Apple’s Satellite Emergency Texts, How Do They Work?

There is always some hype surrounding an Apple product announcement, and while maybe it’s not in the same league as those for the original iPod or iPhone, their iPhone 14 model will include emergency texting by satellite has generated quite a bit of coverage. It’s easy to find a lot about the system from the software end in terms of its interface and even Apple’s use of compression, but what about the radio side? Whose satellite constellation are they using, and how does it work?

As has been widely reported, their communication partner for the service is Globalstar, a provider of satellite data services that like their competitor Iridium have their origins in the 1990s when satellite phones were briefly seen as the Next Big Thing. They have a 24-satellite constellation, and they sell a range of off-the-grid voice, data, paging, tracking, and IoT connectivity services. The Apple emergency texting looks a lot like Globalstar’s Spot texting service. It’s only available in North America for now, we’re guessing because the satellites aren’t smart relays but straightforward transponders, and the network lacks sufficient ground station coverage outside that region.

With all the talk about low-earth-orbit connectivity surrounding services such as SpaceX’s Starlink it’s a bit unexpected to find ourselves back with a satellite constellation using 1990s technology. But we can see that as well as a major win for Globalstar as their service begins to look outdated by comparison to Starlink, it’s a perfect match for Apple in not requiring a complex ground station for low-bandwidth text messages. We expect that there will be some form of exclusivity in the deal, so it will be interesting to see how the larger Android vendors respond.

It’s worth noting, we’ve looked at satellite IoT services before.

Wilderness image: U.S. Fish and Wildlife Service, Public Domain.

24 thoughts on “Apple’s Satellite Emergency Texts, How Do They Work?

    1. It’s CDMA/GSM (2G) and works like a cellular network in the S-band between 2-4 GHz. It just doesn’t support very many concurrent users, since the network cell size is so large. It can only sustain about 20-30,000 simultaneous phone calls across the US service area. It’s just a satellite relay, so if you have a 2G modem at the correct frequency, and you’re registered in their network, and you have enough transmitting power to be heard by the satellite, they can patch you through.

        1. You don’t need high-power, you need a clear shot to the satellite and adequate power of a couple watts, just for a couple moments while you’re text message is sent in one or two ‘burps’ of data.

          Of course, the overlooked requirement is no cell coverage or wifi – since the presence of those signals will overwhelm at least the downlink signal, as well as the uplink signal.

          Hams communicate through non-geostationary satellites all the time, but they use lower frequencies (144 & 430 MHz are most common/popular bands) and have modest antennas, for them one of their struggles is tracking the satellite in motion.

          1. I suspect that the antenna in the phone for this is highly directional, so the ERP you get is boosted a little bit and that also explains the non-trivial aiming requirements.

      1. “and you have enough transmitting power to be heard by the satellite”,

        As Shakespeare (I think) wrote:
        “Therein lies the rub”.
        I’m guessing that the phones will only be able to do that under optimal conditions. So, if you are standing on a mountain ⛰ top, and holding the phone above your head, internal antenna oriented to the satellite…
        But, I am pessimistic.

        1. It says in the link exactly how to hold the phone:

          – Hold your phone naturally in your hand. You don’t need to raise your arm or hold your phone up, but don’t put it in a pocket or backpack.
          – Make sure that you’re outside with a clear view of the sky and the horizon.
          – Be aware that trees with light foliage might slow down the connection, and dense foliage might block it. Hills or mountains, canyons, and tall structures can also block the connection.
          – In case you need to turn left or right or move to avoid a blocked signal, your iPhone provides guidance—just follow the onscreen instructions.
          – The satellite connection can be maintained even if your phone screen is locked.

          However the antenna is oriented on the phone, you’ve got to maintain some approximate azimuth for the connection to work. It doesn’t sound like elevation is as important but there’s something to it by the way they say “hold it naturally”. Now that you are transmitting from ground to space at a certain allocated frequency, there might be more allowance for transmission power.

