Cross-Correlated EVM (DVB-S2/S2X)

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).

Each resource element (subcarrier x symbol) is weighted equally when computing the ccEVM average.

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.

Both channels must make a measurement at the same point in time. The signals don't need to be phase-aligned, but both DVB-S2/S2X measurements must demodulate the same frame. If there is a difference between the frame data, the Cross-Correlated EVM Summary trace will show a DATA? trace LED. This won't necessarily catch the case where two different frames with the same data are analyzed by each measurement. To avoid this case, make sure that no more than one frame is captured (adjust the parameters on the Time tab and verify with the Search Time trace).

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

To perform a successful measurement, make sure the following are true:

Same signal is connected to two hardware channels through a splitter.

Input > Channel configuration is set to two channels.

CC0 and CC1 share the same component carrier definition.

Input for CC0 is measurement Ch1 and input for CC1 is Ch2.

The same frame is being analyzed by both CC0 and CC1

Sequential acquisition is not in use.

Enabled - Turns on Cross-Correlated EVM and enables the Cross-Correlated EVM Summary trace for viewing results.

Configure - Opens a dialog to select the CC to be duplicated to CC0 and CC1, and sets the input channels appropriately.