[opendtv] Re: DTT tuner design
- From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
- To: "OPENDTV" <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 05 Jul 2007 16:49:10 -0700
That is, assuming the combined trellis and R-S FEC schemes are
more cleverly exploited as you suggest. The potential is clearly
there but, do you believe that this will actually happen in the
US system? I know that I'm a pessimist but it is for good reasons.
>
> > -----Original Message-----
> > From: Dale Kelly [mailto:dalekelly@xxxxxxxxxxx]
> > Sent: Wednesday, July 04, 2007 7:04 PM
> > To: opendtv@xxxxxxxxxxxxx
> > Subject: RE: [opendtv] Re: DTT tuner design
> >
> >
> > Thanks for the update Bert, I'll recalibrate my C/N references.
> > With a good front end the Gemini should be impressive.
> >
> > > -----Original Message-----
> > > From: opendtv-bounce@xxxxxxxxxxxxx
> > > [mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Albert Manfredi
> > > Sent: Wednesday, July 04, 2007 5:52 PM
> > > To: opendtv@xxxxxxxxxxxxx
> > > Subject: [opendtv] Re: DTT tuner design
> > >
> > >
> > > Dale Kelly wrote:
> > >
> > > >I misspoke, either modulation system requires increased C/N
> > > >to handle multipath.
> > >
> > > I this strictly true? I don't think so. And I believe that's why
> > > the Chinese
> > > standard adopted a training sequence in the GI (same one they use
> > > in their
> > > single carrier mode), rather than using the end of the previous
> > > symbol, as
> > > standard COFDM does. And that's also my bet for DVB-T2. (Just
> > > speculation.)
> > >
> > > The ideal equalizer should not require a higher C/N to twist
> multipath
> > > distortion back into shape.
> > >
> > > Here is an example. I'm assuming here that the numbers provided
> > > are C/(N+I),
> > > and that when this value is less than 15 dB, what you're actually
> > > seeing is
> > > a (C+I)/N that is close to 15 dB.
> > >
> > > (I also believe that eventually we'll be seeing (C+I)/N better
> > > than 15 dB,
> > > when the combined trellis and R-S FEC schemes are more cleverly
> > > exploited.)
> > >
> > > These are C/N numbers that apply to the Samsung Gemini chip.
> > >
> > > No multipath 15.2 dB
> > > Brazil A 15.0
> > > Brazil B 17.0
> > > Brazil C 13.5
> > > Brazil D 13.8
> > > Brazil E 19.9
> > >
> > > Compare this to the CSA values for 64-QAM and 3/4 FEC (same spectral
> > > efficiency if GI is 1/16).
> > >
> > > No multipath is 18 dB, Ricean is 18.6 dB, and their Rayleigh,
> > > which is less
> > > strenuous than Brazil E, is 21.7 dB. (Brazil E has 3 dB
> echoes, vs two.)
> > >
> > > So basically, the planning factors used by the CSA do assume a
> > > deficit of ~3
> > > dB or more in C/N margin, compared with a well executed equalizer
> > > demod. And
> > > that's reflected in the field strength minima. If good demods are
> > > used, the
> > > FCC and CSA planning factors should provide very close to the
> > > same coverage,
> > > is my thinking.
> > >
> > > Bert
> > >
> > > _________________________________________________________________
> > > http://liveearth.msn.com
> > >
> > >
> > >
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