Vector propagation channel studies for smart antenna wireless communication systems

The explosive demand coupled with an expanding range of services for digital mobile communication systems has led to certain challenges such as spectral crowding and co-channel interference. In seeking solutions to these problems, researchers have recently turned their attention to smart antenna systems which employ antenna arrays and perform signal processing in both space and time at the base station. By exploiting the spatial dimension, smart antennas allow multiple users to transmit co-channel signals, thereby increasing capacity, extending range, and improving quality in wireless communications.; For a smart antenna system operating in moving mobile scenarios, its space-time signal processing capability and performance is limited by fast fading effects in the propagation channel. Vector channels describe the channel propagation characteristics of the signals (originated from a mobile) existing at the antenna array. Fast fading in a narrowband smart antenna wireless communications system can be overcome in the downlink by predicting spatial signatures (narrowband vector channels) of the antenna array and in the uplink by using a transmit diversity configuration at the mobile. This dissertation studies narrowband vector channels in various wireless environments (indoor, suburban, and urban) with typical propagation conditions based on extensive experimental studies using a 1.8 GHz smart antenna testbed. Variation of vector channel parameters in non-stationary wireless scenarios due to small displacement and antenna height change is explored for hallway-type indoor and suburban-type outdoor environments. An empirical statistical model is developed for the distribution functions of spatial signature correlations, thereby providing a tool for predicting variation of spatial signatures in fast fading (moving mobile) scenarios. Also investigated in this dissertation is that the two spatially-separated, cross-polarized antennas at the mobile alleviate fast fading effects in the uplink. In the downlink, pseudoinverse spatial signature based beamforming is superior to conjugate spatial signature based beamforming in fast fading environments.