JP2013046137A - Receiving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate per-carrier likelihood using noise power averaged in frequency direction by nullifying symbol differential power before and after the FFT section updating without using phase rotation correction processing.SOLUTION: A setting unit 102 sets an FFT start position in an arithmetic unit 103 or updates the set position in it and outputs information on a position update notification. The arithmetic unit 103 converts a reception time signal into a frequency signal, and an extraction unit 104 extracts a pilot carrier from the frequency signal. A power calculation unit 106 (204) calculates a differential power of the pilot carrier. A determination unit 106 (206) determines whether the differential power is valid by using the information on a position update notification. A frequency direction averaging unit 107 calculates an average of valid differential power and makes it to be average noise power. Furthermore, an estimation unit 105 performs frequency interpolation on the pilot carrier to estimate transmission line characteristics. An equalization unit 108 calculates an equalization signal by using the transmission line characteristics and the reception frequency signal. A likelihood calculation unit 109 calculates likelihood by using the equalization signal, the transmission line characteristics, and the average noise power.

Description

  The present invention relates to a receiving apparatus that receives a signal modulated by OFDM (Orthogonal Frequency Division Multiplexing) by a transmitting apparatus and performs demodulation processing and decoding processing.

  Due to the orthogonality, an OFDM system using an FFT (Fast Fourier Transform: Fast Fourier Transform algorithm) is widely used as a digital modulation / demodulation system for information communication regardless of whether it is wired or wireless.

In the OFDM method, the noise power is generally calculated by using a difference between the guard interval interval of the reception time signal at the reception device and the difference between the ideal value of the known signal of the reception frequency signal converted by FFT or the like. Are known.
In addition, in the demodulation processing, decoding processing, error correction processing, and the like of the receiving apparatus, likelihood may be calculated from the received signal and noise power and given.

  Patent Document 1 derives an estimate of noise and estimation error due to at least one pilot subband that is zeroed out and not used for pilot transmission, and uses the estimate of noise and estimation error to log An apparatus is described that applies to a communication system that includes at least one processor that calculates a likelihood ratio (LLR) and a memory coupled to the at least one processor.

  Patent Document 2 discloses a receiving unit that receives an OFDM signal from a wireless transmission device that transmits the OFDM signal, an estimation unit that estimates a propagation path response of the received OFDM signal, and the received OFDM signal in a frequency domain. A Fourier transformer for converting the signal into a signal; a coupling means for combining the received signals of two subcarriers at symmetrical positions around the center frequency of the frequency domain for the converted OFDM signal; and the estimated propagation Calculating means for calculating the likelihood of each bit of the signal transmitted on the two subcarriers based on the path response; and a center of the band from both ends of the band of the two subcarriers of the plurality of likelihoods And a multiplying means for multiplying the likelihood corresponding to at least one or more subcarrier numbers by a weighting factor of less than one. To have.

  Patent Document 3 discloses a first adaptive equalization process for removing an inter-symbol interference component before and after the present time from signals orthogonally frequency-division multiplexed received by one or a plurality of antennas, inter-carrier interference at the present time, Second adaptive equalization processing for removing inter-interference components, signal detection processing for processing signals equalized by the first and second adaptive equalization processing, error correction decoding processing for error correction decoding, and the first And an OFDM (Orthogonal Frequency Division Multiplexing) adaptive equalization receiving system composed of a channel estimation process for estimating a channel response used in the second adaptive equalization process.

  Patent Document 4 discloses, as a reference signal, a reference signal generation unit that generates a spatially multiplexed pilot subcarrier signal, and a spatially multiplexed pilot that extracts a spatially multiplexed pilot subcarrier signal from a multicarrier modulated reception signal. The phase error of the received signal by comparing the reference signal obtained by the subcarrier extracting means, the reference signal generating means, and the spatially multiplexed pilot subcarrier signal obtained by the spatially multiplexed pilot subcarrier extracting means And a phase compensation means for compensating for the phase error is described.

  Patent Document 5 discloses a transmission signal determination function, a propagation channel estimation result, and a function for estimating an error with respect to the transmission signal based on the received signal, and the transmission signal weighted based on the estimated error. There is described a wireless communication apparatus that receives a spatially multiplexed transmission signal having a function of performing error correction decoding processing using likelihood information for.

