World Library  
Flag as Inappropriate
Email this Article

Carrier-to-noise ratio

Article Id: WHEBN0003994748
Reproduction Date:

Title: Carrier-to-noise ratio  
Author: World Heritage Encyclopedia
Language: English
Subject: Signal-to-interference ratio, Noise, Noise (electronics), DVB-S2, Orthogonal frequency-division multiplexing
Collection: Engineering Ratios, Noise
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Carrier-to-noise ratio

In telecommunications, the carrier-to-noise ratio, often written CNR or C/N, is the signal-to-noise ratio (SNR) of a modulated signal. The term is used to distinguish the CNR of the radio frequency passband signal from the SNR of an analogue base band message signal after demodulation, for example an audio frequency analogue message signal. If this distinction is not necessary, the term SNR is often used instead of CNR, with the same definition.

Digitally modulated signals (e.g. QAM or PSK) are basically made of two CW carriers (the I and Q components, which are out-of-phase carriers) . In fact, the information (bits or symbols) is carried by given combinations of phase and/or amplitude of the I and Q components. It is for this reason that, in the context of digital modulations, digitally modulated signals are usually referred to as carriers. Therefore, the term carrier-to-noise-ratio (CNR), instead of signal-to-noise-ratio (SNR) is preferred to express the signal quality when the signal has been digitally modulated.

High C/N ratios provide good quality of reception, for example low bit error rate (BER) of a digital message signal, or high SNR of an analogue message signal.

Contents

  • Definition 1
  • See also 2
  • References 3
  • External links 4

Definition

The carrier-to-noise ratio is defined as the ratio of the received modulated carrier signal power C to the received noise power N after the receiver filters:

\mathrm{CNR} = \frac{C}{N} .

When both carrier and noise are measured across the same impedance, this ratio can equivalently be given as:

\mathrm{CNR} = \left( \frac{V_C}{V_N} \right) ^2 ,

where V_C and V_N are the root mean square (RMS) voltage levels of the carrier signal and noise respectively.

C/N ratios are often specified in decibels (dB):

\mathrm{CNR_{dB}} = 10 \log_{10}\left( \frac {C}{N} \right) = C_{dBm} - N_{dBm}

or in term of voltage:

\mathrm{CNR_{dB}} = 10 \log_{10}\left( \frac{V_C}{V_N} \right)^2 = 20 \log_{10}\left( \frac {V_C}{V_N} \right)

The C/N ratio is measured in a manner similar to the way the signal-to-noise ratio (S/N) is measured, and both specifications give an indication of the quality of a communications channel.

In the famous Shannon–Hartley theorem, the C/N ratio is equivalent to the S/N ratio. The C/N ratio resembles the carrier-to-interference ratio (C/I, CIR), and the carrier-to-noise-and-interference ratio, C/(N+I) or CNIR.

See also

References

External links

  • Digital Transmission: Carrier-to-Noise, Signal-to-Noise & Modulation Error Ratio
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.