the transmission apparatus 100 is used as a tap coefficient. The cross correlation unit 1130 is configured as shown in FIG. 5, for example.

  The symbol clock generation unit 1140 generates a symbol clock at an optimal timing for OFDM demodulation based on the delay profile generated by the cross correlation unit 1130. The symbol clock generated here is output to GI removal section 11015.

  The AFC unit 11013 detects a frequency offset from the digital signal input from the reception radio unit 11011. The detected frequency offset is output not only to the multiplier 11014 of the OFDM demodulator 1101 but also to the multiplier 11014 of the OFDM demodulator 1102 to 110m.

  The multiplier 11014 multiplies the digital signal input from the reception radio unit 11011 by the frequency offset detected by the AFC unit 11013, thereby correcting the frequency offset included in the digital signal. The digital signal whose frequency offset is corrected in this way is output to the GI removal unit 11015.

  GI removal section 11015 removes the guard interval from the digital signal input from multiplier 11014 based on the symbol clock generated by symbol clock generation section 1140, and outputs a data symbol. The data symbols extracted in this way are output to the FFT unit 11016.

  The FFT unit 11016 performs FFT processing on the data symbols input from the GI removal unit 11015, thereby converting the data on the time axis into the data on the frequency axis, and divides it into symbol data corresponding to the subcarrier. To do. The symbol data obtained in this way is output to MIMO demodulator 1150. Similarly, in OFDM demodulation sections 1102 to 110m, symbol data corresponding to subcarriers is obtained and output to MIMO demodulation section 1150.

  The MIMO demodulator 1150 estimates and separates the transmission path for each subcarrier from the symbol data input from the OFDM demodulator 1101 to 110m, and performs demapping. And with respect to this demapping result, the MIMO demodulator 1150 makes a hard decision and decodes the original data D1 to Dn. Depending on the modulation method, the original data D1 to Dn are decoded by error correction decoding using soft decision or the like.

  As described above, the receiving apparatus 1100 having the above configuration includes one AFC unit 11013, and each OFDM demodulation unit 1101-110m uses the frequency offset obtained thereby to remove the frequency offset. In addition, the received power level is measured by the received power measuring unit 11012 in each of the OFDM demodulating units 1101 to 110m, a correlation level is detected from a digital signal based on a signal having a large received power level, and a symbol clock generated at a timing based on the detected correlation level. The OFDM demodulation is performed in the above.

  Therefore, according to the reception apparatus having the above configuration, since only one AFC unit 11013 is mounted, a correlation level is obtained based on a signal having a small circuit scale and a large reception level, and a path suitable for reception at a timing based on this Can be demodulated with high accuracy.

  Since the frequency offset is caused by the local frequency on the transmitting apparatus 100 side and the local frequency on the receiving apparatus 1100 side, the same frequency offset value is used even in a plurality of receiving systems such as the receiving apparatus 1100. Therefore, even if the detection result of one AFC unit 11013 is also used, a sufficient effect can be exhibited.

  Next, the case where the present invention is applied to a CSMA (Carrier Sense Multiple Access) wireless communication system will be described. A CSMA receiver performs CS (Carrier Sense) to determine whether there is a transmitter that transmits a signal at all times or at regular time intervals when waiting.

  This CS is to detect whether there is any signal having power above a certain threshold in the frequency band to be used. This detection is also performed by RSSI (Received Signal Strength Indicator) measurement in the radio unit. The reception power measuring unit provided in each reception system is also possible.

  FIG. 12 illustrates an example of a CSMA wireless communication system. The transmission apparatus corresponds to the base station BS, the reception apparatus corresponds to the terminals MS-a and MS-b, and the terminals MS-a and MS-b exist within the coverage of the base station BS. Further, the base station BS, the terminal MS-a, and the terminal MS-b employ a MIMO-OFDM scheme.

  As shown in FIG. 13, the terminals MS-a and MS-b are both performing CS to check whether a signal is transmitted from the base station BS. Thereafter, it is assumed that data is first transmitted from the base station BS to the terminal MS-a. Terminal MS-a demodulates the data transmitted to itself according to the MIMO-OFDM scheme.

  On the other hand, the terminal MS-b measures received power by a received power measuring unit provided in each reception system while data is being transmitted from the base station BS to the terminal MS-a. The terminal MS-b stores the measurement result.

