Cognitive Radios - What are They and Why are the Military and Civil Users Interested in Them

The expected trend toward ubiquitous communications to satisfy user expectations will most likely increase the demand for radio spectrum access, the need for co-existence and inter-working of heterogeneous networks. Most of today\´s radio systems, however, are not aware of their radio spectrum environment and are designed to operate in a specific frequency band using a specific, pre-ordained, spectrum access system. Investigations of spectrum utilisation also regularly show that not all the spectrum is in use at any one time. A radio, therefore, that can sense and understand its local radio spectrum environment and identify temporary vacant spectrum and local users, has the potential to provide enhanced communications services, increase spectrum efficiency and minimise the need for centralised spectrum management. The highly dynamic spectrum access required could be achieved by a radio that can make autonomous (and rapid) decisions on how it accesses spectrum - such radios have come to be known as Cognitive Radios (CRs). Many challenges must be overcome if the promise of CR is to be realised. This includes formulating appropriate rules for the regulation of such radios, co-existence prediction, certification etc. In addition to these the behaviour of CRs in a wide range of civil, military and mixed user scenarios need to be carefully considered and, where necessary constrained, to maximise the economic potential of this new way of accessing spectrum. In this paper we will outline the various forms of CR being considered from licence exempt radios to full licence shared "cognitive" radios. Some key drivers and the benefits of these radios from both a military and civil perspective will be summarised and the potential regulatory/management challenges in controlling such radios will be introduced. The relevance of CR radios to the Antennas and Propagation community will be outlined.