Reception apparatus, reception method, and program

The present invention relates to a receiving device, a receiving method, and a program, and more particularly to a receiving device, a receiving method, and a program capable of avoiding deterioration of reception performance.

Orthogonal Frequency Division Multiplexing (OFDM) is a modulation method for terrestrial digital broadcasting that uses a large number of orthogonal carriers and modulates each carrier with PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation). Proposed.

Since the OFDM method divides the entire transmission band among a large number of subcarriers, the band per subcarrier becomes narrower and the transmission speed becomes slower, but the total transmission speed is the same as that of the conventional modulation method. Have.

Further, the OFDM method has a feature that the symbol speed becomes slow because a large number of subcarriers are transmitted in parallel. Therefore, the OFDM method also has a feature that the time length of the multipath relative to the time length of one symbol can be shortened, and thus the influence of the multipath can be reduced.

Furthermore, since data is assigned to a plurality of subcarriers, the OFDM method can construct a transmission circuit by using an IFFT (Inverse Fast Fourier Transform) arithmetic circuit that performs an inverse Fourier transform at the time of modulation. It has the feature that the receiving circuit can be configured by using the FFT (Fast Fourier Transform) arithmetic circuit performed at the time of demodulation.

Due to the above characteristics, the OFDM method is often applied to terrestrial digital broadcasting that is strongly affected by multipath interference. Examples of terrestrial digital broadcasting standards that employ the OFDM system include DVB-T (Digital Video Broadcasting-Terrestrial), ISDB-T (Integrated Services Digital Broadcasting-Terrestrial), and ISDB-TSB.

FIG. 1 is a diagram showing an OFDM symbol.

In the OFDM system, signal transmission is performed in units called OFDM symbols.

As shown in FIG. 1, the 1OFDM symbol is composed of a valid symbol, which is a signal section in which IFFT is performed at the time of transmission, and a guard interval (hereinafter referred to as GI) in which the waveform of a part of the latter half of the valid symbol is copied. To. The GI is inserted in front of the valid symbol on the time axis.

In the OFDM method, it is possible to prevent interference between OFDM symbols that occur in a multipath environment by inserting a GI.

A plurality of such OFDM symbols are collected to form one OFDM transmission frame. For example, in the ISDB-T standard, one OFDM transmission frame is formed from 204 OFDM symbols. The insertion position of the pilot signal is determined based on the unit of this OFDM transmission frame.

In the OFDM method that uses the QAM modulation method as the modulation method for each subcarrier, the amplitude and phase of each subcarrier are those at the time of transmission and those at the time of reception due to the influence of multipath etc. at the time of transmission. Will be different. Therefore, on the receiving side, it is necessary to equalize the signal so that the amplitude and phase of the received signal are equal to those transmitted.

In the OFDM method, pilot signals having a predetermined amplitude and a predetermined phase are discretely inserted into the transmission symbol on the transmitting side, and the frequency characteristics of the transmission line are determined on the receiving side based on the amplitude and phase of the pilot signal. The received signal is equalized according to the characteristics of the obtained transmission line.

The pilot signal used to calculate the transmission line characteristics in this way is referred to as a scattered pilot signal (hereinafter referred to as SP signal). Figure 2 shows the arrangement pattern of SP signals used in the DVB-T standard and ISDB-T standard within the OFDM symbol.

FIG. 3 is a block diagram showing a configuration example of a conventional OFDM receiver.

The OFDM receiver 100 in FIG. 3 has a receiving antenna 1, a tuner 2, an A / D (Analog / Digital) conversion circuit 3, an orthogonal demodulation circuit 4, a carrier wave generation circuit 5, an FFT circuit 6, an FFT section control circuit 7, and a transmission path. It is composed of a distortion compensation circuit 8, an error correction circuit 9, a delay profile estimation circuit 10, and a frequency interpolation filter selection circuit 11.

The tuner 2 frequency-converts the RF signal received by the receiving antenna 1 into an IF signal, and outputs the IF signal to the A / D conversion circuit 3.

The A / D conversion circuit 3 performs A / D conversion on the IF signal supplied from the tuner 2 and outputs a digital IF signal to the orthogonal demodulation circuit 4.

The orthogonal demodulation circuit 4 acquires the baseband OFDM signal from the IF signal supplied from the A / D conversion circuit 3 by performing orthogonal demodulation using the carrier wave supplied from the carrier wave generation circuit 5, and acquires the acquired OFDM. Output a signal. This baseband OFDM signal is a so-called time domain signal before the FFT calculation is performed.

Hereinafter, the baseband OFDM signal before the FFT calculation is performed is referred to as an OFDM time domain signal. As a result of orthogonal demodulation, the OFDM time domain signal becomes a complex signal including a real axis component (I channel signal) and an imaginary axis component (Q channel signal). The OFDM time domain signal output from the orthogonal demodulation circuit 4 is supplied to the carrier wave generation circuit 5, the FFT circuit 6, the FFT section control circuit 7, and the delay profile estimation circuit 10.

The carrier wave generation circuit 5 generates a carrier wave having a predetermined frequency synchronized with the received signal based on the OFDM time domain signal supplied from the orthogonal demodulation circuit 4, and outputs the generated carrier wave to the orthogonal demodulation circuit 4. ..

The FFT circuit 6 extracts a signal in the effective symbol length range by removing the signal in the GI range from the signal of one OFDM symbol based on the FFT trigger pulse supplied from the FFT section control circuit 7.

Further, the FFT circuit 6 extracts data quadrature-modulated to each subcarrier by performing an FFT calculation on the extracted OFDM time domain signal. Specifically, the start position of the FFT calculation by the FFT circuit 6 is any position between the position A in FIG. 1, which is the boundary of the OFDM symbol, and the position B, which is the boundary position between the GI and the effective symbol. .. The FFT calculation range is called an FFT section, and the start position of this FFT section is specified by the FFT trigger pulse supplied from the FFT section control circuit 7.

The FFT circuit 6 outputs an OFDM signal representing the extracted data. This OFDM signal is a signal in the so-called frequency domain after the FFT calculation is performed. Hereinafter, the OFDM signal after the FFT calculation is performed is referred to as an OFDM frequency domain signal. The OFDM frequency domain signal output from the FFT circuit 6 is supplied to the SP extraction circuit 8-1 and the division circuit 8-4 of the transmission line distortion compensation circuit 8.

The FFT section control circuit 7 determines the FFT section based on the OFDM time region signal supplied from the orthogonal demodulation circuit 4 and the delay profile estimated by the delay profile estimation circuit 10, and specifies the start position of the determined FFT section. Outputs the FFT trigger pulse to the FFT circuit 6.

The transmission line distortion compensation circuit 8 is composed of an SP extraction circuit 8-1, a time direction transmission line characteristic estimation circuit 8-2, a frequency interpolation circuit 8-3, and a division circuit 8-4.

The SP extraction circuit 8-1 extracts the SP signal from the OFDM frequency domain signal supplied from the FFT circuit 6 and removes the modulation component of the SP signal to obtain the transmission line characteristics of the subcarrier at the position where the SP signal is arranged. presume. The SP extraction circuit 8-1 outputs a signal representing the estimated transmission line characteristics to the time direction transmission line characteristic estimation circuit 8-2.

The time-direction transmission line characteristic estimation circuit 8-2 is arranged in the time direction (OFDM symbol direction) of the subcarriers on which the SP signal is arranged based on the transmission line characteristics estimated by the SP extraction circuit 8-1. Estimate the transmission line characteristics at the position of the OFDM symbol. In FIG. 2, the vertical direction is the time direction and the horizontal direction is the frequency direction.

For example, the time-direction transmission line characteristic estimation circuit 8-2 uses the SP signal SP of FIG. 2 estimated by the SP extraction circuit 8-1.₁Transmission line characteristics at the position of, and SP signal SP₂Using the transmission line characteristics at the position of, region A in FIG.₁Estimate the subcarrier transmission line characteristics at the positions of other symbols within.

As shown in FIG. 2, since the SP signal is inserted every 12 subcarriers on the same time, in the time-direction transmission line characteristic estimation circuit 8-2, every 3 subcarriers at the position of each OFDM symbol. The transmission line characteristics of the subcarrier are estimated. The time-direction transmission line characteristic estimation circuit 8-2 outputs a signal representing the estimated transmission line characteristics for each of the three subcarriers. The signal output from the time channel characteristic estimation circuit 8-2 is supplied to the frequency interpolation circuit 8-3 and the delay profile estimation circuit 10.

The frequency interpolation circuit 8-3 performs an interpolation process for interpolating the transmission line characteristics in the frequency direction, and from the transmission line characteristics for each of the three subcarriers supplied from the time direction transmission line characteristic estimation circuit 8-2, each in the frequency direction. Estimate the transmission line characteristics of the subcarrier at the position of the OFDM symbol. A plurality of interpolation filters having different filter bands are given to the frequency interpolation circuit 8-3, and interpolation processing is performed using the plurality of interpolation filters.

For example, the frequency interpolation circuit 8-3 is in region A in FIG.₂Among the positions of the OFDM symbols included in, the transmission line characteristics of the subcarriers at the positions of the OFDM symbols whose transmission line characteristics have not been estimated yet are estimated. The transmission line characteristics are estimated using the transmission line characteristics already estimated by the SP extraction circuit 8-1 and the time direction transmission line characteristic estimation circuit 8-2.

As a result, the transmission line characteristics of all subcarriers at the positions of each OFDM symbol are estimated. The frequency interpolation circuit 8-3 estimates the transmission line characteristics of the signal obtained by performing interpolation processing using the interpolation filter of the filter band specified by the filter selection signal supplied from the frequency interpolation filter selection circuit 11. It is output to the interpolation circuit 8-4 as a signal indicating the result.

The dividing circuit 8-4 divides the components of the signal representing the transmission line characteristics of all the subcarriers supplied from the frequency interpolation circuit 8-3 from the OFDM frequency domain signal supplied from the FFT circuit 6, and depends on the transmission line. The distortion component is removed from the OFDM frequency domain signal. The division circuit 8-4 outputs an OFDM frequency domain signal from which the distortion component has been removed to the error correction circuit 9.

The error correction circuit 9 performs deinterleave processing on the signal interleaved on the transmitting side, and further performs processing such as denunciation, Viterbi decoding, diffusion signal removal, and RS decoding. The error correction circuit 9 outputs the data obtained by performing various processes to the subsequent circuit as decoded data.

The delay profile estimation circuit 10 estimates the delay profile of the transmission line by obtaining the time response characteristic of the transmission line. For example, the delay profile estimation circuit 10 estimates the delay profile by applying IFFT to the transmission line characteristics estimated by the time direction transmission line characteristic estimation circuit 8-2. The transmission line characteristic estimated by the time-direction transmission line characteristic estimation circuit 8-2 is a frequency characteristic, and the time response characteristic obtained by applying IFFT to this is a delay profile.

The signal representing the delay profile estimated by the delay profile estimation circuit 10 is supplied to the FFT section control circuit 7 and the frequency interpolation filter selection circuit 11. As a method of estimating the delay profile, a method of estimating from the OFDM time domain signal by using a matched filter (MF (Matched Filter)) having a GI period as a tap coefficient is also known.

The frequency interpolation filter selection circuit 11 obtains the delay spread based on the delay profile (the position of the path on the time axis) estimated by the delay profile estimation circuit 10, and determines the filter band according to the delay spread in the frequency interpolation circuit 8-. Select from the filter bands of the interpolation filter given in 3. The frequency interpolation filter selection circuit 11 outputs a filter selection signal for designating the selected filter band to the frequency interpolation circuit 8-3.

FIG. 4 is a diagram showing a configuration example of the frequency interpolation circuit 8-3.

As shown in FIG. 4, the frequency interpolation circuit 8-3 is the frequency interpolation filter circuit 8-3a.₀~ 8-3a_N-1, And the selector circuit 8-3b. The signal representing the transmission line characteristics for each of the three subcarriers output from the time-direction transmission line characteristic estimation circuit 8-2 is the frequency interpolation filter circuit 8-3a.₀~ 8-3a_N-1The filter selection signals that are input to and output from the frequency interpolation filter selection circuit 11 are input to the selector circuits 8-3b.

Frequency interpolation filter circuit 8-3a₀~ 8-3a_N-1Each performs interpolation processing using the given interpolation filter, and outputs a signal representing the interpolation result to the selector circuit 8-3b. In the example of FIG. 4, the frequency interpolation filter circuit 8-3a₀Is a circuit that performs interpolation processing using an interpolation filter with a filter band of BW0, and is a frequency interpolation filter circuit 8-3a.₁Is a circuit that performs interpolation processing using an interpolation filter with a filter band of BW1. Frequency interpolation filter circuit 8-3a_N-1Is a circuit that performs interpolation processing using an interpolation filter with a filter band of BW (N-1). Figure 5 shows the filter bands BW0 to BW3 on the time axis.

