JP5076239B2 - OFDM receiver - Google Patents

Description

  The present invention relates to a technique for estimating a transmission path function of a received signal in an OFDM transmission system.

  In Japanese terrestrial digital television broadcasting, an OFDM (Orthogonal Frequency Division Multiplexing) system is adopted as a transmission system. The OFDM scheme is one of multicarrier transmission schemes in which transmission data is divided into a plurality of carrier waves and transmitted. The spectrum of each subchannel, which is strong against frequency selective fading of a multipath transmission path, can be densely arranged, There are advantages such as high frequency utilization efficiency.

  The ISDB-T, which is the Japanese standard for terrestrial digital television broadcasting, and the DVB-T / H, which is the European standard, employs a synchronous modulation method, so transmission path estimation and signal equalization using pilot data are possible. is necessary.

  Pilot data with known amplitude and phase is embedded in the OFDM signal. The receiving device extracts pilot data from the received OFDM signal. Then, the transmission path function is calculated by comparing the pilot data extracted from the received signal with the pilot pattern held in advance.

  Further, the receiving apparatus estimates the transmission path function for all received data by interpolating the transmission path function calculated for the pilot data also for other data. The receiving device equalizes the received signal by dividing the received OFDM signal by the transmission path function.

  Further, recently, a terrestrial digital broadcast receiving apparatus for one segment (for receiving one segment) is also installed in a mobile phone. Alternatively, on-vehicle one-seg receivers are sold. These receiving devices for mobile phones and the like need to support reception while moving.

  When receiving an OFDM signal while moving at high speed, Rayleigh fading (flat fading) occurs in the time domain, and it is necessary to improve Rayleigh fading characteristics.

  In addition, although not a problem limited to reception with high-speed movement, in OFDM, high demodulation accuracy is generally required for interference due to multipath delay waves.

Japanese Patent No. 3842614

  As described above, an OFDM receiver obtains transmission path functions for all data by interpolating transmission path functions. As an interpolation method of the transmission path function, there are a method of interpolating the transmission path function in the time direction and a method of interpolation in the frequency direction.

  By interpolating the transmission path function in the time direction, it is possible to eliminate the effects of multipath interference with a large delay. However, the interpolation in the time direction has a problem that it is vulnerable to Rayleigh fading in the time domain.

  By interpolating the transmission path function only in the frequency direction, it is possible to increase resistance to Rayleigh fading in the time domain. However, interpolation only in the frequency direction has a problem that it is easily affected by multipath interference having a large delay. That is, there is a problem that it is vulnerable to frequency selective fading.

  Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for estimating a transmission path by switching between a case where interpolation is performed by combining a time direction and a frequency direction and a case where interpolation is performed only in the frequency direction. In this document, when the equalizer is started, equalization is performed using the output of a two-dimensional interpolation filter that performs interpolation in the time direction and the frequency direction, and after the second time, the interpolation is performed in only one direction. The output of the insertion filter is used. In this way, the operation of the equalizer is accelerated.

  Accordingly, in view of the above problems, the present invention provides an OFDM receiver capable of demodulating a received signal with high accuracy while eliminating the effects of multipath interference and the effects of Rayleigh fading that occurs due to high-speed movement. The purpose is to do.

In order to solve the above-described problem, an OFDM receiving apparatus according to claim 1, a multipath detection unit that detects a maximum multipath delay time from a received signal, a fading detection unit that detects fading information from the received signal, A transmission path function calculation unit that calculates a transmission path function of the reception signal using pilot data extracted from the reception signal, and a maximum multipath delay time detected by the multipath detection unit is smaller than a first threshold; A switching unit for selecting a first interpolation method for interpolating transmission line functions for all data by interpolation in the frequency direction when the fading information detected by the fading detection unit is equal to or greater than a second threshold; comprises a first interpolator for interpolating the transmission channel functions in the frequency direction, a second interpolation circuit for interpolating the transmission channel functions in the frequency direction, wherein the first When the interpolation method is selected, after the transmission path function is interpolated in the frequency direction by the first interpolation circuit, the transmission path function is further interpolated in the frequency direction by the second interpolation circuit, so that transmission paths for all data are transmitted. and features that you interpolation function.

  According to a second aspect of the present invention, in the OFDM receiver according to the first aspect, when the switching unit has a maximum multipath delay time detected by the multipath detection unit equal to or greater than the first threshold value. The second interpolation method for interpolating the transmission path functions for all data is selected by combining the interpolation in the time direction and the interpolation in the frequency direction.

