Dvb constellation

Patches for Linux kernel (v4l code) and for v4l-utils should be applied to obtain I&Q constellation described in this article.

Patch for Linux kernel: http://stand.netup.tv/downloads/iq_constellation.patch

Patch for v4l-utils: http://stand.netup.tv/downloads/iq_constellation_v4l-utils.patch

Receiving I&Q data from DVB demodulator

dvb_const -f /dev/dvb/adapter0/frontend1 -o iq_dvbc_qam256.txt -p 100000

received data (100000 points) will be saved into iq_dvbc_qam256.txt file. File format is simple text csv. Example of received data:

-175,-45
-46,110
-241,-178
176,11
-50,173
16,44

Values are signed. First I part, second Q part.

Visualization of received data

dvb_const_plot utility build PNG image with constellation:

dvb_const_plot -i iq_dvbc_qam256.txt -o iq_dvbc_qam256.png -c "SNR=38dB QAM256" 

resulting image will be saved into iq_dvbc_qam256.png. Here is example of images received with NetUP Dual DVB-T/C-CI RF and NetUP Dual DVB S2 CI cards.

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  QAM16 constellation (DVB-C)

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  QAM64 constellation (DVB-C)

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  QAM128 constellation (DVB-C)

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  QAM256 constellation (DVB-C)

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  32APSK constellation (DVB-S2)

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  16APSK constellation (DVB-S2)

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  8PSK constellation (DVB-S2)

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  QPSK constellation (DVB-S2)

Also See

• Quadrature Amplitude Modulation
• Quadrature Phase Shift Keying

External links

[1] Constellation diagram

[2] Digital Transmission: Carrier-to-Noise, Signal-to-Noise & Modulation Error Ratio