On the selection of adaptive modulation and coding modes over OFDM

In this paper we address the problem of how best selecting the smallest set of transmission modes (i.e. modulation and channel code formats) to be employed in adaptive modulation and coding (AMC) schemes for OFDM. In fact, by decreasing the number of allowable modes, the complexity of the ACM scheme is greatly reduced. The method makes use of an optimum throughput maximization algorithm for the bit and power allocation. We start with a large set of possible transmission modes. Then, for a given channel, we iterate the loading algorithm with mode sets having successive removal of the mode which yields the smallest contribution to the overall throughput. By using this method in a Rayleigh fading channel, we are able to show that in the test case of the HIPERLAN/2 modes, up to five modes out of seven can be removed with a very small impact on the average achievable throughput.