KR100747558B1 - Digital TV receiver - Google Patents

Abstract

In particular, the present invention relates to a digital TV receiver. In particular, a digitized baseband signal is integrated at a predetermined symbol period using an integrator, and then a horizontal sync signal is detected using the integrated signal, and the detected horizontal sync signal is used for channel equalization and timing recovery. By using this method, timing recovery and channel equalization can be performed accurately and stably even in a severe ghost channel environment and a channel whose ghost characteristics change with time, thereby improving performance of a receiver. In particular, even in the case where the characteristics of the transmission channel are good, instantaneous moving objects and the like exist on the channel, and thus the timing recovery and channel equalization can be accurately and stably performed even if the channel characteristics deteriorate momentarily and again have good characteristics.

Time-varying ghost, horizontal sync signal, timing recovery

Description

Digital TV receivers {Digital TV receiver}

Figure 1 (a) is a diagram showing a general example of the horizontal synchronization signal in the analog stage

Figure 1 (b) is a view showing a general example of the horizontal synchronization signal after the analog signal of (a) is converted into a digital signal

2 is a general diagram illustrating an example of a horizontal synchronization signal and data in a case where a ghost having a size of one symbol and a half size of the original signal is present on a transmission channel.

3 is a configuration block diagram related to horizontal sync signal detection and timing recovery in a general digital TV receiver;

4 is a block diagram of a configuration related to horizontal synchronization signal detection and timing recovery in a digital TV receiver according to the present invention.

5A and 5B are block diagrams illustrating embodiments of the integrator of FIG. 4.

6 is a diagram illustrating an example of a horizontal synchronization signal integrated at a horizontal synchronization period in the integrator of FIG. 4 and a horizontal synchronization signal at an analog stage;

Explanation of symbols for main parts of the drawings

41: antenna 42: analog processing unit

43: A / D converter 44: channel equalizer                 

45: integrator 46: horizontal sync signal detector

47: timing recovery unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to digital televisions, and more particularly, to digital television receivers for stably detecting horizontal synchronization signals to perform timing recovery and channel equalization.

The ATSC (Advanced Television Systems Committee) 8 VSB (Vestigial Side Band) transmission system, which is currently proposed as a digital TV transmission system for the United States, periodically transmits a synchronization signal during transmission in order to accurately recover a received signal from a receiver. Insert into and send. In addition, the receiver may recover timing, channel equalization, and decoding only by restoring synchronization signals inserted during transmission between the received signals. To this end, synchronization signals inserted in a transmitter such as the 8 VSB transmission system should have higher transmission reliability than data. This is because the instantaneous error of data is transmitted using methods such as channel coding in order to be corrected by the receiver, but the synchronization signals are inserted and transmitted periodically without using any method for error correction.

In addition, if the synchronization signals cannot be restored, the data cannot be correctly restored even if there is no error in the data. This is because the signals are configured to recover data only when the synchronization signal section is known correctly. Therefore, if the performance of the restoration of the synchronization signal is improved, the performance of the entire receiver is also improved.

When the restoration of the synchronization signal is completed, data is restored through timing restoration, channel equalization, and decoding.

Here, the timing restoration serves to accurately convert the received analog signal into a digital signal, and also reduces the burden on the channel equalizer. Therefore, when the performance of timing recovery is improved, the burden of other digital processing units is reduced, thereby contributing to the performance improvement of the receiver.

Therefore, in the ATSC standard, which is currently adopted as a digital TV standard for the United States, the synchronization signal detection and timing recovery unit is configured to perform the synchronization signal detection and timing recovery well even when there is a severe white Gaussian noise on the channel.

However, when ghost, which is noise due to multipath propagation, exists on a channel, the performance of the above-described sync signal detection and timing recovery decreases in proportion to the magnitude of the ghost noise. In particular, in regions where multipath propagation may occur, such as Korea, it is important to minimize performance degradation of the receiver due to ghosts.

Therefore, various methods have been proposed to minimize the performance degradation of the receiver that occurs when ghosts are present. Thus, when a constant ghost always exists on a transmission channel, it is possible to solve the problem with various algorithms developed to cope with the US DTV standard.

