JP5689271B2 - OFDM receiver - Google Patents

Description

  The present invention relates to an OFDM receiver that receives broadcast waves of an OFDM (Orthogonal Frequency Division Multiplex) scheme.

  In OFDM, a wideband digital signal is divided into a plurality of relatively slow digital streams, which are transmitted on a plurality of carriers having carrier frequencies that are orthogonal and close to each other. Currently, DVB-T (Digital Video Broadcasting-Terrestrial) and ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) are known as broadcasting standards adopting such OFDM. In these DVB-T and ISDB-T OFDM broadcast waves, a scattered pilot signal (hereinafter referred to as an SP signal) having a predetermined complex amplitude is dispersed and superimposed on a predetermined subcarrier. .

  In a receiving apparatus that receives such an OFDM broadcast wave, first, the received OFDM signal is subjected to down-conversion, AD conversion, quadrature detection, guard invar removal, etc., and then subjected to FFT to calculate a reception subcarrier complex amplitude in the frequency domain. To do. Then, based on the reception subcarrier complex amplitude, the SP transmission path transfer characteristic for the subcarrier on which the SP signal is superimposed is obtained. Next, an interpolation filter process is performed on the SP transmission line transfer characteristic in the symbol time direction to obtain a partial area transmission line transfer characteristic. Further, an interpolation filter process is performed in the subcarrier frequency direction for the partial region transmission line transfer characteristics to obtain estimated transmission line transfer characteristics for all subcarriers. Then, using the estimated transmission path transfer characteristic, the reception subcarrier complex amplitude is equalized, and processing such as demapping and Reed-Solomon decoding is performed to restore the transmission data.

  Here, in performing the interpolation process in the subcarrier frequency direction in the sub-domain transmission line transfer characteristic, a filtering process in which a pass band is limited using a complex BPF (Band Pass Filter) in order to remove aliasing components due to aliasing To give. At this time, the complex BPF needs to set an appropriate passband in consideration of various multipath reception environments.

  Therefore, in order to suppress interference due to multipath, inverse fast Fourier transform (hereinafter referred to as IFFT) processing is performed on the transmission characteristics of the partial area transmission line, thereby reducing the delay time due to the difference in the arrival distance of each path in the reflected wave. A technique has been proposed in which a delay profile representing a power distribution is obtained, and a passband of a complex BPF is set based on the delay profile (see, for example, FIG. 5 of Patent Document 1).

By the way, in such a method, for example, in the case of ISDB-T, the partial area transmission path transfer characteristic can be obtained only for every three subcarriers. Therefore, the delay time range of the delay profile obtained by performing the IFFT processing on the partial area transmission path transmission characteristics is only 1/3 (± 1/6) of the effective symbol length in the OFDM signal. Therefore, in a multipath reception environment exceeding this delay time range, aliasing may occur in the delay profile obtained as described above. When the complex BPF passband is set based on the delay profile in which aliasing occurs, there is a problem that reception performance is greatly deteriorated because the complex BPF is set so as to deviate from the desired passband.
Japanese Patent No. 0360648

An object of the present invention is to provide an OFDM receiver capable of appropriately equalizing a received OFDM signal and restoring transmission data with high accuracy.

