Smart Antennas in Wireless Networks : Systems Issues and Performance Limits

This work deals with performance limits when using smart antennas in future wireless systems. The current evolution in the field of wireless communication implicates a substantially increased demand on transport capacity. Smart antennas is one very powerful means to fulfill these demands. In this work the use of smart antennas, deployed at either the access point or both the access point and the mobile terminal is investigated. In order to find out how the evolution within wireless communication will continue during the ten years to come, a scenario analysis is performed where driving forces are identified and scenarios are created. The system aspects of uplink and downlink communications utilizing smart antenna algorithms are investigated. For the uplink case, the impact of different smart antenna algorithms on a packet switched radio interface is investigated. In the downlink case, the use of joint optimal beamforming and power control is examined and compared to suboptimal downlink algorithms. Further, an algorithm for admission control is introduced and evaluated and the issue of optimal access point assignment is assessed. The extension to use smart antennas with both multiple transmitters and multiple receivers, i.e dual arrays, can provide high link capacity in future wireless systems. An analysis of indoor environment channel measurements in the 5.8 GHz band is performed and the possible increase in link capacity is examined. It is found that in the measured indoor environment, the scattering is sufficiently rich to provide substantial link capacity increase and that moderate intra-antenna-element distances is enough to give this capacity increase. It is concluded that smart antennas promise substantial capacity increase and remains a strong enabling technology for future systems for wireless communication.