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IFFT feeding order in DVB-T

Started by dirkpitt March 12, 2007
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+172=1876 after that use fftshift to change the order