Code-aided turbo synchronisation using irregular low-density parity check codes

An efficient scheme for iterative carrier recovery by using irregular low-density parity check (LDPC) codes is proposed at low signal-to-noise ratio (SNR) conditions. Owing to the significant effect of decoding extrinsic information on the carrier estimation algorithms, deficiency of extrinsic information from decoding caused by large residual frequency or phase offsets in initial iterations will result in incorrect parameter estimation and compensation, which would fail to converge toward low BER in decoding process. Irregular LDPC codes have inherence unequal error protection (UEP) capabilities wherein the highdegree nodes tend to correct their value more quickly than low-degree nodes. The more reliable information, which is provided by the high-degree nodes of irregular LDPC code in initial iterations, can be used to offer more reliable soft information for carrier synchronisation even in poor channel conditions, which leads to improvement of the carrier parameter estimation performance. The simulation results indicate that the more reliable information from irregular LDPC codes can cope with large frequency, phase uncertainty region and speed up the convergence properties for iterative synchronisers when comparing with regular LDPC codes with same parameters.