Eb/N0 to SNR

Sure..

SNR = signal power / noise power = ( energy per bit * bits per second ) / (noise desntiy * bandwidth) = Eb/N0 * R/W

...where R/W is "bits per second per Hertz," an indication of the efficiency of the modulation format (albeit boiling down a modulation's efficiency to a single number tends to really only work for realtively high SNR systems with hard-wired connections... for wireless systems problems such as multi-path distortion vs. frequency, power amplifier linearity, doppler shift, etc. can significantly alter a system's overall efficiency). The following table -- cribbed from Dixon's "Radio Receiver Design," who credits his own cribbing to Oetting -- gives a few values of R/W vs. modulation type:

OOK (coherent detection) -> 0.8 FSK (non-coherent detection) -> 0.8 BPSK (coherent detection) ->0.8 QPSK (coherent detection) -> 1.9 QAM (coherent detection) -> 1.7

The actual table has more, but this should get you started. Most communication textbooks have similar tables -- or of course you can derive this as a homework exercise!

For back-of-the-envelope calculations, people often just assume R/W=1. Notice from the table that the increase in R/W with modulation complexity doesn't go up as quickly as you might intuitively had expected.

---Joel Kolstad

So, for back-of-the-envelope calculations, SNR = Eb/N0?

Yes... for simple modulation systems Eb/N0 will be about 1dB above SNR, whereas for complex systems you'll get around 2-4dB below SNR. Given that relatively small range, for rough calculation Eb/N0=SNR is reasonable.

---Joel