Novel spatial diversity techniques for mobile communications in correlated fading environments

In this thesis we analyze the performance of antenna arrays in cellular communication systems. Since an antenna array exploits the spatial dimension, it has the advantage to improve the performance of a communication system when the signals are distributed in space. Most researchers until now has concentrated on the case where the antenna elements receive independently faded signals, which typically results from signals that are 360 degrees distributed in space. We consider here the more realistic case where the signals are only partially distributed and the antenna elements therefore receive correlated faded signals. Using the knowledge of the faded environment, we will try to build better transceiver structures and analyze the performance of both the uplink and the downlink of such systems.; For the uplink an estimator which makes use of the knowledge of the spatial distribution of the signal is proposed, and compared with other estimates where either this knowledge is not available, or only an estimate of it is available. As the signal gets spread more in space, the value of this information is reduced, until for the case of isotropic scattering the estimate which uses the spatial distribution is equivalent to the estimate which does not. We derive the approximate theoretic performance of the array as a function of both angular spread and input SNR. Performance results are presented that compare the performance of the different estimators, as well as the proposed theoretic performance, as a function of input SNR.; For the downlink we derive the structure of a transmit diversity system which can be optimized for a Rayleigh fading environment in which the fading may be correlated. The system tries to maximize the array gain to diversity gain ratio, by implementing the smallest possible number of beamformers which would cover the signal space. We use space-time codes as inputs to these beamformers. We derive the transmitter and receiver structure and present a detailed performance analysis, validated by simulation results. A closed form expression for the Probability of Error for this system is presented.