JP2003309498A - Delay wave canceler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten a coefficient update interval of an adaptive filter applied to a delay wave canceler for canceling a delay wave of a desired wave due to a multipath, radio wave wraparound or the like. <P>SOLUTION: A cancel residual calculating part for calculating a frequency characteristic showing the cancel residual component of the delay wave included in an output signal of a subtracter and calculating a filter coefficient for the adaptive filter with the cancel residual component is provided with an FFT circuit for converting an input signal from the subtracter into data of a frequency domain and outputting the data, a data distribution circuit for dividing the data of the frequency domain into respective data for a plurality of domains and outputting the data for the plurality of domains, a plurality of residual frequency characteristic calculation circuits for parallelly calculating a frequency characteristic showing the cancel residual component from the data of the frequency domains inputted from the data distribution circuit in each of the circuits, a data combination circuit for combining and outputting respective signals from the residual frequency characteristic calculation circuits, and an IFFT circuit for applying inverse fast Fourier transformation to the frequency characteristic data from the data combination circuit to generate a filter coefficient for update. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, in digital transmission and digital broadcasting using OFDM signals, retransmits multipaths included in a reception signal from a master station and a reception signal from the master station at the same frequency as reception. The present invention relates to a delayed wave canceller for electrically canceling a delayed wave of a desired wave due to wraparound of a radio wave generated at the time of using an adaptive filter.

[0002]

2. Description of the Related Art In this type of conventional delay wave canceller,
For example, Japanese Patent Application Laid-Open No. 2001-237749 filed by the applicant
In calculating the frequency characteristic showing the cancellation residual component, as seen in the "wraparound canceller" in Japanese Patent Publication,
Most of the processing is done serially.

[0003]

However, the FFT
The detection of the error of the frequency phase characteristic due to the deviation of the window from the effective symbol period has a problem that it takes a long time to calculate because the calculation amount is particularly large. Therefore, it takes time to observe the signal with the canceller and generate a new filter coefficient for the adaptive filter, and there is a problem that the coefficient update interval becomes long.

SUMMARY OF THE INVENTION An object of the present invention is to provide a delayed wave canceller which requires a short coefficient update interval of an adaptive filter.

[0005]

The present invention provides a subtractor having a subtracted terminal to which an input signal from a receiving system is supplied and a subtraction terminal to which a cancel signal for delay wave cancellation is supplied, and An output signal from the subtractor is supplied, an adaptive filter that generates the cancellation signal by convolving the characteristics of the filter coefficient with the output signal, and a delay wave included in the output signal that receives the output signal of the subtractor Of the cancellation residual component and calculates a filter coefficient based on the cancellation residual component, and an updated filter obtained based on the output from the cancellation residual calculation unit. A coefficient for calculating a new filter coefficient to be supplied to the adaptive filter from the coefficient and the filter coefficient at the time of the previous update supplied to the adaptive filter. In the delay wave canceller which comprises a data coefficient updating unit, the year cancel residual calculating unit, F
An FFT circuit that extracts a signal in the time domain of the effective symbol period by using an FT window, performs FFT (Fast Fourier Transform), converts the signal into data in the frequency domain, and outputs the data, and data in the frequency domain output from the FFT circuit. L (L is a natural number)
And a data distribution circuit for outputting to a plurality of residual frequency characteristic calculation circuits of the same number as the number of divisions, and a signal from the data distribution circuit is input, and cancellation residuals are input from the input frequency domain data. A plurality of residual frequency characteristic calculation circuits for calculating and outputting frequency characteristics showing components, and a data synthesizing circuit for synthesizing respective signals from the residual frequency characteristic calculation circuits and outputting as continuous frequency characteristic data. And the frequency characteristic data output from the data synthesis circuit to IFFT
(Inverse fast Fourier transform) and an IFFT circuit that generates the updated filter coefficient, and the calculation of the frequency characteristic indicating the cancellation residual component is performed in parallel by the plurality of residual frequency characteristic calculation circuits. It is characterized by being configured as described above.

In a preferred embodiment of the present invention, the cancellation residual calculation section includes two residual frequency characteristic calculation circuits, and the data distribution circuit includes the two residual frequency characteristic calculation circuits in the FFT circuit. Data output from 2
At the time of distribution, the data closest to the DC carrier is output to both residual frequency characteristic calculation circuits.