  Patent Document 6 discloses receiving means for receiving a transmitted OFDM signal, OFDM demodulating means for OFDM demodulating the received signal received by the receiving means, and signal strength of the OFDM demodulated signal demodulated by the OFDM demodulating means. A weight coefficient calculating means for calculating the likelihood information, likelihood generating means for generating likelihood information for performing error detection iterative decoding from the OFDM demodulated signal, and the likelihood information based on the calculated value in the weight coefficient calculating means. Likelihood changing means for changing, a buffer for holding until the likelihood information changed by the likelihood changing means is accumulated for the error correction decoding unit, and error correction iterative decoding using the likelihood information held in the buffer A receiving apparatus including error correction iterative decoding means for performing is described.

Special table 2008-516563 JP 2008-17144 A JP 2004-211702 A JP 2007-208967 A JP 2007-336532 A JP 2008-10987 A

In order to improve the performance of demodulation processing, decoding processing, and error correction processing in the receiving apparatus, it is necessary to calculate likelihood for each subcarrier.
In calculating the likelihood for each subcarrier, it is possible to refer to the characteristics of the transmission path between transmission and reception and noise power information.
The state of the transmission path can be estimated from a known signal included in a received signal such as a preamble signal or a pilot signal, for example.

In addition, when using the difference between the reception signal and the ideal value of the known signal, processing such as phase rotation correction is required in the previous stage in order to obtain the difference correctly.
As an alternative, if a fixed FFT window is provided, the noise power can be calculated by using a one-symbol difference of a known signal of the received frequency signal. The calculation principle and details will be described later.

However, when calculating the difference in the time direction of the known signal included in the received signal, the FFT interval that gives the time signal for conversion to the frequency signal is updated to follow the time variation, so that the amount of rotation of the frequency signal is increased. Change.
For this reason, even if the time direction difference of the known signal before and after the update of the FFT interval is used, there is a problem that correct noise power cannot be calculated because the phase rotation amounts of the two differ.

Further, if a phase rotation correction process is added after the FFT calculation, symbols before and after the update of the FFT interval can be used, but the phase rotation correction process has a problem that the circuit scale becomes large.
In addition, when equalization is performed using transmission path characteristics calculated from pilot carriers, the subcarrier locations where power is reduced due to fading such as multipath also raises noise power. However, there is a problem that the S / N ratio decreases.

  An object of the present invention is to provide a receiver that solves the above-described problems without using a phase rotation correction process with a large circuit scale.

  In order to solve the above-mentioned problems, the present invention performs FFT interval update detection on an input time signal, and invalidates the time direction difference of the known signal before and after the update, thereby making it possible to reduce the transmission path characteristics and the magnitude of noise power. The above problem is solved without using a phase rotation correction process with a large circuit scale.

  Specifically, the receiving apparatus according to the present invention is a receiving apparatus that receives an OFDM-modulated signal and performs demodulation processing and decoding processing, and the FFT start position setting unit sets the FFT start position in the FFT calculation unit. Alternatively, the position is updated, and the set or updated position is output as FFT position update notification information, and the FFT calculation means performs an FFT calculation on the reception time signal and converts it into a frequency signal. Then, the pilot carrier extraction means extracts the pilot carrier signal from the reception frequency signal converted by the FFT calculation means, the power calculation means calculates the differential power of the extracted pilot carrier, and the determination means notifies the FFT position update notification Information is used to determine whether the differential power is valid or invalid, and the average noise power of the differential power for which the average noise power calculation means is valid is calculated. Further, the transmission path characteristic estimation means estimates the transmission path characteristic by performing frequency interpolation on the extracted pilot carrier, and the equalization means uses the transmission path characteristic and the converted received frequency signal. An equalized signal is calculated. Then, likelihood calculating means calculates likelihood using the equalized signal, the transmission path characteristic, and the average noise power.

Here, various modes can be adopted as the average noise power calculation means in the present invention.
For example, the average noise power calculation means may calculate the average noise power by performing an average calculation in the frequency direction, or calculate the average noise power by performing an average calculation in the frequency direction and an average calculation in the time direction. But you can. Alternatively, the average noise power calculation means may further include frequency interpolation means for calculating an average noise power by performing an average calculation in the time direction and interpolating the average noise power in the frequency direction.

