LDPC Code Aided Phase Ambiguity Resolution

Low-density parity-check codes (LDPC) are known to perform close to the Shannon limit as the block length increases. Residual frequency offsets make iterative decoding difficult for longer block lengths. Sub-block decoding techniques provide a practical, low-complexity approach to deal with residual frequency offsets. However they require phase ambiguity resolution (PAR) in every sub-block. This paper presents a new approach called ´localized decoding´ to resolve the phase ambiguity over sub-blocks. The algorithm involves modifying the parity-check matrix of the existing LDPC code to create ´local check nodes´ and operating on them to resolve phase ambiguity. Simulation results of this approach show a negligible loss for small residual frequency offsets.