WaveRider LMS4000, User Manual

Page: 84 / 282

5 Radio Network Planning
66 APCD-LM043-4.0
configuration would triple the traffic-handling capacity of the site. Figure 33 illustrates the
sectoring of a previously center-illuminated omnidirectional cell.
Figure 33 Sectored Cell
Corner I llumination
Corner illumination is generally used when it is not possible to establish a suitable CAP site
near the middle of the target serving area. Implementation of a corner-illuminated cell requires
more extensive site and system engineering than does the implementation of a center-
illuminated cell. This is particularly true when additional traffic-handling capacity is required,
since techniques such as overlay/underlay sectors (adding a second CCU to provide coverage
to the same geographical area) may have to be applied.
The use of omni-directional antennas at CAP sites, although simple in implementation, is only
recommended for simple network installations with low risk of interference and limited
exposure to other sites. Omni-directional antennas, by definition, are designed to provide
coverage in all directions (360°) horizontally around the antennas. This wide angle-of-view
provides for simplicity of an omni-directional antenna installation but also means that the omni-
directional antenna is susceptible to any interference in the area. As such, the RF network
designer, when faced with interference or system expansion will generally need to replace the
omni-directional antenna(s) (and possibly multiple CCUs) in order to serve the same coverage
area and to make use of the directional properties of the antennas to address system issues.
System Loading
Sometimes, even with well-engineered RF coverage, the user traffic may be so high that you
need to expand the network to a multi-CAP system.
The answer to the question “How many subscribers can each CCU support?” is a qualified “It
depends.” Refer to
Performance Modelling on page 42 for a description of the method used by
WaveRider to predict the number of end-users that can be supported by the LMS4000
network. Total system traffic is very dependent on the usage profile of the end users and the
tariff structure that has been implemented by the system operator. For instance, an LMS4000
900 MHz system that is providing service to a number of small businesses, each supporting
CAP