A Cognitive Way to Access the Frequency Spectrum
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Cognitive radio (CR) is an emergent technology in wireless communication. It aims at improve considerably spectrum use by allowing dynamic spectrum access (DSA). The DSA can be performed in different ways, e.g. interweave and underlay approach. In the interweave approach the CR systems can access frequency bands that are not occupied. In the underlay approach, CR systems can transmit over busy bands with a low power spectrum density. In this paper, a new architecture for CR system implementation with a hybrid DSA is proposed. To maintain stability and improve the spectrum efficiency, a system combining interweave and underlay approach is proposed. Using spectrum sensing the CR system determines the free and busy bands. Then, the system performs a classification method to obtain the modulation over the busy bands. Knowing the modulation, the system determines the maximum power to transmit. Over the free bands, the system use interweave approach meanwhile, an underlay approach is use to access the busy bands. When considering an OFDM CR system that cohabits with another OFDM system, simulation results show the performance of the proposed system.