ADC InterReach Fusion Installation, Operation And Reference Manual page 100

Link Budget Analysis
Consideration Description
Noise Rise On the uplink, the noise floor is determined not only by the Fusion system, but also by the number of
mobiles that are transmitting. This is because when the base station attempts to de-spread a particular
mobile's signal, all other mobile signals appear to be noise. Because the noise floor rises as more mobiles
try to communicate with a base station, the more mobiles there are, the more power they have to transmit.
Hence, the noise floor rises rapidly:
where loading is the number of users as a percentage of the theoretical maximum number of users.
Typically, a base station is set to limit the loading to 75%. This noise ratio must be included in the link
budget as a worst-case condition for uplink sensitivity. If there are less users than 75% of the maximum,
then the uplink coverage will be better than predicted.
Hand-off Gain CDMA supports soft hand-off, a process by which the mobile communicates simultaneously with more
than one base station or more than one sector of a base station. Soft hand-off provides improved receive
sensitivity because there are two or more receivers or transmitters involved. A line for hand-off gain is
included in the CDMA link budgets worksheet although the gain is set to 0 dB because the in-building
system will probably be designed to limit soft-handoff.
6-32
CONFIDENTIAL
Additional Link Budget Considerations for CDMA (continued)
Table 6-24
noise rise = 10log (1 / (1 – loading))
10
Other CDMA Issues
• Never combine multiple sectors (more than one CDMA signal at the same fre-
quency) into a Fusion system. The combined CDMA signals will interfere with
each other.
• Try to minimize overlap between in-building coverage areas that utilize different
sectors, as well as in-building coverage and outdoor coverage areas. This is impor-
tant because any area in which more than one dominant pilot signal (at the same
frequency) is measured by the mobile will result in soft-handoff. Soft-handoff
decreases the overall network capacity by allocating multiple channel resources to
a single mobile phone.
InterReach Fusion Installation, Operation, and Reference Manual
D-620610-0-20 Rev D