CPFSK(Continuous Phase Frequency Shift Keying), whose phase is a continuous function of time and instantaneous frequency is constant, is a bandwidth efficient constant envelope signaling scheme.
The transmitting signal is formed by the combined coding of a convolutional encoder and a CPFSK modulator. It is assumed that channel is AWGN. Good error probability properties can be obtained maximum likelihood detection, where error probability can be written in terms of the minimum Euclidean distance. The Euclidean distances are studied as a function of modulation index, observation interval and the number of code delay element for rate 1/3, 1/2, 2/3 codes.
Rate 2/4 code is also studied for the improvement in error performance without sacrificing data rate or requiring more bandwidth.
