60ms cross continent

Tue Jul 7 06:51:41 UTC 2020

On 2020-07-07 08:32, Eric Kuhnke wrote:
> "no clouds" is overstating the effect somewhat. I've operated a number
> of mission critical Ku band based systems that met four nines of
> overall link uptime. The operational effect of a cloud that isn't an
> active downpour of rain is negligible. Continual overcast of clouds is
> not much of a problem at all, it's active rain rate in mm/hour and its
> statistical likelihood, climate parameters of the location.
> 
> Yes, during rain fade events, current generation VSAT modems will drop
> all the way down to BPSK 1/2 code rate to maintain a link, with
> corresponding effect on real world throughput in kbps each direction,
> but entirely dropping a link is rare.
> 
BPSK 1/2 is quite extreme. In my case it was 32APSK 8/9 at 36Mhz 
transponder
(yes it was quite large antenna), ~140Mbit, so switching to 1/2 BPSK 
will make it
~16Mbit/s, which is pretty useless for telco purposes.
For corporate, end-users, with QoS - it can be ok, but still depends on 
climatic zone.
Remember, it is not downlink only issue, but uplink too. And depends on 
antenna elevation angle
as well.
Even for end-user it is not fun to have 1/10 of capacity, most likely 
means unable to do
video conferencing anymore, for few days, just because it is few rainy 
days.
And as Ku is often covering specific regions, often it means rainy days 
for most transponder customers.
This is why in zones closer to equator, with their long-term monsoon, 
C-Band was only option,
no idea about now.