An approximation for the phase offset sensitivity of Viterbi detected continuous phase modulation signals

An approximation is presented for the loss in performance when the Viterbi algorithm receiver for CPM (continuous phase modulation) signals is subject to a phase offset. Pairs of symmetric error events are used to derive a closed-form result that approaches the asymptotic expression, based solely on minimum distance, as E_s/ N₀ approaches infinity. The improved accuracy of the approximation is demonstrated by comparison with a Monte Carlo simulation