SNR vs CNR-C/N ratio(CNR) versus S/N ratio(SNR)
This page describes on SNR vs CNR describes signal to Noise Ratio(S/N ratio) and Carrier to Noise Ratio(C/N ratio).
C/N Ratio (CNR) stands for Carrier to Noise Ratio. It is measured after modulation.
S/N Ratio (SNR) stands for Signal to Noise Ratio. It is measured before modulation.
S/N = Psignal/Pnoise = [Asig(rms)/Anoise(rms)]2
(S/N)dB= 10 log(Psignal/Pnoise) Both CNR and SNR are expressed in Decibel (dB).
Relation between C/N Ratio (CNR)and Eb/N0 ratio
Eb/N0 = ((C/Fb )/ (N/BW))
Where Fb is bit rate, C is the total carrier power,
N is the total noise power, BW is the bandwidth of the modulated signal.
Eb/N0 and S/N ratio required for complex digitally modulated signal for WiMAX system is as follows.
| Modulation/Code rate | Eb/No(dB) | S/N ratio(dB) |
| QPSK-1/2 | 10.5 | 9.4 |
| QPSK-3/4 | 10.5 | 11.2 |
| 16QAM-1/2 | 14.5 | 16.4 |
| 16QAM-3/4 | 14.5 | 18.2 |
| 64QAM-2/3 | 19 | 22.7 |
| 64QAM-3/4 | 19 | 24.4 |
SNR vs CNR is very useful for RF field engineers to analyze complex power spectrum using spectrum analyzer and readings obtained in the satellite modem used for VSAT.
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