  According to the present invention, it is possible to detect the update of the FFT interval to be updated in order to follow the time variation and invalidate the difference between the known signals of the reception frequency signals before and after the update. It is possible to calculate noise power from a known signal included in. Then, the estimation result of the channel characteristic obtained by interpolating the known signal of the received frequency signal, the equalized signal, and the noise power are used to calculate the likelihood for each carrier, thereby performing the demodulation process, the decoding process, and the error correction. Quality in processing can be improved.

It is a figure which shows the structure of the principal part of the receiver which concerns on 1st Example of this invention. It is a figure which shows the structure of the 1 symbol difference calculation part which concerns on 1st Example of this invention. It is a timing chart of the process using substitution of the 1 symbol difference calculation part which concerns on 1st Example of this invention. It is a timing chart of the process using the average of the 1 symbol difference calculation part which concerns on 1st Example of this invention. It is a truth table in the process using replacement of the differential power valid / invalid determiner according to the first embodiment of the present invention. It is a truth table in the process using the average of the differential power valid / invalid determiner according to the first embodiment of the present invention. It is a figure which shows the structure of the principal part of the receiver which concerns on the 2nd Example of this invention. It is a figure which shows the structure of the 1 symbol difference calculation part which concerns on the 2nd Example of this invention. It is a timing chart of the process of the 1 symbol difference calculation part which concerns on the 2nd Example of this invention. It is a truth table of the differential power valid / invalid determiner according to the second embodiment of the present invention. It is a figure which shows the structure of the principal part of the receiver which concerns on the 3rd Example of this invention.

A receiving apparatus according to the present invention will be specifically described based on the embodiment shown in the drawings.
<First Example>
FIG. 1 shows the configuration of an OFDM signal receiving apparatus according to the first embodiment of the present invention.
The receiving apparatus of this embodiment includes a guard interval (GI) correlation calculation unit 101, an FFT window start position setting unit 102, an FFT calculation unit 103, a pilot carrier extraction unit 104, a frequency interpolation unit 105, and one symbol. A difference calculation unit 106, a frequency direction averaging unit 107, an equalization unit 108, and a likelihood calculation unit 109 are provided.

  The guard interval correlation calculation unit 101 delays the reception time signal y (n, m) by an effective symbol length, calculates a correlation value COR (n, m), and outputs it to the FTT window start position setting unit 102. Here, n is a sample number and m is a symbol number.

The FFT window start position setting unit 102 sets or updates the FFT window start position from the correlation value COR (n, m) of the guard interval correlation calculation unit 101, outputs the set or updated position to the FFT calculation unit 103, and The flag FLAG is output to the 1-symbol difference calculation unit 106 to notify the set or updated position.
The FFT window start position is updated in a certain time (symbol) in order to follow the fluctuation.

  The FFT operation unit 103 converts the received time signal y (n, m) into a frequency signal Y (k, m) based on the FFT window start position set by the FFT window start position setting unit 102, and extracts a pilot carrier. To the unit 104 and the equalization unit 108. Here, k is a carrier number.

Pilot carrier extraction section 104 extracts a pilot carrier from reception frequency signal Y (k, m), and outputs the extracted pilot carrier signal Y _P (k, m) to frequency interpolation section 105 and 1-symbol difference calculation section 106. To do. Here, Y _P (k, m) is obtained by replacing the received frequency signal Y (k, m) with 0 except for the pilot carrier.

The frequency interpolation unit 105 performs, for example, frequency interpolation such as an interpolation filter or linear interpolation using the input pilot carrier extraction signal Y _P (k, m), and the transmission path characteristics estimated by this frequency interpolation. The result H (k, m) is output to the equalization unit 108 and the likelihood calculation unit 109. That is, the frequency interpolation unit 105 constitutes a channel estimation unit that estimates channel characteristics by performing frequency interpolation on the pilot carrier.

The 1-symbol difference calculation unit 106 calculates the 1-symbol difference power N _P (k, m) of the pilot carrier extracted by the pilot carrier extraction unit 104 and outputs it to the frequency direction averaging unit 107.
The 1-symbol difference calculation unit 105 will be described in detail with reference to FIG.

FIG. 2 shows a configuration of the one symbol difference calculation unit 106.
The 1-symbol difference calculation unit 105 includes a real part / imaginary part separator 201, a 1-symbol delay unit 202 provided in each of the real part and the imaginary part, an adder 203 provided in each of the real part and the imaginary part, A power calculator 204, a symbol counter 205, and a differential power valid / invalid determiner 206 are provided.

