基于FPGA自适应回波滤除系统的研究.pdf

基于 FPGA 自适应回波滤除系统的研究
摘 要

在长途通信及数字同频直放站中，由于发射天线和接收天线之间的物理
位置关系加上地面折射和反射，接收端会接收到很强的多径回波，严重影响
信号通信质量。这些回波是由输出信号经过多路衰减信道衰减后返回到输入
端得到的同频干扰信号，传统的双工器或者滤波器可以滤除工作频带外的干
扰信号，对工作频带中的同频干扰信号难以滤除。因此，需要一种专门的回
波滤除系统来滤除回波干扰，这种系统开始被人们所广泛关注。
文章首先对回波滤除系统的工作原理进行了分析，针对回波信号的特点
选取了有限长的自适应滤波器。自适应算法根据精度、收敛速度、稳定性等
指标选定了LMS算法，并对传统的LMS算法进行改良，提高了系统的精
度。在此基础上建立系统的基本模型并对其进行仿真分析，通过仿真确定了
设计中的权系数和步长的取值。然后以FPGA为核心建立了整个回波滤除系
统，阐述了信号的中频和速率在FPGA内外的处理，在FPGA外部主要依靠
AD5512和DA9779，内部主要依靠编程生成的各个模块。最后对实验设备的
组成、调试的原理及方法进行了阐述，并搭建了调试模块，进行了回波滤除
系统的联机调试。对系统参数调整后，通过输入CMMB信号进行仿真和实
际运行，结果表明，回波滤除系统可以有效的滤除回波干扰，提高系统的通
信质量。
关键词 PN序列；信道估计；回波抵消；相关性
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System of Adaptive Echo Filter based on FPGA
Abstract

In the long-distance communications and digital co-channel repeater,
because the transmitting antenna and receiving antenna, the physical location
relationship between the refraction and reflection with the ground, the receiver
will receive a strong multi-path echoes, seriously affect the signal quality of
communication. The echo is a multiple output signal attenuation through the
channel attenuation and returned to the input received signal with frequency
interference, conventional duplexers or filters can filter out the interference
signal band work, work in the same frequency band Difficult to filter out signal
interference. Thus, Need a special filter system to filter out echo echo
interference. This system began to be widespread concern by people.
This article first echo filter system works analyzed the characteristics of
echo signal for the selected finite length Adaptive Filter. Adaptive algorithm
based on the accuracy, convergence speed, stability and other indicators selected
LMS algorithm, and the traditional LMS algorithm is modified to improve the
accuracy of the system. Based on this basic model of the system and