JP2006050413A - Ofdm receiver, and ofdm receiving program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration in calculation of a phase correction value under frequency selective fading in an OFDM receiver. <P>SOLUTION: An OFDM receiver 10 extracts a plurality of pilot carriers from a received signal (61), calculates phase error information with respect to a reference pilot carrier (62) for each of the pilot carriers (63), calculates a phase correction value based on a plurality of calculated phase error information (64, 65, 66) and corrects (67) a phase error of the received signal based on the calculated phase correction value. If a phase difference from a phase correction value in the past stored on a storage medium exceeds a threshold value for some of the plurality of calculated phase error information in the calculation of the phase correction value, the phase error information is replaced with a phase correction value of a preceding symbol, and a phase correction value is then calculated based on the other phase error information and the replaced phase correction value in the past. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an OFDM receiving apparatus and an OFDM receiving program for correcting a phase error of a received signal of a wirelessly transmitted signal transmitted by the OFDM method.

  In recent years, Orthogonal Frequency Division Multiplexing (Orthogonal Frequency Division Multiplexing) has been adopted as a transmission method for terrestrial digital broadcasting and multimedia mobile access communication (MMAC) systems. This OFDM scheme is a kind of multicarrier transmission scheme in which information to be transmitted is divided into a plurality of carrier waves (subcarriers) and transmitted.

  In this OFDM transmission scheme transmission apparatus, a transmission bit string is symbolized by subcarrier modulation such as QPSK or 16QAM, and the modulated symbols are arranged in parallel in the frequency domain by the number of subcarriers. Thereafter, the symbols arranged in the frequency domain are subjected to inverse fast Fourier transform to obtain an OFDM waveform which is a time domain signal, and the OFDM waveform is subjected to IF / RF processing and then wirelessly transmitted.

  FIG. 1 shows a schematic configuration of a conventional OFDM receiver 10 that receives a signal wirelessly transmitted by such an OFDM method. The OFDM receiver 10 receives a signal wirelessly transmitted by the OFDM method with an antenna 1, performs RF / IF processing on the received signal with an RF / IF converter 2, and then converts it into a digital signal with an A / D converter 3. The signal is converted and further subjected to fast Fourier transform processing by the FFT unit 4 to obtain a frequency domain signal. In addition, the equalization processing unit 5 performs equalization processing for channel estimation using the frequency domain signal. After the equalization processing, the phase error compensation processing unit 6 performs phase correction processing for correcting the phase shift of the received signal. The subcarrier demodulator 7 demodulates the received signal after correction for each subcarrier to generate a received bit string.

  Hereinafter, the phase correction processing in the phase error compensation processing unit 6 will be described. FIG. 2 shows the structure of the received signal after the equalization processing unit 5 performs the equalization process. In this way, the received signal is composed of signals arranged in the frequency domain and the time domain, and symbols occupying a specific time domain are arranged for each subcarrier consisting of a signal sequence occupying a specific frequency domain. . In addition to the pilot symbols arranged on all subcarriers at predetermined symbol intervals, the received signal is a sub signal that provides information for performing phase error information compensation on the received signal in order to establish symbol synchronization. A pilot carrier as a carrier is included. In the example of FIG. 2, the received signal includes four pilot carriers. The contents of pilot symbols and pilot carriers are known on both the transmission and reception sides.

  FIG. 3 shows an internal configuration of the phase error compensation processing unit 6. The phase error compensation processing unit 6 extracts the pilot carrier from the received signal equalized by the pilot extraction unit 161. Then, for each extracted pilot carrier, phase error calculation section 162 calculates a phase error between the pilot carrier and a reference pilot carrier corresponding to the pilot carrier generated by pilot generation section 163. Then, the averaging processor 164 averages the calculated phase error for each pilot carrier. Then, the signal correction processing unit 165 corrects the phase error of the received signal based on the averaged phase error.

Patent Document 1 describes the configuration of an OFDM receiver that calculates phase error information by calculating phase error information from a plurality of pilot carriers inserted in a transmission signal and averaging them. .
JP 2002-152168 A

  However, in the OFDM scheme, there is a case where a phenomenon called frequency selective fading in which only a specific subcarrier is affected by fading may occur, and the conventional OFDM receiving apparatus as described above has such frequency selective fading. However, it has the following problems. In other words, under frequency selective fading, only a specific frequency is affected by fading, so the reception level does not decrease for the entire line, but only the reception level (amplitude) of any pilot carrier is greatly reduced by the effect of fading. It is possible. That is, the S / N may be deteriorated only for a certain pilot carrier. In such a case, since the conventional phase error compensation processing unit 6 also averages the phase error calculated from the pilot carrier having a poor S / N, the average result is dragged to the pilot carrier having a poor S / N. Therefore, phase correction with reduced correction accuracy is applied to all subcarriers, and communication quality deteriorates.

  The present invention has been made in view of such a problem, and an object of the present invention is to suppress deterioration in calculation of a phase correction value under frequency selective fading in an OFDM receiver.

