User Manual

AXELL MBF MULI-BAND FIBRE REPEATER
PRODUCT DESCRIPTION AND USER’S MANUAL
22 © Axell Wireless Ltd
It must also be kept in mind that the OMU might have separated input/output ports for each band
(UL/DL) while the interface with the BTS may well be duplex. In that case some duplexing network
must be provided to allow these to be brought together. If there is more than one operator’s BTS per
band the loss of any combining network and any equipment room cabling also becomes part of the
overall attenuation required to reach the correct interface level in each frequency band.
The illustration on the next page shows a more complicated arrangement where the same three BTSs
feed multiple MBF repeaters (up to 6 is possible using the standard splitter card which fits the OMU
rack). In this case an OMU per frequency band is shown. The internal splitter has an insertion loss of
14 or 16dB depending on frequency band. This loss is again a contribution to the overall attenuation
which must be provided between BTS and the input ports of the UFO-M for the correct operational
levels to be achieved.
The interface levels must be modified to maintain the same composite power if a greater number of
carriers is to be applied from the BTS.
The DL POI / OMU Adjustment must be made considering the fully loaded condition – e.g. a BTS
capacity of 8 carriers must include a back off of 6dB compared to the 2 carrier level and -
11dBm/carrier is then the correct UFO-M drive level for GSM 900. The same rule for back off
applies in other bands.
Note that a UMTS BTS at idle (no traffic) will be radiating only a pilot – approx -10dB compared to
the average power when it is in traffic. See also section about UMTS Signal Measurement below.
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The optical link between the UFO-M of the OMU and the UFO-S in the repeater is equipped with a
calibrated pilot tone transmitter/receiver which enables compensation for the loss of the optical fibre
plant between them.
The OLA procedure requires a computer running Axell RMC software and an RS232 connection to
the LMT Port of the repeater controller.
Start the RMC and login to the repeater as described in the appropriate section of the handbook. Click
on the Actions tab on top of the RMC screen. A drop down list will appear where a command will be
found to execute the optical link adjustment for each UFO-S module that is fitted to the repeater.
Click the command for the desired optical link and following a short delay (2-3 secs) an information
screen will be shown describing the result of the automatic setup process.
This procedure is described in the OMU Manual section 4.10.
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When the DL POI levels and the repeater optical links have both been set up as described in the
foregoing the MBF repeater set at maximum gain should produce a composite signal level at the
output connector of +37dBm for GSM900 and 1800 and +39dBm for UMTS.
The RMC provides sub screens for each band where the downlink power from UFO-S optical
receiver /input to the DL radio board and the composite output power level from the MCPA can be
viewed.
The power amplifier for each frequency band can be enabled /disabled and the preset DL attenuation
in the radio board for each band can be adjusted. A saturation status indicator (red/green) shows
whether the radio board ALC is in operation. This indicator should be green. A red indication
indicates overdrive the cause of which should be investigated and rectified.
In each band the DL output power per carrier should be measured using a spectrum analyzer.
Allowing for the maximum DL carrier quantity in each band the composite level per band under full
loading should be calculated to ensure it does not exceed the rated maximum otherwise ALC will be
in operation when traffic levels are high. See also section about UMTS Signal Measurement below.