# BPSK AWGN variance calculation from SNR

Discussion in 'Electronic Design' started by Sherrie Laraurens, Feb 18, 2007.

1. ### Sherrie LaraurensGuest

Hi all,

I'm trying to write a simple BPSK through an AWGN channel.
I'm currently taking a file of binary data and going 1 bit
at a time through it and doing the following:
if the bit is 1 equate the bpsk form to +1/sqrt(2)
if the bit is 0 equate the bpsk form to -1/sqrt(2)

So far so go, now I want to simulate an AWGN channel, with
the hopes of calculate a BER from between what went into
the AWGN channel and what came out.

I've setup a Gaussian / normal distribution random number
generator, with mean of 0.0, but I've having difficulty
calculating the variance. I'm simulating this only using
Eb/No or SNR in dB form.

Is the formula for variance like so:

sigma = sqrt(1.0 / 2.0 * 10 ^ ((Eb/_No) / 10.0));

or

sigma = sqrt(1.0 / 2.0 * 10 ^ (SNR / 10.0));

all help and comments will be appreciated very much.

-Sherrie

2. ### joseph2kGuest

Lookup Shannon's law.

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