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The fifth generation (5G) wireless communication standard aims to provide users with high speed, reliable and secure communication in areas with dense network traffic. However, increase in the number of wireless devices and high-speed multimedia based services has resulted in acute spectrum scarcity. For this reason, there has been a lot of research interest on techniques that can increase spectrum utilization efficiency. In cellular communications, use of a high frequency-reuse factor and deployment of heterogeneous networks are efforts in this direction. Most of such techniques are limited by their tendency to increase co-channel interference. For this reason, interference management techniques are being investigated by researchers in recent years. Underlay cognitive radio framework offers a natural way to manage interference and increase spectrum utilization efficiency. In this thesis, various optimization and resource allocation issues are examined that maximize secondary throughput in such frameworks. Resource allocation and optimization to maximize secondary secrecy performance is also examined, and use of jamming techniques is investigated. Finally, the impact of underlay frameworks on secrecy performance of the primary network is analyzed.

In a two-hop underlay secondary network, an analytical expression is derived for secrecy outage probability, assuming that a passive eavesdropper overhears the secondary transmission. Unlike prior works, the direct channel from the secondary source to destination is not ignored (by not assuming it to be weak), and that optimal combining of the direct and relayed signals at the …