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Apple Leading In Merger Of Satellite and Cellular Networks
Two big announcements regarding new satellite-based communications options for cell phones dropped in the past month, giving us a view of the next big frontier in wireless communications. First, Elon Musk’s Starlink (a division of SpaceX) and T-Mobile U.S. agreed to interconnect their networks, allowing T-Mobile cellular devices to roam onto Starlink’s next-generation low-earth orbit satellites (LEOS). That announcement became a footnote a week later when Apple announced a partnership with LEOS provider Globalstar to provide an emergency alert capability called Emergency SOS By Satellite on its new iPhone 14 models, to be available in the U.S. and Canada in November.
To be sure, people have been talking about an integrated satellite-cellphone capability for decades, and there is a reason we don’t have it yet: getting a cell phone to talk to a satellite is really difficult! There has been speculation about Doppler effects, synchronization requirements, and the like. But they all pale to the challenge of establishing and maintaining a reliable radio path between a tiny, low-powered cell phone and a satellite zooming by hundreds of miles away. BTW—no one is talking about any satellite-cellphone capability working indoors.
To get a clear understanding of the potential outcomes, you have to look at the whole problem, which means considering both the handset and the satellite network. From that standpoint, Apple’s plan has far more credibility, because the company has already designed the required components into all models of the iPhone 14 handset (including support for a 2.4 GHz radio channel Globalstar owns); no earlier iPhone models are supported. Globalstar has been offering a similar capability under the name SPOT since 2007 using its own proprietary devices.
The proposed Starlink/T-Mobile service cannot operate on the V1 satellites in Starlink’s existing LEOS network, i.e., the network it is using to provide its fledgling fixed wireless access (FWA) service. Starlink’s next generation V2 satellites will employ much larger (i.e., 25-meters2), more sophisticated antennas, and support for a special swath of 1.9 GHz radio band T-Mobile owns. However, it is still unclear what—if any—modifications to the handsets or operating instructions might be needed to make the service work.
The ability to have untethered communications capabilities seamlessly covering the entire earth, including the oceans, for voice/Internet access/text and even video communications is a long-held dream. Given the realities of radio communications, the only realistic architecture uses the terrestrial cellular infrastructure for populated areas and satellite coverage for the rest. We are finally launching on the path to making this vision a reality.
Who Is In The Satellite Game?
Current mobile satellite-based systems are based on either geosynchronous satellites (GEOS), like Intelsat, or low-earth orbit satellites (LEOS), like Iridium and Globalstar. In either case, a specially designed handset is required to access the service, and each provider sells handsets designed to operate on its network.
While the Starlink/T-Mobile announcement to support cell phones communicating directly with Starlink satellites made the national news in August, I found three other startups that had already been working on satellite networks to integrate with cellular devices.
Omnispace has two satellites launched and claims the advantage of being standards-based—particularly, the 3GPP Release 17 standard for Non-Terrestrial Networks (NTNs). Omnispace has recently demonstrated satellite-to-cellphone text transmission.
AST SpaceMobile has one of its BlueWalker 3 satellites up and has backing from cellular operators Rakuten and Vodafone. The satellite has a 64 meter2 phased array antenna, the back of which is covered with photovoltaic cells for power. Radio signals spread out as they travel, so a larger antenna allows you to collect and process more of the dispersed radio energy.
Lynk Global claims to have solved the problem of integrating with the tight synchronization parameters of cellular protocols, and also demonstrated its ability to send a text message from one of its satellites to a standard cell phone. It plans to launch three additional satellites by the end of 2022, giving it the four satellites it will need to go into commercial service.
All of these providers are committed to communicating with standard cell phones, though none has come up with a workable solution to the handset-to-satellite challenge.
How Steep Is the Hill?
As I noted earlier, getting a small, battery-powered cell phone (with an internal antenna) to send a signal reliably to a satellite hundreds of miles away is a big lift, and success will likely require improvements by both the handset and the satellite. Initially, all the options I mentioned are planning to use unmodified cell phones. Though at a minimum, the phone will require a radio capable of sending on whatever frequency the satellite service uses.
At the satellite end of the link, all of the providers are banking on continuing developments in smart antenna technologies to pull this off. The key technology is what’s called a phased array antenna. We have long had antennas that could physically focus the radio signal on a particular direction, but a phased array uses a number of antenna elements working in unison to focus the radio beam electronically. Since the signal is focused electronically, it can also be redirected or “aimed” in any direction at will.
The primary purpose of this focus is to increase the range by increasing the power sent in that particular direction. However, it also serves to focus the receiver so you also “hear” better. This phased array idea is also what’s behind what the industry has taken to calling Massive MIMO or beam-forming antennas. (MIMO is something else entirely.)
So, by combining a really big antenna array to capture as much of the cell phone’s dispersed signal as possible and the ability to focus the antenna dynamically, Starlink hopes its satellites will be able to hear your cell phone clearly enough to communicate. We know from the outset that the downstream path (i.e., sending a signal to the cell phone) should be the easier of the two because you have the power of the satellite combined with the focusing ability of the phased array antenna in your favor.
In simple terms, the better the quality of the received signal, the more bits you’ll be able to send, and the more likely you will be to get services like real-time voice/video and broadband internet. In the meantime, every provider (at least the sober ones) is only talking about bandwidth-efficient text-based services accessed outdoors with a clear view of the sky for the foreseeable future.
