[opendtv] Re: Spectrum is too valuable

  • From: Ron Economos <w6rz@xxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Mon, 09 Nov 2015 04:16:20 -0800

DOCSIS 3.1 is based on LDPC FEC, so it uses a 16,200 bit (2025 byte) frame (just like the short FEC frames in DVB-S2, DVB-T2 and DVB-C2). The frame has 225 bytes of LDPC parity, 21 bytes of BCH parity and a 2 byte codeword header, leaving 1777 bytes of payload.

The minimum channel size is 24 MHz (of which 22 MHz contains active carriers). Bandwidth can be increased in 2 MHz minimum sized chunks up to 192 MHz (190 MHz of active carriers). The additional chunks don't have to be contiguous.

Ron

On 11/05/2015 07:42 AM, Craig Birkmaier wrote:

On Nov 5, 2015, at 7:35 AM, Ron Economos <w6rz@xxxxxxxxxxx <mailto:w6rz@xxxxxxxxxxx>> wrote:

It's the other way around. All DOCSIS 2.0 and 3.0 downstream data is encapsulated in 188-byte MPEG-2 TS packets. It has to be, because the ITU-T J.83B 256QAM format requires 188-byte TS packets.

Fair enough. This makes sense given the fact that through DOCSIS 3.0 all traffic was using the standard channel bandwidths in each region (e.g. U.S. = 6 MHz, Europe = 8 MHz).

What is going to happen with DOCSIS 3.1, which uses 4096 QAM and eliminates the 6 and 8 MHz channels? This seems a bit confusing, as what I see in the description on Wiki is that much smaller channels using OFDM subcarriers will be combined into channels as large as 200 MHz:


DOCSIS 3.1
First released October 2013, and updated several times since. The
DOCSIS 3.1 suite of specifications supports capacities of at
least 10 Gbit/s downstream and 1 Gbit/s upstream using 4096 QAM
<https://en.m.wikipedia.org/wiki/Quadrature_amplitude_modulation>. The
new specs do away with 6 MHz and 8 MHz wide channel spacing and
instead use smaller (20 kHz to 50 kHz wide) orthogonal
frequency-division multiplexing

<https://en.m.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexing>
(OFDM)
subcarriers; these can be bonded inside a block spectrum that
could end up being about 200 MHz wide.

So will MPEG-2 TS still be used to encapsulate IP packets, or will another transport protocol be used?

Regards
Craig

Other related posts:

  1. Home
  2. opendtv
  3. Archive
  4. 11-2015