how can i add AWGN noise to signal

Hello

I have a communcation system and i need to calculate the bit error rate by comparing the I/P stream with O/P stream

i added the AWGN noise using awgn(x,snr) function but it add random values with each run and the error rate is changing according to that. therefore i can't find thresold value for snr to calculate the correct bit error rate

how can i solve this issue?

thanks in advance

Answer 1

[Abderrahim. B]

Perhaps setting random number generator will be helpful. use rng

MWs Example:

% Generate random data symbols and the 4-PSK modulated signal.
M = 4;
k = log2(M);
snr = 3;
data = randi([0 M-1],2000,1);
x = pskmod(data,M);

% Set the random number generator seed.
seed = 12345;
rng(seed);
y = awgn(x,snr);

% Compute the bit errors.
dataHat = pskdemod(y,M);
numErr1 = biterr(data,dataHat,k)

numErr1 = 300

% Reset the random number generator seed.
rng(seed);

% Demodulate the PSK signal and compute the bit errors.
y = awgn(x,snr);
dataHat = pskdemod(y,M);
numErr2 = biterr(data,dataHat,k)

numErr2 = 300

% Compare numErr1 to numErr2. The errors are equal even after you reset the random number generator seed.
isequal(numErr1, numErr2)

ans = logical
   1