[opendtv] Re: CableLabs Proposes Specifications for OTA Reception in Cable B

  • From: Tom Barry <trbarry@xxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Sat, 10 Mar 2007 20:09:14 -0500

I think you have to measure spectral efficiency as being AFTER any correction for errors. That is, subtract both the FEC overhead plus any resulting average number of error bits that survive FEC. It is only the resulting throughput of good original data bits that counts (per Mhz).


- Tom


Albert Manfredi wrote:
iclaustrum wrote:

CBS and NBC affiliates begin to switch to 720p because it
compresses to lower bitrates more easily than 1080i
(especially 24p film content). This however is sold to the
public as a defiant station manager who finally "sees the
progressive light."


Except that there has been so much blather in the press about "full 1080i resoltuion," and how 720p is the lower end of HDTV, that this will be a hard sell. Consumers will see this as an effort to dumb down of HDTV.

Broadcasters start to wish they had in-the-clear H.264
primary video option and 64 QAM like their European
counterparts, and begin lobbying the FCC to amend ATSC.


H.264, likely. But 8-VSB and 64-QAM are identical in terms of spectral efficiency. Any minor differences are only caused by error correction mechanisms layered over the symbol stream. If anything, this almost always results in the COFDM stream being somewhat lower in spectral efficiency, to gain a measure of robustness.

If some European broadcasters have tuned their channels to 24 Mb/s, it is only because they have 8 MHz of bandwidth to play with, vs 6 MHz here.

Bert

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Tom Barry                  trbarry@xxxxxxxxxxx  



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