[opendtv] Re: China OKs its own terrestrial DTV spec
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sun, 10 Sep 2006 19:23:34 -0400
Bob Miller wrote:
> China was going to go with a dual standard but took some time
> and come up with a compromise which incorporates some of the
> VSB stuff but is still a multi-carrier TD-OFDM modulation.
> Broadcasters are not going to be using a single carrier for
> rural areas and a multi-carrier for cities. I think the VSB
> part is more face saving to get this done. Notice no one is
> talking about dual receivers or broadcasters having to chose
> what modulation to use anymore which they were doing in the
> summer.
Problem is, Bob, I can't tell how much of this is fact that you are
reporting, and how much is your repeated editorial comment on VSB.
The article could be completely wrong, of course. But as written, the
article states clearly that VSB is used to fixed sets, in cities or in
rural areas, and that time-synchronous COFDM is used to handheld
devices, in cities. Presumably, there won't be a lot of coverage in
rural areas for handheld devices, since that requires a rather dense
distribution of towers.
Just like in the US and Europe, broadcast transmissions to handhelds and
to fixed sets are different. Different programming. So there's no reason
to expect dual-mode sets, although of course in principle that should be
possible. In China or elsewhere.
> I thought it would have been interesting to see them go head
> to head and was disappointed when they compromised. The VSB
> had mobile test in one city and fixed in some others but the
> DMB-T test were taking place in 30 or more cities. If they
> had gone head to head no one would have implemented the VSB.
But again, are you reporting that you know for a fact that VSB was not
tested against COFDM at any time? Note that if they already chose
TS-COFDM as a service for handheld devices only, by this summer the only
comparison tests that would make sense would be against DMB-T. Not
against the unrelated VSB signal.
On a slightly related note, last night I finally managed to receive
WETA-DT (local DC PBS station, low power, adjacent to high power analog
WETA-TV). Very marginal signal. Probably because the analog station was
off the air at that late hour. No such luck again this afternoon,
though.
This is as much fun as playing with shortwave radio when I was a kid.
Bert
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