The OFDM receiver according to claim 1 includes a plurality of subcarriers each subcarrier modulated according to a modulation parameter, and a scattered pilot signal is distributed and superimposed in each of the subcarriers in a time direction and a frequency direction. An OFDM receiver for receiving an orthogonal frequency division multiplex transmission signal, a Fourier transform unit for converting the orthogonal frequency division multiplex transmission signal into a reception subcarrier complex amplitude for each subcarrier, and superimposing on the reception subcarrier complex amplitude An SP transmission line transmission characteristic calculating unit for calculating an SP transmission line transmission characteristic in the scattered pilot signal, and a partial area transmission in a part of the subcarrier by interpolating the SP transmission line transmission characteristic in a time direction. A time direction interpolation unit for calculating a path transfer characteristic, and the partial region A frequency direction interpolation unit for calculating an estimated transmission line transfer characteristic by interpolating a transmission line transfer characteristic in the frequency direction; and dividing the received subcarrier complex amplitude by the estimated transmission line transfer characteristic to obtain the received subcarrier complex amplitude. An equalization division unit that calculates equalized subcarrier complex amplitudes, and a signal point that is closest to the equalized subcarrier complex amplitude among signal points mapped based on the modulation parameter of each subcarrier. Based on the signal point determination unit that is calculated as the determination subcarrier complex amplitude, and the determination subcarrier complex amplitude and the reception subcarrier complex amplitude , the distribution of power with respect to the delay time due to the difference in the reach of each path in the reflected wave A delay profile calculator for calculating a delay profile; and the frequency direction compensation based on the delay profile. Comprising a filter control unit for controlling the filter characteristic parts, wherein the frequency direction interpolation unit includes a complex band-pass filter, the filter control unit of the passband of the complex band-pass filter on the basis of the delay profile A central time point detection unit for detecting a central time point and generating an offset signal indicating the central time point; a memory in which low-pass filter coefficients having the same pass bandwidth as the pass band width of the complex band pass filter are stored; A filter coefficient generation unit that generates a filter coefficient of the complex bandpass filter based on the low-pass filter coefficient and the offset signal.

It is a figure which shows the whole structure of an OFDM receiver. It is a figure which shows the internal structure of the equalization part 6 shown by FIG. It is a figure which shows an OFDM frame structure. It is a figure which shows the position in the OFDM frame of the transmission-line transfer characteristic value obtained by interpolating in a time direction. 7 is a diagram illustrating an example of an internal configuration of a delay profile calculation unit 65. FIG. It is a figure which shows an example of the delay profile calculated by the delay profile calculation part. It is a figure which shows the operation | movement of the convolution process performed in the BPF center detection part 661. It is a figure which shows another example of the internal structure of the delay profile calculation part.

  An orthogonal frequency division multiplex transmission signal in which SP signals are dispersed and superimposed in the time direction and the frequency direction in each subcarrier modulated by each subcarrier according to a modulation parameter is converted into a reception subcarrier complex amplitude for each subcarrier, The SP transmission path transfer characteristic in the SP signal superimposed on the reception subcarrier complex amplitude is calculated. Next, the estimated transmission path transmission characteristics in all subcarriers are obtained by interpolating the SP transmission path transmission characteristics in the time direction and the frequency direction. Then, an equalized subcarrier complex amplitude obtained by equalizing the received subcarrier complex amplitude is calculated by dividing the received subcarrier complex amplitude by the estimated transmission path transfer characteristic.

  Here, when interpolation in the frequency direction is performed by the complex bandpass filter, the central time point of the passband (period) of the complex bandpass filter is controlled based on the delay profile calculated as follows. That is, the signal point closest to the equalized subcarrier complex amplitude among the signal points mapped based on the modulation parameter of each subcarrier is obtained as the determination subcarrier complex amplitude. Then, the reception subcarrier complex amplitude is divided by the determination subcarrier complex amplitude, and an IFFT process and a square operation process are performed on the division result to obtain a delay profile.

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

  FIG. 1 is a diagram illustrating a configuration of an OFDM receiving apparatus.

  The OFDM receiver shown in FIG. 1 includes an antenna 1, a tuner unit 2, an A / D conversion unit 3, an orthogonal detection unit 4, an FFT (Fast Fourier Transform) unit 5, an equalization unit 6, and a decoder unit 7.

  The antenna 1 supplies a received signal obtained by receiving an OFDM broadcast wave wirelessly transmitted from the broadcast station side to the tuner unit 2.

  The tuner unit 2 extracts a signal in a desired band from the received signal, and supplies the A / D conversion unit 3 as an OFDM received signal after down-converting the signal to an intermediate frequency band signal.

  The A / D conversion unit 3 samples the OFDM reception signal at a predetermined sampling timing, converts it to an OFDM reception sample value sequence composed of a digital sample value sequence, and supplies this to the quadrature detection unit 4.

  The quadrature detection unit 4 performs quadrature detection on the OFDM reception sample value series, further removes the guard interval, thereby converting it into a baseband OFDM modulated signal, and supplies this to the FFT unit 5.

  The FFT unit 5 performs fast Fourier transform processing (hereinafter referred to as FFT processing) on the OFDM modulated signal to convert it to a reception subcarrier complex amplitude Y representing the complex amplitude of each subcarrier in the frequency domain, This is supplied to the equalization unit 6.

