设计性能逼近信道容量、编译码复杂度较低的实用好码是信道编码领域中最重要的工作之一。低密度奇偶校验码就是一种能逼近Shannon容量限的渐进好码，在码长较长时，其性能甚至超过了Turbo码。由于低密度校验码具有译码复杂度低、错误平层低等诸多优点，使其在信息可靠传输中具有良好的应用前景，已引起世界各国学术界和IT业界的高度重视，成为当今信道编码领域的研究热点之一。 本文在深入理解LDPC码编、译码原理的基础上，首先详细介绍了构造有较大围长LDPC码的PEG算法，给出了一种改进的算法，仿真了该算法的性能；并与随机构造的LDPC码和802.16e标准中的LDPC码作了比较。在此基础上，采用速率匹配思想，深入研究了其校验矩阵的扩展算法和校验位的删除算法，比较了各算法的优缺点；综合扩展和删除算法，构造有较大码率变化范围的RC-LDPC码，对其进行了理论分析和计算机仿真。 针对不同重传机制和合并方式的HARQ技术,提出了LDPC-HARQ系统；重点讨论了递增冗余型HARQ(IR-HARQ)系统，分析了各型ARQ/FEC的吞吐量；理论分析和仿真结果证明了基于RC-LDPC码的HARQ系统性能的优越性。 结合参与的项目，使用m序列作为帧头，对本地序列和接收序列进行帧同步检测，采用滑动相关运算，通过设定信噪比，推导门限值，对不同长度m序列统计假同步和漏同步概率，并进行了计算机仿真。

Designing codes with approaching Shannon’s capacity performance and low coding and decoding complexity is a challenging and meaningful issue in channel coding field. Low-Density Parity-Check codes are a class of capacity approaching error-correcting codes. For long code lengths, LDPC codes can even outperform Turbo codes. Due to the advantages of LDPC codes, such as lower complexity of decoding and lower error floor, their applications in reliable communications have received great interests and have become one of most attractive field in channel coding community. In this dissertation, based on the analysis of LDPC codes coding and decoding algorithm, PEG algorithm to construct a large girth for LDPC codes is interpreted in detail. An improved PEG algorithm is proposed in this thesis. An analysis and comparison results show that the improved algorithm has a good performance. Based on the LDPC codes, Extending and puncturing methods with rate-compatible are investigated. Additionally, Combining Extending with puncturing algorithm, we construct RC-LDPC codes that have a wide range of code rates. For HARQ with different retransmission and combining, we proposed LDPC-HARQ system. The incremental redundancy HARQ (IR-HARQ) system is discussed significantly and the throughput is analyzed. The theoretical analysis and simulation results show the advantage of HARQ system with RC-LDPC codes. According to the accomplished project, m sequence is used before frame, local m sequence correlates with receiving information sequence and data must be detected synchronously. Given the SNR and the threshold, we calculate the probability of false synchronization and missed synchronization. The simulation is also given.