Gigabit/s indoor wireless systems with directional antennas

Abstract

The design of a high speed (>150 Mb/s) wireless local area network (WLAN), requires that many factors be considered, including technical, economic, and regulatory. A major technical factor is the channel response behavior (multipath) in the indoor environment as a function of the frequency band, building type and radio system architecture. The consequences of designing indoor wireless systems with directional antennas at one or both ends of a line-of-sight (LOS) link are investigated. We determine how narrow the beamwidth must be so that the maximum data rate is not limited by multipath effects. For such beamwidths, simple unequalized two-level frequency shift keying (FSK) or phase shift keying (PSK) modems can be used in place of the more costly and complex anti-multipath modems, and data rates above 1 Gb/s may be achieved. The channel impulse response in an empty room is estimated using geometrical optics, observing that with directional antennas, multipath rays must arrive from the same direction as the LOS ray. The link outage probability is then estimated as a function of the antenna beamwidth, and guidelines are established for the selection of the frequency band and antenna placement. Experiments using a 19-GHz 622-Mb/s binary phase shift keying (BPSK) link and 15/spl deg/ beamwidth horn antennas in an office building with plaster walls and large metallized windows have demonstrated error-free performance on both LOS and non-LOS (NLOS) links.