Next generation cognitive cellular networks: spectrum sharing and trading [Guest editorial]

In the past few years, fundamental research has demonstrated great potentials of cognitive radio (CR) in increasing the spectrum agility and system capacity of wireless communications systems. With the ability to detect and adapt to the surrounding environment, CR has become one of the widely recognized features for future wireless communication systems. Specifically, CR has been recommended as a key technology to solve the spectrum scarcity problem in the next generation cellar networks. For example, the IEEE 802.16h standard was recently published for the license-exempt operation of WiMAX networks by defining a set of CR capabilities. On the other hand, a lot of efforts are being made to introduce CR features into 3GPP LTE-Advanced.