It was clear going into the Satellite 2023 show this month that Non-Terrestrial Networks (NTN) would be a big topic. The 3GPP consortium of standards organization has been quietly working on 5G-NTN specifications for several years, but when Apple unveiled its “Emergency SOS via Satellite” feature on the iPhone 14 last September, everyone became interested.
Apple did more than just talk. It said it had budgeted $450 million for related infrastructure, mostly earmarked for satellite operator GlobalStar. By November, there were enough pieces in place to go live in the U.S. and Canada. Since then, the service has been rolled out in these regions as well as parts of Europe.
Other companies have also been issuing press releases, if not actually launching services. In July 2022, Ericsson and Thales announced plans for testing and validation of 5G-NTN. In August 2022, T-Mobile said it was working with SpaceX and its second-generation Starlink satellites to support 5G coverage. Related news from AST SpaceMobile, Lynk Global, and Iridium, among others, appeared at the end of 2022 and start of 2023. The momentum for 5G-NTN integration was reflected in the Satellite 2023 program agenda.
“A majority of the sessions have a strong focus on telecoms and mobile wireless services, and the merging of terrestrial cellular and satellite network infrastructures,” said Conference Chair Jeffrey Hill in Via Satellite. “The terrestrial wireless community is coming to a realization that it cannot expand on its long-term business plans in the 5G era without the help of satellite services.”
NR-NTN and IoT-NTN
It’s worth making a few caveats. Apple’s “Emergency SOS” service, the only one yet to deploy commercially, is not a full-fledged 5G communications platform, allowing only for limited texting when in line of sight of a satellite. And the use cases seem niche. This ad, for instance, features a mountain rescue by helicopter. Moreover, 5G itself is far from ubiquitous. According to GSMA, it only covers about 15% of the globe.
Is there really a business case for NTN? According to Hill, the answer is yes. The “long-term business plans” of wireless operators depend on NTN integration. The 3GPP standards community would agree that the use cases are, indeed, compelling. And with enough solid use cases comes net new revenue streams, making the business case very compelling for the entire supply chain.
A lot depends on what you believe will emerge over time. In that light, it may be useful to recall that Steve Jobs liked the Wayne Gretzky quote about “chasing where the puck is going, not where it’s been.” And one place where connectivity is going is to devices beyond smartphones.
To be more specific, a crossover occurred in 2020 when analysts noticed that for the first time ever there were more IoT than non-IoT connections. In other words, more smart home devices, connected industrial equipment, connected cars laptops, smart watches, sensors, and computers exist than smartphones. That gap continues to widen.
The standards work reflects this split. In the context of NTN, there are roughly two streams: New Radio (NR)-NTN, developed as a 5G successor to LTE; and IoT-NTN, which covers enhancements to Narrowband (NB)-IoT and LTE-Massive machine-type communication (M). Both NB-IoT and LTE-M are low-cost technologies that draw minimal power for non-latency sensitive devices.
Use Cases and Challenges
The 3GPP has identified three main categories of use cases for satellite-based NTN: service continuity, service ubiquity, and service scalability. The first involves combinations of terrestrial and non-terrestrial networks; the second addresses areas where terrestrial networks may not be available; and the third uses satellites to broadcast content.
Service continuity relates to aircraft or maritime vessels. Ubiquity involves IoT (agriculture, asset tracking, metering) public safety(emergency networks), and home access. An example of scalability is the distribution of TV programming.
Regardless of use case and endpoint (whether smartphone or IoT device), NTN integration faces certain challenges. Distance is the biggest issue. On land, a mobile device may be one to 10 km from a base station. In a Low Earth Orbit (LEO) satellite-based NTN, that span lengthens to between 600 and 1,400 km.
The impact on communication is drastic. A one-way signal that can reach a base station on land in one millisecond may take 30 milliseconds to reach a LEO satellite. (That’s still a fraction of the time it takes to access geostationary satellites, at 35,000 km above the earth.) Longer round-trip times mean more opportunities for channel conditions to change, which can impact quality of service.
Another challenge involves non-geostationary satellites. Their relatively fast movement in the sky creates Doppler shifts, which means that the frequency at which they transmit signals will not be the same at which they are received.
As it happens, insofar as a smartphone has Global Navigation Satellite System (GNSS) capability, it can deal to some extent with Doppler shifts. That’s because it already receives one-way signals from Global Positioning System (GPS) satellites. It’s the combination of those signals with ephemeris data on satellite orbits that allows a phone to know its geographic position.
This capability, which 3GPP assumes for NR-NTN and IoT-NTN endpoints, also enables a device to calculate the relative speed between itself and any GPS satellite. Then it can determine the correct pre-compensation for the Doppler shift. How to best manage these adjustments, as well as handle the moving beams of non-geostationary satellites (such as LEO or MEO), are matters of ongoing research.
Propagation delays create more challenges. As a result, service providers – and manufacturers of wireless network components, like us at Octasic – are finding new ways of handling other functions, such as timing relationships, channel state information, modulation and coding, random access channel, and retransmission.
To move forward, however, wireless network components need to be enhanced, tested, and tweaked. Even if your 3GPP-compliant code is battle-tested for terrestrial delivery, it’s impossible to run it ‘as is’ over a satellite network.
The Satellite 2023 conference had a significant emphasis on NTN, as well as related news and demonstrations from technology providers. It’s an exciting time to be working with the satellite community. Reusable delivery vehicles have reduced launch costs, as have the smaller form factor of LEO satellites, which have performance characteristics highly favorable to integration with land-based communications.
The use cases for NTN cover a lot of untapped territory, and many operators are eager to integrate and deploy.