Cooperative wireless communications: The impact of channel uncertainty and physical-layer security considerations

In this thesis, cooperative wireless communication strategies are studied in the presence of channel uncertainty and physical-layer security considerations. Initially, achievable rates and resource allocation strategies for imperfectly-known fading relay channels are investigated. Amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes with different degrees of cooperation are considered. The corresponding achievable rate expressions are obtained and efficient resource allocation strategies are identified. Then, the analysis is extended to two-way decode-and-forward (DF) fading relay channels. In the second part of the thesis, the concentration is on wireless information-theoretic security. First, collaborative beamforming schemes for both DF and AF relaying are studied under secrecy constraints. The optimal selection of the beamforming vector is formulated as a semidefinite programming problem and an iterative algorithm is proposed to numerically obtain the optimal beamforming structure and maximize the secrecy rates. In addition, for DF relaying, the worst-case robust beamforming design is identified when channel state information (CSI) is imperfect but bounded, and the statistical robust beamforming design based upon minimum non-outage probability criterion is analyzed. Collaborative relay beamforming for secure broadcasting is subsequently investigated. Novel DF-based null space beamforming schemes are proposed and the optimality of these schemes is investigated by comparing them with the outer bound secrecy rate region. Then, information-theoretic security in cognitive radios is explored. AF relay beamforming designs in the presence of an eavesdropper and a primary user are studied and compared with sub-optimal null space beamforming schemes. Secrecy capacity limits and optimal power allocation of opportunistic spectrum-sharing channels in fading environments are investigated. Finally, secrecy rates are analyzed over weak Gaussian interference channels for different transmission schemes.