SDH中恢复四次群时钟的数字化预处理方法

同步数字系列（ＳＤＨ）中的指针调整引入了８ｂｉｔ或２４ｂｉｔ的大幅度抖动。为了处理这一抖动，提出了一种数字化处理方法——自适应预测法，可以作为预处理方法应用于ＳＤＨ中的四次群时钟恢复。该方法在一个统计周期内统计指针调整和码速调整的次数，并根据统计结果，在下一个周期内自适应地预测出四次群支路时钟。该时钟不含指针抖动，便于利用模拟锁相环进行最终处理，得到均匀的四次群时钟。从该方法的基本原理，以及对它的静态抖动和抖动转移性能分析中可知，相对于以往的减小指针抖动的方法，如比特泄漏法等，自适应预测法具有输出抖动小，抖动转移性能好，捕捉范围宽等特点。

Digital preliminary processing method of regenerating E4 clock in SDH

Pointer adjustments bring 8bit, or even 24bit large jitter in synchronous digital hierarhy (SDH). In order to smooth the jitter, this paper presents a digital processing method, self adaptive prognostication method, which can be applied as a preliminary processing method to regenerate the fourth order (E4) clock in SDH. By counting the number of pointer adjustments and justification in a period, the method can self adaptively prognosticate the tributary clock in the next period. The prognosticated clock without jitter caused by pointer adjustments can be processed by analog phase lock loop at last, so as to get the smoothed E4. From the scheme of the method and analyses of its static jitter and jitter transfer performance, it can be known that the method has smaller output jitter, better transfer performance and wider catching bound than some other methods, such as bit leaking method.