ances can be used up by a single call with low enough path gain. Since poor coverage is a capacity-limiting phenomenon, even the early stage of CDMA system development is a capacity engineering phase. We also would point out that those people who engineer conventional reuse and those people who design initial system layouts come from the same community of wireless telephony engineers as long-term CDMA capacity planners. We should not be too sur- prised if "those people" turned out to be us. What is our point? That the automatic radio reuse and automatic power control of CDMA may make our lives easier in some important ways, but we still had better learn about radio propagation models and how to use them if we want our CDMA systems to carry the quantity of calls the financial planners promised the investors who ultimately pay us. 47.2 Variation in Radio Propagation The cellular principle depends on radio path gain decreasing considerably as a cellular telephone gets further away from a base station. This is true for the most part, but real- world radio has some surprises. Terrain has a dramatic effect on radio propagation. Higher-frequency radio waves are less likely to find their way around hilltops into the valleys beyond. And increasing demand creates increasing pressure to move wireless telephony into higher frequen- cies. The 900-MHz band was bold in 1977, whereas 1800 MHz is routine for cellular service in 2002. Cellular engineers, who had to pay some attention to orography¹ in planning Advanced Mobile Phone System (AMPS) networks, are faced with more seri- ous engineering challenges in hilly terrain and at higher frequencies. The less obvious impairment is the texture of the ground. Pavement is highly reflec- tive, whereas shrubbery is not. Big leafy trees not only impair microwave transmission, but their impairment is seasonal. Weather is less of an issue for us wireless telephone folks than it is for higher- frequency microwave engineers. The rain factor at 30 GHz is serious, several decibels at a typical