  In order to achieve the above object, a first feature of the present invention is that a plurality of pilot carriers are extracted from a received signal of a signal wirelessly transmitted by OFDM, and a storage medium for each of the extracted pilot carriers is extracted. The phase error information for the reference pilot carrier stored in is calculated, a phase correction value is calculated based on the calculated plurality of phase error information, and the phase error of the received signal is corrected based on the calculated phase correction value The OFDM receiver stores the calculated phase correction value in a storage medium, and among the calculated plurality of phase error information, a phase that is more than a deviation reference from a past phase correction value stored in the storage medium After making the magnitude of the contribution of the error information to the calculated phase correction value smaller than the magnitude of the contribution of other phase error information, the multiple phases Is that which is adapted to calculate a phase correction value based on the difference information.

  Since this is the case, the OFDM receiver performs the calculation of the current phase correction value by reducing the influence of the phase error information that is far from the previously calculated phase correction value, and thus the frequency correction frequency. Even if a pilot carrier with a poor S / N is included in the received signal due to selective fading, the influence is reduced. Therefore, it is possible to suppress the deterioration of the calculation of the phase correction value under frequency selective fading.

  The phase error information is a concept including not only the phase error itself but also a value that can lead to the phase error based on the value such as a value corresponding to the phase error value on a one-to-one basis.

  Further, the phase error information that is more than the deviation reference may be, for example, phase error information in which the phase difference from the past phase correction value is equal to or greater than a threshold value, or, for example, a plurality of calculated plural Of the phase error information, the phase error information having the largest phase difference from the past phase correction value may be used.

  Further, when the phase error information to be calculated is a complex number having, as a phase component, the phase error with respect to the reference pilot carrier stored in the storage medium for each of the plurality of extracted pilot carriers, The phase correction value may be subjected to complex subtraction, the absolute value of the result of the complex subtraction may be calculated, and the determination based on the phase difference may be performed based on the absolute value.

  By adopting such a calculation method, for example, the arc tangent, such as calculating the arc tangent of the value obtained by complex division of the phase error information by the past phase correction value and dividing the imaginary part of the result by the real part, etc. It is not necessary to perform processing assuming the occurrence of division by zero, which is necessary in the case of the calculation method using.

  In addition, after replacing phase error information that is more than the deviation standard from the past phase correction value with the past phase correction value, the phase correction value based on the other phase error information and the replaced past phase correction value You may come to calculate.

  Furthermore, the magnitude of the contribution of the replaced past phase correction value to the calculated phase correction value is made smaller than the contribution of other phase error information, and then the other phase error information and the past past phase replaced. A phase correction value based on the correction value may be calculated.

  The past phase correction value may be a phase correction value one symbol before the currently calculated phase correction value.

  The second feature of the present invention that achieves the above object is that a plurality of pilot carriers are extracted from a received signal of a signal wirelessly transmitted by OFDM, and a storage medium for each of the extracted pilot carriers is extracted. The phase error information for the reference pilot carrier stored in is calculated, a phase correction value is calculated based on the calculated plurality of phase error information, and the phase error of the received signal is corrected based on the calculated phase correction value In the OFDM receiver, among the calculated plurality of phase error information, the magnitude of contribution to the phase correction value of the phase error information that has changed more than the change reference from the past phase error information calculated for the same pilot carrier. Calculate the phase correction value based on multiple pieces of phase error information, after making the contribution of other phase error information smaller Is Rukoto.

  As a result, the OFDM receiving apparatus calculates the current phase correction value by reducing the influence of the phase error information that has greatly changed from the phase error information calculated for the same pilot carrier in the past. Therefore, even if a pilot carrier with a poor S / N is included in the received signal due to frequency selective fading, the influence is reduced. Therefore, it is possible to suppress the deterioration of the calculation of the phase correction value under frequency selective fading.

  Further, the phase error information that is more than the change reference may be, for example, phase error information whose phase difference from the phase error information calculated for the same pilot carrier in the past is equal to or greater than a threshold value, or For example, phase error information having the largest phase difference from the phase error information calculated for the same pilot carrier in the past among the plurality of calculated phase error information may be used.

  Further, when the phase error information to be calculated is a complex number having, as a phase component, a phase error with respect to the reference pilot carrier stored in the storage medium for each of the extracted pilot carriers, the same is applied in the past from the phase error information. The phase error information calculated for the pilot carrier may be subjected to complex subtraction, the absolute value of the result of the complex subtraction may be calculated, and the determination based on the phase difference may be performed based on the absolute value.

  By adopting such a calculation method, for example, the arc tangent of the value obtained by complex-dividing the phase error information by the past phase error information and dividing the imaginary part of the result by the real part is calculated. It is not necessary to perform processing assuming the occurrence of division by zero, which is necessary in the case of the calculation method using.

  In addition, such an OFDM receiver stores the calculated phase correction value in a storage medium, and stores phase error information that is more than the change reference from the past phase error information in the storage medium. Alternatively, the phase correction value based on the other phase error information and the replaced past phase correction value may be calculated after replacing with the past phase correction value.

