OFDM Avg MER Spectrum (DOCSIS 4.0 Downstream)
is a plot of the Root Mean Square (RMS) average of multiple Error Vector Spectrum data results. The "RMS Error Vector Spectrum" (or "Avg MER Spectrum") trace is the same as averaging multiple Error Vector Spectrum trace measurements, one Error Vector Spectrum measurement is made per average count (does not apply in MER mode).
You can enable and disable the display of each subcarrier type using the Display Data Subcarriers, Display PLC Data Subcarriers, Display PLC Preamble Subcarriers, and Display Pilot Subcarriers checkboxes on the MeasSetup > Advanced tab.
This trace can be viewed in either MER or EVM mode (default is MER, Show MER on Error Vector Traces selected). It's often easier to see problems in EVM mode, because subcarriers with poor EVM spike up and stand out from the signal (as opposed to MER mode, where subcarriers with poor MER spike down and are easily lost in the signal).
| Trace Annotation | Description |
|---|---|
| xHarm: n |
When Show MER on Error Vector Traces is selected, xHarm: n is displayed as a harmonic A mathematical term for the way that MER is averaged--MER is translated to EVM first, then averaged, then translated back to MER. average of n points (subcarriers in this case). |
| xRMS: n |
When Show MER on Error Vector Traces is not selected, xRMS: n indicates that n number of OFDM symbols are included in each "RMS subcarrier EVM" measurement result (see Error Vector Spectrum trace). |
Trace Color coding Scheme
A multi-color coding scheme is used to make it easy to visually identify common symbols, subcarriers, and data results within various OFDM Traces. This makes cross trace data comparisons and analysis easy to accomplish. Different colors are assigned to symbols representing a common subcarrier type including: Preamble, Pilot, and Data subcarrier types. Some common color scheme Traces include: Error Vector Spectrum, Error Vector Time, and IQ Meas, and OFDM Frame Summary.
You can also customize and re-assign Trace colors schemes, see the Display Preferences Color tab (click tab and select a new color for the active Mod Type element).
See Also
