54 Chapter3
Making EDGE (with GSM) Measurements
Making the Transmit Power Measurement
Making the Transmit Power Measurement
Purpose
Transmit Power is the measure of in-channel power for EDGE (with
GSM) systems. Mobile stations and base transceiver stations must
transmit enough power, with sufficient modulation accuracy, to
maintain a call of acceptable quality without leaking into frequency
channels or timeslots allocated for others. EDGE (with GSM) systems
use dynamic power control to ensure that each link is maintained with
minimum power. This gives two fundamental benefits: overall system
interference is kept to a minimum and, in the case of mobile stations,
battery life is maximized.
The Transmit Power measurement determines the average power for
an RF signal burst at or above a specified threshold value. The
threshold value may be absolute, or relative to the peak value of the
signal.
At the base transceiver station, the purpose of the Transmit Power
measurement is to determine the power delivered to the antenna
system on the radio-frequency channel under test. The Transmit Power
measurement verifies the accuracy of the mean transmitted RF carrier
power. This can be done across the frequency range and at each power
step.
Measurement Method
The instrument acquires a EDGE (with GSM) signal in the time
domain. The average power level above the threshold is then computed
and displayed. This measurement uses the “power-above-threshold”
method instead of the “useful part of the burst” method defined in the
EDGE (with GSM) standards. The measured Transmit Carrier Power
will be very nearly the same for these two methods. The
power-above-threshold method has the advantages of being faster and
allows power measurements to be made at somewhat lower power
levels. It also has the advantage of not requiring the carrier to have a
valid TSC (Training Sequence Code).
Note that this measurement does not provide a way to specify which
timeslot is to be measured. Therefore if multiple timeslots are on, they
should all be set at the same power level, or the levels of those timeslots
to be excluded need to be kept below the threshold level. If you want to
measure Transmit Carrier Power using the GSM specified useful part
of the burst method, use the Power vs. Time measurement, which also
measures the power ramping of the burst.
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