MXPA06005783A - Apparatus and method of decision feedback equalization in terrestrial digital broadcasting receiver - Google Patents

Abstract

The present invention is related to a decision feedback equalizing apparatus and a method thereof. The object of the invention is to provide to an apparatus and a method of decision feedback equalization that make a channel property of an inferior receiving signal to mild by using a channel-matched filter and decreases decision errors of symbol detector output signals by using a trellis decoder with decreased complexity, whose trace back depth is 1 (TBD=1).

Description

WO 2005/050987 Al IIII1IIII0I0IIIII1 Declarations under Rule 4.17: - with a declaration as to non-prejudicial disclosures or ex¬ - as to non-prejudicial disclosures or exceptions to lack of ceptions to lack of novelty novelty (Rule 4.17 (v)) for all designations - as to non-prejudicial disclosures or exceptions to lack of For two-letter codes and other abbreviations, referto the "Guidnovelty (Rule 4.17 (v)) for all designations ance Notes on Codes and Abbreviations" appearing at the beginning - as to non-prejudicial disclosures or exceptions to lack of any regular issue of the PCT Gazette. novelty (Rule 4.17 (v)) for all designations Published: APPARATUS AND METHOD FOR THE EQUALIZATION OF FEEDBACK OF DECISIONS IN DIGITAL TERRESTRIAL TRANSMISSION RECEIVERS FIELD OF THE INVENTION The present invention relates to a channel equalization technology in digital terrestrial transmission receivers and more particularly to an apparatus and method of decision feedback equalization that makes a channel property of a lower reception signal to be smooth by using a channel equalization filter and decreasing the decision errors of the symbol detector output signals by using a lattice decoder with decreased complexity, whose trace depth is 1 (TBD = 1) and a symbol detection method using the same PREVIOUS ART In a general digital transmission system, because the data is transmitted through a limited frequency bandwidth, a time dispersion effect, which means that the pulse energy of a predetermined symbol is scattered to the symbols neighbors, generating interference to neighboring symbols. Therefore, the transmitted data is affected by several channel distortions.

As distortion of the channel, there is for example a pluridirectional, a frequency deviation and a phase of instability of the image. The channel distortion occurs in an Inter-symbol Interference (ISI), which means interference or a distortion between a predetermined symbol and its neighboring symbols and generates a problem to receive the desired data in the digital transmission system.

To prevent channel distortion and decrease the symbol error due to an ÍSI, the general receiver, for example, a digital transmission receiver, uses a channel equalizer.

Most communication channels need an adapter equalizer to update a derivation coefficient in accordance with time because the distortions in the general digital transmission system are time variants.

The configuration of a conventional channel equalizer is described in Figure 1.

As shown in Figure 1, the conventional channel equalizer includes a digital filter 11, a symbol detector 12, a derivation coefficient update unit 13, a regulation sequence storage 14, a statistical data calculator 15, a switch 16 and an equalizer input signal storage 17.

The digital filter 11 eliminates an inter-symbol interference (ISI) causing a distortion of a received baseband signal for a digital transmission receiver. The symbol detector 12 receives the output signal of the digital filter 11 and calculates a determined data by comparing the output signal for a predetermined threshold by means of which the determined data is produced.

The derivation coefficient update unit 13 receives the output signals from the input signal storage of the equalizer 17 and the digital filter 11 and some error data selected by the switch 16 by means of which a filter bypass coefficient is updated. digital 11 Also, the regulation sequence storage 14 stores the regulation data sequence already known in a transmitter of a digital transmission system. The regulation data sequence is read in a regulation mode and is produced for the derivation coefficient update unit 13.

The statistical data calculator 15 calculates a statistical error to produce the statistical error for the update unit of the derivation coefficient 13 in a hidden mode.

The switch 16 selects one of regulation storage 14, the statistical data calculator 15 and the symbol detector 12 in accordance with an operation mode and yields the error data produced from the derivation coefficient update unit 13. Then, the update unit of the derivation coefficient 13 calculates an error signal corresponding to the error data and updates the derivation coefficient by using the corresponding data for the derivation coefficient of the digital filter 11 in the input signal storage of the equalizer 17 to produce the derivation coefficient for the digital filter 11.

Like the channel equalizer, the decision feedback equalizer (DFE) is widely used in the digital transmission receiver. In general, an eye diagram of an output signal is opened in the decision feedback equalizer, where the diagram is a kind of factor for determining the operation of the equalizer, that is, a function for making a signal decision of output straight and easily. Also, if an output signal from the symbol detector is determined correctly, the feedback filtering block erases a Symbol Interference (YES) in accordance with the predetermined symbol and there is no such problem as a noise amplification phenomenon in the equalization of the linear equalizer channel. For now, the decision feedback equalizer is widely used in the digital transmission receiver.

Therefore, for proper use, it is important that the output signal of a symbol detector should not have a decision error and for most of all, the eye diagram is opened.