  After that, when data is transmitted from the base station BS to the terminal MS-b, the terminal MS-b outputs from the reception radio unit of the reception system having the largest received power among the stored measurement results. Is input to the AFC unit, and the output of the reception radio unit of each reception system is multiplied by the frequency offset detected by the AFC unit.

  The configuration of the terminal MS-b that performs such an operation is shown in a receiving apparatus 1400 in FIG. 14 as a fourth embodiment of the receiving apparatus 200 shown in FIG. The receiving apparatus 1400 includes m antennas, OFDM demodulation units 1401 to 140m corresponding to the respective antennas, a switching control unit 1410, a switching unit 1420, an AFC (Auto Frequency Control) unit 1430, and a MIMO demodulation unit 1440. With.

  The OFDM demodulator 1401 includes a reception radio unit 14011, a received power measurement unit 14012, a cross-correlation unit 14013, a symbol clock generation unit 14014, a multiplier 14015, a GI (Guard Interval) removal unit 14016, and an FFT (Fast Fourier Transform) unit. 14017 is provided. Since the OFDM demodulating units 1402 to 140m have the same configuration as that of the OFDM demodulating unit 1401, description thereof will be omitted.

  Reception radio section 14011 performs filtering processing on the signal input from the corresponding antenna to limit the signal to a predetermined band, performs frequency conversion, performs low noise power amplification, and then performs orthogonal demodulation processing. The baseband signal thus obtained is converted into a digital signal having a predetermined sampling frequency by A / D conversion. This digital signal is output to received power measuring section 14012, cross-correlation section 14013, multiplier 14015, and switching section 1420.

Received power measuring section 14012 measures the received power level based on the digital signal, and outputs the measured received power level to switching control section 1410.
The switching control unit 1410 receives each received power measurement unit 14012 of the OFDM demodulation units 1401 to 140m when data is being transmitted from the transmission device 100 (base station BS) to another reception device (terminal MS-a). When measurement values are input from, average values of these measurement values are obtained and stored in a built-in memory.

  Eventually, when data is transmitted from the transmitting apparatus 100 (base station BS) to the receiving apparatus 1400 (terminal MS-b), the switching control unit 1410 reads the average value from the memory and determines the largest value. Are detected, and the switching unit 1420 is switched based on the detected OFDM demodulating units 1401 to 140m, and the AFC unit 1430 outputs the digital signals of the OFDM demodulating units 1401 to 140m from which the highest received power level is obtained. .

  The AFC unit 1430 detects a frequency offset from the digital signal input from the switching unit 1420. The detected frequency offset is output to each multiplier 14015 of OFDM demodulation sections 1401 to 140m.

  Cross-correlation section 14013 performs matched filter processing on the digital signal input from reception radio section 14011 to create a delay profile, and outputs this to symbol clock generation section 14014. In this matched filter processing, a time waveform of a synchronization symbol signal obtained by OFDM-modulating the synchronization symbol pattern used in the transmission apparatus 100 (base station BS) is used as a tap coefficient. The cross correlation unit 14013 is configured as shown in FIG. 5, for example.

  The symbol clock generation unit 14014 generates a symbol clock at an optimal timing for OFDM demodulation based on the delay profile generated by the cross-correlation unit 14013. The symbol clock generated here is output to GI removal section 14016.

  A multiplier 14015 multiplies the digital signal input from the reception radio section 14011 by the frequency offset detected by the AFC section 1430, thereby correcting the frequency offset included in the digital signal. The digital signal whose frequency offset is corrected in this manner is output to the GI removal unit 14016.

  GI removal section 14016 removes the guard interval from the digital signal input from multiplier 14015 based on the symbol clock generated by symbol clock generation section 14014, and outputs a data symbol. The data symbols extracted in this way are output to the FFT unit 14017.

  The FFT unit 14017 performs FFT processing on the data symbols input from the GI removal unit 14016, thereby converting the data on the time axis into the data on the frequency axis, and divides it into symbol data corresponding to the subcarrier. To do. The symbol data obtained in this way is output to MIMO demodulator 1440. Similarly, in OFDM demodulation sections 1402 to 140m, symbol data corresponding to subcarriers is obtained and output to MIMO demodulation section 1440.

