[opendtv] Re: Latest S/N test
- From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 25 Jan 2005 13:18:15 -0500
As I recall, TV channels are 8 MHz wide in mainland China.
Al Limberg
----- Original Message -----
From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
Sent: Tuesday, January 25, 2005 11:19 AM
Subject: [opendtv] Re: Latest S/N test
> Bob Miller wrote:
>
> > Recent test of DMB-T, DVB-T, ATSC
> >
> > S/N
> > 18.5 db ATSC OQam Linx
> > 16 db DVB-T
> > 15 db DMB-T
> > and
> > 12.5 db DMB-T using a similar scheme to DVB-S-2
> > with LDPC
> >
> > How close is that to Shannon limit?
>
> Can't tell, unless you give the actual bandwidth used
> in the RF channel and the channel capacity (b/s). With
> that info, the limiting S/N for error-free
> communications can be computed.
>
> Strange that the OAM scheme measured lower than ATSC,
> but again, need more information. When Linx first
> developed that, they claimed 15 dB for the wide
> channel. Perhaps having those two extra pilots,
> while it does increase robustness, also demands more
> power. But they were rather low power. Weird.
>
> If I remember, DMB-T uses a CDMA spread spectrum scheme
> to transmit the training sequence, and COFDM for the
> signal. Not positive, though.
>
> > So the latest DVB-T compared to the latest 8-VSB
> > gives DVB-T a 2.5 db advantage.
>
> That's doubtful, as it would mean DVB-T is capable
> of 12.5 dB C/N in a 5.38 MHz channel for ~20 Mb/s.
> Perhaps you need to supply more detail on these
> tests. And no silly propaganda, please!
>
> BTW, the Shannon limit for 20 Mb/s in a 5.38 MHz
> channel would be that you need 10.85 dB of C/N
> for error-free comms.
>
> Bert
>
>
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