For the eye diagram to be opened in the digital transmission system of the Committee of the Advanced Television System (ATSC) which is an American standard for terrestrial digital television, a method is used to open the eye diagram by inserting a segment of regulation sequence, where one segment is 208 bytes, in each data segment 312 even if the efficiency of the data is reduced.

However, since the inserted regulatory sequence segment is short under a pluridirectional environment that has a large phantom, it is commonly failed to open the eye design. In particular, although the regulation sequence exists, it is commonly faulted if a derivation coefficient is not large enough to converge or if the environment is under a lower pluridirectional environment that has a time-varying channel, a large phantom or a signal phantom of a large level. If the eye diagram does not open, the possibility of the decision error in the symbol detector is very high. As a result, a problem of error propagation can be generated whereby the decision error is accumulated through a feedback circuit of the decision feedback equalizer.

Therefore, a method is required to decrease the decision error during the period of data that does not have a regulation sequence segment and in particular, the total derivation energy must be decreased to decrease the decision error by opening the diagram of the eye of the decision feedback equalizer.

In the first, most conventional methods for decreasing the decision error use a viterbi decoder that has a decoding delay. There is a method for making a predetermined delay in an equalizer derivative coefficient adjuster so that it is identical to the decoiter delay of the viterbi decoder. In this document, this method is proposed by G. Long entitled "The LMS Algorithm with Delayed Coefficient Adaptation", IEEE Trans. Acoust., Speech, Signal Processing, vol. ASSP-37, October 1989.

In addition, there is a method to resolve a decoder delay of the viterbi decoder by periodically adding an interleaver and a deinterleaver proposed by. V. Eyuboglu, entitled "Detection of Coded Modulation Signals on Linear, Severly Distorted Channels Using Decision-Feedback Noise Prediction with Interleaving", IEEE Trans. Common., Vol. COM-36, pp. 401-409, April 1988 and in U.S. Patent No. 4,833,693 issued to Eyuboglu, May 23, 1989.

Due to the previously described methods for decreasing the decision error that are used in the viterbi decoder having the decoding delay as TDB-1 behind the equalizer that serves as the symbol detector of the decision feedback equator, such devices are required additional to clear the decoding delay. Also the viterbi decoder behind the equalizer has enough performance, the TDB should be 5 times more than the number of memories in the lattice decoder used for the decoding process. However, the decoding delay should be as small as possible to use the output of the viterbi decoder as a feedback input of the decision feedback equalizer.

Particularly, the decoding delay is not TBD-1 but 12x (TBD-1) in the digital transmission system using 12 TCm is encoded by the lattice code interleaver as shown in Figure 5 and approximately, the decoding delay it reaches 168 because there are 2 memories in the TCM decoder. It is very inefficient that the viterbi decoder having 168 decoding delay is actually used in the digital transmission system.

Therefore, to use the viterbi decoder as the symbol detector of the decision feedback equalizer in the digital transmission receiver, the decoding delay is as small as possible and also, it is the best so that there is no delay of decoding And a complex for the implementation of the decoder should be as low as possible.

In the meantime, to decrease the derivative energy of the feedback filter, there are methods to increase the derivation number that removes the column phantom and to change the channel property of a receiving signal by using a training beam or an equalization filter. channel.

The method for increasing the bypass number of the front I power filter is inefficient and the performance improvement is lower compared to the increased bypass number. The method to change the channel property by using the channel equalization filter, which is proposed in a document by Richard Citta, entitled "A VSB Receiver Designed for Indoor and Distributed Transmission Environments", IEEE 52nd Annual Broadcast Symposium, Oct. 9-11, 2002 is more effective than the method to increase the number of derivation.

Because the channel equalization method proposed by Richard Citta generates the channel equalization filter based on the oversampling data and uses a fractionally spaced equalizer, the complexity is very high. Also, since a simple slider is used as the symbol detector, the error propagation problem due to the decision error may occur.

Therefore, the development of a channel equalization filter, which has low complexity in a symbol base and a symbol detector that has exceptional decision error are highly required.

Description Technical Problem Therefore, it is an object of the present invention to provide an apparatus and method of decision feedback equalization that makes a channel property of a lower reception signal to be moderated by the use of a channel equalization filter and decrease the decision errors of the output signals of the symbol detector by using a lattice decoder with decreased complexity, whose stroke depth is 1 (TBD = 1).

The other object of the present invention provides a lattice decoder symbol detection method with decreased complexity, of which TDB is 1, which can use an output signal from the lattice decoder as an input signal of the EQ feedback fil decision feedback by decreasing a decoding delay.