In still another preferred embodiment of the present invention, the residual frequency characteristic calculation circuit calculates a frequency characteristic of a propagation path from input frequency domain data and outputs the frequency characteristic calculation circuit, and the frequency characteristic calculation circuit. An FFT window error calculation circuit for calculating an error of a frequency phase characteristic due to an error of the FFT window of the FFT circuit from a normal position of an effective symbol period from the frequency characteristic signal output from the circuit, and each residual frequency characteristic calculation The output of the FFT window error calculation circuit in the circuit is input respectively, the FFT window error average circuit which calculates and outputs the average value of the data from each FFT window error calculation circuit, and the signal from the frequency characteristic calculation circuit, The FFT
An FFT window error correction circuit for performing phase correction using the FFT window error component output from the window error averaging circuit and outputting the same;
The main wave calculation circuit that calculates and outputs the main wave component included in the output of the T window error correction circuit and the output of the main wave calculation circuit of each residual frequency characteristic calculation circuit are input, and the main wave calculation circuit outputs Main frequency averaging circuit that calculates and outputs the average value of the data, and cancel residual calculation that calculates the frequency characteristic matched with the delay wave characteristic from the output of the main wave averaging circuit and the output of the FFT window error correction circuit. It is equipped with a circuit.

Furthermore, in another preferred embodiment of the present invention, the cancellation residual calculation circuit outputs a frequency characteristic F (k, n) (where k is a carrier number representing a frequency) output from the FFT window error correction circuit. , N is a natural number indicating the number of times the filter coefficient is updated by the filter coefficient updating unit) and the main component D (n) output from the main averaging circuit, and the cancellation residual component E (k, n) is obtained. The following equation, And a filter coefficient for canceling the multipath included in the input signal is generated.

In still another preferred embodiment of the present invention, the cancellation residual calculation circuit outputs a frequency characteristic F (k, n) (where k is a carrier number representing a frequency) output from the FFT window error correction circuit. , N is a natural number indicating the number of times the filter coefficient is updated by the filter coefficient updating unit) and the main component D (n) output from the main averaging circuit, and the cancellation residual component E (k, n) is obtained. The following equation, And a filter coefficient for canceling the wraparound included in the input signal is generated.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a delayed wave canceller according to the present invention, in which 1 is a delayed wave canceller of the present invention, 2 is a subtractor, 3 is a band pass filter, and 4 is an adaptive filter. 5 is a filter coefficient generation circuit, 6
Is a cancellation residual calculation unit, 7 is a filter coefficient updating unit, and 8 is
Is an FFT circuit, 9 is a data distribution circuit, 10-1, 10-
2, ..., 10-L are residual frequency characteristic calculation circuits, 11 is a data synthesis circuit, and 12 is an IFFT circuit.

The delayed wave canceller 1 is configured to receive a time domain signal and output a time domain signal after canceling the delayed wave.

The subtracter 2 subtracts the cancel signal for canceling the delay wave output from the adaptive filter 4 from the canceller signal input to the delay wave canceller 1, and outputs the subtraction signal to the bandpass filter 3.

The bandpass filter 3 attenuates the frequency component outside the signal band of the signal output from the subtractor 2 and outputs it as a delayed wave canceller output, and also outputs it to the adaptive filter 4 and the filter coefficient generation circuit 5.

The adaptive filter 4 is a bandpass filter 3
The cancel signal is generated by convoluting the filter coefficient from the filter coefficient generation circuit 5 with the signal from
Output to the subtraction terminal of.

The filter coefficient generation circuit 5 is composed of a cancellation residual calculation unit 6 and a filter coefficient updating unit 7, and the delay wave canceller output signal input from the bandpass filter 3 is first canceled residual calculation unit 6. Is input to.

The FFT circuit 8 extracts the effective symbol period of the delayed wave canceller output signal, which is a signal in the time domain input from the bandpass filter 3, using an FFT window, and extracts the extracted data from an FFT (Fast Fourier Transform). ) And converts it into frequency domain data, and outputs it to the data distribution circuit 9.

The data distribution circuit 9 divides the data in the frequency domain from the FFT circuit 8 into L (L is a natural number) regions, and outputs to L residual frequency characteristic calculation circuits 10 of the same number as the number of divisions. Output each.

