Comparison of coherent and non-coherent modulation schemes for low-data rate hand-held satellite terminals subject to high phase noise

The object of this paper is to compare the performance degradation of coherent and non-coherent modulation schemes for low data rate transmissions in the presence of oscillator phase noise. The effect of phase noise on coherent binary phase shift keying (CPSK), differential binary phase shift keying (DPSK) and non-coherent orthogonal M-ary frequency shift keying (MFSK) has been considered. Results are presented in the form of bit error rate (BER) versus E_b/N_o plots. It has been shown that in noncoherent schemes MFSK is more robust than DPSK and CPSK performs better than either noncoherent scheme when the correct choice of optimum noise bandwidth of the phase locked loop (PLL) in the carrier recovery circuit is made. It is assumed that there is no cycle slipping in the CPSK demodulator. However, for hand-held technology which requires low complexity and low cost receiver structure, a noncoherent scheme may be more attractive, and hence, MFSK can be considered to be more suitable for hand-held satellite terminals