Frequency band sharing: utopia or reality towards specification of operational scenarios

The increasing numbers of equipment using the electromagnetic spectrum obliges the ITU (International Telecommunication Union) to place more constraints on frequency allocation. The main condition of success of this policy has so far been that the transmitted spectra were confined within limits representing the spectrum extensions just about necessary to fulfil the functions of each piece of equipment, the main objective being to obtain the "best spectrum efficiency" by placing the spectra one next to the other. Nowadays the ITU tends to increasingly authorise a greater sharing of bands. All manufacturers will then be obliged to insist not only on the limits and levels of transmitted spectra according to ITU recommendations but also on a higher risk of jamming. One has also to remember that radioastronomy, and other similar radio sensing techniques (i.e. receiving not transmitting) are unique in their use of precious spectrum resources: all that is required is clear access to the frequency spectrum, because radioastronomy and radio sensing techniques are highly vulnerable to environmental pollution. The increasing number of equipment entails the need to share the same band in the same geographical area between various services. This is contemplated, for example, for the operation of UMTS/IMT 2000 network and air traffic control radionavigation systems in the 2700-2900 MHz band. The usual optimal bands for radar (L, S, X, Ku) which are of course the most frequently used for civil and military applications, are now becoming also optimal for new services. This is for example the case in the S band for mobile phones and the Ku band for TV broadcasting by satellite. The compatibility of equipment is important, in particular to ensure the integrity of certain services (instrument landing equipment). However this compatibility does not only apply to a few isolated fittings, but to a whole complex environment which comprises (a) a large number of fittings and (b) a great variety of operations.