Joint iterative detection and decoding in the presence of phase noise and frequency offset

In this paper, we present an iterative decoding algorithm for turbo and LDPC codes transmitted over channels affected by a time-varying phase noise and an uncompensated frequency offset. The proposed algorithm is obtained as an application of the sum-product algorithm to the factor graph representing the joint a posteriori distribution of the information symbols and the channel parameters given the channel output. The resulting algorithm employs the soft-output information on the coded symbols provided by the decoder and performs forward-backward recursions taking into account the joint probability distribution of phase and frequency offset. We present numerical results for binary LDPC codes and LDPC-coded modulation schemes, showing that, despite its low complexity, the algorithm is able to cope with a strong phase noise and a significant uncompensated frequency offset, thus avoiding the use of complicated data-aided frequency estimation schemes operating on a known preamble.