Capacity of coherent frequency-hop spread-spectrum communications

Abstract

In this paper the capacity of coherent frequency-hopped (C-FH) spread-spectrum system is investigated. The channel comprises an M-ary phase-shift keying (M-PSK) modulator, a frequency hopper with phase-continuous carrier, the transmission medium, a nonideal phase-coherent frequency dehopper, an M-PSK demodulator, and a carrier tracking system. Additive white Gaussian noise is considered. The analysis focuses on the effect of imperfect recovery of the carrier phase on the demodulation process. The carrier tracking system includes an estimator of the phase error and a first order digital phase-lock loop. The phase error is modeled as a Markov process. Lower bounds to the capacity of a C-FH channel with memory introduced by imperfect synchronization are calculated. The performance of trellis-coded C-FH systems is computed and compared to that of M-PSK with ideal phase recovery.