【作者】 陈智雄；

【导师】 苑津莎；

【作者基本信息】 华北电力大学（北京） ， 电力系统及其自动化， 2010， 博士

【摘要】 为了降低通信系统的差错率,提高系统的可靠性,先进的信道编码技术是宽带无线通信和电力线通信系统中不可缺少的部分。LDPC码是目前世界上距离香农限最近的码字,在宽带无线通信和电力线通信系统中具有广阔的应用前景。本文对结构化LDPC码的帧同步、译码和构造等问题作了深入研究,主要内容及成果如下：提出两种LDPC码译码辅助的盲帧同步算法,分别为基于最大值法和基于门限法的帧同步算法。推导了它们的帧同步错误概率。两种算法均无需一次完整的迭代译码过程,可借助LDPC码译码器硬件资源实现,节约了帧同步搜索的时间和功耗,还可提高译码器的利用率。仿真结果表明,基于最大值法的帧同步算法性能明显优于硬判决的同步算法,且接近已有的码字软信息辅助的帧同步算法。针对基于门限法的同步算法,提出一种准最佳帧同步门限的确定方法,并进行了算法仿真和验证。它的帧同步性能比基于最大值法的要差,但在帧同步搜索速率上有明显的优势。译码方面,针对采用扰码来解决帧同步“斜坡现象”的系统,提出联合扰码校验图案的BP译码算法；提出了改进的双分层BP译码算法,并行计算两个校验行分组的信息,来提高分层译码算法的译码速率；解决了BP译码算法在放大和译码前传协作中继中应用的初始化问题。仿真验证了改进BP译码算法的有效性和可靠性。针对结构化LDPC码译码器,归纳并证明了Banyan交换结构在信息置换时的选路交换规律,设计了一种基于可预置选路算法的新型循环移位置换单元及其出线转换单元。相比Benes和Reverse Banyan等交换结构,设计的新型循环移位置换单元提高了信息循环移位交换的速率,且占用较少的硬件资源和面积。提出一种基于快速高斯消元算法的结构化LDPC码的构造方法。快速高斯消元算法在基本分组运算的基础上,以单位置换阵为基本单元进行整体消元,降低消元算法的复杂度。分析了小四环和小六环的构成条件,提出小环的快速检测方法。仿真结果表明,当码率为1／2和2／3时,新构造的第一类S1-LDPC码都具有相对较好的译码性能,尤其帧错误概率(FER)译码性能都是最佳的。提出一种基于多重置换阵的结构化LDPC码的构造方法。研究并证明了多重置换阵的一些重要性质；该结构化LDPC码的生成矩阵具有结构化和稀疏的特点,适用基于网络编码的协作中继策略。通过仿真对比,当码率为1／2时,第二类S2-LDPC码的译码性能要差一些；当码率为2／3时S2-LDPC码具有仅次第一类S2-LDPC码的次优译码性能。更多还原

【Abstract】 Advanced channel coding technology is a necessary part of broad wireless communication and power line communication with an aim to reduce error ratio and to increase the reliability of the systems. LDPC codes have most excellent performance close to the Shannon limit in the world. They can be widely used in broad wireless communication and power line communication system. Frame synchronization, decoding and construction technology for structure LDPC codes are explored and investigated in this paper. Main content and results are shown as follows.Two LDPC code-aided frame synchronization algorithms based on maximum method and threshold method are proposed. The frame synchronization error ratios for both algorithms are derived. Using part of LDPC decoder hardware resource, the algorithms don’t need additional hardware resource and a full iterative decoding process. Compared to other code-aided frame synchronization algorithms, favorable synchronization performance and decoding performance using the algorithm based on maximum method that approaches the performance of ideal frame synchronization are presented by simulations. A frame synchronization threshold for the synchronization algorithm based on threshold method is proposed and its performance is checked by simulations. Although the frame synchronization performance of the algorithm based on threshold is not as good as the algorithm based on maximum method, it has obvious advantage in synchronization search speed.A BP decoding algorithm joint with check pattern under PN disturbance is proposed for the system adapting PN codes to solve the frame synchronization ramp. An improved double layered BP decoding which computes two check row grouping simultaneously to reduce the number of sub-iterative computation and thus to increase decoding speed is proposed. The initialization of BP decoding for amplify-and-forward and decode-and-forward cooperative relaying is solved. Simulation results show efficiency and validity of all the improved BP decoding algorithms.When the information is exchanged, a connecting law of basic switch units in Reverse Banyan network for structre LDPC decoder is discovered and proved. Then a non-blocking permutation structure based on presetting routing algorithm is designed, which are suitable for structure LDPC codes decoders. Compared to Benes exchange structure and Reverse Banyan exchange structure, the novel structure increases the exchange speed for information cyclic shift and occupies less hardware resource and area. Finally, an output converting unit is designed, which is adaptable for all kinds of switch structures.Based on fast gauss elimination algorithm, a constructing method for structure LDPC codes with multiform structure and rational column weight distributing is proposed. The fast gauss elimination based on basic grouping operation eliminates the whole permutation matrix considered as a unit, which reduces the complexity of the algorithm. The condition forming length-four loop and length-six loop are analyzed and check methods for loops with small length are proposed. Compared to other structure LDPC codes, simulation results show better decoding performance of S1-LDPC codes with 1/2 and 2/3 code rate by the first constructing method, especially in the performance of frame error ratio.Based on multi-permutation matrix, another constructing method for LDPC codes with sparse generation matrix is proposed. The conception of multi-permutation matrix is given firstly, than important characteristics of the matrix are explored and proved. It is analyzed that the generation matrix of the structure LDPC codes take on structure and sparse characteristics applicable of joint encoding and decoding for cooperative relaying based network coding. By simulation comparison, the second kind of LDPC codes named as S2-LDPC codes show dissatisfied decoding performance when the code rate is 1/2. When code rate is 2/3, S2-LDPC codes show favourable performance only inferior to S1-LDPC codes.更多还原