Rau Attenuation And Alc - ADC InterReach Fusion Installation, Operation And Reference Manual

6.8.2
D-620610-0-20 Rev D
inputs. This SNR can not be better than the SNR of Fusion by itself, although it can
be significantly worse.
A good rule of thumb is to set the uplink attenuation such that the noise level out of
Fusion is within 10 dB of the base station's sensitivity.

RAU Attenuation and ALC

The RAU attenuation and ALC are set using the AdminBrowser Edit Unit Proper-
ties screen.
Embedded within the uplink RF front-end of each Fusion RAU band is an ALC cir-
cuit. This ALC circuit protects the Fusion system from overload and excessive inter-
modulation products due to high-powered mobiles or other signal sources that are
within the supported frequency band and are in close proximity to the RAU.
Each individual Band (1, 2, or 3) of a Fusion RAU has an uplink ALC circuit that
operates as a feedback loop. A power detector measures the level of each band's
uplink RF input and if that level exceeds –30 dBm, an RF attenuator is activated. The
level of attenuation is equal to the amount that the input exceeds –30 dBm. The fol-
lowing sequence describes the operation of the ALC circuit, as illustrated in
Figure 6-2.
The RF signal level into either Band of the RAU rises above the activation thresh-
1.
old (–30 dBm), causing that ALC loop to enter into the attack phase.
During the attack phase, the ALC loop increases the attenuation (0 to 30 dB) until
2.
the detector reading is reduced to the activation threshold. The duration of this
attack phase is called the attack time.
After the attack time, the ALC loop enters the hold phase and maintains a fixed
3.
attenuation so long as the high-level RF signal is present.
The RF signal level drops below the release threshold (–45 dBm) and the ALC
4.
loop enters the release phase.
During the release phase, the ALC loop holds the attenuation for a fixed period
5.
then quickly releases the attenuation.
An important feature of the ALC loop is that in Step 3, the attenuation is maintained
at a fixed level until the signal drops by a significant amount. This prevents the ALC
loop from tracking variations in the RF signal itself and distorting the waveform
modulation.
Help Hot Line (U.S. only): 1-800-530-9960
Connecting a Main Hub to a Base Station
6-39
CONFIDENTIAL