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Chapter 6 195
BERT Testing
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.
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