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Space Cellphones

SpaceX's Thursday Launch Enables Starlink's New Satellite-to-Cellphone Internet Service (newatlas.com) 50

Posted by EditorDavid from the long-distance-calling dept.
"SpaceX has launched 20 of its Starlink satellites up into Earth's orbit, enabling direct-to-cellphone connectivity for subscribers anywhere on the planet," reports the tech blog New Atlas. That completes the constellation's first orbital shell, following a launch of an initial batch of six satellites for testing back in January. The satellites were launched with a Falcon 9 rocket from California's Vandenberg Space Force Base on December 5 at 10 PM EST; they were then deployed in low Earth orbit. SpaceX founder Elon Musk noted on X that the effort will "enable unmodified cellphones to have internet connectivity in remote areas." He added a caveat for the first orbital shell — "Bandwidth per beam is only ~10 Mb, but future constellations will be much more capable...."

The big deal with this new venture is that unlike previous attempts at providing satellite-to-phone service, you don't need a special handset or even a specific app to get access anywhere in the world. Starlink uses standard LTE/4G protocols that most phones are compatible with, partners with mobile operators like T-Mobile in the U.S. and Rogers in Canada, and has devised a system to make its service work seamlessly with your phone when it's connecting to satellites 340 miles (540 km) above the Earth's surface. The SpaceX division noted it's also worked out latency constraints, ideal altitudes and elevation angles for its satellites, along with several other parameters, to achieve reliable connectivity. Each satellite has an LTE modem on board, and these satellites plug into the massive constellation of 6,799 existing Starlink spacecraft, according to Space.com.

Connecting to that larger constellation happens via laser backhaul, where laser-based optical communication systems transmit data between satellites. This method leverages the advantages of lasers over traditional radio frequency communications, enabling data rates up to 100 times faster, increased bandwidth, and improved security.
The direct-to-cell program was approved last month, the article points out — but it's ready to ramp up. "You'll currently get only text service through the end of 2024; voice and data will become available sometime next year, as will support for IoT devices (such as smart home gadgets). The company hasn't said how much its service will cost. " (They also note there's already competing services from Lynk, "which has satellites in orbit and launched in the island nation of Palau back in 2023, and AST SpaceMobile, which also has commercial satellites in orbit and contracts with the U.S. government, Europe, and Japan.")

Elon Musk's announcement on X.com prompted this interesting exchange:

X.com User: You've stated that purchasing Starlink goes toward funding the journey to Mars, yes?

Elon Musk: Yes.

SpaceX's Thursday Launch Enables Starlink's New Satellite-to-Cellphone Internet Service More | Reply

SpaceX's Thursday Launch Enables Starlink's New Satellite-to-Cellphone Internet Service

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  • So that's it? We're all in touch anywhere now, regardless of where? It's good, but also just a little uncomfortable.

    • >"So that's it? We're all in touch anywhere now, regardless of where?"

      Well, yes and no. The *potential* exists for it. It depends on who your phone service provider is and IF you subscribe to what is likely going to be an expensive, optional add-on service. And then, likely only if you are outside. Presumably, although the signaling is the same, it is likely to be much weaker. Imagine your handset trying to reach hundreds of miles into space instead of just fractions of a mile to a nearby land tower

  • I thought the timeslot limits in cell phone network limited the range to something like 3 km, 6 km if you used the double amount of time slots?

    Besides, if the satellites are at 540 km, that is about 100 times further away than a base station on the ground. Even if it is uninterrupted, perfect line of sight, doesn't the signal strength decrease with the square (cube?) of the distance? That is, it is 10 000x (1 000 000x) weaker than for ground based networks. How can this be enough??

    • Re:Doesn't this violate the range limits in 4G? (Score:5, Interesting)

      by Moryath ( 553296 ) on Saturday December 07, 2024 @11:18AM (#64997963)

      Not entirely, but you're not entirely off either - which is likely why it's limited to text-only with voice and other functions theoretically "coming later" and the low bandwidth.

      It would be pointless to use an omnidirectional antenna. They're likely using rather directional antennas and targeting specific areas (thus the "per beam" comment). So they can ramp up the power to their antenna on the satellite, and also they don't face some of the other line-of-sight constraints that a terrestrial system does.

      But still, selling this as something revolutionary is... overselling at best. 10 megabit data squirts that can barely carry text signals is "better than nothing" for extremely rural zones outside of cell network coverage, but it's also unlikely they'll be able to ramp it up without needing something more akin to the "so you mounted a pretty-honking-large antenna to your car, truck or RV" existing starlink service that costs $50/month for a less-than-dsl, high-latency setup. There's simply going to be too much noise in the signal trying to catch the output of an unmodified cell phone, to say nothing of what will happen with the slightest atmospheric interference (same thing that causes problems for satellite TV services that are just receiving the downstream beam during a thunderstorm).

