Filtering Gaussian noise with Matlab

[guru]

I’m generating a 1 kHz square wave and adding Guassian noise to obtain a SNR of 0 dB (using Matlab6.5). The task is to design a filter that will filter out as much noise as possible from the square wave plus noise signal.
The sampling frequency is 100kHz.
Noise signal: 100.0*randn(1, length(t))
Square wave: 100*square(2*pi*1000*t)
What else do I need to know in order to design this filter using Butterworth or Chebyshev I or any filter? How do I determine the cut-off frequency for my filter?
The MATLAB function filter(B,A,x) will be used for the time-domain filtering operation.
I've started out by considering the frequency characteristics of each signal, but don't know how that will help i the design process.
Any help will be greatly appreciated.
Thanks

 

[osilmag]

You can design a low, high, or bandpass filter with the bessel function in matlab. Here is the link to it:
https://www.mathworks.com/help/signal/ref/besself.html

So, if the sampling frequency is 100khz, you should cut it off at 50khz. That is the Nyquist Frequency.