Rohde & Schwarz CMW 500 - Detecting GSM Multislot Frames

R&S
®
CMW 500 GSM Applications
GSM TX Measurements
Operating Manual 1202.3986.32 – 03 219
+24 –23 –26 –30 –33
+22 –23 –26 –31 –35
e20 –23 –26 –32 –36
8.1.1.9 Detecting GSM Multislot Frames
This application sheet describes the use of the R&S CMW 500 trigger system for
detecting and measuring GSM frames filled with a particular burst sequence. With
appropriate trigger settings the R&S CMW 500 can filter frames with the following
properties:
Frames with several active timeslots but with 1 to 3 slot gap.
Frames with a particular pattern of inactive bursts and bursts of a definite
modulation scheme.
Measurement Principle
With an active "Acquisition" trigger, the R&S CMW 500 analyzes the RF input signal
and derives a frame trigger using information about the active slots. After frame
detection, the acquisition trigger events are repeated periodically according to the GSM
frame clock. TSC detection is performed continuously in order to compensate for a
possible drift. Two different acquisition trigger modes – "Gap" and "Pattern" – are
available.
Gap Trigger
In the gap trigger mode the R&S CMW 500 searches for a gap in the sequence of
active slots. A gap is a series of 1 to 3 inactive slots. The trigger event is generated at
the beginning of the first slot after the gap and is repeated periodically.
To use the gap trigger as shown above,
1. Feed the GSM uplink signal to the input connector and perform the necessary
analyzer settings.
2. Open the "GSM Measurement – Multi Evaluation Configuration" menu.
3. Select "Trigger > Trigger Source: Acquisition (Internal)", "Trigger > Acquisition >
Mode: Gap", "Trigger > Acquisition > Gap Length: 3".
4. Start the GSM Multi Evaluation measurement and observe the triggered frames in
the "Power vs. Time" diagram.
深圳德标仪器 135-1095-0799