An OFDM/Zero Forcing Beamformer For Smart Antennas in Indoor Environments

Abstract - This paper investigates the effect of the dimensions of an arbitrary indoor environment on the coherence bandwidth of the wireless wideband channel as well as its effect on the beamformer patterns. An algorithm for adapting the weights of a zero-forcing smart antenna beamformer operating in conjunction with an Orthogonal Frequency Division Multiplexing (OFDM) system is then proposed targeting HIPERLAN/2 applications in indoor scenarios. Keywords - HIPERLAN/2, Smart Antennas, Spatial Indoor Channel Model, OFDM. I. INTRODUCTION This paper represents a further step in studying smart antennas in indoor environments targeting high data rate Wireless Local Area Network (WLANs) . In [1], the use of smart antennas for HIgh PERformance Radio Local Area Network type 2 (HIPERLAN/2) was proposed in order to increase the overall data rate in a new domain of applications namely an infrastructure WLAN serving electronic archiving intranet applications in broadcasting studios. A deterministic 2D Ray tracer was developed allowing the estimation of the Channel Impulse Response (CIR) (the Power-Delay-Angle Profile: PDAP) for any arbitrary indoor architecture and wall properties in the 5 GHz band taking into account Line of Sight (LOS) , single and double reflections, diffraction from corners and transmission loss through walls. Using this model, an adaptive beamformer in the case where the number of users is equal, more (overloaded array) or less (underloaded array) than the number of antenna elements was investigated based on the zero forcing algorithm. The simulation results showed that it is not recommended to have an overloaded array (underdetermined system or more users than array elements) since the resulting SIR values may not guarantee an adequate Packet Error Rate (PER) at the maximum bit rate that can be supported by HIPERLAN/2 (30 dBs for 10