  Based on the reception subcarrier complex amplitude Y, the equalization unit 6 estimates the estimated transmission path transfer characteristic DD in the transmission path between the OFDM receiver and the broadcast station. Then, the received subcarrier complex amplitude Y is waveform-equalized by the estimated transmission line transfer characteristic DD to obtain an equalized subcarrier complex amplitude X, which is supplied to the decoder 7.

  The decoder 7 performs a decoding process on the equalized subcarrier complex amplitude X. That is, the decoder 7 performs deinterleaving processing, error correction processing, and the like, and outputs decoded data.

  In the present invention, the configurations of the antenna 1, the tuner unit 2, the A / D conversion unit 3, the quadrature detection unit 4, and the decoder unit 7 are not limited to such examples.

  FIG. 2 is a diagram showing a detailed configuration of the equalization unit 6 according to the present invention.

  2 includes an SP transmission path transfer characteristic calculation unit 60, a memory 61, a time direction interpolation unit 62, a frequency direction interpolation unit 63, a delay unit 64, a delay profile calculation unit 65, a filter control unit 66, and the like. The division unit 68 and the signal point determination unit 69 are provided.

The SP transmission path transfer characteristic calculation unit 60 includes an SP extraction unit 601, an SP signal generation unit 602, and an SP division unit 603. The SP extraction unit 601 extracts the SP signal in the reception subcarrier complex amplitude Y supplied from the FFT unit 5. That is, the SP extraction unit 601 extracts SP signals (indicated by black circles) that are dispersed and superimposed in the frequency direction (subcarrier direction) and the time direction (symbol direction) in the OFDM frame as shown in FIG. Do. In FIG. 3, the SP signal is superimposed on 12 subcarriers at a rate of 1 in the frequency direction, and the superposition position circulates by 3 subcarriers per symbol. SP extracting unit 601 supplies the extracted SP signals to the SP division unit 603 as a received SP complex amplitude _{S R.} SP signal generation unit 602 generates a known transmission SP complex amplitude _{S T} at the receiving SP complex amplitude _{S R,} and supplies the SP divider 603. SP division unit 603, in each sub-carrier of the SP signal in FIG. 3 (indicated by black circles), determined the SP transmission path transfer characteristic SD by dividing the received SP complex amplitude _{S R} by the transmission SP complex amplitude _{S T} To the memory 61. Note that the SP transmission path transfer characteristic SD in each subcarrier (indicated by white circles) of the information transmission signal in FIG.

  The memory 61 stores the SP transmission path transfer characteristic signal SD supplied from the SP extraction unit 601 and supplies it to the time direction interpolation unit 62.

  The time direction interpolation unit 62 includes, for example, a 9-tap FIR (Finite Impulse Response) filter, and interpolates the SP transmission path transfer characteristic SD in the time direction. As a result, as shown in FIG. 4, interpolated transmission line transfer characteristics (indicated by double circles in FIG. 4) corresponding to each of three symbols existing between SP signals adjacent to each other in the time direction are obtained. Then, as shown in FIG. 4, the time direction interpolation unit 62 uses the interpolated transmission line transfer characteristic and the SP transmission line transfer characteristic, so that the partial area transmission line transfer characteristic in every third subcarrier, that is, in one third of all subcarriers. TD is supplied to the frequency direction interpolation unit 63.

  The frequency direction interpolation unit 63 includes a complex bandpass filter (hereinafter referred to as a complex BPF) composed of, for example, a 25-tap FIR filter. Note that the coefficient of this complex BPF is a variable coefficient filter supplied from the filter coefficient generation unit 662 as the filter coefficient k. The frequency direction interpolation unit 63 sets the partial area transmission line transfer characteristic TD, that is, the interpolation transmission line transfer characteristic (shown by a double circle) and the SP transmission line transfer characteristic (shown by a black circle) as shown in FIG. 4 in the frequency direction. By performing the interpolation, the estimated transmission line transfer characteristic DD in all subcarriers is obtained and supplied to the equalization division unit 68.

