CN1151672C - A Modulation Method of Channel Coding Using Multilayer Block Product Codes - Google Patents

Abstract

The invention belongs to the technical field of digital information transmission, and relates to a Multi-level Block Product Code (Multi-level Block Product Code) error correction coding modulation method, which includes: firstly passing multiple input data code streams with different priorities through their respective groups After the product code BPC encoder, the group product code stream is obtained, and the group product code stream is mapped to the different bits of the constellation symbol of the set modulation mode according to the definition, and multiple signals with different degrees of anti-interference ability are obtained. Layer modulation signal output. The invention has the advantages of simple implementation, multiple priorities, strong error correction capability, high reliability, etc., and can meet the requirements of various services, for example, it can be applied to a terrestrial digital television broadcasting system.

Description

A Modulation Method of Channel Coding Using Multilayer Block Product Codes

technical field

The invention belongs to the technical field of digital information transmission, and relates to a multi-level block product code (Multi-level Block Product Code) error correction coding modulation method, and more specifically relates to multi-level block product code error correction coding modulation in terrestrial digital television broadcasting systems method.

Background technique

In digital information transmission, no matter what type of channel the signal is transmitted through, due to the influence of attenuation, distortion and various interferences, there will be bit errors in the received data. Therefore, any actual digital communication system needs to adopt channel coding and modulation technology for error correction. Generally, the forward error correction (FEC) method is used, which is to add redundant symbols to the data according to certain rules at the sending end. , forming an error-correcting code with error-correcting capability. After the receiving end receives the codeword, it decodes according to the predetermined rules to determine whether there is any error in the received codeword, and if there is an error, it will be automatically corrected.

The composition of a typical digital communication system is shown in Figure 1, which includes a channel coding modulation unit composed of channel coding and digital modulation. At the sending end, the encoder processes the incoming data to minimize the amount of data transmitted. For example, a digitized video signal is sent to an MPEG source encoder for compression to reduce the amount of data. At the receiving end, the MPEG decoder restores the compressed data to the original data. If the MPEG encoder and decoder are directly connected, then only the image quality loss caused by compression. But in most applications, there are bit errors introduced during transmission in the data received by the receiving end. Of course, these bit errors need to be removed as much as possible before being sent to the decoder.

To remove these errors, channel coding is required, one of its functions is error correction, and there are many error correction methods. At the sending end, Forward Error Correction (FEC) adds redundant information to the code stream so that the receiving end can unilaterally detect and correct transmission errors. The simplest scheme is that each bit is repeatedly transmitted N times, and the receiving end judges each transmitted bit by a large number decision criterion. Although the way of repeating N times is simple to implement, the coding efficiency is very low. When a more efficient FEC is used, the increased redundancy can lead to huge system gains.

In a digital communication system, a very important indicator is the system bit error rate (Bit Error Rate, BER). The degree to which a FEC error correction code reduces the system BER depends on the type and efficiency of FEC.

FEC can be classified in many ways according to different starting points. Commonly used in digital transmission are block codes (such as Reed-Solomon RS codes, BCH codes) and convolutional codes, Turbo codes, block product codes (Block Product Code, BPC), etc., in order to obtain better error correction coding performance , they can be cascaded serially or in parallel, and error correction coding and modulation combined. A concatenation of simpler error-correcting codes can achieve higher performance than a purely more complex single code.

The block product code error correction coding method uses two systematic error correction codes to process a single data set.

Figure 2 shows a rectangular interleaved product code. The first encoder (n1, k1) performs error correction coding in the row direction to generate a check code for each row; then the information bits are reordered after the interleaver, and the entire information bits and their check bits are sent to the second Encoder(n2, k2). Usually, reordering is just a rearrangement between the rows and columns of information bits plus check bits, and a (n1n2, k1k2) code is obtained as a result, hence the name.

