JP5925137B2 - Digital broadcast receiving apparatus and digital broadcast receiving method - Google Patents

Description

  The present invention relates to a digital broadcast receiving apparatus and a digital broadcast receiving method for receiving a digital broadcast wave using an OFDM (Orthogonal Frequency Division Multiplexing) scheme.

  Patent Document 1 discloses a technique for determining a coefficient of a carrier interpolation filter using a delay profile estimation result after inverse Fourier transform of symbol interpolation.

International Publication No. 2004/100413

  In the conventional technique represented by Patent Document 1, a filter band that can be generated is determined by the number of taps of a carrier interpolation filter. For this reason, for example, when a plurality of incoming waves arrive and are received while moving at high speed, if the number of filter taps is small, the pseudo delayed wave generated by symbol interpolation cannot be removed, The reception performance is deteriorated. Further, when the number of taps is increased, there is a problem that the circuit scale increases.

  The present invention has been made to solve the above-described problems, and a digital broadcast receiver and a digital broadcast receiver capable of performing transmission path estimation with high accuracy even when moving and receiving at high speed The purpose is to obtain a broadcast receiving method.

A digital broadcast receiving apparatus according to the present invention includes a first Fourier transform unit that receives a digital broadcast wave using the OFDM method, Fourier-transforms the received OFDM signal and outputs a subcarrier component, and a first Fourier transform A pilot extraction unit that extracts a pilot signal included in the subcarrier component output from the conversion unit, a known signal generation unit that generates a known signal corresponding to the pilot signal, and a pilot signal extracted by the pilot extraction unit A first division unit that calculates a transmission line characteristic signal corresponding to the pilot signal by dividing by the known signal generated by the generation unit, and a transmission line characteristic signal that corresponds to the pilot signal calculated by the first division unit A symbol interpolation filter that performs interpolation in the symbol direction, and a channel characteristic signal that is interpolated in the symbol direction by the symbol interpolation filter. Inverse Fourier transform unit that outputs a delay profile by performing inverse Fourier transform on the carrier direction, filtering unit that filters the delay profile, and Fourier transform of the delay profile filtered by the filtering unit to support all subcarrier components A second Fourier transform unit that outputs a transmission path characteristic signal to be transmitted, and a subcarrier component output from the first Fourier transform unit to a transmission path characteristic corresponding to the subcarrier component output from the second Fourier transform unit in division to example Bei a second divider for outputting a demodulated signal, filtering section in the delay profile for each sample by inserting 0 data by a plurality of samples characterized in that to perform low-pass filtering is there.

  According to the present invention, there is an effect that transmission path estimation can be performed with high accuracy even when moving and receiving at high speed.

It is a figure which shows the dispersion | distribution arrangement | positioning of a scattered pilot signal. It is a figure which shows the transmission-line estimated value interpolated in the time direction. It is a figure which shows the transmission-line estimated value interpolated by the time direction and the frequency direction. It is a figure which shows an example of a delay profile. It is a figure which shows the case where the transmission-line estimated value containing an error is obtained by the interpolation of the time direction at the time of high-speed movement. It is a figure which shows the pseudo | simulation arrival wave which generate | occur | produces in SP base delay profile at the time of high-speed movement. It is a block diagram which shows the structure of the conventional digital broadcast receiver. It is a block diagram which shows the structure of the digital broadcast receiver which concerns on Embodiment 1 of this invention. It is a flowchart which shows the digital broadcast receiving method in Embodiment 2 of this invention. It is a flowchart which shows the digital broadcast receiving method in Embodiment 3 of this invention. It is a figure which shows the pseudo | simulation arrival wave (multiple arrival wave) which generate | occur | produces in SP base delay profile at the time of high-speed movement.

Embodiment 1 FIG.
In the OFDM scheme, information to be transmitted is allocated to a plurality of subcarriers, and each subcarrier is subjected to digital modulation such as a QPSK (Quadrature Phase Shift Key) scheme, a QAM (Quadrature Amplitude Modulation) scheme, or a multilevel PSK scheme. .
A known signal is multiplexed on a specific subcarrier as a signal used when demodulating the subcarrier on the receiving side. These multiplexed subcarriers are orthogonally transformed by inverse Fourier transform processing, and frequency-converted to a desired transmission frequency and transmitted.
A transmission unit for performing inverse Fourier transform is called a symbol.

