JP2002111621A - Digital-signal receiving apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital-signal receiving apparatus capable of accurately compensating the distortion of a signal even when the position of an FFT window is changed. SOLUTION: A digital broadcasting receiver 100 receives digital signals being transmitted by an orthogonal frequency division multiple system and having guard periods at every section among a plurality of effective symbols. An FFT window setting circuit 5 sets a processing period, when an FFT circuit 4 conducts fast Fourier transformation processing. An equivalent circuit 6 separates the first distortion with the position of the setting of the processing period (the FFT window) and the second distortion with the fluctuation of the propagation path of a receiving signal and compensates the distortion to an output from the FFT circuit 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal receiving apparatus for receiving a broadcast wave broadcast by an orthogonal frequency division multiplex transmission system.

[0002]

2. Description of the Related Art In recent years, orthogonal frequency division multiplexing (hereinafter referred to as OFDM (Orthogonal Frequency D
ivisionMultiple)) A transmission system is drawing attention.

The OFDM transmission system is a system in which a large number of subcarriers (hereinafter, referred to as subcarriers) orthogonal to each other are modulated by digital data to be transmitted, and the modulated waves are multiplexed and transmitted. This method has a feature that when the number of subcarriers to be used is increased to several hundreds to several thousands, the symbol period of each modulated wave becomes extremely long, so that it is hardly affected by multipath interference.

FIG. 7 is a schematic block diagram showing a configuration of a conventional terrestrial digital broadcast receiver 200.

[0005] A signal received by an antenna is input to an input terminal 1. The input signal is tuner 2
, And is input to the synchronization circuit 3. In the synchronization circuit 3, symbol synchronization, clock synchronization, and carrier synchronization are established, and a synchronized signal and symbol pulse are output.

A synchronized signal is an FFT (Fast Fourier T)
ransform) input to the circuit 4 and the symbol pulse
It is input to the T window setting circuit 5.

The FFT window setting circuit 4 generates an FFT window setting pulse having an effective symbol period width based on the position of the input symbol pulse.
To set the FFT range.

The signal output from the FFT circuit 4 is divided into an equalizer circuit 15, a deinterleave circuit 7, an error correction circuit 8,
The signal is output from the output terminal 10 as a TS (transport stream) signal through the TS reproduction circuit 9.

Here, the setting of the FFT window position will be further described. In the OFDM transmission method,
Since the transmission data is dispersed and modulated over several hundred to several thousand subcarriers, the modulation symbol rate of each subcarrier becomes extremely low, and the period of the known signal becomes extremely long. For this reason, it is less susceptible to multipath as described above. Further, by setting a guard period before an effective symbol period to prevent a ghost signal generated in radio wave propagation, it is possible to effectively remove the influence of multipath interference.

The guard period is formed by cyclically copying the latter half of the effective symbol period. If the delay time of the multipath interference is within the guard period, it is possible to prevent interference due to delayed adjacent symbols by demodulating only the signal in the effective symbol period during demodulation.

FIG. 8 is a diagram for explaining the effect of the FFT window when a desired signal (OFDM signal) and an interference signal are present.

As shown in FIG. 8A, in the OFDM signal, guard periods G1, G2,... Are added at the head of each effective symbol period S1, S2,.

The signals in the guard periods G1, G2,... Correspond to the latter half of the effective symbol periods S1, S2,.
1 ', G2',... Are copied.

FIG. 8B shows a multipath interference signal.
This is a signal (post-ghost) delayed from the main signal.

FIG. 8 (c) shows a received signal that has undergone interference. A part (X part) in the guard interval receives interference by adjacent symbols, and the other part (Y part) receives interference by the same symbol. is recieving.

With respect to the received signal, a symbol pulse of a main signal (a signal of a desired signal) is referred to FIG.
A FFT window setting pulse is generated as shown in FIG. By setting the effective symbol period of the main signal in the FFT range, the signal to be actually subjected to the FFT calculation becomes
The signal area shown in FIG.

Although this signal is subject to interference,
Since the symbols are based on the same symbol, the carriers maintain an orthogonal relationship, and the carrier data after FFT can be normally reproduced without receiving interference between carriers.

