User Manual

DELTANODE FIBER DAS MANUAL
©DeltaNode Solutions 2012
41
Revision 12-03
6.1.1 Noise load on Radio Base Station
The system will inevitable add some noise to the receiver. Properly set up the noise figure in a system
like this will be better than 3 dB. However, if the gain is set up poorly (not enough gain in the remote,
too much gain in the head-end) it is possible to create a very bad noise figure. In order to avoid this the
Fiber-DAS Calculator
should be used to calculate the noise figure of the system in the uplink.
If you have not familiarized yourself with the Fiber-DAS Calculator then I suggest you do so before
moving on in this manual. The figures in the Fiber-DAS calculator relates to the settings of all steps in the
chain. By using the calculator you can figure out the proper settings once you know the fiber loss
between the Remote Unit and the Master Unit.
Let us assume your have arrived at a Noise Figure NF of 3 dB for this chain. However your system may
contain more remotes, perhaps connected like this:
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
RU
RU
RU
FOI
FOI
FOI
Now the noise load can be calculated by adding the noise contribution from each step of the chain.
Below is an example of noise figures from each of the remotes:
Chain NF Gain Noise Load
RU 1 2,8 0,0 2,8
RU 2 3,2 1,0 4,2
RU 3 3,8 -2,0 1,8
RU 4 2,6 -1,0 1,6
8,7
Base station 4,0
Fiber-DAS noise load 8,0
Total noise into BTS 9,5
Desensitization -5,5
Sum of noise load
There is a sheet in the Fiber-DAS calculator that lets you add your figures and that will calculate it for
you.
What we see here is that if we set the system up in this fashion we will desensitize the base station with
about 5,5 dB. This can be okay if the base station coverage is only through the Fiber-DAS system but if
the base station is also being used for outdoor coverage it is not good. We need to change the net gain