数字可视电话系统中的G.168回声消除技术

由于数字可视电话系统的性能需求和系统中回声的特点，传统的回声消除技术应用于数字可视电话系统时无法满足ITU-T G.168标准要求。该文利用NLMS算法的滑动窗自适应滤波器和简化非线性处理器设计，实现一种数字可视电话系统中的G.168自适应回声消除器，介绍其基本结构和各个功能模块的算法，并以ARM 920T为硬件平台实现该系统。仿真结果显示，简化的回声消除算法运算复杂度小、消除回声有效性高、稳定性强。利用ITU-T G.168标准定义的CSS信号对G.168回声消除器进行测试，测试结果均符合或优于标准要求。

G.168 Echo Cancellation Technique in Digital Video Telephone System

This paper analyzes the principle and problems of the echo cancellation in digital video telephone system. According to these characteristics, a modified adaptive echo canceller based on sliding-window NLMS adaptive filtering algorithm and simplified nonlinear processor is presented. The structure of the proposed echo canceller as well as its composing modules is introduced. It shows how to accomplish the modified adaptive echo canceller on ARM 920T chip of ARM Co.. Simulation results show that the new system performs better than the original system in algorithm complexity and convergence rate. Objective tests are made using Composite Source Signals(CSS) according to ITU-T recommendation G.168. The performances meet with G.168 well.