Operation Manual

Fiber Distributed Antenna System (Fiber DAS)
115
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 to reflect this. In general we should
lower the gain so that we desensitize the BTS only about 3 dB. This value is a good compromise and similar to
adding a second antenna to the same receiver port (which is kind of what we are doing with the Fiber-DAS).
Here are the new values:
Table 74
Chain NF Gain Noise Load
RU 1
2.8 -5.5 -2.2
RU 2
3.2 -5.5 -1.8
RU 3
3.8 -5.5 -1.2
RU 4
2.6 -5.5 -2.4
Sum of Noise Load 4.1
Base Station
4.0
Fiber-DAS Noise Load
4.1
Total Noise into BTS
7.1
Desensitization -3.1
Adjusted Noise Load
As you can see we should set the system up with a net gain of about -5 dB. Going back to the settings we had before
which was:
Table 75 Example Link Budget
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
We only need to change the BIU setting using the attenuators in the BIU to lower the gain with 5 dB. This will
accomplish what we need to do and the uplink should then be commissioned.