Performance Study Of MIMO Systems Using Multi-Polarized Antennas

At present, there is a high demand for an increasing data rate transmission over wirelesscommunication systems, in order to serve a recent development of multimedia applications onterminals. In1996, one important technique was proposed by Bell laboratory researchers in order toimprove data throughput and quality without increasing additional bandwidth and power oftransmission. The basic aim of this technique is to create the independent sub-channels by usingmultiple antennas at the transmitter and receiver sides. However, MIMO systems suffer from thecorrelation between the sub-channels that might occur, especially, when the distance betweenantennas is limited and when the angular spread is narrow. This incident affects the performance ofMIMO systems. Therefore, the main objective of this thesis is to implement a MIMO system withpolarization diversity so as to reduce the correlation between the sub-channels under physicallimitation of antenna array size.First of all, the thesis studies several kinds of channel models. A three dimensional modelling ofthe polarized MIMO transmission channel is proposed. In order to accurate the channel, thecharacteristic of the antenna polarization and the depolarization of the scatterers are taken intoaccount.Secondly, the channel capacity for the multiple antenna systems is examined when thereceiver adopts different combining techonology. And the performance of MIMO systems isimproved by the water-filling techonology when the channel state information is known at theemitter. Finally, we extend our study by focusing on the multiple antenna systems with thepolarization diversity. We analyse that the capacity of MIMO systems is affected by some elementssuch as cross polarization discrimination, angle spread and line of sight channel.The spatial correlation depends on the angle spreading of azimuth in single polarized systems.There is no correlation when the antennas at the transmitter and receiver are completely orthogonal.In non-line of sight channel, the capacity of single polarized TITO systems does not depend onXPD. It increases by the the angle spreading of azimuth. The capacity of dual polarized TITOsystems is sensitive to XPD. It does not vary with the the angle spreading. In Rice channels, thecapacity decreases with the power of LOS channel.