VSS and R&S Integration

This page describes the integration between Cadence VSS and Rohde&Schwarz (R&S) software products: WinIQSim2, VSE, Direct DPD. The co-simulation between VSS and R&S SW allows:

VSS can replay signal sources created with R&S WinIQSim2, which are the same signal sources used in R&S signal generators.
R&S VSE can be used for demodulation and measurement of standard signals passed through VSS DUTs.
Direct DPD (part of option K18 in VSE) implements a DPD algorithm that does not require prior knowledge of the device model.

Step-by-step guide

VSESIM-VSS

The integration of R&S WinIQSim2 and VSE with Cadence VSS is done by the VSESIM-VSS add-on, which is distributed with VSE and can be purchased directly from R&S. Once installed, the add-on will add two new blocks to VSS:

RS_SRC adds the ability to replay R&S encrypted signal waveform files in VSS. These files typically have the extension ".wv" and can be generated by WinIQSim2 or captured by R&S instruments.
RS_SNK allows a VSS signal to be stored into an encrypted waveform file, which can then processed by R&S SW, such as VSE, or replayed in R&S signal generators.

Signal Generation

Signal generation is done with WinIQSim2 from R&S, which is free to use.

Install WinIQSim2 from https://www.rohde-schwarz.com/software/winiqsim2/
Start WinIQSim2 and configure as described below: (or you can use configuration file 5GNR_FR1_TM3_1.savrcltxt, if desired)
1. Click on Baseband box and select 5G NR...
2. On the new window that pops up, click on Test Models… box and select NR-FR1-TM3_1_FDD_100MHz_30kHz (1)
3. Make sure signal is turned on (2)
4. Generate waveform, save as "NR-TM3_1_FR1_100MHz_30kHz.wv" (3) – waveform should be saved in the same folder as the VSS project, if not the path in RS_SRC should be modified accordingly

Signal Conditioning

Most signals in WinIQSim2 are generated at 1 sample/symbol. The R&S ARB Toolbox, which is free to use, can be used to resample the signals to the desired sample/symbol rate.

Install ARB Toolbox from https://www.rohde-schwarz.com/us/applications/r-s-arb-toolbox-application-note_56280-15443.html
Start ARB Toolbox, and on the left window pane navigate to the directory where the "*.wv" file from WinIQSim2 was saved
Right-click on the file, select Edit/Resample
1. Set the new sample rate (multiple of the existing sample rate), and press OK. Then click the ">>" button.
2. Set the Output File name, as desired, then click Run.

Signal Analysis

Signal demodulation and measurements are performed by R&S VSE, which is a SW package that can be purchased from R&S at https://www.rohde-schwarz.com/software/vse/.

Once a license for VSE is obtained from R&S and VSE (including the VSESIM-VSS option) is successfully installed, you are ready to run the demos below.

Note: When VSESIM-VSS is installed, it will automatically locate the latest version of AWR DE and copy a new DLL in the corresponding AppData directory, under the \models64 folder (you can locate this directory by clicking on Help/Show Files/Directories, AppData in AWR DE). If multiple versions of AWR DE are installed, you will need to manually copy the \models64 folder and its content to the previous versions.

IO Demo

This demo shows a signal generated with WinIQSim2, passed through a DUT in VSS, then demodulated with VSE, which also shows performance metrics specific to the signal standard.

For the VSS part of the demo, you can use the VSS project RnS_5GNR.emp (RnS_5GNR.vin). If the waveform file was not already created with WinIQSim2, download NR-TM3_1_FR1_100MHz_30kHz.wv. The signal power is swept manually and results stored in different data files. This process could be easily automated, if needed. The simulations take several minutes since the RF link is rather complex. For a faster demo, we could use as single device as DUT.
1. In RS_SRC set OUTLVL to -20 (dBm), in RS_SNK set FILENAME to ".\NR-TM3_1_FR1_100MHz_30kHz_m20dBm.wv", run simulation.
2. In RS_SRC set OUTLVL to -10 (dBm), in RS_SNK set FILENAME to ".\NR-TM3_1_FR1_100MHz_30kHz_m10dBm.wv", run simulation.
3. In RS_SRC set OUTLVL to -5 (dBm), in RS_SNK set FILENAME to ".\NR-TM3_1_FR1_100MHz_30kHz_m5dBm.wv", run simulation.
  Hint: For demo purposes, you can rename FILENAME in RS_SNK so it does not overwrite the existing file on disk. Then, you can run the simulation, look at the spectral measurements in VSS, stop simulation and continue in VSE without having to wait for the VSS simulation to complete.
Once VSS demo is complete, open R&S VSE. Download the QuickSave2.dfl file and save it to your machine. In VSE, click File/Recall. The first time you run the demo, click on the Recall tab, navigate to where you saved the QuickSave file, and select it.
1. In order to make it easier for future demos, click File/Save, make sure you are on the Quick Recall tab, and then select QuickSave2 location - Do not use QuickSave 1 if you will run the DPD demo.
QuickSave configuration will create three channels, each pointing to the "*.wv" files created during the VSS simulation. If the links are not updated, manually load each file and save the configuration again.
For each channel, select it and click Auto Demod Once button in the top right. This will load the data and demodulate it. You should see the results.
You can now select each channel and visually see the performance degradation due to compression in the DUT elements, as well as monitor the EVM values.

DPD Demo

This demo shows how to use the R&S Direct DPD algorithm with the standard signals created in WinIQSim2 and demodulated in VSE. This will require installing Python on your machine. A guide to getting started with Python for the AWR environment can be found in this KB page. This demo will also require installing the rskfd package.

Download the DPD demo package and unzip it in a local folder. It contains the following:

Folder simulation contains the AWR project used for running the VSS simulations
Folder testdata contains TDNN models for several amplifiers, which were extracted from measured or simulated data using the Amplifier Model Generator in AWR DE.
Folder waveforms contains signals used to drive the amplifier. This is a signal generated with WinIQSim2 and resampled with ARB Toolbox.
Python file VSSFileDef.py contains device definitions used during simulations. There are several sections in this file corresponding to the amplifier models in the testdata folder. User can uncomment the desired section and comment all the others.
Python file VSSOfflineDemo-Init.py runs the simulation once, showing the performance of the amplifier without DPD.
Python file VSSOfflineDemo-RunDDPD.py runs the simulation in Cadence VSS, calls R&S VSE to run the Direct DPD, creates a new stimulus for the amplifier, then repeats the process. It is set to run 5 iterations cycling between Cadence VSS and R&S VSE. At the end of the simulation, ACPR and spectral measurements after each iteration are displayed in VSS and compared. The results show improvement in spectral regrowth and reduction in ACPR levels.