Joint admission control and beamforming with adaptive modulation for cognitive radio network

This paper considers the spectrum sharing multiple-input multiple-output (MIMO) cognitive radio network, in which single primary user (PU) coexists with multiple secondary users (SUs). Joint beamforming and admission control with adaptive modulation technique is designed to maximize the number of the serviced SUs and the transmit rate of the secondary links while imposing upper limits on the interference temperature to the PU by using the least transmit power. In the proposed cross-layer design, the SINR target is dynamically adapted with channel condition and bit-error rate (BER) requirement, and works as admission control implicitly, that is, the cognitive link is dropped as long as its SINR requirement is equal to zero. With the pre-fixed receiver, the multi-objective optimization problem is NP-hard, which is further transformed into single problem by introducing a utility function. The optimum solutions are achieved via second-order cone programming (SOCP) with an iterative bisection search method. Simulation results show that the proposed scheme achieves desirable spectrum and power efficiency, and the maximum number of the total active SUs are intelligently selected.