User Manual

MBF, Multi Band Repeater
PRODUCT DESCRIPTION AND USER'S MANUAL
© Axell Wireless Ltd A 200 93 00, rev E 68 (105)
5.1.6 UMTS Signal Measurement
The UMTS signal carries wideband and complex modulation and its properties vary depending on the level
of traffic carried.
5.1.6.1 Bandwidth
The first issue is the wideband nature of the signal. It occupies around 3.8MHz and measurements through a
narrower filter will reduce the apparent power level since only a portion of the signal reaches the detector in
the test equipment.
Equipment that includes a UMTS/3G measurement personality simplifies the task considerably. Usually a
stored configuration for power measurement will integrate many samples taken using a narrower filter to
display the correct power level for the bandwidth of the signal. Settings can easily become corrupted however
leading to erroneous results. In such cases following the manufacturers instructions in detail is advised.
Measuring with a simple spectrum analyzer must use a wider resolution bandwidth than 3.8MHz or else a
bandwidth correction factor has to be applied to the observed result. E.g. if measuring with a 300kHz RBW
the power level in the centre of the signal would appear to be around 11dB lower than actual (10Log
3.84/0.3).
5.1.6.2 Traffic
A further complication is that the power level of a UMTS signal depends on the traffic level being carried.
UMTS carrier power is usually quoted as average values e.g. a 5Watt or 37dBm signal can contain peaks up
to 10dB greater when traffic is high. An idling base station carrying no traffic radiates only a Pilot in which
case the power observed is around 10dB below the average value with traffic.
Advanced test equipment that can measure the different code power components in the UMTS signal avoids
this problem but more often in the field repeater commissioning must be done when only simple test
equipment is available. This leads to the need to know and allow for the state of traffic when making repeater
setup and diagnostic measurements. It is obvious that adjusting a repeater to maximum rated output power by
using BTSs that are idling radiating only the pilot will lead to overloading when they are in traffic.