An interleaver changes the order of a data sequence in a predetermined manner. The rectangular interleaver is the simplest one and works on fixed-length blocks of data. The input code stream is written into an M×N rectangular storage array by row, and then read out from this storage array by column to obtain the scrambled code stream. Of course, other pre-defined schemes may be used instead of the rectangular way, which may obtain better interleaving effects, such as along the diagonal way, convolutional interleaving way, and the like. The information bit rearrangement of the product code adopts the traditional matrix interleaving, which is encoded in the row direction first, and then encoded in the column direction.

Multimedia communication is the development trend of current communication technology. Multimedia communication needs to transmit various types of media information such as sound, data, text, graphics, images, animations, etc. in the communication network at the same time, and has integrated, synchronous and interactive communication. way, while the traditional telephone network, computer network and broadcasting network often only transmit a single medium. Generally speaking, data, text, graphics, and still images are discontinuous media, and the required average bit rate is not high, but it has strong burst and short-term high rate, and the data has a great impact on transmission error. Very sensitive, and sound and video information are continuous media, which require high real-time and transmission bit rate, and are less sensitive to transmission errors. Therefore, for different information media, different application environments, different service objects and different purposes, it is necessary to impose different transmission priorities on the transmitted information, which can be realized by hierarchical digital modulation.

Digital modulation is the process of converting digital symbols into waveforms that match channel characteristics. From the perspective of the frequency characteristics of the transmission channel, some channels are low-pass, such as twisted pair cables, coaxial cables, etc.; while some channels are band-pass, such as various wireless channels, fiber optic channels, etc. Obviously, the low-pass channel is suitable for transmitting digital baseband signals, while the band-pass channel must carry out necessary modulation on the digital baseband signal before transmission. In the case of baseband modulation, these waveforms are pulses. Band-pass modulation is to modulate the data signal onto a fixed-frequency carrier (usually a sine wave). In fact, in a broad sense, modulation is the mapping and spectrum shifting from source information to channel waveforms or vectors.

Corresponding to different transmission media, the structure of the transmitting system is the same, but the modulation methods are different. Now commonly used modulation methods include phase shift keying modulation PSK, quadrature amplitude modulation QAM, vestigial sideband modulation VSB and orthogonal frequency division multiplexing OFDM. Among them, PSK and QAM technologies are very mature and widely used in the communication field. When mPSK and mQAM have the same number of signal points, the power spectrum is the same, and the bandwidth is twice the bandwidth of the baseband signal. Ideally, the highest frequency band utilization of mPSK and mQAM is log ₂ Mb/s/Hz.

For example, the highest frequency band utilization rate of QPSK is 2b/s/Hz, that is, 2 bits of the baseband digital signal are mapped to a transmission symbol of the modulated signal; the highest frequency utilization rate of 16QAM is 4b/s/Hz, and 4 bits are mapped to a transmission symbol; 64QAM The highest frequency band utilization rate is 6b/s/Hz, and the 6bit of the baseband digital signal is mapped to a transmission symbol of the modulated signal. That is to say, theoretically, the amount of information that can be transmitted by 64QAM modulation is three times that of QPSK alone, and twice that of 16QAM alone. In other words, the sum of the maximum amount of information that can be transmitted by QPSK and 16QAM modulation is equal to 64QAM modulation.

Both QPSK and 64QAM are quadrature modulations, therefore, their modulation signals can be divided into two mutually orthogonal components, that is, the in-phase component I and the quadrature component Q, and the IQ components are represented by the coordinate axis to obtain the corresponding modulation constellation picture. Generally speaking, for the same modulation method, although the modulation mapping relationship may be different, that is, the digital signal values represented by the constellation points in the constellation diagram are different, but the positions of the constellation points in the constellation diagram are the same. The constellation diagrams of QPSK and 64QAM are shown in Figure 3 and Figure 4. They are uniform constellation diagrams, that is, α=1, where α is the ratio of the shortest distance between constellation points between adjacent quadrants in the constellation diagram and the shortest distance between constellation points in a quadrant.