  According to a third aspect of the present invention, in the OFDM receiver according to the first or second aspect, the switching unit is configured such that the multipath maximum delay time detected by the multipath detection unit is less than the first threshold. If the fading information detected by the fading detection unit is smaller than the second threshold value, the transmission path function for all data is interpolated by combining time direction interpolation and frequency direction interpolation. The second interpolation method is selected.

A fourth aspect of the present invention is the OFDM receiver according to any one of the first to third aspects, further comprising a third interpolation circuit for interpolating the transmission path function in the time direction, wherein the second interpolation method is When selected, after the transmission path function is interpolated in the time direction by the third interpolation circuit, the transmission path function for all data is interpolated by further interpolating the transmission path function in the frequency direction by the second interpolation circuit. It is characterized by that.

According to a fifth aspect of the present invention, in the OFDM receiver according to any one of the first to fourth aspects of the present invention, the OFDM receiver is further disposed between the first interpolation circuit and the second interpolation circuit. A noise removing unit that removes noise of the interpolated transmission path function is provided.

According to a sixth aspect of the present invention, in the OFDM receiver according to the fourth aspect of the present invention, the transmission path is further disposed between the third interpolation circuit and the second interpolation circuit, and is interpolated by the third interpolation circuit. A noise removing unit for removing function noise is provided.

  The OFDM receiver of the present invention switches the interpolation method of the transmission path function based on the multipath maximum delay time and fading information. Accordingly, it is possible to receive a high-quality broadcast signal even in a Rayleigh fading environment accompanying high-speed movement while ensuring multipath characteristics.

  In addition, the OFDM receiving apparatus of the present invention estimates the transmission path by two frequency direction interpolation circuits even when the transmission path function is estimated by interpolation only in the frequency direction, so that the circuit scale of the interpolation circuit is reduced. be able to.

  Furthermore, since a noise removal unit can be interposed between the two frequency direction interpolation circuits, it is possible to improve the noise characteristics of the transmission path function.

{Overall configuration and processing flow of OFDM receiver}
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an OFDM receiving apparatus according to the present embodiment. An RF (Radio Frequency) signal 1 transmitted from an OFDM transmitter (not shown) is received by a receiving antenna 2 through a transmission path. The received RF signal is frequency-converted by the tuner 3 into an IF (Intermediate Frequency) signal. The IF signal is input to the mixer 5 via the BPF (band pass filter) 4, multiplied by the signal supplied from the carrier wave oscillator 6, and then output to the LPF (low pass filter) 7.

  The reception signal from which the high-frequency component has been removed by the LPF 7 is output to the A / D converter 8, and is converted to a digital signal (symbol signal) at a predetermined sampling frequency by the A / D converter 8. The received signal converted into a digital signal is converted into a parallel signal by a serial-parallel converter and then output to an FFT (Fast Fourier Transform) calculator 9.

  The FFT calculator 9 performs Fourier transform on the input time-domain symbol signal to a frequency-domain signal (hereinafter, this signal is referred to as a received OFDM signal). The received OFDM signal in the frequency domain is input to the equalizer 10 that performs waveform equalization. The equalizer 10 equalizes the received OFDM signal based on the calculation result in the transmission path estimation circuit 20. Although the transmission line estimation circuit 20 will be described later, it is a characteristic part of the present invention.

  On the other hand, the received OFDM signal subjected to equalization processing in the equalizer 10 is subjected to Viterbi decoding and Reed-Solomon decoding in the channel decoder 11, and then MPEG (Moving Picture Experts Group) in the source decoder 12. -2 method or the like, the analog signal is output by the D / A converter 13 and output.

{2. Configuration of transmission path estimation circuit}
Next, the configuration of the transmission path estimation circuit 20 will be described. FIG. 2 is a block diagram of the transmission path estimation circuit 20 according to the present embodiment.

  The multipath detection circuit 21 receives the symbol signal output from the A / D converter 8 and detects the maximum delay time of the multipath. The received signal may include a plurality of delayed waves, but the multipath detection circuit 21 detects the delay time of the delayed wave that arrives the latest from the direct wave among the plurality of delayed waves. The multipath detection circuit 21 calculates the multipath maximum delay time using the guard interval of the received signal.

