The performance of a wireless LAN access node using antenna beamforming for dynamic and static users

In the IEEE 802.11 wireless LAN (WLAN) standard, users transmit and receive within a common frequency band to achieve frequency re-use, but this creates capacity limitations. In this paper we examine link signal-to-noise ratio (SNR), as a function of time, when using a single linear array of sensors at the access node to provide spatial re-use, and hence, increased capacity. Multiple independent beamformers are established at the base station to spatially isolate transmit and receive signals at the WLAN access node. Specifically, parallel generalized sidelobe cancellers are implemented. The SNR as a function of time is of concern here since we assume that the users wish to transfer data while moving about the building. Furthermore the dynamics of a mobile user are modeled using actual indoor trajectories. System performance is characterized in terms of time varying link SNR. The use of multiple constraints, when possible, improves performance. Beamformer and angle-of-arrival processor update rates are varied to determine degradation thresholds.