[opendtv] Re: Spectrum is too valuable

  • From: Craig Birkmaier <brewmastercraig@xxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Sun, 08 Nov 2015 07:47:17 -0500



Regards
Craig
On Nov 7, 2015, at 11:16 PM, John Shutt (Redacted sender "shuttj" for DMARC)
<dmarc-noreply@xxxxxxxxxxxxx> wrote:


Are we keeping in mind that because of the more benign RF environment, 6 MHz
on a cable system can carry roughly twice the data payload that 6MHz OTA can?

Yes, even Bert noted that in his back of the hand analysis. Remember this?

So, if a single DOCSIS 6 MHz channel can support 38 Mb/s downstream
(256-QAM), that should be more than adequate for two homes, each steaming 3
HD shows simultaneously (or many more streams in SD). So, rough estimate, how
many homes can be fed with the spectrum used up by the broadcast MPEG-2 TS
streams?

So I did the math:
For 0 dB operating margin, the analyses for DS (8K FFT) and US (4K FFT)
showed that DOCSIS 3.1 spectral efficiencies can be 8.1996 bps/Hz and 7.8589
bps/Hz, respectively, which is about 30% and 90% gain over the estimated DS
and US DOCSIS 3.0 spectral efficiencies of 6.33 bps/Hz and 4.15 bps/Hz,
respectively.

Let's assume that there are 900 MHz available for downstream service in a
modern 1 GHz HFC system - the rest is upstream and other system overhead.

So the best we can do today with DOCSIS 3.0 is 6.33 X 900,000,000 = 5.697 Gbps

I went on to note that the average number of homes per PON is now about 500, so
with DOCSIS 3.0 each home could get:

5,697,000,000 / 500 = 11,394,000 which is roughly 11.4 Mbps per home

Or doing the math Bert's way:

5,697,000,000 / 19,000,000 = 299.8 homes at 19 Mbps

Even with the added efficiency of DOCSIS 3.1 we still fall far short of
providing each home served by the PON with the 25/3 Mbps service that the FCC
now defines as broadband.

Thanks for asking John.

Regards
Craig


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