（数式１） Here, the principle that the noise power can be calculated using the 1-symbol difference of the pilot carrier will be described. This principle is the case where there is no change in the transmission path between the symbols.
Assuming that the received signal on the frequency axis from which only the pilot carrier is extracted is r (k, m), and r (k, m) and the signal one symbol before it are r (k, m-1), respectively, It is expressed in
Here, s (k, m) is a desired signal component of the received signal r (k, m), n (k, m) is a noise component of the received signal r (k, m), and s (k, m− 1) is a desired signal component of the received signal r (k, m-1), and n (k, m-1) is a noise component of the received signal r (k, m-1).

(Formula 1)

（数式２） Taking the difference between these two signals r (k, m) and r (k, m-1), the pilot carrier is regarded as s (k, m) = s (k, m-1) and The electric power N _P (k, m) is expressed by Equation 2.

(Formula 2)

（数式３） Here, an expected value of the power N _P (k, m) is considered.
When Formula 2 is expanded, Formula 3 is obtained.
Here, * indicates a complex conjugate.

(Formula 3)

（数式４）

（数式５）

（数式６） Further, n (k, m) and n (k, m-1) are assumed to be Gaussian noises and are independent of each other. Therefore, when the variance is σ ² , the relational expressions of Expression 4 and Expression 5 are established. .
Therefore, from these relational expressions, Expression 3 can be summarized as Expression 6.

(Formula 4)

(Formula 5)

(Formula 6)

  From the above, twice the noise power is obtained from the one-symbol difference of the pilot carrier.

3 and 4 show timing charts of operation examples of the one-symbol difference calculation unit 106. FIG.
This operation example shows a case where the FFT window start position is updated at intervals of 10 symbols.
FIG. 3 shows the value of the previous symbol held in the 0th order, and FIG. 4 shows the value replaced with the average value of the previous nine symbols.

The real part / imaginary part separator 201 separates the input signal (pilot carrier extraction signal) Y _P (k, m) into a real part and an imaginary part, and outputs them to the 1-symbol delay unit 202 and the adder 203, respectively.

In the real part, the 1-symbol delay unit 202 delays the input signal real (Y _P (k, m)) by one symbol and outputs the delayed signal to the adder 203. The adder 203 outputs the input signal real (Y _P (Y _P ( k, m)) and the signal real (Y _P (k, m−1)) delayed by one symbol, and outputs the sum E _I (k, m) to the power calculator 204.

In the imaginary part, the 1-symbol delay unit 202 delays the input signal imag (Y _P (k, m)) by one symbol and outputs it to the adder 203, and the adder 203 outputs the input signal imag (Y _P (Y _P ( k, m)) and the signal imag (Y _P (k, m-1)) delayed by one symbol, and output the sum E _Q (k, m) to the power calculator 204.

（数式７） The power calculator 204 calculates power N ′ _P (k, m) using two input signals and outputs the power to the valid / invalid determiner 206.
Here, the calculation of the power N ′ _P (k, m) is performed by Equation 7. Note that 1/2 in Equation 7 is for canceling the double of Equation 6.

(Formula 7)

  The symbol counter 205 treats the input FFT window update flag FLAG as a counter reset, increments the counter value for each symbol, and outputs the counter value COUNT to the valid / invalid determiner 206.

The valid / invalid determiner 206 selects a signal N _P (k, m) to be output based on the input counter value, and outputs it to the frequency direction averaging unit 107.
The selection of this signal is performed, for example, using a truth table as shown in FIG. Incidentally, N _U in the truth table is a FFT window starting position update interval number of symbols.
That is, the valid / invalid determination unit 206 invalidates the differential power before and after the update of the FFT window start position based on the counter value COUNT based on the FFT window update flag FLAG, and outputs valid differential power to the frequency direction averaging unit 107.

（数式８） The frequency direction averaging unit 107 performs, for example, an average calculation in the frequency direction as in Expression 8 on the input differential power N _P (k, m), and the calculation result N (m) is used as the likelihood calculation unit 109. Output to.
Here, in Equation 8, K is the number of carriers in one symbol, and K _P is the number of pilot carriers in one symbol.

