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数字用户环(DSL)收发器中采用自适应回波抵消技术达到的回波减小程度,业已证明对定时抖动非常敏感。本文报导采用预先滤波器、非线性、二阶锁相环的144kb/s DSL定时恢复系统,用计算机仿真的试验研究结果,对各种用户线路长度,桥接支线条件,环路与滤波器参数的非线性的选择进行计算机仿真。结果发明,设计得当的、预滤波器带宽为20kH z的定时恢复系统,即使对有桥接支线的长环路也能取得满意的回波减小性能。对于较短的环路,尽管可以实现的回波减小量比较小,但仍足可以达到满意的性能。
The echo reduction achieved with Adaptive Echo Cancellation in Digital Subscriber Loop (DSL) transceivers has proven to be very sensitive to timing jitter. This paper reports a 144kb / s DSL timing recovery system with prefilter, non-linear, second-order phase-locked loop. The computer simulation results show that the length of the subscriber line, the conditions of the bridge branch, loop and filter parameters Nonlinear selection for computer simulation. As a result, the well-designed timing recovery system with a prefilter bandwidth of 20 kHz provides satisfactory echo reduction even for long loops with bridge branches. For shorter loops, the desired reduction is still sufficient, although the amount of echo reduction that can be achieved is small.