(A) space-time coding scheme for decode-and-forward based cooperative relaying

Abstract

Next generation network (NGN) is a all IP network able to provide telecommunication services through IP packets. NGN consolidates heterogeneous core and access networks such as commercial cellular systems, sensor networks and ad-hoc communications. In this thesis, we assume a nomadic user moves from a cellular system to a sensor network in NGN and discuss how to improve the performance of the user. Different networks require different communications technologies. However, communication over a point-to-point link is a basic unit of all kinds of communications. For example, a multi-hop communication is a combination of point-to-point communications and a cooperative communication can be considered as two point-to-point communications happening at the same time. Therefore, first of all, we introduce a scheme that improves the performance of the point-to-point link communication. Then we suggest efficient resource allocation algorithms to increase the signal quality of the user adopting the scheme at the cell edge area. Finally, we solve a global synchronization problem that arisen when the user moves to a sensor network. We have three parts in this thesis. As mentioned above, those parts have a close connection with each other in viewpoint of performance enhancement of the nomadic user, although each part is related to different communication layers. In Part II, we are interested in the physical layer. To improve the point-to-point communication, we propose a space-time coding scheme for decode-and-forward cooperative relaying in a multi-antenna system. The optimal relay gain is derived to maximize the instantaneous block capacity in the high and low SNR regimes respectively. We also provide a symbol combining scheme for the maximum likelihood (ML) receiver. Through the link level simulation, we show the diversity gain in the high SNR regime and capacity improvement in the low SNR regime can be achieved. In Part III, we move to the system-level approa...