However, the algorithms described above are usually in good condition, and in the case where an interfering object such as a moving object is present and disappears momentarily in the transmission channel, it causes a performance degradation of the receiver.

In other words, when a moving object existing on a transmission channel moves momentarily, ghost-like noise that changes with time (time varying) occurs. In this case, the receiver may have good reception characteristics when it operates well even with a momentary change of the ghost noise. On the other hand, the removal of ghost noise occurring here is performed by the channel equalizer in the receiver. Therefore, this should be taken into account when designing a channel equalizer.

In this case, as a precondition for the operation of the channel equalizer, the receiver detects synchronization signals already inserted between the transmission signals and the analog / digital (A / D) converter is in such a state that the channel equalizer can operate best. The received signals must be converted into digital signals.

Therefore, if the detection of the synchronization signal interval from the received signal is not properly performed, or if the timing restoration for determining the timing of converting the analog signal into the digital signal is not normally performed, the channel equalizer may operate well even with a momentary change of the transmission channel. Even if it is designed, the channel equalizer cannot operate normally. As a result, the performance of the entire receiver is naturally degraded.

In this case, the receiver restores the synchronization signal inserted in transmission by looking at the form of the synchronization signal in the received signal where the data and the synchronization signal coexist, or the synchronization inserted in transmission by viewing the correlation value with the reference synchronization signal generated by the receiver The signal can be restored. For example, a horizontal sync signal (i.e., data segment sync signal) section existing for 4 symbol intervals every data segment period is correlated with a pattern match or reference horizontal sync signal from all received signals. Detection using.

However, when time-varying ghosts exist on the transmission channel, the synchronization signal present in the received signal is also affected, causing distortion in the shape of the synchronization signal, and decreasing the correlation value with the reference signal generated by the receiver. In this case, determination of the synchronization signal becomes difficult.

In particular, when restoring the horizontal synchronizing signal (i.e., data segment synchronizing signal) interval existing for 4 symbol intervals every data segment period, if there is a near ghost within 4 symbols, the synchronization signal included in the ghost component and the original signal Severe deformations in the shape and correlation of the synchronization signal result in extreme degradation of the horizontal synchronization signal detection performance. In this case, the ghost component has an average of '0' and does not significantly affect the detection performance of data having random characteristics.

Therefore, if the shape of the horizontal synchronization signal is severely distorted due to the ghost, the detection of the horizontal synchronization signal section becomes impossible. On the other hand, even though the detection of the horizontal synchronizing signal is made, the convergence position is out of the optimum state during timing restoration due to the influence of the ghost. This case degrades the performance of the channel equalizer, resulting in performance degradation of the receiver. In this case, when detecting the vertical synchronization signal (that is, field synchronization) section existing during one data segment, the usable synchronization signal length is quite long. It is relatively insignificant than performance deterioration.                         

1 is a form of a horizontal synchronization signal in the case where the channel is ideal. FIG. 1A is a form of a horizontal synchronization signal at an analog stage after reception and restoration of a baseband signal and before conversion to a digital signal. At this time, since the average of the remaining sections except for the horizontal synchronization signal is '0', it is represented as '0'. FIG. 1B is a form of a horizontal synchronizing signal after the analog signal of (a) is converted into a digital signal. In this case, it is assumed that the symbol timing is correctly restored.

FIG. 2 shows the shape of the horizontal synchronization signal and data when there is a ghost having a half symbol compared to the original signal with a delay characteristic of one symbol on a transmission channel. That is, the distortion occurs in the horizontal synchronization signal section of the original signal by the horizontal synchronization signal and data by the ghost. Of course, the case of Figure 2 is not a serious ghost environment, the receiver works well. However, when the size of the ghost is about the same as the original signal or when several ghosts exist at the same time, it is difficult for the receiver to operate normally. In addition, when a ghost occurs due to a momentary deterioration of the channel and the channel returns to a clean state, the information on the horizontal sync signal section, which has already been restored when the state of the channel deteriorates, or the convergence position is changed in the symbol timing restoration unit. This affects the rest of the digital processing of the receiver. In particular, the channel equalizer is designed under the assumption that the symbol timing recovery is correct, and the instantaneous change of the convergence position of the timing recovery unit makes it impossible to perform channel equalization normally. In addition, adaptive equalization, which is mainly used as a channel equalization method, has a feedback structure, and thus, even if the symbol timing recovery unit continues to accumulate information of the previous distorted state, the normal operation cannot be performed. Occurs.

