This paper discusses finding an optimal solution, by using the Pareto boundary of the power gain region, to realize the secrecy rate performance in a cognitive radio (CR) environment with the existence of a multi-antenna equipped eavesdropper.

The multi-antenna primary transmitters (PTs), primary receivers (PRs), secondary transmitters (STs), secondary receivers (SRs), and a multi-antenna eavesdropper node with unknown wiretap target are the players in the scene. The STs constitute a cooperative transmission association among the chosen nodes. They organize dynamic transmission clusters by sharing channel-side information. A virtual multi-input multi-output (MIMO) transmission scheme to perform distributed collaborative beamforming is created: a virtual secondary transmitter (VST).

An overlay coexistence radio technique, spectrum leasing policy for STs, is devised to improve the secrecy performance of the whole network and maximize the worst user’s secrecy rate.

Parameterizing the Pareto boundary of the power gain region in the multi-user, multi-input single-output (MISO) environment is the key and starting lemma in the paper. Maximum power gain values around the single antenna receivers at different directions, achieved by multi-antenna transmitters, form a region that is called the outer boundary of the process gain region. This boundary is relaxed by using the Pareto boundary theorem; its effective parameters, like power adjusting, eigenvalues, channel gains, and dissemination powers, are defined. This view is extended to a new scenario where multi-antenna receivers are present and their secrecy performance rate discussed with the existence of an eavesdropper, in the aforementioned framework.

Although the reasoning in the paper is strongly coupled with one of its references, it doesn’t tarnish its contribution to the problem of deploying the framework in the MIMO scenario and achieving valuable results.