In the example of FIG. 5, the bandwidth of the filter band BW0 is the widest, and the bandwidth of the filter band BW3 is the narrowest. The position of the white triangle pointing upward represents the center position of the filter band. Interpolation processing is performed so that the center position of the filter band is the same as the center position of the delay spread.

The selector circuit 8-3b is a frequency interpolation filter circuit 8-3a.₀~ 8-3a_N-1Among the signals supplied from, the signal obtained by performing the interpolation processing using the interpolation filter of the filter band specified by the filter selection signal is selected, and the selected signal is output to the division circuit 8-4.

Patent Document 1 discloses a technique of detecting the quality of a signal after equalization and controlling an optimum filter coefficient from a plurality of filter coefficients according to the detected quality.

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2006-311385</text></patcit></p>

<p> As described above, the estimated delay profile is used by the frequency interpolation filter selection circuit 11 for selecting the filter band.</p><p> Therefore, the filter band may be erroneously selected in a multipath environment where there are paths that exceed the detection limit and cannot be detected. This causes deterioration of reception performance because the distortion of the transmission line cannot be fully compensated.</p><p> FIG. 6 is a diagram showing an example of a delay profile in a three-wave environment. The horizontal axis of FIG. 6 is the time axis, and the vertical axis represents the power of the path.</p><p> In the example of FIG. 6, there are three paths, path P, path Q, and path R, and only path P and path Q are detectable, and path R has a small power, so the delay profile estimation circuit 10 It is said that it cannot be detected by some.</p><p> In this case, since the only paths that can be detected are the path P and the path Q, the delay spread is the interval between the path P and the path Q even though there is actually an amount corresponding to the interval between the path P and the path R. It is judged as only the amount corresponding to, and the filter band is selected accordingly.</p><p> In the example of FIG. 6, when the center position of the path P and the path Q and the center position of the filter band are set to the same position, the filter band BW3 that can fit the path P and the path Q in the filter band is selected. .. For the quality of the OFDM frequency region signal after compensation for the final transmission line distortion, the transmission line characteristics are interpolated using an interpolation filter that can also accommodate the path R in the filter band, and the transmission line distortion is compensated. It will be inferior to the quality of the obtained OFDM frequency region signal.</p><p> If a filter band with a wide bandwidth is always selected, such as the filter band BW0 in Fig. 5, interpolation can be performed including paths that cannot be detected, but the power is higher than that of path R in Fig. 6. Since a large amount of noise with a small noise is included in the filter band and interpolation is performed, it is preferable that the filter band is a band as close as possible to the width of the delay spread while including all the paths.</p><p> The present invention has been made in view of such a situation, and makes it possible to avoid deterioration of reception performance.</p>

<p> The receiving device of the first aspect of the present invention is a pilot from an FFT calculation means that performs an FFT calculation on an OFDM time region signal and an OFDM frequency region signal obtained by performing the FFT calculation by the FFT calculation means. Pilot signal extraction means for extracting signals, estimation means for estimating transmission line characteristics with respect to the pilot signal and obtaining transmission line characteristics for each predetermined subcarrier by interpolating in the time direction, and for each predetermined subcarrier. The frequency interpolation process is performed by using a control means for controlling the width and center position of the passing band of the interpolation filter used for the frequency interpolation process, which is a process of filtering the transmission line characteristics of the above and interpolating in the frequency direction, and the interpolation filter. To obtain the transmission line characteristics of all subcarriers, the width and center position of the pass band of the interpolation filter are set for the transmission line characteristics of each predetermined subcarrier obtained from the OFDM frequency region signals representing the same symbol. Distortion that corrects the distortion of the OFDM frequency region signal representing the same symbol by using the interpolation means that is changed according to the control by the control means and the transmission line characteristics of all the subcarriers obtained by the interpolation means. Based on the correction means, the calculation means for calculating the quality of each distortion-corrected OFDM frequency region signal, and the quality calculated by the calculation means, the best quality distortion-corrected OFDM frequency region signal is obtained. The width and center position of the passing band were determined by the estimation means using the selection means for selecting the interpolation filter used in the above and the interpolation filter having the same characteristics as the interpolation filter selected by the selection means. A variable coefficient interpolation means for obtaining the transmission line characteristics of all subcarriers by performing the frequency interpolation processing for the transmission line characteristics for each predetermined subcarrier, and a transmission line for all subcarriers obtained by the variable coefficient interpolation means. It is provided with an equalization means for correcting the distortion of the OFDM frequency region signal using the characteristics and performing equalization.</p><p> The interpolation means can use interpolation filters having different widths and center positions of the pass band to perform the plurality of frequency interpolation processes in parallel in time.</p><p> The control means has one of the widths of the pass band of the interpolation filter centered on a predetermined position between the position of the earliest arrival path and the position of the latest arrival path among the paths constituting the delay profile. The center position of the pass band of the interpolation filter can be changed within the range expanded by the width of / 2.</p><p> In the receiving method of the first aspect of the present invention, an FFT calculation is performed on an OFDM time region signal, a pilot signal is extracted from the OFDM frequency region signal obtained by performing the FFT calculation, and a transmission line for the pilot signal is obtained. Frequency interpolation processing, which is a process of estimating the characteristics of the above, obtaining the transmission line characteristics for each predetermined subcarrier by interpolating in the time direction, filtering the transmission line characteristics for each predetermined subcarrier, and interpolating in the frequency direction. The width and center position of the pass band of the interpolation filter used for are controlled, the frequency interpolation processing is performed using the interpolation filter, and the transmission line characteristics of all subcarriers are obtained from the OFDM frequency region signal representing the same symbol. Targeting the obtained transmission line characteristics for each predetermined subcarrier, the width and center position of the pass band of the interpolation filter are changed, and the transmission line characteristics of all the subcarriers are used to obtain the same symbol. Corrects the distortion of the OFDM frequency region signal that represents, calculates the quality of each distortion-corrected OFDM frequency region signal, and obtains the best quality distortion-corrected OFDM frequency region signal based on the calculated quality. Select the interpolation filter used in the above, and use an interpolation filter having the same characteristics as the selected interpolation filter for the width and center position of the passing band, and use the interpolation filter for the transmission line characteristics for each predetermined subcarrier to perform the frequency interpolation. It includes a step of performing processing, obtaining the transmission line characteristics of all the subcarriers, correcting the distortion of the OFDM frequency region signal using the obtained transmission line characteristics of all the subcarriers, and performing equalization.</p><p> The program of the first aspect of the present invention performs an FFT calculation on an OFDM time region signal, extracts a pilot signal from the OFDM frequency region signal obtained by performing the FFT calculation, and sets a transmission line for the pilot signal. For frequency interpolation processing, which is a process of estimating the characteristics and interpolating in the time direction to obtain the transmission line characteristics for each predetermined subcarrier, filtering the transmission line characteristics for each predetermined subcarrier, and interpolating in the frequency direction. The width and center position of the pass band of the interpolation filter to be used are controlled, the frequency interpolation processing is performed using the interpolation filter, and the transmission line characteristics of all subcarriers are obtained from the OFDM frequency region signal representing the same symbol. Targeting the transmission line characteristics for each of the predetermined subcarriers, the width and center position of the pass band of the interpolation filter are changed, and the same symbol is used by using the transmission line characteristics of all the subcarriers. To correct the distortion of the represented OFDM frequency region signal, calculate the quality of each distortion-corrected OFDM frequency region signal, and obtain the best quality distortion-corrected OFDM frequency region signal based on the calculated quality. The frequency interpolation process is performed by selecting the used interpolation filter and using an interpolation filter having the same characteristics as the selected interpolation filter for the width and center position of the passing band, targeting the transmission line characteristics for each predetermined subcarrier. Is performed, the transmission line characteristics of all the subcarriers are obtained, the distortion of the OFDM frequency region signal is corrected by using the obtained transmission line characteristics of all the subcarriers, and the computer is made to execute the process including the step of performing equalization.</p><p> The receiving device of the second aspect of the present invention is a pilot from an FFT calculation means that performs an FFT calculation on an OFDM time region signal and an OFDM frequency region signal obtained by performing the FFT calculation by the FFT calculation means. Pilot signal extraction means for extracting signals, estimation means for estimating transmission line characteristics with respect to the pilot signal and obtaining transmission line characteristics for each predetermined subcarrier by interpolating in the time direction, and for each predetermined subcarrier. Control means for controlling the center position of the passing band of the interpolation filter used for the frequency interpolation processing, which is the processing for filtering the transmission line characteristics of the above, and performing the frequency interpolation processing using the interpolation filter, and all the subs. The control means is used to determine the center position of the pass band of the interpolation filter for the transmission line characteristics of each predetermined subcarrier obtained from the OFDM frequency region signals representing the same symbol in order to obtain the transmission line characteristics of the carriers. An interpolation means that is changed according to the control, a distortion correction means that corrects the distortion of the OFDM frequency region signal representing the same symbol by using the transmission line characteristics of all the subcarriers obtained by the interpolation means, and the distortion. Was used to obtain the best quality distortion-corrected OFDM frequency region signal based on the calculation means for calculating the quality of each corrected OFDM frequency region signal and the quality calculated by the calculation means. Among the selection means for selecting the interpolation filter and the path in the frequency region obtained by applying IFFT to the data representing the transmission line characteristics for each predetermined subcarrier estimated by the estimation means, the selection means is selected. It is provided with a delay profile estimation means for obtaining a delay profile composed of paths included in a predetermined frequency band centered on the same position as the center position of the pass band of the interpolation filter.</p><p> The width of the predetermined frequency band can be set to be the same as the width of the pass band of the interpolation filter.</p><p> In the receiving method of the second aspect of the present invention, an FFT calculation is performed on the OFDM time domain signal, a pilot signal is extracted from the OFDM frequency domain signal obtained by performing the FFT calculation, and a transmission path for the pilot signal is obtained. Frequency interpolation processing, which is a process of estimating the characteristics of the above, obtaining the transmission line characteristics for each predetermined subcarrier by interpolating in the time direction, filtering the transmission line characteristics for each predetermined subcarrier, and interpolating in the frequency direction. The central position of the pass band of the interpolation filter used in the above is controlled, the frequency interpolation processing is performed using the interpolation filter, and the transmission line characteristics of all subcarriers are obtained from the OFDM frequency domain signal representing the same symbol. Targeting the transmission line characteristics of each of the predetermined subcarriers, the center position of the pass band of the interpolation filter is changed according to the control by the control means, and the obtained transmission line characteristics of all the subcarriers are used. Corrects the distortion of the OFDM frequency domain signals that represent the same symbol, calculates the quality of each distortion-corrected OFDM frequency domain signal, and based on the calculated quality, the best quality distortion-corrected OFDM frequency domain signal. The pass band of the selected interpolation filter among the paths in the frequency domain obtained by selecting the interpolation filter used to obtain the above and applying IFFT to the estimated data representing the transmission path characteristics for each subcarrier. It includes a step of finding a delay profile consisting of paths included in a predetermined frequency band centered on the same position as the center position of.</p><p> The program of the second aspect of the present invention performs an FFT calculation on an OFDM time region signal, extracts a pilot signal from the OFDM frequency region signal obtained by performing the FFT calculation, and sets a transmission line for the pilot signal. For frequency interpolation processing, which is a process of estimating the characteristics and interpolating in the time direction to obtain the transmission line characteristics for each predetermined subcarrier, filtering the transmission line characteristics for each predetermined subcarrier, and interpolating in the frequency direction. It was obtained from the OFDM frequency region signal representing the same symbol that the center position of the pass band of the interpolation filter to be used was controlled, the frequency interpolation processing was performed using the interpolation filter, and the transmission line characteristics of all subcarriers were obtained. Targeting the transmission line characteristics of each predetermined subcarrier, the center position of the pass band of the interpolation filter is changed according to the control by the control means, and the same transmission line characteristics of all the obtained subcarriers are used. Corrects the distortion of the OFDM frequency region signal that represents the symbol of, calculates the quality of each distortion-corrected OFDM frequency region signal, and based on the calculated quality, obtains the best quality distortion-corrected OFDM frequency region signal. Of the paths in the frequency region obtained by selecting the interpolation filter used for obtaining and applying IFFT to the estimated data representing the transmission line characteristics for each predetermined subcarrier, the pass band of the selected interpolation filter. The computer is made to perform a process including a step of obtaining a delay profile consisting of paths included in a predetermined frequency band centered on the same position as the center position.</p><p> In the first aspect of the present invention, the width and center position of the pass band of the interpolation filter used in the frequency interpolation processing, which is the processing of filtering the transmission line characteristics for each predetermined subcarrier and interpolating in the frequency direction, are controlled. Performing the frequency interpolation processing using an interpolation filter to obtain the transmission line characteristics of all subcarriers is intended for the transmission line characteristics of each predetermined subcarrier obtained from the OFDM frequency domain signals representing the same symbol. , The width and center position of the pass band of the interpolation filter are changed. Further, using the transmission line characteristics of all the subcarriers, the distortion of the OFDM frequency domain signal representing the same symbol is corrected, and the quality of each distortion-corrected OFDM frequency domain signal is calculated and calculated. Based on the quality, the interpolation filter used to obtain the best quality distortion-corrected OFDM frequency domain signal is selected. With respect to the width and center position of the pass band, the frequency interpolation processing is performed for the transmission line characteristics for each predetermined subcarrier using an interpolation filter having the same characteristics as the selected interpolation filter, and all the subcarriers are subjected to the frequency interpolation processing. The transmission line characteristics are obtained, and the distortion of the OFDM frequency domain signal is corrected and equalized by using the obtained transmission line characteristics of all the subcarriers.</p><p> In the second aspect of the present invention, the center position of the pass band of the interpolation filter used in the frequency interpolation processing, which is the processing of filtering the transmission line characteristics for each predetermined subcarrier and interpolating in the frequency direction, is controlled, and the interpolation filter The frequency interpolation process is performed using the above to obtain the transmission line characteristics of all the subcarriers, by interpolating the transmission line characteristics of each predetermined subcarrier obtained from the OFDM frequency domain signal representing the same symbol. This is done by changing the center position of the pass band of the filter. Further, using the transmission line characteristics of all the subcarriers, the distortion of the OFDM frequency domain signal representing the same symbol is corrected, and the quality of each distortion-corrected OFDM frequency domain signal is calculated and calculated. Based on the quality, the interpolation filter used to obtain the best quality distortion-corrected OFDM frequency domain signal is selected. Of the paths in the frequency domain obtained by applying IFFT to the estimated data representing the transmission line characteristics for each predetermined subcarrier, a predetermined position centered on the same position as the center position of the pass band of the selected interpolation filter. A delay profile consisting of paths included in the frequency band of is obtained.</p>