  Furthermore, the magnitude of the contribution of the replaced past phase correction value to the calculated phase correction value is made smaller than the contribution of other phase error information, and then the other phase error information and the past past phase replaced. A phase correction value based on the correction value may be calculated.

  The past phase correction value may be a phase correction value one symbol before the currently calculated phase correction value.

  The first and second features of the present invention can also be realized as an OFDM reception program that causes a computer to realize the above functions.

(First embodiment)
The first embodiment of the present invention will be described below. FIG. 1 is a block diagram of a hardware configuration of an OFDM receiver 10 according to this embodiment. This OFDM receiver 10 includes an antenna 1, an RF / IF conversion unit 2, an A / D conversion unit 3, an FFT (Fast Fourier Transform) unit 4, an equalization processing unit 5, a phase error compensation processing unit 6, and a subcarrier demodulation. It consists of part 7 and the like.

  In this OFDM receiver 10, an antenna 1 receives an OFDM signal that is wirelessly transmitted by an OFDM transmitter and passes through a propagation path. The RF / IF unit 2 performs RF / IF processing, timing recovery processing, and the like on the OFDM signal received by the antenna 1 to obtain a baseband OFDM signal. The A / D converter 3 converts the analog signal generated by the RF / IF converter 2 into a digital signal. The FFT unit 4 converts a time domain signal into a frequency domain signal. The equalization processing unit 5 performs channel estimation and performs equalization processing on the received signal using the estimated value. The equalization processing unit 5 outputs the reception signals after the equalization processing to the phase error compensation processing unit 6 as serial data arranged in the order of symbols and arranged in the order of a predetermined subcarrier within each symbol.

  The phase error compensation processing unit 6 calculates a phase error due to phase noise, residual frequency offset, etc., calculates a phase correction value from the phase error, and corrects the phase error for each symbol. The subcarrier demodulator 7 demodulates the symbol corrected by the phase error compensation processor 6 to obtain a received bit string. This received bit string is processed by a processing device (not shown) subsequent to the subcarrier demodulator 7 to perform image display processing, audio display processing, and the like according to the received bit string.

  FIG. 4 shows a hardware configuration of the phase error compensation processing unit 6 of FIG. The phase error compensation processing unit 6 includes a pilot extraction unit 61, a pilot generation unit 62, a phase error calculation unit 63, a selection processing unit 64, a storage unit 65, an averaging processing unit 66, and a signal correction processing unit 67. Yes.

  The reception signal output from the equalization processing unit 5 to the phase error compensation processing unit 6 is received by the pilot extraction unit 61 and the signal correction processing unit 67.

  The pilot extraction unit 61 extracts only the pilot carrier from the received signal received and inputs it to the phase error calculation unit 63. At this time, the amplitude value of each pilot carrier may be normalized and then input. In the present embodiment, it is assumed that the number of pilot carriers in one symbol is four.

  The pilot generation unit 62 reads out the same pilot carrier as the pilot carrier previously inserted in the transmission signal by the OFDM transmission apparatus from the storage medium as a reference pilot carrier and inputs it to the phase error calculation unit 63.

  The phase error calculation unit 63 performs complex division between the pilot carrier input from the pilot extraction unit 61 and the reference pilot carrier input from the pilot generation unit 62 corresponding to the pilot carrier (that is, occupying the same subcarrier frequency band). The result is input to the selection processing unit 64 as phase error information.

  Based on the input from the signal correction processing unit 65, the selection processing unit 64 averages the phase error information calculated from the pilot carriers having poor S / N out of the phase errors of the input pilot carriers. The phase error is selected so as not to be input to 66. This sorting method will be described in detail later. Then, the sorting processor 64 inputs the sorted phase error information to the averaging processor 66.

  The storage unit 65 stores the data input from the averaging processing unit 66 in a storage medium, and inputs the data in the storage medium to the selection processing unit 64. Further, when receiving new data input from the averaging processing unit 66, the storage unit 65 rewrites the value in the current storage medium with the value of the new data.

  The averaging processing unit 66 is configured to input the average value of the data input from the selection processing unit 64 to the signal correction processing unit 67 and the storage unit 65 as a phase correction value. FIG. 5 shows a hardware configuration of the averaging processing unit 66. The averaging processing unit 66 includes a complex addition unit 661 and a normalization processing unit 662, and phase error information input from the selection processing unit 64 is output by the complex addition unit 661 for one symbol (four in this embodiment). ) Is complex-added, and the value obtained by the complex addition is normalized by the normalization processing unit 662 so that the amplitude value becomes 1, and is input to the signal correction processing unit 67. As shown in FIG. 6, the normalization processing unit 662 described above includes an absolute value calculation unit 6621 that outputs the absolute value of the signal input from the complex addition unit 661, and the complex addition unit 661 using this absolute value. A division unit 6622 is provided for dividing the input signal and inputting the result to the signal correction processing unit 67.

  The signal correction processing unit 67 performs complex division on the received signal input from the buffered equalization processing unit 5 by the phase correction value calculated by the averaging processing unit 66 to correct the phase error of the received signal. .