Technical Solution In accordance with one aspect of the present invention, a decision feedback equalizer is provided in a digital estrial transmission receiver, including, a channel estimation unit for estimating a channel of a symbol based reception signal based on the reception signal and a regulation sequence; a channel equalization filng unit for changing a channel property of the reception signal by maximizing a signal-to-noise ratio (SNR) of the estimated channel; an input signal storage unit for storing a reception symbol whose channel property is changed by the channel equalization filng unit; a channel equalization unit for performing a performance feedback equalization by repeatedly filng the reception signal passing through the channel equalization filng unit, a lattice decoding unit for detecting a symbol, which are decision data , based on the lattice decoding algorithm with diminished complexity, whose tracing return depth is 1, from the equalized channel reception symbols and the symbol output in a directed decision mode, a statistical data calculation unit to calculate statistical error data used in a hidden mode and taking statistical error data; a regulation sequence storage unit for storing the regulation sequence, an exchange unit for selecting a mode between the regulation mode, the directed decision mode and the hidden mode; a calculation unit of error signal to calculate an error signal by comparing an output signal in the mode selected by the exchange unit for an output signal of the channel equalization unit and a derivation coefficient update unit for updating a derivation coefficient to be provided for the channel equalization equalization unit based on the error signal, the output signal of the latched decoding unit and the output signal gives the input signal storage unit.

In accordance with one aspect of the present invention, a method of decision feedback equalization is provided in a digital estrial transmission receiver including the steps of: a) estimating a channel of a signal reception based on symbols based on a signal of reception and a regulation sequence; b) changing a channel property of the reception signal to maximize a signal-to-noise (SNR) supply of the estimated channel by passing the reception signal through a channel equalization fil c) deining a parameused for a decision feedback of the reception symbol whose channel property is changed and a channel equalization parameis initiated; d) detecting a symbol from an output signal of an equalizer in a specific time index signal in accordance with the deined paramebased on a lattice decoder with decreased complexity, whose return line depth is 1; e) calculate the statistical error data used in a hidden mode; f) select a mode between a regulation mode, a decision mode and the hidden mode; g) calculating an error signal by comparing an output signal of the mode selected in step f) to output the equalizer signal in a directed decision mode and updating a derivation coefficient based on the error signal and h) performing an equalization of decision feedback based on the updated derivation coefficient.

In accordance with one aspect of the present invention, there is provided a method of symbol detection for channel equalization in a terrestrial digital transmission receiver, the method including the steps of: a) calculating an absolute paired distance between the pairs of symbols in an input signal of a symbol detector and lattice diagram, b) selecting an absolute distance having a small value for each absolute distance of distance between the absolute distance pairs; c) calculate an accumulated absolute distance by adding a previous absolute distance for a current calculated absolute distance for each state in the lattice diagram in a time index; d) eliminate the accumulated absolute distances except the smallest cumulative distance for each state in the lattice diagram in the time index; e) select a state in which the cumulative absolute distance is the smallest among all the states in the lattice diagram in the time index and obtaining an output signal from the symbol detector, which is the lattice decoding unit, to starting from a division shown in the lattice diagram transited to the selected state and f) repeatedly performing steps a) to e) for each time index symbol.

The present invention relates to an apparatus and method for decision feedback equalization having a channel equalization filter and a latched decoder in a terrestrial digital transmission receiver, wherein the channel estimator estimates the signal channel of reception based on the reception signal and the regulation sequence, generates the channel equalization filter based on the information of the estimated channel, equalizing the reception signal that passes through the channel equalization filter by using the equalizer of decision feedback that has the viterbi decoder with decreased complexity, whose TBD is 1 and by means of which the channel equalization is effectively done under a lower environment such as in a room or in a mobile.

The present invention can change the channel property of the reception signal under a lower environment such as in a room or mobile to be smoothed by placing the channel equalization filter generated from the channel-based estimator in front of the feedback equalizer. of conventional decisions and decrease the decision error of the symbol detector by using the viterbi decoder with decreased complexity, whose TBD is 1, in place of the simple slider as the symbol detector in the conventional decision feedback equalizer and by means of which a convergence speed and stability of the digital filtering block are increased and the residual MSE is decreased in a normal state after convergence.

Advantageous Effect As mentioned above, the present invention can change the channel property of the reception signal under a lower environment such as in a room or mobile to be smoothed by placing the channel equalization filter generated from the channel based estimator. in symbols in front of the conventional decision feedback equalizer and decrease the decision error of the viterbi decoder symbol detector with decreased complexity, whose TBD is 1, instead of the simple slider served as the symbol detector in the decision feedback equalizer conventional and therefore a convergence speed and the stability of the digital filter block are increased and the residual MSE is decreased in a normal state after convergence.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which: Figure 1 is a diagram of conventional block illustrating a decision feedback equalizer, where: A = equalizer output signal B = band base signal C = decision mode D = hidden mode E = regulation mode.

Figure 2 is a block diagram illustrating a decision feedback equalizer in accordance with an embodiment of the present invention, wherein: F = regulation sequence G = reception signal H = channel estimation block I = copy of mirror of the derivation coefficient of the estimated channel filter J = equalizer input signal.

Figure 3 is a block diagram illustrating a coded trellis modulation coder (TCM) used in a residual sideband transmission system 8 (8-VSB) of the Advanced Television System Committee (ATSC) and a lattice diagram of the same, where K = lattice encoder L = mapping.