<p> According to the present invention, deterioration of reception performance can be avoided.</p>

<figref num="1">It is a figure which shows the OFDM symbol.</figref><figref num="2">It is a figure which shows the example of arrangement of SP signal.</figref><figref num="3">It is a block diagram which shows the configuration example of the conventional OFDM receiver.</figref><figref num="4">It is a figure which shows the structural example of the frequency interpolation circuit of FIG.</figref><figref num="5">It is a figure which shows the example of a filter band.</figref><figref num="6">It is a figure which shows the example of the delay profile.</figref><figref num="7">It is a block diagram which shows the structural example of the OFDM receiver which concerns on one Embodiment of this invention.</figref><figref num="8">It is a figure which shows the structural example of the signal quality detection circuit of FIG.</figref><figref num="9">It is a figure which shows the selection sequence.</figref><figref num="10">It is a figure which shows the example of the filter band selected by the control circuit.</figref><figref num="11">It is a figure which shows the example of another filter band selected by a control circuit.</figref><figref num="12">It is a figure which shows the example of the other filter band selected by a control circuit.</figref><figref num="13">It is a flowchart explaining the OFDM demodulation processing of the OFDM receiver of FIG.</figref><figref num="14">It is a flowchart explaining the signal selection process performed in step S12 of FIG.</figref><figref num="15">It is a block diagram which shows the other configuration example of an OFDM receiver.</figref><figref num="16">It is a figure explaining the signal quality.</figref><figref num="17">It is another figure explaining the signal quality.</figref><figref num="18">Yet another diagram illustrating signal quality.</figref><figref num="19">It is a block diagram which shows the structural example of the OFDM receiver.</figref><figref num="20">It is a figure which shows the structural example of the frequency interpolation circuit 32 of FIG.</figref><figref num="21">It is a figure which shows the time direction characteristic estimation data.</figref><figref num="22">It is a figure which shows the frequency direction characteristic interpolation data.</figref><figref num="23">It is a figure which shows the example of the data of the time domain of 0 value interpolation characteristic data.</figref><figref num="24">It is a figure which shows the structural example of the optimum filter coefficient selection circuit of FIG.</figref><figref num="25">It is a flowchart explaining the reception process of an OFDM receiver.</figref><figref num="26">It is a flowchart explaining the filter coefficient selection process performed in step S58 of FIG.</figref><figref num="27">It is a block diagram which shows the other structural example of the optimum filter coefficient selection circuit.</figref><figref num="28">It is a block diagram which shows the structural example of the OFDM receiver.</figref><figref num="29">It is a block diagram which shows the structural example of the optimum filter coefficient selection circuit of FIG. 28.</figref><figref num="30">It is a figure which shows the example of the variable range of the center position of the pass band of an interpolation filter.</figref><figref num="31">It is a block diagram which shows the structural example of the OFDM receiver.</figref><figref num="32">It is a block diagram which shows the structural example of the optimum filter coefficient selection circuit of FIG.</figref><figref num="33">It is a figure explaining the estimation of the delay profile.</figref><figref num="34">It is a block diagram which shows the configuration example of a personal computer.</figref>

&lt;First embodiment&gt; FIG. 7 is a block diagram showing a configuration example of an OFDM receiver according to an embodiment of the present invention. The same components as those in FIG. 3 are designated by the same reference numerals.

The OFDM receiver 101 in FIG. 7 has a receiving antenna 1, a tuner 2, an A / D conversion circuit 3, an orthogonal demodulation circuit 4, a carrier generation circuit 5, an FFT circuit 6, an FFT section control circuit 7, and a transmission path distortion compensation circuit 8. It is composed of an error correction circuit 9, a delay profile estimation circuit 10, a frequency interpolation filter selection circuit 11, and an optimum frequency interpolation filter selection circuit 21. The OFDM receiver 101 differs from the OFDM receiver 100 of FIG. 3 in that the optimum frequency interpolation filter selection circuit 21 is further provided.

The tuner 2 frequency-converts the RF signal received by the receiving antenna 1 into an IF signal, and outputs the IF signal to the A / D conversion circuit 3.

The A / D conversion circuit 3 performs A / D conversion on the IF signal supplied from the tuner 2 and outputs a digital IF signal to the orthogonal demodulation circuit 4.

The orthogonal demodulation circuit 4 acquires an OFDM time region signal from the IF signal supplied from the A / D conversion circuit 3 by performing orthogonal demodulation using the carrier wave supplied from the carrier wave generation circuit 5, and obtains the acquired OFDM time. Output the area signal. The OFDM time domain signal output from the orthogonal demodulation circuit 4 is supplied to the carrier wave generation circuit 5, the FFT circuit 6, the FFT section control circuit 7, and the delay profile estimation circuit 10.

The carrier wave generation circuit 5 generates a carrier wave having a predetermined frequency based on the OFDM time region signal supplied from the orthogonal demodulation circuit 4, and outputs the generated carrier wave to the orthogonal demodulation circuit 4.

The FFT circuit 6 extracts a signal in the effective symbol length range by removing the signal in the GI range from the signal of one OFDM symbol based on the FFT trigger pulse supplied from the FFT section control circuit 7.

Further, the FFT circuit 6 extracts the data orthogonally modulated to each subcarrier by performing the FFT calculation on the extracted OFDM time domain signal, and outputs the OFDM frequency domain signal representing the extracted data. The OFDM frequency domain signal output from the FFT circuit 6 is supplied to the SP extraction circuit 8-1 and the division circuit 8-4 of the transmission line distortion compensation circuit 8 and the division circuit 21-4 of the optimum frequency interpolation filter selection circuit 21. To.

The FFT section control circuit 7 determines the FFT section based on the OFDM time region signal supplied from the orthogonal demodulation circuit 4 and the delay profile estimated by the delay profile estimation circuit 10, and specifies the start position of the determined FFT section. Outputs the FFT trigger pulse to the FFT circuit 6.

When determining the FFT interval using the OFDM time domain signal, the FFT interval control circuit 7 determines the correlation value between the latter part of the effective symbol used as the copy source of the GI in the OFDM time domain signal of the 1 OFDM symbol and each part. Find and detect the part with high correlation value as GI. The FFT section control circuit 7 determines the boundary position between the detected GI and the valid symbol as the start position of the FFT section.

When the FFT section is determined using the delay profile, the FFT section control circuit 7 determines the boundary position between the GI and the effective symbol represented by the delay profile as the start position of the FFT section.

The transmission line distortion compensation circuit 8 is composed of an SP extraction circuit 8-1, a time direction transmission line characteristic estimation circuit 8-2, a frequency interpolation circuit 8-3, and a division circuit 8-4.

The SP extraction circuit 8-1 extracts the SP signal from the OFDM frequency domain signal supplied from the FFT circuit 6 and removes the modulation component of the SP signal to obtain the transmission line characteristics of the subcarrier at the position where the SP signal is arranged. presume. The SP extraction circuit 8-1 outputs a signal representing the estimated transmission line characteristics to the time direction transmission line characteristic estimation circuit 8-2.

The time-direction transmission line characteristic estimation circuit 8-2 is based on the transmission line characteristics estimated by the SP extraction circuit 8-1 at the position of each OFDM symbol arranged in the time direction of the subcarrier in which the SP signal is arranged. The transmission line characteristics are estimated, and a signal representing the estimated transmission line characteristics for each of the three subcarriers is output. The signal output from the time-direction transmission line characteristic estimation circuit 8-2 is supplied to the frequency interpolation circuit 8-3, the delay profile estimation circuit 10, and the frequency interpolation circuit 21-3 of the optimum frequency interpolation filter selection circuit 21.

The frequency interpolation circuit 8-3 interpolates the transmission line characteristics in the frequency direction, and from the transmission line characteristics for each of the three subcarriers supplied from the time direction transmission line characteristic estimation circuit 8-2, each OFDM symbol in the frequency direction. Estimate the transmission line characteristics of the subcarrier at the position of.

The frequency interpolation circuit 8-3 has the same configuration as that shown in FIG. As shown in FIG. 5, the frequency interpolation circuit 8-3 supplies one of the signals representing the interpolation results obtained by using a plurality of interpolation filters having different filter bands from the control circuit 21-2. Select according to the filtered filter selection signal. The frequency interpolation circuit 8-3 outputs the selected signal to the division circuit 8-4 as a signal representing the estimation result of the transmission line characteristics.

The dividing circuit 8-4 divides the components of the signal representing the transmission line characteristics of all the subcarriers supplied from the frequency interpolation circuit 8-3 from the OFDM frequency domain signal supplied from the FFT circuit 6, and depends on the transmission line. The distortion component is removed from the OFDM frequency domain signal. The division circuit 8-4 outputs the OFDM frequency domain signal after the transmission line distortion compensation from which the distortion component is removed. The OFDM frequency domain signal after the transmission line distortion compensation output from the division circuit 8-4 is supplied to the selection circuit 21-1 of the optimum frequency interpolation filter selection circuit 21 and the signal quality detection circuit 21-5.

The error correction circuit 9 performs deinterleave processing on the OFDM frequency domain signal supplied from the selection circuit 21-1 of the optimum frequency interpolation filter selection circuit 21, and further performs denunciation, bitabi decoding, diffusion signal removal, and RS decoding. And so on. The error correction circuit 9 outputs the data obtained by performing various processes to the subsequent circuit as decoded data.

The delay profile estimation circuit 10 estimates the delay profile of the transmission line by obtaining the time response characteristic of the transmission line, and outputs a signal representing the estimated delay profile. The signal output from the delay profile estimation circuit 10 is supplied to the FFT section control circuit 7 and the frequency interpolation filter selection circuit 11.

The frequency interpolation filter selection circuit 11 obtains the delay spread based on the delay profile estimated by the delay profile estimation circuit 10, and optimizes the filter selection signal representing the filter band according to the delay spread. The control circuit of the frequency interpolation filter selection circuit 21. Output to 21-2.

The optimum frequency interpolation filter selection circuit 21 is composed of a selection circuit 21-1, a control circuit 21-2, a frequency interpolation circuit 21-3, a division circuit 21-4, and a signal quality detection circuit 21-5. Of the configurations of the optimum frequency interpolation filter selection circuit 21, the frequency interpolation circuit 21-3 is a circuit that performs the same processing as the frequency interpolation circuit 8-3 of the transmission line distortion compensation circuit 8, and is therefore realized by one circuit. You may do so. Further, since the division circuit 21-4 is a circuit that performs the same processing as the division circuit 8-4 of the transmission line distortion compensation circuit 8, it may be realized collectively by one circuit.

