Demodulation of Differentially Encoded LDPC Coded Modulation Schemes with Non-ideal Phase Reference

Soft decoding of coded modulation schemes based on the serial concatenation of low-density parity check (LDPC) codes and differentially encoded (DE) quadrature amplitude modulations (QAMs) in the presence of Wiener phase noise is considered. Log-likelihood ratios, required to perform soft decoding, are first derived for the case where the phase of the received carrier is assumed to be perfectly known and then used to obtain the performance in case of non-ideal reference of phase. Numerical results obtained by computer simulations are shown where the performance loss compared to ideal coherent demodulation is evaluated for a practical blind carrier phase recovery algorithm in case of quadrature-phase shift keying and 16-QAM transmission.