  As described above, according to the present embodiment, the phase correction value can be calculated without using the phase error calculated from the pilot carrier having the poor S / N among the pilot carriers inserted in the transmission signal. The influence of selective fading on the phase correction value calculation can be eliminated.

  In the following, a sorting method in the sorting processing unit 64 will be described. As described above, the role of the selection processing unit 64 is to prevent the phase error calculated from the pilot carrier having a poor S / N from being input to the averaging processing unit 66 due to the influence of frequency selective fading or the like. .

  For this purpose, the selection processing unit 64 is separated from the past phase correction values stored in the storage medium by the storage unit 65 among the plurality of phase error information calculated by the phase error calculation unit 63 by a predetermined deviation criterion or more. The phase correction value based on the plurality of phase error information is calculated after making the magnitude of the contribution of the phase error information to the calculated phase correction value smaller than the magnitude of the contribution of other phase error information. It has become.

  FIG. 7 shows a hardware configuration of the sorting processing unit 64 in the present embodiment. The selection processing unit 64 includes a phase difference calculation unit 641, a determination processing unit 642, and a selector 643.

  The phase difference calculation unit 641 calculates phase difference information between the phase error information input from the phase error calculation unit 63 and the phase correction value one symbol before input from the storage unit 65, and inputs the phase difference information to the determination processing unit 642. . In the present embodiment, the phase difference information is a complex value of the phase error information input from the phase error calculation unit 63, C1, and a phase correction value of one symbol before stored in the input from the storage unit 65. Let C2 be the absolute value | C2-C1 | of the value obtained by complex subtracting C1 from C2. In order to calculate this value, as shown in FIG. 8, the phase difference calculation unit 641 calculates a difference between two input complex values by the complex subtraction unit 6411, and the absolute value calculation unit 6412 calculates the difference. Is output to the determination processing unit 642.

  This | C2−C1 | is a monotonically increasing function of the phase difference ΔΦ between C1 and C2 (where 0 ° ≦ ΔΦ ≦ 180 °). Therefore, if | C2−C1 | The phase difference between the obtained phase error information and the phase correction value one symbol before stored in the storage unit 65 becomes large.

  The determination processing unit 642 determines whether or not the phase difference information input from the phase difference calculation unit 641 exceeds a predetermined threshold value. If the phase difference information exceeds the predetermined threshold value, the determination processing unit 642 determines a value of 1 if it does not exceed the value. Is sent to the selector 643. The reference that the value input from the phase difference calculation unit 641 exceeds a predetermined threshold corresponds to the predetermined deviation criterion. As the predetermined threshold value, for example, a value such that the phase difference indicated by the phase difference information is 28 ° is used.

  The selector 643 displays the phase error information input from the phase error calculation unit 63 when the value input from the determination processing unit 642 is 0, and the phase before one symbol stored in the storage unit 65 when the value is 1. The correction value is output to the averaging processing unit 66. Here, the phase correction value one symbol before means the phase correction value one symbol before the phase correction value currently calculated by the averaging processing unit 66.

  As described above, when the value input from the determination processing unit 642 is 1, the selector 643 replaces the phase error information input from the phase error calculation unit 63 with the phase correction value one symbol before, The magnitude of the contribution of the phase error information to the currently calculated phase correction value is zero.

  As described above, the OFDM receiver 10 according to the present embodiment uses a received signal after performing RF / IF processing, A / D conversion, FFT processing, and equalization processing on a signal wirelessly transmitted by the OFDM method. Then, a plurality of pilot carriers are extracted (see pilot extraction unit 61), and phase error information for each of the extracted pilot carriers is calculated with respect to the reference pilot carrier (see pilot generation unit 62) stored in the storage medium. (See the phase error calculation unit 63), calculates a phase correction value based on the calculated plurality of phase error information (see the selection processing unit 64, the storage unit 65, and the averaging processing unit 66), and calculates the calculated phase correction value. The phase error of the received signal is corrected based on (see signal correction processing unit 67).

  In the calculation of the phase correction value, the calculated phase correction value is stored in the storage medium (see the storage unit 65), and the past phase stored in the storage medium among the plurality of calculated phase error information. When there is a case where the phase difference information with the correction value exceeds a predetermined threshold value (see the phase difference calculation unit 641 and the determination processing unit 642), the phase error information is replaced with the phase correction value one symbol before. (See the selector 643), the phase correction value is calculated based on the other phase error information (that is, phase error information that is not more than a predetermined deviation reference) and the past phase correction value that has been replaced (the averaging processing unit 66). reference).

Since it is like this, the OFDM receiver 10 performs the calculation of the current phase correction value by reducing the influence of the phase error information that is far away from the phase correction value calculated in the past, and calculating the current phase correction value. Even if a pilot carrier with a poor S / N is included in the received signal due to frequency selective fading, the influence is reduced. Therefore, it is possible to suppress the deterioration of the calculation of the phase correction value under frequency selective fading.
(Second Embodiment)
Next, a second embodiment of the present invention will be described. The present embodiment differs from the first embodiment in the hardware configuration of the sorting processing unit 64. FIG. 9 shows a configuration of the selection processing unit 64 in the present embodiment. In addition, about the component which has the function equivalent to 1st Embodiment in the selection process part 64, the same code | symbol as 1st Embodiment is attached | subjected and the description is abbreviate | omitted.

