[opendtv] Re: The "real" problem with OFDM in the U.S.
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
- Date: Sun, 6 Mar 2005 19:27:43 -0500
Tom Barry wrote:
> Yes, I guess that is true but it's such a bad decision I
> wish we wouldn't perpetuate it.
Not quite the case. FCC 96-317 (from 1996)
ftp://www.fcc.gov/pub/Bureaus/Engineering_Technology/Notices/1996/fcc9631=
7.pdf
summarizes past decisions and makes new rules. One of the new
proposals, by the way, was to add VHF into the spectrum
available for ATSC, but to limit DTT to channels to 7-51.
Before that, only UHF was being considered for ATSC.
Anyway, on the subject of coverage, the FCC had to establish
a frequency plan for DTT, which included questions of
radiated power and antenna height. So they had to set down
criteria for the new ATSC service.
To do this, you need an objective. The objective proposed
in this document was to equal NTSC (grade B) coverage of the
analog signal of each station with the digital signal of
that same station. Now the FCC could figure out how much
signal the DTT stations would need to transmit, and how to
prevent interference with other markets and with existing
NTSC stations.
Greater than NTSC coverage would be gravy. But that couldn't
be allowed if it created interference. So this is NOT a
question of "no greater than NTSC," but rather "at least as
good as NTSC," subject to a set of (sensible) constraints.
I see nothing bad about any of this. It seems quite logical.
Anyway, here's the part that addresses coverage compared with
NTSC. Notice the part about going beyond this amount of
coverage, as long as it didn't interfere with other signals:
-----------------------------
13. Proposal. In reviewing this issue, we agree with those in
the broadcasting industry who have argued that replication of
existing service areas in the new DTV allotments offers
important benefits for both viewers and stations. Replication
would generally maintain the 19 service areas of existing NTSC
stations, thereby preserving viewers' access to off-the-air TV
service and the ability of stations to reach the audiences
that they now serve. Accordingly, we are proposing to identify
digital TV allotments that, to the extent possible, will allow
all existing broadcasters to provide digital TV service to a
geographic area that is comparable to their existing NTSC
service area. In this regard, we also propose to specify for
each DTV 21 allotment a maximum permissible effective radiated
power (ERP) and antenna height above average terrain (HAAT)
that would, to the extent possible, provide for replication of
the station's existing service area. Furthermore, as discussed
below, we are proposing to allow stations to maximize or
increase their service area where such an increase would not
create additional interference. (Footnote 22)
14. We request comment on all aspects of our proposal to use
the service replication plan in allotting and assigning initial
channels for digital TV service. We also request comment on
whether it might be more desirable instead to adopt our
original plan to allot DTV channels using an approach that
maximizes the service areas of all DTV stations. This approach
would tend to equalize the coverage areas of all stations
within a market and reduce the current disparities among
stations. We request comment on whether our original approach
would be more appropriate and would provide more incentives for
broadcasters to implement digital service more quickly than the
service replication approach.
Footnote 22. Stations would be permitted to increase their
power and antenna height up to that permitted for maximum
facilities, as discussed below in Section IX.
-----------------------------
I'm not sure what would have been a more appropropriate
stategy.
Bert
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