Digital modulation and coding for mobile communications

M-ary phase shift-keying (MPSK) and M-ary frequency-shift-keying (MFSK) are compared for transmission over a Rayleigh faded radio channel of limited bandwidth. Both diversity and coding improvements are assessed for coupling with the M-ary signal alphabet. It is shown that phase modulation, with coherent or differentially coherent detection, outperforms orthogonal MFSK signalling if both power and bandwidth are constrained. It is also shown that the use of lower-alphabet MFSK with a higher-order diversity is more advantageous than the use of higher-ary modulation. Some situations are exhibited in which a comparable performance can be obtained by an increase in signal alphabet or diversity; the choice of modulation and coding format depends on the relative complexity of higher-ary modulation compared to increasing the order of diversity