Achievable performance for coded modulation over fading channels

We compute the random coding error exponent for memoryless flat fading channels with ideal channel state information (CSI) and inputs drawn from a discrete alphabet. The signal sets we consider here are standard signal constellations commonly used in digital coded modulation. In addition, estimates of the code lengths required to achieve a certain error probability are determined and compared to those required for the AWGN channel. Finally, the effect of receiver diversity combining on improving communications reliability over the fading channel is considered. The results we obtain here shed light on the achievable performance over the fading channel with coded modulation.