A SIMPLE COHERENT RECEIVER FOR FREQUENCY-HOPPED PULSE-DRIVEN GMSK*

Abstract−Bandwidth efficient modulations are being considered to increase the throughput over existing MILSATCOM channels. Pulse-driven GMSK (PDGMSK), is a variation of Gaussian minimum shift keying (GMSK) that uses GMSK at the highest data rate and gradually devolves to symmetric differential phase shift keying (SDPSK) at slower data rates for simplified detection. By using a pulse amplitude modulation (PAM) representation of the PDGMSK signal, a near optimal receiver can be implemented using a single matched filter. For pure GMSK demodulation, we develop a simplified Viterbi receiver that approximates the response of the successive PAM components using scaled delayed samples from a single matched filter. Carrier phase recovery is accomplished each frequency hop with an initial reference sequence and a decision feedback phase tracking algorithm. I