The selection circuit 21-1 is one of the transmission line distortion-compensated OFDM frequency domain signal supplied from the dividing circuit 8-4 and the transmission line distortion-compensated OFDM frequency domain signal supplied from the dividing circuit 21-4. One of them is selected according to the selection signal supplied from the control circuit 21-2, and the selected OFDM frequency domain signal is output to the error correction circuit 9.

The control circuit 21-2 outputs a selection signal instructing to select the OFDM frequency domain signal having the better quality to the selection circuit 21-1 based on the information supplied from the signal quality detection circuit 21-5. .. For the signal quality detection circuit 21-5 to the control circuit 21-2, information indicating the quality of the OFDM frequency domain signal obtained by compensating the transmission line distortion by the division circuit 8-4 and the division circuit Information representing the quality of the OFDM frequency domain signal obtained by performing in 21-4 is provided respectively. Further, the control circuit 21-2 outputs the filter selection signal to the frequency interpolation circuit 8-3 and the frequency interpolation circuit 21-3.

The frequency interpolation circuit 21-3 interpolates the transmission line characteristics in the frequency direction from the transmission line characteristics for each of the three subcarriers supplied from the time direction transmission line characteristic estimation circuit 8-2 of the transmission line distortion compensation circuit 8. , Estimate the subcarrier transmission line characteristics at the position of each OFDM symbol in the frequency direction.

The frequency interpolation circuit 21-3 also has the same configuration as that shown in FIG. As shown in FIG. 5, the frequency interpolation circuit 21-3 supplies one of the signals representing the interpolation results obtained by using a plurality of interpolation filters having different filter bands from the control circuit 21-2. Select according to the filtered filter selection signal. The frequency interpolation circuit 21-3 outputs the selected signal to the division circuit 21-4 as a signal representing the estimation result of the transmission line characteristics.

The dividing circuit 21-4 divides the components of the signal representing the transmission line characteristics of all the subcarriers supplied from the frequency interpolation circuit 21-3 from the OFDM frequency domain signal supplied from the FFT circuit 6, and depends on the transmission line. The distortion component is removed from the OFDM frequency domain signal. The division circuit 21-4 outputs the OFDM frequency domain signal after the transmission line distortion compensation from which the distortion component is removed to the selection circuit 21-1 and the signal quality detection circuit 21-5.

The signal quality detection circuit 21-5 describes the quality of the OFDM frequency domain signal after transmission line distortion compensation supplied from the division circuit 8-4 and the OFDM frequency domain after transmission line distortion compensation supplied from the division circuit 21-4. Each signal quality is detected, and signal quality information indicating the detected quality is output to the control circuit 21-2. For example, the quality is determined by the amount of noise, and the signal quality detection circuit 21-5 detects the amount of noise contained in the OFDM frequency domain signal after each transmission line distortion compensation.

FIG. 8 is a diagram showing a configuration example of the signal quality detection circuit 21-5.

As shown in FIG. 8, the signal quality detection circuit 21-5 includes a rigid determination circuit 21-5a, a subtraction circuit 21-5b, a square calculation circuit 21-5c, a carrier direction averaging circuit 21-5d, and a time direction. It consists of averaging circuits 21-5e. The OFDM frequency domain signal after transmission line distortion compensation output from the division circuit 8-4 or the division circuit 21-4 is supplied to the rigid determination circuit 21-5a and the subtraction circuit 21-5b.

The rigid determination circuit 21-5a performs a rigid determination on the signal after transmission line distortion compensation according to a modulation method such as PSK or QAM. The rigid determination circuit 21-5a outputs the rigid determination value, which is the determination result, to the subtraction circuit 21-5b.

The subtraction circuit 21-5b outputs the difference between the hard judgment value and the value of the OFDM frequency domain signal after the transmission line distortion compensation to the square calculation circuit 21-5c. The difference between the rigid judgment value and the OFDM frequency domain signal is the amount of noise.

The square calculation circuit 21-5c squares the amount of noise calculated by the subtraction circuit 21-5b and converts it into power. The square calculation circuit 21-5c outputs the noise power obtained by the square calculation to the carrier direction averaging circuit 21-5d.

The carrier direction averaging circuit 21-5d improves its accuracy by averaging the power in the carrier direction obtained by the square calculation circuit 21-5c. The carrier direction averaging circuit 21-5d outputs the averaging of the power in the carrier direction to the time direction averaging circuit 21-5e.

When applying one filter selection signal over multiple symbols, it is also possible to average in the time direction. In this case, the time direction averaging circuit 21-5e is the power of the noise contained in the OFDM frequency domain signal after the transmission line distortion compensation generated when the same filter selection signal is output from the control circuit 21-2. The average in the time direction is calculated, and the information representing the calculated average in the time direction is output to the control circuit 21-2. A reset signal for erasing the information used in the calculation up to that point is input to the time direction averaging circuit 21-5e every time the filter selection signal is changed.

Here, the sequence of filter band selection by the control circuit 21-2 and selection of the OFDM frequency domain signal after transmission line distortion compensation will be described.

FIG. 9 is a diagram showing an example of a selection sequence.

In FIG. 9, the characters shown in the ellipse representing each state represent the filter selection signals output from the control circuit 21-2 to the frequency interpolation circuit 8-3 and the frequency interpolation circuit 21-3, and from one state to another. The characters shown near the arrow indicating the transition to the state of are the conditions under which the transition occurs and the contents of the signal output from the control circuit 21-2 at that time. Of the characters shown near the arrow, the left side of the slash (/) represents the transition condition (action list), and the right side represents the content of the signal (state of the next transition destination).

Hereinafter, the filter selection signal output from the control circuit 21-2 to the frequency interpolation circuit 8-3 is referred to as FLT_A, and the filter selection signal output from the control circuit 21-2 to the frequency interpolation circuit 21-3 is referred to as FLT_B. And. Further, the information indicating the quality of the OFDM frequency domain signal obtained by compensating the transmission line distortion by the division circuit 8-4 is set as the signal quality information NPWR_A, and is obtained by the division circuit 21-4. The information indicating the quality of the OFDM frequency domain signal is referred to as signal quality information NPWR_B.

Further, the filter band selected by the frequency interpolation filter selection circuit 11 based on the delay profile estimated by the delay profile estimation circuit 10 is defined as BWX (X = 0 to 3). The filter selection signal supplied from the frequency interpolation filter selection circuit 11 to the control circuit 21-2 represents this BWX. The state of the delay profile is the state described with reference to FIG. That is, there are three paths, path P, path Q, and path R, of which only path P and path Q can be detected by the delay profile estimation circuit 10, and path R cannot be detected due to its low power. It is said that.

The initial state s0 is the state of FLT_A = BWX, FLT_B = BW0. In state s0, the frequency interpolation circuit 8-3 is instructed to select the filter band selected based on the delay profile. In the control circuit 21-2, the OFDM generated by the division circuit 8-4 when FLT_A = BWX and FLT_B = BW0 are set based on the signal quality information NPWR_A and NPWR_B supplied from the signal quality detection circuit 21-5. The amount of noise contained in the frequency domain signal is compared with the amount of noise contained in the OFDM frequency domain signal generated by the dividing circuit 21-4.

As shown in the upper part of FIG. 10, when BWX = BW3, since there is an undetected path R, the division circuit 8-4 cannot compensate for the transmission line distortion, and the reception performance deteriorates. On the other hand, as shown in the lower part of FIG. 10, in the frequency interpolation circuit 21-3, interpolation is performed using an interpolation filter in the filter band BW0 including the undetected path R, and the interpolation result is shown. The transmission line distortion is compensated in the interpolation circuit 21-4 based on the signal.

The signal quality information supplied from the signal quality detection circuit 21-5 is NPWR_A&gt; = NPWR_B, and since X = 3, the state of the control circuit 21-2 transitions from the state s0 to the state s1. The larger the value of the signal quality information, the larger the amount of noise, and the poorer the quality of the OFDM frequency domain signal from which the amount of noise is detected.

At this time, the filter selection signal for the frequency interpolation circuit 8-3 is switched to FLT_A = BW2. Further, as the selection signal SEL for the selection circuit 21-1, SEL = FLT_B instructing to select the OFDM frequency domain signal output from the division circuit 21-4 is output from the control circuit 21-2.

The state s1 is the state of FLT_A = BW2 and FLT_B = BW0. In the control circuit 21-2, the OFDM generated by the division circuit 8-4 when FLT_A = BW2 and FLT_B = BW0 are set based on the signal quality information NPWR_A and NPWR_B supplied from the signal quality detection circuit 21-5. The amount of noise contained in the frequency domain signal is compared with the amount of noise contained in the OFDM frequency domain signal generated by the dividing circuit 21-4.

Even in the state s1, since there is an undetected path R as shown in the upper part of FIG. 11, the division circuit 8-4 cannot compensate for the transmission line distortion, and the reception performance deteriorates. On the other hand, as shown in the lower part of FIG. 11, in the frequency interpolation circuit 21-3, interpolation is performed using an interpolation filter in the filter band BW0 including the undetected path R, and the interpolation result is shown. The transmission line distortion is compensated in the interpolation circuit 21-4 based on the signal.

The signal quality information supplied from the signal quality detection circuit 21-5 is NPWR_A&gt; = NPWR_B, and since X = 3, the state of the control circuit 21-2 transitions from the state s1 to the state s3.

At this time, the filter selection signal for the frequency interpolation circuit 8-3 is switched to FLT_A = BW1. Further, as the selection signal SEL for the selection circuit 21-1, SEL = FLT_B instructing to select the OFDM frequency domain signal output from the division circuit 21-4 is output from the control circuit 21-2.

The state s3 is the state of FLT_A = BW1 and FLT_B = BW0. In the control circuit 21-2, the OFDM generated by the division circuit 8-4 when FLT_A = BW1 and FLT_B = BW0 are set based on the signal quality information NPWR_A and NPWR_B supplied from the signal quality detection circuit 21-5. The amount of noise contained in the frequency domain signal is compared with the amount of noise contained in the OFDM frequency domain signal generated by the dividing circuit 21-4.

Even in the state s3, since there is an undetected path R as shown in the upper part of FIG. 12, the division circuit 8-4 cannot compensate for the transmission line distortion, and the reception performance deteriorates. On the other hand, as shown in the lower part of FIG. 12, in the frequency interpolation circuit 21-3, interpolation is performed using an interpolation filter in the filter band BW0 including the undetected path R, and the interpolation result is shown. The transmission line distortion is compensated in the interpolation circuit 21-4 based on the signal.

The signal quality information supplied from the signal quality detection circuit 21-5 is NPWR_A&gt; = NPWR_B, and since X = 3, the state of the control circuit 21-2 transitions from the state s3 to the state s0. Similarly, when X = 2, the state of the control circuit 21-2 transitions from the state s3 to the state s0.

At this time, the filter selection signal for the frequency interpolation circuit 8-3 is switched to FLT_A = BWX. Further, as the selection signal SEL for the selection circuit 21-1, SEL = FLT_B instructing to select the OFDM frequency domain signal output from the division circuit 21-4 is output from the control circuit 21-2.

In this way, even if there is a path R that exceeds the detection limit of the delay profile estimation circuit 10 and the division circuit 8-4 cannot compensate for the transmission line distortion, the division circuit 21- By making the OFDM frequency domain signal generated by 4 selected according to the selection signal SEL = FLT_B, the result of compensation for the transmission line distortion including the path R is supplied to the error correction circuit 9. It is possible to prevent deterioration of reception performance.

In other cases as well, the state of the control circuit 21-2 transitions as appropriate. For example, when NPWR_A &lt;NPWR_B in state s0, state s0 is maintained.

On the other hand, when NPWR_A&gt; = NPWR_B and X = 2 in the state s0, the state of the control circuit 21-2 transitions from the state s0 to the state s3. At this time, the filter selection signal for the frequency interpolation circuit 8-3 is switched to FLT_A = BW1. Further, as the selection signal SEL for the selection circuit 21-1, SEL = FLT_B instructing to select the OFDM frequency domain signal output from the division circuit 21-4 is output from the control circuit 21-2.

When NPWR_A &lt;NPWR_B and X = 3 in the state s1, the state of the control circuit 21-2 transitions from the state s1 to the state s2. At this time, the filter selection signal for the frequency interpolation circuit 21-3 is switched to FLT_B = BW3. Further, as the selection signal SEL for the selection circuit 21-1, SEL = FLT_A instructing to select the OFDM frequency domain signal output from the division circuit 8-4 is output from the control circuit 21-2.

