 up internationally, for the There are regulations requiring frequency co-ordination between arrangement of emissions within specific frequency bands. Typi- geostationary satellite networks, to ensure that the orbital separation cally, such plans cover frequency bands where radio propagation between satellites can be minimised. The level of interference conditions lead to long interference distances and where system which is to be permitted, as the basis of co-ordination, has been parameters are uniform and change only slowly. The other common raised over the years, allowing the angular separation between application is for mobile systems, where the value of planning is satellites to be further reduced (CCIR, 1990, Recommendations mainly operational. The three basic forms of plan, namely radio 466, 483, 523) SO that more satellites can operate satisfactorily. channelling, frequency allotment and frequency assignment plans, There are regulations setting tolerances on satellite East West sta- are described briefly in Section 26.2.3. tion keeping (ITU, 1990), typically at 0.1°. The accuracy of satellite Planning of this kind can make an important contribution to antenna beam pointing is to be maintained within 10% of the half efficient spectrum utilisation. It provides a means of requiring radio power beamwidth or 0.3°, whichever is the greater. users to implement a set of stringent spectrally efficient operational However, as is apparent from Figures 26.4 to 26.6, interference practices and technical standards in a specified frequency band if between satellite networks arises largely from unwanted radiation they are demonstrably necessary to enable that band to carry the of energy from antennas in the transmit mode (mainly satellite traffic load which is required of it. Also frequency allotment and antenna radiation to locations outside the service area and earth frequency assignment plans provide what may be an efficient station antenna radiation towards arcs of the geostationary satellite method for optimising th