Smart Cooperation with Network Coding in Hierarchical Wireless Networks

Abstract: To achieve more dynamic, efficient and intelligent use of the scarce wireless spectrum resource, the concept of cooperation has been formalized into several hierarchical network models in future mobile networks. Cooperative communications, such as relaying, can potentially increase communication efficiency and spectrum utilization due to the broadcast nature of wireless networks, and may lead to a better support for diverse communication modes with flexible spectrum sharing. In this thesis, we investigate the cooperation between users with different priorities in hierarchical wireless networks. Especially, by coinciding the idea of relaying and network coding, we explore cooperation schemes from several aspects.First we discuss orthogonal time-frequency access for cooperation between primary and secondary users in a cognitive radio network, where two binary network coding schemes are developed. We analyze the transmission process and propose a novel methodology for performance evaluation. Second we propose a selective cooperation mechanism for intelligent resource sharing. By evaluating the system throughput with the approxiamtion method, we further discuss the spectrum sharing strategy by formulating an optimization problem to maximize the secondary system throughput. Besides, we extend our model to larger cognitive radio networks with multiple primary/secondary users. Finally we investigate non-orthogonal multiple access combined with orthogonal multiple access with hierarchical users. We define and study two cooperation schemes, where we derive the achievable rate regions with diverse communication modes supported. We formulate a problem jointly optimizing the strategy on time sharing and transmit power allocation at transmitters.Throughout the thesis we progressively reveal the importance of smart cooperation in hierarchical wireless networks, through rendering our models more realistic with smart strategies.