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5G Waveform Generator app from the 5G toolbox constellation diagram question

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christopher zarod
christopher zarod on 27 Jan 2021
Answered: Sriram Tadavarty on 31 Jan 2021
I am trying to analyze constellation diagrams in the 5G Waveform Generator app. I am using 5G test models option with FR2 frequency range with test model NR-FR2-TM3.1 (full band, uniform 64 QAM) with channel bandwidth of 200MHz and subcarrier spacing of 60kHz with duplex mode TDD. Why are the constellation diagrams produced by this not looking like a 64 QAM contellation diagram? It looks like a collection of 9 points randomly spread out but generally located at the center of the constellation diagram.

Answers (1)

Sriram Tadavarty
Sriram Tadavarty on 31 Jan 2021
Hi Christopher,
The constellation diagram observed in the 5G Waveform Generator App are those of the OFDM modulated waveform. Since, the 64 QAM modulated symbols, are performed OFDM modulation, they no longer be in the 64 QAM modulation. The constellation plot shows only the symbols after OFDM modulation.
One way to check the constellation diagram before OFDM modulation is through, performing OFDM demodulation for resultant waveform, using nrOFDMDemodulate and then plot functions.
Try these steps:
  • Export the waveform to workspace, using Export To Workspace. This gives the structure containing the waveform details
  • Let the variable name be var. For the example in question, 200 MHz bandwidth and 60 kHz SCS, there are 264 resource blocks. With this information, use nrOFDMDemodulate function. Like,
rxGrid = nrOFDMDemodulate(var.waveform,264,60,0); % waveform,nrb,scs,initalSlot
  • Now, use the plot function, to plot the constellation of each OFDM symbol. For example, plot symbols present in first OFDM symbols, Like
plot(rxGrid(:,1),'+')
Hope this helps.
Regards,
Sriram

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