  The delay unit 64 delays the reception subcarrier complex amplitude Y supplied from the FFT unit 5 by a time corresponding to the processing time spent in the time direction interpolation unit 62 and the frequency direction interpolation unit 63. Is supplied to the delay profile calculation unit 65 and the equalization division unit 68.

  The equalizing / dividing unit 68 calculates an equalized subcarrier complex amplitude X by dividing the received subcarrier complex amplitude YD by the estimated transmission line transfer characteristic DD, and supplies the equalized subcarrier complex amplitude X to the decoder 7 and the signal point determining unit 69. Supply.

The signal point determination unit 69 transmits a signal point having the closest distance to the equalized subcarrier complex amplitude X among a plurality of signal points mapped based on the modulation parameter (for example, QPSK or QAM) of each subcarrier. The signal point is determined and supplied to the delay profile calculator 65 as a determined subcarrier complex amplitude Q. However, since the transmission signal points in each sub-carrier of the SP signal is known, determination subcarrier complex amplitude Q uses a transmission SP complex amplitude S _T generated by the SP signal generation unit 602.

  The delay profile calculation unit 65 is based on the reception subcarrier complex amplitude YD supplied from the delay unit 64 and the determination subcarrier complex amplitude Q supplied from the signal point determination unit 69 to determine the arrival distance of each path in the reflected wave. A delay profile PFD representing the power distribution with respect to the delay time due to the difference is calculated.

  FIG. 5 is a diagram showing an internal configuration of the delay profile calculation unit 65.

  As illustrated in FIG. 5, the delay profile calculation unit 65 includes a delay profile division unit 651, an IFFT (Inverse Fast Fourier Transform) processing unit 652, and a square calculation unit 653.

The delay profile division unit 651 calculates the determination transmission path transfer characteristic R by dividing the reception subcarrier complex amplitude YD by the determination subcarrier complex amplitude Q, and supplies it to the IFFT processing unit 652. The IFFT processing unit 652 performs inverse fast Fourier transform processing (hereinafter referred to as IFFT processing) on the determined transmission path transfer characteristic R, thereby converting the determined transmission path transfer characteristic R expressed in the frequency domain into the time domain. This is converted into a determination transmission path impulse response TR and supplied to the square calculation unit 653. The square calculation unit 653 squares the determination transmission path impulse response TR. As a result, for example, as shown in FIG. 6, in the delay time range equal to the effective symbol length T ₀ in OFDM, the received power PM corresponding to the direct wave and the delayed wave received by delaying the direct wave by the multipath The delay profile PFD representing the received power PD corresponding to is calculated.

  The square calculation unit 653 supplies the calculated delay profile PFD to the filter control unit 66.

  The filter control unit 66 includes a BPF (Band Pass Filter) center detection unit 661 and a filter coefficient generation unit 662.

The BPF center detection unit 661 detects an offset signal CF indicating the passband center position of the filter characteristics in the complex BPF included in the frequency direction interpolation unit 63 based on the delay profile PFD. Specifically, the BPF center detection unit 661 first convolves the trapezoidal wave ZT with the delay profile PFD as shown in FIG. 6 as shown in FIG. Incidentally, the upper base width _{T H} of the trapezoidal wave ZT, the passband width of the complex BPF, for example, the effective symbol length _T 1/3 of _{0 (± T 0/6)} , lower base width _{T L} is the effective symbol length T _It is 1/2 of ₀ (± T _0/4 ). In addition, it is assumed that the delayed wave in FIG. 6 is received with a delay of [(effective symbol length T _0/3 ) + (effective symbol length T _0/20 )] from the direct wave. As shown in FIG. 7, by convolving the trapezoidal wave ZT over the first time point S1 to the eighth time point S8, convolution power that changes as shown in FIG. 7 at each time point (S1 to S8) is obtained. Here, the BPF center detection unit 661 detects the largest convolution power among the convolution powers described above. For example, in the example shown in FIG. 7, the maximum convolution power is obtained at the fourth time point S4, that is, when the received power PM corresponding to the direct wave is located at the left edge portion EG at the upper base of the trapezoidal wave ZT. Next, BPF center detection section 661, 1/2 of the width of the upper base width _{T H} of the trapezoidal wave ZT, that is, in the effective symbol length _T by the width of 1/6 of the ₀ maximum convolution time axis from the position S4 in power The delayed position is supplied to the filter coefficient generation unit 662 as the offset signal CF. The passband center position indicated by the offset signal CF represents a relative time position within the unit processing period for each effective symbol length T ₀ by the FFT unit 5.

