Cognitive radio: A path in the evolution of public wireless networks

The concept of cognitive radio has arisen as a generalization of the principle of multiple access in radio channels initially developed in the late sixties and early seventies including the pioneering methods of channel sharing depicted in the ALOHA and CSMA protocols. The intent is to go beyond the context of a single homogeneous system or network with a number of terminals that operate according to a well defined and known physical layer including fixed modulation and error control coding algorithms. The cognitive radio is supposed to be a “smarter radio” in the sense that it can sense channels that contain signals from a large class of heterogeneous signals, networks, and services, and that based on this sensing the radio will implement sophisticated algorithms to share the channel as an additional user, in order to achieve the goals of efficient communication over a shared wireless medium which is ultimately spectrum limited. Included in these concepts is the idea that devices belonging to different systems will have different priorities in accessing the spectrum. One example is the well known classification of users as primary or secondary in the case of the TV spectrum being opened up to new uses. From this standpoint, we may view cognitive radio as generalizing the area of multiple access involving devices in a single homogeneous system, from the physical layer standpoint, to multiple access involving devices in different systems. We may view it as inter-system multiple access as opposed to the more traditional intra-system multiple access.