OFDM on AWGN channel performance

Dear my friends. 

I have some problems with OFDM simulation on AWGN channel.I have 260 bits
lenght data

After ifft block of OFDM transmitter. I add cyclic prefix and I have 300
bits lenght data.

I want to add AWGN noisy signal (sigma*randn(1,300)) on to my signal
(y_ps)

ynoisy = y_ps+sigma*randn(1,300) my noisy signal became like this


but my AWGN noisy signal is bigger than my y_ps signal.I think it is
because of ifft we are dividing N to my signal.  how do ı normalized my
awgn signal.

My channel parameters and my signals are below.

% Fading amplitude; a=1 in AWGN channel
   a = 1;          

   for nEN = 1:length(EbN0db)
   en = 10^(EbN0db(nEN)/10);      % convert Eb/N0 from unit db to normal
numbers
   L_c = 4*a*en*rate; 	% reliability value of the channel
   %sigma = 1
   sigma = 1/sqrt(2*rate*en); 	% standard deviation of AWGN noise
  
      ynoisy = y_ps+sigma*randn(1,300);


thanks.

On Jun 2, 8:44 am, "volkanizma2003" <ozduranvol...@gmail.com> wrote:
> Dear my friends.
>
> I have some problems with OFDM simulation on AWGN channel.I have 260 bits
> lenght data
>
> After ifft block of OFDM transmitter. I add cyclic prefix and I have 300
> bits lenght data.
>
> I want to add AWGN noisy signal (sigma*randn(1,300)) on to my signal
> (y_ps)
>
> ynoisy = y_ps+sigma*randn(1,300) my noisy signal became like this
>
> but my AWGN noisy signal is bigger than my y_ps signal.I think it is
> because of ifft we are dividing N to my signal.  how do &#305; normalized my
> awgn signal.
>
> My channel parameters and my signals are below.
>
> % Fading amplitude; a=1 in AWGN channel
>    a = 1;
>
>    for nEN = 1:length(EbN0db)
>    en = 10^(EbN0db(nEN)/10);      % convert Eb/N0 from unit db to normal
> numbers
>    L_c = 4*a*en*rate;   % reliability value of the channel
>    %sigma = 1
>    sigma = 1/sqrt(2*rate*en);   % standard deviation of AWGN noise
>
>       ynoisy = y_ps+sigma*randn(1,300);
>
> thanks.

Choose sigma = sqrt(mean(abs(y_ps)^2))/sqrt(2*rate*en) instead.
That will make your average SNR=rate*en

Thanks,
Dilip.

>On Jun 2, 8:44 am, "volkanizma2003" <ozduranvol...@gmail.com> wrote:
>> Dear my friends.
>>
>> I have some problems with OFDM simulation on AWGN channel.I have 260
bits
>> lenght data
>>
>> After ifft block of OFDM transmitter. I add cyclic prefix and I have
300
>> bits lenght data.
>>
>> I want to add AWGN noisy signal (sigma*randn(1,300)) on to my signal
>> (y_ps)
>>
>> ynoisy =3D y_ps+sigma*randn(1,300) my noisy signal became like this
>>
>> but my AWGN noisy signal is bigger than my y_ps signal.I think it is
>> because of ifft we are dividing N to my signal.  how do =C4=B1
normalized=
> my
>> awgn signal.
>>
>> My channel parameters and my signals are below.
>>
>> % Fading amplitude; a=3D1 in AWGN channel
>>    a =3D 1;
>>
>>    for nEN =3D 1:length(EbN0db)
>>    en =3D 10^(EbN0db(nEN)/10);      % convert Eb/N0 from unit db to
norma=
>l
>> numbers
>>    L_c =3D 4*a*en*rate;   % reliability value of the channel
>>    %sigma =3D 1
>>    sigma =3D 1/sqrt(2*rate*en);   % standard deviation of AWGN noise
>>
>>       ynoisy =3D y_ps+sigma*randn(1,300);
>>
>> thanks.
>
>Choose sigma =3D sqrt(mean(abs(y_ps)^2))/sqrt(2*rate*en) instead.
>That will make your average SNR=3Drate*en
>
>Thanks,
>Dilip.
>Dear Dilip 

Thanks for your intereset and your help
But I changed my sigma, I wrote yours 
sigma = sqrt(mean(abs(y_ps)^2))/sqrt(2*rate*en)

But matlab gave error
??? Error using ==> mpower
Matrix must be square.

Error in ==> aes_turbo_ofdm_demo at 320
    sigma = sqrt(mean(abs(y_ps)^2))/sqrt(2*rate*en)

and at the same time you wrote 3D1 I didnt understant 3D1.


I would like to give some info about my codes
%%%%%%%OFDM TRANSMITTER%%%%%%%%%%%%%%%%%%%%%%%
en_output_sp = reshape(en_output,26,10)  %serial to paralel
en_output_sp_ifft= ifft(en_output_sp); %%%ifft
y=[en_output_sp_ifft(23:26,:); en_output_sp_ifft]; %add cyclic prefix(last
4 bits)
y_ps=reshape(y,1,300); %paralel to series

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%Channel%%%%%%%%%%%%%%%%%%%%%%%
EbN0db = input(' Please enter Eb/N0 in dB : default 1.00]    ');
if isempty(EbN0db)
  EbN0db = [1.00];
end


 % Fading amplitude; a=1 in AWGN channel
  a = 1;          

   for nEN = 1:length(EbN0db)
   en = 10^(EbN0db(nEN)/10);      % convert Eb/N0 from unit db to normal
numbers
   L_c = 4*a*en*rate; 	% reliability value of the channel

sigma = sqrt(mean(abs(y_ps)^2))/sqrt(2*rate*en)
ynoisy = y_ps+sigma*randn(1,300);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%Channel%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%OFDM Receiver%%%%%%%%%%%%%%%%%%%%%%%%%%5

ynoisy_ps = reshape(ynoisy,30,10);  %%% serial to paralel
ynoisy_ps(1:4,:)=[]; %Remove cyclic prefix
y_fft=fft(ynoisy_ps);  %%fft Blocks
y_fft_ps = reshape(y_fft,1,260); %%Paralel to series
r= real(y_fft_ps); % received bits

Thanks for your time Best wishes