  The pilot extraction circuit 22 receives the received OFDM signal output from the FFT calculator 9 and extracts a pilot signal included in the received OFDM signal. The pilot symbols adopted in the terrestrial digital broadcasting standards in Japan and Europe are called scattered pilot symbols (SP). As shown in FIG. 3, pilot symbols are inserted at 12 carrier intervals in the frequency direction (carrier direction). Also, the position of the carrier into which the pilot symbol is inserted is shifted by 3 carriers in the time direction.

  The phase and amplitude of the pilot symbol are determined in advance, and the transmission path estimation circuit 20 holds the pilot pattern PP in a predetermined storage unit. As will be described later, the transmission path estimation circuit 20 compares the phase and amplitude value of the pilot symbol extracted by the pilot extraction circuit 22 with the phase and amplitude value of the pilot pattern PP, thereby transmitting the transmission path related to the pilot symbol. A function can be calculated.

  The time direction interpolation circuit 24 is a circuit that interpolates the transmission path function calculated for the pilot symbols in the time direction (symbol direction). As shown in FIG. 3, the position of the carrier (carrier wave) into which the pilot symbol is inserted is 12 carrier intervals in the frequency direction and is shifted by 3 carriers in the time direction. Therefore, if attention is paid to the same carrier, pilot symbols are inserted at intervals of 4 symbols in the time direction. The transmission path function calculated for this pilot symbol is interpolated in the time direction.

  In other words, it is possible to calculate a transmission path function for every 12 carriers by inserting pilot symbols for every 12 carriers, but transmission for every 3 carriers by interpolating the transmission path function in the time direction. The road function can be estimated. Thus, the time direction interpolation circuit 24 interpolates the transmission path function four times in the frequency direction as a result. As an interpolation method, linear interpolation may be performed, or an FIR filter may be used.

  For example, in the example of FIG. 4, for the symbol with symbol number K = 4, for carrier number L = 3, the transmission path function of the pilot symbol corresponding to symbol number K = 1 and carrier number L = 3 is used. To perform interpolation. For carrier number L = 6, a method of performing interpolation using a transmission path function of a pilot symbol corresponding to symbol number K = 2 and carrier number L = 6 can be used. In this way, the transmission path function for every three carriers is estimated.

  The frequency direction interpolation circuit 25 is a circuit that interpolates the transmission path function calculated for the pilot symbols in the frequency direction (carrier direction). As shown in FIG. 3, the position of the carrier into which the pilot symbol is inserted is 12 carrier intervals. The transmission path function calculated for this pilot symbol is interpolated in the frequency direction.

  In other words, it is possible to calculate a transmission path function for every 12 carriers by inserting pilot symbols for every 12 carriers, but transmission for every 3 carriers by interpolating the transmission path function in the frequency direction. The road function can be estimated. Thus, the frequency direction interpolation circuit 25 executes a process of interpolating the transmission line function four times in the frequency direction. As an interpolation method, linear interpolation may be performed, or an FIR filter may be used.

  For example, in the example of FIG. 5, for the symbol with symbol number K = 4, the carrier number L = 3, L = 6, and L = 9 correspond to symbol number K = 4 and carrier number L = 0. For example, a method of performing interpolation using a transmission path function of a pilot symbol. In this way, the transmission path function for every three carriers is estimated.

  The fading detection circuit 26 receives the received OFDM signal after the FFT operation and detects fading information. The fading detection circuit 26 detects fading information by calculating the maximum average Doppler shift value. The maximum average Doppler shift value is estimated from the rate of change of the pilot symbol power. For example, fading detection circuit 26 calculates the average power of pilot symbols in each symbol, obtains the rate of change of average power of pilot symbols over a plurality of symbols, and estimates the maximum Doppler shift value from this rate of change. . Alternatively, the fading detection circuit 26 may estimate the maximum Doppler shift value based on the calculation result of the frequency synchronization circuit.

  The switching circuit 27 selectively outputs the output result of the time direction interpolation circuit 24 or the frequency direction interpolation circuit 25 to the noise removal filter 28. As will be described later, the switching circuit 27 is based on the information on the maximum delay time of the multipath output from the multipath detection circuit 21 and the maximum Doppler shift value output from the fading detection circuit 26. The output of 24 and 25 is switched.

  The noise removal filter 28 removes a noise component from the transmission path function interpolated four times by the time direction interpolation circuit 24 or the frequency direction interpolation circuit 25.

  The frequency direction interpolation circuit 29 is a circuit that further interpolates the transmission path function interpolated four times in the time direction interpolation circuit 24 or the frequency direction interpolation circuit 25 in the frequency direction.

