Decision-Directed Carrier Phase and Symbol Timing Recovery for LDPC-Coded Systems

In this paper, we consider the effect of different rules of symbol decision on the performance of decision-directed synchronizers for LDPC-coded systems. Different from the conventional hard symbol decision based on the Maximum-A- Posteriori (MAP) criterion, soft symbol decision can be considered as the Minimum-Mean-Square-Error (MMSE) estimation of the transmitted symbol. By whether or not the coding constraints are taken into account, soft symbol decision is derived in non-code-aided (NCA) mode and code-aided (CA) mode, respectively. The performance of the soft decision-directed (SDD) synchronizer is compared with that of the hard decision-directed (HDD) counterpart in both NCA and CA mode. Simulation results show that, without much implementation complexity increase, the jitter performance of the synchronizer in CA mode significantly outperforms that in NCA mode. It is also observed that, in the scenario of this paper, SDD synchronizer works only slightly better than HDD synchronizer.