(Formula 8)

（数式９） The equalization unit 108 calculates the equalized signal X (k, m) using the reception frequency signal Y (k, m) and the transmission path characteristic estimation signal H (k, m), and then proceeds to the likelihood calculation unit 109. Output.
Here, X (k, m) can be calculated as in Equation 9.

(Formula 9)

（数式１０） Likelihood calculation section 109 uses equalization signal X (k, m), transmission path characteristic estimation signal, H (k, m), and average noise power N (k, m) interpolated in frequency for each carrier. A likelihood L (k, m, d _i ) is calculated and output.
Here, the log-likelihood ratio LLR (k, m) is generally expressed as Equation 10. P (α) is a probability, and d _i is the i-th bit of the bit string D assigned to the mapping point.

(Formula 10)

（数式１１） Then, when Formula 10 is expanded, it is expressed as Formula 11.
Here, _SK is an ideal symbol point.

(Formula 11)

（数式１２） P (Y (k, m) | S _K ) in Expression 11 is expressed as Expression 12.

(Formula 12)

（数式１３）

（数式１４）

（数式１５）

（数式１６） Using the received signal Y (k, m), the transmission path characteristic H (k, m), the equalized signal X (k, m), the ideal symbol point _SK, and the noise power σ ² , It is expressed in such a proportional relationship.
Then, when Equation 13 is transformed, Equation 14 is obtained.
And if it is set to Numerical formula 15, it will be put together like Numerical formula 16.

(Formula 13)

(Formula 14)

(Formula 15)

(Formula 16)

（数式１７） Equation 16 can calculate the likelihood for each carrier in consideration of the transmission path characteristics.
In the present invention, the log likelihood ratio L (k, m, d _i ) can be given by Equation 17 using the noise power N (m) calculated from the received signal.

(Formula 17)

  According to the first embodiment described above, it is possible to invalidate the symbol difference power before and after updating the FFT interval and calculate the likelihood for each carrier using the noise power averaged in the frequency direction.

<Second embodiment>
FIG. 7 shows the configuration of an OFDM signal receiving apparatus according to the second embodiment of the present invention.
The receiving apparatus includes a guard interval correlation calculation unit 101, an FFT window start position setting unit 102, an FFT calculation unit 103, a pilot carrier extraction unit 104, a frequency interpolation unit 105, a 1-symbol difference extraction unit 301, A frequency direction average unit 107, a time direction average unit 302, an equalization unit 108, and a likelihood calculation unit 109 are provided.

  In the present embodiment, the guard interval correlation calculation unit 101, the FFT window start position setting unit 102, the FFT calculation unit 103, the pilot carrier extraction unit 104, the frequency interpolation unit 105, the frequency direction average unit 107, and the like. Since the converting unit 108 and the likelihood calculating unit 109 are the same as those in the first embodiment, the description thereof is omitted.

FIG. 8 shows the configuration of the 1-symbol difference extraction unit 301.
The 1-symbol differential power calculation unit 301 includes a real part / imaginary part separator 201, a 1-symbol delay unit 202 provided in each of the real part and the imaginary part, and an adder 203 provided in each of the real part and the imaginary part. , A power calculator 204, a symbol counter 205, and a differential power valid / invalid determiner 401.

  In this embodiment, the real part / imaginary part separator 201, the 1-symbol delay unit 202, the adder 203, the power calculator 204, and the symbol counter 205 are the same as those in the first embodiment. Description is omitted.

FIG. 9 shows a timing chart of an operation example of the 1-symbol differential power calculation unit 301.
This operation example shows a case where the FFT start position is updated at intervals of 10 symbols. As shown in the figure, the invalid power difference is replaced with 0.

The valid / invalid determination unit 401 selects a signal N _f (k, m) to be output based on the input counter value COUNT, and outputs the signal N _f (k, m) to the frequency direction averaging unit 107.
The selection of this signal is performed using, for example, a truth table as shown in FIG.

（数式１８） Time direction averaging section 302 averages N _f (m) input from frequency direction averaging section 107 in the time direction (symbol direction), and outputs the average value N (m) to likelihood calculating section 109.
This average value N (m) can be calculated as shown in Equation 18, for example.