Figure 4 is a diagram illustrating a symbol detection process of a lattice decoder (TBD = 1 and having increased complexity) included in a decision feedback equalizer of the present invention, wherein: a = transmission signal b = equalizer input signal c = output signal of the conventional symbol detector d = output signal of the symbol detector of the present invention.

Figure 5 is a block diagram illustrating a coded trellis interleaver using in an ATSC 8-VSB transmission system, where: 0 = coder # 0 TCM 1 = coder # 1 TCM 2 = coder # 2 TCM 3- = coder # 10 TCM 4 = encoder # 1 5 = multiplier 6 = demultiplier and Figure 6 is a flow chart describing a decision feedback equalization method according to an embodiment of the present invention, wherein: I = start.

DETAILED DESCRIPTION OF THE INVENTION The foregoing and other objects and features of the present invention will become apparent from the following description in conjunction with the accompanying drawings. In the following part of this document, the preferred embodiments of the present invention will be described in detail with reference to the drawings.

Figure 2 is a block diagram illustrating a decision feedback equalizer in accordance with one embodiment of the present invention.

To understand the present invention, prior to the configuration and operation of a decision feedback equalizer having a channel equalization filtering block 21 and a lattice decoding block 23, a calculation process of equation 20 and a block is described. of main filtration 22 are described as follows.

First of all, the input signals of the channel estimation block 20 and the main filtering block 22, a reference signal and a derivation coefficient are defined as follows. hc is a derivation coefficient of a channel estimation filter 201 of the channel estimation block 20. r [k] is a desired signal needed to update the derivation coefficient of the channel estimation filter 201 at time k and is an input signal from a channel equalization filtering block 21. s [k] is an output signal of the channel estimation filter 201 at time k. hm is a derivation coefficient of the channel equalization filter block 21. x [k] is an input signal from the main filter block 22 at time k or an output signal from the channel equalization filtering block 21. and [k] is an output signal of the main filtering block 22 at time k. bi [k] is a bypass coefficient of a feed front filter (FFF) 221 in the main filtration block 22 at time k. ai [k] is a coefficient of a feed return filter (FBF) 222 in the main filtration block 22 at time k.

The derivation coefficient hc of the channel estimation filter 201 is expressed as: Where, N is a derivation number of the channel estimation filter 201, hc, ¡is a derivation coefficient rth of the estimation filter of channel 201, d [i] is a unit sample function. The output signal of the channel estimation filter 201 based on hc is expressed as: * * -1 ÍEs. 2) Where, d [k] is a regulation sequence stored in a regulation sequence storage block 25.

An error signal e-¡[k] for updating the derivation coefficient of the channel estimation filter 201 is expressed as: Wherein, an update unit of the channel estimation derivation coefficient 203 updates the derivation coefficient of the channel estimation filter 201 based on the error signal e-, [k].

The derivation coefficient of the channel equalization filtering block 21 obtained based on the updated derivation coefficient of the channel estimation filter is expressed as: Where, * denotes a complex conjugate. hM is obtained by calculating a symmetric pair of hc. In accordance with the aforementioned process, the channel equalization filtering block 21 is also known as a channel mirror filter.

An equalizer input signal obtained based on the channel equalization filtering block 21 is expressed as: V-j * Mβ? * T • *. { * - *] ÍEq- 5) Wherein, N is a derivation number of the channel equalization filter 21 and has an identical derivation number and a derivation length with them of the channel estimation filter and hM, it is a derivation coefficient of the equalization filter of channel? h 21.

An equation of the output signal and [k] of the main filter 22 obtained based on the equalizer input signal x [k] is expressed as: Wherein, Nb is a derivation number of the FFF 221, Na is a derivation number of the FBF 222, cf [k] is an output signal decided by comparison with the output signal and [k] of the main filter 22 for the start determined by the simple slider, that is, the symbol detector 11 in advance. In this document, the error signal e2 [k] for updating the derivation coefficient is expressed as: M = ^ > M (E, 1) If the error signal for updating the derivation coefficient is expressed as Eq. 7, the equations for the update of the derivation coefficient of the FFF 221 and the FBF 222 are expressed as: * +? J = «, IJ-H * M * -. / J Where, μ is a stage size, which is a value that determines a convergence rate and a Minimum Squares Error (MSE) of a normal state.

That is, if the μ is large, the convergence speed becomes much higher and the residual MSE of the normal state becomes higher. However, if the μ is small, the residual MSE becomes much smaller but the convergence speed becomes slower.

As mentioned above, because an eye diagram of the output signal of the decision feedback equalizer is generally opened, if the output signal ff [k] of the symbol detector 12, that is, the simple slider, is a symbol decided correctly, the feedback filtering block eliminates the ISI due to the pre-decided symbol and the Noise amplification phenomenon in an output signal of a filtering block does not occur in a linear equalizer during equalization. For the feature mentioned above, the decision feedback equalizer is widely used.

However, if the symbol decided by the symbol detector 12, ie the simple slider, has an error, because the error accumulates and propagates while passing through the feedback filtering block, security is not guaranteed.

