Subcarrier and power adaptation for multiuser OFDM-based cognitive radio systems

This paper investigates the subcarrier and power allocation problem for an OFDM-based multiuser cognitive radio (CR) system. For CR systems it is important to keep the interference introduced to the primary user (PU) band within a tolerable range. Since the joint subcarrier and power allocation problem is a non-convex integer problem and a closed form solution is difficult to find, a suboptimal algorithm that separates subcarrier and power allocation is proposed. First, a suboptimal subcarrier algorithm is proposed that allocates subcarriers to CR users that not only increase the capacity, but also reduces the interference introduced to the primary user (PU) band. Further, for a given subcarrier allocation an optimal power loading algorithm is proposed that maximizes the capacity of CR users while keeping the interference introduced to the PU band and the total power below a threshold. Simulation results show that for CR systems the proposed algorithm is able to load power into the subcarriers while keeping the interference below a specified threshold.