  In the present embodiment, the phase correction value from the storage unit 65 is not directly input to the selector 643 but directly input to the weighting α processing unit 644 and the result of processing of the signal in the weighting α processing unit 644 is obtained. A value is input to the selector 643.

  The weighting α processing unit 644 multiplies the input phase correction value by a predetermined weighting factor α and inputs the result to the selector 643. However, the value of the weight coefficient α is 1 or less (for example, 0.5).

  As a result, the OFDM receiver 10 has the phase difference information with the past phase correction value stored in the storage medium out of the calculated plurality of phase error information exceeds a predetermined threshold value. If there is something (see the phase difference calculation unit 641 and the determination processing unit 642), the phase error information is replaced with the phase correction value of the previous symbol (see the selector 643), and the replacement value is multiplied by the weighting factor α. (See the weighting α processing unit 644), the magnitude of the contribution of the replaced past value to the calculated phase correction value is made smaller than the magnitude of the contribution of the other phase error information, and then the other phase error. A phase correction value is calculated based on the information and the replaced previous phase correction value.

Thus, since the phase error calculated for the current symbol is more greatly reflected when averaging than the phase correction value of one symbol before, a more accurate phase correction value is calculated.
(Third embodiment)
Next, a third embodiment of the present invention will be described. The present embodiment differs from the first embodiment in the hardware configuration of the sorting processing unit 64. FIG. 10 shows the configuration of the sorting processing unit 64 in the present embodiment. In addition, about the component which has the function equivalent to 1st Embodiment in the selection process part 64, the same code | symbol as 1st Embodiment is attached | subjected and the description is abbreviate | omitted.

  In the present embodiment, the past phase correction value from the storage unit 65 is input only to the phase difference calculation unit 641, and the signal from the phase error calculation unit 63 is the phase difference calculation unit. 641 and the selector 643, the weighted β processing unit 645 is input, and the signal of the processing result of the weighted β processing unit 645 is input to the selector 643.

  The weighting β processing unit 645 multiplies the input phase error information by a predetermined weighting factor β and inputs the result to the selector 643. However, the value of the weight coefficient β is 1 or less (for example, 0.1).

  The selector 643 receives the phase error information directly input from the phase error calculation unit 63 when the value input from the determination processing unit 642 is 0, and the weighting coefficient input from the weighting β processing unit 645 when the value is 1. The phase error information multiplied by β is output to the averaging processing unit 66.

  As a result, the OFDM receiver 10 has the phase difference information with the past phase correction value stored in the storage medium out of the calculated plurality of phase error information exceeds a predetermined threshold value. When there is something (see the phase difference calculation unit 641 and the determination processing unit 642), by multiplying the phase error information by the weighting coefficient β (see the weighting β processing unit 645), the phase error information exceeding the threshold value is After the magnitude of the contribution to the calculated phase correction value is made smaller than the magnitude of the contribution of the other phase error information, a phase correction value based on the other phase error information and the weighted phase error information is calculated.

As described above, since the phase error information calculated from the pilot carrier having a good S / N is more greatly reflected when weighted than the one not so by weighting, a highly accurate phase correction value is calculated. The
(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. The present embodiment differs from the first embodiment in the hardware configuration of the sorting processing unit 64. FIG. 11 shows a configuration of the selection processing unit 64 in the present embodiment. In addition, about the component which has the function equivalent to 1st Embodiment in the selection process part 64, the same code | symbol as 1st Embodiment is attached | subjected and the description is abbreviate | omitted.

  In the present embodiment, the past phase correction value from the storage unit 65 is output only to the phase difference calculation unit 641. The phase error information from the phase error calculation unit 63 is input to the storage unit 646 in addition to the phase difference calculation unit 641. In addition, a signal is input from the storage unit 646 to the phase difference calculation unit 641.

  The storage unit 646 stores the phase error information input from the phase error calculation unit 63 for one symbol in the storage medium, and inputs data in the storage medium to the phase difference calculation unit 641. Further, when receiving new phase error information from the phase error calculation unit 63, the storage unit 646 obtains a value for the same pilot carrier as the phase error information in the current storage medium, and stores the new phase error information. Rewrite the value.

  The phase difference calculation unit 641 calculates phase difference information between the phase error information input from the phase error calculation unit 63 and the phase information about the pilot carrier that is the same as the phase error information input from the storage unit 646, The data is input to the determination processing unit 642.

  As a result, the OFDM receiver 10 differs from the calculated phase error information by a threshold value or more from the past phase error information (see the storage unit 646) calculated for the same pilot carrier ( In other words, when there is an object that changes more than the change reference (see the phase difference calculation unit 641 and the determination processing unit 642), the phase error information is replaced with the phase correction value one symbol before (selector 643 Reference), and other phase error information (that is, phase error information that has not changed more than a predetermined change reference) and a past phase correction value that has been replaced are calculated (see the averaging processing unit 66).

