About Error Summary Data (802.11a/g/j/p OFDM)

This topic provides additional measurement and analysis information unique to Error Summary trace data and OFDM Orthogonal Frequency Division Multiplexing: OFDM employs multiple overlapping radio frequency carriers, each operating at a carefully chosen frequency that is Orthogonal to the others, to produce a transmission scheme that supports higher bit rates due to parallel channel operation. OFDM is an alternative tranmission scheme to DSSS and FHSS. modulation analysis. The Error Summary results are shown in the upper section of the Syms/Errs trace display. This topic contains the following measurement, analysis, and programming information:

Available Error Summary Data
Averaging and Error Summary Data
Using Band Power markers to limit Error Information
COM API 1) Access Preamble Indicator, or 2) Application Programming Interface Programming Information

Available Error Summary Data

A list of the available error data is provided in the Available Error Summary Data topic, which also links to detailed descriptions for each error result.

Averaging and Error Summary Data

When averaging is on, averaging is applied to the numeric error data in the symbol/errors table with the following exception. Averaging applies only to peak 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., peak magnitude, and peak phase error data for the Continuous Peak Hold averaging type.

Error data from the current scan is not included in the average if any of these conditions exist:

Pulse Not Found
Sync Not Found
Carrier Unlock
DATA?
Pulse too Short

For more information see Averaging with Digital Demodulation.

Using Band Power markers to limit Error Information

To view EVM error information for all points over a selected region, use the band-power markers with the Error Vector Spectrum and Error Vector Time trace data. The Error Vector Spectrum trace data will compute the EVM for all symbols within a specified subcarrier region and Error Vector Time trace data with compute the EVM for all subcarriers within a specified symbol-time region.

For example, here's how to compute the symbol EVM for OFDM subcarriers 11, 12, and 13. Click Trace > Data > Error Vector Spectrum to display the Error Vector Spectrum trace data, then click Markers > Calculation, select the Band Power check box to turn on the band-power markers.

Now position the band-power markers to select the region of interest; place the markers so that they are exactly on or close to the specific subcarriers of interest. Center the marker at subcarrier 12, enter 12 in the Center text box, and set the width to two carriers, enter 2 in the Width text box, this encloses the region of interest (subcarriers 11, 12, and 13). Then set Calculate to Rms to display the EVM in %rms, this is the EVM (%rms) for all symbols within subcarriers 11, 12, and 13.

Use the same procedure with the Error Vector Time trace data display to find the EVM (%rms) for all subcarriers within a specific range of symbols.