User's Manual Part 1

5: Radio Network Planning
APCD-LM043-8.0 (DRAFT C) 79
The location of the CAP site in relation to the serving area determines whether the site will be
a corner- or center-illuminated cell. Figure 38 illustrates the difference between these two
methods of illumination.
Figure 38 Corner- and Center-illuminated cells
Although the difference between the two approaches may seem academic at first, the choice
you make affects the system design, in particular, the selection of sites, site antennas, and the
system growth path.
Center Illumination
A center-illuminated cell is generally the simplest to implement. In this case, a site is
established at a suitable location near the middle of the target serving area. An omnidirectional
antenna is usually installed to deliver 360-degree coverage around the site.
When system traffic increases beyond the capacity of a single CCU because, for example,
many subscribers have been added to the system, more CCUs can be added to the CAP site
(up to a total of three operating CCUs per CAP site). The omnidirectional antenna would, in
this case, be replaced with sectored antennas, for example, three 120-degree sectored
antennas. The selection of the sectored antennas would depend on how evenly the
subscribers are distributed throughout the serving area. In this example, the resulting
CAP
CAP
Center-
Illuminated Cell
Corner-
Illuminated Cell
Serving Area