  The MIMO demodulator 1440 estimates and separates the transmission path for each subcarrier from the symbol data input from the OFDM demodulator 1401 to 140m, and performs demapping. Then, the MIMO demodulator 1440 performs a hard decision on the demapping result, and decodes the original data D1 to Dn. Depending on the modulation method, the original data D1 to Dn are decoded by error correction decoding using soft decision or the like.

  As described above, the reception power measurement requires a certain amount of time, but the reception device 1400 having the above configuration receives a signal addressed to another reception device prior to reception of the signal addressed to itself, and the reception power is reduced. The largest receiving system is obtained, and when a signal addressed to itself is received, a frequency offset is obtained based on the obtained signal of the receiving system. In addition, one AFC unit 1430 is mounted, and each OFDM demodulation unit 1401 to 140m uses the frequency offset obtained thereby to remove the frequency offset.

  Therefore, according to the reception apparatus having the above-described configuration, since only one AFC unit 1430 is mounted, the circuit scale is small, and a good reception system is obtained in advance by measuring the reception power of other communications. Can be requested.

  Since the frequency offset is caused by the local frequency on the transmission device 100 side and the local frequency on the reception device 1400 side, the same frequency offset value is used even in a plurality of reception systems such as the reception device 1400. Therefore, even if the detection result of one AFC unit 1430 is also used, a sufficient effect can be exhibited.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. Further, for example, a configuration in which some components are deleted from all the components shown in the embodiment is also conceivable. Furthermore, you may combine suitably the component described in different embodiment.

The figure which shows the structure of the radio | wireless communications system concerning this invention. FIG. 2 is a circuit block diagram illustrating a configuration of the transmission device illustrated in FIG. 1. The figure which shows the transmission frame format of the transmitter shown in FIG. FIG. 2 is a circuit block diagram showing a configuration according to the first embodiment of the receiving apparatus shown in FIG. 1. The figure which shows the structural example of the cross correlation part of the receiver shown in FIG. The figure which shows an example of the environment where the radio | wireless communications system shown in FIG. 1 is operate | moved. The figure for demonstrating the delay profile of the electromagnetic wave which arrives at a receiver in the environment shown in FIG. The circuit block diagram which shows the structure concerning 2nd Embodiment of the receiver shown in FIG. The figure which shows an example of the table produced | generated by the timing likelihood calculation part of the receiver shown in FIG. The figure which shows an example of the delay profile produced | generated by the cross correlation part of the receiver shown in FIG. The circuit block diagram which shows the structure concerning 3rd Embodiment of the receiver shown in FIG. The figure for demonstrating the case where the radio | wireless communications system shown in FIG. 1 employs a CSMA system. The figure for demonstrating operation | movement of the receiver concerning 4th Embodiment of the receiver shown in FIG. The circuit block diagram which shows the structure concerning 4th Embodiment of the receiver shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Transmission apparatus, 101-10n ... Modulation part, 110 ... Switching part, 200 ... Reception apparatus, 201-20m ... OFDM demodulation part, 210 ... MIMO demodulation part, 1011 ... Serial / parallel (S / P) conversion part, 1012 ... Mapping section, 1013 ... IFFT section, 1014 ... GI addition section, 1015 ... D / A conversion section, 1016 ... transmission radio section, 1100 ... reception apparatus, 11011 ... reception radio section, 11012 ... reception power measurement section, 11013 ... AFC , 11014... Multiplier, 11015... GI removal unit, 11016... FFT unit, 400... Reception device, 401 to 40 m... OFDM demodulation unit, 410 ... MIMO demodulation unit, 4011 ... reception radio unit, 4012 ... cross-correlation unit, 4013 Symbol clock generation unit, 4014 ... AFC unit, 4015 ... Multiplier, 4016 ... GI removal unit, 4 DESCRIPTION OF SYMBOLS 17 ... FFT part, 501-50j ... Shift register, 511-51j ... Multiplier, 520 ... Adder, 531-53k ... Adder, 541-54k ... Memory, 800 ... Receiver, 801-80m ... OFDM demodulation part, 810: Timing likelihood calculation unit, 820: Symbol clock generation unit, 830 ... MIMO demodulation unit, 8011 ... Reception radio unit, 8012 ... Cross correlation unit, 8013 ... AFC unit, 8014 ... Multiplier, 8015 ... GI removal unit, 8016 ... FFT section, 1101 to 110m ... OFDM demodulation section, 1110 ... switching control section, 1120 ... switching section, 1130 ... cross-correlation section, 1140 ... symbol clock generation section, 1150 ... MIMO demodulation section, 1400 ... reception apparatus, 1401 to 140m ... demodulation unit, 1410 ... switch control unit, 1420 ... switch unit, 1430 ... AFC unit, 1 40 ... MIMO demodulator, 14011 ... reception radio section, 14012 ... received power measuring unit, 14013 ... cross-correlation unit, 14014 ... symbol clock generator, 14015 ... multiplier, 14016 ... GI removing unit, 14017 ... FFT unit.

