Design Of SRW-QC-LDPC Codes In The High-speed Mobile Environment

Low Density Parity Check (LDPC) Codes is a type of linear block codes defined bythe sparse matrix, its BER performance is closest to Shannon limit. Compared withTurbo Codes, LDPC Codes have many advantages, such as low decoding complexity,low error floor and self interleaving. The BER performances of LDPC Codes are evenbetter than Turbo Codes when the code length is large enough, so they attractresearchers’ attention. The random LDPC Codes have complexity structure and largestorage, but the check matrices of Quasi-Cyclic (QC) LDPC Codes are composed ofsub-block matrix, and the sub-block matrix is a zero matrix or a cyclic shift matrix.These codes have a simple construction and small storage device, so the codes are easyto hardware implementation and have become a research hotspot in error correctioncoding.When the national high-speed railway network is becoming more and more perfect, thepeople taking trips by using the high-speed railway are becoming more frequently, andthe demand of communication is becoming more greatly. But the wirelesscommunication channel will become terrible with deep fade, long time delay anddoppler frequency shift when the speed of train increases quickly. Researching the BERperformance of LDPC Codes has great significance in improve the quality of thecommunication on the high-speed railway. Furthermore, the wireless channel modelingis very difficult in high-speed mobile environment, there are many factors need toconsider. This thesis research the BER performances of QC-LDPC codes in the COST207channel model which using in the European GSM-R system. The mainly work andthe innovation points are as follows:1. A software simulation platform of digital communication system is built whichthe channel code is the LDPC code. Some structures such as approximate lowertriangular, the dual-diagonal and corresponding encoding algorithm are realized on thisplatform. The BER performances with different QC-LDPC Codes are compared.2. A SRW-QC-LDPC codes with flexible variable length and rate is proposedbecause of the random LDPC Codes are hard to hardware implementation. A method ofeliminating the cyclic4without computer search was improved. The dual-diagonalstructure will have a high error floor, which is attributed to too many variable nodeswith low weight, so the quasi-triple-diagonal structure was introduced that can eliminatesome of them. Simulation results show that the proposed method can expand QC-LDPC codes lengths and rates with less performance loss.3. Build multiple channel models, three kinds of models of high-speed mobileenvironment are mainly researched, and the BER performance of QC-LDPC Codes withdifferent structures have testified on the platform.