  Next, the last part of the signal after the inverse Fourier transform is added to the head of the symbol. This added portion is called a guard interval, which makes it possible to reproduce a signal without intersymbol interference on the receiving side even if there is an incoming wave having a delay time shorter than the guard interval length.

Next, a known signal inserted in advance in the transmission signal will be described.
Taking the ISDB-T system or the European DVB-T system, which is a domestic terrestrial digital broadcast, as an example, a scattered pilot (SP) signal is periodically inserted into a transmission signal.
As shown in FIG. 1, scattered pilot signals (hereinafter referred to as SP signals) are distributed every four symbols in the time direction and twelve carriers in the carrier (frequency) direction, and their insertion. The positions are arranged while shifting by 3 carriers for each symbol so as to be the same frequency position in a period of 4 symbols.

In the digital broadcast receiver, the received SP signal is divided by a known SP signal to estimate the amount of variation (hereinafter also referred to as transmission path characteristics) of the amplitude and phase of each SP signal (hereinafter also referred to as transmission path estimation). Call).
Further, the SP signal transmission path characteristic estimation result is interpolated in the symbol (time) direction as shown in FIG. 2, and then is interpolated in the carrier (frequency) direction as shown in FIG. Thus, it is possible to obtain transmission path characteristics for all subcarriers.
Here, the reason why the interpolation is performed in the symbol direction is that the SP signal dispersedly arranged by 12 carriers is interpolated in the symbol direction to be a signal dispersed by 3 carriers in the carrier direction, and the transmission path that can be estimated This is because the time range of characteristics is expanded from Ts / 12 to Ts / 3, and transmission path estimation can be performed correctly even in an environment where the arrival time difference of incoming waves is large.
Ts represents the effective symbol length.

In addition, it is known that by performing inverse Fourier transform on the transmission path characteristic value, as shown in FIG. 4, a delay profile indicating the intensity for each arrival time of the received signal can be obtained.
However, in an environment where reception is performed while moving at high speed, the received signal is subjected to Doppler fluctuations, and the transmission path characteristics for each symbol fluctuate.
When the maximum frequency of the fluctuation (also referred to as the maximum Doppler frequency) exceeds 1 / ((Ts + Tg) / 8) (Hz), which is the maximum frequency that can be interpolated by symbol interpolation, as shown in FIG. Interpolation cannot be performed correctly, and as a result, a pseudo delay wave appears in the delay profile as shown in FIG.
Here, Ts is the effective symbol length, Tg is the guard interval length, and the above equation is derived from the sampling theorem and the SP signal interpolated in a 4-symbol period.
At this time, if the carrier direction interpolation processing is performed based on the channel characteristics in which the erroneous symbol interpolation is performed, there is a problem that correct channel characteristics cannot be obtained and reception performance deteriorates.

FIG. 7 is a block diagram showing a configuration of a conventional digital broadcast receiving apparatus. As shown in FIG. 7, the conventional digital broadcast receiving apparatus includes an FFT unit 100, a pilot extraction unit 101, a delay adjustment unit 102, division units 103a and 103b, a known signal generation unit 104, a symbol interpolation filter unit 105, a delay profile. An estimation unit 106, a carrier interpolation filter unit 107, and a data reproduction unit 108 are provided (for example, see Patent Document 1).
In order to solve the above-described problem, in the conventional digital broadcast receiving apparatus, the FFT unit 100 cuts out only one symbol period from the received OFDM signal and performs fast Fourier transform. As a result, the received signal changes from the time axis signal to the frequency axis signal.
That is, by performing Fourier transform, the signal is converted into a signal for each subcarrier which is a carrier unit of the frequency axis signal.

Next, pilot extraction section 101 extracts only the SP signal inserted at a predetermined subcarrier position by the pilot extraction section from the signal for each subcarrier.
Since the SP signal is a known signal, the known signal generation unit 104 generates a known SP signal corresponding to a predetermined subcarrier position (hereinafter referred to as a known SP signal).
Subsequently, the division unit 103a divides the SP signal extracted by the pilot extraction unit 101 by the known SP signal generated by the known signal generation unit 104 to obtain a transmission path characteristic signal.
Since the SP signal is distributed and inserted every 12 subcarriers, it is necessary to perform an interpolation process in order to obtain transmission path characteristics of all subcarriers.

