Relay Diversity Techniques for OFDM and MC-CDMA
The future of mobile and personal communications requires a system that can support a large number of users and has the ability to provide high-speed services. Meeting this demand is challenging since wireless communications are subject to these four major constraints: complex fading channels, a scarce usable radio spectrum, and limitations on the power and size of the mobile terminals. Space-time codes, such as the Alamouti/space-time block coding (STBC) and cyclic delay diversity (CDD) can provide diversity and coding gains in multipleinput multiple-output (MIMO) systems over fading channels. However in an ad-hoc network, nodes are often constrained in hardware complexity and size, which makes MIMO systems impractical for certain applications. Cooperative relay diversity schemes have been introduced in an eort to overcome these limitations. Cooperative techniques allow a collection of communication nodes to cooperate with to relay signals amongst each other, eectively creating a virtual antenna array, which combat multipath fading in wireless channels. This thesis investigates relay diversity techniques in cooperative communications, namely the distributed space-time block coding (DSTBC) and relay cyclic delay diversity (RCDD) for OFDM and MC-CDMA systems. The performance analysis of the wireless relay networks under dierent protocols and fading channels are investigated. We derived the formulas for the symbol error rate (SER) of the investigated schemes in fading channels. Finally, a novel hybrid relay diversity (HRD) is presented for OFDMbased system. This new relay structure addresses the issue of achieving a full spatial and multipath diversity by developing a hybrid for CDD and STBC. Simulation on the system performance of HRD shows the superiority of the technique compared to standalone DSTBC and RCDD.
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