[opendtv] Re: COFDM and equalization
- From: "John Willkie" <jmwillkie@xxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 26 Apr 2004 20:29:30 -0700
Synchronous transmission is old hat; was perfected several decades ago for
TV and FM.
What has kept it from widespread use that that the atomic clock required at
each transmit point cost more than were "ecomonically justified." I don't
know if you can get the same degree of precision as is required with GPS.
I'd tend to doubt it: the deltas are in wave phase, not the number of
waves.
John Willkie
-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx
[mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Tom Barry
Sent: Monday, April 26, 2004 4:43 PM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: COFDM and equalization
All this talk about adjacent area interference makes me wonder. Is
there any way or technology to cooperate and synchronize different
adjacent channels on the same frequency such that they do not
interfere with each other?
- Tom
Craig Birkmaier wrote:
> At 6:32 AM -0700 4/21/04, Doug McDonald wrote:
>
>>It most certainly is licensed to serve this market,
>>Champaign-Decatur-Springfield. Our market is
>>long and thin, it's at one end, we are at the
>>other. The owners have a station way beyond us,
>>even farther at the other end, which would serve
>>us better if it were on ... but it is simply
>>a mirror of this one, they have absolutely
>>identical programming, even the local stuff
>>comes from the Springfield end.
>>
>>In any case, "market" means a different thing out here
>>than in the East where you are: out there
>>markets are smaller than the Grade B contours
>>of stations, here they are much larger ...
>>there are substantial areas even in a state
>>like Illinois that are essentially unserved by
>>analog TV. At full power they will be served
>>by ATSC.
>
>
> Thios is one way to serve these markets, however it is very
> inefficient in terms of spectral re-use. The proper way to serve your
> market is with several lower powered transmitters distributed
> geographically through the long thin market; this provides good RF
> thresholds EVERYWHERE in the intended market, with much less
> interference into adjacent markets.
>
> The reality is that where you live is "in-between." you are close
> enough to other major markets that market-into-market interference is
> a real problem. The big stick technique does have merit in
> geographically isolated markets like Salt Lake City - but you still
> need translators/repeaters to fill in all the gaps.
>
> Even in SLC COFDM still has major advantages...you just have the
> luxury of using higher power levels for the main transmitters.
>
>
>>Interference is simply not an issue at all.
>>In the absence of tropo, where I live, with
>>a reasonable antenna, we get grade A analog signals
>
>>from chs. 3, 12, 15, 17, 23, and 27. There are
>
>>low power ones, none grade B where I live, though
>>within 8 miles (!), on 7, 39, 46, and 58. With
>>a good antenna you can also get (from the other
>>end of the same market) 20 and 55. There are other
>>LPs in the market, but they are not visible at all
>>except under the most stong of tropo, except for
>>occasionally a 29.
>>
>>There are NO out of market stations visible at
>>all analog, period, here, without tropo.
>>Not even the slightest hint.
>
>
> But tropo does exist, and transmitter locations and power levels must
> be determined to prevent worst case interference. Hence very poor
> spectral efficiency.
>
>
>>All more power does around here ... and in the west
>>in general ... is serve more people.
>
>
> As stated before, this is an option for ANY transmission system where
> market-into-market interference is NOT a problem. If we are going to
> continue to protect local markets, then we need to evolve to
> transmission networks with better spectral efficiency. Bert will be
> quick to point out that this is possible with 8-VSB too.
>
> Regards
> Craig
>
>
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