Modulation Accuracy Measurement Description
Last updated: September 1, 2009
This measurement is only applicable to EGPRS.
How is a Modulation Accuracy (EMAC) measurement made?
Modulation accuracy is a measure of how much a real 8PSK modulated signal differs from an ideal 8PSK signal carrying the same information.This measurement is used to measure the modulation accuracy of an 8PSK modulated signal in a single timeslot. For multiple uplink multislot configurations, bursts are measured from a single timeslot that you specify.
The measurement assumes that the specified burst in the multislot configuration is 8PSK modulated, but it is tolerant of occasional GMSK bursts present in the signal. In real mobile calls, GMSK bursts carrying control information occur during an 8PSK data transmission. If the specified burst is found to be GMSK modulated, it is discarded and the measurement is re-armed. This will result in an apparent increase in measurement time.
This measurement is made on normal bursts only. Access bursts are not supported as they never use 8PSK modulation.
You can measure one of up to six adjacent uplink bursts of the multislot configuration at any one time. You can specify the burst to measure using
CALL:(PDTCH|PDTChannel):MSLot:MEASurement:BURSt
.
The most important measurements returned are Error Vector Magnitude (Peak and RMS), Frequency Error, Origin Offset Suppression, and 95th Percentile EVM. The AM-PM timing offset result for a polar modulation is returned when the AM-PM Timing Offset Calculate State is set to ON,
Operating Considerations
As the uplink burst number increases, the measurement speed is expected to decrease.
The measurement must know the training sequence code (TSC) to be able to synchronize to the burst's midamble. In an active cell mode, this information is received from the protocol processor. When using a test mode, you must manually specify the TSC using the CALL:BURSt:TYPE command (see
CALL:BURSt:TYPE[:SELected]
for more information) or from the front panel by accessing the
Receiver Control
screen and selecting the
Expected Burst
parameter.
The modulation accuracy measurement does not trigger unless an uplink burst using 8PSK modulation is present. You can control the modulation and coding scheme (either 8PSK or GMSK modulation) used by the data connection to be measured using
CALL:(PDTCH|PDTChannel):MCSCheme
. Additionally, you can manually control what modulation should be expected for individual bursts using
CALL:MODulation[:FORMat]:CONTrol:AUTO
. See
Modulation Format Control (EGPRS only)
for more information. If the test set is not configured properly, the measurement returns an "Unsupported Configuration" integrity indicator.The affected test set configuration parameters are:
-
Operating Mode - The modulation accuracy measurement is only valid for the Active Cell operating mode and EGPRS BCH+PDTCH test mode.
-
Serving Cell must be set to EGPRS. This can be done in one step from the front panel using the
Active Cell (EGPRS)
operating mode.
-
Modulation and Coding Scheme must be set to use an 8PSK MCS (MCS-5 through MCS-9) for the measurement to return results. The modulation accuracy measurement is only valid for 8PSK modulation.
-
Connection Type - This measurement is valid for all connection types except BLER. In a BLER connection, the mobile station sends PACCH control channels on the uplink. Since control channels only use GMSK modulation, this connection type cannot be used to perform modulation accuracy measurements.
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