Data Recovery in Differentially Encoded Quadrature Phase Shift Keying

Information in a PSK modulation format is contained in the phase. For Gray-coded DEQPSK, this information is contained in the change in phase. With advances in DSP technology, fundamental trigonometric signal processing functions which have, in the past, been unavailable now provide a mechanism for recovering phase differential directly from the phase plane. This paper presents a new algorithm for recovering step phase changes for a DEQPSK modulated signal by computing the phase angle from the arctangent of the ratio Q/I, and comparing it with the previous phase. This phase difference is then mapped to a monotonic metric for the purpose of soft-decision Viterbi decoding.