# Noise Power calculations

1. Dec 7, 2011

### viperfx

I have values of time, and volts of a noise signal.

I am trying to determine the noise power, signal to power ratio and bit error probability.

How would I go about doing this?

Thanks.

2. Dec 7, 2011

### yungman

You start out with average power if you have the time and voltage.

Usually people use noise figure:

http://en.wikipedia.org/wiki/Noise_figure

Is that what you want? If so and you still have question, come back.

3. Dec 7, 2011

### viperfx

Ah ok, thank you.

Is this the method for volt and time values obtained from scope? Currently I have the data in excel. I will read into noise figure.

If you have any particular formulas that could give me a start that would be great.

4. Dec 7, 2011

### yungman

As power is average, you need to take the average of the volt to the resistance or if you know the current you can calculate as

$$P= I_{RMS}V_{RMS}=\frac {V_{RMS}^2} R$$

You have to use your data to find the RMS. Someone might want to come in about $\frac 1 2$. I just don't remember when to put the half in or not.

You calculate the power of the signal, This is the easy part. The trick is knowing your noise source. You need to give a lot more information about the noise before you can get the signal to noise ratio. If it is electronic component noise, then you need to give your circuit and calculate from there.

5. Dec 8, 2011

### viperfx

Yea I have come across many formulas like this, however the problem is I have values for only the time, and volts.

6. Dec 8, 2011

### viperfx

Never mind. The Noise power is the variance (S.D. ^2), and the SNR is the Signal Power/Noise Power. Signal Power is A^2/2.
PE = 0.5erfc(V/2*variance*sqrt(2))

Thanks anyways.