An adaptive learning approach to adaptive OFDM

Orthogonal frequency division multiplex (OFDM) technique has been successfully deployed in indoor wireless LAN and outdoor broadcasting applications. It is well-known that under a frequency-selective fading channel the resultant sub-channel frequency functions are frequency-variant and may also be time-variant, i.e. the channel magnitude may be highly fluctuating across the sub-carriers and varies from symbol to symbol. Hence adaptive modulation may be appropriately applied to improve the error performance and data throughput in an OFDM modem by assigning different modulation and coding schemes to different sub-carriers. One fundamental issue in deploying adaptive modulation is to determine what modulation and coding scheme to use. Virtually all past investigations were either based on heuristic methods or analytical means. This paper proposes a novel adaptive learning control approach that is capable of dynamically adjusting the switching thresholds to improve or maximize the data throughput.