[opendtv] Re: Mobile TV: $2 Billion in Ad Buys
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 21 Apr 2008 13:09:58 -0400
John Shutt wrote:
>> So what you are saying is that when the broadcaster
>> decides to go to HM, if the wide stream is kept up at
>> 13.5 Mb/s, it's okay to drop a healthy fraction of
>> the viewers, either letting their screens go dark or
>> Assuring frequent macroblocking and freezing images
>> and sound.
>
> http://www.hdtvmagazine.com/archives/pbsbalit.html
Ah yes, when all else fails, trot out the comparison tests from 1999,
whether they pertain to the discussion or not.
If you want to tout the advantages of having HM, the only way to make
the argument is to show that the wide stream remains as robust as the
wide channel always was, and then you add in a robust mode. If you use
numbers for the wide stream that are less robust than previously, then
those numbers don't mean a lot. I could give you even more Mb/s in the
wide channel. So what?
> And what does A-VSB do to effective bitrate?
The wide stream retains the same C/N as before. The robust stream
varies, depending on the FEC used. So again, just as we have already
dicussed before, you have to look at the C/N margin of the robust stream
and of the wide stream, when making comparisions.
Where HM gives you 10 dB of C/N for the robust stream, A-VSB gives you 4
or less dB of C/N, in the mode that eats up bitrate. And if you insist,
it can be tweaked to give more bit rate and lower robustness.
But the bottom line is this: with A-VSB, the robust stream, when it uses
turbo code FEC, is within less than 2 dB of the Shannon limit. So that's
the ultimate measure. The rest is just words.
> However, I wouldn't hang my hat on multicasting as the driving
> force behind HD Radio. The HD reception radius of a station is
> very small, and the multicast channel has no analog fallback mode,
> so I see limited adoption of multicasting for commercial stations.)
That's because "there's no such thing as a free lunch."
I was never so taken by the IBOC concept in hybrid mode, compared with
other digital possibilities, because in order to allow this supposed
coexistence, you pay a huge penalty in allowable ERP. I discussed this
recently with Barry Wilkins. One could use, for example, DRM in the FM
band, limit the ERP to 23 dB below an adjacent FM analog station, and
get the same effect as IBOC. But reception will definitely suffer. Just
as the digital IBOC stream is made to suffer.
Bert
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