The filter coefficient generation unit 662 calculates the filter coefficient k of the complex BPF. The filter coefficient k is calculated based on an LPF (LowPassFilter) whose passband is limited and an offset signal CF. The filter coefficient generation unit includes a memory in which filter coefficients of LPFs whose passbands are limited are stored in advance. For example, the filter coefficients of a time length of 1/3 of the pass bandwidth effective symbol length _{T 0 (± T 0/6} ) LPF is stored in advance. The filter coefficient generation unit 662 calculates the filter coefficient k of the complex BPF based on the LPF whose passband center position is the offset signal CF and the passband width is 1/3 of the effective symbol length T ₀ , and the frequency direction interpolation unit 63. Specifically, the filter coefficient k of the complex BPF obtained by moving the LPF pass band by the offset signal CF is calculated using a frequency movement theorem.

  That is, the filter control unit 66 including the filter coefficient generation unit 662 and the BPF center detection unit 661 controls the filter characteristics of the complex BPF in the frequency direction interpolation unit 63 based on the delay profile calculated by the delay profile calculation unit 65. To do.

  The frequency direction interpolation unit 63 convolves the filter coefficient k of the complex BPF with the partial area transmission path transfer characteristic TD supplied from the time direction interpolation unit 62 and performs a filtering process. By such filtering processing, the complex BPF has an interpolated transmission line transmission characteristic (indicated by a double circle in FIG. 4) and an SP transmission line transmission characteristic (indicated by a black circle in FIG. 4) indicated by a partial area transmission line transmission characteristic TD. ) Is interpolated in the frequency direction to obtain the estimated transmission line transfer characteristic DD for all subcarriers. The frequency direction interpolation unit 63 supplies the estimated transmission line transfer characteristic DD to the equalization division unit 68.

  The equalizing / dividing unit 68 divides the received subcarrier complex amplitude YD by the estimated transmission line transfer characteristic DD, thereby calculating an equalized subcarrier complex amplitude X appropriately waveform-equalized corresponding to the influence of the transmission line. This is supplied to the decoder 7 and the signal point determination unit 69.

As described above, in the equalization unit 6 shown in FIG. 2, first, the reception subcarrier complex amplitudes (Y, YD) after FFT processing are distributed in the time direction (symbol direction) and the frequency direction (subcarrier direction). Each SP signal (S _R ) extracted is extracted, and the SP transmission path transfer characteristic (SD) at each SP signal position is obtained based on the extracted SP signal. Next, by interpolating the SP transmission line transfer characteristic (SD) in the time direction, the partial area transmission line transfer characteristic (TD) in 1/3 of all the subcarriers is obtained. Next, the estimated transmission path transfer characteristic (DD) in all subcarriers is obtained by interpolating the partial area transmission path transfer characteristic (TD) in the frequency direction by the complex BPF. Then, the reception subcarrier complex amplitude (Y, YD) is divided by the estimated transmission path transfer characteristic (DD), thereby appropriately equalizing the subcarrier complex amplitude (X) following the influence of the transmission path. Get.

At this time, in the equalization unit 6 shown in FIG. 2, the passband width of the complex BPF is fixed to 1/3 of the effective symbol length (T ₀ ), and the passband center position of the filter characteristic in the complex BPF is set. (CF) is controlled based on the delay profile. That is, by controlling the position of the passband (period) within the unit processing period having an effective symbol length (T ₀ ) for the complex BPF, the direct wave is reduced from the direct wave together with the direct wave indicated by the delay profile. This makes it possible to reliably make the delayed wave transmitted after being delayed for a period of (T _0/3 ) to be subject to frequency interpolation.

In the equalizer 6, when seeking such a pass band center position (CF), the pass band width of the upper base width _{(T H)} is a complex BPF _(T 0/3), the lower base width _{(T L)} is It is convoluted to 1/2 of detectable delay time range delay profile _(T 0/2) equal to trapezoidal wave (ZT) a delay profile (PFD).

