KR100762135B1 - Apparatus and method for channel equalizing in digital broadcasting receiving system - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a channel equalization apparatus and method according to the equalizer state in a digital broadcasting reception system. In particular, the present invention relates to equalization by calculating a signal-to-noise ratio of an equalizer output periodically and comparing the signal-to-noise ratio with a preset threshold. The present invention relates to improving channel equalization performance by controlling whether a filter in the equalizer is suitable for the determined equalizer state after determining whether the previously state is a convergent state or a trace state.

Convergence, Tracking, Equalizer Status, SNR

Description

Channel equalizer and method in digital broadcasting reception system {APPARATUS AND METHOD FOR CHANNEL EQUALIZING IN DIGITAL BROADCASTING RECEIVING SYSTEM}

1 is a block diagram illustrating a general channel equalizer.

2 is a block diagram of a channel equalizer according to the present invention;

3 is a diagram of a structure of a data frame of a general VSB transmission method.

4 is a diagram of a structure of a field sync segment of FIG. 3; FIG.

5 is a block diagram of an embodiment of the equalizer state detector of FIG. 2;

FIG. 6 is a block diagram of another embodiment of the equalizer state detector of FIG. 2; FIG.

* Description of the symbols for the main parts of the drawings *

101: shear filter 102: feedback filter

103: determination unit 104: control unit

105: adder 201: equalizer state detection unit

202: channel equalizer 501, 601: SNR calculator

502, 602: SNR / Threshold Comparators

603: Reliability Counter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terrestrial digital broadcast reception system, and more particularly, to a channel equalizer and a method of equalizer output of a terrestrial digital TV signal transmitted in a VSB scheme.

In the United States, ATSC 8T-VSB (Terrestrial-Vestigial Side Band) transmission method was adopted as a standard in 1995 and broadcasted since the second half of 1998.In Korea, the same ATSC 8T-VSB transmission method is used. The experiment began in May 1995, and the test broadcast system was switched to August 31, 2000. Since October 2001, each broadcasting company has been broadcasting.

In the digital communication system, digital information (voice, data, or video) of a transmitting end is mapped to a symbol, and each symbol is converted into an analog signal proportional to a magnitude or a phase and transmitted to a receiving end through a transmission channel. The signal arriving at the receiving end, for example, the ATSC 8T-VSB receiving system passes through a multi-path transmission channel, causes interference with adjacent signals, and becomes severely distorted. Therefore, in order to recover the original signal from the distorted received signal, it is necessary to employ a channel equalizer for channel compensation.

In general, the most popular channel equalizer is a decision feedback equalizer (DFE) using a Least Mean Square (LMS) algorithm. The DFE regards the most energy-intensive path as the main path when the received signal enters through a multipath channel, and considers all remaining paths as neighboring signal interference (ISI) or ghost signals coming through the reflection path. After that, only the signals coming through the main path are extracted by correcting the phase and magnitude, and the signals coming through the remaining paths are removed.

FIG. 1 shows the configuration of a general decision feedback equalizer operating in the time domain.

Referring to the operation of FIG. 1, the signal of the path arriving in time earlier than the main path through the feed forward filter 101, that is, the influence of the near ghost is removed, and the rear end filter or the feedback filter ( Through 102, the signals of the path arriving later in time than the main path, that is, the effect of distant ghosts are eliminated. In this case, the adder 105 compares the output signal of the front end filter 101 with a preset reference signal level and determines a reference signal level closest to the output signal of the adder 105 as a determination value. At this time, the output of the determination unit 103 is fed back to the feedback filter 102 and the control unit 104. In other words, the input of the feedback filter 102 is not an output of the adder 105 but a determination value that has passed through the determining unit 103.

On the other hand, the control unit 104 receives the output of the equalizer, that is, the output value of the adder 105 and the determination value, and updates the coefficients of the front end filter 101 and the feedback filter 102.

In the decision feedback equalizer, when the decision is made accurately by the decision unit 103, the noise amplification phenomenon does not occur because the noise contained in the equalizer output component is re-input to the input of the feedback filter 102. In general, the performance is superior to that of a linear equalizer.

In this case, the decision feedback equalizer uses the LMS algorithm as a method of updating the coefficients of the filter. The step-size used in the LMS algorithm is updated by the product of the equalizer input and the error. The error used at this time is calculated using the field synchronization value in the field synchronization segment section, and is calculated using the determinant output value in the other sections. This method is called Decision-Directed.