As for the multipath capability, normal reproduction can be performed if the delay time is within the guard interval period.

[0019]

Generally, multipath interference is mainly caused by a signal delayed after the main signal (post-ghost), but depending on a reception environment, interference caused by a signal advanced from the main signal (post-ghost). Pre-ghosting) can also occur.

FIG. 9 is a diagram for explaining the influence of interference due to such a front ghost. It is assumed that the interference wave is ahead of the main signal as shown in FIG. 9B with respect to the main signal shown in FIG. 9A.

In this case, if the FFT window is set to the effective symbol period of the main signal as described above,
The target of T calculation is a signal period as shown in FIG. 9 (f), which includes an interference part X due to adjacent symbols having no orthogonal relationship. For this reason, the data after the FFT is subjected to inter-carrier interference and cannot be normally reproduced.

In order to avoid this ghost problem, a method of setting the FFT window earlier than the effective symbol sequence by a fixed predetermined period has been adopted.

That is, if the FFT window is set at the position shown in FIG. 9 (g), the calculation target of the FFT becomes as shown in FIG. 9 (h). Although receiving interference, they are caused by the same symbol, so that each carrier maintains an orthogonal relationship. Therefore, each carrier data after the FFT can be normally reproduced without receiving the inter-carrier interference.

However, when the FFT window position is changed, distortion occurs in the output of the FFT circuit.

That is, when the position of the FFT window is changed as a countermeasure against the previous ghost, the FFT output data distortion is generated accordingly, and the distortion amount is increased. As a result, there is a problem that the accuracy of the equalizing circuit for compensating the distortion is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to reduce the accuracy of the equalizer circuit even when the FFT window position is changed. An object of the present invention is to provide a digital signal receiving apparatus capable of compensating for signal distortion.

[0027]

According to a first aspect of the present invention, there is provided a digital signal receiving apparatus for receiving and demodulating a digital signal transmitted by an orthogonal frequency division multiplexing method and having a guard period between a plurality of effective symbols. A digital signal receiving apparatus, comprising: a processing period setting means for setting a processing period for performing a fast Fourier transform process after synchronizing a received signal; and performing a fast Fourier transform on the received signal during the processing period. Conversion means for equalizing means for separating and compensating the output of the conversion means for the first distortion associated with the set position of the processing period and the second distortion associated with the fluctuation of the propagation path of the received signal; A reproducing unit for receiving data output from the equalizing unit and extracting data corresponding to an effective symbol;

According to a second aspect of the present invention, there is provided a digital signal receiving apparatus.
In addition to the configuration of the digital signal receiving device according to claim 1,
The guard period has a first period length, is provided at the front of the effective symbol for each effective symbol, and includes a copy of a signal within the first period length of the second half of the corresponding effective symbol. The setting unit sets the processing period to a position having the same period length as the effective symbol period and shifted forward by a second period length shorter than the first period length of the effective symbol.

According to a third aspect of the present invention, there is provided a digital signal receiving apparatus,
In addition to the configuration of the digital signal receiving device according to claim 2,
An equalizing unit configured to receive an output of the converting unit and perform a compensation process for the first distortion based on setting information of a processing period position by the processing period setting unit; Second compensating means for receiving the output and compensating for the second distortion.

[0030]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic block diagram showing a configuration of a digital broadcast receiver 100 according to an embodiment of the present invention.

Digital broadcast receiver 100 includes an input terminal 1 to which a signal received by an antenna (not shown) is input, a tuner 2 for receiving a signal input from input terminal 1, and selecting a channel. A synchronizing circuit 3 is provided for receiving the output from the tuner 2, establishing symbol synchronization, clock synchronization, and carrier synchronization, and outputting a synchronized signal and symbol pulse.

The digital broadcast receiver 100 further receives the synchronizing signal output from the synchronizing circuit 3, receives the FFT circuit 4 for fast Fourier transform, and receives the symbol pulse from the synchronizing circuit 3 to open the FFT window. It further includes an FFT window setting circuit 5 for setting, and an equalization circuit 6 for compensating for distortion of a received signal due to propagation path fluctuation.