(Formula 18)

  According to the second embodiment, the symbol difference power before and after the FFT interval update is invalidated, and the noise power averaged in the frequency direction is further averaged in the time direction, so that each carrier with higher accuracy is used. It is possible to calculate the likelihood of.

<Third embodiment>
FIG. 11 shows the configuration of an OFDM signal receiving apparatus according to the third embodiment of the present invention.
The receiving apparatus includes a guard interval correlation calculation unit 101, an FFT window start position setting unit 102, an FFT calculation unit 103, a pilot carrier extraction unit 104, a frequency interpolation unit 105, a 1-symbol difference extraction unit 106, A frequency direction averaging unit 501, a frequency interpolation unit 105, an equalization unit 108, and a likelihood calculation unit 502 are provided.

  In this embodiment, a guard interval correlation calculation unit 101, an FFT window start position setting unit 102, an FFT calculation unit 103, a pilot carrier extraction unit 104, a frequency interpolation unit 105, a 1-symbol difference extraction unit 106, Since the equalizing unit 108 is the same as that in the first embodiment, description thereof is omitted.

（数式１９） The time direction average unit 501 averages the signal N _P (k, m) input from the 1-symbol difference extraction unit 106 for each carrier, and the average value N _t (k, m) is a frequency interpolation unit. To 105.
This average value N _t (k, m) is calculated as in Equation 19, for example.
Then, the frequency interpolation unit 105 performs the average calculation in the frequency direction as described above on the input average value N _t (k, m), and sends the calculation result N (m) to the likelihood calculation unit 502. Output.
The

(Formula 19)

（数式２０） The likelihood calculation unit 502 uses the equalized signal X (k, m), the transmission path estimation signal H (k, m), and the average noise power N (k, m) interpolated in frequency, for each carrier. The degree L (k, m, d _i ) is calculated.
This likelihood L (k, m, d _i ) can be given as in Expression 20 based on Expression 17.

(Formula 20)

  According to the third embodiment described above, it is possible to invalidate the symbol difference power before and after the FFT interval update, and to calculate the carrier likelihood with higher accuracy using the transmission path characteristics and the noise characteristics for each carrier.

101: Guard interval correlation calculation unit, 102: FFT window position setting unit,
103: FFT calculation unit, 104: Pilot carrier extraction unit,
105: Frequency interpolation unit, 106: 1 Symbol difference calculation unit,
107: Frequency direction average part 108: Equalization part
109: Likelihood calculation unit 201: Real part / imaginary part separator,
202: 1 symbol delay unit, 203: adder,
204: Power calculator, 205: Symbol counter,
206: differential power validity / invalidity determination unit, 301: 1 symbol difference calculation unit,
302: Time direction average part 401: Differential power valid / invalid determiner,
501: Time direction average unit 502: Likelihood calculation unit

Claims (4)

In a receiving apparatus that receives an OFDM-modulated signal and performs demodulation processing and decoding processing,
FFT calculation means for performing FFT calculation on the reception time signal and converting it to a frequency signal;
FFT start position setting means for setting or updating the FFT start position in the FFT calculation means, and outputting the set or updated position as FFT position update notification information;
Pilot carrier extraction means for extracting a pilot carrier signal from the reception frequency signal converted by the FFT operation means;
Power calculating means for calculating the differential power of the pilot carrier extracted by the pilot carrier extracting means;
Determination means for determining validity and invalidity of the differential power using the FFT position update notification information;
Average noise power calculation means for calculating average noise power of the differential power validated by the determination means;
Transmission path characteristic estimation means for estimating transmission path characteristics by performing frequency interpolation on the pilot carrier extracted by the pilot carrier extraction means;
Equalization means for calculating an equalized signal using the transmission path characteristics obtained from the transmission path estimation means and the received frequency signal;
A likelihood apparatus comprising: likelihood calculation means for calculating likelihood using the equalized signal, the transmission path characteristic, and average noise power obtained from the average noise power calculation means. The receiving device according to claim 1,
The average noise power calculation means calculates an average noise power by performing an average calculation in a frequency direction. The receiving device according to claim 1,
The average noise power calculating means calculates an average noise power by performing an average calculation in a frequency direction and an average calculation in a time direction. The receiving device according to claim 1,
The average noise power calculation means calculates the average noise power by performing an average calculation in the time direction,
A receiving apparatus, further comprising frequency interpolation means for interpolating the average noise power in the frequency direction.

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