  Since the SP signals are arranged every four symbols in the symbol direction, the symbol interpolation filter unit 107 performs an interpolation process in the symbol direction on the transmission path characteristic signal output from the division unit 103a. For example, in the symbol interpolation filter unit, linear interpolation or a plurality of symbols is used, and symbol direction interpolation processing is performed by an FIR (Finite Impulse Response) filter or the like. When the symbol interpolation process is completed, a transmission path characteristic signal is obtained for every three carriers in the carrier direction.

The channel characteristic signal subjected to the symbol interpolation processing is output to delay profile estimation section 106 and carrier interpolation filter section 107.
The delay profile estimation unit 106 determines the arrival time and level of the incoming wave from the input transmission path characteristic signal, and notifies the carrier interpolation filter unit 107 of the arrival time.
The carrier interpolation filter unit 107 sets a filter coefficient (FIR filter or the like) based on the notification content, and performs filtering processing on the input transmission path characteristic signal.

The division unit 103b divides (referred to as equalization) the subcarrier component from the FFT unit that has been delay-adjusted by the delay adjustment unit 102 by the channel characteristic corresponding to the subcarrier component output from the carrier interpolation filter unit 107. To output a demodulated signal. The data reproducing unit 108 reproduces the demodulated signal to reproduce the original transmission data. By passing through the interpolation filter in this manner, unnecessary noise components are removed, and deterioration in reception performance can be reduced.
However, since the conventional digital broadcast receiving apparatus uses the carrier interpolation filter unit 107, there is a problem that the pass band and the amount of attenuation of the filter are limited depending on the number of tap stages of the carrier interpolation filter.

  Therefore, in the present invention, after the SP signal is interpolated in the symbol direction, a delay profile is calculated by inverse Fourier transform in the carrier direction, and filtering processing is performed on the delay profile in units of samples. As a result, there are no restrictions on the passband and attenuation amount of the filter, transmission path estimation can be obtained more accurately, and reception performance can be improved. In addition, since the interpolation filter in the carrier direction is not necessary, the circuit scale can be reduced.

  FIG. 8 is a block diagram showing the configuration of the digital broadcast receiving apparatus according to Embodiment 1 of the present invention. In FIG. 8, the digital broadcast receiving apparatus according to Embodiment 1 includes an FFT unit 1, a pilot extraction unit 2, a delay adjustment unit 3, division units 4a and 4b, a known signal generation unit 5, a symbol interpolation filter unit 6, and unnecessary. A signal determination unit 7, a filtering unit 8, and a data reproduction unit 9 are provided. The FFT unit 1 is an FFT unit that can perform fast Fourier transform (FFT) and fast inverse Fourier transform (IFFT) on an input signal. The FFT function unit is FFT1a (first Fourier transform unit, second FFT unit). The Fourier transform unit) and the IFFT function unit are IFFT1b (inverse Fourier transform unit). The pilot extraction unit 2 extracts the SP signal included in the subcarrier component output from the FFT unit 1. The known signal generation unit 5 generates a known SP signal corresponding to the SP signal. The delay adjustment unit 3 delay-adjusts the subcarrier component from the FFT unit 1 and outputs it to the division unit 4b.

  The division unit 4a is a first division unit that calculates the transmission path characteristic signal corresponding to the SP signal by dividing the SP signal extracted by the pilot extraction unit 2 by the known SP signal generated by the known signal generation unit 5. . The symbol interpolation filter unit 6 performs symbol direction interpolation on the transmission path characteristic signal corresponding to the SP signal calculated by the division unit 4a. The unnecessary signal determination unit 7 determines unnecessary data from the delay profile obtained by performing the fast inverse Fourier transform on the output from the symbol interpolation filter unit 6. The filtering unit 8 filters the delay profile using the determination result of the unnecessary signal determination unit 7 and the like. The division unit 4b divides the subcarrier component from the FFT unit 1 subjected to delay adjustment by the delay adjustment unit 2 by a transmission path characteristic corresponding to the subcarrier component obtained by performing fast Fourier transform on the delay profile filtered by the filtering unit 8. And a second division unit for outputting a demodulated signal. The data reproduction unit 9 reproduces the demodulated signal to reproduce the original transmission data.

Next, the operation will be described.
The received OFDM signal is cut out for one symbol period by the FFT 1a of the FFT unit 1 and subjected to fast Fourier transform to be converted from a time axis signal to a frequency axis signal. By performing Fourier transform, the signal is converted into a signal for each subcarrier which is a carrier unit of the frequency axis signal.
The pilot extraction unit 2 extracts only the SP signal inserted at a predetermined subcarrier position from the signal for each subcarrier. The known signal generator 5 generates a known SP signal at a predetermined subcarrier position.

