KR20020080992A - communication system of VSB digital TV - Google Patents

Abstract

PURPOSE: A VSB communication system of a digital TV is provided to produce a new VSB transmission system adapted for transmitting additional data and improve additional data symbol decoding efficiency. CONSTITUTION: A VSB transmission system includes a unit for encoding additional data and outputting it through the first path, a unit for outputting MPEG data through the second path, and a controller for controlling a multiplexer to determine the multiplexing position of the additional data according to the number of packets of the additional data. The transmission system modulates the data output from the multiplexer into VSB transmission mode to transmit the modulated data. A VSB reception system includes a decoder for decoding a signal inputted through a transmission channel, a multiplexing information detector for detecting multiplexing information to judge the position of the additional data in the signal, a separator for separating the additional data and MPEG data from the data output from the decoder, an additional data processor and an MPEG data processor for processing the separated additional data and MPEG data, respectively.

Description

Digital TV's VSB Communication System {communication system of VSB digital TV}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital communication system, and more particularly, to a digital communication system for modulating and transmitting it in a VSB method.

In the United States, ATSC 8T-VSB transmission system was adopted as a standard in 1995 for terrestrial digital broadcasting, and broadcasted since the second half of 1998.In Korea, ATSC 8T-VSB transmission system, which is identical to the US method, was adopted as a standard in May 1995. Experimental broadcasting was started, and on August 31, 2000, the test broadcasting system was switched.

1 shows a conventional ATSC 8T-VSB transmission system. The data randomizer randomizes the input MPEG video / audio data, the Reed-Soloron encoder adds 20 bytes of parity code by reed-solomon encoding the data, and the data interleaver interleaves the data, and the trellis encoder. Converts the data from bytes into symbols and then trellis-codes them. The mux muxes the symbol strings and sync signals, the pilot inserter adds the pilot signal to the symbol strings, the VSB modulator modulates the symbol strings into an 8 VSB signal of the intermediate frequency band, and the RF converter converts the intermediate frequency signal into an RF band signal. Transmit and transmit via an antenna. For example, USP5636251, USP5629958, and USP5600677, which are registered in the United States and filed by Zenith of the United States in relation to the existing VSB.

The 8T-VSB transmission system, adopted as a digital broadcasting standard in North America and Korea, is a system developed for transmission of MPEG video / audio data. However, with the rapid development of digital signal processing technology and the widespread use of the Internet, digital home appliances, computers, and the Internet are being integrated into one big framework. Therefore, in order to meet various needs of users, it is necessary to develop a system capable of transmitting various additional data in addition to video / audio data through a digital broadcasting channel.

Some users of supplementary data broadcasting are expected to use supplementary data broadcasting by using PC card or portable device equipped with simple indoor antenna. In the room, signal strength is greatly reduced by wall blocking and influence of proximity moving body. Due to the effects of ghosts and noise caused by reflected waves, broadcast reception performance may deteriorate. However, unlike general video / audio data, the additional data transmission should have a lower error rate. In the case of video / audio data, the error of not being able to detect human eyes and ears is not a problem. In the case of additional data (eg program execution file, stock information, etc.), a bit error may cause serious problems. It can cause problems. therefore There is a need to develop a system that is more resistant to ghosting and noise in the channel.

The transmission of additional data will usually be done in a time division manner over the same channel as the MPEG video / sound. Since the beginning of digital broadcasting, however, ATSC VSB digital broadcasting receivers that receive only MPEG video / audio have been widely used in the market. Therefore, additional data transmitted on the same channel as MPEG video / audio should not affect the existing ATSC VSB-only receivers that have been used in the market. Such a situation is defined as ATSC VSB compatible, and the additional data broadcasting system should be compatible with the ATSC VSB system.

In addition, in a poor channel environment, the reception performance of the conventional ATSC VSB receiving system may be degraded. In other words, the present applicant has previously filed a related patent (Application No .: P00-83533, Application Date: December 28, 2000, Application No .: P01-3304, Application Date: 2001). , 1.19).

In such a system, when the additional data and MPEG data are multiplexed in units of segments, the multiplexing order can determine the decoding performance when decoding the additional data, that is, the decoding performance can be significantly reduced depending on the multiplexing order.

Accordingly, an object of the present invention is to propose a novel VSB transmission system suitable for additional data transmission and resistant to noise. Another object of the present invention is to improve decoding performance of additional data symbols. .

Another object of the present invention is to provide a transmission system and a reception system for improving decoding performance of additional data symbols.

Another object of the present invention is a method for multiplexing additional data and MPEG data that can be applied in a VSB transmission system described in the patent application (P00-83533, 2000.12.29) filed by the applicant for excellent decoding performance in a receiver; To provide a device.

