[LibreQoS] [Starlink] tarana strikes back
david at lang.hm
Mon Sep 25 04:11:28 EDT 2023
On Sun, 24 Sep 2023, Dave Taht via Starlink wrote:
> My purpose in asking the list here was to ask if the analysis of cell
> size was correct and reasonable (it certainly looked so to me), and
> the economic argument that falls out of the resulting information
> density seems compelling for designing hybrid fiber and wireless
> networks of all sorts, not as an endorsement of tarana.
>>> Can anyone question these Starlink numbers for cell size, etc?
I think they have the cell size reasonably accuarate (for now), But if the cell
sizes were of fixed size and unable to be re-used, once there were enough
satellites to provide global coverage, adding more would not provide any value.
But even their first phase includes many times the number they needed to provide
global coverage, so the assumptions around the capacity being fixed by the
initial cell size and a single satellite covering it cannot be correct.
I question the assumption that there will only be a single satellite serving the
cell at a time. With directional antennas (including phased arrays) you can aim
both your uplink and downlink.
Even without having multiple satellites covering a single cell, you can shrink
the cells by having the ground stations further from the center of the cell aim
at different parts of the sky.
Lower altitude satellites will have smaller cells with the same antennas,
reducing the altitude from ~560km to ~340km reduces the spot size by ~2.5 so you
get somewhere around 7 spots in the same footprint (and need less power, so you
generate less interference to other cellss, so you can re-use the same
frequency in closer proximity, a virtue cycle), it also reduces the latency.
Larger satellites allow for physically bigger antennas, which increase the
ability to focus, use less power on both ends, and be more immune to signals
from the wrong direction, very similar to what the lower altitude gives you
(without the decreased latency that the lower altitude provides)
So in the big picture, they are correct with the basic idea that WISPs can
outperform Starlink, the real questions are around where the crossover point is,
and if WISPs are going to build out in enough areas. It doesn't matter if a WISP
could outperform Starlink if they don't build it, or don't run sufficient
capacity of wired Internet to the tower.
WISP endpoint equipment could be cheaper than Starlink dishes (it's far simpler,
but Starlink now has economies of scale kicking in that have reduced their
production costs by 5x or better, even in the face of inflation, the early
dishies were reported to cost ~$3k each to build, now with them selling for $600
(less in some places, don't know the average selling price) they are no longer
losing money on each dishy sold. That's getting down into the price for the WISP
endpoint equipment costs. and the WISP has to pay installers to setup that
equipment as well as covering the hardware costs.
This doesn't mean that Starlink will outperform WISPs in raw speed, but they may
be cheaper in many areas, pushing the crossover point to denser population areas
before it becomes congested enough for people to prefer the WISP
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