  The division unit 4a divides the SP signal extracted by the pilot extraction unit 2 by the known SP signal to obtain transmission path characteristics. Since the SP signal is distributed and inserted every 12 subcarriers, it is necessary to perform interpolation processing in order to acquire the transmission path characteristics of all the subcarriers. Since the SP signals are arranged at intervals of 4 symbols in the symbol direction, interpolation processing is performed in the symbol direction.

The symbol interpolation filter unit 6 uses linear interpolation or a plurality of symbols, and performs symbol direction interpolation processing using an FIR filter or the like. When symbol interpolation processing is performed, a transmission path characteristic signal is obtained for every three carriers in the carrier direction.
Next, the IFFT 1b of the FFT unit 1 performs IFFT (fast inverse Fourier transform) in the carrier direction on the data subjected to the symbol direction interpolation processing.
The data after IFFT is a signal representing the level of an incoming wave for each delay time, generally called a delay profile. Here, all the carriers for every three carriers are IFFTed.

The filtering unit 8 inserts 2 data of 0 for each sample into the data after IFFT to triple the total data, and further performs a low-pass filter using an FIR filter or the like. Thereby, all the data are smoothly connected, and the delay profile is expanded to 3 times the number of samples as a whole.
At this time, the unnecessary signal determination unit 7 may detect unnecessary data that is not the original incoming wave, and the filtering unit 7 may replace the corresponding sample with approximate data of zero or a plurality of samples before and after. Thereby, it is possible to improve the transmission path estimation accuracy. This process may not be performed.

The delay profile expanded three times and from which unnecessary data has been deleted is sent to the FFT unit 1 and is subjected to FFT by the FFT 1a. As a result, transmission path characteristics corresponding to all subcarrier components can be obtained.
The division unit 4b reproduces the transmission signal (referred to as equalization) by dividing by the transmission path characteristic for each subcarrier. Thereafter, the original transmission data is reproduced by the subsequent data reproducing unit 9.

  As described above, according to the first embodiment, a digital broadcast wave using the OFDM method is received, and the received OFDM signal is Fourier-transformed to output a subcarrier component, and an SP included in the subcarrier component. Extract a signal, generate a known SP signal corresponding to the SP signal, divide the extracted SP signal by the known SP signal, calculate a transmission path characteristic signal corresponding to the SP signal, and correspond to the calculated SP signal The transmission path characteristic signal is interpolated in the symbol direction, and the transmission path characteristic signal interpolated in the symbol direction is subjected to inverse Fourier transform in the carrier direction to output a delay profile, and this delay profile is filtered. , Fourier-transform the filtered delay profile, and output a channel characteristic signal corresponding to all subcarrier components, and receive OFDM Subcarrier component obtained by Fourier transform, and the delay profile are filtered divided by the channel characteristics corresponding to the sub-carrier components obtained by Fourier transform to output a demodulated signal No.. Since filtering processing is performed on the delay profile in units of samples in this way, there are no restrictions on the passband and attenuation amount of the filter, transmission path characteristics can be estimated more accurately, and reception performance can be improved. . That is, even when the mobile station is moving at a high speed, transmission path estimation can be performed with high accuracy.

  Further, according to the first embodiment, since the FFT 1a and IFFT 1b are configured to be shared by the FFT unit 1 which is one Fourier transform circuit, an interpolation filter in the carrier direction as described above is unnecessary. In addition to this, the circuit scale can be significantly reduced as compared with the prior art.

  Further, according to the first embodiment, the filtering unit 8 performs low-pass filtering by inserting 0 data for each sample by a plurality of samples in the delay profile. For example, the low pass filter is performed after inserting 2 samples of 0 data for each sample. By doing so, it is possible to suppress noise components included in the data interpolated in the symbol direction, to obtain transmission path estimation more accurately, and to improve reception performance.

  Note that the low-pass filter used in the filtering unit 8 is a filter for oversampling and does not require steep characteristics. For this reason, it is realizable with a filter with few taps compared with a carrier interpolation filter part. The filter shown in the present invention is not limited to the FIR filter, and may be an arbitrary filter such as an IIR filter or a linear interpolation filter.