As a result, for example, as shown in FIG. 7, the delayed wave transmitted with a delay [[T _0/3 ) + (T _0/20 )] slightly longer than the pass bandwidth (T _0/3 ). Can be detected as the detection target of the passband center position (CF) together with the direct wave. In the case where convolution of equal rectangular wave upper base width (T _H) and the lower base width (T _L) are both pass bandwidth (T _0/3) is such a delayed wave passband It cannot be included.

  Further, in the equalization unit 6 shown in FIG. 2, in order to obtain a delay profile, first, from the equalization subcarrier complex amplitude (X) as the output result, the modulation parameter of this equalization subcarrier complex amplitude (X) is obtained. Among the signal points mapped based on, the signal point closest to the equalized subcarrier complex amplitude is obtained as the determination subcarrier complex amplitude (Q). Then, a transmission path transfer characteristic (R) is obtained by dividing the reception subcarrier complex amplitude (YD) by the determination subcarrier complex amplitude (Q), and subjected to IFFT processing and square calculation processing to obtain a delay profile. (PFD) is calculated.

Therefore, since the delay profile is calculated based on the transmission path transmission characteristics of all subcarriers, the aliasing signal component is not superimposed within the unit processing period having the effective symbol length (T ₀ ). Therefore, according to such a delay profile, the passband center position (CF) of the filter characteristic in the complex BPF can be detected with high accuracy, so that a highly reliable equalized subcarrier complex amplitude (X) can be obtained. It becomes possible. Further, since the range of the delay time that can be detected is the effective symbol length (T ₀ ), even in a multipath reception environment where there is a delayed wave whose delay time is ¼ of the effective symbol length, aliasing by sampling is performed. No signal component is generated. Accordingly, the passband center position (CF) as described above can be detected with high accuracy.

  In this way, the equalization unit 6 controls the center position of the pass band of the filter responsible for frequency direction interpolation based on the delay profile whose detectable delay time range is equal to the effective symbol length. The path transfer characteristic can be obtained with high accuracy, and the reception performance can be improved.

  Note that the delay profile may be calculated only for continuous subcarriers having a modulation parameter with higher error tolerance or a lower error rate for determination in the signal point determination unit 69. For example, when the delay profile is calculated only for the one-segment subcarrier that is the center segment subjected to QPSK modulation recommended by ISDB-T, the delay profile calculation unit 65 is replaced with the internal configuration shown in FIG. A device having an internal configuration as shown in FIG. 8 is employed. In the configuration shown in FIG. 8, the one-seg extraction unit 650 is added to the configuration shown in FIG. 5, and the other configurations are the same as those shown in FIG.

  In FIG. 8, the one seg extraction unit 650 extracts only the subcarrier of the one seg part that is the central segment in the reception subcarrier complex amplitude YD and the determination subcarrier complex amplitude Q, and supplies this to the delay profile division unit 651. Therefore, the delay profile division unit 651, the IFFT processing unit 652, and the square calculation unit 653 calculate a delay profile using only the subcarrier corresponding to the one-segment part in the reception subcarrier complex amplitude YD and the determination subcarrier complex amplitude Q. . By adopting such a configuration, it is possible to calculate the delay profile more accurately by using only the subcarriers of the modulation parameter with higher error tolerance. In addition, the processing time is shortened and the circuit scale is reduced.

  Further, in order to improve the accuracy of the delay profile, the delay profile calculated for each OFDM symbol may be averaged in the symbol direction and output to the filter coefficient generation unit 66. For example, as an averaging method, an IIR (Infinite Impulse Response) filter may be applied in the symbol direction.

Further, in the above embodiment, the passband width of the complex BPF is fixed to 1/3 of the effective symbol length, but may be set to 1/4 or 1/6 of the effective symbol length. good. In this case, the coefficients of the LPF stored in the memory mounted on the filter coefficient generator 662, 1/4 of the pass bandwidth data is valid symbol length _{T 0 (± T 0/8} ) or 1/6 ( ± _T 0/12) may be rewritten to the filter coefficient is. Furthermore, the upper base width _{T H} of the trapezoidal wave signal ZT to be convoluted in the delay profile, to follow the change of the pass bandwidth of such complex BPF, 1/4 of the effective symbol length _{T 0 (± T 0/8} ) or 1/6 may be changed to (± _T 0/12).

