Radio spectrum is today not efficiently utilized because of a complicated and time-consuming radio regulation processes and inflexibility in standardization. In this book, intelligent technologies to help overcoming these barriers, namely, cognitive radios, are discussed.

Access to radio spectrum is frustratingly difficult. The access is restricted by an old radio regulatory regime that emerged over the last 100 years. Large parts of our radio spectrum are allocated to licensed radio services. Open access to most of the radio spectrum is only allowed with very low transmission powers, in a so-called underlay approach, as for example used by Ultra Wideband. The overlay approach, i.e., the free access to open spectrum, is generally not permitted.

Only some small fractions of the radio spectrum, the unlicensed bands, are openly available, under certain limitations. This restricting bottleneck slows down the development of new radio services that can substantially improve our health, safety, work environment, and quality of leisure time.

Cognitive radios coordinate the usage of radio spectrum without involvement of restrictive radio regulation. They operate in spectrum when it is not used by licensed radio systems, and therefore share spectrum with radio systems that have priority access. This is referred to as "vertical sharing". Unused radio spectrum is called a "spectrum opportunity". In the vertical sharing scenario, cognitive radios adapt their transmission schemes such that they fit into the identified spectrum usage patterns of the incumbent radio systems. Note that cognitive radio refers not only to the radio technology: It also requires a revolutionary change in how our spectrum will be regulated. However, with this change and the new cognitive radio approach for open spectrum sharing, it will be difficult to achieve fairness and efficient spectrum sharing. Spectrum etiquette rules, also referred to as policies, are voluntary rules based on mechanisms like dynamic channel selection, transmission power control, adaptive duty-cycles, or carrier sensing. Details about spectrum etiquette are provided in this tutorial. We then provide insights on cognitive algorithms and reasoning based on machine-understandable languages and logics. The support of quality of service in spectrum sharing scenarios is a challenging problem. Decentralized cognitive algorithms on the basis of spectrum observation for mutual coordination are discussed.

Today’s popular IEEE 802.11 WiFi networks are sharing limited available unlicensed spectrum. New technologies, like 802.16 WiMAX, might also operate in these frequency bands. The coexistence and interworking of WiFi and unlicensed WiMAX in the 5 GHz band is therefore discussed in this tutorial. The IEEE 802.11 standard with its extensions for support of quality of service (802.11e), for dynamic radio resource management (802.11h), and for new types of radio resource measurements (802.11k), is a well suited candidate technology for future cognitive radios. In this tutorial, we describe and evaluate these extensions, and describe how they can be used to build cognitive radios.

Lars Berlemann (lars.berlemann@swisscom.com) is project leader at Swisscom Innovations, Berne, Switzerland. Lars has published more than 40 reviewed publications including 6 journal articles and was scientific organizer of European Wireless Conference 2005 and IEEE PIMRC 2005. Before joining Swisscom in August 2006, Lars worked as research assistant and senior researcher at ComNets, RWTH Aachen University, Germany. Lars received his Dr.-Ing. And Masters degree in Electrical Engineering from RWTH Aachen University, Germany, in 2006 and 2002 respectively. He additionally holds a Diploma degree in Business and Economics from the same university.