Abstract:
A digital television system performing modulation/demodulation by VSB (vestigial side band) is provided. The invention includes a VSB transmitter including an additional error correction encoder designed such that a signal mapping of a TCM encoder is considered, a multiplexer (MUX), a TCM encoder operating in correspondence with state transition processes of the additional error correction encoder, and a signal transmission part including an RF converter. The invention further includes a VSB receiver including a signal receiver part receiving a signal transmitted from the transmitter, a TCM decoder, a signal processing part including a derandomizer, and an additional error correction decoder part.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 13/831,178, filed Jul. 6, 2010, currently pending, which is a continuation of U.S. application Ser. No. 11/932,521, filed Oct. 31, 2007, now U.S. Pat. No. 8,428,150, which is a continuation of application Ser. No. 11/050,298, filed Feb. 2, 2005, now U.S. Pat. No. 7,742,530, which is a continuation of U.S. application Ser. No. 09/962,263, filed Sep. 26, 2001, abandoned, which pursuant to 35 U.S.C. §119, claims the benefit of earlier filing date and right of priority to Korean Application No. 10-2000-56473, filed Sep. 26, 2000, the contents of all of which are hereby incorporated by reference herein in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a digital television system carrying out modulation/demodulation by VSB (vestigial side band). 
       RELATED ART 
       [0003]    An 8VSB transmission system for terrestrial wave digital broadcasting is taken as a U.S. standard system in 1995 is test-broadcasted from the latter half of the year 1998. Such a test broadcasting using a terrestrial wave digital broadcasting standard based on the U.S. standard system is being carried out in Korea as well. 
         [0004]    In such a digital broadcasting system, a transmitted signal is received by a receiver through a terrestrial channel. In order to restore the signal in the receiver despite the noise caused by the channel, the signal is variously coded to be transmitted. In response to the various coding process, the receiver carries out the corresponding decoding process so as to restore the transmitted signal. 
         [0005]    Lately, a broadcasting station tries to transfer such a digital broadcasting, which transfers mainly audio and video data, to which various additional data are attached. The additional data includes stock-market information, weather casting, program guide information, HTML, execution files and the like. 
         [0006]      FIG. 3  illustrates a structural diagram of a TCM encoder according to a related art. 
         [0007]    Referring to  FIG. 3 , a TCM encoder includes a precoder  1  outputting a first output signal by precoding a first input bit d 1  and an encoder outputting a third output signal by encoding a second input bit as a second output signal c 1 , where a reference numeral ‘ 3 ’ indicates a 8VSB mapper. 
         [0008]    Meantime, the precoder  1  includes an adder  1   a  outputting the first output signal c 2  by adding the first input bit d 1  to a delayed signal and a memory  1   b  providing the adder  1   a  with the delayed signal attained by delaying an output signal of the adder  1   a.    
         [0009]    The TCM encoder according to a related art may cause a fatal damage on the additional data when using it. 
         [0010]    Different from general audio/video data in channel transmission, the additional data is vulnerable fatally to an influence of the channel noise. For example, the damaged additional data of which information itself is defected may inform a viewer with wrong information, while the damaged general audio/video data just result in light image/voice loss. 
         [0011]    Specifically, when the additional data include numbers or an execution file, a minor data error causes a devastating result of failing the entire operation. 
       SUMMARY OF THE INVENTION 
       [0012]    Accordingly, the present invention is directed to a digital television system that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
         [0013]    An object of the present invention is to provide a digital television system fitting for transmitting additional data. 
         [0014]    Another object of the present invention is to provide a digital television system robust to a noise. 
         [0015]    A further object of the present invention is to provide a digital television system compatible with a conventional digital television system. 
         [0016]    Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
         [0017]    To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a VSB transmitter includes an additional error correction encoder carrying out state transition processes on additional data inputted to correct an error and designed for a TCM coding to be considered wherein the TCM coding will be carried out later, a multiplexer multiplexing the additional data and Advanced Television Systems Committee (ATSC) data wherein the additional and ATSC data are inputted thereto, a TCM encoder operating in a manner corresponding to the state transition processes of the additional error correction encoder and encoding the ATSC and additional data outputted from the multiplexer, and a signal transmission part converting the ATSC and additional data outputted from the TCM encoder into an RF(radio frequency) signal and transmitting the RF signal to a receiver. 
         [0018]    In another aspect of the present invention, a VSB receiver includes an RF tuner tuning RF signal transmitted from a VSB transmitter, a VSB demodulator demodulating IF signal outputted from the RF tuner, a TCM decoder decoding the ATSC data and additional data, a deinterleaver deinterleaving soft output of the TCM decoder, a limiter carrying out a hard decision on the soft-outputted ATSC data, an RS decoder decoding the hard-outputted ATSC data, a derandomizer derandomizing the ATSC data having passed through the RS decoder, and an additional error correction decoder part carrying out an error correction on the soft-outputted additional data. 
