User's Manual

5 Radio Network Planning
APCD-LM043-4.0 63
approach would be to assign a higher frequency to sector A, such as 915MHz or
925MHz.
Figure 31 Network Design in the Presence of Out-of-band Interference
5.2.5 Using Bandpass Filters at CAP Sites
WaveRider provides high-quality, specially designed bandpass filters for use with the CCU.
These filters reduce the effect of unwanted out-of-band and off-channel in-band interference.
As discussed in Propagation Path on page 31, it is highly desirable to locate the CAP site so
that the CCU antennas are high enough to provide clear line of sight paths to the maximum
number of EUMs in the serving area. The goal is to make sure the CCU can see the maximum
number of EUMs and conversely, to make sure the maximum number of EUMs can see the
CCU.
Attaining this goal, however, has a consequence since it may mean the CCU will be in an ideal
location to see interferers in its sector as well. Bandpass filters at the CCU reduce the effect of
interference from out-of-band or off-channel in-band interferers.
On-channel interference may result from
• on-channel interferers in the ISM band, or
• transmitter phase noise or intermodulation products generated by out-of-band
interferers.
Bandpass filters cannot resolve on-channel interference; instead, you must change to a more
suitable CCU operating frequency.
For CAP sites in which multiple CCUs are installed, use of bandpass filters to ensure non-
interfering operation of CCUs is mandatory. It is important to remember that in the 900 MHz
ISM band, the radio transmit and receive occur on the same frequency and use Time Division
Duplexing (TDD) to switch between the transmit and receive cycles. Multi-CCU installations
pose the highest threat of CCU to CCU adjacent channel interference. For the RF network
Sector C
Sector A
Sector B
Cellular
Transmitter
CAP