软判决译码在多进制扩频系统中的应用

Application of Soft-Decision Decoding in M-ary Spread Spectrum Communication System

摘要:

扩频通信技术能有效提高系统抗干扰能力，因此得到广泛应用。随着频带资源越来越拥挤，多进制扩频因其能够很好的对带宽和传输速率折中，越来越受到关注。同步一直是多进制扩频技术中的关键技术，对采用同步头同步法以及参考信号同步法的误码性能进行对比。系统采用软判决方式做数字调制解调输出提供给译码器，从对数似然比出发，提出一种适用于多进制扩频系统的次最优的软信息提取方式，分析了分别采用硬判决和软判决对系统带来的影响。仿真结果表明，单纯提取软信息后判决的方式对系统误码性能的提升不明显，在误码率时，相比硬判决有0.2dB左右的增益；加入卷积编码后，仿真参数不变分析对整个系统的性能改善时，相比于DSSS(Direct Sequence Spread Spectrum直接扩频系统)系统的误码性能有5.2dB左右的提升，软判决译码比硬判决译码有大约1dB的增益；而考虑到编码效率，单独的分析软判决和硬判决对系统的误码性能的影响时，结果表明，在信噪比较高的信道环境下系统的误码性能得到较大改善，在误码率时软判决译码比硬判决译码有0.7dB左右的增益，软判决译码对整个系统的误码性能有2.5dB左右的增益的。

Abstract:

Spread spectrum communication technology can effectively improve the anti-interference ability of the system, so it is widely used. As frequency band resources become more and more crowded, more and more attention is paid to M-ary spread spectrum because of its ability to balance bandwidth and transmission rate. Synchronization has always been the key technology in the M-ary spread Spectrum technology. System compares the error performance of the synchronous head synchronization method and the reference signal synchronization method. The soft digital method is used as the output of digital modulation and demodulation to the decoder. Based on the log-likelihood ratio, a suboptimal soft information extraction method suitable for M-ary spread spectrum system is proposed, and the influenced of hard decision and soft decision on the system is analyzed. The simulation results show that the error performance of the system is not significantly improved by the decision. When the convolutional coding is added, the error performance of the whole system is improved by the simulation parameter invariant analysis, which is about 5.2dB compared with that of the DSSS(Direct Sequence Spread Spectrum) system. Soft decision decoding has a gain of about 2dB over hard decision decoding. Considering the coding efficiency, the influence of soft decision and hard decision on the error performance of the system is analyzed separately . The results show that the error performance of the system is greatly gain compared with high signal-to-noise ratio. When the bit error rate , the soft decision decoding has about 0.7dB gain compared with the hard decision decoding . Soft decision decoding on the whole system error performance has 2.5dB gain.