KR20000045635A - Apparatus for generating error signal for removing dynamic ghost effect in ntsc same channel interference mode of hdtv equalizer - Google Patents

Abstract

PURPOSE: An apparatus for generating error signal for removing dynamic ghost effect in NTSC same channel interference mode of HDTV equalizer is provided to generate an error signal representing the error between equalizer output slicing signal and output of the equalizer. CONSTITUTION: An apparatus for generating error signal for removing dynamic ghost effect in NTSC(National Television System Committee) same channel interference mode of HDTV(High Definition Television) equalizer includes a mode determiner and a coefficient update determiner(100). The mode determiner determines whether a decision directed mode is to be applied or not by comparing absolute values of error signal. The coefficient update determiner(100) determines whether the coefficient is to be updated by outputting error signal from a rounder(21) and a signal from the multiplexor selectively.

Description

Error signal generator for eliminating dynamic ghost effects in cochannel interference mode of high definition television equalizer

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a channel equalizer of a Grand Alliance (GA) type High Definition TeleVision (HDB) system, and in particular, a National Television System Committee (NTSC) of an HDTV channel equalizer. One of the standard methods) Dynamic in cochannel interference mode of high definition television equalizer which generates error signal for tap coefficient update in random data interval to handle dynamic ghost in cochannel interference mode. The present invention relates to an error signal generator for removing ghost effects.

In general, the physical channel of a digital communication system including an HDTV is free space, and the actual transmission signal is received through multiple paths due to a deflection of a path propagated by weather changes or the influence of the sun such as air, clouds, and atmospheric layers. In addition, fixed multi-paths reflected, transmitted and propagated by terrains such as mountains, cliffs, and earth, and forests and buildings, and time-varying multi-paths reflected by planes, cars, etc. are generated. Such multipath propagation has different propagation times in the transmission of the same signal, causing inter-symbol interference (ISI). For this reason, the channel does not satisfy the ideal characteristics and causes signal distortion during signal transmission. This signal distortion causes a bit detection error at the receiving side in a digital transmission method such as HDTV so that the entire screen cannot be restored or a completely different image appears.

In order to overcome this phenomenon, a channel equalizer reduces the bit detection error at the receiving end by processing the received signal passing through the distorted channel away from the ideal characteristic to compensate for the characteristic of the channel that changes with time. .

The channel equalizer in the digital communication system has various techniques, but here, the LMS (Least Mean Square) algorithm is used. The LMS algorithm is an algorithm that continuously adjusts and equalizes coefficients of a filter so that a mean square error (MSE) between a desired signal and a filter output signal is minimized.

A block configuration of a VSB HDTV channel equalizer using the LMS algorithm is shown in FIG. 1, and the operation thereof is as follows.

The error signal generator 15 generates an error signal by performing a subtraction operation between the reference signal of the channel equalizer and the equalizer output signal. The error signal thus calculated is correlated with the channel equalizer input signal in a forward filter 10 and correlated with the channel equalizer output signal in a backward filter 17. This correlation, correlated in the forward filter 10 and the backward filter 17, respectively, is multiplied by the step size, respectively, and then each tap coefficient of the forward filter 10 and the backward filter 17 (coefficient) Used for update. The output signal of the forward filter 10 and the output signal of the backward filter 17 are added by the adder 18 to generate a final equalized output signal of the channel equalizer.

The reference signal used in the error signal generator 15 is a training sequence when the channel equalizer is operated in the training mode, and is output from the channel equalizer output when the channel equalizer is operated in the decision directed mode (DD mode). A decision signal is used.

The training mode sends a known signal promised by the transmitting side, and the receiving side compares the signal with the original signal to estimate the distortion level of the channel to adjust the tap coefficient of the equalizer. The decision based mode equalizes using the data determined at the equalizer output when the training period is over and random data including actual information is input.

2 shows a data frame of the VSB standard by GA.

As shown, one frame consists of two fields, each field consisting of one field sync segment followed by 312 random data segments. Each segment consists of 832 symbols, the first four symbols of each segment being a segment sync signal.

