Research On Construction Of LDPC Codes And Encoding And Decoding Algorithm In CMMB

Among the many types of linear block codes,low density parity check （LDPC）codes with its unique low-density characteristics, the performance is far beyond thescope of the same error correction code to other code, is far from the nearest accesscharacteristics Shannon limit of good code.LDPC codes makes it excellentcharacteristics have been widely applied to various fields, such as fiber opticcommunications,deep space communications,digital audio broadcasting, nowoccupies a pivotal position in the channel coding, to guide the future direction of thechannel coding.In practical applications, LDPC codes system, select a suitableencoding and decoding scheme is very important,this paper based on China MobileMultimedia Broadcasting （CMMB） transmission system,the right choice fordecoding scheme.Specific work papers are as follows:1、Do a research of the structure of an LDPC code parity check matrix H, and acombination of both from the random structure section describes the structure ofseveral classical methods, a clear structure of the parity check matrix H in theimportant issues need to be considered, i.e., should be avoid leaving a short girthdensity characteristic code is damaged, or to code influence the convergence of thedecoder decoding the like. CMMB standard column header row under the standardrate1/2and3/4code rate LDPC code parity check matrix encoding analyzed bysimulation;1/2good3/4both rate, based CMMB standard LDPC codes constructedusing the index table check matrix method directly or indirectly through the ranks ofthe converted using Constructor check matrix, their different situations subject linemarked out column, and the experimental results of the simulation are compared infigure. 2、Create bodies with information symbols based on the encoding method usingthe triangle, calculating the encoding efficiency; While using the minimum and（MS） decoding method, decoding the waveform before and after each simulation,and decoding performance test results were analyzed random bit errors.3、Made a careful research on encoding algorithm of LDPC codes，especiallycyclic code encoding algorithm and further extended to the coding algorithm CMMBtransmission systems with highly structured quasi-cyclic LDPC codes, Choose theappropriate encoding scheme for the CMMB system, which uses algorithms to encodeapproximate lower triangular matrix. The algorithm is to be applied in the actualCMMB system, validated simulation results show the feasibility of the program.4、This paper focuses on the decoding algorithm for LDPC codes, especially thebelief propagation （BP） decoding algorithm class. Updating check node messagesfor the transverse BP algorithm iteration, and the improved in-depth study on the partof several decoding algorithms, such as the logarithmic domain （LLR-BP）algorithm, and the minimum （MS） algorithm. An algorithm for the MS MBPimproved algorithms are introduced and studied to highlight and conclusion of thealgorithm to Finally, the MBP algorithm is transplanted to CMMB system, choose agood compromise can be achieved between the decoding algorithm decodingaccuracy and complexity of CMMB system, And the system of rate1/2and3/4coderate LDPC codes are experimentally verified by BER Simulation results underdifferent decoding algorithms is more intuitive and powerful demonstration of theprogram can be useful sex.Finally, the work done on the thesis summary and outlook pointed out that theresearch process deficiencies and limitations for future research highlighted thatdirection.