Research On Secure Two-way Relaying In Cognitive Wireless Networks

Cognitive radio and cooperative relaying,as two hot techniques in the wireless field,can improve effectiveness and reliability of wireless communications.Based on the effectiveness and reliability,the security of wireless communications has become the focus in current research.Due to the openness of wireless channels,however,wireless communications are much easier to be attacked.It is worth-mentioning that conventional cryptography scheme based secure methods are much more susceptible when the eavesdropper has powerful computing capabilities or the cryptography keys are distributed on wireless channels directly.Physical layer secure technologies can provide secure transmission-links of a legal communication peer,and guarantee absolute security in theory.This thesis investigates secure two-way relaying with an active eavesdropper in cognitive wireless networks.First,an optimization problem concerning the minimization of system transmit power subject to secure capacity of the source is studied under the cases that the interference power of eavesdropper is known and unknown,giving a secure beamforming method at the source.Simulation results verified that the proposed beamforming method can reduce the transmit power.Second,a joint beamforming and power allocation technique maximizing the secure capacity of the system is proposed.Simulation results confirmed that the joint technique can increase the secure capacity of the system.Third,considering a two-way relaying system with multiple relays,secure relay selection is investigated with the goal of maximizing the secure capacity or minimizing the transmit power of the system.As a result,two optimal and suboptimal relay selection strategies are proposed.Simulation results confirmed the effectiveness of the proposed strategies and the superiority of the optimal strategies.