预编码Turbo码的最大似然译码性能分析.pdfVIP

摘要 预编码Turbo 码是传统Turbo 码的一种改进方案。它是以预编码为外码，Turbo 码为内码的串行级联码。其预编码器的实现是在传统 Turbo 码之前添加一个累加 器，该累加器对Turbo 码的输入信息序列进行预处理，从而改变Turbo 码的码字重 量分布，减少最小汉明距离所对应的码字个数，提高译码性能。 本文主要对预编码Turbo 码的编码原理、迭代译码算法以及最大似然译码性能 分析进行了讨论。首先介绍了累加器的和积译码算法和Turbo 码的MAP 译码算法， 然后参考 SCCC 迭代译码过程中外信息的传递方式，总结出了预编码 Turbo 码的 迭代译码步骤，在高斯加性白噪声信道上和独立瑞利衰落信道上进行了译码仿真。 最后，为了研究预编码Turbo 码在高信噪比区域的性能，即错误平层性能，本文推 导了预编码Turbo 码集和Turbo 码集的平均距离谱。借助联合限给出了这两类码集 在高信噪比区域的误比特率的数值上界。研究结果表明，优化设计的预编码Turbo 码比Turbo 码具有更好的瀑布区域性能。 关键字：Turbo 码 预编码Turbo 码 平均距离谱 联合界 Abstract Precoded Turbo codes, improved sheme of traditional Turbo codes, are a class of serially concatenated codes with Precoded codes as outer codes and Turbo codes as inner codes. The realization of Precoder is to add a accumulator to the traditional Turbo encoder, which preprocessing the input information bits to the Turbo enceoder so that it could change the codewords weight distribution of Turbo codes, lower down the number of codewords having minimum hamming distance and improve the decoding performance. This thesis mainly discusses the encoding principle, interative decoding algorithm and analysis of maximum likelihood decoding performance of Precoded Turbo codes. Firstly, the MAP decoding algorithm of Turbo codes and Sum-Product decoding algorithm of accumulator are introduced. Secondly, refering to the transmission of extrinsic information of serially concatenated convolutional codes, the decoding procedure of Precoded Turbo codes are concluded, and decoding simulations are given over AWGN channel and independent Rayleigh fading channel. Finaly, in order to study the performance of Precoded Turbo codes in the high SNR (signal to noise ratio) areas, the average distance spectra of codewo