Since the dual field sync segment has a certain pattern known to each other at the transmitting and receiving side, it can be used as a training sequence in the training mode.

In general, VSB channel equalizers have 8 VSB modes (Terristrial Mode) for terrestrial broadcast and 16VSB modes for cable TV. Here, 16 VSB mode does not share a channel with NTSC (National Television System Committee) system, which is a kind of analog transmission method, and 8VSB mode shares channel with NTSC system. Thus, the 8 VBB mode in the 16 VSB mode and the absence of NTSC co-channel interference can operate the channel equalizer in the DD mode.

In the case of terrestrial broadcasting, ghost by fixed multipath is called static ghost, and ghost by multipath such as time-varying multipath is called dynamic ghost. If the linear channel distortion is confined to static ghosts, you can simply run the channel equalizer in training mode to get a converged state where the distortion is compensated, but when a sudden ghosting situation occurs, it becomes divergent and cannot restore a normal signal. do.

Therefore, the channel equalizer must be operated in the decision mode. However, the 8VSB mode with NTSC co-channel interference cannot apply the decision mode.

NTSC cochannel interference mode data has 15 levels of 14,12,10,8,6,4,2,0, -2, -4, -6, -8, -10, -12, -14 ) Value. If the absolute value of the error value between the output signal of the channel equalizer and the input signal of the channel equalizer is greater than 1, a decision error occurs in the random data section. That is, the transmitting side transmits a value of 8, but when the receiving side receives a value of 9.2, it determines that it is 10 and a determination error occurs. This decision error adversely affects the channel equalizer operating in the decision based mode in the NTSC co-channel interference mode. For this reason, the decision based mode is difficult to use in the NTSC co-channel interference mode.

3 shows the configuration of a general error signal generator used for coefficient update of a channel equalizer in the case of NTSC co-channel interference.

As shown, a subtractor 20 for calculating a difference between the reference signal of the channel equalizer and the output signal of the channel equalizer; A rounding unit 21 for rounding a signal output from the subtractor 20 by a set number of bits; The coefficient update prohibition signal for preventing the output signal of the rounding unit 21 and the tap coefficient of the filter in the channel equalizer from being updated according to the training mode control signal generated by the processor of the channel equalizer (not shown in FIG. 1). It consists of a multiplexer 22 for selectively outputting.

Referring to the error signal generator operation of the conventional channel equalizer as follows.

First, the channel equalizer is controlled to operate in a training mode during a section in which a training sequence is received, and the channel equalizer is controlled to operate in a determination mode during a section in which random data is received. Here, the determination base mode is operated to equalize random data using the reference signal determined as the equalizer output signal without using the tap coefficient updated in the training mode without updating the tap coefficient.

Therefore, the processor of the channel equalizer outputs the training mode control signal to an active state during a section in which a training sequence is received, and inactives the training mode control signal equal_mode during a section in which random data is received. Output in the state.

When the channel equalizer is in the training mode, the reference signal is provided as the training sequence, and in the determination mode, the output signal of the channel equalizer is provided as the reference signal. The subtractor 20 outputs an error signal by subtracting the output signal of the channel equalizer from the reference signal provided in this way. The rounding unit 21 rounds this error signal by the set number of bits. In this example, a 6-bit error signal is used, so round to 6 bits. When the training mode signal is output from the processor, the multiplexer 22 outputs the output signal of the rounding unit 21 as an error signal to update the tap coefficient of the filter in the channel equalizer. Therefore, the channel equalizer uses this error signal to update the tap coefficient. When the inactive training mode signal for operating in the judgment based mode is output from the processor, the multiplexer 22 outputs a coefficient update prohibition signal "0" in order not to update the tap coefficient. Therefore, the channel equalizer does not update the tap coefficient in the random data section.

In the conventional channel equalizer, the determination mode is applied in such a manner that the tap coefficient is not updated in the random data section. However, in this case, the tap coefficient is not updated, and thus, the influence of the dynamic ghost cannot be removed. Therefore, the reliability of system performance is lowered.

