JP2002111625A - OFDM signal receiver - Google Patents

Abstract

(57) [Summary] (With correction) [PROBLEMS] In an OFDM signal receiving apparatus, when a received signal includes a delayed wave having a delay time exceeding a guard interval length, convergence to an optimum value is performed every time the number of delayed waves increases. It takes a long time to reduce the estimation accuracy of the tap coefficient. SOLUTION: A pilot signal included in a signal transmitted through a transmission path and a waveform equalizing filter 2 arranged in an OFDM signal receiving apparatus and a pilot signal held in the receiving apparatus in advance are used. Means for estimating the entire transmission path response including the waveform equalization filter;
7. Means 10 for obtaining a multipath cancellation residual from the estimated transmission path response and the frequency characteristics of the waveform equalization filter, and the waveform and the like so that the multipath cancellation residual obtained by the means becomes zero. And means 12 for controlling the tap coefficients of the filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to OFDM (Orthog
TECHNICAL FIELD The present invention relates to an OFDM signal receiving apparatus for receiving an OFDM signal transmitted by an onal Frequency Division Multiplexing (Orthogonal Frequency Division Multiplexing) transmission method, and more particularly to a multipath environment with a delay time exceeding a guard interval length and an SFN (Single Frequency Network). : Single frequency network)
TECHNICAL FIELD The present invention relates to an OFDM signal receiving apparatus provided with an adaptive equalization filter for reducing degradation of transmission characteristics due to inter-symbol interference in a signal.

[0002]

2. Description of the Related Art In an OFDM transmission system, a transmitting side normally transmits a guard interval period to an effective symbol period in order to avoid inter-symbol interference due to multipath.

[0003]

If the delay time of the delayed wave is within the guard interval length based on the transmitted guard interval period, the effective symbol period is cut out in a window so as to prevent interference between symbols. Can be demodulated. However, if the delay time of the delayed wave exceeds the guard interval length, the effective symbol period cannot be cut out in the window, so that inter-symbol interference also occurs and transmission characteristics deteriorate.

[0004] Therefore, when there is a delayed wave having a delay time exceeding the guard interval length, it is necessary to equalize the waveform of the received signal in order to compensate for transmission characteristics in order to prevent the occurrence of intersymbol interference. Becomes

Japanese Patent Laid-Open Publication No. H11-298434 discloses an FF regarding waveform equalization of a delayed wave that causes intersymbol interference.
Prior to T (Fast Fourier Transform) processing, it is described that the autocorrelation of the received signal is obtained and the waveform is adaptively equalized. In this case, the phase at which the autocorrelation peaks is determined. Since the tap coefficient of the adaptive equalization filter is set by detection, there is a problem that it takes time to converge to the optimum value every time the number of delay waves due to multipath increases. Also, in this method, since signals including noise are compared with each other, the estimation accuracy of tap coefficients required for waveform equalization is also reduced.

Accordingly, an object of the present invention is to provide a conventional equalizing filter for waveform equalization using a conventional adaptive equalizing filter when a received signal contains a delayed wave having a delay time exceeding the guard interval length.
Each time the number of delay waves due to multipath increases, it takes time to converge to the optimal value, and the accuracy of estimating tap coefficients required for waveform equalization also decreases.
An object of the present invention is to provide an OFDM signal receiving apparatus in which these problems are eliminated.

[0007]

In order to achieve the above object, an OFDM signal receiving apparatus according to the present invention comprises a transmission line and an OFDM signal.
A pilot signal Y (ω) included in a signal transmitted through a waveform equalization filter having a frequency characteristic W (ω) disposed in the signal receiving apparatus, and a pilot signal Y (ω) previously stored in the OFDM signal receiving apparatus. Means for estimating the entire channel response Z ′ (ω) including the waveform equalization filter from the pilot signal S (ω) included in the transmitted signal, and including the waveform equalization filter estimated by the means. Transmission path response Z '(ω) and frequency characteristic W of the waveform equalization filter
Means for obtaining a multipath cancellation residual by the waveform equalization filter from (ω), and controlling a tap coefficient of the waveform equalization filter such that the multipath cancellation residual obtained by the means becomes zero. It is characterized by comprising means.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on embodiments of the present invention with reference to the accompanying drawings. In addition,
An embodiment of the present invention described below is an ISDB-T
(Integrated Services Broadcasting for Terrestria
l: terrestrial integrated digital broadcasting).
In the following embodiments, it is assumed that an SP (Scattered Pilot) signal, which is a reference for amplitude and phase, is used as a pilot signal.

