一种新的减少SDH指针调整抖动的方法

针对指针调整在SDH网络边缘会引起大幅度低频率抖动的问题，在传统相位泄漏法的基础上，提出了一种新的减小指针调整抖动的方法--自适应调制泄漏法。该方法采用新的相位扩散机理，先将指针调整引起的大幅度多比特抖动泄漏为多个小幅度单比特的抖动，然后对每1个泄漏bit进行序列调制，从而将泄漏频率由低频段移到高频段，使泄漏相位易于被锁相环滤除，最终达到减小输出抖动的目的。另外，该方法通过监视比特泄漏缓存器的满度来自适应地调整比特泄漏周期，可以在保证泄漏缓存器不发生溢出的前提下，最大限度地减小输出抖动。仿真表明，自适应调制泄漏法在网络处于劣化模式和非劣化模式时都可以有效地抑制指针调整抖动。

A New Method for Reducing the Jitter in SDH Pointer Adjustment

The phase jitter with high amplitude and low frequency induced by SDH(Synchronous Digital Hierarchy) pointer adjustment represents a serious technical problem in the edge of SDH network. Based on the traditional phase leaking techniques, a novel method named adaptively modulated bit leaking method is presented in this paper for the reduction of the jitter in pointer adjustment. It leaks multiple bits jitter as several single bit jitters so that the amplitude of jitter is cut down. Furthermore, it adopts a novel phase spreading technique to carry out sequence modulation to per leaked bit. Thus, the frequency of bit leaking is transferred from the low frequency band to the high frequency band, which makes leaked phase to be filtered by the phase locked loop easily. Meanwhile, the method adjusts the period of bit leaking adaptively according to the space of leaking buffer, which can maximally reduce the output jitter without causing the buffer overflow. Simulations show that adaptively modulated bit leaking method can reduce the jitter in pointer adjustment effectively in both the normal mode and the degraded mode of SDH network.