It can be seen from the above that for the same amount of transmitted information, it can be transmitted by 64QAM modulation alone, or by multiple QPSK, 16QAM or a combination of both. They have their own advantages and disadvantages. The former is simple to implement, but the priority of the transmission service is equal; the latter is more complicated to implement, but it can realize hierarchical transmission and thus provide hierarchical services. The same is true for other multi-level modulations (such as 256QAM).

In terrestrial digital TV broadcasting, hierarchical modulation and coding can be used to realize hierarchical services. For example, in order to overcome the problem of radio and television receiving signal interruption in low field strength coverage areas, hierarchical modulation is realized by providing two bit streams with lower code rate, high reliability and high code rate, low reliability, so as to avoid signal interruption . The European Terrestrial Digital Video Broadcasting (DVB-T) system adopts hierarchical modulation on the Orthogonal Frequency Division Multiplexing (OFDM) carrier, and the multi-resolution 64QAM constellation diagram is composed of QPSK and 16QAM, as shown in Figure 5(a)(b) As shown, two levels of service are provided in one TV channel, using high priority (HP) code stream and low priority (LP) code stream respectively. The HP stream can provide basic DTV programs and some audio programs, while the LP stream is used for additional DTV or data services or a service like HDTV quality. The LP data stream is used to cover the core service area, usually within the coverage of the LP stream, the HP stream is always valid.

The disadvantage of the above-mentioned method is that the modulation adopts 16QAM, so the implementation is complicated, and because there are only two layers of modulation, the priority is less, so it cannot meet the requirements of various services; in addition, the hierarchical 64QAM in European DVB-T The previous error correction codes used convolutional codes, and the error correction performance of convolutional codes was poor, resulting in reduced reliability.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, and propose a channel coding modulation method that adopts multi-layer block product codes. Each layer of modulation adopts QPSK, which has the advantages of simple implementation, many priorities, strong error correction capability, and reliability. It has the advantages of high reliability and can meet the requirements of various businesses.

A kind of multilayer block product code error correction coding and modulator method that the present invention proposes is characterized in that, it comprises:

The multiple input data streams with different priorities are first passed through their respective block product code BPC encoders to obtain the block product code stream, and the block product code stream is mapped to the set modulation mode according to the definition. Different bits of the constellation diagram symbols can obtain multi-layer modulated signal output with different degrees of anti-interference capability; the block product code is the punctured and truncated block product code BPC (3762, 3249).

The generation method of said puncturing and truncating block product code BPC (3762,3249) may comprise the following steps:

1) Adopt the BCH (63, 57) code, and expand it into BCH (64, 57) by adding a check digit;

2) The BCH (64, 57) performs error correction coding on the input data in the row and column directions to obtain the BPC (4096, 3249) code;

3) The first 4 columns of BPC (4096, 3249) and the first 33 bits of the first row of BPC (4096, 3249) are set to 0 to obtain the truncated block product code BPC (3811, 2992);

4) Delete 49 double parity bits from the truncated BPC (3811, 2992) to obtain the punctured and truncated block product code (3762, 2992).

The modulation method can be 64QAM or 256QAM.

The multiple data code streams with different priorities may include high priority data code streams, medium priority data code streams, and low priority data code streams.

The block product code BPC data generated by the high-priority data code stream can be mapped to the upper bits of the set modulation constellation symbols.

The block product code BPC data generated by the medium priority data code stream can be mapped to the middle bits of the set modulation constellation symbol.

The block product code BPC data generated by the low-priority data code stream can be mapped to the low bits of the set modulation constellation symbols.

Features of the present invention:

The multi-layer modulation adopted in the present invention adopts QPSK, which has the advantages of simple implementation, multiple priorities, strong error correction capability and high reliability, and can meet the requirements of various services, for example, it can be applied to terrestrial digital TV broadcasting systems.

Description of drawings

Figure 1 is a diagram of a typical digital communication system.