      • There's another possible problem for rural use in third world countries: it's text only. What's the literacy rate for peasants out in the boonies in those countries, and how much education to the children get? I knew and worked with some Mexicans back in the '70s who'd grown up on farms before heading north to find better jobs. Yes, they could read and write Spanish and were learning English, but they'd only had three years or so of formal schooling. That wasn't because the schools only provided that mu

      • Going to point this out, in relation to the part of your comment relating to the standard starlink service:
        This is from a rural area but - Personal experience that starlink gets ~200mbps, and the "mini" antennas are /very/ small. No issues in /any/ weather (rain, snow, whatever.) So all of what you mentioned (about the existing service - not the new cell based ones) appears to be incorrect.

      • It would be pointless to use an omnidirectional antenna. They're likely using rather directional antennas ....

        They can use high-gain antennas and high-powered transmitters on the satellites, but if they really can pick up usable signals from 3-watt "unmodified cellphones" using "standard LTE/4G protocols" from 340 miles (540 km) away, that's impressive. (Which also suggests that military technology for surveillance is probably even more advanced.)

    • I thought the timeslot limits in cell phone network limited the range to something like 3 km, 6 km if you used the double amount of time slots?

      I'm not an expert on 4g but that makes no sense to me whatsoever. The purpose of hoisting those on a tower to begin with is, in addition to getting around things like trees and buildings, to work around the 12.2 mile limit that you inevitably deal with due to the curvature of the earth. And the whole point of using 600mhz spectrum is to go even further than that, up to about 45 miles in rural areas, or about 72km.

      • No, you clearly are not an expert. You are completely wrong. Mansplainer.

      • Re:Doesn't this violate the range limits in 4G? (Score:4, Informative)

        by dgatwood ( 11270 ) on Saturday December 07, 2024 @09:49PM (#64998709) Homepage Journal

        I thought the timeslot limits in cell phone network limited the range to something like 3 km, 6 km if you used the double amount of time slots?

        I'm not an expert on 4g but that makes no sense to me whatsoever. The purpose of hoisting those on a tower to begin with is, in addition to getting around things like trees and buildings, to work around the 12.2 mile limit that you inevitably deal with due to the curvature of the earth. And the whole point of using 600mhz spectrum is to go even further than that, up to about 45 miles in rural areas, or about 72km.

        Low-band LTE follows the curvature of the earth better. Your longer-range cell sites are likely to be 900 MHz or lower. That's why they were in a hurry to drop 3G to free up those critical frequency bands.

        That said, there is a limit that has nothing to do with line-of-sight, and that second limit exists because LTE towers try to time things so that each cell phone occupies a single time slice at the tower for both sending and receiving data. To achieve this, the cell phone starts sending data ahead of that time window so that it will be received by the tower during that time slot. It determines the amount of delay after a handshake with the tower that results in the tower providing a timing advance value. Each increment of that value moves the cell phone's transmission window earlier by about 0.52 microseconds. The anti-delay/premature transmission amount therefore gets larger the farther away the phone is. And unfortunately, that value is only 11 bits long, which probably seemed like a good idea at the time. :-D

        As a result of that limit, the official upper limit for LTE, according to the spec, is 100 km, and even StarLink LEO satellites are at several times that limit. More than that, and you won't be able to compensate for the latency, and the phone's signal will overlap with some other phone's time slot.

        But here's the thing, the satellites *know* that they're in orbit. Presumably they set a timing advance of zero for the ground position directly below the satellite and go from there. As long as the satellite covers a ground area with no more than a 100 km radius per cell, and as long as it allocates two time slices per cell phone — one for the transmit window and one for the receive window — then the rest is just software.

        I *think*. That said, this is mostly just me thinking about it off the top of my head. I'm not an RF engineer, and I haven't dealt with any of this directly, so take that with a huge grain of salt. :-)

        There's also a theoretical upper limit to speed because of doppler shift, but I'm assuming they're compensating for that as needed, and given that the satellites are moving mostly sideways relative to you rather than towards or away from you, I'm not going to do the trig to figure out how bad the doppler shift would be, but that part might not even be outside the spec limit as long as they have enough birds to have one nearly overhead covering a narrow enough arc.

        Anyway, just thinking out loud, and feel free to correct me if I'm wrong on the finer points here, but I'm pretty sure that's the gist, anyway.

  • o|= Nowhere to run to, baby - nowhere to hide. o|=

    It's 'handy' to have massive MIC contracts.

  • Bad for those claiming electromagnetic sensitivity (Score:4, Interesting)

    by Teun ( 17872 ) on Saturday December 07, 2024 @11:26AM (#64997973)
    Too bad for those claiming to be sensitive to phone signals :)

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