         [0019]    Preferably, the TCM decoder in the VSB receiver is a decoder producing a soft output signal with a soft input signal. 
         [0020]    It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
           [0022]      FIG. 1  illustrates a TCM encoder and a signal mapper in an ATSC 8VSB system according to a related art; 
           [0023]      FIG. 2  illustrates a diagram for a set partitioning used in the TCM encoder in  FIG. 1 ; 
           [0024]      FIG. 3  illustrates a structural diagram of a TCM encoder according to a related art; 
           [0025]      FIG. 4  illustrates a performance graph of a TCM encoder in an 8VSB system on an AWGN (additive white Gaussian noise) channel; 
           [0026]      FIG. 5  illustrates a VSB communication system according to the present invention; 
           [0027]      FIG. 6  illustrates a VSB transmitter according to the present invention; 
           [0028]      FIG. 7  illustrates a TCM encoder according to the present invention; and 
           [0029]      FIG. 8  illustrates a VSB receiver according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
         [0031]      FIG. 4  illustrates a performance graph of a TCM code of an 8VSB system in AWGN (additive white Gaussian noise) channel. 
         [0032]    A bit error rate of an uncoded bit d 1 , another bit error rate of a coded bit d 0 , and a total bit error rate when regarding the uncoded and coded bits d 1  and d 0  as one stream are shown in  FIG. 4 . 
         [0033]    Referring to  FIG. 4 , the bit error rate of the uncoded bit is lower than that of the coded bit. And, the bit error rate of the entire bits corresponds to an average between the respective bit error rates of the uncoded and coded bits. It is because a sub-set is determined by the coded bit, while a signal in the determined sub-set is determined by the uncoded bit. 
         [0034]    When a set partitioning of the TCM code, a performance of the uncoded bit determining signals in the sub-set is superior to that of the coded bit since a distance between signals in one sub-set is allotted so as to be longer than that that between signals two different subsets. 
         [0035]    In use of such a characteristic, data having a higher significance are inputted using the uncoded bit d 1  having a relatively lower bit error rate than the coded bit d 0  and another data having a less significance are inputted using the coded bit c 0  having a higher bit error rate than the uncoded bit d 1 . Therefore, it is able to design a more efficient digital television system. 
         [0036]      FIG. 5  illustrates a VSB communication system according to the present invention. 
         [0037]    Referring to  FIG. 5 , the VSB communication system is divided into a VSB transmitter and a VSB receiver. 
         [0038]    The VSB transmitter is constructed with an additional error correction encoder  10  encoding additional data to correct an error thereof additionally and designed in a manner that a signal mapping of a TCM encoder is considered, a multiplexer(MUX)  20  multiplexing an output signal of the additional error correction encoder  10  and inputted ATSC data, a TCM encoder  30  operating in a manner corresponding to state transition processes of the additional error correction encoder  10 , and a signal transmission part  40  transmitting an output of the TCM encoder  30  as a radio base to a receiver side. 
         [0039]    The VSB receiver is constructed with a signal receiver part  50  receiving a signal transmitted from the signal transmission part  40 , i.e. a transmitter side, a TCM decoder  60  decoding a signal outputted from the signal receiver part  50 , a signal processing part  70  processing an output signal of the TCM decoder  60 , and an additional error correction decoder  80  restoring the additional data by decoding the output signal of the TCM decoder  60  additionally. 
         [0040]    The signal processing part  70  is constructed with a limiter limiting the output signal of the TCM decoder  60 , an RS decoder decoding an output signal of the limiter, and a derandomizer derandomizing an output signal of the RS decoder. 
         [0041]      FIG. 6  illustrates a VSB transmitter according to the present invention. 
         [0042]    Referring to  FIG. 6 , a VSB transmitter is constructed with an additional error correction encoder  110  carrying out an encoding for correcting an error additionally on additional data, a multipluxer(MUX)  120  multiplexing the additional data and the general ATSC data failing to pass through the additional error correction encoder  110 , a randomizer  130  randomizing an output signal of the multiplexer  120 , an RS(reed-solomon) encoder  140  RS-encoding an output signal of the randomizer  130  to add a parity code, an interleaver  150  interleaving an output signal of the RS encoder  140  to protect transmission data from a burst noise possibly occurring on a transmission channel, a TCM encoder  160  encoding an output signal of the interleaver  150  into a TCM code, a VSB modulator  170  VSB-modulating an output signal of the TCM encoder  160 , an RF converter  180  converting an output signal of the VSB modulator  170  into an RF signal, and a transmission antenna  190  transmitting the RF signal to a receiver side. 