Figure 2(a) is a schematic diagram of the product error correction code (BPC).

Figure 2(b) is a block diagram of the product error correction code (BPC).

Fig. 3 is a QPSK modulation constellation diagram.

Fig. 4 is a 64QAM modulation constellation diagram.

Fig. 5(a) is a European DVB-T non-uniform 64QAM constellation diagram (α=2).

Figure 5(b) is a European DVB-T non-uniform 64QAM constellation diagram (α=4).

Fig. 6 is a functional block diagram of a channel coding modulation method using multi-layer block product codes according to the present invention.

Fig. 7 is a constellation diagram of high priority QPSK modulation (64QAM high bit) according to an embodiment of the present invention.

Fig. 8 is a constellation diagram of medium priority QPSK modulation (64QAM middle bits) according to an embodiment of the present invention.

FIG. 9 is a constellation diagram of low priority QPSK modulation (64QAM low bit) according to an embodiment of the present invention.

Fig. 10 is a block diagram of the transmitting end of the terrestrial digital multimedia television broadcasting system of the present invention.

Fig. 11 is a block diagram of the receiving end of the terrestrial digital multimedia television broadcasting system of the present invention.

Detailed ways

Specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

According to the characteristics of digital communication transmission and digital TV broadcasting, the present invention proposes an embodiment of a channel coding modulation method using a multi-level block product code (Multi-level Block Product Code), which can achieve priority transmission information and meet various requirements. Various priority service needs, and the purpose of better service coverage.

The process flow of the method in this embodiment is shown in Figure 6, including: the input data code streams of three paths with different priorities (high, medium, and low) first pass through respective block product code BPC (3762, 2992) encoders respectively , to obtain the block product code stream, and map the block product code stream to different bits of the constellation symbol of the 64QAM modulation mode according to the definition, and obtain multi-layer modulated signal output with different degrees of anti-interference ability.

Each part of the above method is described in detail as follows:

1) Block product code encoding

The principle of the group product code is as mentioned above, as shown in Figure 2. The block product code BPC (3762, 2992) used in the present invention is the puncturing and truncation of the two-dimensional block product code BPC (4096, 3249).

BPC (4096, 3249) is the product of two extended block error correction codes BCH (64, 57) codes, and the BCH (64, 57) code is expanded by adding a parity bit to the BCH (63, 57) code . The generator polynomial of BCH(63,57) code is defined as

x ⁶ +x+1

BCH (63, 57) code, also known as Hamming code (Hamming Code), is one of the earliest block codes discovered.

The definition of the truncated block product code of BPC (4096, 3249) is to set the first 4 columns of BPC (4096, 3249) and the first 33 bits of the first row of BPC (4096, 3249) to 0 to obtain a truncated block product code BPC (3811, 2992). The definition of the punctured and truncated block product code BPC (3762, 2992) is to remove 49 double parity bits from the shortened BPC (3811, 2992).

For the transport stream (Transport Stream, TS) in digital TV transmission, the payload data length in the TS stream is 187 bytes. Two 187bytes data blocks can be compiled into one BPC(3762, 2992) block. The transmission sequence of the block product code is to start from the first column and proceed column by column.

The block product code BPC (3762, 2992) of the present invention is a kind of systematic code (Systematic Code), and its decoder can adopt high-performance TURBO algorithm.

2) Mapping and Constellation Diagram

In an embodiment of the present invention, the system's multi-layer block product codes are divided into three layers—high, medium, and low priority. The code streams obtained by the block product codes of different layers are mapped to different bits of 64QAM constellation symbols by definition, so they have different degrees of anti-interference ability.

