[opendtv] Re: The "real" problem with OFDM in the U.S.
- From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 08 Mar 2005 13:33:33 -0800
Bert wrote:
> So bottom line, if you have to cover large markets
> while making efficient use of frequencies, big sticks
> are a reasonable approach. Especially if these can be
> assisted by on-channel repeaters, to improve the
> signal level in challenged locations.
You have it right, in my opinion.
Many large big stick markets have marginal DTV C/N in the more distant or
shielded portions on their market. This condition can impact a significant
portion of their total coverage area, where significant population clusters
might exist. Properly designed on channel repeaters, together with advanced
receivers such as the 5G, can significantly increase useable C/N ratios to
these locations and greatly simplify the antenna system hardware required to
achieve reliable service.
Of course, as you say, such a system must be designed without creating
additional interference and that can often be accomplished.
----- Original Message -----
From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
Sent: Tuesday, March 08, 2005 1:07 PM
Subject: [opendtv] Re: The "real" problem with OFDM in the U.S.
> Tom Barry wrote:
>
>> > If you want to avoid dead zones, as we must here,
>> > then adjacent markets won't be able to share
>> > frequencies. Even with the small stick approach.
>> > But the next market over can use those frequencies,
>> > *same as now*.
>>
>> Is there any topography where someone located equally
>> (at any distance) between two stations with the same
>> power and channel is not in a dead zone?
>
> On the same channel, I'd say no. That's why if there is
> no wilderness between adjacent markets, the frequencies
> of one market cannot be used in the adjacent market.
> And that buffer zone, where no reception is possible on
> a given frequency band, may either consist of a complete
> lack of signal or a lot of co-channel interference.
>
> I'm basically rebutting the oft-repeated notion that
> SFNs or small sticks will allow greater frequency reuse.
> Taken in a vacuum, that statement seems unarguable. But
> taken in context of TV transmission in real markets,
> where coverage must be ubiquitous, it's just not the
> case.
>
> Take VHF Channel 11. It is used in Baltimore and NYC.
> If the Philadelphia market were a wilderness, then
> Channel 11 could be reused in two adjacent markets.
>
> But the fact is, Phildelphia exists. The Balt Channel
> 11 must serve communities up into northern MD and must
> overlap with signals from the Philadelphia market. And
> the NYC Channel 11 must also serve communities which
> approach Phildelphia. Because people from these
> communities may commute to either market. In Phildephia
> itself, Channel 11 can go ahead and be a mess of
> co-channel interference or low signal level.
>
> So whether you create the Ch 11 coverage patterns with
> big sticks, with small sticks in SFNs, or with a
> combination of big sticks and on-channel gap fillers,
> the end result is largely the same. Frequency reuse
> will depend on HOW LARGE the markets are and on whether
> or not adjacent markets are contiguous. As things are
> now with big sticks, Channel 11 is used efficiently in
> this part of the East Coast.
>
> If you really want to use the *same* frequencies in
> adjacent markets, then you must create buffer zones
> where signals will be difficult or impossible to
> receive. There's no logical excuse to create such
> zones today, along the East Coast. Or you could
> establish a network of low power translators throughout
> the market, but that would require use of more
> frequencies, not fewer. It just creates the same
> problem on a smaller scale. That's all.
>
>
> Bert
>
>
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