Each residual frequency characteristic calculation circuit 10
Calculates the frequency characteristic indicating the cancellation residual component in parallel from each input frequency domain data in each circuit and outputs it to the data synthesizing circuit 11. The details of the operation of the residual frequency characteristic calculation circuit 10 will be described later in detail with reference to FIG.

The data synthesizing circuit 11 outputs to the IFFT circuit 12 frequency characteristic data obtained by synthesizing the frequency characteristic indicating the cancel residual component from each of the L residual frequency characteristic calculating circuits 10 so that the frequency becomes continuous. .

The IFFT circuit 12 performs IFFT (Inverse Fast Fourier Transform) on the input frequency characteristic data to generate filter coefficient update data, which is output to the filter coefficient update unit 7 as the output of the cancellation residual calculation unit 6. To do.

The filter coefficient update unit 7 generates a new filter coefficient from the filter coefficient update data from the cancellation residual calculation unit 6 and the filter coefficient at the time of the previous update supplied to the adaptive filter 4 to generate an adaptive filter. Output to 4.

The operation of the delayed wave canceller according to the present invention has been described above. However, the cancel residual calculator 6 includes L residual frequency characteristic calculation circuits 10-1, 10-2 ,.
Except for performing parallel processing using 0-L, this is a known process such as "wraparound canceller" in Japanese Patent Application Laid-Open No. 2001-237749, filed by the applicant of the present application. Omit it.

FIG. 2 is a block diagram showing an embodiment of the residual frequency characteristic calculation circuit 10 in the cancellation residual calculation unit 6 of FIG. 1. In this example, the configuration in the case of L = 2 is shown. . In addition, the same block as in FIG.
The same reference numerals are given and the same reference numerals are given to those showing the same components in each of the residual frequency characteristic calculation circuits 10-1 and 10-2.

In this example, the data distribution circuit 9 distributes the frequency domain data output from the FFT circuit 8 into two.

The signals input from the data distributor 9 to the respective residual frequency characteristic calculation circuits 10-1 and 10-2 are first input to the frequency characteristic calculation circuit 13 and are subjected to OFDM.
The frequency characteristic of the propagation path is calculated by using the SP (Scattered Pilot) inserted in the signal and the judgment value of the data carrier, and the FFT window error calculation circuit 14 and the FFT are calculated.
Output to the window error correction circuit 15.

The FFT window error calculation circuit 14 calculates and outputs the error of the frequency phase characteristic due to the error from the normal position of the FFT window of the FFT circuit 8 in the effective symbol period of the OFDM signal. The simple operation principle of the circuit 14 will be described. Error τ from the normal position of the effective symbol period
(Τ is a real number indicating time) is exp (jω
τ) (where j is an imaginary unit), this component becomes an error of the primary slope in the frequency phase characteristic. Therefore,
The FFT window error calculation circuit 14 calculates the error of the frequency phase characteristic by linear approximation by the least square method.
For the detailed operation, refer to the "OFDM demodulator" of Japanese Patent Laid-Open No. 2000-295195, which is the invention of the present inventors. Further, the FFT window error calculating circuit 14 outputs the error calculation result of the frequency phase characteristic to the FFT window error averaging circuit 16 in the same residual frequency characteristic calculating circuit 10, and at the same time, the FFT in the other residual frequency characteristic calculating circuit 10. It is also output to the window error averaging circuit 16 at the same time.

The FFT window error averaging circuit 16 calculates the average value of the error data of the frequency phase characteristics input from each FFT window error calculating circuit 14 and outputs it to the FFT window error correcting circuit 15. Here, the output from each FFT window error averaging circuit 16 has the same input, so the same data is output.

The FFT window error correction circuit 15 corrects the error of the frequency phase characteristic included in the output from the frequency characteristic calculation circuit 13 by using the average error data of the frequency phase characteristic from the FFT window error averaging circuit 16. , As a result F (n, k)
(Where, k is a carrier number indicating a frequency, and n is a natural number indicating the number of times the filter coefficient updating unit 7 updates the filter coefficient) are output to the main wave calculation circuit 17 and the cancellation residual calculation circuit 18.