As mentioned above, each symbol of 64QAM modulation can carry 6 bits of digital information, so that the in-phase I component and the quadrature Q component carry 3 bits respectively, which are divided into high, middle and low bits. Similarly, as mentioned earlier, multiple modulations with lower levels can be used to achieve the same amount of transmitted information as modulations with higher levels. For example, for the amount of information transmitted by 64QAM modulation, three QPSK modulations can be used. For transmission, the three different bits of the 64QAM modulation I and Q components correspond to the three QPSK modulation I and Q components respectively, that is, high priority QPSK modulation, medium priority QPSK modulation, and low priority QPSK modulation.

For the high-priority data stream, the code stream after block product code error correction coding is mapped to the high bit of 64QAM modulation, that is, the high-priority QPSK modulation is adopted. Every 2 bits in the serial code stream form a group, and each bit in the group is mapped to the I and Q components of high-priority QPSK respectively. The mapping relationship is shown in Table 1, and the corresponding constellation diagram is shown in Figure 7. , the four coordinate points (00, 01, 10, 11) in the figure represent the four constellation points of high-priority QPSK modulation.

Table 1 QPSK mapping table symbol I Q phase 0 1 1 π/4 1 0 1 3π/4 2 0 0 5π/4 3 1 0 7π/4

For the medium-priority data stream, the code stream after block product code error correction coding is mapped to the middle bit of 64QAM modulation, that is, medium-priority QPSK modulation is adopted. Every 2 bits in the serial code stream form a group, and each bit in the group is mapped to the I and Q components of the medium priority QPSK respectively. The mapping relationship is shown in Table 1, and the corresponding constellation diagram is shown in Figure 8 , the figure shows the 4 constellation points (0000-1111) of priority QPSK modulation in 4 groups, and the relative position relationship with the high priority QPSK constellation point, wherein one constellation point of high priority QPSK is located in each group priority Level QPSK modulates the center of 4 constellation points.

For the low-priority data stream, the code stream after block product code error correction coding is mapped to the low bit of 64QAM modulation, that is, the low-priority QPSK modulation is adopted. Every 2 bits in the serial code stream form a group, and each bit in the group is mapped to the I and Q components of the low-priority QPSK. The mapping relationship is shown in Table 1, and the corresponding constellation diagram is shown in Figure 9. , the figure shows 16 groups of 4 constellation points (000000-111111) of low priority QPSK modulation, and the relative position relationship with high and medium priority QPSK constellation points, wherein one constellation point of medium priority QPSK is located in each group Low priority QPSK modulates the center of the 4 constellation points.

To sum up, for multiple data streams with different input priorities, the specific implementation steps of the layered block product code error correction coding and modulation method in this embodiment are as follows:

1) Generate the error correction code BCH (63, 57) code, which is expanded into BCH (64, 57) by adding a parity bit.

2) BCH (64, 57) performs error correction coding on the input data in the row and column directions to obtain BPC (4096, 3249) codes.

3) Obtain the truncated block product code BPC(3811, 2992) from BPC(4096, 3249).

4) Delete 49 double parity bits from the truncated BPC (3811, 2992) to obtain the punctured and truncated block product code (3762, 2992).

5) The data stream generated by the high-priority punctured and truncated block product code BPC (3762, 2992) is mapped to the upper bits of 64QAM.

6) The data code stream generated by the middle priority puncturing and truncating block product code BPC (3762, 2992) is mapped to the middle bits of 64QAM.

7) The data code stream generated by the low-priority punctured and truncated block product code BPC (3762, 2992) is mapped to the lower bits of 64QAM.

8) Finally, the hierarchical block product code 64QAM modulation as shown in FIG. 9 is completed.

After the above-mentioned modulated signal is transmitted through the actual channel, due to the existence of interference and noise, the positions of the constellation points will change, and some constellation points may be very close, which is prone to misjudgment. It can be seen from the communication principle that the greater the Euclidean distance between constellation points, the smaller the probability of misjudgment, that is, the stronger the anti-interference ability. From the QPSK constellation points corresponding to the high, middle and low bits of 64QAM shown in Figure 7, Figure 8, and Figure 9, the Euclidean distance of the high-priority QPSK modulation (corresponding to the high-bit bits of 61QAM) is the largest, and the medium-priority second In other words, low priority is the smallest. Therefore, the layered block product code error correction coding and modulator of the present invention maps the data code stream after the block product code error correction coding to different layers of 64QAM modulation to realize hierarchical modulation, and the constellation points on different layers The Euclidean distance between them is different, so that the hierarchical modulation has different degrees of anti-interference ability.

