Upper bounds on the free distance for a class of convolutional coded CPFSK signals

Abstract

In this letter, we construct new encoder-independent upper bounds on the free distance for the rate (n - 1)/n convolutional encoders that are formed by using rate 1/2 encoders and combined with 2 n-level constant-envelope full-response CPFSK signals of single-h, by generalizing the bounding technique employed for the existing bounds. The new bounds coincide with the existing bounds for h ≤ 0.25, but are generally better for h > 0.25. We also present actual encoder combinations achieving the constructed new bounds with short constraint lengths.