Figure 1a is an 8VSB transmission system for additional data transmission

Figure 1b is an 8VSB transmission system

2 is a block diagram of a data field when decoding performance is not good

3 is a diagram illustrating a data field in the case of 1: 3 multiplexing according to the present invention.

4 is a configuration diagram of data fields in the case of 1: 1 multiplexing according to the present invention.

5 is a block diagram of a data interleaver in case of 1: 3 multiplexing according to the present invention

6 is a data input / output diagram of the data interleaver of FIG.

7 is a block diagram of a trellis encoder in case of 1: 3 multiplexing of the present invention

Fig. 8 is a diagram showing the segment structure between field moving mechanisms existing in the data field of the present invention.

9 is an 8VSB receiving system of the present invention.

A feature of the present invention for achieving the above object is that a segment consisting of additional data packets inputted through a first path and a segment consisting of MPEG transport packets inputted through a second path are defined in a data field. Multiplexed by The number of packets of the additional data multiplexed above varies from 0 to 156. In addition, the multiplexing information may include multiplexing information for identifying the multiplexing position of the additional data when the additional data and the MPEG data are multiplexed in the data field. The multiplexing information may also include a spare area of a segment having a field synchronization signal in the data field. It consists of the number of additional data packets located in the (Reserved Area) and multiplexed to the current data field, the number of fields until the number is changed in the future, and the number of additional data packets to be changed. In addition, the multiplexed information includes information inverted by 12 bits so that the multiplexed information can be recovered even if there is NTSC signal interference at the receiver.

Hereinafter, the features and advantages of the present invention will be described with reference to FIGS. 1 to 9. First, the additional data transmission system of the present invention will be described with reference to FIGS. 1a and 1b. [0016] First, the first and second embodiments of the present invention have the same configuration as the patents P00-83533, 2000.12.29 filed by the present applicant. As shown in FIG. 1, some encoding processes are performed to transmit additional data to a receiver through a channel (public or cable) at a broadcast station through a first path. First, an error is encoded by a Reed Solomon encoder (R-S encoder) to perform error correction. An interleaving process is performed to improve burst noise performance on the encoded additional data. In this case, the interleaver may be omitted as necessary. A null sequence is inserted in the null sequence inserter to generate a predetermined sequence at an input terminal of a trellis encoder for the interleaved or Reed Solomon-coded additional data. do. The reason for inserting null sequence is to make it possible to receive well even in poor channel environment.Additional data inserted with null sequence is input to multiplexer after MPEG header is added for compatibility with existing VSB receiver. The broadcast program (eg, movie, sports, entertainment, drama, etc.) data in two paths is input to the multiplexer through MPEG encoding process. The multiplexer (eg, mux) outputs data to the VSB transmission system based on the control operation (not shown) of the additional data and MPEG data input through the first and second paths. With respect to the multiplexed data, the VSB transmission system processes the data in the same manner as the conventional method and transmits the data to the receiver through the channel.

In addition, 164 bytes of additional data packets are Reed-Solomon encoded and converted into 184 bytes of packets, which are interleaved and reordered, and a null sequence is inserted to output two 184 bytes of packets, each of which has three bytes of The MPEG transport header is added to output two 187 byte packets. The two packets thus generated are multiplexed with MPEG transport packets in segments of VSB systems and transmitted.

Multiplexing of the additional data packet and the MPEG transport packet is performed by time division by segment within the VSB data field. One segment consists of 187 bytes and the data field consists of 312 segments.

Packets multiplexed on a segment basis are processed by the VSB transmission system, and the order is changed by the data interleaver. This reordered byte of data is converted into a trellis encoder after byte-symbol conversion. Therefore, the symbols of one packet are not continuously input to the trellis encoder, but the symbols of different packets are mixed and input to the trellis encoder. Both the trellis decoder and slicer predictor used in the digital VSB receiving system It uses the Viterbi algorithm, which predicts the state transition over time of the trellis coder, that is, the path with the highest probability.

In the Viterbi algorithm, the ACS (Accumulate / Compare / Select) section calculates the metric of all possible routes for each state, selects the path with the lowest value (highest probability), and stores the metric value. do. The path metric calculated here is the sum of the path metric and the branch metric of the previous time corresponding to the path, so that the path metric calculated up to the previous symbol affects subsequent symbols.

The above is described in detail in the patent application P00-83533, 2000, 12, 29, which is filed by the present applicant. Therefore, the above patent will reveal the details of the transmission system.

