Code-aided synchronization algorithm based on posterior probability

For the error-correcting performance deterioration of Low Density Parity Check Code (LDPC) due to the synchronization loss at very low signal to noise ratio (SNR) environment, a code-aided synchronization algorithm named maximum-mean posterior probability is proposed. Firstly, improved data-aided method is adopted. Cursory synchronization parameters are estimated using encoded training sequence to ensure the timing error less than one symbol period. And then error information is fed back according to the distribution of posterior probability. The algorithm takes the decoding information as reference and brings the error correcting function of decoder into play supporting synchronous step. Synchronization accuracy is effectively improved. Finally, LDPC-CPM simulation model is established in allusion to Continuous Phase Modulation (CPM) signal. Simulation results show that the algorithm can accurately complete the timing and phase estimates and make the iterative system achieve reliability as ideal synchronization at very low SNR.