Symbol Error Probability of M-QAM in Multihop Communication Systems with Regenerative Relays

We analyze the performance of multihop communication systems with regenerative relays in terms of the average symbol error probability (SEP) for M-ary quadrature amplitude modulation (M-QAM). We derive an exact analytical closed- form expression for the average SEP in time-invariant additive white Gaussian noise channels as well as a generic expression for slow, frequency-flat fading channels, which might be easily evaluated numerically for a wide variety of different fading distributions. For the important case of independent but not necessarily identical Nakagami-m fading on all hops, the average SEP is furthermore given analytically in closed-form. Our results are valid for general rectangular signal point constellations as well as an arbitrary number of intermediate relay stations.