I am looking for the optimum modulation scheme to build a half-duplex modem minimizing the required SNR at the expense of bandwidth efficiency. The key system parameters are described below:

  • Target bitrates: 15 - 100 Kbps
  • Available BW: 1.6 MHz
  • Power amplifier operating at saturation level

Given that the maximum required bitrate has plenty of room in the available BW and that the power amplifier will be operating at saturation level, I was thinking that a constant envelope modulation such as FSK would be a good choice.

In an effort to minimize the required SNR for a given BER, it seems that higher order M-FSK perform better in low SNR environments:

enter image description here

The plot above has been generated with: https://www.mathworks.com/help/comm/ref/fskdemod.html

By carefully choosing a frequency spacing so that the modulation index (h=1), a 32-FSK or even a 64-FSK modulation seems to be the best choice to minimize the required SNR. However, the lack of existing modem solutions for this type of scheme makes me think whether I am missing something important to take into consideration before attempting to implement a high order FSK modulator + demodulator...

Thank you in advance!



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