User Manual

DELTANODE FIBER DAS MANUAL
©DeltaNode Solutions 2012
40
Revision 12-03
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.
6.1 Setting up the uplink
Setting up the downlink 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.
RU
FOI
POI BIU
C
RBS
Antenna
Remote Unit
Fiber
Fiberoptic
Interface
Master Unit
Point of
interconnect
Base station
interface
Base station
Coupler
Base Station
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 – POI loss +
BIU gain – coupler loss. Basically this takes form of a link budget and here is an example:
System part Gain [dB] Accumulated [dB]
Remote Unit 40 40
Fiber -10 30
FOI Gain 20 50
POI Loss -35 15
BIU Gain 0 15
Coupler loss -15 0
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