Therefore, the eye diagram is opened by periodically inserting the regulation sequence determined between a transmitter and a forward receiver and subsequently if the regulation sequence period is higher and the data period is started, the output signal c / [k] of the symbol detector 12, that is, the simple slider is used because a transmission symbol is unknown.

As mentioned above, that output signal from the symbol detector 12, that is, the simple slider, is used to update the derivation coefficient as decision-directed equalization.

The present invention changes the channel property of this received reception signal in a lower environment such as in a room and mobile to be smoothed by placing the channel equalization filtering block 21 generated from the channel estimation block 20 in a base of the symbol in front of the conventional decision feedback equalizer and decreases the decision error of the symbol detector 12 by using the viterbi decoder with decreased complexity, whose TBD is 1, instead of the simple slider used in the symbol detector 12 and by from which the convergence speed of the digital filtering block can be increased and the residual MSE can be decreased in the normal state after convergence.

The decision feedback equalizer having the channel equalization filtering block and the lattice decoding block whose TBD is 1 and having decreased complexity, in accordance with the present invention can be applied to the 8-VSB which is standard of digital television American terrestrial and therefore the decision error in the output signal of the symbol detector is decreased and the equalization operation can be increased.

The system 8-VSB uses a segment 313 as the regulation sequence, wherein the transmission symbol is a level 8 signal of ± 1, ± 3, ± 5, ± 7, which has 1 dimensional feature in different width with a quadrature amplitude modulation scheme (QAM).

Hereinafter, the configuration and operation of the decision feedback equalizer having the channel equalization filtering block 21 and the lattice decoding block 23 in the terrestrial digital transmission receiver according to the present invention is described in detail.

As shown in Figure 2, the decision feedback equalizer having the channel equalization filtering block 21 and the lattice decoding block 23 in the terrestrial digital transmission receiver according to the present invention includes the estimation block of channel 20 for the estimation of a channel of a reception signal in a symbol base based on the reception signal and the regulation sequence, the channel equalization filtering block 21 for changing a signal to noise ratio (SNR ) of the channel estimated by the channel estimation block 20, an equalizer input signal storage block 28 for storing the symbol having the channel property changed by the channel equalization filtering block 21, the filtering block 22 to perform decision feedback equalization, that is, channel equalization, by filtering the signal passing the channel equalization filtering block 21 repeatedly, a lattice decoding block 23 for detecting the symbol, that is, the decision data of the received symbol performing the channel equalization, based on the decoding algorithm lattice whose Stroke Return Depth (TDB) is 1 and emitting the detected symbol in the directed decision mode, the statistical data calculation block 24 to calculate and output the statistical error data in a hidden mode, the storage block of regulation sequence 25 for storing the regulation sequence, switch 26 for selecting one of the signal of a regulation mode, the directed mode of decision and the hidden mode, the calculation block of the error signal 27 for calculating the error signal by comparing the output signal of the mode selected by the switch 26, which can be the decision data, the statistical error data or the regulation sequence for the output signal which are equalized data of decision feedback of the main filtering block 222, the update block of the derivation coefficient FFF 29 for updating the derivation coefficient provides the FFF 221 of the main filtering block 22 based on the error signal of the error signal calculation block 27 and the output signal of the equalizer input signal storage block. and the derivation coefficient update block FBF 30 for updating the derivation coefficient to provide the FBF 22 based on the error signal of the error signal calculation block 27 and the output signal of the lattice decoding block 23.

However, the channel estimation block 20 includes the channel estimation filter 201, the error signal calculator 202, and the channel estimation derivation coefficient update unit 203.

The main filtering block 22 includes the equalization FFF 221 and the equalization FBF 222 and an equalizer output calculator 223.

The operations of each element of the decision feedback equalizer having the channel equalization filtering block 21 and the lattice decoding block 23 in accordance with the present invention will be described as follows.

The estimation block of channel 20 estimates the channel based on the reception signal r [k] and the regulation sequence d [k] during the regulation sequence period. In this document, the error signal calculator 202 calculates the error signal e-i [k] based on the reception signal r [k] and the output signal s [k] of the channel estimation filter 201 and the update unit of the derivation coefficient of the channel estimation filter 203 updates the derivation coefficient hc to be provided for the channel estimation filter 201 based on the calculated error signal ß? [k]. The channel estimation block 20 estimates a channel of the reception signal in a symbol base based on the regulation sequence and the reception signal for each L field (the regulation sequence segment 1 is inserted for each 312 data segments , where field 1 has 313 segments and L is greater than 1) or for a first field, generates the filtering block of channel 21 to maximize the SNR of the estimated channel and changes the property of the channel generated from the signal of reception by passing the reception signal through the channel equalization filtering block 21 and whereby the channel property of the reception signal can be smoothed.

The channel equalization filtering block 21 generates the channel equalization filter derivative h based on the derivation coefficient of the channel estimation filter hc calculated by the channel estimation block 20 and maximizes the SNR of the signal reception r [k] based on the derivation coefficient of the generated channel equalization filter hM and the reception signal r [k].

