Hi everyone! It's my first post here, so please be patient if I'm too newbie 
;)
I've tried a search in the newsgroup but no valid results.

I'm trying to make a DVB-T transmitter in VHDL, but I find some problems 
when feeding the IFFT.
For example, I'm using the 2k mode. After insertion of TPS and pilots, I 
have 1705 (sub)carriers.
The IFFT accepts 2048 couples-data of real and imaginary, so I have put the 
1705 subcarriers in a 2048 buffer (from position 0 to 1704), padding all the 
other 343 words with zeros.
But now, I don't know hot to feed the IFFT. I think it's wrong to feed it in 
natural order (e.g. first couple is the 0-subcarrier)
What should I do?
Sorry for bothering
Simone 

dirkpitt wrote on Monday 12 Mar 2007 07:33:

> Hi everyone! It's my first post here, so please be patient if I'm too
> newbie ;)
> I've tried a search in the newsgroup but no valid results.
> 
> I'm trying to make a DVB-T transmitter in VHDL, but I find some problems
> when feeding the IFFT.
> For example, I'm using the 2k mode. After insertion of TPS and pilots, I
> have 1705 (sub)carriers.
> The IFFT accepts 2048 couples-data of real and imaginary, so I have put
> the 1705 subcarriers in a 2048 buffer (from position 0 to 1704), padding
> all the other 343 words with zeros.
> But now, I don't know hot to feed the IFFT. I think it's wrong to feed it
> in natural order (e.g. first couple is the 0-subcarrier)
> What should I do?
> Sorry for bothering

Annex D of the DVB spec (ETSI EN 300 744 v1.5.1) gives details on how the
sub-carriers are to be mapped onto IFFT inputs.


-- 
Oli

On Mar 12, 8:58 am, Oli Charlesworth <c...@olifilth.co.uk> wrote:
> dirkpitt wrote on Monday 12 Mar 2007 07:33:
>
> > Hi everyone! It's my first post here, so please be patient if I'm too
> > newbie ;)
> > I've tried a search in the newsgroup but no valid results.
>
> > I'm trying to make a DVB-T transmitter in VHDL, but I find some problems
> > when feeding the IFFT.
> > For example, I'm using the 2k mode. After insertion of TPS and pilots, I
> > have 1705 (sub)carriers.
> > The IFFT accepts 2048 couples-data of real and imaginary, so I have put
> > the 1705 subcarriers in a 2048 buffer (from position 0 to 1704), padding
> > all the other 343 words with zeros.
> > But now, I don't know hot to feed the IFFT. I think it's wrong to feed it
> > in natural order (e.g. first couple is the 0-subcarrier)
> > What should I do?
> > Sorry for bothering
>
> Annex D of the DVB spec (ETSI EN 300 744 v1.5.1) gives details on how the
> sub-carriers are to be mapped onto IFFT inputs.
>
> --
> Oli

Thank you for the quick answer.
Well, it's seems I'm really dumb. I have read it and I keep reading it
and I haven't understanding anything! :)
Can you please explain it in a very simple way for dummies like me?
Simone

On 12 Mrz., 11:57, "dirkpitt78" <dirkpit...@gmail.com> wrote:
> On Mar 12, 8:58 am, Oli Charlesworth <c...@olifilth.co.uk> wrote:
>
>
>
>
>
> > dirkpitt wrote on Monday 12 Mar 2007 07:33:
>
> > > Hi everyone! It's my first post here, so please be patient if I'm too
> > > newbie ;)
> > > I've tried a search in the newsgroup but no valid results.
>
> > > I'm trying to make aDVB-T transmitter in VHDL, but I find some problems
> > > when feeding the IFFT.
> > > For example, I'm using the 2k mode. After insertion of TPS and pilots, I
> > > have 1705 (sub)carriers.
> > > The IFFT accepts 2048 couples-data of real and imaginary, so I have put
> > > the 1705 subcarriers in a 2048 buffer (from position 0 to 1704), padding
> > > all the other 343 words with zeros.
> > > But now, I don't know hot to feed the IFFT. I think it's wrong to feed it
> > > in natural order (e.g. first couple is the 0-subcarrier)
> > > What should I do?
> > > Sorry for bothering
>
> > Annex D of theDVBspec (ETSI EN 300 744 v1.5.1) gives details on how the
> > sub-carriers are to be mapped onto IFFT inputs.
>
> > --
> > Oli
>
> Thank you for the quick answer.
> Well, it's seems I'm really dumb. I have read it and I keep reading it
> and I haven't understanding anything! :)
> Can you please explain it in a very simple way for dummies like me?
> Simone- Zitierten Text ausblenden -
>
> - Zitierten Text anzeigen -

2k mode
kmin = 0 kmax = 1704
N = 2048
kmin to n = 172, kmax to n= 1704+17276
after that use fftshift to change the order