In the case of a dynamic channel or a channel having a high distortion, the equalizer is difficult to converge in the above method, and thus a blind method is used.

When the blind algorithm is applied, the equalizer convergence is better in dynamic or severely distorted channels, but in the static channel, the residual Mean Square Error (MSE) is increased, which reduces the immunity to noise generated in the channel. There is this.

The equalizer converges and tracks differently depending on which blind algorithm is applied.

Accordingly, an object of the present invention is to detect an SNR of an equalizer output in a dynamic channel and adjust an error value calculation method of the equalizer in a digital broadcast reception system, thereby improving equalization performance in a dynamic channel. There is provided an equalizing device and a method thereof.

In order to achieve the above object, the channel equalizer in the ATSC 8T digital broadcasting reception system according to the present invention periodically calculates the SNR of the equalizer output to determine whether the equalizer is in the converged state or the trace state. An equalizer state detector; And a channel equalizer for controlling the parameter of the internal filter according to the equalizer state detected by the equalizer state detector to compensate for the channel distortion included in the received signal.

In this case, the equalizer state detector preferably calculates the SNR by using the training sequence included in the field sync segment whenever the field sync segment is received.

In addition, the equalizer state detection unit compares the SNR calculated by the equalizer output with the SNR calculated by the calculator and the preset first threshold value to determine whether the equalizer state is the converged state or the trace state, and determines the state. It is preferably configured with a comparator that outputs the result to the channel equalizer.

In this case, the calculator preferably calculates the SNR at each equalizer segment at the equalizer output.

The equalizer state detector may further include a calculator for calculating the SNR at each equalizer segment, a comparator comparing the SNR calculated by the calculator with a second preset threshold value, and counting values according to the comparison result of the comparator. Reliability counter that increases or decreases and compares the count value with the preset count threshold value and determines that the equalizer state is converged when the count value is less than the count threshold value, and when the count value is larger, the trace state is output and the result is output to the channel equalizer. It is preferably configured as (confidence counter).

In this case, the reliability counter increases the count value if it is determined that the SNR calculated by the calculator is greater than the second preset threshold value, and if it is determined not to be large, decreases the count value and then compares the count value with the preset count threshold value. If the value does not exceed the count threshold value, it is preferable to determine the converged state, and if it exceeds the value, determine the trace state.

In addition, the channel equalizer uses a constant modulus algorithm (CMA) error value as the blind error value when the equalizer state is determined to be converged when performing channel equalization using the G-Pseudo method, which is a blind adaptive method, and when the channel equalizer is determined to be traced, is blind. It is desirable to update the coefficients of the filter by using a Sato error value or a decision-directed error value as the error value.

In the channel equalization method in the digital broadcast reception system according to the present invention,

(a) calculating and outputting the SNR of the equalizer output each time a field sync segment is received;

(b) comparing the equalizer with the SNR output in step (a) and a preset threshold to determine whether the equalizer is in a converged state or a trace state; And

and (c) compensating for channel distortion included in the received signal by controlling a parameter of a filter inside the channel equalizer according to the equalizer state determined in step (b).

Here, step (b) compares the SNR value calculated in step (a) with a preset first threshold value and determines that the equalizer state is a converged state if it is less than the first threshold value, and the equalizer state is a trace state if it is large. It is desirable to.

In addition, step (b) compares the SNR value calculated in step (a) with a second preset threshold value, and increases or decreases the count value according to the comparison result in the above-described step, and adjusts the count value at this time. It is preferable that the equalizer state is determined as a converged state when the count value is less than the count threshold value, and when the count value is larger than the preset count threshold value, the tracking state.

Here, step (c) uses a constant modulus algorithm (CMA) error value as a blind error value when the equalizer state is determined to be a converged state when the channel equalizer performs channel equalization using a blind adaptive G-Pseudo method. If the tracking state is determined, it is preferable to update the coefficient of the filter by using the Sato error value or the decision-directed error value as the blind error value.

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

Hereinafter, with reference to the accompanying drawings illustrating the configuration and operation of the embodiment of the present invention, the configuration and operation of the present invention shown in the drawings and described by it will be described as at least one embodiment, By the technical spirit of the present invention described above and its core configuration and operation is not limited.

