Year

2008

Degree Name

Master of Engineering by Research

Department

School of Electrical, Computer and Telecommunications Engineering - Faculty of Informatics

Abstract

Wireless communications are developing at a booming speed, with plenty of research emerging on the next generation wireless communications. This thesis presents an advanced system for the next generation wireless communications. The proposed system is called block spread OFDMA combined with STC-MIMO (STC-MIMO BS-OFDMA). The system is based on OFDM, which is able to deliver high data rates in highly dispersive channels and is thereby considered as a good candidate of modulation techniques for 4G. The block spreading technique and STC-MIMO scheme are used to provide the system with frequency and spatial diversity, therefore significantly improving system performance.

In this system, there are two stages to combine block spreading and STC-MIMO with OFDMA. Firstly, a novel block spreading approach is applied to effectively achieve frequency diversity in the OFDMA system without any explicit precoding process. The STC-MIMO using Alamouti code is then incorporated on block basis and performs in space and frequency. Accordingly, the signal model and architectures of the proposed system are presented. Two receiver architectures are designed for different STC-MIMO schemes: the receiver with one antenna and receiver with two antennas.

Simulations are carried out to demonstrate the expected performance improvement. The BER performance comparisons indicate that the proposed system can achieve significant performance improvement. The research project also investigates the system performance when different parameters are used. Our results show that using a larger block spreading size and more receive antennas can further improve system performance because of higher order of diversity advantages. In terms of linear equalizations, the MMSE equalization achieves better performance than the ZF equalization.

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