Wide-range and fast-convergence frequency offset estimator by BER-aiding for optical coherent receivers

Optical coherent detection with digital signal processing (DSP) attracts more and more interests owing to its high performance. Due to a free-running local oscillator (LO) on the receiver, a frequency offset (FO) to the optical carrier brings phase distortion with which data can not be correctly decided and decoded. All-digital feed-forward FO estimation algorithms for optical (D)QPSK coherent receivers, such as PADE, have advantages of low complexity and stable-running wide range of estimation. However, it only converges under the condition that the initialed FO is near enough to the real FO while possible FO with typical tunable lasers can be very large. In order to solve this problem, we present a novel FO estimation scheme by BER aiding. This scheme has been demonstrated to be accurate and effective to break the restriction of PADE by simulation.