Adaptive Modulation for Limited Diversity Fading Channels

In this paper, we describe a recently proposed bit-loading algorithm and a novel power-loading algorithm for block fading channels with channel state information (CSI) at the transmitter. We consider channels that offer a relatively small order of diversity, the so-called limited diversity fading channels. Limited diversity channels such as those encountered in indoor orthogonal frequency division multiplexing systems are characterized by the fact that achievable diversity orders are small and are limited by the channel and not by complexity of the code used. We first discuss a recently proposed analysis technique for the performance of bit-interleaved coded modulation on block fading channels. We then describe a bit-loading technique for maximizing the throughput at a fixed bit error probability. We also propose a new and simple power loading solution to minimize the bit error probability at a fixed rate. Lastly, we show comparative simulation results that corroborate the arguments presented in this paper.