Cognitive Radio networks: A survey

Cognitive Radio (CR) technology is developed to overcome the spectrum scarcity due to rapid development in wireless networks. Both licensed and unlicensed users can utilize the spectrum using this technology. Spectrum is allocated dynamically in cognitive radio networks thus it increases the spectrum utilization. The unlicensed users can transmit in the vacant spectrum already assigned to licensed users with minimum level of interference. It senses the spectrum to find the vacant spectrum and choose the best spectrum which meets the required QoS of the unlicensed users. The unlicensed users leave the spectrum whenever the licensed users return. This paper tries to give a comprehensive description of cognitive radio and its functions such as spectrum sensing, spectrum decision, spectrum sharing and spectrum mobility.