In this paper, an optimal spectrum sharing strategy is proposed to enhance the sum capacity of the secondary users (SUs) in multiuser orthogonal frequency division multiplexing (OFDM)-based cognitive radio network. Even though many schemes are available for spectrum sharing, improvement is needed due to practical constraints in wireless communication. Here, energy efficient clustering based resource allocation (RA) method is presented in which all the SUs are placed into different groups based on their interference degree. The different groups can use the same subchannels which improves the efficiency of the spectrum utilization. Then, resource allocation algorithm is implemented in each group to maximize the sum rate of the SUs in each cluster. The simulation results show that the sum rate of all SUs in each group is significantly improved compared to existing approaches. Moreover, our proposed RA algorithm converges stably and quickly.
