低信噪比下BICM系统同步机制

发布时间：2018-04-22 21:03

本文选题：编码调制系统 + 低信噪比　；参考：《西安电子科技大学》2014年硕士论文

【摘要】：对于BICM系统来说,它可以在距离Shannon限很近的信噪比(SNR)区域工作。但是这个结论的前提是BICM系统中能达到完全同步,即符号定时和载波同步能完美进行。但是在实际运用中,只有在信噪比较高的区域才能实现。在低信噪比区,解调器传给译码器的信息中包含一定数量的误差,这就使得BICM系统的译码性能差。因此,当BICM系统中采取解调和译码分离的方案时,整个系统只能在距离Shannon容量限较远的区域工作。作者结合中国电子科技集团公司第54研究所的合作项目,在理解BICM(比特交织编码)系统的基础上,深入研究了载波同步和符号定时同步的原理,通过解调器利用译码器的反馈信息改善定时和载波相位恢复的性能,构造定时误差和相位偏移的联合解调译码方案,使迭代译码能很好地工作在距离Shannon限很近在低信噪比区域。本文作者主要完成的工作有以下几个方面：1.构造包含同步过程的BICM系统框架,在这基础上得到了容量限的表达式,并得出仿真结果。通过与CM系统容量的对比,指出了在调制星座确定的情况下,格雷映射可以使BICM系统的容量最大化。2.介绍了载波相位同步方法：独特字辅助下载波相位同步,利用软信息的最大似然相位估计,利用软信息计算相位搜索步长的相位迭代以及基于PLL(锁相环)的载波相位同步。通过仿真结果的比较,得出联合译码反馈的最大似然相位估计方法的性能最佳。3.对符号定时同步框架以及各个结构的功能和实现进行说明,然后对于迭代定时误差检测介绍了MM定时误差检测器,加窗迭代搜索算法；对于非迭代的定时误差检测,介绍了Gardner定时检测器,并分别给出仿真性能图。在这基础上,提出通过解调器利用译码器的反馈信息改善定时和载波相位恢复的性能的联合方案,仿真效果说明,低信噪比下,BICM系统中Turbo同步的效果性能很好。
[Abstract]:For the BICM system, it can work in the SNR region which is very close to the Shannon limit. But the premise of this conclusion is that the BICM system can achieve complete synchronization, that is, symbol timing and carrier synchronization can be carried out perfectly. But in practice, it can only be realized in the region with high signal-to-noise ratio (SNR). In the low signal-to-noise ratio region, the demodulator's information to the decoder contains a certain number of errors, which makes the decoding performance of the BICM system poor. Therefore, when the scheme of demodulation and decoding is used in BICM system, the whole system can only work in a region far from the Shannon capacity limit. On the basis of understanding the BICM (bit Interleaved coding) system, the author has studied the principle of carrier synchronization and symbol timing synchronization in combination with the cooperative project of the 54th Research Institute of China Electronic Science and Technology Corporation, and based on the understanding of BICM (bit Interleaved coding) system, By using the feedback information of the decoder to improve the performance of timing and carrier phase recovery, a joint demodulation and decoding scheme with timing error and phase offset is constructed, so that the iterative decoding can work well in the region of low signal-to-noise ratio (SNR) close to the Shannon limit. The main work accomplished by the writer is as follows: 1. The BICM system framework including synchronization process is constructed, and the expression of capacity limit is obtained on this basis, and the simulation results are obtained. By comparing with CM system capacity, it is pointed out that when the modulation constellation is determined, Gray map can maximize the capacity of BICM system. This paper introduces the carrier phase synchronization methods: unique word aided download wave phase synchronization, maximum likelihood phase estimation of soft information, phase iteration of phase search step size calculated by soft information and carrier phase synchronization based on PLL (PLL). By comparing the simulation results, it is concluded that the maximum likelihood phase estimation method with joint decoding feedback has the best performance. The symbol timing synchronization framework and the function and implementation of each structure are described. Then the MM timing error detector and windowed iterative search algorithm are introduced for iterative timing error detection, and for non-iterative timing error detection, non-iterative timing error detection is introduced. The Gardner timing detector is introduced, and the simulation performance diagram is given. On this basis, a joint scheme is proposed to improve the performance of timing and carrier phase recovery by using the feedback information of the decoder. The simulation results show that the performance of Turbo synchronization in low SNR system is very good.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN911.3

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