[Starlink] Re: Starlink and Iran

[David Lang <david@lang.hm>]

Ulrich Speidel wrote:

> Either way, it's worth noting here that while the relationship between 
> transmit power and and received power is linear, the relationship between 
> received power and achievable bit rate is logarithmic in nature. For those 
> not so mathematically inclined: Starlink is starting off with 64QAM (6 bits 
> per symbol) at current EPFD limits, and each extra bit beyond that requires a 
> doubling of the received power. Turning up the volume is not a game you can 
> stay ahead in for long, regardless of regulatory constraints.

I think that the value in allowing higher radiated power at the receive end 
isn't to increase the bit rate from a single satellite, but to allow multiple 
satellites to cover the same area with the beam steering on the receiver 
differentiating between the satellites.

allowing two satellites with significantly different angles to cover the same 
area allows for (close to) 2x the aggregate bandwidth to spread between all 
receivers in that area.

> Some interesting tidbits from the grant document though:
>
> * 4. a. No more than 8 satellite beams "in the same frequency" (I
>   presume there's the word "band" missing here) into the same or
>   overlapping areas at a time. That means at most 8 beams per cell.

if that's a step up from a single beam, that will allow for close to 8x the 
aggregate bandwidth.

And if they can show (over time) that this doesn't cause problems, it will be 
reasonable to expect raising this limit over time

it may be band, or it may be frequency/channel (like wifi has 3 bands, 2.4G, 5G, 
6G), but 5G has many non-overlapping channels, and operating on multiple 
channels at the same time is quite reasonable for high-end APs

> * 4. b. "SpaceX must maintain a minimum GSO arc exclusion zone of at
>   least four (4) degrees with respect to operational GSO satellites".
>   Finally a clear word?

that geo exclusion has been in place for a while, but I thought it was a lot 
wider than 8 degrees (4 degrees to each side) I seem to remember hearing 25 
degrees being thrown around in discussions (I may very well be misremembering)

David Lang