3 is a block diagram illustrating a horizontal synchronization signal detection and symbol timing recovery unit shown in the ATSC standard.

First, the airwave signal input from the antenna 31 is restored to the baseband signal by the analog processor 32 and then output to the A / D converter 33. The A / D converter 33 converts an input baseband analog signal into a baseband digital signal to the channel equalizer 34, the horizontal synchronization signal recovery unit 35, and the symbol timing recovery unit 36. Output

The horizontal synchronizing signal recovery unit 35 detects the horizontal synchronizing signal inserted during transmission using the digitally converted baseband signal and outputs the horizontal synchronizing signal to the channel equalizer 34 and the symbol timing recovery unit 36.

The channel equalizer 34 uses the horizontal synchronization signal restored by the horizontal synchronization signal recovery unit 35 as a training signal, and linear distortion, amplitude, or linear distortion of amplitude causing inter-symbol interference included in the digital baseband signal. Equalization is performed to correct ghosts generated by reflections from the lamps.

In this case, since the transmitter carries only data in the transmission signal, the same clock as used at the time of transmission should be generated in order to recover these data on the receiving side. The part performing this role is the timing recovery unit 36.

In the currently proposed ATSC standard, timing restoration is performed by using a horizontal synchronization signal regularly inserted by a transmitter.

Accordingly, the symbol timing recovery unit 36 uses the horizontal synchronization signal detected by the horizontal synchronization signal recovery unit 35 as an A / D clock (A / D clk) of the A / D converter 33. Restore the timing to use. As an example, the symbol timing recovery unit 36 performs timing recovery using symmetry of the synchronization signals existing for each horizontal synchronization detected by the horizontal synchronization signal recovery unit 35.

At this time, if there is a severe ghost or time-varying ghost on the channel, the effect of the ghost affects the baseband signal, the restoration of the horizontal synchronization signal is impossible, or the convergence position of the symbol timing recovery unit is changed. In this case, as described above, the A / D conversion and channel equalizer are affected to degrade the performance of the receiver.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to integrate the baseband digital signal in a symbol period corresponding to a horizontal synchronization signal interval, and to use the detected horizontal synchronization signal as a training signal for the baseband. The present invention provides a digital TV receiver that compensates for channel distortion included in a digital signal, and stably detects a horizontal synchronizing signal even in a channel having a severe instantaneous change to accurately and stably perform timing restoration and channel equalization.

A digital TV receiver according to the present invention for achieving the above object is a digital TV receiver for demodulating a received passband analog signal into a baseband digital signal, which corresponds to a horizontal synchronization signal interval by an enable signal. An integrator for integrating the baseband digital signal at a symbol period and outputting the integrated signal to a horizontal synchronization signal detector and a timing recovery unit; A horizontal synchronization signal detector for detecting a horizontal synchronization signal by comparing the output of the integrator with a preset reference value; A timing recovery unit which receives the output of the integrator and the output of a horizontal synchronization signal detector, obtains a timing error of current symbols during a horizontal synchronization signal period, and outputs the demodulated signal to a baseband digital signal; And an equalizer for compensating for channel distortions included in the baseband digital signal by using the horizontal sync signal detected by the horizontal sync signal detector as a training signal.
The enable signal is a horizontal synchronization signal. The integrator integrates the baseband digital signal into a symbol period corresponding to a data segment period regardless of the enable signal, and outputs the integrated signal to the horizontal sync signal detector and the timing recoverer.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The present invention improves the performance of a receiver by accurately and stably performing horizontal sync signal detection and timing recovery even in a channel in which a momentary change exists. Particularly, the present invention accurately and stably performs horizontal sync signal detection and timing recovery even in the case where instantaneous moving objects exist on the channel under instantaneous characteristics of the transmission channel and the channel characteristics deteriorate momentarily and then have good characteristics. It is.

