Rayleigh fading in OFDM

  Hello,

    I have maganged to simulate an OFDM system using Matlab. It works 
   fine in AWGN channel and SNR vs BER curve matches the theoretical one.
   But I have problem when I add Rayleigh to it (I get similar amount of
   BER for all SNR). I have used standard matlab functions to gerenate 
   static flat fading:
       
   c=raylieghchan();
   y = filter(c,ofdm_symbol);
   % then I add AWGN
 
   Is there anything else I need to do? 

   Best regards
   Shahin

persian_eagle wrote:
> Hello,
>
>     I have maganged to simulate an OFDM system using Matlab. It works
>    fine in AWGN channel and SNR vs BER curve matches the theoretical one.
>    But I have problem when I add Rayleigh to it (I get similar amount of
>    BER for all SNR). I have used standard matlab functions to gerenate
>    static flat fading:
>
>    c=raylieghchan();
>    y = filter(c,ofdm_symbol);
>    % then I add AWGN
>
>    Is there anything else I need to do?

Just some random ideas, since I've never used those matlab functions (I
tend to create my own low-level functions). Is the BER you're getting
close to 0.5? This might indicate the fading you're introducing is too
strong. What happens if you don't introduce noise? What happens if you
substitute your rayleigh filter by a constant attenuator and a phase
shift?

HTH.