An SINR Balancing Based Beamforming Technique for Cognitive Radio Networks with Mixed Quality of Service Requirements

We consider an underlay cognitive radio network, in which the cognitive users (also referred to as secondary users (SUs)) are allowed to access the licensed spectrum simultaneously with the primary users (PUs). Specifically we solve a beamforming and power allocation problem in the downlink with mixed quality-of-service (QoS) requirements where a set of SUs are required to achieve a specific signal-to-interference and noise ratio (SINR) targets whilst the SINRs for the remaining SUs are balanced. This mixed QoS requirement problem is more complicated in the downlink because of the coupled structure of beamformers and power allocations. Hence, we solve an equivalent uplink problem based on the uplink-downlink duality and subgradient method. An iterative algorithm is proposed to determine the optimal beamformers and power allocation. Simulation results are provided to validate the optimality of the result and the convergence of the proposed algorithm.