基于滤波器设计的快速短波扩频系统研究

Research on performance optimization in short-wave wideband system basedon filter design

在短波宽带系统中,为了更好地改善系统性能,消除码间干扰,针对传统OFDM扩频算法低信噪比情况下误码率较高、在不满足采样定理情况下失真较严重、容易受到码间干扰和多径噪声影响等弊端,将Nyquist滤波器和LDPC码等纠错码算法引入到OFDM扩频系统中,并且对MC-CDMA系统进行改进,提出了优化MC-CDMA扩频方案的无失真系统,其核心思想是对MC-CDMA系统的子载波和扩频码采取不同的处理顺序,并且在系统发送端和接收端分别设计Nyquist滤波器,消除码间干扰,将信号在ITS信道中进行分集合并处理。深入研究了主要参数对系统性能的影响。理论分析和仿真结果表明:基于滤波器设计的分集接收扩频系统,能够有效改善系统在信噪比较低时的误码率性能,提高系统可靠性,有效地抑制了OFDM码间干扰。

In the short-wave broadband system,in order to improve the system performance and eliminate inter-symbol interference,this paper focuses on the drawback that the error rate is high when the SNR is low,and the distortion is very serious while not satisfying the sampling theory and is susceptible to the intersymbol interference and multipath noise and so on in the traditional OFDM system.The Nyquist filter and LDPC code algorithms are introduced to the OFDM spread spectrum and the MC-CDMA system.An optimal MC-CDMA spread spectrum scheme without distortion is proposed,whose core idea is to take a different treatment for the sub-carrier and the spreading code,and separately design the Nyquist filter for the transmitter and the receiver to eliminate intersymbol interferences,then treat the signal in the ITS channel with the technologies of diversity and combine.This paper deeply studies the major parameters of the system.Theoretical analysis and sim-ulation results show that：the diversified spread spectrum system based on the filter design can effectively improve the BER performance in low SNR,and the system reliability,and effectively suppresses the OFDM inter-symbol interferences.