Accordingly, the present invention has been proposed to solve the conventional problems as described above, and an object of the present invention is to generate an error signal so that tap coefficients can be updated in a random data section in the NTSC co-channel interference mode of an HDTV channel equalizer. Accordingly, an object of the present invention is to provide an error signal generator for eliminating the effects of dynamic ghost in NTSC co-channel interference mode of an equalizer for HDTV that can remove the effects of dynamic ghost.

In order to achieve the above object, the error signal generator for removing the dynamic ghost effect in the NTSC co-channel interference mode of the equalizer for HDTV according to the present invention, the training signal as a reference signal during the training sequence interval and Detects whether the absolute value of the error signal between the channel equalizer output signals is within a certain range that does not cause a determination error. Thus, if the absolute value of the error signal for all input symbols during the training sequence is included in a range that does not cause a determination error, an error signal is generated to update the channel equalizer tap coefficient during the random data interval. That is, an error signal between the signal determined at the channel equalizer output and the channel equalizer output signal is generated during the random data period so as to operate in the determination mode.

1 is a block diagram of a general HDTV channel equalizer block,

2 is a structural diagram of a GA VSB frame,

3 is a configuration diagram of a conventional error signal generator,

4A is a configuration diagram of an error signal generator according to the present invention;

FIG. 4B is a diagram illustrating a configuration of a DD mode determiner for controlling the coefficient update unit of FIG. 4A.

<Explanation of symbols for main parts of drawing>

100: coefficient update decision unit 200: DD mode determination unit

210: determination error prevention symbol detection unit 220: training heat counting unit

230: counter control unit 240: DD mode signal generator

Hereinafter, an error signal generating apparatus for removing the dynamic ghost effect in the NTSC co-channel interference mode of the present invention HDTV equalizer will be described in detail with reference to the accompanying drawings.

4A and 4B show the configuration of an error signal generator according to the present invention.

The error signal generator includes a subtractor 20 that calculates a difference between a reference signal of the channel equalizer and an output signal of the channel equalizer, as shown in FIG. 4A; A rounding unit 21 for rounding a signal output from the subtractor 20 by a set number of bits; A multiplexer (22) for selectively outputting a coefficient update prohibition signal for not updating the output signal of the rounding unit (21) and the tap coefficient according to a training mode control signal generated by a processor of a channel equalizer; Coefficient update by selectively outputting an error signal from the rounding unit 21 and a signal from the multiplexer 22 according to the decision based on the determination mode determiner 200 determining whether the tap coefficient is updated during a random data interval. It is composed of a coefficient update unit 100 for determining whether or not.

As shown in FIG. 4B, the determination based mode determiner 200 detects a symbol capable of preventing a determination error by checking an error signal output from the rounding unit 21 and detects a symbol capable of preventing a determination error. )Wow; A counter controller 230 for controlling counting during a training sequence; A training sequence counting unit 220 driven under the control of the counter control unit 230 to count an output signal of the determination error prevention symbol detection unit 210; The training sequence counting unit 220 includes a DD mode determination unit 240 for determining a determination determination mode by comparing a value counted in the decision directed mode (DD mode) operation.

The set value for the determination mode operation of the DD mode determiner 240 is set to 688.

The determination error prevention symbol detection unit 210 includes a comparator 211 for comparing whether the error signal falls within the channel equalizer output determination error prevention range by comparing the upper two bits of the error signal for the input symbol; The multiplexer 212 selectively outputs the output signal of the comparator 211 and a specific signal according to the training mode control signal output from the processor of the channel equalizer, and the output signal of the multiplexer 212 for a predetermined time. It consists of a delay unit 213 for delaying.

The specific signal is set to " 0 " as a value set so as not to count.

The counter control unit 230 performs an OR operation on a delay unit 231 for delaying a field synchronizing signal for a predetermined time, a signal inverting the field synchronizing signal, and a signal through the delay unit 231. Thus, when the training train section is started, the training train counting unit 220 is configured to clear the (nor gate) (nor gate) (232).

