About Error Summary Data (802.11b/g DSSS/CCK/PBCC)

Menu Path: Trace > Data > Syms/Errs

This topic provides additional measurement and analysis information unique to Error Summary trace data and 802.11b/g DSSS Direct sequence spread spectrum. The data transmission scheme (sometimes referred to as a "'modulation" scheme) used in 802.11b WLANs. DSSS uses a radio transmitter operating at a fixed centre frequency, but using a relatively broad range of frequencies, to spread data transmissions over a fixed range of the frequency band. 802.11a and 802.11g (when not operating in 802.11b mode) use Orthogonal Frequency Division Multiplexing (OFDM)./CCK complementary code keying/PBCC packet binary convolutional code modulation analysis. The Error Summary results are shown in the upper section of the Syms/Errs trace display. This display also shows the PLCP Physical layer convergence protocol Header information. This topic contains the following measurement, analysis, and programming information:

Averaging and Error Summary Data

The following numeric error summary data are averaged for the specific averaging types available:

Averaging Types

Error Summary Data

RMS (video)

RMS Exponential

Continuous Peak Hold

802.11-2007 1000 chip 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.

 x x x

EVM (%rms)

 x x x
EVM (%pk)     x

Mag Err (%rms)

 x x x
Mag Err (%pk)     x

Phase Err (deg)

 x x x
Phase Err (deg pk)     x

Freq Err

 x x x

IQ Offset

 x x x

Quad Err

 x x x

Gain Imb

 x x x

Sync Corr

 x x x

SymClkErr

 x x x

Status

      

Burst Type

      

Bit Rate

      

Octets

      

Data Len

      

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

For more information see Averaging with Digital Demodulation.

Using Band Power Markers to Limit Error Information

For error information for all points over a selected region, use the band-power markers with an error trace.

For example, here's how to compute the phase error for all points within a region. Click Trace > Data > Channel 1 > IQ Phase Error to display the IQ phase-error trace for channel 1, then click Markers > Calculation and 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 and set Calculate to Rms to display the phase error for the selected region.

At this point, click Trace > Data > IQ Mag Error to display the magnitude error for the same region.

How EVM and Magnitude Error Data is Calculated (%RMS)

In the symbol table, the VSA displays the error-vector magnitude and magnitude error as a percentage. Before computing this percentage, the VSA normalizes the constellation diagram such that the outer-most, ideal states have a magnitude of one.

The VSA computes the overall percent error by first computing the error-vector magnitude, magnitude error, and phase error at each chip time.

Next, the VSA derives the RMS average for each parameter. For example, to compute the RMS average for the magnitude error, the VSA takes the square root of the sum of the squares of the individual magnitude-error values at each chip time.

Because the magnitude of the constellation diagram's outer-most state has been normalized to one, the RMS average is the overall percent error.

Querying summary table data results programmatically

To programmatically query the Trace Summary Table data results using the Summary() and SummaryUnit() methods in the MeasurementData object.

See the How To Query Summary Table Data Results topic for more information.

See Also

Available Error Summary Data (802.11b/g DSSS/CCK/PBCC)

Symbol Table Overview