Downlink joint subchannel and power allocation in cognitive OFDM systems with QoS guarantee for primary users

In this paper, the problem of joint subchannels and power allocation for a OFDM based downlink cognitive radio system is studied. The joint allocation problem is formulated as an optimization problem under multiple constraints. Different from recent researches, we consider a more practical scenario and choose the outage probability as the constraint guaranteeing QoS of primary users. Then the constraint is transformed to make the optimization problem easier to deal with. The optimization problem is solved by Lagrangian duality method which can realize the joint subchannel and power allocation uniformly. Simulation results show that the proposed scheme can effectively guarantee the QoS of primary users with quick convergence.