signal-to-noise ratio

In analog and digital communications, signal-to-noise ratio, often written S/N or SNR, is a measure of signal strength relative to background noise. The ratio is usually measured in decibels (dB).

If the incoming signal strength in microvolts is V_s, and the noise level, also in microvolts, is V_n, then the signal-to-noise ratio, S/N, in decibels is given by the formula

S/N = 20 log₁₀(V_s/V_n)

If V_s = V_n, then S/N = 0. In this situation, the signal borders on unreadable, because the noise level severely competes with it. In digital communications, this will probably cause a reduction in data speed because of frequent errors that require the source (transmitting) computer or terminal to resend some packets of data.

Ideally, V_s is greater than V_n, so S/N is positive. As an example, suppose that V_s = 10.0 microvolts and V_n = 1.00 microvolt. Then

S/N = 20 log₁₀(10.0) = 20.0 dB

which results in the signal being clearly readable. If the signal is much weaker but still above the noise -- say 1.30 microvolts -- then

S/N = 20 log₁₀(1.30) = 2.28 dB

which is a marginal situation. There might be some reduction in data speed under these conditions.

If V_s is less than V_n, then S/N is negative. In this type of situation, reliable communication is generally not possible unless steps are taken to increase the signal level and/or decrease the noise level at the destination (receiving) computer or terminal.

Communications engineers always strive to maximize the S/N ratio. Traditionally, this has been done by using the narrowest possible receiving-system bandwidth consistent with the data speed desired. However, there are other methods. In some cases, spread spectrum techniques can improve system performance. The S/N ratio can be increased by providing the source with a higher level of signal output power if necessary. In some high-level systems such as radio telescopes, internal noise is minimized by lowering the temperature of the receiving circuitry to near absolute zero (-273 degrees Celsius or -459 degrees Fahrenheit). In wireless systems, it is always important to optimize the performance of the transmitting and receiving antennas.

Do you have something to add to this definition? Let us know. Send your comments to techterms@whatis.com

Digg This!     StumbleUpon     Del.icio.us

RELATED CONTENT Network management takes interface tips from gaming industry, Google Simplified user interfaces are helping harried networking professionals stay on top of ever-more complex networks. Internet monitoring vendor adds throttling, filtering, to its appliance eTelemetry announced at Interop that it has added bandwidth throttling and filtering technologies to Metron 2.0, the new version of its Web activity... How green is my network? -- A look at the cost-savings benefit of green IT Find out how going green applies in network operations, and why the potential cost savings can be more persuasive than the goal of saving the...

RELATED GLOSSARY TERMS Terms from Whatis.com − the technology online dictionary 10-high-day busy period  (SearchNetworking.com) ACK  (SearchNetworking.com)