The FFT window setting circuit 5 generates an FFT window setting pulse having an effective symbol period width based on the position of the input symbol pulse, and outputs the pulse to the FFT circuit 4.

At this time, as a response to the previous ghost, FFT
The window setting pulse is output so as to be at a predetermined position slightly before the effective symbol position within the transmission symbol period. However, the moving amount of the FFT window setting pulse may be variable according to the reception environment or the like.

The FFT window setting circuit 5 also outputs FFT window position information to the equalization circuit 6.

The signal output from the FFT circuit 4 is
Compensated by the equalizing circuit 6 based on the T window position information,
The signal is output from an output terminal 10 as a transport stream signal (TS signal) through a deinterleave circuit 7, an error correction circuit 8, and a TS reproduction circuit 9.

Next, the operation of the equalizing circuit 6 will be described below. First, as a prerequisite for the description of the operation of the equalization circuit 6, the distortion generated in the output of the FFT circuit 4 when the FFT window position is changed in order to eliminate the influence of the previous ghost will be examined.

FIGS. 2, 3 and 4 show such an FF.
It is a conceptual diagram for explaining distortion accompanying change of a T window position.

FIG. 2 shows an FFT output and a constellation (IQ quadrature axis plot) when the FFT window position is not changed. FIG. 3 shows an FFT output and a constellation when the FFT window position is moved one clock before. FIG. 4 shows an FFT output and a constellation when moving two clocks earlier.

As shown in FIGS. 2 to 4, the distortion due to the change in the FFT window position is only the phase rotation of the data.

The equivalent circuit 6 needs to compensate for the distortion due to the change in the FFT window position and the distortion due to the fluctuation of the propagation path. At this time, as in the case of the conventional equalizing circuit 15, when the compensating circuit 13 also compensates for both the distortion due to the change in the FFT window position and the distortion due to other causes (such as phasing), the increased distortion amount for,
Equalization accuracy will be degraded.

FIG. 5 is a diagram for explaining the compensating operation of the conventional equalizing circuit 15 on a constellation, and FIG. 6 is a diagram showing the digital broadcast receiver 100 of the present invention shown in FIG. FIG. 5 is a diagram for explaining a compensation operation of the equalization circuit 6 on a constellation.

First, referring to FIG. 5, the original data DA
Is moved to the DB position as a result of the distortion due to the movement of the FFT window position and the distortion due to other causes. In the case of the conventional equalizing circuit 15, the amount of this distortion must be detected and compensated at once.

For this reason, if the compensating detection circuits have the same capability, detecting a large amount of distortion increases the detection error. In other words, distortion due to other causes that should originally be equalized substantially deteriorates the equalization accuracy.

Next, the operation of the equalizing circuit 6 according to the present invention will be described with reference to FIG. First, FFT from the FFT circuit
The processed signal is input to the first compensation circuit 11.
In the same manner as in FIG. 5, the input data is subjected to the distortion due to the change in the FFT window position and the distortion due to other causes.
It exists at the position of DB.

The first compensation circuit 11 compensates for distortion due to the change of the FFT window position. That is, the compensation amount calculation circuit 12 sends the FF
The T window position information is obtained, and the compensation amount is calculated.

This compensation amount is uniquely determined by how many clocks before the FFT window position is shifted from the effective symbol position.

That is, as shown in FIG. 3, when the data is shifted one clock before, the data makes one round in the effective symbol period. Similarly, when the shift is made two clocks earlier, two rounds are performed as shown in FIG. That is,
The distortion due to the change in the FFT window position is only the phase rotation, and the rotation amount is also constant in proportion to the FFT window position change amount.

Therefore, a compensation amount (rotation amount) is uniquely determined from an arbitrary carrier data position and a window position change amount.
Is possible.

As a result of such compensation by the first compensation circuit 11, data on a constellation of certain carrier data moves to a point DC in FIG.

The distortion remaining in the data DC is the FFT
The distortion is caused by a cause other than the change in the window position. The second compensation circuit 13 and the compensation amount detection circuit 14 function so that this data compensates for the original data (DA position).