The present invention estimates the SNR at the equalizer output for each field sync segment that is periodically received, calculates the value of the estimated SNR, compares it with a preset threshold, and tracks whether the state of the equalizer is converged based on this. The characteristics of the channel equalizer are controlled by determining whether the state is equal to the state of the equalizer.

FIG. 2 is a block diagram illustrating an example of a channel equalizer according to the present invention. The SNR at the equalizer output is calculated each time a field sync segment is input, and the state of the equalizer converges by comparing with a preset threshold. The equalizer state detector 201 for determining whether the device is in a state of tracking or tracking, and the filter parameters are controlled according to the state of the equalizer detected by the equalizer state detector 201 to compensate for the channel distortion included in the received signal. Channel equalizer 202.

The channel equalizer 202 may use the above-described FIG. 1 or may use a general channel equalizer.

An embodiment of the present invention improves the performance of channel equalization by using the equalizer state detector 201 in a decision feedback equalizer as shown in FIG. That is, the equalizer state detection unit 203 is composed of the front end filter 101, the feedback filter 102, the determination unit 103, the control unit 104, and the adder 105 as in FIG. 1.

In the present invention configured as described above, the equalizer state detection unit 201 calculates the SNR for each field sync segment from the equalizer output whenever the field sync segment is input, and the equalizer converges with the preset threshold value. You can determine whether it is in the state or the trace state.

A method of calculating the SNR in the field sync segment period may be expressed by Equation 1 as follows.

Here, ref denotes a value known to the receiver in the field sync interval, and Dist denotes an output value of the equalizer.

Then, the equalizer state detector 201 outputs the state of the current equalizer to the control unit 104 of the channel equalizer 202.

3 shows a data frame structure of a typical ATSC 8T-VSB system. One data frame consists of an odd data field and an even data field, and each data field is further divided into 313 data segments. The above-mentioned 313 data segment is composed of one field sync segment and 312 general data segments including a training sequence signal. Each data segment consists of four segment sync symbols and 828 data symbols.

4 shows the structure of the field sync segment. It consists of one data segment length, and the data segment sync pattern is present in the first four symbols, followed by 511 PN 511 which is a pseudo random sequence, PN 63, PN 63, and 63, respectively 63. The next 24 symbols contain VSB mode related information. Here, the polarity of the second PN 63 of the three PN 63 section is changed each time. That is, '1' is changed to '0' and '0' is changed to '1'. Therefore, one frame may be divided into an even / odd field according to the polarity of the second PN 63.

The remaining 104 symbols after the 24 symbols in which the aforementioned VSB mode related information exists are reserved. The last 12 symbols of the unused region are copied with the last 12 symbol data of the previous segment (pre-code symbol).

At this time, since one data field has a period of about 24.2 ms, it can be seen that about 41.3 field sync segments are transmitted per second.

Therefore, the equalizer state detection unit 201 of the present invention calculates the SNR at the equalizer output each time a field sync segment is received, and compares the equalizer state with the preset threshold to determine whether the state of the equalizer is in the converged state or the trace state. Determine.

if SNR ≤ threshold then  Convergence

else trace status

Then, the determined equalizer state is output to the control unit 104 of the channel equalizer 202.

5 to 6 are detailed block diagrams illustrating an embodiment in which the equalizer state detection unit 201 determines the equalizer state.

5 is a detailed block diagram illustrating an example of an equalizer state detector to which Equation 2 described above is applied. The SNR calculator 501 calculates the SNR at the equalizer output, and compares the SNR value calculated by the calculator 501 with a preset threshold to determine whether the equalizer is in the converged state or the trace state. And an SNR / Threshold comparator 502 for outputting the determination result to the channel equalizer 202.

Each time a field sync segment is input from the equalizer configured as described above, the calculator 501 calculates the SNR from the current equalizer output for each field sync segment, and the comparator 502 compares the state of the equalizer with a preset threshold. After discrimination, the discrimination result is output to the channel equalizer 202.

In addition to the method of determining as shown in FIG. 5, a final determination may be performed by using a confidence counter after comparing with a threshold and determining a convergence state or a tracking state.

6 is a detailed block diagram illustrating an example of an equalizer state detector to which the reliability counter is applied. SNR calculator 601 that calculates the SNR at each equalizer output at the equalizer output, an SNR / Threshold comparator 602 that compares the SNR calculated by the calculator 601 with a preset threshold, and a comparator 602 If the count value is smaller than the count threshold value, the equalizer state is considered converged if the count value is smaller than the count threshold value. The reliability counter 603 outputs a result to the channel equalizer 202.

