1. An Overview of Cognitive Radio Networks

Wireless communication is the fastest growing segment of the communication industry. With the successful deployment of cellular networks in licensed bands and Wi-Fi networks in unlicensed bands, users have anytime, anywhere connectivity with the networked systems leading to the Internet of Things (IoT). Traditional wireless networks rely on static spectrum assignment where the government regulatory bodies, such as the Federal Communication Commission (FCC) in the United States, assign the Radio Frequency (RF) spectrum to the service providers in an exclusive manner for long term and vast geographic area. Most of the usable RF spectrum are already assigned to certain services leaving no bands for further development of new wireless systems. Furthermore, when everything (such as refrigerator, microwave oven, smart car, etc) is connected to internet, this scarcity would be more severe. However, recent studies show that the static RF spectrum assignment leads to inefficient use of RF spectrum since most of the channels are used only from 15 to 85 % or idle most of the time [2, 12, 14]. Thus the bottleneck created is not because of lack of RF spectrum but because of wasteful static assignments of RF spectrum for long-time and vast geographic area. In this chapter, we present an overview of cognitive radio network, spectrum sensing techniques, and spectrum access methods.