  As a result, the OFDM receiving apparatus calculates the current phase correction value by reducing the influence of the phase error information that has greatly changed from the phase error information calculated for the same pilot carrier in the past. Therefore, even if a pilot carrier with a poor S / N is included in the received signal due to frequency selective fading, the influence is reduced. Therefore, it is possible to suppress the deterioration of the calculation of the phase correction value under frequency selective fading.

  In each of the above embodiments, the pilot extraction unit 61 corresponds to a pilot carrier extraction unit, and the phase error calculation unit 63 corresponds to a phase error information calculation unit. In each of the above embodiments, the selection processing unit 64, the storage unit 65, and the averaging processing unit 66 correspond to a phase correction value calculation unit, and the signal correction processing unit 67 corresponds to a phase error correction unit. The storage unit 65 corresponds to a storage control unit, and the selection processing unit 64 and the averaging processing unit 66 correspond to a weighted calculation unit.

  In the above embodiment, each component of the OFDM receiving apparatus 10 (that is, the RF / IF conversion unit 2, the A / D conversion unit 3, the FFT unit 4, the equalization processing unit 5, and the phase error compensation processing unit 6). , Subcarrier demodulation unit 7, pilot extraction unit 61, pilot generation unit 62, phase error calculation unit 63, selection processing unit 64, storage unit 65, averaging processing unit 66, signal correction processing unit 67, complex addition unit 661, normal Processing unit 662, absolute value calculation unit 6621, division unit 6622, phase difference calculation unit 641, determination processing unit 642, selector 643, weighted α processing unit 644, weighted β processing unit 645, storage unit 646, complex subtraction unit 6411 The absolute value calculation unit 6412) may be realized as a circuit that realizes each function described above. The circuit may be realized by an ASIC or FPGA whose circuit configuration is programmable.

  Each of these components is a single microcomputer having a CPU, a RAM, and a ROM, and each function is such that the CPU executes a program for the function stored in the ROM using the RAM. It may be. Moreover, each said structural requirement may be implement | achieved when one microcomputer runs the program which implement | achieves all said functions.

  Further, in the fourth embodiment, the OFDM receiver 10 outputs phase error information that differs from the past phase error information calculated for the same pilot carrier by a threshold value or more among the calculated plurality of phase error information. The phase correction value based on the other phase error information and the replaced past phase correction value is calculated after replacing with the phase correction value of one symbol before. However, this need not be the case.

  For example, the OFDM receiver 10 replaces phase error information that differs from the past phase error information calculated for the same pilot carrier by a threshold value or more from the calculated phase error information with the phase correction value one symbol before. Furthermore, after the replaced value is multiplied by the weighting factor α described in the second embodiment, a phase correction value based on the other phase error information and the replaced previous phase correction value is calculated. It may be. In FIG. 11, the phase correction value from the storage unit 65 is not directly input to the selector 643 but directly input to the weighting α processing unit 644 described in the second embodiment. This can be realized by inputting the value of the processing result of the signal in the processing unit 644 to the selector 643.

  Further, for example, the OFDM receiving apparatus 10 applies the weight described in the third embodiment to phase error information that differs from the past phase error information calculated for the same pilot carrier by a threshold value or more among the calculated plurality of phase error information. After multiplying by the coefficient β, a phase correction value based on other phase error information and weighted phase error information may be calculated. This removes the storage unit 65, and in FIG. 11, the signal from the phase error calculation unit 63 is input to the weighted β processing unit 645 described in the third embodiment in addition to the phase difference calculation unit 641 and the selector 643. Thus, the signal of the processing result of the weighting β processing unit 645 can be realized by being input to the selector 643.

  That is, the OFDM receiving apparatus 10 has a magnitude of contribution to the phase correction value of the phase error information that has changed more than the change reference from the past phase error information calculated for the same pilot carrier among the plurality of phase error information. It is sufficient to calculate a phase correction value based on a plurality of pieces of phase error information after making the value smaller than the contribution of other phase error information that has not changed more than the change reference.

  In the first to third embodiments, the phase error information in which the phase difference with the past phase correction value stored in the storage medium by the storage unit 65 exceeds the threshold is more than the deviation standard. The phase error information is not necessarily required. For example, phase error information having the largest phase difference from the past phase correction value among the plurality of calculated phase error information may be phase error information that is separated by more than a deviation reference.

  In the fourth embodiment, the phase error information in which the phase difference with the past phase error information of the same pilot carrier stored in the storage medium by the storage unit 646 exceeds the threshold value changes more than the change reference. However, this is not always necessary. For example, among the plurality of calculated phase error information, the phase error information having the largest phase difference from the past phase error information of the same pilot carrier may be phase error information that has changed more than the change reference. .