That is, when the channel characteristics deteriorate instantaneously in a good state and then return to a good state, blocks having all feedback structures in the receiver are not affected by the instantaneous channel deterioration. In this case, the blocks that are not the feedback structure have a very short time required to return to the normal state even though they are affected by the instantaneous channel degradation. However, blocks having a feedback structure need much time to return to the original state once degradation occurs. Therefore, only blocks having a feedback structure need to be considered for instantaneous degradation of the channel.                     

Since it is difficult to consider a block having all feedback structures in the present invention, only embodiments of horizontal synchronization signal detection and symbol timing recovery are considered. That is, the present invention is not limited only to the horizontal synchronization signal detection and symbol timing recovery.

4 is a block diagram of a digital TV receiver according to the present invention, which is a block diagram related to horizontal synchronization signal detection and symbol timing recovery.

4, an analog processor 42 for converting an RF signal received through an antenna 41 into a baseband signal, an A / D converter 43 for digitizing the analog baseband signal, and the A / D converter ( A channel equalizer 44 for performing channel equalization to the digitized baseband signal at 43), an integrator 45 for integrating the digitized baseband signal at a predetermined period, and the integrator 45 A horizontal synchronization signal detector 46 for detecting a horizontal synchronization signal from the output of the A / D signal, and calculating timing errors of current symbols during the horizontal synchronization signal interval output from the integrator 45 and the horizontal synchronization signal detector 46. The symbol timing recovery unit 47 outputs to the conversion unit 43.

In the present invention configured as described above, the airwave signal of the pass band received through the antenna 41 is input to the analog processor 42 and demodulated into a baseband signal and then output to the A / D converter 43. The A / D converter 43 converts the analog baseband signal into a digital signal according to the A / D clock provided by the symbol timing recovery unit 47 and outputs the digital signal to the channel equalizer 44 and the integrator 45. .

The integrator 45 continuously integrates the input baseband signal in a horizontal synchronization signal period. In this case, the signal input to the integrator 45 is severely distorted due to the influence of the instantaneous channel and the data around the horizontal synchronization signal when there is a severe ghost. However, since the output of the integrator 45 has already integrated values, it is less affected by the instantaneous channel state change. In addition, the influence by the data around the horizontal synchronizing signal present in the ghosts present in the horizontal synchronizing signal is eliminated. This is because the average of the data is '0', so the influence of the data on the horizontal synchronization signal section is removed at the output of the integrator 45. FIG. 6 shows the result after the horizontal synchronizing signal passes through the integrator 45 when there is a ghost having a one symbol delay characteristic.

Here, there may be various implementation examples of the integrator 45. In the present invention, an integrator which continuously integrates a baseband digital signal input as shown in FIG. FIG. 5B shows an integrator that integrates a baseband digital signal input in one data segment period. In this case, as shown in FIG. 5A, an enable signal is required when integrating with the horizontal synchronization signal cycle, and the enable signal may use the horizontal synchronization signal detected by the horizontal synchronization signal detector 46. In this case, the delays in the integrator are activated only during the horizontal synchronization signal period. In addition, in the case of integrating in one data segment period as shown in FIG. 5B, the data section has a value close to zero, and thus there may be no enable signal. In this way, the results of the integrators of Figs. 5A and 5B are almost identical. The number of delay elements of the integrator 45 may vary by a designer.

The integrated signal from the integrator 45 is output to the horizontal synchronization signal detector 46 and the symbol timing recovery unit 47, and the horizontal synchronization signal detector 46 is horizontally synchronized from a signal from which time-varying ghost is removed. The signal is detected and output to the channel equalizer 44, the symbol timing recovery unit 47, and the integrator 45.