The main filtering block 22 performs equalization of the channel by filtering the output signal from the channel equalization filtering block 21 repeatedly.

The lattice decoding block 23 detects a symbol from the transmitted signal of the main filtering block 22 based on the viterbi decoding algorithm whose TBD is 1. The lattice decoding block 23 detects the symbol based on the viterbi decoding algorithm with decreased complexity , whose TBD is 1, in the digital transmission system in which 12 TCM decoders are used by the lattice code interleaver as shown in Figure 5 and by means of which the decoding delay can be 0.

The statistical data calculation block 24 calculates the necessary statistical data in the hidden mode.

The regulation sequence storage block 25 stores the regulation sequence used by the channel estimation block 20 in the regulation mode.

The switch 26 selects one of the output signal of the regulation mode, the directed decision mode and the hidden mode.

The error signal calculation block 27 calculates the error signal e2 [k] by comparing the output signal and [k] of the main filtering block 22 for the output signal c / [k] of the lattice decoding block 23 or the output signal of the statistical data calculation block 24.

The derivation coefficient update unit FFF 29 updates the derivation coefficient bj [k] to provide the FFF 221 based on the output signal of the input signal storage block of the equalizer 28 and the error signal e2 [k ] calculated by the error signal calculation block.

The derivation coefficient update block FBF 30 updates the derivation coefficient a.sub.j [k] provided for the FBF 222 based on the output signal ff [k] of the lattice decoding block 23 and the error signal of the latch signal. error e2 [k] calculated by the calculation block 27.

The operation of the lattice decoding block 23 which detects a symbol based on the viterbi decoding algorithm with decreased complexity, whose TBD is 1, will be described together with Figures 3 and 4 as follows.

Figure 3 is a block diagram illustrating a lattice encoder, which is a trellis-coded modulation encoder (TCM) 300 used in a residual sideband transmission system 8 (8-VSB) of the Advanced Television System Committee ( ATSC) and a lattice diagram 320 thereof.

In a lattice diagram 320 of Figure 3, a solid line 321 denotes a state transition of a memory 311 when an input signal x of a convolution encoder is 0 and a dotted line 322 denotes the state transition of the memory 311 when the input signal ^ of the convolution encoder 310 is 1.

The 3-bit output signal (zo, zj, z2) is obtained after 2 bits is entered into the coding ratio of the lattice encoder 2/3, which is composed of two delay units and 1 binary calculator in a band of base and 8 classes of information expressed by the 3 bits mapped to the symbols of. { -7, -5, -3, -1, 1, 3, 5, 7.}. .

An output signal of a symbol mapper is passed through a VSB modulator and a frequency spectrum to be transmitted.

In accordance with the 2/3 coding ratio of the lattice encoder 300, ie the TCM encoder of the transmission system, the transmission symbol is increased from 2 bits to 3 bits so that the output symbol is presented in 8 constellations . Therefore, the distance between the constellations of the near symbol becomes 2 so that a noise margin is decreased. However, the symbol error correction is made by the lattice decoder, that is, the TCM encoder of the transmitter so that the distance between the constellations of exit it is transformed from a distance of an amateur to a distance euclidíana and later, an effective distance increases. Therefore, the operation is better than a case in which the TCM encoder does not apply in a Visibility Start (TOV) view.

It is assumed that an initial state of the TCM 311 encoder, ie, delay unit, of Figure 3 is "0 (m? = 0, m0 = 0)" and an output signal, ie, transmission signal is 1.0 , 1.0, 1.0, -3.0 and -5.0. Also, it is assumed that the output signal of the main filtering block of the equalizer 22, which is the input signal of the symbol detector, ie the lattice decoding block 23 is 1.7, -0.4, 2.5, -1.8 and -5.2 . Then, an output signal from the sample slider used as the symbol detector 12 in the conventional decision feedback equalizer in the digital transmission receiver becomes 1.0, -1.0, 3.0, -1.0 and -5.0 so that a error occurs in three symbols -1.0, 3.0 and -1.0.

However, if the symbol is detected based on the lattice decoding algorithm, that is, the viterbi decoding algorithm with decreased complexity, whose TBD is 1, an error of the lattice decoding block 23, that is, the symbol detector. it can be diminished remarkably.

Figure 4 is a diagram illustrating a symbol detection process of a lattice decoder of the decision feedback equalizer in accordance with an embodiment of the present invention, which is the process of symbol detection based on the viterbi decoding algorithm as an example of latticed decoding.

As shown, unlike the conventional viterbi decoder, the viterbi decoder 23 with decreased complexity, whose TBD is 1, calculates the absolute distance 410 between the input signal and [k] of the symbol detector and the 4 pairs of symbols [D0 (= -7 or +1), D- ^ (= -5 or +3), D2 (= -3 or +5), D3 (= -1 or +7)] shown in lattice diagram 320 based on Equation 9 expressed as: Absolute Distance = j, f] -D (j, í = 0.1, 2.3 ÍEq. 9) Then, the absolute smallest distance 420 is selected for each of the calculated absolute distance pairs 410.