Here, when the frequency domain data output from the FFT circuit 8 is divided into two by the data distribution circuit 9,
The data distribution circuit 9 is configured to output the data closest to the DC carrier (center carrier of the OFDM signal) to both the residual frequency characteristic calculation circuits 10-1 and 10-2. Since the DC carrier is a carrier that does not receive the error of the frequency phase characteristic due to the FFT window error, the residual frequency characteristic calculation circuit 10 uses the carrier as a reference to determine the F
The frequency phase characteristic is corrected by the FT window error.
Therefore, each residual frequency characteristic calculation circuit circuit 10 has an FF.
By having the frequency domain data output from the T circuit 8, the two circuits can independently correct the frequency phase characteristic due to the FFT window error, and thus the processing speed of the cancellation residual calculation unit is improved. Is possible. But F
In the FT window error correction circuit 15, since it is necessary to correct the error of the frequency phase characteristic with the DC carrier as a reference, even if parallel processing is performed by three or more circuits, the frequency characteristic of the output from each circuit is It is necessary to determine whether or not they are continuous, and if they are not continuous, it is necessary to correct them so that they are continuous. Therefore, even if this processing is performed by using three or more FFT window error correction circuits 15, that is, three or more residual frequency characteristic calculation circuit circuits 10, improvement in processing speed cannot be expected very much.

The main wave calculation circuit 17 calculates the average value of the main wave component contained in the output of the FFT window error correction circuit 15, that is, F (n, K) from the FFT window error correction circuit 15 in the frequency direction. The main wave component D1 (n) represented by the following equation (1) is output to the main wave averaging circuit 19. Here, K indicates the number of F (n, K) data.

The main wave averaging circuit 19 calculates an average D (n) of the output D1 (n) of the main wave calculating circuit 17 and the output D2 (n) of another main wave calculating circuit 17 and cancels the remaining cancellation. Output to the difference calculation circuit 18. The average D (n) is expressed by the following equation.

The cancellation residual calculation circuit 18 uses the output F (n, K) of the FFT window error correction circuit 15 and the output D (n) of the main wave averaging circuit 19 to indicate a frequency characteristic E (n) indicating a cancellation residual component. ,
k) is calculated and output to the data synthesis circuit 11. here,
For the frequency characteristic E (k, n) indicating the cancellation residual component, the following equation (3) is used when the delay wave canceller is used as a multipath scan cellar (ghost canceller), and when it is used as a detour canceller (echo canceller). Is calculated using the following equation (4). This is because the propagation paths of the delayed waves to be canceled are different, and therefore the conditions for canceling the delayed waves by the delayed wave canceller having the configuration shown in FIG. 1 are different.

[0034]

According to the present invention, it is possible to realize a delayed wave canceller that shortens the coefficient update interval of the adaptive filter and quickly cancels the delayed wave of the desired wave.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a delayed wave canceller according to the present invention.

2 is a block diagram showing an embodiment of a residual frequency characteristic calculation circuit in the delayed wave canceller of FIG.

[Explanation of symbols]

1 Delayed Wave Canceller 2 Subtractor 3 Bandpass Filter 4 Adaptive Filter 5 Filter Coefficient Generating Circuit 6 Cancel Residual Calculating Section 7 Filter Coefficient Updating Section 8 FFT Circuit 9 Data Distribution Circuits 10-1, 10-2, ..., 10-L Residual frequency characteristic calculation circuit 11 Data synthesis circuit 12 IFFT circuit 13 Frequency characteristic calculation circuit 14 FFT window error calculation circuit 15 FFT window error correction circuit 16 FFT window error averaging circuit 17 Main wave calculation circuit 18 Cancel residual calculation circuit 19 Main wave Average circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuhiko Shibuya             1-10-11 Kinuta, Setagaya-ku, Tokyo, Japan             Broadcasting Association Broadcast Technology Institute F term (reference) 5K022 DD01 DD13 DD19 DD23 DD33                 5K046 AA05 BB05 EE06 EF11 HH02                       HH18

Claims (5)