In addition, in the patent application (P00-83533, 2000.12.29) filed by the applicant, a description is made of inserting a predefined sequence in the additional data symbol and transmitting it to the receiver. However, since the MPEG transmission data symbol does not include a predefined sequence, the reliability of the accumulated path metric is inferior to the additional data symbol in the MPEG transport symbol interval. Therefore, when the MPEG transport symbol and the additional data symbol are mixed, the decoding performance of the additional data symbol is degraded because the preceding MPEG transport symbol affects the subsequent additional data symbol. At this time, since the range of influence is within a few symbols, there is a difference between the decoding performance of the additional data symbol near the boundary and the decoding performance (error rate) of the additional data symbol after a certain degree. In other words, among the additional data symbols, the error rate of the additional data symbol at the boundary between the MPEG transport symbol interval and the additional data symbol interval is high. Therefore, to maximize the decoding performance of the additional data symbol, the additional data symbols are continuously transmitted as much as possible. It is desirable to. In other words, the boundary between the MPEG transport symbol interval and the additional data symbol interval should be small. This is related to multiplexing, interleaver and trellis coder.

2 shows a case where the decoding performance of symbols of additional data is not good as an example of multiplexing. The figure on the left shows multiplexing of data fields in the form of two additional data segments and six MPEG transport segments. Is showing. The figure on the right shows, in this case, the first 52 bytes and the next 52 bytes of output from the data interleaver are input to the 12 trellis encoders. In the figure on the right, each column represents the input of each trellis encoder. As can be seen from the figure, it can be seen that since the multiplexing pattern does not have a 12-byte period, additional data bytes are not driven to a specific trellis encoder.

3 to 4 show the case of 1: 3 and the case of 1: 1 multiplexing as the most preferred examples of the multiplexing. The basic principle of such multiplexing provides a multiplexing method based on the number of additional data packets (P value) as shown in the following equations.

In other words, making the period of the multiplexing pattern into four segments is a method of maximizing the decoding performance of the additional data . Since one additional data packet corresponds to two segments, it is possible to multiplex additional data packets from 0 to 156 (= 312/2) in the data field. The following describes the multiplexing method according to the number of additional data packets. will be. In Equation, P denotes the number of additional data packets multiplexed in one data field, and MAP is a set indicating a location where additional data is multiplexed in the field. The value of P is divided into four ranges and multiplexed as follows. The element s in the set indicates the segment position in the field after the field synchronization signal. Once the P value is determined, the MAP is determined, and the additional data segments are multiplexed in the order of s in the MAP.

0 <= P <= 39: MAP = {s | s = 4i + 1, i = 0,1, ..., 2P-1}, (1 <= s <= 312)

40 <= P <= 78: MAP = {s | s = 4i + 1, i = 0,1, ..., 77} U

{s | s = 4i + 3, i = 0,1, ..., 2P-79}

79 <= P <= 117: MAP = {s | s = 4i + 1, i = 0,1, ..., 77} U

{s | s = 4i + 3, i = 0,1, ..., 77} U

{s | s = 4i + 2. i = 0,1, ..., 2P-157}

118 <= P <= 156: MAP = {s | s = 4i + 1, i = 0,1, ..., 77} U

{s | s = 4i + 3, i = 0,1, ..., 77} U

{s | s = 4i + 2. i = 0,1, ..., 77} U

{s | s = 4i + 4. i = 0,1, ..., 2P-235}

3 shows a multiplexing method in 1: 3 multiplexing, where P is 0 <= P <= 39. In addition, FIG. 4 shows a multiplexing method for 1: 1 multiplexing, where P is 40 <= P <= 78.

Data multiplexed on the basis of this method are processed by the trellis encoder shown in FIG. 6 of the data interleaver shown in FIG. 5. The data are multiplexed continuously so that the decoding performance of the aforementioned additional data symbol can be maximized. It is transmitted.

Hereinafter, the case of 1: 3 multiplexing will be described in detail with reference to FIGS. 5 to 7. 5 shows a data interleaver in an 8VSB system, which is a convolutional interleaver with a branch number B = 52 and a unit memory byte M = 4. The interleaver operates in synchronization with the first byte of the data field. First, when the first byte is input, it is directly output through the first branch, the second byte is input through the second branch, and 52X4 bytes earlier are output. do.

FIG. 6 shows the input and output order of the data interleaver shown in FIG. Data input is entered from top to bottom in segment units, and bytes within a segment are entered first temporally from left to right. The numbers on the figure show the output order of the interleaver. The first byte of the data field after the field sync signal is input to branch 1 and immediately output. That corresponds to the number 1 in FIG. 6. The next input byte is branch 2 input and the output is the byte 52 x 4 = 208 bytes before the input byte. Therefore, the byte corresponding to the number 2 is output in FIG. If the next byte is entered, the byte 52 x 8 = 416 bytes before the input byte is output. Therefore, the byte corresponding to the number 3 is output. In this way, 52 bytes are output in the order shown in the trellis encoder shown in FIG. 7, and the 53 th input byte is inputted into branch 1 and immediately output. The interleaver operates at 52 segment depth. The interleaver's 52-byte power is input into the trellis encoder by 12 bytes, and after 4 cycles (12 bytes X 4 cycles = 48), 4 bytes remain. It is then input to twelve trellis encoders with the first 8 bytes of the 52-byte output being input.