Claims (12)

In a receiving apparatus including a first demodulating unit and a second demodulating unit that respectively demodulate OFDM-modulated radio signals,
The first demodulating means and the second demodulating means are respectively
Frequency conversion means for converting a radio signal into a baseband signal;
A / D conversion means for converting the output of the frequency conversion means into a digital signal;
A correlation detection unit that obtains a correlation between an output of the A / D conversion unit and a preset symbol pattern and creates a delay profile indicating a relationship between a plurality of symbol timings and a correlation level;
A clock generation means for generating a symbol clock at a timing based on the delay profile created by the correlation detection means;
Correction means for correcting the frequency offset from the output of the A / D conversion means based on frequency offset information;
OFDM demodulation means for OFDM-demodulating the output of the correction means using the symbol clock generated by the clock generation means,
A frequency offset is detected based on an output of an A / D conversion unit included in the first demodulating unit, and the first demodulating unit and the second demodulating unit use the detected frequency offset as the frequency offset information. Frequency offset detection means for outputting to the correction means respectively provided;
A receiving apparatus comprising: MIMO demodulating means for performing MIMO demodulation using outputs of the OFDM demodulating means respectively provided in the first demodulating means and the second demodulating means. In a receiving apparatus including a first demodulating unit and a second demodulating unit that respectively demodulate OFDM-modulated radio signals,
The first demodulating means and the second demodulating means are respectively
Frequency conversion means for converting a radio signal into a baseband signal;
A / D conversion means for converting the output of the frequency conversion means into a digital signal;
A correlation detection unit that obtains a correlation between an output of the A / D conversion unit and a preset symbol pattern and creates a delay profile indicating a relationship between a plurality of symbol timings and a correlation level;
Correction means for correcting the frequency offset from the output of the A / D conversion means based on frequency offset information;
OFDM demodulation means for OFDM demodulating the output of the correction means using a symbol clock,
A frequency offset is detected based on an output of an A / D conversion unit included in the first demodulating unit, and the first demodulating unit and the second demodulating unit use the detected frequency offset as the frequency offset information. Frequency offset detection means for outputting to the correction means respectively provided;
The OFDM demodulating means respectively provided in the first demodulating means and the second demodulating means at timings based on delay profiles created by the correlation detecting means provided in the first demodulating means and the second demodulating means, respectively. Clock generation means for generating a symbol clock used in
A receiving apparatus comprising: MIMO demodulating means for performing MIMO demodulation using outputs of the OFDM demodulating means respectively provided in the first demodulating means and the second demodulating means. The clock generation means includes
Symbol clock generation timing used in the OFDM demodulating unit by performing a calculation using the correlation level indicated by the delay profile created by the correlation detecting unit provided in each of the first demodulating unit and the second demodulating unit as a likelihood. Computing means for obtaining
The receiving apparatus according to claim 2, further comprising a generating unit that generates a symbol clock used by the OFDM demodulating unit at a generation timing obtained by the timing calculating unit.   The calculation means performs a calculation using a correlation level equal to or higher than a preset threshold among the correlation levels indicated by the delay profile as a likelihood, and obtains a generation timing of a symbol clock used in the OFDM demodulation means. The receiving device according to claim 3. In a receiving apparatus including a first demodulating unit and a second demodulating unit that respectively demodulate OFDM-modulated radio signals,
The first demodulating means and the second demodulating means are respectively
Frequency conversion means for converting a radio signal into a baseband signal;
A / D conversion means for converting the output of the frequency conversion means into a digital signal;
Power measuring means for measuring the received power level from the output of the A / D conversion means;
Correction means for correcting the frequency offset from the output of the A / D conversion means based on frequency offset information;
OFDM demodulation means for OFDM demodulating the output of the correction means using a symbol clock,
A frequency offset is detected based on an output of an A / D conversion unit included in the first demodulating unit, and the first demodulating unit and the second demodulating unit use the detected frequency offset as the frequency offset information. Frequency offset detection means for outputting to the correction means respectively provided;
A / D conversion means provided in the first demodulation means or the second demodulation means based on the received power level measured by the power measurement means provided in each of the first demodulation means and the second demodulation means. Switching means for selectively outputting the output of