The Apple-Globalstar Plan
Announced at Apple's 2022 Worldwide Developers’ Conference, the Globalstar/Apple partnership had been making the rounds on the rumor mill for a month prior. The thing to understand about Apple is how carefully it optimizes its product launches for success, always keeping in mind its premium brand reputation and setting rigorous standards for any of its partner companies. So, while Globalstar couldn’t match Mr. Musk’s drawing power, they were able to convince Apple they could deliver on their service expectations.
When it came to choosing a LEOS partner, it looks like Apple made a smart pick with Globalstar. The company has struggled to provide LEOS voice service, but it has a lot to offer in this partnership:
- A long track record operating a LEOS network.
- An existing emergency alerting system called SPOT, so the company is familiar with the market and the technology challenges involved.
- A network with a relatively simple LEOS architecture compared with networks like Starlink or Iridium.
- A usable 11.5 MHz swath of radio frequency at the high end of the 2.4 GHz band, which the 3GPP has now designated Band 53/n53 (currently available on iPhone 14 exclusively). Importantly, that 3GPP acceptance could open the door to a worldwide rollout of Emergency SOS if the U.S./Canada trial pans out.
To offer the Emergency SOS service, Apple has formed a partnership with the Globalstar, which the latter described in its SEC filing as “transformational.” Apple has also agreed to fund 95% of the capital cost of the satellites Globalstar will need to deliver the service. In return, Globalstar agreed to devote 85% of its network capacity to the Emergency SOS service. Apple says the service will be free to iPhone 14 users for two years.
Globalstar is one of two LEOS networks, the other being Iridium, and both initially focused on providing voice services, though each offers a relatively low speed (i.e., <1 Mbps) data service. I described Iridium’s operation in an earlier post, but Globalstar has taken a much simpler approach in its architecture.
Where the Iridium network routes calls from satellite to satellite to a downlink connection, a Globalstar satellite will only accept calls from subscribers if it is in contact with one of the network’s 24 downlink gateways; additional gateways are being added for the Emergency SOS service. A Globalstar connection goes from the phone to the satellite, directly to the downlink gateway; there are no satellite-to-satellite connections. In essence, the simplicity comes from the fact that all of the “network smarts” remain on the ground. Globalstar describes its connection as a “bent pipe” as opposed to a “dynamically reconfiguring packet switching network in space.”
While the uplink (from the phone) transmission is still a challenge, Globalstar and Apple have taken major steps to address reliability. First they compress the amount of data they have to transmit by a factor of three, and then use a highly reliable transmission format. There is also an app on the iPhone 14 to help the user point the phone at the satellite, but it can still take several seconds to a few minutes to send an emergency alert. A clear view of the sky with no obstructions is recommended.
Globalstar has been supporting a similar capability on its SPOT Satellite Devices though those operate on a separate 1.6 GHz L-Band radio channel. There is an app available to connect an iPhone to (but not replace) a SPOT device. The partnership also plans a number of relay centers to forward alerts to PSAPs (i.e., 911 Centers) that only accept voice calls.
As an added benefit, Apple’s activities on the emergency alert front might raise awareness of the sorry state of our public mobile E911 location capabilities—and finally, embarrass enough politicians to get the money to bring our 911 system into the 21st Century.
How Does Starlink Stack Up?
The Starlink and T-Mobile announcement was something of a surprise, and the two have talked about the solution in only the most general terms. Since neither makes handsets, they will need some way to incentivize handset manufacturers to join in the offering; the 1.9 GHz channel they are using should be available on virtually all cell phones.
However, if Apple chooses to freeze them out (something Apple has already done with technologies like Rich Communication Services [RCS]), you have to wonder about the viability of a service that only works in some parts of the diverse Android ecosystem but not on iPhones.
While the initial service would offer some form of text capability, the longer-term plan envisions a satellite-based service that cell phones would transparently roam onto once they moved out of the T-Mobile coverage area. The only hint of a network architecture is Starlink’s description of “cell zones” for coverage. A Starlink described cell zone would be much larger than a standard cell site coverage area, and Starlink expects each zone to provide 2 M to 4 Mbps of shared capacity. Not a lot for possibly dozens to hundreds of square miles.
The traditional cellular protocols will need to be modified to eliminate most of the background chatter that goes on between the phone and the cell tower even when you’re not using it; that’s where the 3GPP NTN standard will come in to play. Cellular management and roaming concepts like a Visitor Location Register might also need to change.
In short, until we get more details regarding how the two companies intend to make this service a reality in the face of handset challenges (possibly emulating some of the steps Apple is taking), this announcement sounds a bit like “the sound of one hand clapping.”
Great Days For Wireless
The great thing about the wireless business is its persistence. The dream of integrating cellular and satellite systems for worldwide coverage has existed for decades despite the significant challenges involved. (Iridium was invented as a workable alternative to something like this.) However, the technology continues to advance relentlessly on all fronts (e.g., antennas, transmission formats, operating requirements, etc.) until one morning, we wake up, and one last development has taken what was once a pipe dream and turned it into a profit center.
Sure, companies like Apple and Globalstar are only talking about emergency alerts today, and with where we are on the technology front, even that might be a stretch initially. However, all of these elements will continue to improve with experience. Clearly, the first step will be to develop this beyond something you hope you’ll never need into something you’re using every day.
Before you get too excited about any of this, it’s important to remember that “it takes two to tango,” and any solution that doesn’t include a realistic plan to address the handset challenge might just be science fiction.