About Despread Channel Error Summary Data (W-CDMA(3GPP)/HSPA)

When W-CDMA Code Division Multiple Access: One of several digital wireless transmission methods in which signals are encoded using a specific pseudo-random sequence, or code, to define a communication channel. A receiver, knowing the code, can use it to decode the received signal in the presence of other signals in the channel. This is one of several "spread spectrum" techniques, which allows multiple users to share the same radio frequency spectrum by assigning each active user an unique code. CDMA offers improved spectral efficiency over analog transmission in that it allows for greater frequency reuse. Other characteristics of CDMA systems reduce dropped calls, increase battery life and offer more secure transmission. See also IS-95. (3GPP) Demodulation is enabled, selecting Syms/Errs trace data, shows the symbol table and error summary trace data for the specified Code Channel and Spread Code Length. The error summary data results are shown in the upper section of the Channel Symbol Table display.

This topic provides additional measurement and analysis information unique to Channel Error Summary trace data and W-CDMA(3GPP)/HSPA modulation analysis. This topic contains the following measurement, analysis, and programming information:

Available Channel Error Summary Data (W-CDMA)
Selecting the Code Channel and Layer
Averaging and Error Data Results
Using Band Power markers to limit Error Information
How 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. and Magnitude Error data results are calculated (%RMS)
Querying summary table data results programmatically

Available Channel Error Summary Data

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

Selecting Chan Error Trace Data

The Chan Error Summary display shows the error data results for the specified Code Channel and Spread Code Length. These parameters are specified in the Despread Channel Spread Code Length and Despread Channel Code Channel text boxes, located in the Channel/Layer tab of the W-CDMA (3GPP) Demodulation Properties dialog box (MeasSetup > Demod Properties > Channel/Layer tab).

You can use the Copy Mkr To Despread Channel marker feature to automatically enter the Despread Channel Spread Code Length, Code Channel, and IQ Branch settings to match the display Marker values.

Averaging and Error Data Results

If averaging is on, averaging is applied to most numeric error data in the error summary table with the following exceptions. The peak data values, such as peak EVM, peak Magnitude, and peak Phase error are averaged only for the Continuous Peak Hold averaging type. The Slot number is never averaged. 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 occur:

CARRIER LOCK?.
DATA? (if caused by a temporary condition like partial data record)

Using Band Power markers to Limit Error Information

If you want error information for all points over a selected region, you can use the band power markers with an error trace.

For example, here's how you could compute the phase error for all points within a region. Click Trace > Data > Antenna1 Comp > IQ Phase Error to display the composite IQ Phase Error trace, 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, you could simply click Trace > Data > Antenna1 Comp > IQ Mag Error to display the magnitude error for the same region.

How EVM (%rms)and Magnitude Error (%rms) data results are calculated (%RMS)

In the channel error summary table, the analyzer shows the error vector magnitude and magnitude error as a percentage. Before computing this percentage, the analyzer normalizes the constellation diagram such that the outer most, ideal states have a magnitude of one.

The analyzer computes the overall, percent error by first computing the error vector magnitude and magnitude error at each symbol time.

Next, the analyzer derives the rms average for each parameter. For example, to compute the rms average for the magnitude error, the analyzer takes the square root of the sum of the squares of the individual magnitude error values at each symbol 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.

How RCDE(dB) is calculated

The UE User Equipment (e.g. cell phone) Relative Code Domain Error (RCDE) for every non-zero beta code in the domain is defined as the ratio of the mean power of the projection onto that non-zero beta code, to the mean power of the non-zero beta code in the composite reference waveform. This ratio is expressed in dB. The BTS Base Transceiver Station - Although specifications differ for each system, the BTS effects radio communication with mobile stations (MS) via its respective radio access system and transmits/receives signals to/from connected radio network controllers (RNC) located along transmission routes. RCDE for every active code is defined as the ratio of the mean power of the error projection onto that code, to the mean power of the active code in the composite reference waveform. This ratio is expressed in dB.

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.