  In each of the above embodiments, the phase error calculation unit 162 calculates the phase error information by performing complex division of the pilot carrier from the pilot extraction unit 161 by the reference pilot carrier from the pilot generation unit 163, and In the signal correction processing unit 67, the received signal is complex-divided by a phase correction value that is approximately the average of the phase error information. However, this need not be the case. For example, pilot generation section 163 divides the imaginary part of the value obtained by complex division of the input from pilot extraction section 161 by the input from pilot generation section 163 by the real part, and outputs the arctangent arctan thereof as a phase error. It may be like this. In this case, in the calculation of arc tangent, there is a need for handling division by zero, a need to have a correspondence table for speeding up, etc. In this respect, each of the above embodiments It can be said that the method in is simpler.

  In each of the above embodiments, the phase difference calculation unit 641 calculates the phase difference by complex subtracting the past phase correction value from the phase error information and calculating the absolute value of the result of the complex subtraction. This is not necessarily the case. For example, the phase difference calculation unit 641 may divide one input value by the other input value and output an arctangent arctan thereof as a phase difference. In this case, in the calculation of arc tangent, there is a need for handling division by zero, a need to have a correspondence table for speeding up, etc. In this respect, each of the above embodiments It can be said that the method in is simpler.

2 is a block diagram showing a hardware configuration of an OFDM receiver 10. FIG. It is a figure which shows the structure of the received signal which the OFDM receiver 10 receives. It is a block diagram which shows the hardware constitutions of the phase error compensation process part 6 in the conventional OFDM receiver 10. FIG. It is a block diagram which shows the hardware constitutions of the phase error compensation process part 6 which concerns on embodiment of this invention. 2 is a block diagram showing a hardware configuration of an averaging processing unit 66. FIG. FIG. 3 is a block diagram illustrating a hardware configuration of a normalization processing unit 662. It is a block diagram which shows the hardware constitutions of the averaging process part 64 in 1st Embodiment. 3 is a block diagram showing a hardware configuration of a phase error calculation unit 63. It is a block diagram which shows the hardware constitutions of the averaging process part 64 in 2nd Embodiment. It is a block diagram which shows the hardware constitutions of the averaging process part 64 in 3rd Embodiment. It is a block diagram which shows the hardware constitutions of the averaging process part 64 in 4th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Antenna, 2 ... RF / IF conversion part, 3 ... A / D conversion part, 4 ... FFT part,
5 ... Equalization processing unit, 6 ... Phase error compensation processing unit, 7 ... Subcarrier demodulation unit,
DESCRIPTION OF SYMBOLS 10 ... OFDM receiver, 61 ... Pilot extraction part, 62 ... Pilot production | generation part,
63 ... Phase error calculation unit, 64 ... Selection processing unit, 65 ... Signal correction processing unit,
66 ... Averaging processing unit, 67 ... Signal correction processing unit, 161 ... Pilot extraction unit,
162 ... phase error calculation unit, 163 ... pilot generation unit, 164 ... averaging processing unit,
165: Signal correction processing unit, 661: Complex addition unit, 662: Normalization processing unit,
641 ... Phase difference calculation unit, 642 ... Determination processing unit, 643 ... Selector,
644 ... Weighting α processing unit, 645 ... Weighting β processing unit, 646 ... Storage unit,
6411 ... complex subtraction unit, 6412 ... absolute value calculation unit, 6621 ... absolute value calculation unit,
6622: Dividing unit.

Claims (16)