FIG. 1 is a block diagram showing an embodiment of the OFDM signal receiving apparatus according to the present invention. In FIG.
1 is a subtraction circuit, 2 is a FIR (Finite Impulse Response)
) Filter, 3 is a window circuit, 4 is FFT (Fast
Fourier Transform) circuit, 5 is S
P signal extraction circuit, 6 is an SP demodulation circuit, 7 is a reference SP signal generation circuit, 8 is a complex division circuit, 9 is a signal demodulation circuit, 10
Is a residual information detection circuit, and 11 is an IFFT (Inverse Fast F
an ourier Transform (fast inverse Fourier transform) circuit, 12 is a coefficient extraction circuit, and 13 is an FFT circuit. Also,
In FIG. 1, for convenience of explanation, observation points P ₁ and P ₂ are shown.

First, referring to the drawing of the embodiment shown in FIG.
The principle of the present invention will be described. According to the present invention, the transfer function of the multipath in the transmission path is estimated in the receiving apparatus, and the multipath is canceled by the FIR filter 2 (see FIG. 1).

A detailed description will be given. Now, if the SP signal included in the OFDM transmission signal is represented by S (ω) and the frequency characteristic of the multipath other than the main wave in the transmission path is represented by H (ω), the signal input to the receiving apparatus is S (ω). ω) (1+
H (ω)). SP at observation point P ₁
When the signal is represented by R (ω), the transfer function F (ω) at the observation point P ₁ is represented by the following equation (1).

(Equation 1)

The frequency characteristic of the FIR filter 2 is represented by W
(Ω), and the SP signal at the observation point P ₂ is represented by Y (ω)
, The transfer function C (ω) in the receiving device is expressed by equation (2).

(Equation 2)

From equations (1) and (2), the FIR filter 2
The transfer function Z (ω) obtained by combining the transmission function and the transmission path is expressed by equation (3).

(Equation 3)

The optimum condition of the multipath scancer is W
Since (ω) = H (ω) is satisfied, the cancel residual signal Err (ω) at this time is expressed by equation (4).

(Equation 4) Multipath cancellation is performed by minimizing the cancellation residual signal Err (ω).

Specifically, the cancel residual signal E
In order to obtain rr (ω), the receiving apparatus estimates a transfer function Y (i, ω) (i is a symbol number) of a signal including the transmission path and the FIR filter 2 at the observation point P ₂ and a coefficient extraction circuit. 12 (see FIG. 1), it is necessary to obtain a frequency characteristic W (i, ω) obtained by performing FFT processing on the signal W (i, t) in the time domain of the FIR filter 2.

According to the equation (4), Err (i, ω) obtained by the residual information detection circuit 10 (see FIG. 1) is converted to IDF
T (Inverse Discrete Fourier Transform) processing or IFFT circuit 11 (see FIG. 1)
To perform time-domain signal err
(I, n) (n is an integer in the range of 0 ≦ n <N, where N is the number of conversion points in the IDFT or IFFT processing) is obtained.

Here, as the signal err (i, n) in the time domain, N pieces of complex information are obtained per symbol. If the number of the maximum delay time in which the multipath exists is M, F
The maximum tap length required for the IR filter 2 is also M.
Here, the tap number of the FIR filter 2 is set to m (1 ≦ m <
M).

Normally, N> M (N is the number of conversion points in IDFT processing or IFFT processing), so that when controlling the FIR filter 2, the signal err in the time domain is used.
In (i, n), the main wave number n = 0 and F
The signal of n> M which is a number outside the control of the IR filter 2 is discarded, and only the impulse response err (i, m) of the residual after the multipath cancellation is extracted.
The coefficient extraction circuit 12 is a circuit for controlling the tap coefficients of the FIR filter 2 by the truncation processing and the successive update equation of the equation (5).

(Equation 5) Here, w (i, m) is a tap coefficient of the FIR filter 2, and μ is an update coefficient of 1 or less.

The operation of the OFDM signal receiving apparatus of the present invention for canceling multipath based on the principle of the present invention will be described in detail. In FIG. 1, it is assumed that the signal input to the observation point P ₁ is a digital complex baseband signal R (i, t) that has been A / D converted and quadrature-demodulated. This complex baseband signal R (i, t) is passed through a subtraction circuit 1, a window circuit 3, and an FFT circuit 4 to an observation point P ₂
In the complex baseband signal

[Outside 1] Is obtained.

Here, the SP signal Y (i, ω) is extracted from the complex baseband signal [1] by the SP signal extraction circuit 5. Since the SP signal has a different frequency arrangement for each symbol and is completed with four symbols, the SP signal Y (i-1, ω) Y (i-2, ω) Y (i-3, ω)
And one SP signal

[Outside 2] And

In the SP signal demodulation circuit 6, this SP signal

[Outside 3] Is the reference SP signal generated by the reference SP signal generation circuit 7.