The training sequence counting unit 220 is an adder 221 for adding the signal output from the determination error prevention symbol detection unit 210 and the output signal of the counter 222, and under the control of the counter control unit 230. A counter 222 is driven to count the output signal of the adder 221.

The operation of the error signal generator for removing the dynamic ghost effect in the NTSC co-channel interference mode of the HDTV equalizer according to the present invention configured as described above is as follows.

First, it consists of three level values of 10,0, -10 during the training sequence, and if the error signal during the training sequence is set to e (n)

e (n) = t (n) -y (n)

Becomes Where t (n) is the training sequence and y (n) is the output signal of the channel equalizer. If e (n) consists of 6 bits, the format is sx.xxxx, and the values of the upper two bits are not different, that is, 00.xxxx or 11.xxxx, the absolute value of the error signal is less than one. it means. In this way, when the absolute value of the error signal is smaller than 1, a determination error does not occur. When such a determination error does not occur, that is, when only the absolute value of the error signal is smaller than 1, the determination mode can be applied to the random data section. This allows us to adapt to dynamic ghosts in the steady state, which is a convergent state.

In the training sequence already known on the transmitting and receiving side, 700 symbols are transmitted from the transmitting side in the field sync segment. However, the 12 symbols are lost due to the 12 symbols of the previous field, so that only 688 symbols can be received by the receiver as a training sequence.

The counter controller 230 controls the counter 222 to operate during the training sequence. Thus, when the field sync signal (field_sync) for the field sync is active, the clear signal for clearing the counting value through the noah gate 232 is output to the counter 222. The counter 222 prepares for counting.

In the training mode, the reference signal of the error signal generator uses a training sequence and outputs the difference between the training sequence and the output signal of the channel equalizer as an error signal through the rounding unit 21. Then, the determination error prevention symbol detection unit 210 of the DD mode determination unit 200 compares the upper two bit signals e (5) and e (4) among the error signals e (5: 0). Thus, if e (5) and e (4) are equal to each other, a high signal informing of symbol detection that no determination error occurs is output. The multiplexer 212 selects and outputs a signal output from the comparator 211 when the training mode control signal equal_mode is a training mode and low in indicating that the training mode control signal equal_mode is a determination mode. If it is active, select "0" to output.

When the training sequence counting unit 230 is cleared to count only during the training sequence, if the high signal indicating the detection of the error prevention symbol detection is output from the determination error prevention symbol detection unit 210, the training sequence counting unit 230 counts this high signal. Thus, the training sequence counting unit 230 may count during the training sequence, and if the determination error prevention symbol is detected, the counting value is increased by one.

The DD mode signal generator 240 compares the counting value output from the training string counting unit 220 with 688. Therefore, when the counting value is 688, the channel equalizer outputs the DD mode signal DD_flag in an active state so that the channel equalizer operates in the DD mode.

During a training sequence of 688 symbols, a training mode control signal (equal_mode) is generated from the processor in a high active state, and a reference sequence is used for the training sequence. Thus, in the training mode, the error signal generator generates the difference between the training string and the equalizer output signal as an error signal. The equalization is performed by updating the tap coefficient of the channel equalizer with this error signal.

On the other hand, as described in the operation of the DD mode determiner 200, when the absolute value of all error signals for the 688 symbols in the training mode is detected as a value less than 1 that does not cause a determination error, the DD mode determiner ( 200 generates the DD_flag signal in an active state. At this time, after the training sequence ends and becomes a random data section, the subtractor 20 calculates the difference between the slicing value and the equalizer output signal using a value obtained by slicing the output signal of the channel equalizer as a reference signal. Output the signal.

