Spectral bandwidth doesn't matter so much with beamforming with reasonably narrow beams. At least not until you get to a lot of satellites overhead at once. Dishy probably obtains a beam ~3 degrees wide; there's a lot of 3x3 degree sectors in the sky.
Similarly, the ground "cells" are 300 sq km; there's a lot of these in view of the satellite.
> Starlink's problem is going to be that most profitable areas are better served by terrestrial LTE/5G
Yup, for the most part I agree. Still, there is a pretty large rural population.
Sure, how much data you can exchange per satellite is roughly proportional to the bandwidth.
Increasing bandwidth or increasing satellites increases data rate.
> it's why SpaceX pays so much on legal fees for fcc filings
Note that a whole lot of the paper that goes to the FCC relates to the FCC's statutory authority over space debris and constellation licensing.
Well, sure. It has a multiplicative effect with number of satellites on throughput. Not to mention the proxy warfare they've endured from other constellation vendors through the FCC.
The big point which I responded to was there was a claim that adding more satellites doesn't add throughput ("Do cheap launches help")-- that one could be purely spectrum limited and not benefit from additional satellites. Directional antennas make this not true for any reasonable number of satellites.
If you use a diameter for a circle area, you need to divide by 4, to get like ~7. I was just going to do 3*3 = 9.
> It looks like Starlink has 7 GHz total downlink bandwidth from satellite to customers. A cell may be ~300 sq km, but no way you can pipe all that bandwidth in adjacent cells due to interference
Both the downlink and the uplink are directional. Yes, there's some power lost in side lobes, but..
So, if you have multiple satellites overhead, you can have a mosaic pattern where satellite A illuminates a hex, and then other satellites illuminate its neighbors. And even though some energy spills over, it's strongly rejected by the receivers because it's coming from the completely wrong direction.
> How many people live in places with fewer than a few people/km^2?
In addition to the incorrect pessimism about downlink bandwidth (also, one should expect ~5bits/Hz)... You're not taking into account any reasonable capacity factor, and you're assuming each service is one person. You're also assuming that you sell through to 100% of the populace and there's no one in the cell served by other technologies. If 95% of a suburban area can get FTTH, cable, or reasonable LTE, that still leaves 5% as possible customers for Starlink to fill in.
> Only Alaska averages below that in the US.
OK, but people are concentrated into cities, leaving a whole lot of land area with concentrations below this even in states with much higher average population density.
Yes, obtained by channelization and OFDM, not by limiting modulation.
Reverse engineering of the 10 to 12.7GHz band has shown a mixture of 16-QAM and 64-QAM frames. There's a bit of periodic 4-QAM too, which seems to be for acquisition and synchronization.
Even 16-QAM can climb basically to 5 bits/Hz.
I think you meant 7 Gbps; that only works if the satellite itself has that much inbound, which may not be the case if the satellites around (for sat-to-sat links) it or the base station that it sees are maxed out.
> which may not be the case if the satellites around (for sat-to-sat links)
No real sat-to-sat links yet. The exact specifications aren't disclosed, but they'll likely be 100gbps symmetric links.
> the base station that it sees are maxed out.
You can expect spectral efficiency for the uplinks to be better because of big antennas, and for them to be provisioned with no problem illuminating all the satellites overhead.
> which effectively halve the available bandwidth
I disagree (and I'm not sure where this idea is coming from-- do you think they use the same spectrum or something?) I think they effectively "add" bandwidth for the system by allowing satellites that do not have saturated uplinks to "share" capacity. E.g. a satellite which is mostly over the ocean but can see a ground station can now be more useful.
Yes, sat-to-sat enables new use cases. But it also has other effects.
All the satellites above me have an uplink from a ground station.
Also, satellites above ocean with few people in their footprint can see my uplink but can't use it effectively, because they don't have many users in their footprint (possibly none, because of elevation angle restrictions).
If we have satellite-to-satellite links, then those satellites above ocean can share their bandwidth with satellites above me. Therefore, real system capacity goes up.
Assuming that ground stations are upgraded as the size of the constellation grows-- they're strongly directional. Their throughput is the uplink bandwidth * the spectral efficiency * the number of satellites within LOS of an uplink ground station. Intersatellite links let you use more of this throughput without it going unused and "spoiling"-- that's the main point.
In the current era of phased array antenna prices falling sharply, and assuming they're willing to go for a folding antenna, I think they could probably easily get a 10x antenna area boost without much extra cost.
I don't get the question. Do costs matter when revenue is limited?
Of course they matter. They matter even more the more limited is the potential revenue.
Starlink's problem is going to be that most profitable areas are better served by terrestrial LTE/5G, leaving only truly remote areas that are low density enough. But not many people live there...