1.A joint resource allocation algorithm for multiuser OFDMbased cognitive radio systems

In spectrum sharing environments,the resource optimization problem which consider both transmit power constraints of cognitive users and interference power constraints of primary users,is studied for multiuser OFDM based cognitive radio systems.With the objective of maximizing the sum rate of cognitive users,the multi-level waterfilling power allocation is analyzed under the constraint of continuous bit rate constraint.For the more practical condition when integral bit rate requirement is present,the joint method of subchannel selection based on RG factors as well as bit and power allocation based on multi-constraint greedy mechanism is proposed to enhance the spectrum efficiency.Simulation results show that the proposed joint subchannel,power and bit allocation algorithm could make efficient use of spectrum with various system parameter values.