Low Complexity Adaptive Modulation for 802.11N Beamforming Systems

We study transmit beamforming in IEEE 802.11n systems, where perfect channel state information is available at the transmitter. We first derive the achievable diversity order on each eigenmode. It is found that these eigenmodes are almost Gamma distributed for small number of antennas, which is the typical configuration for IEEE 802.11n systems. Finally, we develop a tight lower- and upper-bound to the average bit error rate performance over each eigenmode.