In the equalizing device configured as described above, the reliability counter 603 increases the count value by a predetermined value when it is determined that the SNR value calculated by the calculator 601 is greater than a preset threshold value, and decreases the count value by a preset value when it is determined that the SNR value is not greater than the preset threshold value. Let's do it. The increasing and decreasing values can be determined by the designer.

For example, it may be designed to increase or decrease by one as in the embodiment of the present invention, or may be designed to decrease by one when increasing and by one when decreasing. Therefore, the present invention is not limited to the example given.

Then, the count value is compared with the preset count threshold value, and if the count value does not exceed the count threshold value, it is determined as a converged state, and if it is exceeded, it is determined as a trace state.

That is, the method using the reliability counter of the present invention has a structure in which the reliability counter value is increased by one when the SNR value of the equalizer state is larger than the threshold value, and the counter value of the reliability counter is decreased as shown in Equation 3 below. If it does not exceed a certain counter threshold (count_threshold), it is determined as a converged state and if it exceeds the trace state.

if SNR ≤ threshold, then decrease the reliability counter value

Increasing the else confidence counter value

Where 0≤reliability counter value≤count_max

if confidence counter value≤count_threshold, then convergence state

else trace status

Next, a process of controlling a parameter in the controller 104 of the channel equalizer 202 according to the equalizer state determined as described above will be described. That is, the control unit 104 receives the output of the channel equalizer, that is, the output of the adder 105 and the output of the determination unit 103, and accordingly determines the parameters of the channel equalizer according to the result of the discrimination of the equalizer state detection unit 201. For example, an error value, a step size, and the like are selected to update the coefficients of the front end filter 101 and the rear end filter 102.

The time domain decision feedback equalizer and the frequency domain LMS adaptive equalizer of the channel equalizer both use the LMS algorithm as a method for updating the coefficients of the filter. That is, in the channel equalizer of FIG. 2, the coefficient w (n) of the front end filter 101 and the feedback filter 102 is updated by Equation 4 as follows. That is, the value obtained by multiplying the step size μ by the product of the input u (n) of the filter tap and the error e (n) is added to the current filter coefficient w (n) and updated to the next filter coefficient w (n + 1).

In the above formula, d (n) is a desired signal, a training sequence is used for the field sync segment section, and a determination value determined by the determination unit 103 of FIG. 2 is used for the data segment section. As such, the method of adapting the channel equalizer by subtracting the output y (n) of the channel equalizer from the desired signal is called a decision-directed adaptation scheme.

On the other hand, when the channel equalizer is difficult to initially converge the channel equalizer, the blind adaptation method is used instead of the above-described decision-oriented adaptation method. A blind adaptive scheme commonly used is a G-Pseudo scheme, each of which replaces the error term of Equation 4 with the following equation to update the coefficient of the filter.

Equation 5 shows an error term of a G-Pseudo method, and K ₁ and K ₂ are constant constants, respectively. In Equation 6, 5.25 and -5.25 are reference values when the 8-level VSB signal is set to {-7, -5, -3, -1, +1, +3, +5, +7}. 37 in Equation 7 is also a Godard constant value in the 8 level VSB signal.

Here, as a blind error value of the G-Pseudo algorithm, a constant modulus algorithm (CMA) error value may be used as in Equation 7, or a Sato error value may be used as in Equation 6. In case of using the CMA error value, the initial convergence performance is good in the dynamic channel or the ghost channel, but the noise jitter is large when the equalizer goes to the steady state and the equalizer operates in the tracking mode. Therefore, the SNR is calculated for each field sync segment interval to check whether the equalizer state is in convergence mode or tracking mode after convergence. Control the use of Sato error values or just use Decision-Directed error values.

This control solves the disadvantage that the noise jitter of the equalizer output in the tracking mode after convergence is large, thereby showing the equalization performance of the equalizer.

Meanwhile, a frequency domain LMS adaptive equalizer has been proposed that overcomes the disadvantages of the decision feedback equalizer and improves channel equalization performance.

The equalizer tap update method using the SNR value proposed in the present invention is not limited to the decision feedback equalizer but can be applied to the frequency domain LMS adaptive equalizer described above in the same manner.

