Code-Aided Turbo Iterative Synchronization Algorithm Based on Likelihood Ratio

In view of the error-correcting performance deterioration of Turbo codes due to the synchronization loss at low SNR environment, a code aided synchronization algorithm named maximum-mean likelihood ratio (MMLR) based on the log-likelihood ratio is proposed by combining with Turbo iterative mechanism. Firstly, improved data aided (DA) method is adopted to ensure the timing error less than one symbol period. And then error information is fed back according to the distribution of likelihood ratio. The iterative phase estimation is carried out. Since the decoder has the error correcting function, the synchronization accuracy of the algorithm is effectively improved. Turbo-minimum shift keying(MSK) simulation model is established. Simulation results show that the algorithm can accurately complete the timing and phase estimates and achieve the reliability close to that of ideal synchronization at very low SNR.