60ms cross continent

Fri Jul 10 12:11:37 UTC 2020

On 10/Jul/20 10:50, Eric Kuhnke wrote:
> With common Ku band TVRO (receive only) dishes and decoders, one of
> the constraints for moving to higher bitrates is the physical sizes of
> the customer dish and economics.
>
> For a good example go to a very densely populated developing nation
> environment. Saddar, central Rawalpindi, Pakistan would be one such
> place. Get up on a tall roof and look at the numerous low cost Ku dish
> and LNB setups on other roofs.
>
> Achievable bps/Hz and modulation type, code rates, and type of FEC are
> very limited when the antenna has to be so small. Usually something
> like qpsk 3/4. In order to have something like a 4k stream and not
> require end users to replace their 75-100cm size dishes with something
> much bigger, you'd need to use a lot more MHz on the geostationary
> satellite's transponder. Greatly increasing monthly transponder fees
> for the tv broadcaster. Any sort of modulation like 8PSK or a 16QAM is
> probably not achievable as long as the end user consumer antennas
> remain so small.
>
> For people who are accustomed to a terrestrial microwave link budget
> and path loss, Geostationary will seem weird. For SCPC two way data
> links you can spend a lot of money and construct 3.8-4.5m size earth
> stations, definitely a construction project with a capital P, but the
> laws of physics will dictate your link sees only 4 bps/Hz or less.
> Even with the very best modems on the market now. 
>
> Ultimately advances in codecs may help this somewhat. 4k AV1 at fairly
> low bitrates is remarkably not terrible. H.266 was just standardized.
> It'll take a long time for full hardware decode to show up in ultra
> low cost satellite TV boxes.

When the leading satellite TV provider in Africa first started
delivering service via satellite back in 1997, it was on C-Band, with
the smallest dish needing to be 2.4m.

When they moved to Ku-Band around 2010, every home now has 90cm dishes.
While they do say 60cm dishes are viable, you won't be able to pick up
any HD service with those.

Mark.