Non-terrestrial networks (NTNs) based on Low Earth Orbit (LEO) satellites using 5G direct-to-device (D2D) systems, without the need for dishes or additional antennae, and allowing the signal to be received by ordinary 5G mobile phones, are a reality now (not only in the emergency calls of any iPhone 14, 15 or 16, but also for normal services), and NTNs will likely be offered at grand scale in the market in the coming years 1 .
LEO satellites are those orbiting below 2,000 km, typically above 160 km. For instance, Starlink satellites orbit at 550 Km above Earth. It takes LEO satellites between 90 minutes to 2 hours to complete an orbit. Therefore, you need constellations of satellites in order to offer uninterrupted coverage.
LEO satellites aren’t new but, before the invention of Space X’s reusable Falcon 9 launch rocket, they did not make for good business and all commercial initiatives using non-reusable rockets failed: Teledesic, a company using LEO satellites was founded in the 1990s. The company’s intention was to build a global commercial broadband Internet service based on satellites with a constellation of 840 planned satellites and an incredibly high data rate for that time: downloading files at 720 Mbps 2 . Teledesic launched a demonstration satellite on 26 February 1998. Nevertheless, the project failed because of the high cost of launching LEO satellites with non-reusable rockets. Similar projects in the same timeframe from Iridium and Globalstar were also commercial failures. The cost of using a new launcher each time was comparable to train travel that would require discarding the train and to using a new one for each journey. The reusable Falcon 9 technology allowed the company to launch constellations of LEO satellites at a fraction of the cost 3 . The reliability of Falcon 9 has been remarkable, with no catastrophic failures between 2016 and mid-2024 (more than 350 launches with no catastrophic failures).
As a consequence, a great number of LEO satellites are being launched right now: the total number of active satellites has increased dramatically from less than 2,000 at the end of 2018 to more than 8,000 4 in November, 2024, of which 7,683 are LEO 5 . As of September 2024, there were 6,426 Starlink satellites in orbit, of which 6,371 were working 6 , with almost global coverage 7 , and the goal is 30,000 Starlink satellites 8 . Amazon (Kuiper) asked the FCC in 2020 for International Telecommunication Union (ITU) files for 3,236 satellites 9 , and this number, as well as the long term goal, is probably much higher now. Other players offering 5G in the near future (most of them through the 3GPP 5G standard - see below) are Echostar, OQ Technology, AST SpaceMobile (providing broadband services to AT&T, Google and Vodafone), Eutelsat/OneWeb 10 (with more than 600 satellites already in orbit), Sateliot in partnership with Transatel (NTT), Stellar and Skylo, Galaxy Space, Ligado Networks, Lynk and others. Globalstar, Iridium and Qualcomm have proprietary NTNs for the provision of 5G services. 11 There are now 17 different deployed constellations, and more than 200 others in different deployment statuses 12 , 40 of them from companies with headquarters in China.
Of course, there are also other IoT-connectivity solutions from satellite NTNs, which differ from 5G standards, such as those based on LoRaWan 13 (Echostar, Fossa Systems, Lacuna Space, Innova Space, Eutelsat), or based on Bluetooth from Space (Hubble Network) 14 14 . We shall limit ourselves here to 5G services.
As regards companies launching LEO satellites 15 , China Satellite Network Group is the leader in planned launches in the short term (with 13,000 scheduled LEO satellites), followed by Space X (more than 8,000 new scheduled LEO satellites), according to GSMA 16 . Other sources reference about 60,000 new LEO satellites planned by Space X in the medium and long term.
What is clear, in any case, is that the total number of LEO satellites is going to grow exponentially. Launching a new satellite requires a filing with the ITUt the to obtain the allocation of radiofrequency spectrum to communicate with ground stations and to determine the satellite’s orbit. The filing follows a complex procedure that should be promoted by a member State (operators cannot as such directly submit an applicationto the ITU) 17 and is summarized in the following graph 18 :
There are applications (as received) for around 1 million new LEO satellites 19 , that are called “paper satellites” 20 . Rwanda alone submitted 337,320 new applications (each one corresponding to one satellite) in 2021 21 21 . Even if only a fraction of these satellites is ultimately launched, the difference between the 7,683 LEO active satellites currently in orbit and the more than 100,000 projected LEO satellites gives us an idea of the revolution that is coming.
Antennae (receiving dishes) will not be needed in the short term and this results in D2D systems that will use 3GPP specifications (the name obeys only to historical reasons) notably via Release 17 22 , a standard that now allows 5G services and in the future will allow 6G services 23 .
Data rates are growing exponentially, as a consequence of technology (adoption of 3GPP specifications for 5G) as well as of the number of available satellites. Remember data-rate growth in the evolution of mobile communications services (broadly speaking, 64 Kbps until 2001 with 2G, 2 Mbps with 3G from 2001 to 2009, 100 Mbps with 4G in 2009-2019 and up to 10 Gbps or even more with 5G in 2019). We shall no doubt see similar growth in data rates from now with D2D 5G satellite services using NTN (and 6G in the future). In practice, real downlink data rates of satellite NTN services is sometimes even higher than 5G NSA terrestrial networks, although in uplink the satellite service data rate is still lower than the terrestrial alternative 24 .
It is true that the use of D2D satellites requires a certain amount of latency (it is always faster to connect to a tower than to connect to a satellite in space), but 5G satellite services latency in long distances isn’t necessarily high: using radio frequencies, the information travels 47% faster (at the speed of light, 299,972 Km/s) than via optical fibre cable 25 (at around 206,856 Km/s).
In addition, laser-based communications between satellites in space (communicating with other satellites at the speed of light) are already a reality, allowing an ultra-fast, high-capacity backhaul for global communications 26 .
As of today, there is usually still more latency in the services based on satellite NTNs than in NSA 5G terrestrial networks, but according to a university study that measured service on the ground, “applications requiring latency below 100 ms could be served with 99.99% reliability”, and the maximum observed values for latency are higher in NSA 5G terrestrial networks than in NTNs 27 . Technological improvements will reduce latency in the future, as there aren’t any physical obstacles to obtaining low latency.
Regarding spectrum scarcity, there are also projects involving the use of laser light to communicate between users and satellites 28 , whicht will become more interesting the more the spectrum is saturated (the problem is the need - as of today - for complex reception devices but technology will help in the future).
The price of 5G satellite services will becomesubstantially lower over time, with the increase in communications volume and the growth in the number of available satellites and NTNs. Some operators are already providing these services at the same price as premium 5G terrestrial services, and as part of it 29 .
There will be numerous use cases for D2D 5G satellite communications services in NTN. Exponentially higher data usage by IoT (in industry, agriculture, logistics, etc.) and especially by connected and autonomous vehicles will require extended coverage and backhaul 5G infrastructures that cannot always be provided by the terrestrial network. 5G services in the air, at sea or in less populated areas can be obtained through satellites. The European 5G Observatory has predicted that satellite-enabled 5G mobile networks alone could reach a market value of USD 18 bn by 2031 30 , and GSMA estimates a figure of USD 35 bn by 2035 31 .
Some integration of satellite NTN with terrestrial networks (TN) is already occurring, as evidenced very recently by the European Space Agency through the 5G/6G programme line 32 32 in the context of the Advanced Research in Telecommunications Systems (ARTES) 4.0 programme.
The future of D2D satellite communications services in NTN will probably be even better in the context of 6G 33 , which will pave the path for integrated satellite-terrestrial networks in a way that will not be perceived by the user but will enhance connectivity. These changes in turn should give rise to exponential growth in IoT, connected and autonomous vehicles and many other uses that cannot be well served without the use of non-terrestrial networks.
