Modulation Accuracy Measurement Description

Modulation Accuracy Measurement Description

Last updated: November 25, 2010

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 or 16QAM modulated signal differs from an ideal 8PSK or 16QAM signal carrying the same information.This measurement is used to measure the modulation accuracy of an 8PSK or 16QAM 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 or 16QAM 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 or 16QAM 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 or 16QAM 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 or 16QAM modulation is present. You can control the modulation and coding scheme (either 8PSK, 16QAM 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:

Related Topics

How do I make Modulation Accuracy Measurements?

Programming a Modulation Accuracy Measurement

Modulation Accuracy Troubleshooting

Test Adherence to Standards