Capacity of Hybrid Spectrum Sharing System and Analysis Model in Cognitive Radio

There are two common spectrum sharing modes for cognitive radio (CR) networks: underlay and overlay. By a combination them, we propose here the hybrid spectrum sharing (HSS) model, where the transmission power is changed according to the states of the occupied sub carrier and interference constraints and thus, cognitive users can dynamically handoff between the overlay mode and the underlay mode. The optimal power allocation algorithm for this HSS system is derived under the condition of maximizing system capacity. Simulation results show that capacity can be significantly increased by the proposed HSS system.