Correlation detecting means for detecting a correlation level between the output of the switching means and a preset symbol pattern and creating a delay profile indicating a relationship between a plurality of symbol timings and the correlation level;
Clock generating means for generating symbol clocks used in the OFDM demodulating means respectively provided in the first demodulating means and the second demodulating means at a timing based on a delay profile created by the correlation detecting means;
A receiving apparatus comprising: MIMO demodulating means for performing MIMO demodulation using outputs of the OFDM demodulating means respectively provided in the first demodulating means and the second demodulating means. In a receiving apparatus including a first demodulating unit and a second demodulating unit that respectively demodulate OFDM-modulated radio signals,
The first demodulating means and the second demodulating means are respectively
Frequency conversion means for converting a radio signal into a baseband signal;
A / D conversion means for converting the output of the frequency conversion means into a digital signal;
Power measuring means for measuring the received power level from the output of the A / D conversion means;
A correlation detection unit that obtains a correlation between an output of the A / D conversion unit and a preset symbol pattern and creates a delay profile indicating a relationship between a plurality of symbol timings and a correlation level;
A clock generation means for generating a symbol clock at a timing based on the delay profile created by the correlation detection means;
Correction means for correcting the frequency offset from the output of the A / D conversion means based on frequency offset information;
OFDM demodulation means for OFDM demodulating the output of the correction means using a symbol clock,
Prior to data reception, the first demodulating means or the second demodulating means is provided based on the received power level measured by the power measuring means respectively provided in the first demodulating means and the second demodulating means. Switching means for selectively outputting the output of the A / D conversion means;
A frequency offset is detected based on the output of the switching means, and the detected frequency offset is used as the frequency offset information to be output to the correction means provided in each of the first demodulation means and the second demodulation means. Detection means;
A receiving apparatus comprising: MIMO demodulating means for performing MIMO demodulation using outputs of the OFDM demodulating means respectively provided in the first demodulating means and the second demodulating means. In a receiving circuit comprising a first demodulating means and a second demodulating means for demodulating each of the OFDM modulated radio signals,
The first demodulating means and the second demodulating means are respectively
Frequency conversion means for converting a radio signal into a baseband signal;
A / D conversion means for converting the output of the frequency conversion means into a digital signal;
A correlation detection unit that obtains a correlation between an output of the A / D conversion unit and a preset symbol pattern and creates a delay profile indicating a relationship between a plurality of symbol timings and a correlation level;
A clock generation means for generating a symbol clock at a timing based on the delay profile created by the correlation detection means;
Correction means for correcting the frequency offset from the output of the A / D conversion means based on frequency offset information;
OFDM demodulation means for OFDM-demodulating the output of the correction means using the symbol clock generated by the clock generation means,
A frequency offset is detected based on an output of an A / D conversion unit included in the first demodulating unit, and the first demodulating unit and the second demodulating unit use the detected frequency offset as the frequency offset information. Frequency offset detection means for outputting to the correction means respectively provided;
A receiving circuit comprising: MIMO demodulating means for performing MIMO demodulation using outputs of the OFDM demodulating means respectively provided in the first demodulating means and the second demodulating means. In a receiving circuit comprising a first demodulating means and a second demodulating means for demodulating each of the OFDM modulated radio signals,
The first demodulating means and the second demodulating means are respectively
Frequency conversion means for converting a radio signal into a baseband signal;
A / D conversion means for converting the output of the frequency conversion means into a digital signal;
A correlation detection unit that obtains a correlation between an output of the A / D conversion unit and a preset symbol pattern and creates a delay profile indicating a relationship between a plurality of symbol timings and a correlation level;
Correction means for correcting the frequency offset from the output of the A / D conversion means based on frequency offset information;
OFDM demodulation means for OFDM demodulating the output of the correction means using a symbol clock,
A frequency offset is detected based on an output of an A / D conversion unit included in the first demodulating unit, and the first demodulating unit and the second demodulating unit use the detected frequency offset as the frequency offset information. Frequency offset detection means for outputting to the correction means respectively provided;
