110 Chapter3
Making EDGE (with GSM) Measurements
Making the EDGE PvT Measurement
Making the EDGE PvT Measurement
Purpose
EDGE PvT measures the mean transmit power during the “useful part”
of GSM bursts and verifies that the power ramp fits the within the
defined mask. Power vs. Time also lets you view the rise, fall, and
“useful part” of the GSM burst.
GSM is a Time Division Multiple Access (TDMA) scheme with eight
time slots, or bursts, per RF channel. If the burst does not occur at
exactly the right time, or if the burst is irregular, then other adjacent
timeslots can experience interference. Because of this, the industry
standards specify a tight mask for the fit of the TDMA burst.
The Power vs. Time measurement provides masks for both BTS (Base
Transceiver Station) and MS (mobile station). The timings are
referenced to the transition from bit 13 to bit 14 of the midamble
training sequence. The 0 dB reference is determined by measuring the
mean transmitted power during the “useful part” of the burst. You can
also define a user configurable limit mask to apply to the measured
burst (refer to the “Changing the Measurement Setup” section).
The GSM specifications defines the “useful part” of the normal GSM
burst as being the 147 bits centered on the transition from bit 13 to bit
14 (the “T0” time point).
Measurement Method
The instrument acquires a GSMEDGE (with GSM) signal in the time
domain. The “T0” point and the useful part are computed. If Burst Sync
is set to
Training Seq, a GSM demodulation is performed to find “T0”. If
Burst Sync is set to
RF Amptd, an approximation of “T0” will be used
without performing a demodulation. The average power in the useful
part is then computed and displayed, and the GSM limit mask is
applied. The measurement displays Pass when the burst fits within the
bounds of the mask.
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