ipoint systems in ations have led to earlier implementations of binary (ASK) ampli- built up areas is often the non-availability of LOS paths between a Rural multipoint systems 52/7 subscriber building and a CS. Studies have therefore been carried bands. More recently, following the FCC's authorisation in the out in estimating the number of CSs necessary to provide service to U.S.A. of the use of v.h.f. and u.h.f. bands (150MHz, 450MHz and a certain percentage of customers in a large city (Ogawa, 1984b). 800MHz) for basic exchange telecommunications radio service These rely on the availability of actual building density and height (BETRS), 'basic exchange radio' (BEXR) systems (Bellcore, 1989) distribution information from which the probability of obtaining have been designed for 450MHz band (McGuire, 1989; Mullen, LOS paths is calculated statistically. 1989; Lin, 1990). For rural systems hop lengths can be up to 30km The effect of building reflections has also been examined but it to 50km depending on the terrain and the frequency of operation. has been shown that a very small percentage of subscribers are However, by using synchronised repeaters, the range can be in- likely to be affected from these (Ogawa, 1984b; Rhese, 1986). Other creased further to more than 300km. Designs of these systems have studies (Yoshida, 1984; Dupuis, 1983) have estimated the coverage been influenced by the following factors: area for high frequency systems requiring LOS paths between transceivers e.g. as a function of antenna heights. 1. Systems are required to operate over hostile terrain with poor road access. 52.2.8 Applications 2. Inadequacy of primary power supplies makes solar powered system operation highly desirable. The urban multipoint systems are generally used for serving the 3. Equipment maintenance must be simplified. needs of business customers (e.g. financial and banking com- 4. Equipment must have high reliability. munity) over relatively short distances in built up cities (Rhese, 5. Equipment cost must be low. 198