6 equalization unit 60 SP transmission path transfer characteristic calculation unit 63 frequency direction interpolation unit 65 delay profile calculation unit 66 filter control unit 68 equalization division unit 69 signal point determination unit 661 BPF center detection unit 662 filter coefficient generation unit

Claims (7)

OFDM for receiving an orthogonal frequency division multiplex transmission signal in which each subcarrier includes a plurality of subcarriers modulated according to a modulation parameter, and scattered pilot signals are distributed and superimposed in each of the subcarriers in the time direction and the frequency direction. A receiving device,
A Fourier transform unit for transforming the orthogonal frequency division multiplex transmission signal into a reception subcarrier complex amplitude for each subcarrier;
An SP transmission path transmission characteristic calculation unit for calculating an SP transmission path transmission characteristic in the scattered pilot signal superimposed on the reception subcarrier complex amplitude;
A time direction interpolation unit for calculating a partial region transmission line transfer characteristic in a part of the subcarrier by interpolating the SP transmission line transfer characteristic in the time direction;
A frequency direction interpolation unit that interpolates the partial region transmission line transfer characteristic in the frequency direction to calculate an estimated transmission line transfer characteristic;
An equalization division unit for calculating an equalized subcarrier complex amplitude obtained by equalizing the received subcarrier complex amplitude by dividing the received subcarrier complex amplitude by the estimated transmission line transfer characteristic;
A signal point determination unit that calculates a signal point closest to the equalized subcarrier complex amplitude among signal points mapped based on the modulation parameter of each subcarrier as a determination subcarrier complex amplitude;
And the determination based on a sub-carrier complex amplitude and the received subcarrier complex amplitude, delay profile calculating section for calculating a delay profile representing the distribution of power to the delay time due to the difference between the arrival distances for each path in the reflected wave,
A filter control unit that controls a filter characteristic of the frequency direction interpolation unit based on the delay profile,
The frequency direction interpolation unit includes a complex bandpass filter,
The filter control unit detects a central time point of the pass band of the complex bandpass filter based on the delay profile and generates an offset signal indicating the central time point; and
A memory in which low pass filter coefficients having the same pass bandwidth as that of the complex band pass filter are stored in advance;
An OFDM receiving apparatus, comprising: a filter coefficient generation unit configured to generate a filter coefficient of the complex bandpass filter based on the low-pass filter coefficient and the offset signal. The central time point detection unit moves a position of the predetermined trapezoidal wave on the time axis to a received power value corresponding to each of the direct wave and the delayed wave located on the time axis indicated by the delay profile. 2. The OFDM receiving apparatus according to claim 1 , wherein an offset signal indicating a central time point of a pass band of the complex bandpass filter is generated based on convolution power obtained by convolution . 3. The OFDM reception according to claim 2, wherein the central time point detection unit sets a time point delayed by a half of an upper base width of the trapezoidal wave from a position where the convolution power is maximum as the central time point. apparatus. 4. The OFDM receiver according to claim 3 , wherein an upper base width of the trapezoidal wave is the same as a pass band width of the complex bandpass filter . 5. The OFDM receiver according to claim 2, wherein a passband width of the complex bandpass filter is 1/3, 1/4, or 1/6 of an effective symbol length. . The delay profile calculation unit is configured to calculate a determination transmission path transfer characteristic by dividing the reception subcarrier complex amplitude by the determination subcarrier complex amplitude;
An inverse Fourier transform unit that obtains a time-domain determination transmission path impulse response by performing an inverse Fourier transform process on the determination transmission path transmission characteristics;
OFDM receiving apparatus according to any one of claims 1-5, characterized in that it has a, a square operation unit for calculating the delay profile squaring the determined channel impulse response. The orthogonal frequency division multiplex transmission signal is a terrestrial digital broadcasting signal recommended by ISDB-T (Integrated Services Digital Broadcasting-Terrestrial),
The delay profile calculation unit further includes a one-segment extraction unit that extracts a portion corresponding to a subcarrier of the one-seg unit from each of the determination subcarrier complex amplitude and the reception subcarrier complex amplitude and supplies the extracted portion to the delay profile division unit. OFDM receiver according to claim 6, wherein a has.

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