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signal averaging : ウィキペディア英語版
signal averaging
Signal averaging is a signal processing technique applied in the time domain, intended to increase the strength of a signal relative to noise that is obscuring it. By averaging a set of replicate measurements, the signal-to-noise ratio, S/N, will be increased, ideally in proportion to the square root of the number of measurements.
== Deriving the SNR for averaged signals ==

Assumed that
* Signal s(t) is uncorrelated to noise, and noise z(t) is uncorrelated : E() = 0 = E()\forall t,\tau.
* Signal power S=\int_0^T is constant in the replicate measurements.
* Noise is random, with a mean of zero and constant variance in the replicate measurements: E() = 0 = \mu and 0 < E() = E() = \sigma^2.
* We (canonically) define Signal-to-Noise ratio as SNR=\frac.
=== Noise power for sampled signals ===
Assuming we sample the noise, we get a per-sample variance of
\mathrm(z)=E() = \sigma^2.
Averaging a random variable leads to the following variance:
\mathrm\left(\frac 1n \sum_^n z_n\right) = \frac 1 \mathrm\left(\sum_^n z_n\right)= \frac 1 \sum_^n\mathrm\left( z_n\right).
Since noise variance is constant \sigma^2:
N_\text = \mathrm\left(\frac 1n \sum_^n z_n\right) = \frac 1 n \sigma^2 = \frac 1n \sigma^2,
demonstrating that averaging n realizations of the same, uncorrelated noise reduces noise power by a factor of n.

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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