A NEAR OPTIMUM DIVERSITY COMBINING METHOD ADAPTED TO SLOW FREQUENCY HOPPING DPSK TRANSMISSION

Frequency hopping (FH) is used in communication systems to mitigate interference such as jamming. For low data rate, fast FH and MFSK are often used in combination with diversity, which consists in transmitting every symbol on several hops. It brings additional protection. Several robust diversity combining methods have been developed previously for fast FH. Much attention has been previously focused on slow FH, where several symbols are transmitted during each hop, in order to allow higher data rates. Moreover, for higher data rates, FH MPSK could be preferred as this waveform is more bandwidth efficient and may provide better performance on a gaussian channel. This paper presents an new efficient method derived from the maximum likelihood criterion to combine hops in a slow FH MPSK transmission with diversity. First, theoretical analysis yields the formulation of the optimal receiver. Then, several approximations are used to let the implementation of this algorithm be feasible. Finally, resorting to computer simulations, it is shown that the method introduced in this paper outperforms conventional techniques. Bit error rate performance is presented for a gaussian channel corrupted by partial band jamming