Sequence detection for MPSK/MQAM with adaptive phase tracking

摘要

In [P.Y. Kam, P. Sinha, A Viterbi-type algorithm for efficient estimation of MPSK sequences over the Gaussian channel with unknown carrier phase, IEEE Trans. Commun. COM-43 (1995) 2429-2433], we developed a Viterbi algorithm for efficient detection of M-ary phase-shift keyed (MPSK) sequences received over the additive, white, Gaussian noise (AWGN) channel with an unknown carrier phase. By assuming the carrier phase is constant over some L symbol intervals and using the sequence detection metric in [P.Y. Kam, Maximum-likelihood digital data sequence estimation over the Gaussian channel with unknown carrier phase, IEEE Trans. Commun. COM-35 (1987) 764-767] as the decoding metric, it approaches the performance of coherent detection, provided the observation interval L for forming the decoding metric is sufficiently long. However, this observation interval L is fixed, and chosen based on prior knowledge of the carrier phase characteristics. Thus, the metric is nonadaptive, and cannot be optimized when a priori statistical knowledge of the carrier phase is not available. The work here renders it adaptive by developing a recursive metric that is adapted on-line based on the received signals, without prior knowledge of the carrier phase characteristics. We first derive a metric for the maximum likelihood sequence detector for a general M-ary quadrature amplitude modulation (MQAM) sequence received in the presence of AWGN and an unknown, slowly- and randomly-varying carrier phase. To reduce the receiver complexity, a practical, suboptimal metric is obtained. A recursive form of the metric using adaptive reference estimation as in [P.Y. Kam, K.H. Chua, X. Yu, Adaptive symbol-by-symbol reception of MPSK on the Gaussian channel with unknown carrier phase characteristics, IEEE Trans. Commun. COM-46 (1998) 1275-1279], is proposed. Comparison between the proposed adaptive, recursive metric and those in the literature is provided. Simulation results using a random-walk carrier phase model show the superior performance of the adaptive sequence detector over the original nonadaptive sequence detector of [P.Y. Kam, P. Sinha, A Viterbi-type algorithm for efficient estimation of MPSK sequences over the Gaussian channel with unknown carrier phase, IEEE Trans. Commun., COM-43 (1995) 2429-2433].