        1. Directional/gain 2.4 GHz antennas can be etched into a PCB, perhaps their video simply showed a directional antenna for demonstration purposes? I don’t think apple will add an antenna connector to their iPhone…

          I wonder if we’ll see mesh-lined reflector umbrellas to use to point your signal at a satellite?

  1. Ground station coverage is not a problem. SPOT has global-ish coverage and the ground stations Apple will use are exceedingly likely the same. The problem (and SPOT has it as well) is whom to route your emergency message to. You need contracts with local emergency services, permissions and all that jazz.

  2. All – the comments here re the SOS Satellite Message are way off the mark, only the comment re the FCC link back to the MSS test report is on the mark and little did that person realize how close they are to the entire deal.

    As we all know its Apple and Globalstar. The comment from Hackaday re SPOT message texting, is also on point, its very similar, SPOT uses SIMPLEX, aka One Way so a Spot Trace only sends, never receives. SPOTX is Duplex, but the Globalstar Duplex side has S-Band Amp issues with dead thanks to time and radiation passing through the Van Allen Belt or Southern Atlantic Anomaly (SAA).

    Each Globalstar Gateway took an update from COBHAM to work with the SOS messages and the waveform. Iridium and Globalstar own the 1.6Ghz spectrum, well they share it. So it makes sense for Globalstar to use its own spectrum. MSS is Uplink only, that is from the iPhone14 to the Globalstar Vehicle in orbit, then that vehicle bent pipes it back down to a Globalstar Gateway.

    The EIRP of the Apple SOS burst transmitted by the iPhone14, fits within the spec for the 5G NTN, which is approx 20-23dBm (~500mW). That same FCC article shows the EIRP, Waveform type and a Bandwidth, plus some Signal Designator. Also there are a bunch of Apple Patents on this topic and more. A worthwhile search from FCC is for Globalstar’s FCC ID of L2V and for Apple’s FCC ID of BCG.

    Also FCC is great they post pictures of the waveform if they can to show if they exceed the approved BW and spurious emissions outside that BW…

    Lastly since this is getting big … if you are interested, connect your iPhone14 to your macbook or whatever, run datalog and target a module called scotty …. yes “beam me up scotty”, and this will show all the internal workings of the Satellite Comms and what is logged.

    Ok better address this: the 2.4Ghz portion that is also referenced in the main post thread. That portion is owned by Qualcomm, and is part of the Globalstar Duplex side, this is the Downlink from Globalstar Vehicle to Handset. Loral, Qualcomm essentially started Globalstar, Qualcomm and Apple have been public about things re Apple complaining about costs, fees, patents, etc, so all iPhones run Qualcomm chips/modems for 2/3/4/5G comms. Apple purchased Intel’s Chip division several years back, and have not been able to develop a working chip/modem to replace those SnapDragon Chipsets and more. Intent is for Apple to not pay or use Qualcomm Chips, but its been 7 years already

    Apple clearly have some agreement with Qualcomm as iPhone14 receives a message back via the Globalstar vehicle …. so suggest that the SnapDragon chip handles the Downlink portion, or that Snapdragon provides the IQ stream at a minimum to a process or another chip to process that stream and “read” the downlink burst, which is seen as a response in the iMessage App. Two things, Apple don’t like paying for much, and secondly don’t like sharing, so it makes sense that Apple have some NDA or MOU with Qualcomm over the Downlink portion, of which SnapDragon handles.

    To finish, SOS message uplink is SC-FDMA, whilst downlink is CDMA waveform. SC-FDMA is Single Channel- Frequency Division Multiple Access, CDMA is Code Division Multiple Access.

    SC-FDMA is essentially the 5G NTN Uplink …. for LTE.

    Re the Antenna’s ,,, iFixit did a teardown of the iPhone14 Pro and Max, They show a single chip that is most likely the in-house Apple/Intel Chip to handle the 1.6Ghz Uplink tx. This teardown also shows the Antenna used, so here’s the link for the teardown :

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