[opendtv] Comparisons between systems

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Tue, 14 Nov 2006 18:02:12 -0500

I guess some of you guys saw this Doug Lung column:


but didn't catch this interesting tid-bit.

It is interesting to see two similar design approaches, one being the
new Chinese OFDM-based system with advanced FEC and the other being
A-VSB in the STS mode. For all the skeptics, take a look at the most
robust modes and how they compare:

CDMB-T in 8 MHz channel, 4-QAM (most robust), 4K mode, LDPC FEC:
~5 Mb/s and 1.9 dB C/N margin.

A-VSB in 6 MHz, 1/4 rate STS mode (also most robust), turbo code:
4.5 Mb/s and 1.7 dB C/N margin.

To compare capacity fairly, 5 * 6/8 = 3.75, which shows somewhat lower
spectral efficiency for the CDMB-T system, although that 5 Mb/s figure
was approximate.

Also to be fair, no mention of whether the Chinese system was using a
diversity antenna. But then again, the diversity antenna is more
essential and beneficial in a single carrier scheme.

I'd say, not bad for an afterthought to 8-VSB, eh?

Another point about OCRs is a strange paradox that this column also
mentions. Which is, the newer receivers are the most compatible with OCR
nets, however they are also the ones that benefit from OCRs least. In
the sense that they *already* make use of echo energy created by the
single transmitter, without needing an OCR to sort of shape that energy

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