Real-Time Modulation Filtering compatibility with the ESG/EXG/MXG, is not supported for:
Multicarrier configurations
GSM (GMSK) modulation
frequency offset settings on the carrier node
mixed-format configurations (i.e. real-time modulation needs to apply to all of the timeslots using a single configuration)
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9. Real-time Modulation Filter |
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The real-time modulation filter is available for only the E4438C ESG, N5162/82 MXG, and N5172 EXG connectivity with the advanced waveform capability (Option Qxx). The filter works only with a single carrier.
The cells within this function table provide only information, and they cannot be edited. When you turn the filter on, the software automatically selects the FIR filter type and configures its settings as shown in the above figure. To turn the filter on or off, use the Carrier view.
Unlike the other filter selections in this software, where the filtering is factored into the waveform file, the real-time modulation filter is a physical FPGA filter located on the signal generator. The purpose of this filter is to allow the storage of a large waveform file that if created using the software filters, may exceed the memory capacity of the signal generator.
When the filter is set to on, the software creates a waveform file without any filtering, which essentially equates to a waveform with an oversampling ratio (OSR) of one. This lack of filtering during waveform file creation produces a waveform that just contains the I/Q symbol decision points. This waveform creation process results in a waveform file size that is smaller by a factor of two or more. For example, an OSR of two would create a waveform file that is two times larger than a file using an OSR of one. When the signal generator plays the waveform file, the real-time modulation filter, in real-time, provides the correct filtering to produce the proper signal per the 3GPP specifications. The software stores the real-time modulation filter settings that include the FIR filter parameters in the waveform file header.
While the software does not provide any editing features for the real-time modulation filter, the signal generator does provide editing capability. The settings are located in the signal generator's menu. But if you do make filter changes and then download the waveform, the software changes the parameters back to the software's settings. For more information on the filter or the Dual ARB, refer to the instrument User's Guide.
Choices: On | Off
Default: Off
Display the state of the Real-time Modulation Filter.
This filter is typically applied to an Arb Waveform containing just the I/Q symbol decision points. The Modulation Filter effectively defines the transitions between the symbol decision points. The filter must have an oversample ratio of 2 or more.
When this feature is active, the Sample Clock Rate is actually the Symbol Rate.
On − enables the addition of the Real-time Modulation Filter.
Off − disables the addition of the Real-time Modulation Filter.
You cannot edit this cell.
Choice: None | Root Nyquist | Nyquist | Gaussian
Default: Gaussian
Double-click or use the drop-down menu to select a baseband filter type.
If the oversampling ratio is set to 1, the filter type is automatically set to and the filter types and corresponding filter parameters are unavailable.
If the oversampling ratio is set to any other value, you can select one of the listed filter types and edit the associated parameters.
Choices: 0 to 1
Default: 0.22
Change the Alpha parameter for Root Nyquist and Nyquist filters. This field is unavailable for other filter selections.
Choices: 0 to 1
Default: 0.3
Change the bandwidth bit time (BbT) parameter for a Gaussian filter. This field is unavailable for other filter selections.
This filter menu, , is unavailable when using an HSR (high symbol rate) carrier configuration.
Choice: EVM | ACP
Default: EVM
Slight imperfections in Nyquist/Root Nyquist filters are optimized to minimize either.
EVM - Error Vector Magnitude. Gives the most ideal pass band.
ACP - Adjacent Channel Power. Improves stop band rejection. Bandwidth and alpha do not change.
You cannot edit this cell.