That is, the horizontal synchronizing signal detector 46 detects the horizontal synchronizing signal by using data before the instantaneous channel ghost occurs, that is, data accumulated and output from the integrator 45 even when the instantaneous channel ghost occurs. . The channel equalizer 44 and the timing recoverer 47 perform channel equalization and timing recovery by using the detected horizontal synchronization signal as a reference signal.

As such, the instantaneous severe change of the channel is eliminated by the integrator 45, so that the channel equalizer 44 and the symbol timing recovery unit 47 are not affected. Therefore, it is possible to prevent performance deterioration of the channel equalizer 44 caused by instantaneous channel distortion, and also to convert the baseband analog signal into a digital signal at an accurate position. Can be converted to digital signal continuously. In addition, since the influence of the data existing in the horizontal synchronization signal section is removed, more accurate symbol timing recovery and horizontal synchronization signal recovery are possible in severe ghost environments, thereby contributing to the performance improvement of the receiver.

Application of the present invention to an actual receiver can improve the performance of a receiver in a channel whose stability of a system initial operation, severe ghost channel environment, and ghost characteristics change with time.

 As described above, according to the digital TV receiver according to the present invention, after integrating a digitized baseband signal by a constant symbol period using an integrator, a horizontal synchronization signal is detected using the integrated signal, and the detected horizontal synchronization signal is detected. By using the channel equalization and timing recovery, the timing recovery and channel equalization can be performed accurately and stably even in a severe ghost channel environment and a channel whose ghost characteristics change with time, thereby improving performance of a receiver. In particular, even in the case where the characteristics of the transmission channel are good, instantaneous moving objects and the like exist on the channel, and thus the timing recovery and channel equalization can be accurately and stably performed even if the channel characteristics deteriorate momentarily and again have good characteristics.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (9)

A receiver of a digital TV that demodulates a received passband analog signal into a baseband digital signal, An integrator for integrating the baseband digital signal at a symbol period corresponding to a horizontal synchronization signal interval by an enable signal and outputting the integrated signal to a horizontal synchronization signal detector and a timing recovery unit; A horizontal synchronization signal detector for detecting a horizontal synchronization signal by comparing the output of the integrator with a preset reference value; A timing recovery unit which receives the output of the integrator and the output of a horizontal synchronization signal detector, obtains a timing error of current symbols during a horizontal synchronization signal period, and outputs the demodulated signal to a baseband digital signal; And And an equalizer for compensating for channel distortion included in the baseband digital signal by using the horizontal sync signal detected by the horizontal sync signal detector as a training signal. The method of claim 1, The enable signal is A digital TV receiver, characterized in that the horizontal synchronization signal. The method of claim 1, The integrator is And the baseband digital signal is integrated into the horizontal synchronization signal detector and the timing recovery unit by integrating the baseband digital signal in a symbol period corresponding to a data segment period regardless of the enable signal. A receiver of a digital TV that demodulates a received passband analog signal into a baseband digital signal, An integrator for integrating the baseband digital signal at a symbol period corresponding to a horizontal synchronization signal interval by an enable signal and outputting the integrated signal to a horizontal synchronization signal detector and a timing recovery unit; And And a signal processor configured to receive a baseband digital signal passing through the integrator and perform a corresponding signal processing. The method of claim 4, wherein The signal processor And a horizontal synchronization signal detector, wherein the horizontal synchronization signal detector detects a horizontal synchronization signal by comparing the output of the integrator with a preset reference value. The method of claim 4, wherein The signal processor A timing restoring unit, wherein the timing restoring unit receives the output of the integrator and the output of the horizontal synchronizing signal detector, calculates the timing error of current symbols during the horizontal synchronizing signal period, and outputs the demodulated signal to the baseband digital signal. Featuring a digital TV receiver. The method of claim 5, And an equalizer for compensating for channel distortions included in the baseband digital signal using the horizontal sync signal detected by the horizontal sync signal detector as a training signal. The method of claim 4, wherein And said enable signal is a horizontal synchronization signal. The method of claim 4, wherein The integrator is And outputting the baseband digital signal to the signal processing unit by integrating the baseband digital signal into a symbol period corresponding to a data segment period irrespective of the enable signal.

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