Then, the new cumulative absolute distance is calculated by adding the accumulated absolute distance and the absolute distance currently in each state [0 = (00), 1 = (01), 2 = (20), 3 (1)] shown in the Lattice diagram 320 in time k.

At time k, all accumulated absolute distance except the smallest cumulative absolute distance are eliminated for each state shown in lattice diagram 320.

The state having all the states of the smallest cumulative absolute distance shown in lattice diagram 320 at time k is selected and an output signal is obtained from a branch of the trellis diagram that transits for the selected state.

Finally, the above processes are performed repeatedly at a time index of symbol k.

In accordance with the processes, the output signal of the lattice decoding block 23 that detects a symbol based on the viterbi algorithm with decreased complexity, whose TBD is 1, becomes 1.0, 1.0, 1.0, -3.0 and -5.0 and is identical to the lattice encoder output signal, i.e., the TCM encoder in a digital broadcasting transmission system in Figure 3.

As mentioned above, the decision feedback equalizer having the lattice decoding block 23 with decreased complexity, whose TBD is 1, decreases the decision error in the symbol detector output signal such as the rate of convergence that can be achieved. increase and the residual MSE that can be decreased after convergence.

Figure 6 is a flow chart describing a decision feedback equalization method in accordance with one embodiment of the present invention.

First, a channel estimation block 20 estimates a channel based on a reception signal r [k] and a regulation sequence d [k] during a regulation sequence interval in step S601.

Then, the channel estimation block 20 changes the channel property of the reception signal r [k] by passing it through the channel equalization filtering block 21 to maximize the SNR of the channel estimated in step S602. Therefore the channel property of a reception signal in an indoor environment such as a room and mobile can be changed to soften.

In step S603, a parameter for the effective decision feedback of the reception symbol is determined and a channel equalization parameter is initiated.

The symbols are detected from an equalizer output signal of a specific time index signal based on the determined parameter used by the viterbi decoder with decreased complexity, whose TBD is 1, in step S604.

The statistical data calculation block 24 calculates the statistical data for the hidden mode in step S605.

A mode is selected by using an exchange block 26 between the regulation mode, the hidden mode and the decision mode in step S606.

The error signal calculation block 27 calculates an error signal e2 [k] by comparing an output signal of the selected mode, ie, if the regulation mode is selected, an output signal ff [k] of the lattice decoder 23, furthermore if the hidden mode is selected 24, for an output signal and [k] of the main filtering block 22 in step S607.

The error signal e2 [k] is transmitted to the update block of the feed forward filter bypass coefficient (FFF) 28 and the refresh rate return filter block (FBF) 29 and is used to update the coefficient of derivation FBF a¡ [k] and the derivation coefficient FFF b¡ [k] in step S608. In other words, the update block of the derivation coefficient FFF 28 updates the derivation coefficient FFF bj [k] based on the output signal of the input signal storage block of the equalizer 27 and the signal error e2 [k] and the update block of the derivation coefficient FBF 28 updates the derivation coefficient FFF ai [k] based on the output signal cf [k] of the lattice decoder 23 and the error signal e2 [k].

The main filtering block 22 performs channel equalization based on the updated derivation coefficients FFF / FBF updated b i [k] and a i [k] in step S609.

Steps S601 to S609 are performed repeatedly.

The method of the present invention can be claimed as a program and stored on a computer-readable medium, such as CD-ROM, RAM, ROM, floppy disks, hard drives, magneto-optical disks and the like. Since the process can be easily implemented by those skilled in the art, an additional description will not be provided in this document.

While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.

Claims (10)

1. A decision feedback equalizer in a digital terrestrial transmission receiver, comprising: a channel estimation means for estimating a channel of a signal reception based on symbols based on the reception signal and a training sequence; a channel equalization filtering means for changing a channel property of the reception signal by maximizing a signal-to-noise ratio (SNR) of the estimated channel; an input signal storage means for storing a reception symbol of which the channel property is changed by the channel equalization filtering means; a channel equalization means for performing a decision feedback equalization by repeatedly filtering the reception signal that passes through the channel equalization filtering means; a trellis decoding means for detecting a symbol, which are decision data, based on the lattice decoding algorithm with decreased complexity, whose tracing return depth is 1, of the channel equalized reception symbols and emitting the symbol in a directed mode of decision; a means of calculating statistical data to calculate the statistical error data used in a hidden mode and issuing the statistical error data; a regulation sequence storage means for storing the regulation sequence; an exchange medium for selecting a mode between the regulation mode, the directed decision mode and the hidden mode; means for calculating an error signal for calculating an error signal by comparing an output signal in the mode selected by the exchange means to an output signal of the channel equalization means and a means of updating the derivation coefficient for update a derivation coefficient to be provided to the channel equalization equalization means based on the error signal, the output signal of the lattice decoding means and the output signal of the input signal storage means.