The coefficient update determiner 100 selects and outputs an error signal from the rounding unit 21 according to the DD_flag signal activated by the DD mode determiner 200. Thus, if the absolute values of the error signals for 688 symbols during the 688 training sequence are all less than 1, the error signal is generated to update the tap coefficient in the random data section received after the training sequence. If a symbol larger than 1 of the absolute values of the error signal for the input symbol is detected during the 688 training sequence, it may cause a decision error and adversely affect the equalization. Therefore, the DD mode determiner 200 does not activate the DD_flag signal. During the random data interval, the coefficient update determiner 100 outputs an error signal as “0” so as not to update the tap coefficient. In this operation, the tap coefficient is updated in the NTSC co-channel interference mode of the HDTV channel equalizer during the training sequence, and it is determined whether the determination coefficient mode can be applied. Will be determined. Thus, it is possible to dynamically apply the decision base mode to remove the influence of the dynamic ghost.

As described above, the error signal generating apparatus for removing the dynamic ghost effect in the NTSC co-channel interference mode of the HDTV equalizer according to the present invention, each during the training sequence in the NTSC co-channel interference mode of the HDTV channel equalizer The magnitude of the absolute value of the error signal of the input symbol is compared and equalized with the equalizer output slicing signal to update the tap coefficient in a random data section if the absolute value of the error signal of each symbol falls within a range that does not cause a determination error. By generating an error signal between the output signal, there is an effect to eliminate the effect of the dynamic ghost.

Claims (5)

National Television System Committee (NTSC) One of the channel equalizers for high-definition television (HDTV) with co-channel interference is the difference between the reference signal of the channel equalizer and the output signal of the channel equalizer. A subtractor for calculating; A rounding unit for rounding a signal output from the subtractor by a set number of bits; In the error signal generator comprising a multiplexer for selectively outputting the output signal of the rounding unit and the coefficient update prohibition signal for not updating the tap coefficient according to the training mode control signal generated by the processor of the channel equalizer, A decision based mode determining unit which determines whether to apply a decision directed mode (DD mode) by comparing an absolute value of an error signal for each symbol during a training sequence section; And a coefficient update determining unit for selectively outputting an error signal from the rounding unit and a signal from the multiplexer according to the decision based on the determination mode determining unit to determine whether to update the coefficient during a random data period. Error signal generator for eliminating dynamic ghost effects in NTSC co-channel interference mode of HDTV equalizers. The method of claim 1, wherein the determination based mode determination unit, A determination error prevention symbol detection unit which detects a symbol capable of preventing a determination error by inspecting an error signal output from the rounding unit; A counter controller for controlling counting during a training sequence; A training sequence counting unit driven under the control of the counter control unit to count an output signal of the determination error prevention symbol detection unit; NTSC of the equalizer for HDTV comprising a DD mode decision unit for determining the determination mode by comparing the value counted in the training sequence counting unit with a setting value for the operation of the decision direct mode (DD mode) Error signal generator for removing the effects of dynamic ghost in co-channel interference mode. The method of claim 2, wherein the setting value for the determination mode operation of the DD mode determination unit, An error signal generator for removing dynamic ghosting effects in NTSC co-channel interference mode of an equalizer for an HDTV, which is set to 688 as the number of symbols of a training sequence that can be normally received by an HDTV receiver. The method of claim 2, wherein the determination error prevention symbol detection unit, A comparator for comparing whether the error signal falls within the channel equalizer output determination error prevention range by comparing the upper two bits of the error signal for the input symbol, and according to the training mode control signal output from the processor of the channel equalizer. Error signal for removing the dynamic ghost effect in the NTSC co-channel interference mode of the equalizer for HDTV, characterized in that the output signal of the comparator and a multiplexer for selectively outputting the signal set not to count in the training sequence counting unit Generating device. The method of claim 2, wherein the counter control unit, A delay that delays the field sync signal for the field sync for a predetermined time, and a signal that inverts the field sync signal and the signal delayed by the delay to perform an OR operation, and when the training sequence is started, the training An error signal generator for removing dynamic ghost effects in the NTSC co-channel interference mode of the equalizer for HDTV, characterized in that it comprises a no gate (nor gate) for clearing the thermal counting unit (clear).