Positioning and Channel Estimation Errors and their Impact on a Smart Antenna System in an Indoor WLAN

This paper investigates the impact of Access Point (AP) or user positioning imperfections and channel estimation errors on the performance of a smart antenna system serving multiple users through Space Division Multiple Access (SDMA) in an indoor Wireless Local Area Network (WLAN). A ray-tracing tool is used to predict the Power Delay Angle Profile (PDAP) of the users in an arbitrary indoor environment. A Sample Matrix Inversion (SMI) algorithm is used to calculate the optimal smart antenna weights. The impact of a small displacement of the AP or the user positions on the SINR value from their initial positions is first investigated and compared for the Line of Sight (LOS) and multipath cases. It is shown that, in the multipath case, small AP or user displacements (in the order of λ/4) will cause a variation of the smart antenna patterns and consequently the Signal to Interference plus Noise Ratio (SINR) due to the change of the phase and amplitude of the multipath components (rays) arriving at the AP. The impact of several degrees of channel estimation errors is then investigated. It is shown that small errors in the estimation of the channel transfer matrix coefficients could lead to a large degradation in the SINR value.