Smart-antenna operation for indoor wireless local-area networks using OFDM

This paper reports link-level Monte Carlo simulations for a system that is compatible with the physical layer of the 5-GHz IEEE 802.11a wireless-local-area network and utilizes an adaptive antenna array at the access point for single-user smart-antenna operation, as well as for space-division multiple access (SDMA). For the spatial indoor radio propagation channel, complex impulse-response recordings are used. These are obtained in wideband channel-sounder measurements in three different buildings at 5.3 GHz. Thus, no unrealistic assumptions about channel conditions are involved. The paper studies how the packet-error-rate performance for the downlink (DL) is affected by time evolution of the radio channel that takes place after the uplink operation in which channel estimation is performed, and before DL operation in which the estimated channel information is utilized. Based on simulations two-user SDMA is possible with four-antenna elements under indoor propagation conditions and with six antennas three users can simultaneously be served. Delay spreads, coherence bandwidths, and correlation properties (in space, frequency, and polarization) of the radio channels obtained in the measurements are also discussed. The results suggest that indoor time-division-duplex systems with access-point-controlled scheduling are desirable communication systems which can benefit from SDMA.