Resource allocation in OFDM-based cognitive radio networks with multiple AF relays

This paper investigates the relay selection and power allocation problems in OFDM-based cognitive radio networks with multiple amplify-and-forward relays. The objective is to maximize the total instantaneous capacity of the cognitive radio network while maintaining the interference introduced to the primary network below a given threshold and also maintaining the total transmit power below the individual power limitations at cognitive radio transmitters. The joint optimization problem is a mixed binary integer problem which is NP-hard. Thus, we divide the joint optimization problem into two subproblems, and solve the resource allocation problem suboptimally. Two suboptimal resource allocation methods are proposed and their performance is compared with the joint optimal resource allocation. Results show that near optimal performance can be obtained with less complex suboptimal approaches.