Embodiment 2. FIG.
FIG. 9 is a flowchart showing a digital broadcast receiving method according to Embodiment 2 of the present invention, and shows an example of a determination method by the unnecessary signal determination unit 7.
First, when the result (delay profile) of the fast inverse Fourier transform by the IFFT 1b of the FFT unit 1 is input, the unnecessary signal determination unit 7 calculates a peak value (maximum value) in this delay profile (step ST1). Next, the unnecessary signal determination unit 7 calculates a threshold value at a constant ratio (variable α) with respect to the peak value (step ST2).

  Thereafter, the unnecessary signal determination unit 7 reads the delay profile as the IFFT result one sample at a time (step ST3), and determines sample data at a level below the threshold as unnecessary data (step ST4). The result of this determination is notified from the unnecessary signal determination unit 7 to the filtering unit 8 for each sample. The filtering unit 8 replaces the data determined as unnecessary data by the unnecessary signal determination unit 7 with 0 or approximate data of a plurality of samples before and after (step ST5).

  Finally, the unnecessary signal determination unit 7 determines whether or not the above processing has been performed on all the samples of the delay profile (step ST6). If there is an unprocessed sample (step ST6; NO), the process returns to step ST3 and the above-described processing is repeated. If the processing is completed for all samples (step ST6; YES), the unnecessary data determination processing is terminated.

  As described above, according to the second embodiment, the unnecessary signal determination unit 7 determines a predetermined ratio threshold value from the peak level of the delay profile output from the IFFT 1b, and stores data having a level lower than the threshold value. The filtering unit 8 determines that it is unnecessary data, and replaces the unnecessary data determined by the unnecessary signal determination unit 7 with 0 or approximate data of a plurality of samples before and after. By doing in this way, the noise component contained in SP signal can be suppressed and reception performance can be improved.

Embodiment 3 FIG.
In an environment where signals are received while moving at high speed, the received signal undergoes Doppler fluctuations, and the transmission path characteristics of each symbol vary. When the maximum frequency of this fluctuation (also referred to as the maximum Doppler frequency) exceeds 1 / ((Ts + Tg) / 8) (Hz), which is the maximum frequency that can be interpolated by symbol interpolation, as shown in FIG. Symbol interpolation cannot be performed correctly, and a pseudo delayed wave appears on the IFFT result (delay profile) in the carrier direction.
As shown in FIG. 6, this pseudo delay wave appears in a delay time of ± Ts / 12 corresponding to the sampling frequency of the SP signal with respect to the delay time of the incoming wave.

Therefore, in the third embodiment, unnecessary data is determined by the unnecessary signal determination unit 7 in accordance with the flowchart shown in FIG.
First, the unnecessary signal determination unit 7 reads out the delay profile that is the IFFT result one sample at a time (step ST1a), and at a sample position corresponding to ± Ts / 12 before and after the index, It is determined whether or not an incoming wave (peak) exists (step ST2a).

If a pseudo incoming wave exists (step ST2a; YES), the unnecessary signal determination unit 7 notifies the filtering unit 8 of the determination result. Upon receiving the notification from the unnecessary signal determination unit 7, the filtering unit 8 replaces the sample value (pseudo incoming wave) at the sample position of before and after ± Ts / 12 with approximate data of zero or a plurality of samples (step ST3a). ).
If there is no pseudo incoming wave (step ST2a; NO), the process proceeds to step ST4a.

In step ST4a, the unnecessary signal determination unit 7 determines whether or not the above processing has been performed on all samples of the delay profile. If there is an unprocessed sample (step ST4a; NO), the process returns to step ST1a and the above-described processing is repeated.
Further, when the process is completed for all samples (step ST4a; YES), the unnecessary data determination process is terminated.

  In addition to the determination method described above, unnecessary data may be determined by specifying a pseudo delay wave based on a comparison with a delay profile that does not generate a pseudo delay wave. For example, the IFFT result of the square sum of FFT1a is used. There is also a method of narrowing the band of the symbol interpolation filter.

As described above, according to the third embodiment, the unnecessary signal determination unit 7 detects the pseudo delay wave generated by the symbol interpolation by the symbol interpolation filter unit 6 in the delay profile output from the IFFT 1b. The pseudo delay wave is determined to be unnecessary data, and the filtering unit 8 replaces the unnecessary data determined by the unnecessary signal determination unit 7 with 0 or approximate data of a plurality of samples before and after.
In this way, even in an environment where data is received while moving at high speed, transmission path characteristics can be accurately estimated, and reception performance can be improved.
In particular, as shown in FIG. 11, when the original incoming wave is present in the vicinity of ± Ts / 12, the incoming wave and the pseudo delayed wave are close to each other. In order to remove the pseudo delay wave, it is necessary to construct a filter with many tap stages.
On the other hand, filtering that does not depend on the arrival time can be performed by using the third embodiment.