         [0043]      FIG. 7  illustrates a detailed construction of the TCM encoder  160  in  FIG. 6  according to the present invention, where the TCM encoder  160  is transformed from a conventional precoder. 
         [0044]    Referring to  FIG. 7 , a TCM encoder is constructed with a precoder  161  outputting a second switch input signal s 1  by precoding a first input bit d 1  as a first switch input signal s 0 , an inverter  162  outputting a third switch input signal s 2  by inverting the second switch input signal s 1 , a comparator  163  providing a switching control signal by comparing the first and second switch input signals s 0  and s 1  each other, a switch  164  selectively outputting one of the first to third switch input signals s 0  to s 2  as a first output signal c 2 , and an encoder  165  encoding a second input bit d 0  as a second output signal c 1  so as to output a third output signal c 0  And, a reference numeral ‘ 166 ’ indicates a VSB mapper. 
         [0045]    When the first input bit d 1  is additional data, the input bit d 1  is output through the switch s 0 . At this time, the input bit d 1  is also input to the precoder  161 . When the first input bit d 1  is ATSC data, the input bit d 1  is divided into two depending on the last bit of the additional data. If the output of the switch s 0  at the last bit is equal to the output of the switch s 1 , an output value of the precoder is output, If not so, an inverse value of the precoder is output. 
         [0046]    Meanwhile, the precoder  161  includes an adder  161   a  outputting the second switch input signal s 1  by adding the first input bit d 1  and a delayed signal each other and a memory  161   b  providing the adder  161   a  with a signal attained by delaying an output signal of the adder  161   a  for a predetermined time. 
         [0047]    The above operations on the first bit d 1  is to bypass the precoder in case of additional symbol and maintain compatibility with the related art VSB receiver. The term “compatibility” means that even though the precoder is bypassed in case of additional symbol, the related art VSB receiver can decode ATSC data symbol without error. 
         [0048]    The operation of the VSB transmitter is explained in detail as follows. 
         [0049]    Different from the general ATSC data, the additional data for additional services such as an execution file, HTML and the like require the additional error correction encoder  110  for preventing a performance degradation caused by the noise. 
         [0050]    First, for error correction, the additional data having passed through the additional error correction encoder  110  and the general ATSC data failing to pass through the additional error correction encoder  110  are multiplexed by the multiplexer  120  so that one of the additional and ATSC data is outputted. 
         [0051]    Subsequently, the additional or ATSC data passed through the multiplexer  120  enter the randomizer  130 . 
         [0052]    In this case, the additional data bypasses the randomizer  130 , while the ATSC data becomes random through the randomizer  130 . 
         [0053]    A parity is then added to the additional data and the ATSC data passed through the randomizer  130  in the RS (reed-solomon) encoder  140 . And, the additional and ATSC data are interleaved in the interleaver  150  so as to protect the transmission data from the burst noise might occur in the transmission channel. 
         [0054]    Then, the additional and ATSC data outputted from the interleaver  150  are encoded again in the TCM encoder  160 . 
         [0055]    As mentioned in the above explanation, the additional and ATSC data passed through the TCM encoder  160  are free from errors even if the additional data are inputted thereto, which is different from the case using the conventional precoder failing to have the switching function in  FIG. 3 . 
         [0056]    For instance, let&#39;s assume that a bit  0  is put in the memory  1   b  of the precoder  161  in  FIG. 3  and that a bit stream inputted into the precoder is the following a1. 
         [0057]    10110 0100 001011 1011 001 (a1), where underlines beneath the stream a1 indicates an additional data interval which is additional-error-correction-encoded. 
         [0058]    When the additional data interval of the bit stream a1 fails to pass through the precoder  161  and the ATSC code interval passes through the precoder  161 , the following bit stream a2 is attained. 
         [0059]    11011 0100 01101 1011 001 (a2) 
         [0060]    If all of the bit stream a2 pass through a post decoder, an output of the post decoder is represented by the following bit stream a3. 
         [0061]    10110 1110 01011 0110 101 (a3) 
         [0062]    In the bit stream a3, a bit  1  denoted by a bold (darkened) numeral of 1 belongs to the previous ATSC data interval, which means that an error occurs. Namely, comparing the input bit stream a1 to the output bit stream a3 of the post decoder, the darkened bit of the output bit stream a3 of the post decoder is changed in the previous ATSC data interval excluding the additional data interval (the underlined bits). 
         [0063]    However, after the input bit stream a1 passes through the TCM encoder  160  corresponding to the modified precoder in  FIG. 7 , the following stream a4 shows up. 
         [0064]    11011 0100 01101 1011 110 (a4) 
         [0065]    After all of the bit stream a4 pass through the post decoder, the post decoder outputs the following bit stream a5. 