The OFDM demodulating means respectively provided in the first demodulating means and the second demodulating means at timings based on delay profiles created by the correlation detecting means provided in the first demodulating means and the second demodulating means, respectively. Clock generation means for generating a symbol clock used in
A receiving circuit comprising: MIMO demodulating means for performing MIMO demodulation using outputs of the OFDM demodulating means respectively provided in the first demodulating means and the second demodulating means. The clock generation means includes
Symbol clock generation timing used in the OFDM demodulating unit by performing a calculation using the correlation level indicated by the delay profile created by the correlation detecting unit provided in each of the first demodulating unit and the second demodulating unit as a likelihood. Computing means for obtaining
9. The receiving circuit according to claim 8, further comprising: generating means for generating a symbol clock used by the OFDM demodulating means at a generation timing obtained by the timing calculating means.   The calculation means performs a calculation using a correlation level equal to or higher than a preset threshold among the correlation levels indicated by the delay profile as a likelihood, and obtains a generation timing of a symbol clock used in the OFDM demodulation means. The receiving circuit according to claim 9. In a receiving circuit comprising a first demodulating means and a second demodulating means for demodulating each of the OFDM modulated radio signals,
The first demodulating means and the second demodulating means are respectively
Frequency conversion means for converting a radio signal into a baseband signal;
A / D conversion means for converting the output of the frequency conversion means into a digital signal;
Power measuring means for measuring the received power level from the output of the A / D conversion means;
Correction means for correcting the frequency offset from the output of the A / D conversion means based on frequency offset information;
OFDM demodulation means for OFDM-demodulating the output of the correction means using a symbol clock,
A frequency offset is detected based on an output of an A / D conversion unit included in the first demodulation unit, and the first demodulation unit and the second demodulation unit use the detected frequency offset as the frequency offset information. Frequency offset detection means for outputting to the correction means respectively provided;
A / D conversion means provided in the first demodulation means or the second demodulation means based on the received power level measured by the power measurement means provided in each of the first demodulation means and the second demodulation means Switching means for selectively outputting the output of
Correlation detection means for detecting a correlation level between the output of the switching means and a preset symbol pattern and creating a delay profile indicating a relationship between a plurality of symbol timings and the correlation level;
A clock generating means for generating a symbol clock used in the OFDM demodulating means respectively provided in the first demodulating means and the second demodulating means at a timing based on the delay profile created by the correlation detecting means;
A receiving circuit comprising: MIMO demodulating means for performing MIMO demodulation using the outputs of the OFDM demodulating means respectively provided in the first demodulating means and the second demodulating means. In a receiving circuit comprising a first demodulating means and a second demodulating means for demodulating each of the OFDM modulated radio signals,
The first demodulating means and the second demodulating means are respectively
Frequency conversion means for converting a radio signal into a baseband signal;
A / D conversion means for converting the output of the frequency conversion means into a digital signal;
Power measuring means for measuring the received power level from the output of the A / D conversion means;
A correlation detection unit that obtains a correlation between an output of the A / D conversion unit and a preset symbol pattern and creates a delay profile indicating a relationship between a plurality of symbol timings and a correlation level;
A clock generation means for generating a symbol clock at a timing based on the delay profile created by the correlation detection means;
Correction means for correcting the frequency offset from the output of the A / D conversion means based on frequency offset information;
OFDM demodulation means for OFDM demodulating the output of the correction means using a symbol clock,
Prior to data reception, the first demodulating means or the second demodulating means is provided based on the received power level measured by the power measuring means respectively provided in the first demodulating means and the second demodulating means. Switching means for selectively outputting the output of the A / D conversion means;
A frequency offset is detected based on the output of the switching means, and the detected frequency offset is used as the frequency offset information to be output to the correction means provided in each of the first demodulation means and the second demodulation means. Detection means;
A receiving circuit comprising: MIMO demodulating means for performing MIMO demodulation using outputs of the OFDM demodulating means respectively provided in the first demodulating means and the second demodulating means.

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