we consider a joint beamforming,power, and channel allocation in a multi-user and multi-channelunderlay multiple input single output (MISO) cognitive radionetwork (CRN). In this system, primary users’ (PUs’) spec-trum can be reused by the secondary user transmitters (SU-TXs) to maximize the spectrum utilization while the intra-userinterference is minimized by implementing beamforming at eachSU-TX. After formulating the joint optimization problem asa non-convex, mixed integer nonlinear programming (MINLP)problem, we propose a solution which consists of two stages.In the first stage, a feasible solution for power allocation andbeamforming vectors is derived under a given channel allocationby converting the original problem into a convex form with anintroduced optimal auxiliary variable and semidefinite relaxation(SDR) approach. After that, in the second stage, two explicitsearching algorithms, i.e., genetic algorithm (GA) and simulatedannealing (SA)-based algorithm, are proposed to determinesuboptimal channel allocations. Simulation results show thatbeamforming, power and channel allocation with SA (BPCA-SA)algorithm can achieve close-to-optimal sum-rate while having alower computational complexity compared with beamforming,power and channel allocation with GA (BPCA-GA) algorithm.Furthermore, our proposed allocation scheme has significantimprovement in achievable sum-rate compared to the existingzero-forcing beamforming (ZFBF). Joint Beamforming, Power and Channel Allocation in Multi-User and Multi-Channel Underlay MISO Cognitive
RECENT studies reveal that the existing static spectrumallocation is the key reason for highly inefficient spec-trum utilization [1], [2], which in turn leads to a prob-lem of spectrum scarcity. To overcome this issue, a novelconcept called cognitive radio (CR) was introduced [3]–[5],which allows unlicensed users or secondary users (SUs) toinitiate transmissions with the licensed communications. Foran underlay CR network (CRN) coexisting with a multi-channel primary user (PU) network, managing interference isa critical issue since spectrum reusing among multiple usersmay cause negative effects on received signals at both PUsand SUs. By exploiting multiple antennas, a signal processingtechnology calledbeamforming[6] has been introduced to CR for directional signal transmission, so as to effectively mitigatethe mutual interference and improve the signal-to-interference-plus noise ratio (SINR) .
In the literature, joint beamforming and resources allocationhave been widely studied for multiple-antenna CRNs. Forexample, Xieet al.in [8] considered a sum-rate maximizationproblem in a single PU channel CRN. In this work, the mutualinterference between SUs are nullified by deploying the zero-forcing beamforming (ZFBF). The authors in [9] discussed ajoint beamforming and single PU channel assignment problemto maximize the uplink throughput of the CRN while guaran-teeing a SINR constraint at each secondary user receiver (SU-RX) and interference cancellation at the primary user receiver(PU-RX).