Adaptive Beamforming and Modulation for OFDM in Co-Working WLANs With ACK Eigen-Steering

In this paper, we propose a method to reduce the interference and increase the throughput of orthogonal frequency division multiplexing (OFDM) systems in co-working wireless local area networks (WLANs) by using joint adaptive multiple antennas (AMA) and adaptive modulation (AM) with acknowledgement (ACK) eigen-steering. The calculation of AMA and AM are performed at the receiver. The AMA is used to suppress interference and to maximise the signal to noise plus interference ratio (SNIR) by adjusting its weights dynamically. The improved SNIR is then used by AM as an input to allocate OFDM sub-carriers, power, and modulation mode subject to the constraints of power, discrete modulation, and the bit error rate (BER). The transmit weights, the allocation of power, and the allocation of sub-carriers are obtained at the transmitter using ACK eigen-steering. The derivations of AMA, AM, and ACK eigen-steering are shown. The performance of joint AMA and AM for various AMA configurations are evaluated through the simulations of BER and spectral efficiency (SE) against SIR. The simulation results for joint AMA-AM also show that joint AM and receive beamforming produce the most effective solution in co-working OFDM-WLANs