Power minimization in uni-directional relay networks with cognitive radio capabilities

In this work, we consider a uni-directional (one way) relay network with a pair of primary transmitter and receiver which are relay-assisted by multiple cognitive radio (CR) terminals. A CR base station is deployed to sense the absence/presence of the primary user based on the received signal-to-noise ratio (SNR) at the fusion center. The primary network utilizes a two-step one-way amplify-and-forward (AF) relaying scheme and uses the CRs as its relay nodes. In the first step of AF relaying, the primary transmitter sends its signal to the CRs/relays. A distributed beamforming is then performed in the second step of relaying. In this phase, the CR base station sets the beamforming weights of CR terminals to satisfy the SNR requirements at the primary transmitter and at the CR base station. We aim at minimizing the power dissipated in the cognitive (relay) nodes together with ensuring an accurate spectrum sensing process. This optimization problem is efficiently solved by using semidefinite relaxation (SDR) techniques. Simulation results are provided to compare the relay transmit power in our investigated network with that in a conventional AF relay network.