How to Create NR+CW Waveforms with RFmx Waveform Creator

Updated Aug 28, 2023

Environment

Software

  • RFmx NR
  • RFmx Waveform Creator

The RFmx Waveform Creator software allows users to generate a vast number of radio frequency waveforms. Users can create modulated signals such as LTE, NR, WLAN, and BT. In addition, the software can generate CW signals configured in multiple ways. 

Sometimes, users are required to combine waveforms. A common application is to combine a cellular signal like NR or LTE with a CW tone on top of it. For example, a user might be required to make a 100MHz channel bandwidth NR signal centered at a 3 GHz frequency; and simultaneously send a CW signal at an Offset 100MHz outside the NR signal band.

This article will guide you through the steps required to create such combined waveforms in RFmx Waveform Creator. An NR signal will be used as an example. You must install the RFmx Waveform Creator and the RFmx NR personality. You will also require an NI signal generator instrument like a Vector Signal Generator or a Vector Signal Transceiver. And if you want to review the generated signal with NI's platform, you will require a Vector Signal Analyzer as well.

Finally, even though this article will only show an NR signal as an example, this can be applied to other modulated signals as well. Nevertheless, you require the personality for the signal you will generate. Therefore, if you are going to merge an LTE signal with a CW, you are required to install the RFmx LTE/LTE-Advanced personality.

Creating the NR Signal

  1. Open the RFmx Waveform Creator software and click Modulation >> NR.
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  1. You can now select New Default Settings >> OK or Example Settings >> OK, depending on your preference. The included already-built waveforms explore different settings like Link Direction, Frequency Ranges, Component Carrier Number, Channel Bandwidth, Modulation types, Subcarrier Spacing, and others. This article will move forward with the autoselected example waveform NR_FR1_DL_FDD_SISO_BW-100MHz_CC-1_SCS-30kHz_Mod-256QAM-OFDM-NoSSB.rfws and modify a few settings.
  2. You can now navigate the signal's configuration tree menu and change the signal's properties as you need it. In this case, the Channel Bandwidth property will be set to 10 MHz as an example. This is done in the menu branch Signal Configuration >> Carrier Definition 0. You can then set the Channel Bandwidth property to a required value. Here, 10 MHz is used.
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  1. You now must save the NR waveform as a TDMS file. This is done by clicking the Save Waveform File button in the upper software tab section. Then, click Current Settings... Click Browse to select where to save the TDMS file. You can leave the rest of the settings as they are shown. Then, click Save and pay close attention to the File Summary information shown. Save the Number of Samples and Sampling Rate values. In this example, they are 153600 samples and 15.36 MHz respectively.
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Creating the CW Signal

  1. Click Modulation >> Tones.
  2. ​​​​​Click Add... to add a tone.
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  1. Configure the tone as desired. The Frequency property sets the frequency the tone will have measured from the carrier frequency. In this case, a single tone with a 5 MHz positive offset from the carrier frequency (value defined later) will be configured. Therefore, the Frequency will be set to 10 MHz. Then, click OK.
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  1. You now must uncheck the Auto Settings checkbox and match the values to the ones reported on the NR file summary. We can insert the Sample Rate directly using the Sampling Rate value, which would be 15.36 MHz. Then, the File Length is computed as the Number of Samples divided by the Sampling Rate. Based on the data reported by the NR file summary, the signal is 10 ms long. Double-check the auto-populated Number of Samples section matches the value reported by the NR file summary, 153600 samples.
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  1. You now must save the Tone waveform as a TDMS file. This is done by clicking the Save Waveform File button in the upper software tab section. Then, click Current Settings... Click Browse to select where to save the TDMS file. You can leave the rest of the settings as they are shown. Then, click Save.


Merging the Signals Together

  1. Click Modulation >> Multi-Carrier.
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  1. ​​​​​Click the Add button to open the Add Carrier window.
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  1. Click the File Name option and navigate to where you stored the TDMS files. Select the first waveform. Leave the settings as they are loaded and click OK.
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  1. Repeat steps 2 and 3 to load the second waveform. 
  2. You can go to the Graphics tab inside the Multi-Carrier program window and click on Regenerate Plot to preview the waveform. See below the 10 MHz wide NR signal with the +5 MHz offset tone.
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  1. You can now generate or save the waveform. To generate the waveform, see the next section. To save it, click the Save Waveform File button in the upper software tab section. Then, click Current Settings... Click Browse to select where to save the TDMS file. You can leave the rest of the settings as they are shown. Then, click Save.

To generate the signal using an NI device, click the Instrument tab and the Download & Play option.

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Then, select the device using the Device Name drop-down menu and the Carrier Frequency with the Center Frequency property. In this example, a first-generation Vector Signal Transceiver PXIe-5644R is connected in a loopback. A 2 GHz center frequency is chosen. Finally, click the Create & Play button to generate the combined signal.

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You can use the RFmx Soft Front Panel to analyze the spectrum of the received signal. See below the final result.

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