LTE is being deployed to meet consumer demand for high bit rate mobile wireless. This thesis studies 3 areas of wireless communications; phase noise, Doppler and link adaptation, and multi-antenna system performance. The thesis focuses on the performance of 4 base-station (BS) antennas, simulation results using 3GPP's spatial channel model and the effects of impairments and configurations on the downlink. The best performing antennas evaluated are the 4-transmitter, 4-port, correlated cross-polarized BS antennas when TM4's CLSM is used. Despite added overhead, 4 antennas provides
gain over 2 antennas due to beamforming. When only 2-ports are available, TM3's OLSM outperforms TM4 as UE velocity increases, since 2-port TM3 is less dependent on CSI. Link adaptation latency contributes to degradation starting at low velocity. In addition, high-speed train simulations show throughput degradation at 350km/hr. Finally, the downlink is subjected to phase noise to show the effect of generated and measured phase noise.