A coherent demodulator for fast frequency‐hopping spread‐spectrum signal employing an adaptive algorithm

Abstract

It has been considered impossible to demodulate a fast frequency-hopping (FFH) spread-spectrum signal coherently in a frequency selective fading channel as a result of difficulties with making the receiver local oscillator track the phase of a received signal that lacks phase continuity. This paper proposes a coherent demodulator for both FFH-PSK (phase-shift keying) and FFH-FSK (frequency-shift keying) signal employing a method in which the received signal is noncoherently downconverted and phase-adjusted by an adaptive algorithm.Computer-simulations show that performance is better than in the case of noncoherent demodulators and that the interference-rejection effect of the adaptive algorithm produces strong protection against interferences from other CDMA users.