  As shown in FIG. 4 or FIG. 5, the transmission path function is estimated every three carriers for each symbol by quadruple interpolation of the transmission path function in the time direction interpolation circuit 24 or the frequency direction interpolation circuit 25. ing. The frequency direction interpolation circuit 29 further interpolates the transmission path function estimated for every three carriers three times in the frequency direction. As a result, for each symbol, the transmission path function is estimated for all carriers. As an interpolation method, linear interpolation may be performed, or an FIR filter may be used.

  For example, in the example of FIG. 4 or FIG. 5, for the symbol of symbol number K = 4, for carrier numbers L = 1 and 2, interpolation is performed using the transmission path function of the symbol of carrier number L = 0. Do. For carrier numbers L = 4 and 5, a method of performing interpolation using the transmission path function of the symbol of carrier number L = 3 can be used.

{Flow of transmission path estimation processing}
Next, the flow of transmission path estimation processing executed in the transmission path estimation circuit 20 will be described with reference to FIG. The reception signal converted into a digital signal by the A / D converter 8 is input to the FFT calculator 9 and the multipath detection circuit 21. The FFT arithmetic unit 9 converts the time domain received signal into a frequency domain received OFDM signal. On the other hand, the multipath detection circuit 21 calculates the maximum multipath delay time from the received signal after A / D conversion.

  The received OFDM signal output from the FFT calculator 9 is output to the equalizer 10, the pilot extraction circuit 22, and the fading detection circuit 26. Information on the maximum delay time of the multipath calculated by the multipath detection circuit 21 is output to the switching circuit 27.

  The pilot extraction circuit 22 extracts a pilot symbol (SP) from the input received OFDM signal and outputs it to the divider 23. The divider 23 calculates the pilot symbol transmission path function by dividing the pilot symbol signal value output from the pilot extraction circuit 22 by the pilot pattern PP signal value stored in the storage unit. The transmission path function calculated by the divider 23 is output to the time direction interpolation circuit 24 and the frequency direction interpolation circuit 25. As described above, the divider 23 calculates a transmission path function for pilot symbols every 12 carriers for each symbol.

  The time direction interpolation circuit 24 interpolates the pilot symbol transmission path function calculated by the divider 23 in the time direction. As a result, as shown in FIG. 4, for each symbol, a transmission path function for every three carriers in the frequency direction is estimated.

  The frequency direction interpolation circuit 25 interpolates the pilot symbol transmission path function calculated by the divider 23 in the frequency direction. Thereby, as shown in FIG. 5, the transmission path function for every three carriers in the frequency direction is estimated for each symbol.

  The fading detection circuit 26 calculates the maximum average Doppler shift value and outputs it to the switching circuit 27.

  The switching circuit 27 switches the interpolation method based on the multipath maximum delay time information input from the multipath detection circuit 21 and the maximum Doppler shift value input from the fading detection circuit 26.

  FIG. 6 is a diagram illustrating a determination table 271 indicating the interpolation method switching criteria. The switching circuit 27 performs interpolation control switching control using a determination table 271 stored in a storage unit (not shown).

  When the multipath maximum delay time (μs) is equal to or greater than a predetermined threshold τ, the switching circuit 27 is switched to the switch S1 side. Thereby, as shown in FIG. 2, the switching circuit 27 outputs the transmission path function output from the time direction interpolation circuit 24 to the noise removal filter 28.

  When the multipath maximum delay time (μs) is smaller than the predetermined threshold τ and the maximum Doppler shift value (Hz) is smaller than the predetermined threshold fd, the switching circuit 27 switches to the switch S1 side. It is done. Thereby, as shown in FIG. 2, the switching circuit 27 outputs the transmission path function output from the time direction interpolation circuit 24 to the noise removal filter 28.

  When the multipath maximum delay time (μs) is smaller than the predetermined threshold τ and the maximum Doppler shift value (Hz) is equal to or greater than the predetermined threshold fd, the switching circuit 27 switches to the switch S2 side. It is done. Accordingly, the switching circuit 27 outputs the transmission path function output from the frequency direction interpolation circuit 25 to the noise removal filter 28.

  Subsequently, as shown in FIGS. 4 and 5, the noise removal filter 28 removes a noise component from the transmission path function interpolated four times.