The state s2 is the state of FLT_A = BW2 and FLT_B = BW3. In the control circuit 21-2, the OFDM generated by the division circuit 8-4 when FLT_A = BW2 and FLT_B = BW3 are set based on the signal quality information NPWR_A and NPWR_B supplied from the signal quality detection circuit 21-5. The amount of noise contained in the frequency domain signal is compared with the amount of noise contained in the OFDM frequency domain signal generated by the dividing circuit 21-4.

When NPWR_A &lt;NPWR_B and X = 3 in the state s2, the state of the control circuit 21-2 transitions from the state s2 to the state s1. At this time, the filter selection signal for the frequency interpolation circuit 21-3 is switched to FLT_B = BW0. Further, as the selection signal SEL for the selection circuit 21-1, SEL = FLT_A instructing to select the OFDM frequency domain signal output from the division circuit 8-4 is output from the control circuit 21-2.

On the other hand, when NPWR_A&gt; = NPWR_B and X = 3 in the state s2, the state of the control circuit 21-2 transitions from the state s2 to the state s0. At this time, the filter selection signal for the frequency interpolation circuit 8-3 is switched to FLT_A = BWX, and the filter selection signal for the frequency interpolation circuit 21-3 is switched to FLT_B = BW0. Further, as the selection signal SEL for the selection circuit 21-1, SEL = FLT_B instructing to select the OFDM frequency domain signal output from the division circuit 21-4 is output from the control circuit 21-2.

When NPWR_A &lt;NPWR_B and X = 2 or 3 in the state s3, the state of the control circuit 21-2 transitions from the state s3 to the state s4. At this time, the filter selection signal for the frequency interpolation circuit 21-3 is switched to FLT_B = BW2. Further, as the selection signal SEL for the selection circuit 21-1, SEL = FLT_A instructing to select the OFDM frequency domain signal output from the division circuit 8-4 is output from the control circuit 21-2.

The state s4 is the state of FLT_A = BW1 and FLT_B = BW2. In the control circuit 21-2, the OFDM generated by the division circuit 8-4 when FLT_A = BW1 and FLT_B = BW2 are set based on the signal quality information NPWR_A and NPWR_B supplied from the signal quality detection circuit 21-5. The amount of noise contained in the frequency domain signal is compared with the amount of noise contained in the OFDM frequency domain signal generated by the dividing circuit 21-4.

When NPWR_A &lt;NPWR_B and X = 2 or 3 in the state s4, the state of the control circuit 21-2 transitions from the state s4 to the state s3. At this time, the filter selection signal for the frequency interpolation circuit 21-3 is switched to FLT_B = BW0. Further, as the selection signal SEL for the selection circuit 21-1, SEL = FLT_A instructing to select the OFDM frequency domain signal output from the division circuit 8-4 is output from the control circuit 21-2.

On the other hand, when NPWR_A&gt; = NPWR_B and X = 2 or 3 in the state s4, the state of the control circuit 21-2 transitions from the state s4 to the state s0. At this time, the filter selection signal for the frequency interpolation circuit 8-3 is switched to FLT_A = BWX, and the filter selection signal for the frequency interpolation circuit 21-3 is switched to FLT_B = BW0. Further, as the selection signal SEL for the selection circuit 21-1, SEL = FLT_B instructing to select the OFDM frequency domain signal output from the division circuit 21-4 is output from the control circuit 21-2.

The selection sequence as described above can be constantly operated while the reception process is being performed on the OFDM receiver 101, whereby the optimum OFDM frequency domain signal can always be selected. That is, it can be said that the followability is high even in an environment where the profile changes sequentially.

In addition, the filter band of the interpolation filter used in the two frequency interpolation circuits can be adaptively controlled, and deterioration of reception performance can be prevented without data corruption. Basically, change the filter band of the frequency interpolation circuit used to obtain the characteristics of the transmission line that was the source of the signal after compensation for the transmission line distortion that was not selected by the selection circuit 21-1. , The filter band will be controlled adaptively.

Here, the processing of the OFDM receiver 101 having the above configuration will be described. The processing of each step in the following flowchart is not only performed in numerical order, but is also performed in parallel with the processing of other steps as appropriate.

First, the OFDM demodulation process of the OFDM receiver 101 will be described with reference to the flowchart of FIG.

In step S1, the tuner 2 frequency-converts the RF signal received by the receiving antenna 1 and outputs the IF signal to the A / D conversion circuit 3.

In step S2, the A / D conversion circuit 3 performs A / D conversion on the IF signal and outputs the digital IF signal to the orthogonal demodulation circuit 4.

In step S3, the orthogonal demodulation circuit 4 performs orthogonal demodulation and outputs the OFDM time domain signal to the carrier wave generation circuit 5, the FFT circuit 6, the FFT section control circuit 7, and the delay profile estimation circuit 10.

In step S4, the FFT circuit 6 sets the FFT section based on the FFT trigger pulse supplied from the FFT section control circuit 7, and performs the FFT calculation. The FFT circuit 6 outputs the OFDM frequency domain signal obtained by performing the FFT calculation to the SP extraction circuit 8-1, the division circuit 8-4, and the division circuit 21-4.

In step S5, the SP extraction circuit 8-1 extracts the SP signal from the OFDM frequency domain signal and estimates the transmission line characteristics of the subcarrier at the position where the SP signal is arranged. The SP extraction circuit 8-1 outputs a signal representing the estimated transmission line characteristics to the time direction transmission line characteristic estimation circuit 8-2.

In step S6, the time-direction transmission line characteristic estimation circuit 8-2 estimates the time-direction transmission line characteristics for each of the three subcarriers, and the signal representing the estimated transmission line characteristics is estimated by the frequency interpolation circuit 8-3 and the delay profile. Output to circuit 10 and frequency interpolation circuit 21-3.

In step S7, the delay profile estimation circuit 10 estimates the delay profile and outputs the delay profile to the FFT section control circuit 7 and the frequency interpolation filter selection circuit 11.

In step S8, the frequency interpolation filter selection circuit 11 obtains the delay spread based on the delay profile estimated by the delay profile estimation circuit 10, the fill according to the delay spread to select a data band. The frequency interpolation filter selection circuit 11 outputs a filter selection signal that specifies the selected filter band to the control circuit 21-2.

In step S9, the FFT section control circuit 7 determines the FFT section based on the OFDM time region signal supplied from the orthogonal demodulation circuit 4 and the delay profile estimated by the delay profile estimation circuit 10, and determines the determined FFT section. The specified FFT trigger pulse is output to the FFT circuit 6.

In step S10, the frequency interpolation circuit 8-3 interpolates the transmission line characteristics in the frequency direction, and from the transmission line characteristics for each of the three subcarriers supplied from the time direction transmission line characteristic estimation circuit 8-2, the frequency direction. The transmission line characteristics of the subcarriers at the positions of each OFDM symbol are estimated, and the signal representing the estimation result is output to the division circuit 8-4. Which signal is output as the signal representing the estimation result of the transmission line characteristic from the plurality of signals representing the interpolation result is selected based on the filter selection signal FLT_A supplied from the control circuit 21-2.

In step S11, the division circuit 8-4 removes the distortion component due to the transmission line from the OFDM frequency domain signal supplied from the FFT circuit 6 based on the signal supplied from the frequency interpolation circuit 8-3. The division circuit 8-4 outputs the OFDM frequency domain signal from which the distortion component has been removed to the selection circuit 21-1 and the signal quality detection circuit 21-5.

In step S12, a signal selection process for selecting the OFDM frequency domain signal to be output to the error correction circuit 9 is performed. The signal selection process will be described later with reference to the flowchart of FIG.

In step S13, the error correction circuit 9 performs various processes such as deinterleave processing, denunciation, Viterbi decoding, diffusion signal removal, and RS decoding on the OFDM frequency domain signal supplied from the selection circuit 21-1. The decoded data is output to the subsequent circuit.

The above processing is repeated by the OFDM receiver 101 while receiving the signal.

Next, the signal selection process performed in step S12 of FIG. 13 will be described with reference to the flowchart of FIG.

In the OFDM receiver 101, the processing of FIG. 14 is constantly performed in parallel with the processing of FIG. 13 while the signal is being received.

In step S21, the control circuit 21-2 outputs the filter selection signal FLT_A to the frequency interpolation circuit 8-3, and outputs the filter selection signal FLT_B to the frequency interpolation circuit 21-3. The filter selection signals FLT_A and FLT_B are selected according to the selection sequence described with reference to FIG.

In step S22, the frequency interpolation circuit 21-3 interpolates the transmission line characteristics in the frequency direction, and from the transmission line characteristics for each of the three subcarriers supplied from the time direction transmission line characteristic estimation circuit 8-2, the frequency direction. The transmission line characteristics of the subcarriers at the positions of each OFDM symbol are estimated, and the signal representing the estimation result is output to the division circuit 21-4. Which signal is output as the signal representing the estimation result of the transmission line characteristic from the plurality of signals representing the interpolation result is selected based on the filter selection signal FLT_B supplied from the control circuit 21-2.

In step S23, the division circuit 21-4 removes the distortion component due to the transmission line from the OFDM frequency domain signal supplied from the FFT circuit 6 based on the signal supplied from the frequency interpolation circuit 21-3. The division circuit 21-4 outputs the OFDM frequency domain signal from which the distortion component has been removed to the selection circuit 21-1 and the signal quality detection circuit 21-5. The transmission line characteristics are interpolated by the frequency interpolation circuit 8-3 in step S10 of FIG. 13, and the transmission line distortion is compensated by the division circuit 8-4 in step S11.

In step S24, the signal quality detection circuit 21-5 detects the amount of noise contained in the OFDM frequency domain signal after the transmission line distortion compensation supplied from the division circuit 8-4, and controls the signal quality information NPWR_A 21. Output to -2.

In step S25, the signal quality detection circuit 21-5 detects the amount of noise contained in the OFDM frequency domain signal after the transmission line distortion compensation supplied from the division circuit 21-4, and controls the signal quality information NPWR_B. Output to -2.

In step S26, the control circuit 21-2 compares the signal quality information NPWR_A and NPWR_B, and outputs a selection signal SEL instructing the selection of the OFDM frequency domain signal having the better quality to the selection circuit 21-1.

In step S27, the selection circuit 21-1 determines the better quality OFDM frequency domain signal of the OFDM frequency domain signal supplied from the dividing circuit 8-4 and the OFDM frequency domain signal supplied from the dividing circuit 21-4. The signal is selected according to the selection signal supplied from the control circuit 21-2, and the selected OFDM frequency domain signal is output to the error correction circuit 9. After that, the process returns to step S11 in FIG. 13 and the subsequent processing is performed.

The above processing makes it possible to prevent deterioration of reception performance.

&lt;Modification example&gt; FIG. 15 is a block diagram showing a configuration example of another OFDM receiver. The same components as those of the OFDM receiver 101 in FIG. 7 are designated by the same reference numerals.

The configuration of the OFDM receiver 102 shown in FIG. 15 is different from the configuration of the OFDM receiver 101 of FIG. 7 in that the frequency interpolation filter selection circuit 11 is not provided. That is, in the OFDM receiver 101 of FIG. 7, a filter instructing to select the same filter band as the filter band selected by the frequency interpolation filter selection circuit 11 based on the delay profile estimated by the delay profile estimation circuit 10. The selection signal is appropriately output from the control circuit 21-1 according to the selection sequence described with reference to FIG. 9, but in the OFDM receiver 102, the filter band is always selected by the control circuit 21-2 itself. It is made to be. The signal quality information NPWR_A and NPWR_B are referred to for the selection of the filter band by the control circuit 21-2 itself.

In this way, even when the frequency interpolation filter selection circuit 11 is not provided, of the OFDM frequency domain signal output from the dividing circuit 8-4 and the OFDM frequency domain signal output from the dividing circuit 21-4. , The optimum OFDM frequency domain signal can be selected based on the quality, and deterioration of reception performance can be prevented.

In the above, it is assumed that the frequency interpolation circuit 8-3 and the frequency interpolation circuit 21-3, and the division circuit 8-4 and the division circuit 21-4 can be realized by one circuit each, but on the contrary, the division circuit The signal quality detection circuit that detects the quality of the OFDM frequency domain signal generated by 8-4 and the signal quality detection circuit that detects the quality of the OFDM frequency domain signal generated by the division circuit 21-4 are separated by separate circuits. It may be realized.

That is, a plurality of transmission line characteristics of all subcarriers can be obtained by performing interpolation processing using a plurality of interpolation filters having different filter bands, and a plurality of transmission line distortions are compensated based on the transmission line distortions. If the signal after compensation can be obtained and the quality of the signal after compensation for each transmission line distortion can be detected, the frequency interpolation circuit, the division circuit, and the signal quality detection circuit will be realized in any form. You may do so.

Further, as the signal for which the quality is detected, the signal after error correction may be used instead of the signal after compensation (equalization) of the transmission line distortion.

