Phase splitting timing recovery for coherent optical transmission systems

A new feedback symbol timing recovery technique using timing estimation joint equalization is presented for digital receivers with two samples/symbol or higher sampling rate. The clock recovery algorithm in this paper is different from the traditional method, using different algorithm by distinguishing the phase of adjacent symbols. A new timing algorithm is proposed for the adjacent signals with same phase to estimate the timing offset accurately. It is also shown that by adding the part of eliminating phase modulation interference before timing estimation, the variance can be further reduced, resulting in a smoothed timing estimate. The MSE and BER of the resulting timing estimate are simulated, supporting a satisfactory estimation performance. Good clock tone performance is obtained for MQAM modulation formats and roll-off factor (ROF) values close to 0.