Optimal Cooperative Relaying for Cognitive Radio Networks with Three Unlicensed Links

In this paper, a two-stage cooperative cognitive radio (CR) network is investigated. The studied model includes three unlicensed sources and receivers (i.e. three unlicensed links), an auxiliary relay network, and a licensed source and receiver (i.e. a licensed link). At the 1st stage, the unlicensed users (i.e. SU) can opportunistically use the spectrum white space when the licensed link is idle, and send their information to the relay network at the same time. At the 2th stage, in which the licensed link can be active, the relay network can send the received copy of the messages to all unlicensed receivers using a suggested cooperative beamforming (CBF) technique. The proposed CBF can concurrently maximize the received signal-to-interference-plus-noise power ratio (SINR) at all three unlicensed receivers and keep the received interference-plus-noise (IN) power at the licensed receiver below a predefined threshold. Therefore, the proposed strategy enables three unlicensed sources to concurrently communicate with their receivers without creating harmful interference at the licensed receiver and ensures the needed quality of service (QoS) for all available links, which is the main objective of the proposed strategy. We optimize the proposed CBF technique by solving an optimization problem with the bisection search algorithm. Simulation outcomes are provided to demonstrate the performance and validity of the suggested strategy.