Limiting harmful interference to the primary users through joint power allocation and beamforming in the uplink of cognitive radio networks

A cognitive radio (CR) network is a secondary network operating in the frequency band and geographical area of a primary network to which the spectrum is licensed. In this paper, we consider a primary broadcasting network consisting of a transmitter and a number of primary users (PUs). The secondary users (SUs) make opportunistic unlicensed spectrum access to communicate with their base station (BS). With this system model, a joint power allocation and beamforming scheme is proposed in the uplink of the CR network to minimize the maximum interference to the PUs in two different scenarios. In the first scenario, the primary transmitter does not cooperate with the CR network and it transmits with a fixed power, whereas it cooperates in the joint power allocation and beamforming scheme and adjusts its transmission power accordingly, in the second scenario. In the former case, our proposed joint power allocation and beamforming scheme finds the beamforming weights and transmission power values under quality of service (QoS) constraints of all SUs, taking into account their maximum transmission power constraints. In the latter case, the proposed scheme finds the beamforming weights of the BS and transmission powers of primary transmitter and SUs under their target signal-to-interference-plus-noise ratios (SINRs) and maximum power constraints. Our approach employs Genetic Algorithm (GA) to determine optimum transmission power values and beamforming weight vectors. Simulation results show the performance of the proposed scheme.