An OFDM-MMSE smart antenna for an infrastructure WLAN in an indoor environment

This paper investigates the frequency dependence of the channel transfer matrix and the weights (multipliers´ coefficients) of a smart antenna optimum combiner in an arbitrary indoor environment. A previously developed ray-tracing tool is used to predict statistical multipath wireless channel parameters of interest. A WLAN with multiple users communicating with an access point in an SDMA scheme is used to study the effect of the wideband indoor channel on the performance of an MMSE smart antenna in several architectures of different dimensions, obstructed and non-obstructed. The coherence bandwidth value is calculated from the frequency autocorrelation function and compared with the statistical estimation. A weight interpolation algorithm is proposed for the MMSE beamformer to work in conjunction with an OFDM subsystem of a HIPERLAN/2 or an IEEE802.11a network. A smooth variation of the patterns occurs in the case of a small indoor environment with a relatively large coherence bandwidth.