Abstract
Clock transform and recovery is of significant importance in microwave TDM service, and it is always extracted from the E1 line data stream in most cases. However, intrinsically uncertain delay and jitter caused by packet transmission of E1 data information, may lead to the indexes of the data recovery clock exceed the clock performance template. Through analysis of the E1 clock indexes and measuring methods, this paper proposes a new clock recovery method. The method employs two buffers, the first RAM is used as a buffer to deduct excess information, and the second FIFO is used as a buffer to recovery the clock and data. The first buffer has a feedback from the second one, and is able to actively respond to changes in the data link and requests from the second one. The test results validate the effectiveness of the method, and the corresponding scheme is also valuable for the other communication systems.
Highlights
E1 data transmission standard [1,2,3] defines the criterion of jitter and wander, and provides the related index template about E1 digital timing sequence
Through analysis of the E1 clock indexes and measuring methods, this paper proposes a new clock recovery method
MTIE will increase without limit and clock recovery needs to be corrected
Summary
E1 data transmission standard [1,2,3] defines the criterion of jitter and wander, and provides the related index template about E1 digital timing sequence. The stability index of the E1 service clock is called Wander, which is a slow phase modulation of the time information (the frequency spectral component is lower than 10Hz) and is generated by the dynamic buffers in the whole transmission network [5]. If TIE changes monotonously (increase or decrease linearly), it shows that there is a fixed frequency difference between the recovery and the reference clocks. In this condition, MTIE will increase without limit and clock recovery needs to be corrected. TDEV template defines the additional wander of the clock signal and provides the tracking degree between the recovery and the reference clocks; when the index exceeds the requirements, it shows that the recovery clock has deviated far away from the reference clock
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