how to generate a( 226 × 1 ) vector "b" as a zero mean white Gaussian noise (WGN) sequence with variance =0.24e-4 ?

b=wgn(256,1,??) 

with var(p)=0.24e-4

Answer 1

[William Rose]

@ad lyn

b=wgn(226,1,.24e-4,'linear');
fprintf('Variance of b=%6f\n',var(b))

Variance of b=0.000024

If you run the code above multiple times, you will get slightly different results, since it is (pseudo)random.

[ad lyn]

thank you for answerning!

but here 's what's i have found in matlab

y = wgn(m,n,p) generates an m-by-n matrix of white Gaussian noise. pspecifies the power of y in decibels relative to a watt. The default load impedance is 1 ohm.

so p must be the value of the power of y not its variance

means

b=wgn(226,1,power of b (not var(p)),'linear');

[William Rose]

@ad lyn,

If the impedance is 1Ω, then power equals variance. If the signal's average value is zero - which is true for Gaussian white noise. And if power is measured in natural, or "linear" units, rather than in dB.

[ad lyn]

thank you so much

[William Rose]

Yu're welcome, @ad lyn.