Enable Cross-Correlated EVM (Custom IQ)

Enable Cross-Correlated EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format. - Cross-Correlated EVM (ccEVM) computes EVM by combining the results of two different measurements of the same signal so as to reduce the noise contributed by the acquisition hardware. This procedure causes the ccEVM value to primarily contain the noise coming from the DUT Device under Test: An acronym used to describe some type of electrical apparatus connected to test instrumentation. The apparatus can range from a single component to a complex subsystem such as a mobile phone, base station or MSC. (or source and DUT, in the case of an amplifier).

If the two channels are not completely independent (e.g. shared LO), this technique will not be able to remove the common noise between channels.

The synchronization between channels is accomplished by Pattern Search (which must be enabled to make the Enable Cross-Correlated EVM check box available). Both channels must make a measurement at the same point in time. The signals don't need to be phase-aligned, but both Custom IQ measurements must demodulate the same data symbols. If there is a difference between the data, the Cross-Correlated EVM Summary trace will show a DATA? trace LED. The other indication is that the Valid Points will be less than Total Points in the Cross-Correlated EVM Summary trace.

Refer to the appropriate hardware topic to configure your hardware for a multichannel acquisition.

To perform a successful ccEVM measurement, the following must be done:

Configure the measurement for 2 channels (Input > Channels).

Make sure your device is transmitting a repeating pattern and that the pattern is always found within the Search Length (MeasSetup > Custom IQ Demod Properties).

Enable and configure Pattern Search.

Enable Cross-Correlated EVM once the previous items are done.