Downlink Beamforming under EIRP Constraints in WLAN OFDM Systems
01 January 2006
A downlink beamforming for wireless local area network (WLAN)- type orthogonal frequency-division multiplexing (OFDM) system is addressed, where an access point is equipped with multiple antennas and a terminal uses a single antenna. Conventional beamforming solutions scaled according to the total power (TP) and equivalent isotropic radiated power (EIRP) constraints are compared. It is found that a few dB gap between them in terms of the SNR gain exists in the typical WLAN propagation scenarios. A joint optimization problem for the beamforming weights over all the sub-carriers subject to the EIRP constraint is formulated and a sub-optimal solution is proposed, which is based on grouping of non-adjacent sub-carriers. Its efficiency is illustrated in the IEEE 802.11 environment.