In addition, instead of generating a compensated signal for two transmission line distortions and selecting one of them, generate three or more signals and select the best quality signal from them. You may.

&lt;Second embodiment&gt; In the above, the case where the width of the pass band (filter band) of the interpolation filter is adjusted to improve the signal quality has been described, but in addition to the width of the pass band, the center position (center frequency) of the pass band is adjusted. You may do so.

16A to 16D are diagrams for explaining signal quality when the width of the pass band of the interpolation filter is variable and the center position is fixed.

The horizontal direction represents the time direction, and the vertical direction represents the power of the path. The upward white triangle represents the center position of the pass band of the interpolation filter.

FIG. 16A is a diagram showing an example of a profile of a received signal. The case where three paths P, Q, and R exist will be described.

As shown in FIGS. 16B and 16C, when an interpolation filter is applied so that some passes cannot be included in the pass band, the quality of the final distortion-corrected OFDM frequency domain signal is the quality of all passes. Poor compared to the signal quality obtained when the interpolation filter is applied to include.

Figure 16D shows an example in which an interpolation filter is applied so that all paths are included in the passband. The quality of the OFDM frequency domain signal after distortion correction is the best among the signal qualities obtained by using the interpolation filters of the bands BW3, BW2, and BW1.

17A to 17D are diagrams for explaining signal quality when the width of the pass band of the interpolation filter is fixed as BW2 and the center position is variable.

FIG. 17A is a diagram showing the same paths P, Q, and R as in FIG. 16A.

When the interpolation filter is applied so that the position p1 shown in FIG. 17B is the center position of the pass band, the pass band does not include the path R.

When the interpolation filter is applied so that the position p2 shown in FIG. 17C is the center position of the pass band by slightly shifting to the right from the position p1, the pass band includes all the paths P, Q, and R. The quality of the OFDM frequency domain signal after distortion correction is better than that of the signal quality shown in FIG. 17B or the like centered on a position where all paths are not included in the pass band.

When the interpolation filter is applied so that the position p3 shown in FIG. 17D is the center position of the pass band by slightly shifting to the right from the position p2, the path P deviates from the pass band.

In the case of FIG. 16 in which the width of the pass band of the interpolation filter is variable and the center position is fixed, in the case of FIG. 17 in which the width of the pass band is fixed and the center position is variable, the adjustment is usually performed. Depending on the method, all paths can be included in the passband.

18A and 18B are diagrams for explaining the signal quality when both the width and the center position of the pass band of the interpolation filter are made variable.

FIG. 18A is a diagram showing an example in which an interpolation filter is applied with the width of the pass band as BW1 and the center position as position p11.

FIG. 18B is a diagram showing an example in which the width of the pass band is BW2 and the center position is slightly shifted to the right from the position p11 and the interpolation filter is applied as the position p12.

Fig. 18 All paths can be contained in the pass band of either the interpolation filter A or B, but when comparing the quality of the distortion-corrected OFDM frequency domain signal obtained by using both interpolation filters, the figure shows. The signal quality is better when using the 18B interpolation filter.

As shown in FIGS. 18A and 18B, white noise is actually superimposed over the entire area, and it is desirable to set an interpolation filter that includes all paths but does not include white noise in the pass band as much as possible. Because. Comparing the interpolation filter of FIG. 18A and the interpolation filter of FIG. 18B, the amount of white noise contained in the pass band is smaller than that of the interpolation filter of FIG. 18B by the amount indicated by the alternate long and short dash line.

In the receiver described below, an interpolation filter is set in this way so as to include all paths and not include white noise in the pass band as much as possible.

FIG. 19 is a block diagram showing a configuration example of the OFDM receiver 103.

Of the configurations shown in FIG. 19, the same configurations as those shown in FIG. 7 and the like are designated by the same reference numerals.

The configuration of the OFDM receiver 103 in FIG. 19 is mainly that the frequency interpolation filter selection circuit 11 is eliminated and the optimum filter coefficient selection circuit 31 is provided in place of the optimum frequency interpolation filter selection circuit 21. It is different from the configuration of. Further, as a circuit that performs frequency interpolation processing that is a process of interpolating transmission line characteristics in the frequency direction, a frequency interpolation circuit 32 that performs frequency interpolation processing by changing the width and center position of the pass band of the interpolation filter according to a coefficient is a transmission line distortion. It is provided in the compensation circuit 8.

The tuner 2 frequency-converts the RF signal received by the receiving antenna 1 into an IF signal, and outputs the IF signal to the A / D conversion circuit 3.

The A / D conversion circuit 3 performs A / D conversion on the IF signal and outputs a digital IF signal to the orthogonal demodulation circuit 4.

The orthogonal demodulation circuit 4 acquires and outputs an OFDM time domain signal by performing orthogonal demodulation using the carrier wave supplied from the carrier wave generation circuit 5.

The carrier wave generation circuit 5 generates a carrier wave having a predetermined frequency and outputs the carrier wave to the orthogonal demodulation circuit 4.

The FFT circuit 6 sets the FFT section based on the FFT trigger pulse supplied from the FFT section control circuit 7, and performs the FFT calculation on the OFDM time domain signal in the FFT section. The FFT circuit 6 extracts the OFDM frequency domain signal representing the data quadrature-modulated to each subcarrier extracted by performing the FFT calculation to the SP extraction circuit 8-1, the division circuit 8-4, and the optimum filter coefficient selection circuit 31. Output to.

The FFT section control circuit 7 determines the FFT section based on the delay profile estimated by the delay profile estimation circuit 10, and outputs the FFT trigger pulse to the FFT circuit 6.

The SP extraction circuit 8-1 of the transmission line distortion compensation circuit 8 extracts the SP signal from the OFDM frequency domain signal and estimates the transmission line characteristics for the SP signal. The SP extraction circuit 8-1 outputs transmission line characteristic data representing the estimated transmission line characteristics to the time direction transmission line characteristic estimation circuit 8-2.

The time-direction transmission line characteristic estimation circuit 8-2 estimates the transmission line characteristics for each OFDM symbol arranged in the time direction of the subcarrier in which the SP signal is arranged. The time-direction transmission line characteristic estimation circuit 8-2 applies the time-direction characteristic estimation data, which is data representing the transmission line characteristics for each of the three subcarriers, to the optimum filter coefficient selection circuit 31, the frequency interpolation circuit 32, and the delay profile estimation circuit 10. Output.

The frequency interpolation circuit 32 performs frequency interpolation processing by changing the width and center position of the pass band of the interpolation filter based on the coefficients supplied from the optimum filter coefficient selection circuit 31.

FIG. 20 is a diagram showing a configuration example of the frequency interpolation circuit 32.

As shown in FIG. 20, the frequency interpolation circuit 32 includes a triple upsampling circuit 41 and an interpolation filter circuit 42.

The triple upsampling circuit 41 interpolates, for example, two zeros as new sample values between the sample values of the time direction characteristic estimation data supplied from the time direction transmission line characteristic estimation circuit 8-2. The triple upsampling circuit 41 outputs the time direction characteristic estimation data obtained by doubling the number of sample values to the original data to the interpolation filter circuit 42.

The interpolation filter circuit 42 comprises an LPF (Low Pass Filter) that performs filtering for interpolation of transmission line characteristics in the frequency direction, and filters time-direction characteristic estimation data from the triple upsampling circuit 41. The width and center position of the pass band of the LPF (interpolation filter) used for filtering are adjusted by the coefficient supplied from the optimum filter coefficient selection circuit 31.

The interpolation filter circuit 42 performs filtering using an interpolation filter in which the width and center position of the pass band are adjusted, thereby removing the folding component generated in the temporal characteristic estimation data by the interpolation of zero, and interpolating in the frequency direction. Obtain the characteristics of the transmitted line. The interpolation filter circuit 42 outputs the frequency direction characteristic interpolation data, which is the data representing the transmission line characteristics obtained by interpolating in the frequency direction, that is, the transmission line characteristics of all the subcarriers, to the division circuit 8-4.

Assuming that the effective symbol length, which is the length of the section obtained by removing GI from one symbol, is Tu, the width of the pass band of the interpolation filter is, for example, a width equal to or less than about Tu / 3 [seconds]. ..

The width of the pass band of the interpolation filter will be described.

FIG. 21 is a diagram showing time-direction characteristic estimation data.

The time direction characteristic estimation data as shown in FIG. 21 is obtained by the time direction transmission line characteristic estimation circuit 8-2 using the transmission line characteristic data for the SP signal arranged as shown in FIG. In FIG. 21, white circles and shaded circles represent subcarriers (transmission symbols) of OFDM signals. The shaded circles represent transmission symbols whose transmission line characteristics are estimated after processing by the time direction transmission line characteristic estimation circuit 8-2.

By estimating the transmission line characteristics in the time direction using the transmission line characteristic data for the SP signal, as shown in FIG. 21, the transmission line characteristics for each OFDM symbol are obtained for each of the three subcarriers. The time-direction characteristic estimation data representing the transmission line characteristics as shown in FIG. 21 is supplied from the time-direction transmission line characteristic estimation circuit 8-2 to the frequency interpolation circuit 32.

FIG. 22 is a diagram showing frequency direction characteristic interpolation data.

In the frequency interpolation circuit 32, the time-direction characteristic estimation data representing the transmission line characteristics for each of the three subcarriers is used in the subcarrier number direction, and each of the subcarriers of the OFDM symbol surrounded by the shaded area in FIG. 22 is used. Transmission line characteristics are required.

Specifically, in the triple upsampling circuit 41, the time direction characteristic is that the amount of data is tripled from the original data by interpolating two zeros between the sample values of the time direction characteristic estimation data. Estimated data is generated.

The time-direction characteristic estimation data input to the triple upsampling circuit 41 is a series of sample values representing the transmission line characteristics for each of the three subcarriers as shown in FIG. Therefore, regarding this time-direction characteristic estimation data, there are only two subcarriers whose transmission line characteristics are not estimated among the subcarriers whose transmission line characteristics are estimated. Therefore, in the triple upsampling circuit 41, two zeros, which are sample points of the transmission line characteristics for the two subcarriers whose transmission line characteristics are not estimated, are interpolated.

The number of zeros to be interpolated differs depending on how many subcarrier-specific transmission line characteristic data the time-direction characteristic estimation data obtained by the time-direction transmission line characteristic estimation circuit 8-2 is. ..

In this way, when two zeros are interpolated between the sample values of the time-direction characteristic estimation data, the time-direction characteristic estimation data obtained as a result of the interpolation includes a folding component in the time domain. It becomes a thing. Hereinafter, the time-direction characteristic estimation data in which zeros are interpolated is referred to as 0-value interpolation characteristic data as appropriate.

The reason why the time direction characteristic estimation data includes the folding component will be described.

The time-direction characteristic estimation data is data obtained from the OFDM frequency domain signal, and is frequency domain data.

Then, the time direction characteristic estimation data and the 0 value interpolation characteristic data obtained by interpolating zero in the time direction characteristic estimation data are the same signal as an analog signal. The time domain data of the time direction characteristic estimation data and the time domain data of the 0-value interpolation characteristic data have the same frequency component.

The time direction characteristic estimation data is a series of sample values representing transmission line characteristics for each of the three subcarriers. If the effective symbol length is Tu [seconds] and the interval between subcarriers is Fc [Hz], the equation Fc = 1 / Tu [Hz] holds, so this is a series of sample values representing the transmission line characteristics for each of the three subcarriers. The interval between the sample values of the temporal characteristic estimation data is 3Fc = 3 / Tu [Hz].

Therefore, the interval between the sample values of the 0-value interpolation characteristic data obtained by interpolating two zeros between the sample values of the time-direction characteristic estimation data is Fc = 1 / Tu [Hz].

On the other hand, the time-direction characteristic estimation data in which the interval between sample values is 3Fc = 3 / Tu [Hz] is data in which 1 / 3Fc = Tu / 3 [seconds] is one cycle in the time domain.

In addition, the 0-value interpolation characteristic data in which the interval between sample values is Fc = 1 / Tu [Hz] is the data in which 1 / Fc = Tu [second] is one cycle in the time region, that is, the time direction characteristic estimation data. It is the data that one cycle is three times the cycle of.

As described above, the time domain data of the time domain characteristic estimation data has the same frequency component as the time domain data, and the time domain data of the 0-value interpolation characteristic data having three times the cycle as one cycle is the time domain characteristic estimation. The data in the time domain of the data is repeated three times.

FIG. 23 is a diagram showing an example of data in the time domain of the zero-value interpolation characteristic data.

Here, the case where there are two paths, the main wave and the delayed wave, will be described. The horizontal axis of FIG. 23 represents time, and the vertical axis represents the power level of the path.

