Power allocation and user satisfaction-based switching method in cognitive radio MIMO system

Secondary users (SUs) should have power constraints because primary users (PUs) should not be interfered by SUs in cognitive radio (CR) network. Therefore it is important for SUs to maximize throughput and ensure quality of service (QoS) on the premise of generating no interference to PUs. In this paper, SUs are equipped with multiple antennas. Multiple-input multiple-output (MIMO) wireless communication systems can offer high data rate or reliability through spatial multiplexing or diversity. Therefore we present a method which user satisfaction-based on switching between spatial multiplexing and transmit diversity to maximize total user satisfaction. When we use spatial multiplexing, user satisfaction is formulated as a function with data rate and power consumed. In case we use transmit diversity, user satisfaction is formulated as a function with reliability and power consumed. For estimating reliability, we provide a novel bit error rate (BER) equation. And we use different power allocation method in each case. We apply capped water-filling method for spatial multiplexing and Lagrangian method for transmit diversity. Simulation results show that proposed switching scheme increase user satisfaction. And we study the effect of interference of PU on the performance.