[opendtv] Re: France
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 1 Jun 2005 18:20:58 -0400
Bob Miller wrote:
> You will be able to rent a car with mobile HDTV
> terrestrial by this time next year in France. (no
> matter how crazy you think that might be--not
> advocating it just predicting it)
And again, no matter how crazy mobile reception might
seem, why not here as well? Just as non-critical
antenna aim was simply a matter of the receiver being
capable of tolerating a wide range of echoes, rather
than something tied uniquely to *a* modulation scheme,
mobile reception depends on dynamic echo tolerance.
Who is to say that 5th gen receivers, or future 6th
gen, are or will be unable to achieve this?
Now that you, personally, have witnessed 8-VSB
receivers capable of solid reception without being
overly sensitive to antenna aim, perhaps what follows,
from a year ago, will not sound so fantastic now.
This is for all the skeptics. An article from NAB
2004.
http://www.tvtechnology.com/features/On-RF/f_rf_technology-07.07.04.shtm
l
The first exerpt of note is:
"Andy Bater noted that transmitter performance can
have an impact on DTV reception. Many NTSC transmitters
put out excessive spurious signals on adjacent
channels, making receiver adjacent-channel rejection
moot."
This correlates well with the Linx tests in Chicago, in
March 2003, in which all failures occurred where the
channel attempted had a strong adjacent NTSC signal.
"When the original DTV planning factors were developed,
it was assumed DTV tuners would utilize double
conversion receivers. In practice, most are single
conversion. Based on this, some of the UHF channel
taboos eliminated for interference into DTV tuners may
have to be reinstated."
Gee, doesn't that ever sound familiar? And that only
reinforces Sinclair's request that the FCC set minimum
receiver standards. If the FCC sets the standards for
allowable transmitter sites, then it's up to the FCC to
take that into account when they make assumptions on
reception contours. And their assumptions have to be
reflected in fact. This is basic systems engineering.
An output can only be predicted if you know the input
and the transfer function.
"Wayne Bretl from Zenith and Victor Tawil presented an
update on the performance of fifth-generation 8-VSB
receiver chips in the paper, 'Fifth Generation VSB
Receiver Field Test Report.' Some of these newer chips
are able to take advantage of multiple echoes and
provide reception, even when the uncorrected
signal-to-noise ratio is less than 15.5 dB. Equalizer
response has been extended and is now symmetrical,
which should greatly improve reception from
distributed transmission networks or on-channel
boosters, where multiple transmitters may be received
at one location, leading to 'pre-echoes' that older
8-VSB receivers had trouble handling. Fifth-generation
receivers now initialize the equalizer based on
channel impulse noise response, reducing acquisition
time. The newer chips also have improved capability
for handling reflections with higher Doppler rates,
making them more suitable for portable and mobile
use."
This also sounds awfully familiar.
Wayne Bretl also reported that the 5th gen receiver
was tested in the same worst-case locations in the DC
area as the Linx receiver, and failed to receive the
signal in 14 percent of sites compared with Linx which
failed in 17.7 percent of sites. Interesting. These
were all ground level, in congested urban settings,
and Linx, at least, did not allow reaiming the antenna
after the first channel was received. (The article
suggests that newer Linx receivers would have been
improved.)
Wayne Bretl also reported that in simulations, anyway,
while E-VSB improved the performance of 4th gen
receivers in difficult environments (4th gen meaning
Linx), it only helped 5th gen receivers by lowering
the SNR margin by 6 dB for the E-VSB stream, and also
more rapid acquisition. E-VSB did *not* appreciably
help 5th generation receivers in terms of dynamic echo
tolerance.
So, it might be instructive to see just how good mobile
reception is, with 5th gen, and watch as it improves
over time.
Bert
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