MatLab "generate signal and add white noise"

[knjazik]

Hello,
i need help.

I have to generate signal (120 points), with 4 complex exponent frequency`s 0,1 Hz, 0,25 Hz, 0,4 Hz and -0,1 Hz. Amplitudes 1.
And to add White Noise with 0,1 and 1 power (there are no measures in exercise), 100 realizations.


x=rand(1,120);
How to define frequency`s I have no idea at all..

White noise:
y = awgn(x,snr,0.1);
y = awgn(x,snr,1);
.. or?


and what does it mean 100 realizations and what for it is...?

I promise to receive help..

thanks!