Operation Manual

113
Chapter 6 RF Commissioning
In order to make the process more clear for this part of the manual we will consider setting up a fictitious system,
but based on a standard approach at doing Fiber-DAS. The system that we are considering will have two frequency
bands, let’s assume GSM 900 MHz and UMTS 2100 MHz. The example will have 2 sectors with two remotes in each
sector. Of course your system may look different, be more or less complex but in order to make it clear how the
system is set up this should provide you with a starting point.
Setting up the uplink
Setting up the uplink means to adjust the system for an optimal working point from the antenna port of the Remote
Unit to the actual input on the Radio Base Station. This can be done in different ways depending on how the system
is designed. We will here discuss a standard set-up starting with a small block schematic showing how the system is
connected.
Figure 135
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System Interconnect Diagram
The main parameter that we will be discussing is the ”net gain” of the system. This means the total change in signal
from the Remote Unit antenna port to the receiver port on the base station. There are different ways of setting this
system up but we will look at a 0 dB net gain system which is a good starting point for most systems.
The system gain can be calculated as the gain in the Remote Unit – Loss on fiber + FOI gain – ICU loss + BIU gain –
coupler loss. Basically this takes form of a link budget and here is an example:
Table 72
Unit/Component Gain/Loss (dB) Accumulated Gain/Loss (dB)
Remote Unit (RU)
40 40
Fiber-Optic Cable
-10 30
FOI
20 50
ICU
-35 15
BIU
0 15
Coupler
-15 0
Example Link Budget
Basically this means that whatever is input at the antenna will also be seen at the same level for the Radio Base
Station receiver. This is not a bad starting point but does not take into account the noise load on the base station
which will increase somewhat with this setup.