  The transmission path function from which the noise component has been removed is output to the frequency direction interpolation circuit 29. In the frequency direction interpolation circuit 29, the transmission path function is interpolated three times in the frequency direction, and transmission path functions corresponding to all carriers are estimated.

  When the transmission path function for all carriers is estimated in this way, the estimated transmission path function is output to the equalizer 10. The equalizer 10 equalizes the signal by dividing all the symbol data output from the FFT calculator 9 by the transmission path function.

  Thus, the OFDM receiving apparatus according to the present embodiment selects an interpolation method based on the multipath maximum delay time and fading information.

  First, when the multipath maximum delay time is equal to or greater than a predetermined threshold τ, the output of the time direction interpolation circuit 24 is used. That is, the transmission path estimation circuit 20 estimates the transmission path functions for all carriers by the interpolation processing in the time direction interpolation circuit 24 and the interpolation processing in the frequency direction interpolation circuit 29.

  As described above, when the maximum delay time of the multipath is equal to or greater than the predetermined threshold τ, the influence of the multipath is large. Therefore, the influence of the multipath interference is reduced by using the interpolation in the time direction. ing. That is, even when frequency selective fading occurs due to multipath, a signal with high quality can be obtained by interpolating the transmission path function in the same carrier. Since OFDM is characterized in that a high-quality broadcast signal can be demodulated even in a multipath environment, in order not to impair this feature, when the maximum delay time of multipath is large, the time direction Interpolation is used.

  Second, when the multipath maximum delay time is smaller than the predetermined threshold τ and the maximum Doppler shift value is smaller than the predetermined threshold fd, the output of the time direction interpolation circuit 24 is used. That is, the transmission path estimation circuit 20 estimates the transmission path functions for all carriers by the interpolation processing in the time direction interpolation circuit 24 and the interpolation processing in the frequency direction interpolation circuit 29.

  As described above, even when the maximum delay time of multipath is smaller than the predetermined threshold value τ, if the maximum Doppler shift value is smaller than the predetermined threshold value fd, a high-quality broadcast signal can be demodulated in the multipath environment. Interpolation in the time direction is used so as not to impair the characteristics of OFDM. The predetermined threshold fd may be selected as an optimal value through experiments or the like. That is, even when interpolation in the time direction is performed, the threshold value fd of the maximum Doppler shift value is set in a range where no error occurs in the estimation of the transmission path function.

  Third, when the multipath maximum delay time is smaller than the predetermined threshold τ and the maximum Doppler shift value is greater than or equal to the predetermined threshold fd, the output of the frequency direction interpolation circuit 25 is used. That is, the transmission path estimation circuit 20 estimates transmission path functions for all carriers by the interpolation processing in the frequency direction interpolation circuit 25 and the interpolation processing in the frequency direction interpolation circuit 29.

  Thus, when the maximum delay time of the multipath is smaller than the predetermined threshold τ and the maximum Doppler shift value is equal to or larger than the predetermined threshold fd, the frequency is improved to improve the Rayleigh fading characteristic. An interpolation method based only on the direction is selected. That is, the transmission path function is estimated by interpolation within one symbol. As a result, a high-quality broadcast signal can be demodulated even during high-speed movement. For example, according to experiments, even when the maximum Doppler shift value is 200 Hz, a high-quality broadcast signal can be demodulated. Note that an optimal value for the threshold τ may be selected through experiments or the like. That is, even when the transmission path function is estimated by performing interpolation only in the frequency direction, the threshold τ is set in a range where the influence of multipath is not large.

  As described above, the OFDM receiving apparatus according to the present embodiment switches the interpolation method by determining both the multipath maximum delay time and the fading information based on the maximum Doppler shift value. Thereby, basically, Rayleigh fading characteristics can be improved during high-speed movement, etc. while emphasizing reducing the influence of multipath.

  In addition, even when interpolation is performed only in the frequency direction, two interpolation circuits of the frequency direction interpolation circuit 25 and the frequency direction interpolation circuit 29 are used. That is, after the frequency direction interpolation circuit 25 performs quadruple interpolation in the frequency direction, the frequency direction interpolation circuit 29 further performs triple interpolation in the frequency direction. By adopting such a configuration, the circuit scale can be reduced as compared with the case of performing 12-fold interpolation in the frequency direction with a single interpolation circuit. When the method of interpolating 12 times at a time in the frequency direction as in the prior art, a large number of taps is required as an interpolation filter, and the circuit scale has increased, but according to the configuration of the present embodiment, The interpolation process only in the frequency direction can be executed without increasing the circuit scale.

