User's Manual

Link Budget Analysis
6-26 InterReach Fusion Installation, Operation, and Reference Manual
CONFIDENTIAL D-620610-0-20 Rev F
6.6 Link Budget Analysis
A link budget is a methodical way to account for the gains and losses in an RF system
so that the quality of coverage can be predicted. The end result can often be stated as
a “design goal” in which the coverage is determined by the maximum distance from
each RAU before the signal strength falls beneath that goal.
One key feature of the link budget is the maximum power per carrier explained in
Section 6.3. While the maximum power per carrier is important as far as emissions
and signal quality requirements are concerned, it is critical that the maximum signal
into the Main Hub never exceed 1W (+30 dBm). Composite power levels above this
limit will cause damage to the Main Hub.
WARNING: Exceeding the maximum input power of 1W (+30 dBm)
could cause permanent damage to the Main Hub.
NOTE: Visit the TE customer portal at http://www.te.com/adc for the
on-line Link Budget Tool.
6.6.1 Elements of a Link Budget for Narrowband Standards
The link budget represents a typical calculation that might be used to determine how
much path loss can be afforded in a Fusion design. This link budget analyzes both the
downlink and uplink paths. For most configurations, the downlink requires lower
path loss and is therefore the limiting factor in the system design. It is for this reason
that a predetermined “design goal” for the downlink is sufficient to predict coverage
distance.
The link budget is organized in a simple manner: the transmitted power is calculated,
the airlink losses due to fading and body loss are summed, and the receiver sensitivity
(minimum level a signal can be received for acceptable call quality) is calculated. The
maximum allowable path loss (in dB) is the difference between the transmitted
power, less the airlink losses, and the receiver sensitivity. From the path loss, the
maximum coverage distance can be estimated using the path loss formula presented
in Section 6.5.1.
Table 6-22 provides link budget considerations for narrowband systems.