Huh, I wonder how they manage to pick up the tiny amount of RF energy a normal phone can output from that far away, and through the noise of literally millions of other phones in the satellite's field of view.
Gotta be some real weird RF voodoo happening in there.
Cell phones can supposedly connect to towers up to 25 miles away (presumably at the slowest supported data rate.) Starlink is about 350 miles up. Let's round up to 400 to allow for satellites not being directly overhead. That's 2^4 times farther away, or 24dB of signal difference.
It seems like a sufficiently fancy phased antenna array on the satellite could compensate for that. Also, the atmosphere is 99% gone at 20 miles up, so that probably helps. Also, with the goal of only supporting SMS, a modern software defined radio chipset could probably be made to use an incredibly low data rate that adds more signal margin than currently used by any cell network.
I didn't realise that 4G/5G could connect to receivers that far away. From memory, the maximum Timing Advance in 2G corresponded to ~25km. After that the phones won't get ACKs fast enough due to speed of light and will assume that the response isn't for them.
WiFi has similar limits, but much shorter. I know some usecases of WiFi transceivers with longer distances (~5km) which required tweaked firmware that wasn't technically wifi-compliant, to have longer receive windows.
Even in 2G you have special cells that allocate two+ adjacent time-slots for a channel and so can effectively double the max range at the cost of serving less concurrent clients. This is used in sparsely populated regions (think remote highways etc). It's not a physical, the-signal-can't-reach issue.
You are correct - two things happening here:
1. Picking up RF energy from far away. This is the easy part - cell phone antennas are already a big compromise and can be improved on if you increase size or cost. Instead of omni-directional antennas and low-power amplifiers, a directional antenna and low noise amp will work wonders. Cell phones already have extra power to get through buildings and trees; in this case that power would be used to go extra distance (because there won't be these obstacles).
2. Many users seen at once. Each beam is only a 15-mile-diameter circle. In the really remote areas where this coverage would be needed, I don't suspect that there would be too many cell phones - maybe a few hundred at most.
It's strange that you think that this is so unachievable yet we have things like Bluetooth, WiFi, LoRa and regular cell phone all working with relatively tiny amounts of power and discriminating from the noise generated by other nonparticipants. This would amaze anyone from before the 70s.
What? My wifi barely reaches the other side of my room with a wall in between, how am I supposed to think 350 miles is within reason? Even with clear sky, your signal to a tower an order of magnitude closer would be unusable.
If you look at apple’s latest feature, even them, with specific hardware probably, requires minutes of open-sky pointing directly at the closest satellite, to transmit mere bytes of data.
That tells me that if your phone is just hanging in your pocket, indoors, with a 5G nearby, it’s not going to reach the satellite at in any shape or form.
I know nothing of your own situation, but having personally deployed fully working and operational WiFi for a 10000 plus seat stadium, various other campuses, but also seeing cell phones work in your pocket moving in a car or in a big city shopping centre is amazing. Even the Starlink stuff that is already deployed.
Anyway let's wait and see - I'm pretty sure T-Mobile wouldn't have signed on for something that is just a pipedream
Takes a much bigger radio to get the bandwidth for a starlink, 100mbs. Texting is on the order of bps. Garmin inreach mini is around the size of a tictac box and can send and receive texts.
They're nice, but shouldn't be needed. Ubiquitilink (mentioned as Lynk in the article) has proven 500km two-way connections without them. A large constellation at that height with large antennas and spectrum rights should be able to offer higher bandwidth service than Globalstar's current network offers to iPhones.
Globalstar's capabilities aren't frozen either. The Apple deal uses most of their capacity, but they'll be launching additional satellites. While they're not in the current deal, Globalstar could launch a lower LEO service in the future. Cell phones with bigger antennas, like the case antennas in the new iPhones, would have better sat service communicating at Starlink's range.
We're also in relatively early days of large antenna deployment. AST's record-setting antennas are going to look quaint as launch costs and more complicated deployments continue to advance and benefit every satellite network.
LoRa bitrate is very low and the range of LoRa is not even comparable with satellite communication. Moreover, normal smartphone are not LoRa compatible.
> LoRa provides for long-range communications: up to three miles (five kilometers) in urban areas, and up to 10 miles (15 kilometers) or more in rural areas (line of sight)
500km is one magnitude order more than the supposed range.
And no phone has a LoRa chipset inside, neither the new ones.
I always assumed the main thing with satellite messengers was that they transmit with much higher power. Not that such a system is easy to design, but the “voodoo” mentioned previously was more about achieving compatibility with an existing RF system at much longer ranges than the system was designed for.
Apples solution is in SOS emergency situations only. It is extremely limited in what you can transmit—which near as I can tell is just a well defined message format.
Gotta be some real weird RF voodoo happening in there.