be useful in a commercial context. Military radio equipment does not have the scale economy that cellular phones enjoy. On the other hand, military radios do not have the same cost constraints and may not have the same weight constraints and may be able to use more exotic battery technologies than cellular phones. Components can also be aggressively toleranced to improve performance. This means that the development of a radio technology for military applications does not necessarily guarantee that the technology will be useful in a commercial context. Two examples are software-defined radio, a radio that can self-redefine its modulation and channel coding and cognitive radio, a radio that can scan and then access available radio resources. Software-defined radio is used extensively in military radio systems, partly to overcome interoperability issues. Translating software-defined radio techniques to cellular radio has, however, proved problematic partly because of cost and performance issues including battery drain but also because in the commercial sector interoperability issues have been addressed more effectively through harmonisation and standardisation though this is now beginning to change. Cognitive radio provides another example. Usually combined with software-defined radio, cognitive radio is useful in a military context because radio systems can be made flexible and opportunistic. This makes them less vulnerable to interception and jamming. Cognitive radio is presently being proposed for use in white-space devices in the US UHF TV band and being propositioned for use in other markets including the UK. These devices are designed to sit in the interleaved bands not being used by TV broadcasting (covered in more detail in Chapter 15) There is, however, an important difference. In a military context it does not necessarily matter if cognitive radios interfere with other radio systems. In a commercial context, a guarantee that radios will not create interference is a precondition of deployment. Interference 