  In the present invention, within the scope of the invention, any combination of each embodiment, any component of each embodiment can be modified, or any component can be omitted in each embodiment. .

  1 FFT unit, 1a FFT, 1b IFFT, 2 pilot extraction unit, 3 delay adjustment unit, 4a, 4b division unit, 5 known signal generation unit, 6 symbol interpolation filter unit, 7 unnecessary signal determination unit, 8 filtering unit, 9 Data playback unit.

Claims (5)

A first Fourier transform unit that receives a digital broadcast wave using an OFDM (Orthogonal Frequency Division Multiplexing) method, Fourier-transforms the received OFDM signal, and outputs a subcarrier component;
A pilot extraction unit that extracts a pilot signal included in the subcarrier component output from the first Fourier transform unit;
A known signal generator for generating a known signal corresponding to the pilot signal;
A first division unit that calculates the transmission line characteristic signal corresponding to the pilot signal by dividing the pilot signal extracted by the pilot extraction unit by the known signal generated by the known signal generation unit;
A symbol interpolation filter for performing interpolation in the symbol direction on the transmission path characteristic signal corresponding to the pilot signal calculated by the first divider;
An inverse Fourier transform unit that outputs a delay profile by performing inverse Fourier transform on the transmission path characteristic signal interpolated in the symbol direction by the symbol interpolation filter unit;
A filtering unit for filtering the delay profile;
A second Fourier transform unit that Fourier-transforms the delay profile filtered by the filtering unit and outputs a channel characteristic signal corresponding to all subcarrier components;
The subcarrier component output from the first Fourier transform unit is divided by a transmission path characteristic corresponding to the subcarrier component output from the second Fourier transform unit, and a demodulated signal is output. for example Bei and the division unit,
The filtering unit, in the delay profile, digital broadcast receiving apparatus and performs low-pass filtering by inserting 0 data for each sample by a plurality of samples.   2. The digital broadcast receiving apparatus according to claim 1, wherein the first and second Fourier transform units and the inverse Fourier transform unit are configured to share one Fourier transform circuit. A threshold of a predetermined ratio is determined from a peak level of the delay profile output from the inverse Fourier transform unit, and an unnecessary signal determination unit that determines data having a level lower than the threshold as unnecessary data is provided.
3. The digital broadcast receiving apparatus according to claim 1, wherein the filtering unit replaces unnecessary data determined by the unnecessary signal determination unit with approximate data of zero or a plurality of samples before and after. In the delay profile output from the inverse Fourier transform unit, a pseudo delay wave generated by interpolation in the symbol direction by the symbol interpolation filter unit is determined, and the pseudo delay wave is determined as unnecessary data. Equipped with an unnecessary signal determination unit,
3. The digital broadcast receiving apparatus according to claim 1, wherein the filtering unit replaces unnecessary data determined by the unnecessary signal determination unit with approximate data of zero or a plurality of samples before and after. Receiving a digital broadcast wave using an OFDM (Orthogonal Frequency Division Multiplexing) scheme, Fourier-transforming the received OFDM signal, and outputting a subcarrier component;
Extracting a pilot signal included in the subcarrier component;
Generating a known signal corresponding to the pilot signal;
Dividing the extracted pilot signal by the known signal to calculate a transmission line characteristic signal corresponding to the pilot signal;
Interpolating in the symbol direction the transmission path characteristic signal corresponding to the calculated pilot signal;
A transmission path characteristic signal interpolated in the symbol direction, inverse Fourier transform in the carrier direction and outputting a delay profile;
Filtering the delay profile;
Fourier-transforming the filtered delay profile to output a channel characteristic signal corresponding to all subcarrier components;
The demodulated signal is obtained by dividing the subcarrier component obtained by Fourier transform of the received OFDM signal by the transmission path characteristic corresponding to the subcarrier component obtained by Fourier transform of the filtered delay profile. Bei example and outputting the,
In the step of filtering the delay profile, low-pass filtering is performed by inserting a plurality of samples of zero data for each sample in the delay profile .

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