The Evolution of Cognitive Radio Systems: Part 1

This 10-part series discusses the notion of “cognitive” radio, the combination of a radio transceiver with computerized intelligence to automate coordination of devices, networks and services for improved functionality, interoperation and spectrum utilization. The term originates from parallels with biological systems that interact with their environment using a regime of goals, sensory inputs and reactive behaviors to sustain themselves.

Cognitive radio, formerly the interest of a few, has now entered the “group think” environment, where “cognition” means many things to many people. Outgrowths of the concept have been advanced to address a variety of next-generation wireless origins and current forms. The author also attempts to forecast how FCC cognitive radio rulemaking may proceed in connection with its initiatives to achieve higher spectrum productivity.

What is Cognitive Radio?

Like many modern concepts, “Cognitive Radio” is not entirely new, but rather an amalgam of manual radio resource management techniques invented and proven earlier for enhancing the performance of wireless communication systems, now automated by a computer. Simply put, cognitive radio is the combination of a radio transceiver with computerized intelligence to automate coordination of devices, networks and services for improved functionality, interoperation, and spectrum utilization.

Recently, a focal point has become coexistence of radios in common spectrum. It is termed “cognitive” because the actions it is envisioned to take are analogous to the way a biological entity reacts to its environment based on a regime of goals, sensory inputs, and behaviors. Cognitive radio has become a topic of interest lately because of two important changes in the radio application space:

1. The growth of personal portable communications services
2. The need to provide enough suitable spectrum for such services

Personal communications has changed the face of two-way radio from a microwave relay, push-to-talk, and mobile telephone world to mainstream, anytime, anywhere wireless for the masses. Cellular telephone started this revolution in the 1980s, but today’s broadband multimedia wireless networks have carried the banner forward.

Even at its inception, the very nature of cellular radio dictated some level of cognition: the systems depended upon devices to detect an available wireless network, interact with it to allow a connection to be set up, and to maintain the connection as the user moves about. It is fortunate indeed that cellular and microcomputer technology arose contemporaneously, as much of what cellular telephony has become would have been impossible otherwise. In today’s advanced radio networks, even more is expected: wireless devices may actually be parts of the network as well as clients (as with forwarding mesh topologies), they may have to accommodate a variety of media, rates, and QoS needs, and they may have to operate in a spectrum that is shared with other services while minimizing interference. They may even have to recognize exactly where they are and to notify other devices or networks.

The Origins of Cognitive Radio

Having begun almost 100 years after the development of wired technologies, radio has traversed several stages of maturation, the latest of which is the exploitation of the signal processing techniques that had proved so successful in making broadband transmission possible using wires. However, adoption of these techniques has also forced radio engineers to reconcile with Shannon: Information theory increases consciousness of the bandwidth resource, link attenuation, power and noise floor as fundamental limits of reach and rate. This entry into the “Shannon Zone” has also sparked the realization that spectrum is finite and not all of it is necessarily appropriate for every application.

The realization that spectrum is finite is easily visualized if one thinks of a wireless “cell” as a coaxial cable of the same diameter. Individuals within the cell/cable must share the RF medium efficiently with others while minimizing interference. With wires, one can always add more cables to fixed-use locations because the spectrum is contained and can be reused almost infinitely; with wireless the spectrum is much less contained and can be reused only to the extent to which smaller cells can be used. Even with small cells, the spectrum resource may have to be divided among a significant number of users within the coverage area. With appetite for wireless broadband connections increasing, cells must inevitably become smaller with better resource reuse and higher-channel spectral efficiency absent vast amounts of new spectrum.

In the end, one might envision a “Shannon Communication Volume” (SCV) expressing the maximum number of users at a particular rate that can be sustained over a geographic area in much the same way as the Shannon limit is now routinely used to bound the “reach” and “rate” of transmission over wires.

The Communications Act of 1934 established the FCC as the manager of spectrum for citizens of the United States and a regime of licenses, regulations, and process thereafter ensued to ensure that spectrum use was organized, productive, and efficient. In a sense, the FCC’s goal has been to maximize the SCV of the United States by building rules for various radio services one-at-a-time into a large body of regulations.

Part 2 coming soon…