User Manual

OPTICAL MASTER UNIT
PRODUCT DESCRIPTION AND USER’S MANUAL
© Axell Wireless Ltd 25
Select HUB Status
Check the levels
of the received
optical signals via
the RMC
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To estimate the signal levels in the system, a link budget should be prepared before the system is
made
operational. This section provides background on calculating the required attenuation values along
the link and
describes how to set the attenuation value in the management application.
3.6.1.1.1 Downlink Path
The following two diagrams illustrate the attenuation levels for two types of installations:
• BS with separate Tx and Rx ports – for a total attenuation of 44dB (attenuator set to 0)
• BS with a common Tx and Rx port – for a total attenuation of 45dB (attenuator set to 0)
Also note the following:
• Any additional required attenuation (up to -21dB) is implemented via the Variable Attenuator.
• The input level to the laser should be ≤-3dBm composite power
Note: As the composite power in a multicarrier TETRA/TDMA/W-CDMA/LTE system is traffic
dependent, the maximum laser input power must be calculated for the traffic scenario that will
require highest composite power.
After the downlink attenuation been set, the gain of the connected repeaters should be adjusted
individually in accordance to the relevant section in the manual for each repeater connected to the
OMU.
The following diagram illustrates the attenuation levels for an installation with separate Tx and Rx
ports.
Fiber Fed
Repeater
e
o
OMU
BTS
Directional
Couplers (x2)
Loss in fiber
cable
10 Km

Variable
Attenuator
-14 dB
-30 dB
BTS Output
up to
- 21 dB
Variable
Attenuator
Basic Explanation of Attenuation Levels for BS with
SEPARATE Tx and Rx ports
up to
- 21 dB
-14 dB
Total attenuation = 44dB
Recommended power = -3dBm
RX
TX
-30 dB
BTS Input
Splitter
Measured Power
Combiner