[opendtv] Re: Thomson readies solutions for U.S. Digital TV broadcast transition
- From: Richard Hollandsworth <holl_ands@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 12 May 2006 18:29:58 -0700 (PDT)
The addition of more powerful coding, even it's simple data repeats, can't help
but combat multipath....only a fraction of the bits need to be successfully
received.
Antenna Diversity also can provide significant resistance to multipath.
Although I share your displeasure with allocating much less than about 15-19
Mbps for HD channels,
in a couple years there will be a glut of (mosty UHF) transmitters looking for
revenue streams.....
If the technology pans out, why wouldn't distribution of non-real time HD-DVD
programs (ala Moviebeam) and real-time SD programs (ala USDTV) to simple indoor
antennas via E-8VSB be viable alternatives???
holl_ands
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John Shutt <shuttj@xxxxxxxxx> wrote: The drawback of E-VSB is that it doesn't
directly address multipath. It
lowers S/N for the robust stream, but doesn't lower multipath
susceptibility.
The core technology of A-VSB is that a fixed data pattern is dispersed
before the R-S encoder and interleaver in such a way that it comes out of
the transmitter as a contiguous block in a known pattern. This hunk of
contiguous data can be used by a specially designed receiver as an extended
series of training signals to better track dynamic multipath. Doing this
requires control of the multiplexer, R-S encoder, data interleaver, and
8-VSB modulator as a unit, instead of separate building blocks.
A-VSB also includes the 1/2 or 1/4 rate Turbo modes for portable/mobile use,
that still eat away 2 or 4 standard bits for every robust bit as does
E-8VSB. A-VSB also time slices the robust data, ala DVB-H, for lower
battery consumption. The additional pseudo data training signals allow
this.
The neat thing is that new receivers can find the 120 newly created fixed
data pattern "SRS" supplemental training signals per VSB frame for enhanced
dynamic multipath tracking, while existing receivers simply ignore these
otherwise meaningless data packets. You do pay a payload price, however, so
the magic "19.4 for HD and not a bit less" means we can't use any of this.
Hey, if we were able to do HD in 13.4 Mbps and mobile in 1.5 Mbps, we would
have adopted DVB-T 6 years ago!
John
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