OFDM Avg MER Time (DOCSIS 4.0 Downstream)
is a plot of the Root Mean Square (RMS) average of multiple Error Vector Time data results. Use this trace to obtain an average of the Error Vector Time across multiple measurements.
Each measurement produces one set of "RMS symbol EVM" data results. This is the same measurement as the Error Vector Time trace, one Error Vector Time measurement is made per average count. You specify the number of measurements included in the RMS average calculation using the parameter (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 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