In the compensating operation of the second compensating circuit 13, since the distortion accompanying the change of the FFT window position has already been compensated, the detection error of the compensation amount detecting circuit 14 is not affected, and the equalization accuracy is improved. There is no deterioration.

That is, in the present invention, the distortion of the FFT output data due to the change of the FFT window position is compensated separately from the compensation of the distortion due to other causes. in this case,
This compensation is performed not based on the compensation amount detection based on the received signal but based on the FFT window position information of the FFT window setting circuit 5.

Therefore, FFT is used as a response to the previous ghost.
In the case where the window position is changed, in the present invention, the distortion of the FFT output data due to the change of the FFT window position is compensated separately from the compensation of the distortion due to other causes, so that the accuracy deterioration of the equalizer circuit is prevented. Becomes possible.

The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0057]

As described above, according to the present invention,
Since the distortion of the FFT output data due to the change of the FFT window position is compensated separately from the compensation of the distortion due to other causes, it is possible to prevent the accuracy of the equalizer from deteriorating.

[Brief description of the drawings]

FIG. 1 is a digital broadcast receiver 1 according to an embodiment of the present invention.
It is a schematic block diagram which shows the structure of 00.

[FIG. 2] FF in the case of no FFT window position change
It is a conceptual diagram which shows T output and a constellation.

FIG. 3 is a conceptual diagram showing an FFT output and a constellation when an FFT window position is moved one clock before;

FIG. 4 is a conceptual diagram showing an FFT output and a constellation when moving two clocks earlier.

FIG. 5 is a diagram for explaining a compensating operation of the conventional equalizing circuit 15 on a constellation.

FIG. 6 is a diagram for explaining a compensation operation of the equalization circuit 6 in the digital broadcast receiver 100 of the present invention on a constellation.

FIG. 7 is a schematic block diagram showing a configuration of a conventional terrestrial digital broadcast receiver 200.

FIG. 8 is a diagram for explaining the effect of an FFT window when a desired signal (OFDM signal) and an interference signal are present.

FIG. 9 is a diagram for explaining the influence of interference due to a front ghost.

[Explanation of symbols]

1 input terminal, 2 tuner, 3 synchronization circuit, 4 FF
T circuit, 5 FFT window setting circuit, 6 equalization circuit, 7 deinterleave circuit, 8 error correction circuit, 9
TS regeneration circuit, 10 output terminal, 11 compensation circuit, 1
2 Compensation amount calculation circuit, 13 compensation amount circuit, 14 compensation amount detection circuit, 100 digital broadcast receiver.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K022 DD01 DD33 DD34 DD42 5K046 AA05 BB05 CC28 EE06 EE51 EE56 5K047 AA11 CC01 CC08 GG09 HH03 MM13

Claims (3)

[Claims] 1. A digital signal receiving apparatus for receiving and demodulating a digital signal transmitted by an orthogonal frequency division multiplexing method and having a guard period between a plurality of effective symbols, wherein the received signal is synchronized. On the above, a processing period setting means for setting a processing period for performing the fast Fourier transform processing, a converting means for performing a fast Fourier transform on the received signal of the processing period, and an output of the converting means An equalizing unit that separates and compensates for a first distortion due to a setting position of the processing period and a second distortion due to a propagation path variation of the received signal; A digital signal receiving device, comprising: reproducing means for extracting data corresponding to an effective symbol. 2. The guard period has a first period length, is provided at the front of the effective symbol for each effective symbol, and is within the first period length of the second half of the corresponding effective symbol. Wherein the processing period setting means sets the processing period to a second period having the same period length as the effective symbol period and being shorter than the first period length from the beginning of the effective symbol. 2. The digital signal receiving apparatus according to claim 1, wherein the digital signal receiving apparatus is set at a position shifted forward by the period length of (i). 3. The equalization unit receives the output of the conversion unit, and based on setting information of the processing period position set by the processing period setting unit, sets the first
The first compensating means for performing a compensating process for the distortion of (a), and a second compensating means for receiving an output of the first compensating means and performing a compensating process for the second distortion. Digital signal receiver.