Ldpc Codes In Dvb-s2 System

DVB-S2 (Digital Video Broadcast-Satellite2) is the new generation digital satellite broadcast standard. Compared with DVB-S,It provids many new technical characteristics such as the multi-transmission class input, the adaptive coding modulation (ACM) and the general interface pattern,and also can have better performance and greater flexibility in the condition of effective isotropic radiated power of transmitter. The most noticeable innovation of DVB-S2 lies in the way of channel coding——low-density parity-check code(LDPC).Low-density parity-check code is a type of error correcting block code with sparse check matrix. As LDPC code has better ability of error correcting and closing to the Shannon limit, it is not only accepted by DVB-S2 standarded but also has good prospect of application in some fields, such as high speed wireless network,high speed mobile communication and digital satellite broadcast. However, the existing methods of encoding and decoding of LDPC code have great complexity, it is difficult to achieve in the project. How to reduce the complexity of the LDPC codes becomes hot research in the area of channel coding in recent years. In allusion to problems of LDPC code in DVB-S2 standarded, this paper makes some exploratory reseach in encoding and decoding of LDPC code. The main contents of this paper are as follows:1. As the complexity of LDPC code universal encoding algorithm is in direct proportion to the square of code length, this paper designs one kind of encoder which meets standard request according to the LDPC encoding principle in the DVB-S2 standard. This encoder uses control signal to control generating checking address module and generating checking node module for finishing information collateral process. Then the generating checking bits transmit to repeating module. The codes output through control signal.The encoder uses the special encoding method, therefore it does not need to save the generated matrix, thus reduces the complexity of encoding and can easily realize in the hardware.2. Design a kind of low complexity decoding algorithm. Firstly, Updating checking nodes and information node. In each iteration, all checking nodes receive information from the adjacent information nodes,and then process,transsimit back to adjacent information nodes. Secondly, all information nodes pass the same iterative process. In the iterative decoding process, A simple piecewise linear function substitute for the complex function of containing exponent function and logarithm function.Thirdly, information nodes collect all information and make judgments.Finally, the algorithm was verified in the complexity and the performance.3. This paper designs a module of encoding and decoding LDPC code, which follows the DVB-S2 standard. This process includes: Data source module randomly generate data whose lenth is code length multiplies code ratio; Establishes the BPSK modulation module; Designing the encoding and decoding module. The decoding module uses the low complexity decoding algorithm to complete the corresponding decoding; Using additive white gaussian noise (AWGN) channel. Finally this module is tested to check the performance whether can achieve the DVB-S2 standard the request or not.