The 0-value interpolation characteristic data with a period of Tu [seconds] is the one in which the multipath corresponding to the time-direction characteristic estimation data with a period of Tu / 3 [seconds] is repeated three times in the time domain.

Now, assuming that the central multipath shown by the diagonal line in FIG. 23 is extracted as the frequency direction characteristic interpolation data, the other multipaths are removed in order to obtain the desired multipath corresponding to the frequency direction characteristic interpolation data. There is a need to.

Therefore, in the interpolation filter circuit 42, by filtering the 0-value interpolation characteristic data, the multipaths other than the desired multipaths are removed, and the desired multipaths corresponding to the frequency direction characteristic interpolation data are extracted.

The 0-value interpolation characteristic data is data in the frequency domain, and the filtering of the 0-value interpolation characteristic data in the interpolation filter circuit 42 is performed by combining the filter coefficient of the interpolation filter and the 0-value interpolation characteristic data which is the data in the frequency domain. It becomes a convolution.

Since the convolution in the frequency domain is a multiplication with the window function in the time domain, the filtering of the 0-value interpolation characteristic data corresponds to the 0-value interpolation characteristic data and the pass band of the interpolation filter circuit 42 in the time domain. It can be expressed as a multiplication with a window function. The window function shown by the thick line in FIG. 23 represents a function corresponding to the pass band of the interpolation filter circuit 42, which is used for multiplication as filtering of 0-value interpolation characteristic data.

The multipath cycle repeated three times is Tu / 3 [seconds]. Therefore, the interpolation filter should be, for example, an LPF having a pass band of -Tu / 6 to + Tu / 6, which has the same width as the multipath period Tu / 3 [sec] repeated three times. Therefore, the desired multipath corresponding to the frequency direction characteristic interpolation data can be extracted.

Tu / 3, which is the width of the pass band of the interpolation filter appropriately used in the interpolation filter circuit 42, can obtain the transmission line characteristics for each subcarrier by estimating the transmission line characteristics in the time direction in this way. Determined by.

The interpolation filter circuit 42 outputs the estimation result of the transmission line characteristics of all the subcarriers estimated by the frequency interpolation processing to the division circuit 8-4 in FIG.

The division circuit 8-4 corrects and equalizes the distortion included in the OFDM frequency domain signal based on the transmission line characteristics of all the subcarriers supplied from the frequency interpolation circuit 32. The division circuit 8-4 outputs a distortion-corrected OFDM frequency domain signal (OFDM frequency domain signal after transmission line distortion compensation) to the error correction circuit 9.

The distortion caused by the multipath that the OFDM signal receives in the transmission line is a multiplication of the OFDM signal. The correction of the distortion that the OFDM signal receives on the transmission line is realized by dividing the actually received OFDM signal by the transmission line characteristics.

The error correction circuit 9 outputs the data obtained by performing various processes to the subsequent circuit as decoded data.

The delay profile estimation circuit 10 estimates the delay profile of the transmission line and outputs the delay profile to the FFT section control circuit 7.

The optimum filter coefficient selection circuit 31 tries frequency interpolation processing under a plurality of conditions by using an interpolation filter in which the width of the pass band and the center position are changed. For example, for each pass band of the filter bands BW0 to BW3 in FIG. 5, frequency interpolation processing is tried under each condition in which the center position is shifted by a predetermined width.

Further, the optimum filter coefficient selection circuit 31 corrects the distortion of the OFDM frequency domain signal supplied from the FFT circuit 6 based on the transmission line characteristics of all the subcarriers obtained by trying the frequency interpolation processing. The optimum filter coefficient selection circuit 31 calculates the quality of each distortion-corrected OFDM frequency domain signal.

The optimum filter coefficient selection circuit 31 selects the interpolation filter having the best quality, and outputs a coefficient representing the width and center position of the pass band of the interpolation filter to the frequency interpolation circuit 32.

In the optimum filter coefficient selection circuit 31, for example, the width and center position of the pass band of the interpolation filter that can obtain the best quality signal are obtained for each symbol.

FIG. 24 is a diagram showing a configuration example of the optimum filter coefficient selection circuit 31.

The controller 51 holds the data of the same symbol, and controls the reading and writing of the memories 52 and 53 so that the data of the same symbol held is read. Further, the controller 51 outputs a trial coefficient representing the width and center position of the pass band of the trial interpolation filter to the frequency interpolation circuit 54 and the optimum value selection circuit 57.

The memory 52 holds the OFDM frequency domain signal supplied from the FFT circuit 6 for one symbol under the control of the controller 51. The one-symbol OFDM frequency domain signal held by the memory 52 is read out by the transmission line distortion correction circuit 55.

The memory 53 holds the time-direction characteristic estimation data for one symbol, which is the data representing the transmission line characteristics for each of the three subcarriers estimated by the time-direction transmission line characteristic estimation circuit 8-2 under the control of the controller 51. The time direction characteristic estimation data of one symbol held by the memory 53 is read out by the frequency interpolation circuit 54.

The frequency interpolation circuit 54 has the same configuration as the frequency interpolation circuit 32 of FIG. The frequency interpolation circuit 54 upsamples the sample value of the time direction characteristic estimation data three times, and performs frequency interpolation processing using an interpolation filter that adjusts the width and center position of the passband according to the trial coefficient supplied from the controller 51. Do.

The frequency interpolation circuit 54 outputs the transmission line characteristics of all the subcarriers obtained by performing the frequency interpolation processing to the transmission line distortion correction circuit 55.

In the frequency interpolation circuit 54, the frequency interpolation processing was performed a plurality of times by changing the width and the center position of the pass band of the interpolation filter for the data obtained from the same symbol, and each of them was obtained by the frequency interpolation processing. The transmission line characteristics are output. As described above, the path may or may not be included in the pass band of the interpolation filter depending on the width and center position of the pass band. Therefore, the transmission line characteristics obtained by the frequency interpolation process are obtained for each trial coefficient set by the controller 51. Will be different as appropriate.

The transmission line distortion correction circuit 55 corrects the distortion of the transmission line included in the one-symbol OFDM frequency domain signal read from the memory 52 each time the transmission line characteristic is supplied from the frequency interpolation circuit 54. The transmission line distortion correction circuit 55 outputs the distortion-corrected OFDM frequency domain signal to the signal quality calculation circuit 56.

The signal quality calculation circuit 56 calculates the quality of each time the one-symbol OFDM frequency domain signal is supplied from the transmission line distortion correction circuit 55, and outputs the calculated quality to the optimum value selection circuit 57 as a trial result. For example, the signal quality calculation circuit 56 calculates the power of noise contained in the OFDM frequency domain signal and outputs the value.

The optimum value selection circuit 57 sequentially holds the quality calculated by the signal quality calculation circuit 56, and changes the width and center position of the pass band of the interpolation filter for the one-symbol OFDM frequency domain signal of interest. Continue until all pattern trials are complete.

The optimum value selection circuit 57 selects the interpolation filter used to generate the best quality OFDM frequency domain signal when the trial results of all patterns are acquired, and the passband width and center of the selected interpolation filter. Identify the location. In the optimum value selection circuit 57, for the one-symbol OFDM frequency domain signal of interest, it is best to use an interpolation filter having a pass band of what width and set which position as the center position of the pass band. It will be specified whether a quality signal can be obtained.

The optimum value selection circuit 57 outputs a coefficient representing the width and center position of the pass band of the selected interpolation filter to the frequency interpolation circuit 32.

Hereinafter, the interpolation filter used to generate the best quality OFDM frequency domain signal as appropriate is referred to as an optimum filter. In the frequency interpolation circuit 32, the frequency interpolation processing is performed on the width and the center position of the pass band by using an interpolation filter having the same characteristics as the optimum filter (pass band of the same width and the center position).

[Receiver operation] Next, the operation of the OFDM receiver 103 having the above configuration will be described.

First, the reception process of the OFDM receiver 103 will be described with reference to the flowchart of FIG. 25.

The processing of each step is performed not only in numerical order but also in parallel with or before and after the processing of other steps as appropriate.

In step S51, the tuner 2 frequency-converts the RF signal received by the receiving antenna 1 and outputs the IF signal.

In step S52, the A / D conversion circuit 3 performs A / D conversion on the IF signal and outputs a digital IF signal.

In step S53, the orthogonal demodulation circuit 4 performs orthogonal demodulation and outputs an OFDM time domain signal.

In step S54, the FFT circuit 6 performs the FFT calculation according to the control by the FFT section control circuit 7, and outputs an OFDM frequency domain signal.

In step S55, the SP extraction circuit 8-1 extracts the SP signal from the OFDM frequency domain signal and estimates the transmission path characteristics of the subcarrier with respect to the SP signal.

In step S56, the time-direction transmission line characteristic estimation circuit 8-2 estimates the transmission line characteristics for each of the three subcarriers and outputs the time-direction characteristic estimation data.

In step S57, the delay profile estimation circuit 10 estimates the delay profile based on the time direction characteristic estimation data.

In step S58, the optimum filter coefficient selection circuit 31 performs the filter coefficient selection process. The coefficient selected by the filter coefficient selection process is output to the frequency interpolation circuit 32. The filter coefficient selection process will be described later with reference to the flowchart of FIG.

In step S59, the FFT section control circuit 7 controls the FFT calculation by the FFT circuit 6.

In step S60, the frequency interpolation circuit 32 upsamples the sample value of the time direction characteristic estimation data, and uses an interpolation filter in which the width and center position of the passband are adjusted based on the coefficient selected by the filter coefficient selection process. Frequency interpolation processing is performed.

In step S61, the division circuit 8-4 corrects the distortion contained in the OFDM frequency domain signal based on the transmission line characteristics of all the subcarriers obtained by the frequency interpolation processing.

In step S62, the error correction circuit 9 performs processing such as error correction on the distortion-corrected OFDM frequency domain signal, and outputs the decoded data.

The above processing is repeated by the OFDM receiver 103 while receiving the signal.

Next, the filter coefficient selection process performed in step S58 of FIG. 25 will be described with reference to the flowchart of FIG. 26.

This process is started when the one-symbol OFDM frequency domain signal is read from the memory 52 in FIG. 24 and the time-direction characteristic estimation data for one symbol is read from the memory 53. The OFDM frequency domain signal read from the memory 52 and the time direction characteristic estimation data read from the memory 53 are signals and data for the same symbol.

In step S71, the controller 51 selects the width and center position of the pass band of the interpolation filter, and outputs a trial coefficient representing the selected width and center position.

In step S72, the frequency interpolation circuit 54 performs frequency interpolation processing using an interpolation filter whose width and center position of the pass band are adjusted according to the trial coefficient.

In step S73, the transmission line distortion correction circuit 55 corrects the distortion of the transmission line included in the OFDM frequency domain signal based on the transmission line characteristics obtained by the frequency interpolation processing.

In step S74, the signal quality calculator 56 calculates the quality of the distortion-corrected OFDM frequency domain signal. The quality calculated by the signal quality calculation circuit 56 is held by the optimum value selection circuit 57.

In step S75, the signal quality calculation circuit 56 determines whether or not the frequency interpolation processing of all patterns has been tried for the target symbol by changing the width and center position of the pass band of the interpolation filter. If it is determined in step S75 that the frequency interpolation processing of all patterns has not been tried, the process returns to step S71, and the above processing is repeated by changing at least one of the width and the center position of the pass band.

On the other hand, when it is determined in step S75 that the frequency interpolation processing of all patterns has been tried, the optimum value selection circuit 57 selects the optimum filter based on the trial results of all patterns in step S76. The optimum value selection circuit 57 outputs a coefficient representing the width and center position of the pass band of the optimum filter.

After that, the process returns to step S58 in FIG. 25, and the subsequent processing is performed.

By the above processing, the frequency interpolation processing is applied to the frequency interpolation circuit 32 by using an interpolation filter having a passband width and a center position that can finally obtain a signal of the best quality as an OFDM frequency domain signal after distortion correction. Can be done. As an image, frequency interpolation processing is performed using an interpolation filter as shown in FIG. 18B, which includes all paths in the pass band and does not include white noise as much as possible.

When finding the optimum filter passband by the sequence processing described with reference to FIG. 9, a sufficient number of integrations are required to obtain a correct solution. This is because the reception status such as white noise changes minutely even in a fixed reception environment, and frequency interpolation processing, distortion correction, etc. are performed on the data of different symbols, and the signal quality as the trial result is compared. Then, a reversal phenomenon can occur. Although the inversion phenomenon is originally an interpolation filter that can obtain a signal with better quality than other interpolation filters, it is possible to obtain only a signal with poorer quality than other interpolation filters due to the influence of the reception condition. It is a phenomenon that disappears.