7 shows a detailed diagram of the trellis encoder used in the 8VSB system. Referring to the drawings, it can be seen that 12 trellis encoders are multiplexed. When 12 bytes output from the interleaver are input, one byte is inputted. It is input to 12 trellis encoders each. At this time, each byte is converted into four symbols (2 bits) to perform trellis encoding, and the output of each trellis encoder is output by multiplexing one symbol.

8 shows a segment configuration of a field synchronization signal existing in a field in an 8VSB system, and includes multiplexing information for the receiver to detect the multiplexing information present in the field synchronization segment so that correct decoding can be performed. As described above, when the value of the number of additional data packets P (0 to 156) is determined, the multiplexing position is determined, so the transmitter only needs to transmit the P value . On the other hand, in order to allow the sender to change the amount of additional data multiplexed even during transmission, the number of data fields until the P value is changed and the P value to be changed are transmitted. In this way, the receiver can receive without error even if the P value changes.

As a method of transmitting the multiplexing information, a reserved area within the field synchronization signal is used. As shown in the drawing, it can be seen that 92 symbols are reserved among the total 832 symbols. An example of transmitting multiplexed information may be as follows. It transfers 8 bits of current P value, 8 bits of P value to be changed and 8 bits of field to change. If the number of fields until the change is 0, this means that it will not change for the time being.

However, even when the receiver performs a comb filter due to the interference of the existing NTSC, the inverted information is transmitted together by dividing the bits by 12 bits so as to recover the multiplexing information. For example, as shown in FIG. 9, a total of 24 bits are divided into two by 12 bits and each inverted 12 bits are transmitted together. Inversion here means bit-wise inverse. In order to transmit the multiplexing information more stably even in a poor channel situation, the above-mentioned multiplexing information may be included in the first additional data segment following the field synchronization signal. In this case, of course, as described above with respect to the field synchronization signal, multiplexing information is transmitted.

9 is a diagram showing the configuration of a receiver of 8VSB. The feature of FIG. 9 detects the multiplexing information included in the bitstream input as the multiplexing and reconstructing unit, and outputs a control signal which allows the demux to separate the additional data and the MPEG packet. Decode the additional data with and compare the neutralization information to make more stable multiplexing information. In addition, in the case of additional data, a control signal for bypassing Reed Solomon decoding is also output. The process of processing the data according to the control signal is described in the patent application filed by the present applicant (application number: P01-3304, Same as 2001.1.19).

As described above, the digital communication system according to the present invention has the advantage of being resistant to errors and compatible with existing VSB receivers when transmitting additional data through a channel. In addition, there is an advantage that the additional data can be received without error. Also, the decoding performance of the additional data is improved in the receiver by muxing the additional data and MPEG data according to a certain rule.

As described above, those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (4)

Means for encoding the additional data and outputting the MPEG data through the second path; multiplexing the additional data according to the number of packets of the additional data with the data input through the first and second paths; Control means for controlling the multiplexing unit to determine the position and multiplexing, VSB transmission system for modulating and transmitting the data output from the multiplexing unit in the VSB transmission method. According to claim 1, The additional data multiplexing position is determined based on the number of additional data packets (P). 0 <= P <= 39: MAP = {s | s = 4i + 1, i = 0,1, ..., 2P-1}, (1 <= s <= 312) 40 <= P <= 78: MAP = {s | s = 4i + 1, i = 0,1, ..., 77} U {s | s = 4i + 3, i = 0,1, ..., 2P-79} 79 <= P <= 117: MAP = {s | s = 4i + 1, i = 0,1, ..., 77} U {s | s = 4i + 3, i = 0,1, ..., 77} U {s | s = 4i + 2. i = 0,1, ..., 2P-157} 118 <= P <= 156: MAP = {s | s = 4i + 1, i = 0,1, ..., 77} U {s | s = 4i + 3, i = 0,1, ..., 77} U {s | s = 4i + 2. i = 0,1, ..., 77} U {s | s = 4i + 4. i = 0,1, ..., 2P-235}. A decoder for performing a decoding process on a signal input through a transmission channel, a multiplexing information detector for detecting multiplexing information so as to determine a location of additional data with respect to a signal input through the channel, and according to the detection result VSB receiving system, characterized in that the separation unit for separating the additional data and MPEG data in the data output from the decoder so that it can be properly separated, the additional data processing unit for processing data for each of the separated data and MPEG data processing unit . 4. The VSB receiving system according to claim 3, wherein the multiplexing information detecting unit detects additional data packet information in the field synchronization signal section existing in the field.