[Outside 4] Performs complex division with, and the transfer function of the entire SP signal including the equalizer

[Outside 5] Ask for.

As shown in FIG. 2, the SP signal is intermittently inserted every three carriers in the frequency direction and every four symbols in the time direction. A low-pass filter process is performed on the frequency direction of the function [Eq. 5] to estimate Z ′ (i, ω) having the channel response for all carriers. The complex division circuit 8 uses this Z ′ (i, ω) to calculate the observation point P ₂
Is subjected to complex division to correct the phase and amplitude, thereby demodulating the data.

The tap coefficient W (i, t) of the FIR filter 2 generated by the coefficient extracting circuit 12 is subjected to FFT processing in the FFT circuit 13 to obtain W (i, ω).
(I, ω) and Z ′ (i, ω) from the SP signal demodulation circuit are input to the residual information detection circuit 10, and the residual signal Err (i, ω) is obtained by the equation (4) described in the principle explanation. Ask for. Next, the IFFT circuit 11 obtains an impulse response err (i, n) of the residual signal, and further performs a clipping process to obtain err (i, m) according to equation (5).
The tap coefficients of the FIR filter 2 are updated. The tap coefficient is updated at a timing when the window circuit 3 does not perform the cutout processing. The reason why the tap coefficients are updated at the timing when the clipping process is not performed is to reduce the influence on the data demodulation.

When four or more symbols have elapsed since the tap coefficient was updated, the SP signal demodulation circuit 6 obtains a new frequency characteristic after the coefficient update (see FIG. 2). Therefore, the shortest coefficient update interval is every four symbols. One time. Also, IF
Since it is not necessary for the FT circuit 11 and the FFT circuit 13 to perform processing (calculation) at the same time, the IFFT processing and the FFT processing can be performed in a time-division manner, and the FFT circuit can be shared.

In the above-described embodiment of the present invention, the SP signal is used as the pilot signal. However, the present invention is not limited to this. Generally, the transmission based on the amplitude / phase reference used in the OFDM transmission system is used. Of course, any carrier signal may be used.

The object of the present invention is the above-mentioned ISD
The present invention is not limited to the OFDM signal receiving device used for BT, and it is needless to say that the present invention can be widely and generally applied to the OFDM signal receiving device.

[0027]

According to the present invention, even if an OFDM reception signal includes a delay wave having a delay time exceeding the guard interval length, the influence of the delay wave is determined by using an amplitude / phase reference transmission carrier signal such as an SP signal. If the delay time is within the range of the delay time in which the delay wave can be detected, the delay wave of the delay time within the guard interval can be improved to the same degree as the effect when no waveform equalization is performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an OFDM signal receiving apparatus according to the present invention.

FIG. 2 shows that an SP signal is intermittently inserted every three carriers in the frequency direction and every four symbols in the time direction.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 subtraction circuit 2 FIR filter 3 window circuit 4,13 FFT circuit 5 SP signal extraction circuit 6 SP demodulation circuit 7 reference SP signal generation circuit 8 complex division circuit 9 signal demodulation circuit 10 residual information detection circuit 11 IFFT circuit 12 coefficient extraction circuit P ₁ and P ₂ observation points

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Naohiko Iio 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside the Japan Broadcasting Research Institute (72) Inventor Koichiro Imamura 1-10 Kinuta, Setagaya-ku, Tokyo 11 Japan Broadcasting Corporation Broadcasting Research Laboratory (72) Inventor Hiroyuki Hamazumi 1-10-11 Kinuta, Setagaya-ku, Tokyo F-term in Japan Broadcasting Corporation Broadcasting Research Laboratory 5K022 DD01 DD33 DD34 5K046 AA05 BA06 DD14 EE06 EF15

Claims (1)

[Claims] 1. A pilot signal Y included in a signal transmitted via a transmission path and a waveform equalization filter having a frequency characteristic W (ω) disposed in an OFDM signal receiving apparatus.
(Ω) and a pilot signal S (ω) included in the transmission signal held in advance in the OFDM signal receiving apparatus.
Means for estimating the entire transmission path response Z '(ω) including the waveform equalization filter from the above, the transmission path response Z' (ω) including the waveform equalization filter estimated by the means and the waveform, etc. Means for obtaining a multipath cancellation residual by the waveform equalization filter from the frequency characteristic W (ω) of the equalization filter, and the waveform equalization filter so that the multipath cancellation residual obtained by the means becomes zero. An OFDM signal receiving apparatus comprising means for controlling a tap coefficient of the OFDM signal.