Frequency diversity for a phase-coherent frequency-hopping spread-spectrum system

The direct-sequence spread-spectrum (DS-SS) signal is conventionally received with a correlator followed by a threshold detector. This receiver, which is optimum in the presence of additive white Gaussian noise (AWGN) is far from optimum in the presence of partial-band (thus, non-white) Gaussian interference. Since the optimum receiver is difficult to implement, the communicator may prefer to use a frequency-hopping spread-spectrum (FH-SS) system instead. In fact, the optimum receiver of a FH-SS system is easier to build. Moreover, large spreading can be achieved with no additional effort for time acquisition, and the use of a non-continuous spectrum is possible. Since frequency hopping is considered as mandatory in some applications, we aim in this paper to combine both frequency-diversity spread-spectrum (FD-SS) and FH-SS systems. The main objective is to guarantee coherent demodulation and to avoid noncoherent combining loss.