Sub-carrier Adaptive Modulation and Coding in OFDM

Adaptive Modulation and Coding (AMC) technique exploits the high frequency diversity in wideband OFDM channels to obtain higher data rates. While prior work has discussed the value of AMC from a theoretical perspective, this work presents the design and performance of a real-time sub-carrier AMC system. The measurements from this AMC scheme implemented on an OFDM transceiver prototype indicate how this design achieves accurate and consistent Signal-to-Noise estimates, which are critical for the success of AMC. The performance of this design is compared with a uniform-adaptation scheme that assigns the same modulation and coding to all sub-carriers. The experiments over the wireless channel shows that for a target coded BER of 10^-5, this technique achieves average data rates of 308.3 Mbps and 237.1 Mbps across a variety of line-of-sight (LOS) and non-LOS locations respectively, which result in 34% and 40% gain over the best uniform-adaptation scheme. Finally, the implementation of this AMC incurs a low overhead of 1.1% of the data rate, and a reasonable complexity, occupying 9.95% of the total transceiver gates on the Field Programmable Gate Array.