Error Summary Data (Digital Demod)
At the top of the symbol table are several error data results. The demodulation type determines which error summary data results are displayed in the symbol table (see Available Error Summary Data). The following subjects are discussed in this topic:
- Averaging and Error Summary Data
- Error Information at Symbol Times
- Using Band Power Markers to Calculate Error Information for a Specific Region
- How EVM and Magnitude Error Data is calculated (%RMS)
- EDGE Demodulation
- Querying summary table data results programmatically
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 only applies 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 averaging types. For more information see Averaging with Digital Demodulation.
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
Error Information at Symbol Times
In general, error summary metrics are calculated from only the symbol points and do not include points between symbols. Here are the exceptions:
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MSK Minimum Shift Keying: Includes points between symbols |
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Includes points between symbols |
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Includes points between symbols |
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OQPSK: 2 points per symbol |
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OQPSK: 1 point per symbol (but the point is a complex-valued point where the real and imaginary locations come from different time locations within the symbol) |
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MSK: Includes points between symbols OQPSK: 2 points per symbol |
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Includes points between symbols |
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Includes points between symbols |
In contrast, error traces (such as error vector magnitude (EVM), IQ magnitude error, FSK Frequency Shift Keying: A form of modulation using multiple carrier frequencies to carry the digital information. The most common is the two frequency FSK system using the two frequencies to carry the binary ones and zeros. error, Carrier error magnitude) display the error at the symbol times and at all points between symbols.
Using Band Power markers to Calculate Error Information for a Specific Region
To view phase or magnitude error information for points in a specific region, use band-power markers on an error trace such as IQ Mag Error or IQ Phase Error.
For example, here's how to compute the phase error for all points within a region. Click to display the trace. Then click and select the check box to turn on the band-power markers.
Now position the band-power markers to select the region of interest and then click and select Power to show the phase error for the selected region in the marker readout.
At this point, simply click to display the magnitude error for the same region since the band-power marker's region does not change when you select another trace.
How EVM and Magnitude Error Data is calculated (%RMS)
In the symbol table, the VSA displays the error-vector magnitude (EVM), magnitude error (Mag Err), and phase error (Phase Err) as a percentage.
To compute this percentage, the VSA first normalizes the points in the IQ reference and I/Q measured signals to the EVM Normalization Reference. Then the VSA computes the percent error by calculating the error-vector magnitude, magnitude error, and phase error at each symbol 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 symbol time.
Then the value is multiplied by 100% and the value is shown on the table.
For more information, see the description for each of these metrics.
EDGE Demodulation
For the EDGE Enhanced Data for Global Evolution: A technology that gives GSMA and TDMA similar capacity to handle services for the third generation of mobile telephony. EDGE was developed to enable the transmission of large amounts of data at a high speed, 384 kilobits per second. (It increases available time slots and data rates over existing wireless networks.) demodulation format, the EVM, Phase, and Magnitude Error data results may vary for different points/symbol settings. When points/symbol is set to 1 (default), the trace data results are compensated for ISI Inter-Symbol Interference: An interference effect where energy from prior symbols in a bit stream is present in later symbols. ISI is normally caused by filtering of the data streams. (inter-symbol interference). For points/symbol greater than one, the trace data results are not compensated for the effects of ISI.
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