Therefore, by selecting the width and center position of the pass band of the interpolation filter as described above, it is possible to shorten the time required to obtain the correct solution as compared with the case of performing the sequence processing of FIG. ..

Further, the synchronous pull-in time can be shortened, and even if the OFDM receiver 103 is a mobile body and the receiving environment is a time-varying environment, it is possible to have the ability to follow the fluctuation of the environment.

Furthermore, since the quality of the signals obtained by processing the same symbol under multiple conditions is compared, even if the reception status fluctuates with time, it is not affected by it. It becomes possible to stabilize the comparison result.

&lt;Modification example 1&gt; FIG. 27 is a block diagram showing another configuration example of the optimum filter coefficient selection circuit 31.

Of the configurations shown in FIG. 27, the same configurations as those shown in FIG. 24 are designated by the same reference numerals. Duplicate explanations will be omitted as appropriate.

The frequency interpolation circuit 54 of FIG. 27 is composed of frequency interpolation circuits 54-1 to 54-N, and the transmission line distortion correction circuit 55 is composed of transmission line distortion correction circuits 55-1 to 55-N. The signal quality calculation circuit 56 is composed of signal quality calculation circuits 56-1 to 56-N.

The controller 51 outputs trial coefficients 1 to N representing the width and center position of the pass band of the interpolation filter to the frequency interpolation circuits 54-1 to 54-N and the optimum value selection circuit 57. The trial coefficients 1 to N represent the characteristics of different interpolation filters.

Each of the frequency interpolation circuits 54-1 to 54-N performs frequency interpolation processing using an interpolation filter whose width and center position of the pass band are adjusted according to the trial coefficient supplied from the controller 51. The frequency interpolation circuits 54-1 to 54-N perform frequency interpolation processing under different conditions in parallel in time.

The frequency interpolation circuits 54-1 to 54-N output the transmission line characteristics of all the subcarriers obtained by performing the frequency interpolation processing to the transmission line distortion correction circuits 55-1 to 55-N, respectively.

The transmission line distortion correction circuits 55-1 to 55-N use the transmission line characteristics supplied from the frequency interpolation circuits 54-1 to 54-N, respectively, to convert the 1-symbol OFDM frequency domain signal read from the memory 52. Correct the distortion of the included transmission line. The transmission line distortion correction circuits 55-1 to 55-N output the distortion-corrected OFDM frequency domain signal to the signal quality calculation circuits 56-1 to 56-N, respectively.

The signal quality calculation circuits 56-1 to 56-N calculate the quality each time a 1-symbol OFDM frequency domain signal is supplied from the transmission line distortion correction circuits 55-1 to 55-N, respectively, and select the optimum value. Output to circuit 57.

The optimum value selection circuit 57 maintains the quality calculated by the signal quality calculation circuits 56-1 to 56-N. The optimum value selection circuit 57 selects an optimum filter based on the trial results of all patterns, and outputs a coefficient representing the width and center position of the pass band to the frequency interpolation circuit 32.

In this way, the frequency interpolation processing under different conditions, the processing for correcting the distortion of the transmission line, and the processing for calculating the signal quality are performed in parallel in time, so that the frequency interpolation circuit 32 has a coefficient. It is possible to shorten the time required to output.

As shown in FIG. 27, the frequency interpolation circuit 54, the transmission line distortion correction circuit 55, and the signal quality calculation circuit 56 are not each composed of a plurality of circuits, but only the frequency interpolation circuit 54 is composed of a plurality of circuits for transmission. It is also possible to configure the path distortion correction circuit 55 and the signal quality calculation circuit 56 with one circuit each.

&lt;Transformation example 2&gt; FIG. 28 is a block diagram showing a configuration example of the OFDM receiver 104.

Of the configurations shown in FIG. 28, the same configurations as those shown in FIG. 19 are designated by the same reference numerals. Duplicate explanations will be omitted as appropriate.

In the example of FIG. 28, the information on the position of the center of gravity is supplied from the FFT section control circuit 7 to the optimum filter coefficient selection circuit 31.

The FFT section control circuit 7 determines the FFT section based on the delay profile estimated by the delay profile estimation circuit 10, outputs the FFT trigger pulse, and provides information on the position of the center of gravity determined based on, for example, the following equation (1). Is output to the optimum filter coefficient selection circuit 31. The arrival time and power of each path are represented by the delay profile estimated by the delay profile estimation circuit 10.<maths num="1"><img file="JP2010141907A_D0001.tif" /></maths>

The delay profile is based on the correlation with other sections based on the GI section by utilizing the fact that the GI section and the GI copy source section are the same signal when focusing on one symbol. May be requested. The method of determining the position of the center of gravity can be changed as appropriate.

The optimum filter coefficient selection circuit 31 performs frequency interpolation processing by changing the width and center position of the pass band of the interpolation filter. At this time, the center position of the pass band is the center of gravity position obtained by the FFT section control circuit 7. The processing is performed by changing only within the range determined by the center.

FIG. 29 is a block diagram showing a configuration example of the optimum filter coefficient selection circuit 31 of FIG. 28.

Of the configurations shown in FIG. 29, the same configurations as those shown in FIG. 24 are designated by the same reference numerals. Duplicate explanations will be omitted as appropriate. The information on the position of the center of gravity output from the FFT section control circuit 7 is input to the controller 51.

The controller 51 controls reading and writing of the memories 52 and 53, and outputs a trial coefficient representing the width and center position of the pass band of the interpolation filter to the frequency interpolation circuit 54 and the optimum value selection circuit 57.

FIGS. 30A and 30B are diagrams showing an example of a variable range of the center position of the pass band of the interpolation filter.

A case where there are paths P, Q, and R as shown in FIG. 30A and the position indicated by the black-painted upward triangle is obtained as the position of the center of gravity will be described.

In this case, assuming that the position of the center of gravity is gp and the width of the pass band of the interpolation filter is BWX, the optimum filter coefficient selection circuit 31 sets the center position of the pass band of the interpolation filter to -BWX / 2 + gp as shown in FIG. 30B. Frequency interpolation processing is performed by changing within the range of + BWX / 2 + gp.

By limiting the variable range of the center position of the pass band of the interpolation filter in this way, the number of trials can be reduced as compared with the case where the frequency interpolation process is tried by changing the center position without limitation.

The position of the center of gravity is used as the reference position of the variable range, but any position should be used as the reference if it is a position between the position of the earliest arrival path and the position of the latest arrival path. It may be.

For example, the variable range may be a range extended by BWX / 2 back and forth around the center position of the position of the earliest arrival path and the position of the latest arrival path, which is obtained based on the delay profile. ..

&lt;Modification example 3&gt; FIG. 31 is a block diagram showing a configuration example of the OFDM receiver 105.

Of the configurations shown in FIG. 31, the same configurations as those shown in FIG. 19 are designated by the same reference numerals. Duplicate explanations will be omitted as appropriate.

In the example of FIG. 31, the information of the center position of the pass band of the optimum filter is fed back from the optimum filter coefficient selection circuit 31 to the delay profile estimation circuit 10.

Further, it is assumed that the interpolation filter used by the frequency interpolation circuit 32 has a fixed pass band width of Tu / 3 [seconds] and is variable only at the center position of the pass band. The trial interpolation filter used for the frequency interpolation processing in the optimum filter coefficient selection circuit 31 also has a fixed passband width of Tu / 3 [sec], and only the center position of the passband is variable.

FIG. 32 is a block diagram showing a configuration example of the optimum filter coefficient selection circuit 31 of FIG. 31.

Of the configurations shown in FIG. 32, the same configurations as those shown in FIG. 24 are designated by the same reference numerals. Duplicate explanations will be omitted as appropriate.

The frequency interpolation circuit 54 adjusts the center position of the pass band of the interpolation filter having a pass band with a width of Tu / 3 [seconds] according to the trial coefficient supplied from the controller 51, and performs the frequency interpolation process.

The optimum value selection circuit 57 selects the optimum filter based on the trial results of all patterns, and outputs a coefficient representing the center position of the pass band of the optimum filter to the frequency interpolation circuit 32.

Further, the optimum value selection circuit 57 outputs information indicating the center position of the pass band of the optimum filter. The information output from the optimum value selection circuit 57 is input to the delay profile estimation circuit 10.

The delay profile estimation circuit 10 in FIG. 31 determines the time direction characteristic estimation data supplied from the time direction transmission line characteristic estimation circuit 8-2 and the center position of the pass band of the optimum filter supplied from the optimum filter coefficient selection circuit 31. Estimate the delay profile based on the information represented.

33A to 33D are diagrams illustrating the estimation of the delay profile.

Here, too, the case where there are paths P, Q, and R as shown in FIG. 33A will be described.

In the delay profile estimation circuit 10, the delay profile is obtained by applying IFFT to the time direction characteristic estimation data. Due to the nature of the IFFT, as shown in Fig. 33B, path wrapping occurs every Tu / 3, which is the reciprocal of the SP signal interval (Fig. 2).

The configuration of the desired path extracted from the entire path including the path of the wrapping component is the delay profile, but when looking only at the IFFT result, the path R'before the path P is the path of the wrapping component. The delay profile estimation circuit 10 cannot determine whether the path is the actual path or the path.

Therefore, a mechanism for determining whether or not each path is a path of a folding component is required, and the central position of the pass band of the optimum filter is used for that determination.

As described above, if all the paths do not fit in the pass band of the interpolation filter, the quality of the OFDM frequency domain signal after distortion correction deteriorates.

Further, when the path of the non-existent folding component is included in the pass band of the interpolation filter, the quality of the OFDM frequency domain signal after distortion correction is deteriorated.

That is, selecting the optimum filter results in selecting an interpolation filter that does not include the path of the folding component in the pass band. It is considered that the pass band of the optimum filter contains all the existing paths and does not include the paths of the folding component.

This is utilized in the delay profile estimation circuit 10 to estimate the delay profile.

That is, as shown in FIG. 33C, the delay profile estimation circuit 10 deletes paths other than those in the range of -Tu / 6 to + Tu / 6 centered on the same position as the center position of the pass band of the optimum filter. Then, the desired path as shown in FIG. 33D is extracted. The path configuration in FIG. 33D is the same as the actual path configuration shown in FIG. 33A.

In this way, by using the center position of the pass band of the optimum filter, for example, before and after the path, it is determined that there is a path before that even though it is actually the earliest arrival path. It becomes possible to prevent misrecognition of the relationship. By correctly recognizing the context of the path, it is possible to improve the accuracy of the estimation result of the delay profile.

The series of processes described above can be executed by hardware or software. When a series of processes are executed by software, the programs that make up the software execute various functions by installing a computer embedded in dedicated hardware or various programs. It is installed from a program recording medium on a general-purpose personal computer that can be used.

FIG. 34 is a block diagram showing a configuration example of the hardware of a computer that executes the above-mentioned series of processes programmatically.

The CPU (Central Processing Unit) 71, ROM (Read Only Memory) 72, and RAM (Random Access Memory) 73 are connected to each other by a bus 74.

An input / output interface 75 is further connected to the bus 74. The input / output interface 75 includes an input unit 76 consisting of a keyboard, mouse, microphone, etc., an output unit 77 consisting of a display, a speaker, etc., a storage unit 78 consisting of a hard disk, a non-volatile memory, etc., and a communication unit 79 consisting of a network interface, etc. , The drive 80 that drives the removable media 81 such as an optical disk or a semiconductor memory is connected.

In the computer configured as described above, the CPU 71 loads the program stored in the storage unit 78 into the RAM 73 via the input / output interface 75 and the bus 74 and executes the program, thereby executing the series of processes described above. Is done.

The program executed by the CPU 71 is recorded on the removable media 81, or provided via a wired or wireless transmission medium such as a local area network, the Internet, or a digital broadcast, and installed in the storage unit 78.

The program executed by the computer may be a program that is processed in chronological order according to the order described in this specification, or may be a program that is processed in parallel or at a necessary timing such as when a call is made. It may be a program in which processing is performed.

The embodiment of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention.

101,102 OFDM receiver, 1 receiving antenna, 2 tuner, 3 A / D conversion circuit, 4 orthogonal demodulation circuit, 5 carrier generation circuit, 6 FFT circuit, 7 FFT section control circuit, 8 transmission path distortion compensation circuit, 8-1 SP Extraction circuit, 8-2 Time direction transmission line characteristic estimation circuit, 8-3 Frequency interpolation circuit, 8-4 Dividing circuit, 9 Error correction circuit, 10 Delay profile estimation circuit, 11 Frequency interpolation filter selection circuit, 21 Optimal frequency interpolation filter Selection circuit, 21-1 selection circuit, 21-2 control circuit, 21-3 frequency interpolation circuit, 21-4 division circuit, 21-5 signal quality detection circuit