Comparison of coherent and non coherent modulation in the presence of phase noise

Abstract

The object of the paper is to compare the performance of coherent and noncoherent modulation schemes in the presence of phase noise, and to determine whether the noncoherent schemes might be more robust than the coherent schemes more usually employed. The paper considers the effect of phase noise on two types of noncoherent modulation schemes: wide-shift FSK and differential PSK, and compares the performance with coherently demodulated PSK. Analytical models are derived for the performance of the three schemes, and numerical results are calculated for a system using a typical oscillator subject to phase noise. The results show that noncoherent schemes are indeed more robust than coherent ones, and that wideshift FSK is more robust than differential PSK. Thus the noncoherent schemes will operate successfully at much lower data rates than the coherent. These results are backed up by computer simulations of the three schemes, which show the same increase in susceptibility from FSK to DPSK to coherent PSK.