[Claims] 1. A subtracter having a subtracted terminal to which an input signal from a receiving system is supplied and a subtraction terminal to which a cancel signal for delay wave cancellation is supplied, and an output signal from the subtractor is supplied. An adaptive filter that generates the cancellation signal by convolving the characteristics of the filter coefficient with the output signal, and a frequency that receives the output signal of the subtractor and indicates the cancellation residual component of the delayed wave included in the output signal. A cancellation residual calculation unit that calculates characteristics and calculates a filter coefficient based on the cancellation residual component, an updated filter coefficient obtained based on an output from the cancellation residual calculation unit, and a supply to the adaptive filter. And a filter coefficient updating unit that calculates a new filter coefficient to be supplied to the adaptive filter from the previously updated filter coefficient. In the delayed wave canceller, the cancellation residual calculation unit extracts the signal in the time domain of the effective symbol period using the FFT window, performs FFT (Fast Fourier Transform), and outputs the FFT by converting it into data in the frequency domain. A circuit, and a data distribution circuit that divides the frequency domain data output from the FFT circuit into L pieces (L is a natural number) and outputs the data to a plurality of residual frequency characteristic calculation circuits of the same number as the number of divisions. A plurality of residual frequency characteristic calculation circuits for receiving a signal from the data distribution circuit, calculating a frequency characteristic showing a cancellation residual component from the input frequency domain data, and outputting the calculated frequency characteristic; A data synthesizing circuit for synthesizing each signal from the characteristic calculating circuit and outputting it as continuous frequency characteristic data, and the frequency characteristic data output from the data synthesizing circuit are I
And an IFFT circuit that generates an updated filter coefficient by performing an FFT (Inverse Fast Fourier Transform), and the plurality of residual frequency characteristic calculation circuits perform parallel processing of the frequency characteristic indicating the cancel residual component. A delayed wave canceller characterized by being configured to. 2. The cancellation residual difference calculation unit includes two residual frequency characteristic calculation circuits, and the data distribution circuit includes the two residual frequency characteristic calculation circuits in the FF.
2. When the data output from the T circuit is divided into two, the data closest to the DC carrier is output to both residual frequency characteristic calculation circuits.
The delayed wave canceller described in. 3. A frequency characteristic calculation circuit, wherein the residual frequency characteristic calculation circuit calculates and outputs a frequency characteristic of a propagation path from input frequency domain data, and a frequency characteristic signal output from the frequency characteristic calculation circuit. From the normal position of the effective symbol period, the FFT window error calculation circuit for calculating the error of the frequency phase characteristic due to the error from the normal position of the effective symbol period, and the FFT window error calculation circuit of each residual frequency characteristic calculation circuit. Outputs are input respectively, FFT window error averaging circuit that calculates and outputs an average value of data from each FFT window error calculating circuit, and a signal from the frequency characteristic calculating circuit is output from the FFT window error averaging circuit. The FFT window error correction circuit that performs phase correction using the FFT window error component and outputs the main wave component included in the output of the FFT window error correction circuit. Main wave averaging circuit that outputs and outputs the main wave calculation circuit and the output of the main wave calculation circuit of each residual frequency characteristic calculation circuit, and calculates and outputs the average value of the data from each main wave calculation circuit And a cancellation residual calculation circuit for calculating a frequency characteristic matching the characteristic of the delayed wave from the output of the main wave averaging circuit and the output of the FFT window error correction circuit. The delayed wave canceller according to 2. 4. The cancellation residual calculation circuit comprises:
Frequency characteristic F (k, n) output from FT window error correction circuit
(Where, k is a carrier number indicating a frequency, n is a natural number indicating the number of times the filter coefficient updating unit updates the filter coefficient) and the main wave component D output from the main wave averaging circuit.
From (n), the cancellation residual component E (k, n) is given by The delay wave canceller according to claim 3, wherein the delay wave canceller is configured to generate a filter coefficient for canceling the multipath included in the input signal. 5. The cancellation residual calculation circuit is configured to output the F
Frequency characteristic F (k, n) output from FT window error correction circuit
(Where, k is a carrier number indicating a frequency, n is a natural number indicating the number of times the filter coefficient updating unit updates the filter coefficient) and the main wave component D output from the main wave averaging circuit.
From (n), the cancellation residual component E (k, n) is given by The delay wave canceller according to claim 3, wherein the delay wave canceller is configured to generate a filter coefficient that cancels the wraparound included in the input signal by calculating based on Eq.