         [0066]    10110 1110 01011 0110 001 (a5) 
         [0067]    Hence, after the input stream a1 having passed through the modified predecoder passes the post decoder, the bit stream a5 outputted from the post decoder becomes equal to the input bit stream a1 in the previous ATSC data interval. Namely, no bit stream error takes place in the previous ATSC data interval. 
         [0068]      FIG. 8  illustrates a diagram of a VSB receiver according to the present invention. 
         [0069]    Referring to  FIG. 8 , the VSB receiver is constructed with an RF (radio frequency) tuner tuning the RF signal received through an antenna  200 , a VSB demodulator  220  demodulating IF signal outputted from the RF tuner  210 , a TCM decoder  230  decoding an output signal of the VSB demodulator  220  and then providing soft output, a deinterleaver  240  deinterleaving the ATSC and additional data having the soft signal form outputted from the TCM decoder  230 , a demultiplexer  250  dividing the data outputted from the deinterleaver  240  into the additional data and the ATSC data and then outputting the divided data, a limiter  260  deciding the ATSC data outputted from the demultiplexer  250 , an RS decoder  270  decoding an output signal of the limiter  260 , a derandomizer  280  derandomizing an output signal of the RS decoder  270 , an RS parity removal part  290  removing a parity from the additional data outputted from the demultiplexer  250 , and an additional error correction decoder part  300  decoding an output signal of the RS parity removal part  290  for error correction. 
         [0070]    Operation of the VSB receiver is explained as follows. 
         [0071]    First, the additional and ATSC data received from the VSB transmitter through the antenna  200  are tuned through the RF tuner  210 . 
         [0072]    The ATSC and additional data outputted from the RF tuner  220  are demodulated through the VSB demodulator  220 . the output signal of the VSB demodulator  220  is decoded by the TCM decoder  230  so as to be outputted as the soft signal form. 
         [0073]    At this moment, the TCM decoder  230  should produce a soft output in order to maximize a performance of the additional error correction encoder  110  in the transmitter shown in  FIG. 6 . 
         [0074]    SOVA (soft output viterbi algorithm) and MAP (maximum A posteriori) are algorithms for producing a soft output for a trellis coded data. In aspect of a symbolic error, the MAP algorithm is superior to SOVA. 
         [0075]    However, the optimal MAP algorithm has disadvantages such as a calculation of probability in an exponential domain and a presumption of a noise variance of a transmission channel. 
         [0076]    Besides, there is SSA (suboptimum soft output algorithm) as a sort of the MAP algorithm, in which a probability is calculated in a logarithmic domain without reducing a performance of the receiver and the presumption of the noise variance is unnecessary. 
         [0077]    Therefore, if the SSA algorithm is used as a decoding algorithm, four soft outputs, which are shown in the following calculation formula e1, are produced for the input bits d 1  and d 0  of the additional error correction encoder  110 . 
         [0000]        L (00)∝_Log  P ( d 1 d 0=00|observation)
 
         [0000]        L (01)∝_Log  P ( d 1 d 0=01|observation)
 
         [0000]        L (10)∝_Log  P ( d 1 d 0=10|observation)
 
         [0000]        L (11)∝_Log  P ( d 1 d 0=11|observation)  (e1)
 
         [0078]    The soft outputs produced by the SSA decoder are measurements of the probability values for four kinds of combinations of “d 1 ” and “d 0 ” attained after the decoding. Meanwhile, when a convolutional code as an external code is used, these soft outputs are directly used as the branch metric. 
         [0079]    Successively, the ATSC and additional data of the soft signal form outputted from the TCM decoder  230  are deinterleaved in the deinterleaver  240 . 
         [0080]    In this case, the ATSC data, which are outputted from the deinterleaver  240  are made random in the randomizer  130  of the transmitter, come to pass through the derandomizer  280 . Besides, as the derandomizer  280  needs a hard signal form, hard decision should be carried out on the ATSC data outputted from the deinterleaver  240  as the soft form. 
         [0081]    Yet, the hard decision process is unnecessary for the additional data, which are outputted from the deinterleaver  240  and fail to pass through the derandomizer  280 . 
         [0082]    Therefore, in order to carry out the hard decision process on the ATSC data outputted from the deinterleaver  240 , the ATSC data pass through the limiter  260  and the RS decoder  270  in order and then are inputted to the derandomizer  280 . 
         [0083]    However, in order to remove the parity added thereto in the transmitter without the hard decision process, the additional data outputted from the deinterleaver  240  pass through the RS parity removal part  290  and then go by way of the additional error correction decoder part  300 . 
         [0084]    As mentioned in the above description, the digital communication system according to the present invention enables to carry out a data transmission of a high reliance having a signal to noise ratio by adding an additional error correction encoder having a desirable state transition property when used with the mapping of the TCM encoder to an outside of the TCM encoder, thereby enabling to improve a performance of the digital communication system. 
         [0085]    The forgoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.