A COHERENT DEMODULATOR FOR FAST FREQUENCY-HOPPING SPREAD-SPECTRUM SIGNAL EMPLOYING AN ADAPTIVE ALGORITHM

It has been considered impossible to demodulate a fast frequency-hoppi ng (FFH) spread-spectrum signal coherently in a frequency selective fa ding channel as a result of difficulties with making the receiver loca l oscillator track the phase of a received signal that lacks phase con tinuity. This paper proposes a coherent demodulator for both FFH-PSK ( phase-shift keying) and FFH-FSK (frequency-shift keying) signal employ ing a method in which the received signal is noncoherently down-conver ted and phase-adjusted by an adaptive algorithm. Computer-simulations show that performance is better than in the case of noncoherent demodu lators and that the interference-rejection effect of the adaptive algo rithm produces strong protection against interferences from other CDMA users.