适用于卫星导航系统的结构化LDPC码

Applications and Construction of the Structured LDPC Codes in Satellite Navigation System

结构化低密度奇偶校验码可通过基矩阵和扩展因子描述,具有较低的编译码复杂度和优异的译码性能。相比卫星导航系统IS-GPS-800协议中的非规则LDPC码,在校验位采用双对角和"a-0-a"连接关系的结构化LDPC码,同样可以达到线性复杂度编码。除此以外,通过设置不同的扩展因子和修剪操作,结构化LDPC码可以灵活支持不同多种长度的自适应传输,其中修剪操作的打孔/截短图案可以通过外信息转移(Extrinsic Informa-tion Transfer Charts,EXIT)分析方法优化。结合圈长分布和外信息度数谱联合优化设计方法,提出单个基矩阵的编码方案,通过配置不同的扩展因子和修剪方案,实现多种传输码长配置。译码仿真结果显示经过优化打孔/截短图案修剪的结构化LDPC码的译码性能要略优于IS-GPS-800协议中的非规则LDPC码。

The structured low density parity check （LDPC） codes can be described by the basematrices and lifting factors, which have low encoding/decoding complexity and good coding performance. Compared to the irregular LDPC codes specified in IS-GPS-800, the structured LDPC codes also can be encoded with linear complexity, where the parity bits are connected with dualdiagonal and ＂a-O-a＂ pattern. Moreover, it is very convenience for the structured LDPC codes to support the adaptive transmissions with various lengths using different lifting factors and pruning techniques, where the puncturing and shortening patterns can be easily optimized by PEXIT. Based on the construction method considering cycle conditions and ACE spectrums, a simple coding scheme using only one base-matrix was proposed which can support two different lifting factors and achieve various transmission lengths by puncturing and shortening. The simulation result show that the structured LDPC codes with optimized puncturing/shortening pattern achieve considerable performance gain over the irregular LDPC codes in IS GPS-800.