Detection by Multiple Trellises: an Effective Approach to Phase-Uncertain Communications

Abstract — In this paper, we present a novel technique for detection of an encoded information sequence transmitted over a phase-uncertain channel. In order to limit the complexity of the detector, the phase space (i.e., the interval [0, 2π)) is properly quantized. The proposed detection algorithms are based on an L-fold replication of coherent forward-backward (FB) algorithms operating on L parallel trellises, one per hypothetical phase value. In order to make the receiver robust against a possibly time-varying phase, the proposed algorithms perform a manipulation of the forward and backward metrics computed by the different FB algorithms every N trellis time steps. The performance of the proposed algorithms is investigated considering differentially encoded (DE) quaternary phase shift keying (QPSK). We also consider the serial concatenation of DE-QPSK with an outer low-density parity-check (LDPC) code. Besides having a limited complexity, the proposed SISO algorithms turn out to be robust, flexible, blind, i.e., no knowledge of the channel phase statistics is required, and highly parallelizable, as it is desirable in high-throughput future wireless communication systems. I