Performance study on frequency-domain link adaptation in IEEE 802.11a wireless LAN

The link adaptation scheme in the current IEEE 802.11a technical specifications only consider channel variation in the time-domain, and assume all the data subcarriers use the same modulation mode and coding rate once the transmission data rate is determined. However, in the frequency-selective fading scenario, the BER performance is severely degraded by OFDM subcarriers where deep fading occurs. We propose a frequency-domain link adaptation scheme for IEEE 802.11a, which is based on a modified adaptive bit and power loading algorithm and a modified pilot pattern. Simulation results show our proposal can greatly improve performance when perfect channel information is obtainable. We also investigate the performance of the proposed scheme in two channel mismatch situations, and show it is capable of achieving large performance gain in the most favorable environment for IEEE 802.11a, the low mobile speed environment.