Chapter 9 299
BERT
RF Loopback BER–Option 300
RF Loopback BER–Option 300
Synchronization
Synchronizing the test equipment to the base transceiver station (BTS) is a prerequisite to the BTS looping
back the selected traffic channel (TCH). This can be achieved in two ways: BCH Sync or TCH Sync.
BCH Sync The BTS is set to transmit to the test equipment a BCH on timeslot 0 of a selected
absolute radio frequency channel number (ARFCN). The test equipment uses the BCH
signal to determine its required TCH transmit timing.
On completion, the BTS may be switched into loopback mode on any selected ARFCN
and timeslot number.
TCH Sync This is a very quick mode of synchronization, but take care initially to set the receiver to
the correct timeslot number being transmitted by the BTS.
In this mode the base station must transmit a signal on the selected timeslot prior to data
being looped back. In some base stations this will happen as soon as a timeslot is set to
loopback, regardless of whether the signal to the BTS has the correct timing. In other
base stations, the BTS may need to be set to transmit a signal in the selected timeslot
prior to achieving synchronization.
The test equipment can lock to this signal if it contains the correct midamble. Once
synchronized, the test equipment uses this information to determine the required TCH
transmit timing. If the BTS is set accordingly, any timeslot can be transmitted with the
correct timing to enable it to be looped back by the BTS to the receiver (VSA/ESG).
NOTE The TCH sync mode relies on the user to set the correct timeslot number into both ESG
transmitter and receiver during synchronization. Thereafter, the ESG can correctly test any
timeslot since its relative timing is defined.
This capability can be used to speed up testing of consecutive timeslots in manufacture.
TCH sync mode can be used to test all timeslots consecutively without changing a single
setting on the ESG/VSA. All that is required is to consecutively loopback each timeslot
using the BTS man-machine interface (MMI) and resynchronize and trigger the ESG.
PN synchronization is also a prerequisite to BERT measurements. This is automatic but is dependent on
prior BCH or TCH synchronization.
The pattern to be recognized (PN9 or PN15) is determined by the corresponding transmit timeslot pattern
selection.
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