Patent ID: 8938031
Filing Date: 2015-01-20
Classification: H04B,H04L

Abstract:
1. A phase-slip reduction method for receivers in a coherent communication system transmitting predetermined reference symbols and non-differentially modulated data symbols exhibiting N-ary symmetry and requiring acquisition of absolute phase for demodulation comprising the steps of: a) obtaining a phase estimate modulo 2π/N of the non-differentially modulated signal at times the reference symbols are received; b) forming a trellis with nodes and branches between adjacent nodes wherein N nodes at one time of said times are labeled by absolute angles obtained by adding modulo 2π said estimate at that time plus distinct multiples of 2π/N; c) assigning to the nodes at said one time, weights dependent on the difference modulo 2π between said nodes labels and received reference symbol angle at said time; d) assigning to each branch a length dependent on the difference modulo 2π between the labels of the branch end nodes; e) determining a decision path that is a shortest path traversing the trellis, where the length of a path is the sum of the branch lengths and node weights on said path; and f) for each received data symbol, determining an absolute demodulation angle by interpolating between the node labels on the decision path.