  Furthermore, the frequency direction interpolation circuit 25 and the frequency direction interpolation circuit 29 can share an interpolation filter, and the circuit scale can be further reduced.

  Further, a noise removal filter 28 can be interposed between the frequency direction interpolation circuit 25 and the frequency direction interpolation circuit 29, and noise characteristics can be improved. In the conventional method of interpolating 12 times at a time in the frequency direction, noise removal processing could not be performed on the intermediate data. However, as in the present embodiment, the frequency direction interpolation circuit is distributed in two. Thus, it is possible to perform noise removal processing on intermediate data.

  Similarly, since the noise removal filter 28 is interposed between the time direction interpolation circuit 24 and the frequency direction interpolation circuit 29, it is possible to perform noise removal processing on intermediate data. The noise processing filter interposed between the frequency direction interpolation circuit 25 and the frequency direction interpolation circuit 29 and the noise processing filter interposed between the time direction interpolation circuit 24 and the frequency direction interpolation circuit 29 are made common. It is possible to reduce the circuit scale.

It is a block diagram of the OFDM receiver in this Embodiment. It is a functional block diagram of a transmission path estimation circuit. It is a figure which shows arrangement | positioning of a pilot symbol. It is a figure which shows the interpolation direction in the case of interpolating a transmission line function in a time direction. It is a figure which shows the interpolation direction in the case of interpolating a transmission line function in a frequency direction. It is a figure which shows the switching criteria of the interpolation method of a transmission line.

Explanation of symbols

9 FFT calculator 10 Equalizer 20 Transmission path estimation circuit 21 Multipath detection circuit 22 Pilot extraction circuit 23 Divider 24 Time direction interpolation circuit 25 Frequency direction interpolation circuit 26 Fading detection circuit 27 Switching circuit 28 Noise removal filter 29 Frequency direction Interpolator

Claims (6)

A multipath detector that detects the maximum delay time of the multipath from the received signal;
A fading detector for detecting fading information from the received signal;
A transmission path function calculation unit that calculates a transmission path function of the received signal using pilot data extracted from the received signal;
When the multipath maximum delay time detected by the multipath detection unit is smaller than the first threshold and the fading information detected by the fading detection unit is equal to or greater than the second threshold, the frequency direction A switching unit for selecting a first interpolation method for interpolating the transmission path functions for all data by interpolation of
A first interpolation circuit for interpolating the transmission line function in the frequency direction;
A second interpolation circuit for interpolating the transmission line function in the frequency direction;
Equipped with a,
When the first interpolation method is selected, all the data is obtained by interpolating the transmission path function in the frequency direction by the first interpolation circuit and further interpolating the transmission path function in the frequency direction by the second interpolation circuit. OFDM receiving apparatus characterized that you interpolating transmission path functions related. The OFDM receiver according to claim 1, wherein
When the maximum multipath delay time detected by the multipath detection unit is equal to or greater than the first threshold, the switching unit transmits all data by combining time direction interpolation and frequency direction interpolation. An OFDM receiving apparatus, wherein a second interpolation method for interpolating a path function is selected. In the OFDM receiver according to claim 1 or 2,
The switching unit is configured such that the maximum multipath delay time detected by the multipath detection unit is smaller than the first threshold, and the fading information detected by the fading detection unit is lower than the second threshold. An OFDM receiver characterized by selecting a second interpolation method for interpolating transmission line functions for all data by combining time direction interpolation and frequency direction interpolation in the case of being small. The OFDM receiver according to any one of claims 1 to 3 , further comprising:
A third interpolation circuit for interpolating the transmission path function in the time direction;
With
When the second interpolation method is selected, all the data is obtained by interpolating the transmission path function in the time direction by the third interpolation circuit and further interpolating the transmission path function in the frequency direction by the second interpolation circuit. An OFDM receiver characterized by interpolating a transmission path function. In OFDM receiving apparatus according to any one of claims 1 to 4, further
A noise removing unit that is disposed between the first interpolation circuit and the second interpolation circuit and removes noise of a transmission path function interpolated in the first interpolation circuit;
An OFDM receiving apparatus comprising: The OFDM receiver according to claim 4 , further comprising:
A noise removing unit that is arranged between the third interpolation circuit and the second interpolation circuit and removes noise of the transmission path function interpolated in the third interpolation circuit;
An OFDM receiving apparatus comprising:

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