ABSTRACT
The free space path loss (Friis) equation is a bottom–up model which determines the extent to which a radio signal will be attenuated (reduced) as it travels through a vacuum, uninterrupted by any obstacles whatsoever. The International Telecommunication Union’s (ITU) model for determining spectrum demand for International Mobile Telecommunications (IMT) is undoubtedly one of the most sophisticated models in the field. It is an example of a bottom–up approach. Spectrum policy requires an understanding of the relative demand for frequencies from all of the services which need access to the valuable, limited resource. Decisions over who should access which frequencies, and when, are taken internationally at the World Radiocommunications Conference (WRC) which usually takes place once every 4 years. The longer the period between any known facts against which a forecast can be calibrated and the prediction itself, the greater the likelihood of inaccuracies.
