. power or solar cell arrays with a nominal 12V (or requiring possible use of repeaters to overcome LOS path problems. 48V) d.c., the operational voltages being derived by d.c./d.c. con- In general, the initial cost of the system is significant when only a verters. Power consumption has been minimised by using, for few circuits are provided and the cost of the CS predominates. instance, efficient d.c./d.c. converters, FET amplifiers, low power Subsequently, however, the cost per circuit decreases as more cir- consuming CMOS arrays and surface mount components (Bonne- cuits are added in a flexible manner as the demand grows. Gener- rot, 1987). In some systems, burst mode transmission is also used in ally, the cost per circuit is low when a large number of circuits are the down-link direction (depending on the frame activity) in order provided from an outstation, since the cost of the common hardware to save power. (e.g. RF transceiver) is shared (Figure 52.9). In general, the cost of a circuit provided by radio is constant as a 52.3.9 Frequency re-use function of distance. On the other hand, cable costs generally increase with distance. However, cost comparison with alternative Frequency planning is a complex exercise (Lawson, 1986). In media such as fibre or coaxial cable depends on the extent of considering the use of multipoint systems, it is essential to take existing telecommunications infrastructure and the operational en- account of the following: vironment (CCITT/CCIR, 1976). 52/12 Point to multipoint urban and rural radio Cellular radio systems at 450MHz and 900MHz have proved to be popular in Europe. Although such systems do not provide speech quality as good as that over fixed radio or cable, their popularity is likely to grow rapidly since they offer additional roaming facility. Their use in fixed network (Stern, 1987) may be hindered by lack Number of circuits of spectrum, regulatory constraints and higher infrastructure costs per outstation resulting in higher charges than for fixed service. In Europ