Joint power control and beamforming for cognitive radio networks

We consider a secondary usage of spectrum scenario where a secondary network coexists and/or shares the radio spectrum with a primary network to which the spectrum is licensed. The secondary network uses cognitive radio technology to make opportunistic access of the unused and/or underutilized portions of the spectrum. For such a system, we study the problem of joint power control and beamforming with the objective of minimizing the total transmitted power of the cognitive network such that the received interferences at primary users remain below a threshold level as well as the secondary users who are admitted in the system are guaranteed with their signal to interference plus noise ratio (SINR) requirements. Two iterative algorithms, one based on weighted least square (WLS) approach and the other based on admission control for secondary users, are provided to meet the strict interference protection requirement of the primary users. A numerical study is performed to show the convergence behavior of the iterative algorithms.