Dynamic resource allocation for cognitive radio

Cognitive radio (CR) has been recognized as an effective way to improve the spectrum utilization by allowing unlicensed secondary users (SUs) to coexist either opportunistically or concurrently with the licensed primary users (PUs). Two models of CR operation have attracted most attention, namely, opportunistic spectrum access (OSA) and spectrum sharing. While the former allows only opportunistic transmission of the SUs through spectrum sensing, the latter one permits concurrent transmission by imposing the interference power constraint. In both models, SUs have to strike a balance between optimizing its own performance and maintaining sufficient protection to the PUs. Therefore, efficient resource allocation methods need to be investigated to balance this tradeoff. In this thesis, two major resource allocation problems are studied, namely, sensing-access design in the OSA model and secure transmission in the spectrum sharing model. In the OSA model, the thesis investigates the sensing-access design which aims to balance the intrinsic tradeoffs between the sensing requirement to protect the PUs and the access need to improve the SUs' own performance under two different multi-channel sensing schemes. Specifically, for the case of parallel channel sensing where an SU can sense multiple channels simultaneously, the sensing-access design includes the sensing strategy specifying the optimal sensing time and the access strategy determining the optimal power level upon transmission. The objective is to maximize the sum achievable throughput under the sum transmit power constraint such that the PUs are well protected on each channel by a fixed probability of detection constraint. For the case of sequential channel sensing where an SU can sequentially sense the channels one at a time, the sensing-access design includes the sensing strategy determining when to stop sensing and start transmission, the access strategy specifying the transmit power level upon transmission, and the sensing order design telling the SU which channel to sense next if the current channel is given up for transmission. The objective is to maximize the energy efficiency of the sequential channel sensing process such that the PU is sufficiently protected under a fixed probability of detection constraint. In both schemes, we derive the structures of the optimal sensing-access strategies and propose efficient algorithms to compute the optimal solutions.DOCTOR OF PHILOSOPHY (EEE