Pilot carrier extraction means for extracting a plurality of pilot carriers from a received signal of a signal wirelessly transmitted by OFDM;
Phase error information calculating means for calculating phase error information with respect to a reference pilot carrier stored in a storage medium for each of a plurality of pilot carriers extracted by the pilot carrier extracting means;
Phase correction value calculation means for calculating a phase correction value based on a plurality of phase error information calculated by the phase error information calculation means;
Phase error correction means for correcting the phase error of the received signal based on the phase correction value calculated by the phase correction value calculation means,
The phase correction value calculation means includes storage control means for storing the calculated phase correction value in a storage medium,
Of the plurality of phase error information calculated by the phase error information calculation means, the phase correction value to be calculated of phase error information that is more than a deviation reference from the past phase correction value stored in the storage medium by the storage control means. And a weighted calculation means for calculating a phase correction value based on the plurality of phase error information after making the contribution to the phase smaller than the contribution of other phase error information. OFDM receiver. 2. The phase error information that is more than the deviation reference is phase error information that determines that a phase difference from the past phase correction value is greater than or equal to a threshold value. OFDM receiver. The phase error information that is more than the deviation reference is the phase error information that determines that the phase difference from the past phase correction value is the largest among the plurality of phase error information calculated by the phase error information calculation means. The OFDM receiver according to claim 1, wherein: The phase error information calculated by the phase error information calculating means is a complex number having, as its phase component, a phase error with respect to a reference pilot carrier stored in a storage medium for each of a plurality of pilot carriers extracted by the pilot carrier extracting means. And
The weighted calculation means complex subtracts the past phase correction value from the phase error information, calculates an absolute value of a result of the complex subtraction, and performs a determination based on the phase difference based on the absolute value. The OFDM receiver according to claim 2 or 3. The weighted calculation means replaces phase error information that is more than the deviation standard from the past phase correction value with the past phase correction value, and then replaces the other phase error information and the past phase that has been replaced. 5. The OFDM receiver according to claim 1, wherein a phase correction value based on the correction value is calculated. The weighted calculation means further reduces the magnitude of the contribution of the replaced past phase correction value to the calculated phase correction value from the magnitude of the contribution of the other phase error information, and 6. The OFDM receiver according to claim 5, wherein a phase correction value based on error information and the replaced previous phase correction value is calculated. 7. The past phase correction value is a phase correction value one symbol before the phase correction value currently calculated by the phase correction value calculation unit. OFDM receiver. Pilot carrier extraction means for extracting a plurality of pilot carriers from a received signal of a signal wirelessly transmitted by OFDM;
Phase error information calculating means for calculating phase error information with respect to a reference pilot carrier stored in a storage medium for each of a plurality of pilot carriers extracted by the pilot carrier extracting means;
Phase correction value calculation means for calculating a phase correction value based on a plurality of phase error information calculated by the phase error information calculation means;
Phase error correction means for correcting the phase error of the received signal based on the phase correction value calculated by the phase correction value calculation means,
The phase correction value calculation means includes a plurality of phase error information calculated by the phase error information calculation means, and includes phase error information that has changed more than a change reference from past phase error information calculated for the same pilot carrier. The weight correction means for calculating the phase correction value based on the plurality of phase error information after making the contribution to the phase correction value smaller than the contribution of the other phase error information. An OFDM receiver. 9. The phase error information that changes more than the change reference is phase error information that determines that a phase difference from the past phase error information is a threshold value or more. OFDM receiver. The phase error information that is more than the change reference is phase error information that determines that the phase difference from the past phase error information is the largest among the plurality of phase error information calculated by the phase error information calculation means. The OFDM receiving apparatus according to claim 8, wherein: The phase error information calculated by the phase error information calculation means is a complex number having, as a phase part, a phase error with respect to a reference pilot carrier stored in a storage medium for each of a plurality of pilot carriers extracted by the pilot carrier extraction means. Yes,
The weighted calculation means complex subtracts the phase error information from the phase error information and the past phase error information from the phase error information, and calculates an absolute value of a result of the complex subtraction. The OFDM receiver according to claim 9 or 10, wherein the determination based on the phase difference is performed based on the absolute value. The phase correction value calculation means has storage control means for storing the calculated phase correction value in a storage medium,
The weighted calculation means replaces the phase error information that is more than the change reference from the past phase error information with the past phase correction value stored in the storage medium by the storage control means, and then 13. The OFDM receiving apparatus according to claim 8, wherein a phase correction value based on the phase error information and the replaced past phase correction value is calculated. The weighted calculation means further reduces the magnitude of the contribution of the replaced past phase correction value to the calculated phase correction value from the magnitude of the contribution of the other phase error information, and 13. The OFDM receiver according to claim 12, wherein a phase correction value based on error information and the replaced previous phase correction value is calculated. 14. The past phase error information is phase error information one symbol before the phase error information based on when the phase correction value calculation means calculates a current phase correction value. The OFDM receiver according to any one of the above. Pilot carrier extraction means for extracting a plurality of pilot carriers from a received signal of a signal wirelessly transmitted by OFDM,
Phase error information calculating means for calculating phase error information with respect to a reference pilot carrier stored in a storage medium for each of a plurality of pilot carriers extracted by the pilot carrier extracting means;
A phase correction value calculating means for calculating a phase correction value based on a plurality of phase error information calculated by the phase error information calculating means; and a phase of the received signal based on the phase correction value calculated by the phase correction value calculating means An OFDM reception program for causing a computer to function as phase error correction means for correcting an error,
The phase correction value calculation means includes storage control means for storing the calculated phase correction value in a storage medium,
Of the plurality of phase error information calculated by the phase error information calculation means, the phase correction value to be calculated of phase error information that is more than a deviation reference from the past phase correction value stored in the storage medium by the storage control means. And a weighted calculation means for calculating a phase correction value based on the plurality of phase error information after making the contribution to the phase smaller than the contribution of other phase error information. OFDM reception program. Pilot carrier extraction means for extracting a plurality of pilot carriers from a received signal of a signal wirelessly transmitted by OFDM,
Phase error information calculating means for calculating phase error information with respect to a reference pilot carrier stored in a storage medium for each of a plurality of pilot carriers extracted by the pilot carrier extracting means, and a plurality of values calculated by the phase error information calculating means An OFDM reception program for causing a computer to function as phase correction value calculation means for calculating a phase correction value based on phase error information of:
Phase error correction means for correcting the phase error of the received signal based on the phase correction value calculated by the phase correction value calculation means,
The phase correction value calculation means includes a plurality of phase error information calculated by the phase error information calculation means, and includes phase error information that has changed more than a change reference from past phase error information calculated for the same pilot carrier. Characterized by comprising weighted calculation means for calculating a phase correction value based on the plurality of phase error information after making the contribution to the phase correction value smaller than the contribution of other phase error information. OFDM receiving program.

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