An embodiment of a terrestrial digital multimedia television broadcasting transmitting system adopting the method of the present invention is shown in FIG. 10 . The three-way MPEG TS streams input in the figure have different priorities, and they can be multimedia information such as video, audio frequency, graphics, data, and the data of these different priorities are coded through the multi-layer grouping product code error correction of the present invention And the modulator, it becomes a digital hierarchical 64QAM modulation signal, and then converts it into a suitable analog signal. The RF module receives the analog signal, and the processed result is sent to the transmitting antenna or other signal transmitters.

An embodiment of a terrestrial digital multimedia television broadcast receiving system adopting the method of the present invention is shown in FIG. 11 . In the figure, the antenna or other signal receiver receives the modulated signal, sends it to the down-conversion module for frequency conversion, and then sends it to the analog-to-digital conversion ADC to become a digital signal. This digital signal is demodulated by hierarchical 64QAM to obtain the demodulated high, middle and low bits, and then sent to the corresponding block product code decoder to restore the MPEG TS streams with different priorities.

Specific embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to those embodiments above, without departing from the spirit and scope of the claims of the application, those skilled in the art can make Various modifications or modifications, for example, the system adopts 256QAM modulation, which is correspondingly divided into four-layer block product codes.

Claims (8)

1, a kind of channel coding modulation method that adopts multi-layer block product code, it is characterized in that it comprises: The multiple input data streams with different priorities are first passed through their respective block product code BPC encoders to obtain the block product code stream, and the block product code stream is mapped to the set modulation mode according to the definition. Different bits of the constellation diagram symbols can obtain multi-layer modulated signal output with different degrees of anti-interference capability; the block product code is the punctured and truncated block product code BPC (3762, 3249). 2, according to the channel coding modulation method that adopts multi-layer block product code according to claim 1, it is characterized in that further comprising: the generation method of said puncturing and truncating block product code BPC (3762,3249) comprises the following steps: 1) Adopt the BCH (63, 57) code, and expand it into BCH (64, 57) by adding a check digit; 2) The BCH (64, 57) performs error correction coding on the input data in the row and column directions to obtain the BPC (4096, 3249) code; 3) The first 4 columns of BPC (4096, 3249) and the first 33 bits of the first row of BPC (4096, 3249) are set to 0 to obtain the truncated block product code BPC (3811, 2992); 4) Delete 49 double parity bits from the truncated BPC (3811, 2992) to obtain the punctured and truncated block product code (3762, 2992). 3. The channel coding modulation method using multi-layer block product codes according to claim 1, characterized in that: said modulation method is 64QAM. 4. The channel coding modulation method using multi-layer block product codes according to claim 1, characterized in that: said modulation method is 256QAM modulation. 5. The channel coding and modulation method using multi-layer block product codes according to claim 1, characterized in that: said multiple data code streams with different priorities include high priority data code streams, medium priority data code streams Stream, low priority data code stream. 6. The channel coding modulation method using multi-layer block product codes according to claim 5, characterized in that: the block product code BPC data generated by the high-priority data stream is mapped to the set modulation constellation diagram The high-order bit of the sign. 7. The channel coding modulation method using multi-layer block product codes according to claim 5, characterized in that: the block product code BPC data generated by the medium priority data stream is mapped to the set modulation constellation diagram The middle bit of the sign. 8. The channel coding modulation method using multi-layer block product codes according to claim 5, characterized in that: the block product code BPC data generated by the low-priority data stream is mapped to the set modulation constellation diagram The lower bits of the sign.

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