Trellis coded CPFSK

Abstract

Continuous phase Frequency Shift Keying (CPFSK) is a potentially attractive modulation scheme with constant envelope and good spectral characteristics for energy constrained and band-limited satellite channels. This research deals with Orthogonal Frequency Shift Keying (FSK), Minimum Shift Keying (MSK) which is a special case of CPFSK, uncoded quaternary CPFSK and finally coded quaternary CPFSK. Orthogonal FSK is simulated by making the modulation index (h) equal to one, and all the other simulations are performed with h=1/2. A rate 1/2 convolutional encoder with constraint lengths (k), k=2, 3, and 4 are used in coded quaternary CPFSK simulations. Good coding gains are obtained with only a slight increase in receiver complexity. Soft decision with the Viterbi Algorithm was applied to all CPFSK and one MSK application. Hard decision was applied to Orthogonal FSK and another MSK application.