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This context addresses the subcarrier and power allocation problem in the uplink of an OFDMA system under the cognitive radio environment. The objective is to maximize the sum transmission rate of secondary users, without causing adverse interference to the primary users. We formulate the optimization problem subject to the individual power constraints and the interference constraints. We also propose two suboptimal power loading algorithms that are less complex and a new subcarrier allocation algorithm. The performance of the optimal scheme is compared with the performance of the suboptimal. Simulation results show that the optimal algorithm significantly improves the sum transmission rate, and provides good convergence.