kindly help me in understanding this

hi all,
       i am new to OFDM concept, i took a sequence of +1 and -1 levels
for FFT and before that i ensured that i have to keep 0 at DC CARRIER
and guard carriers in between. and i have ensured a cyclic prefix of 4
samples

the FFT is of 16- point and IFFT is taken and then i am doing FFTSHIFT
again

but my answer is not same as (all along, i took it for granted, but
now i see that the datin which is extract of points without dc, and
guard carriers is not same as original. IS there anything i need to
multiply..

all members of this group..please answer to this question..Is there
any wrong understanding in my approach of OFDM symbol formulation


xya = fftshift([0 0 0 1 -1 1 1 1 0 -1 -1 -1 0 0 0 0]);
yn = ifft(xya);
xyz = ([yn(end-3:1:end) yn]);
xyn = ifftshift((fft(xyz(1,3:18))))
datin = (([xyn(4:8) xyn(10:1:12)])).'


-0.7071 - 0.7071i
   1.0000
  -0.7071 + 0.7071i
        0 + 1.0000i
   0.7071 + 0.7071i
  -0.7071 + 0.7071i
        0 + 1.0000i
   0.7071 + 0.7071i

thanks

On Jan 21, 5:46 pm, vividreddy <vlsire...@gmail.com> wrote:
> hi all,
>        i am new to OFDM concept, i took a sequence of +1 and -1 levels
> for FFT and before that i ensured that i have to keep 0 at DC CARRIER
> and guard carriers in between. and i have ensured a cyclic prefix of 4
> samples
>
> the FFT is of 16- point and IFFT is taken and then i am doing FFTSHIFT
> again
>
> but my answer is not same as (all along, i took it for granted, but
> now i see that the datin which is extract of points without dc, and
> guard carriers is not same as original. IS there anything i need to
> multiply..
>
> all members of this group..please answer to this question..Is there
> any wrong understanding in my approach of OFDM symbol formulation
>
> xya = fftshift([0 0 0 1 -1 1 1 1 0 -1 -1 -1 0 0 0 0]);
> yn = ifft(xya);
> xyz = ([yn(end-3:1:end) yn]);
> xyn = ifftshift((fft(xyz(1,3:18))))
> datin = (([xyn(4:8) xyn(10:1:12)])).'
>
> -0.7071 - 0.7071i
>    1.0000
>   -0.7071 + 0.7071i
>         0 + 1.0000i
>    0.7071 + 0.7071i
>   -0.7071 + 0.7071i
>         0 + 1.0000i
>    0.7071 + 0.7071i
>
> thanks

what i mean to ask is the points which i obtain are not same as the
points which i inserted into IFFT

what is the wrong in my program..