Test Plan Version 1.2.1
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9 Alternately, determine the average power level of each output of the communication tester
and subtract the path loss to each input port to set the corresponding reference level.
10 To obtain the target reference levels using the communication tester in CW mode instead
of a single CW source, attach the communication tester as it will be used for device testing
and repeat steps 3 to 4 for each input of the channel emulator. The measured levels are
then used to set the required reference level for the corresponding communication tester
output power settings. In the event that specific implementation details differ from these
steps, proper documentation shall be generated describing the method to be employed.
2.2.2.2 Output Calibration
The primary goal of the output calibration is to balance the outputs of the channel emulator to
compensate for the differences in path loss to the center of the test volume. Thus, for SIR testing,
only the relative path losses between each output, as well as any relative losses between signal
source and interference source, are required to sufficiently calibrate the system. The net path loss
of the calibrated system is only required for throughput vs. power testing, and is useful for ensuring
that the signal is sufficiently above the platform noise to obtain the desired SIR. However, if a
suitable calibrated reference antenna is used during the output calibration, then the necessary end-
to-end path loss correction can also be extracted from the same set of measured data. Otherwise,
once the relative corrections have been applied to the outputs, a separate path loss measurement
can be performed on any one of the individual paths to determine the net path loss, since all of the
relative errors are compensated separately.
Figure 2.2.2.2-1 illustrates a single path from the communication tester to the center of the test
volume. While the channel emulation and other components are part of the signal path, the
definition of the total path loss from the communication tester to the center of the test volume
remains the same as that for the OTA test plan. Thus, the mechanisms for measuring the end-to-
end loss are the same. Since the channel model and other input and output level setting controls of
the channel emulator will alter the net path loss, the components can be separated into the internal
gain or loss of the channel emulator and the external gain or loss of all of the other system
components, as shown in Figure 2.2.2.2-2. By measuring the end-to-end loss and subtracting the
internal loss term, the resulting external loss corrections can be combined with any other channel
emulator settings to determine the signal levels in the test volume. For isolated signal paths that are
not altered between the calibration step and the EUT measurement step (e.g., between the channel
emulator and amplifier or amplifier and antenna) any standing wave contributions from these
components can be assumed to be corrected by the range calibration. The calibration also embeds
any residual offsets from the inputs and outputs of the channel emulator into the net path loss that
is measured.
Alternatively, subsets of these paths may be measured independently, and the total path gain/loss
of each component combined, minus the loss terms of any additional cables, switches, or other
accessories used during the calibration process that are not part of the test signal path.
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