Improved Code-Aided Symbol Timing Recovery with Large Estimation Range for LDPC-Coded Systems

We present an improved code-aided symbol timing recovery method for low-density parity-check (LDPC) coded systems, which comprises two supporting algorithms: 1) a coarse estimation by utilizing a cost function, the mean absolute value of soft output of the LDPC decoder and 2) a fine estimation based on the Expectation-Maximization (EM) algorithm with a simple maximization step. With low computational complexity, this proposed algorithm can achieve symbol timing recovery at low signal-to-noise ratio (SNR) with large estimation range, eliminating the biased results of many algorithms for large timing offset values. Simulation results for the case of 8-PSK system with (1944,972) LDPC code show that the root-mean-square-error (RMSE) performance of the proposed algorithm approaches the modified Cramer-Rao lower bound (MCRB) at Eb/No=4dB, and the bit-error-rate (BER) curve is very close to that of ideal synchronization.