Link adaptation of wideband OFDM systems in multi-path fading channel

In OFDM systems, because channel fading on different sub-channels is different; when all OFDM sub-carriers use the same fixed modulation scheme, the error probability is dominated by the sub-carriers with the highest attenuation. Link adaptation can be used to enhance system throughput. According to the current link quality, the most appropriate modulation scheme can be selected on each sub-carrier to maintain acceptable error rate performance. In this paper, two link adaptation methods are considered. In the first method, a fixed number of weak sub-carriers which are highly attenuated are left out to improve the BER performance; in the second method, depending on the channel quality of each sub-carrier the modulation level on each sub-carrier is varied to adapt to the link conditions to improve the system throughput. The analysis and simulation results verify that the proposed link adaptation and coding scheme is effective in improving system throughput compared with the system with fixed modulation/coding.