On the other hand, as the control of the channel equalizer using the SNR value, the selection of the blind adaptation scheme of the equalizer has been described, which is just one embodiment. It can be applied to many parts.

As described above, according to the channel equalization apparatus and method in the digital broadcasting reception system according to the present invention, each time a field sync segment is received, the SNR of the equalizer output is calculated, and the SNR is compared with a preset threshold. After determining whether the equalizer state is a convergent state or a tracking state, the channel equalization performance can be improved by controlling the parameters of the filter in the equalizer appropriately for the determined equalizer state.

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 (11)

A channel equalizer for recovering an original signal by compensating for channel distortion from a digital broadcast signal received through a channel, An equalizer state detector for periodically calculating a signal-to-noise ratio of the equalizer output to determine whether the state of the equalizer is in a convergent state or a trace state; And And a channel equalizer for controlling a parameter of an internal filter according to the equalizer state detected by the equalizer state detector to compensate for channel distortion included in the received signal. Device. The method of claim 1, The equalizer state detector And a signal-to-noise ratio is calculated using a training sequence included in the field sync segment whenever a field sync segment is received. The method of claim 1, The equalizer state detector A calculator that calculates the signal-to-noise ratio at the equalizer output, And a comparator configured to compare the signal-to-noise ratio calculated by the calculator and the preset first threshold value to determine whether the equalizer is in the converged state or the trace state, and output the determination result to the channel equalizer. A channel equalizer in a digital broadcast receiving system. The method of claim 3, wherein The calculator is A channel equalizer in a digital broadcast receiving system, characterized in that the signal-to-noise ratio is calculated for each field sync segment at the equalizer output. The method of claim 1, The equalizer state detector A calculator that calculates the signal-to-noise ratio per field sync segment at the equalizer output, A comparator comparing the signal-to-noise ratio calculated by the calculator with a second preset threshold; After the count value is increased or decreased according to the comparison result of the comparator, the count value is compared with the preset count threshold value. If the count value is smaller than the count threshold value, the equalizer state is determined as a converged state, and if the count value is larger, the trace state is determined. And a reliability counter for outputting a determination result to the channel equalizer. The method of claim 5, The reliability counter is If it is determined that the signal-to-noise ratio calculated by the calculator is greater than the preset second threshold value, the count value is increased. If the signal-to-noise ratio is not large, the count value is decreased. The channel equalizer of the digital broadcast receiving system, characterized in that it is determined as a converged state if not exceeding the threshold value, and is determined as a trace state if the threshold value is exceeded. The method of claim 1, The channel equalizer If the equalizer state is determined to be converged when channel equalization is performed using the blind adaptive G-Pseudo method, the CMA (constant modulus algorithm) error value is used as the blind error value. A channel equalizer in a digital broadcast receiving system, characterized by updating a coefficient of a filter by using a value or a decision-directed error value. In the channel equalization method in the channel equalizer of the digital broadcast receiving system for recovering the original signal by compensating for the channel distortion from the digital broadcast signal received through the channel, (a) calculating and outputting a signal-to-noise ratio of the equalizer output each time a field sync segment is received; (b) determining whether the equalizer is in a converged state or a trace state by comparing the signal-to-noise ratio output in step (a) with a preset threshold value; And and (c) compensating for channel distortion included in the received signal by controlling a parameter of a filter inside the channel equalizer according to the equalizer state determined in step (b). Channel equalization method in system. The method of claim 8, Step (b) is The signal-to-noise ratio value calculated in the step (a) is compared with the preset first threshold value to determine the equalizer state as a converged state when the value is smaller than the first threshold value, and when the equalizer state is determined to be the trace state. Channel equalization method in a digital broadcast receiving system. The method of claim 8, Step (b) is (B) -1 comparing the signal-to-noise ratio value calculated in the step (a) with a second preset threshold value; If the count value is increased or decreased according to the comparison result in the step (b) -1 above and the count value at this time is compared with the preset count threshold value, the equalizer state is converged. Determining a tracking state if the channel is large. The method of claim 8, Step (c) is When the equalizer state is determined to be converged when the channel equalizer performs channel equalization using the blind adaptive G-Pseudo method, the channel equalizer uses a constant modulus algorithm (CMA) error value as the blind error value, and if the channel equalizer determines the tracking state, the blind error. A method of equalizing a channel in a digital broadcasting reception system, characterized by updating a coefficient of a filter by using a Sato error value or a decision-directed error value.

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