2. The decision feedback equalizer according to claim 1, wherein the update means of the derivation coefficient includes: a means of updating the forward feed filter bypass coefficient (FFF) to update a derivation coefficient to be provided to an FFF of the channel equalization means based on the output signal of the input signal storage means and the error signal and a refresh rate update means (FBF) of the power return filter to be provided for the FBF of the channel equalization means based on the error signal and the output signal of the lattice decoding means.

3. The decision feedback equalizer according to claim 1, wherein the channel estimation means estimates the channel of the symbol-based reception signal based on the regulation sequence and the reception signal for each field L or for the first field, where field 1 includes 313 segments and L is greater than 1, generates the channel equalization filtering means to maximize the SNR of the estimated channel and passes the reception signal through the matched channel filtering medium and therefore the channel property of the reception signal becomes smoother.

4. The decision feedback equalizer according to claim 1, wherein the lattice decoding means detects a symbol based on a modified viterbi algorithm whose TBD is 1 having decreased complexity in the residual sideband transmission system 8 (8). -VSB) of the American Advanced Television Systems Committee (ATSC) using the twelve lattice encoders, which are TCM decoders, based on a lattice-code interlayer and therefore a decoding delay becomes 0.

5. The decision feedback equalizer according to claim, wherein a lattice decoder symbol detection process includes: a) calculating an absolute distance pair including two absolute distances between the pairs of symbols in an input signal or a detector of symbols and a lattice diagram; b) selecting an absolute distance that has a small value for each pair of absolute distance between the absolute distance pairs; c) calculate an accumulated absolute distance by adding a previous absolute distance for an actual calculated absolute distance for each state in the lattice diagram in a time index; d) eliminate the accumulated absolute distances except the smallest cumulative distance for each state in the lattice diagram in the time index; e) selecting a state in which the accumulated absolute distance is smallest among all the states shown in the lattice diagram in the time index and obtaining an output signal from the symbol detector, which is the lattice decoding means of a branch shown in the trellis diagram transited for the selected state and f) repeatedly performing steps a) to e) for each symbol of the time index.

6. A method of decision feedback equalization in a digital terrestrial transmission receiver, comprising the steps of: a) estimating a channel of a symbol-based reception signal in a reception signal and a regulation sequence; b) changing a channel property of the reception signal to maximize a signal to noise ratio (SNR) of the estimated channel by passing the reception signal through a channel equalization filter; c) determining a parameter used for a decision feedback of the reception symbol whose channel property is changed and initiates a channel equalization parameter; d) detecting a symbol from an output signal of an equalizer in a specific time index signal in accordance with the determined parameter based on a lattice decoder whose tracing return depth is 1 and having decreased complexity; e) calculate the statistical error data used in a hidden mode; f) select a mode between a regulation mode, a decision mode and the hidden mode; g) calculating an error signal by comparing an output signal of the mode selected in step f) for an output signal of a channel equalizer and updating a derivation coefficient based on the error signal and h) performing a feedback equalization based on the updated derivation coefficient.

7. The decision feedback equalization method according to claim 6, wherein the channel estimator estimates the signal reception based on symbols based on the regulation sequence and the reception signal for each field L or for a first field , where field 1 includes 313 segments and L is greater than 1, generates the channel equalization filter to maximize the SNR of the estimated channel and passing the reception signal through the channel equalization filter and therefore the property of the receiving signal channel becomes smoother.

8. The decision feedback equalization method according to claim 6, wherein the lattice decoder detects a symbol based on a modified viterbi algorithm with decreased complexity, whose TBD is 1, in the residual sideband transmission system 8 (8). -VSB) of the American Advanced Television Systems Committee (ATSC) using twelve lattice encoders, which are TCM decoders, based on a lattice code interleaver and therefore a decoding delay becomes 0.

9. The decision feedback equalization method according to claim 8, wherein the channel estimator estimates the channel of the reception signal in the reception signal and the regulation sequence, generates the channel equalization filter based on the estimated channel information, equalizes the reception signal passed through the channel equalization filter by using the decision feedback equalizer that has the viterbi encoder with decreased complexity, whose TBD is 1 and therefore the equalization of the channel is effectively done under a lower environment such as in a room or mobile.

10. A method of symbol detection for channel equalization in a digital terrestrial transmission receiver, the method comprises the steps of: a) calculating an absolute distance pair including two absolute distances between the pairs of symbols in an input signal of a detector of symbols and a lattice diagram; b) selecting an absolute distance that has a small value for each pair of absolute distance between the absolute distance pairs; c) calculate an accumulated absolute distance by adding a previous absolute distance for an actual calculated absolute distance for each state in the diagram at a time index; d) eliminate the accumulated absolute distances except the smallest cumulative distance for each state in the lattice diagram in the time index; e) select a state in which the cumulative absolute distance is the smallest among all the states shown in the lattice diagram in the time index and obtaining an output signal from the symbol detector, which is the lattice decoding means, from a branch shown in the lattice diagram transited to the selected state and f) Repeatedly perform steps a) to e) for each time index symbol.