Equivocation in nonlinear digital carrier synchronizers

The nonlinear (nondecision-aided) digital phase estimator provides rapid phase estimation of an M-ary phase-shift-keyed modulated carrier. This carrier synchronization technique exhibits an anomaly, dubbed equivocation, which can degrade performance. A statistical description of equivocation, a jump in the reference phase trajectory of ≈2π/M rad in a carrier synchronization technique, for the simple case of negligible frequency offset and additive white Gaussian noise is derived. Equivocation is shown to significantly degrade the bit error probability performance even in this benign channel. Since the algorithm as proposed is unsuitable for general use, a modified nonlinear (nondecision-aided) equivocation-free phase estimator is presented. The results of a simulation of this modified architecture developed to demonstrate the improved performance are presented