One of the new capabilities that is being introduced in 5G is integration of terrestrial networks with non-terrestrial networks (NTN), whether those are High-altitude Platforms (HAPS) flying the stratosphere, or satellites in low-Earth orbit (LEO) or geostationary orbit (GEO).
The ability to provide 5G over non-terrestrial networks means expanding high-speed broadband coverage to isolated areas, whether that be small towns or mining sites, or to areas where terrestrial infrastructure cannot reach, such as for airplanes or maritime use cases. (See more potential use cases for 5G over NTN here.)
But there are substantial challenges for this integration of 5G and NTN. “This is unchartered territory for mobile networks, representing an entirely new area of 5G testing and a unique set of challenges,” wrote Spirent Communications’ Senior Solutions Architect Jukka-Pekka Nuutinen in a December 2021 blog post.
Among the challenges:
–Technical challenges, primarily driven by the fact that distances in non-terrestrial networks are “considerably larger than traditional terrestrial networks,” according to Nuutinen, leading to a number of factors to be overcome both in terms of the air interface and networking. For instance, he added, there are multiple possible network routing paths because satellites communicate with each other in a constellation, and additional communication with moving aircraft and airborne base stations would essentially create a dynamic mesh network. Among the challenges influenced by the large distances are delay, large Doppler shifts from rapidly moving satellites, signal attentuation and handovers between terrestrial and satellite links, Nuutinen said.
–Device form factors, power levels and cost. Terminal costs would have to be minimized in order to drive adoption, notes Derek Long, head of telecoms and mobile at Cambridge Consultants, in a recent white paper on 5G and NTN. “Satellite phones are larger than the average smartphone, with a larger battery and antenna. That’s because LEO satellite phones must transmit at ten times the power of a smartphone (around 10 Watts) to reach the network,” he writes. While that will change over time, he emphasized in a related LinkedIn post that it will be important for integrated 5G and non-terrestrial networks to be able to work as dual-mode, standard terminals, rather than specialized ones.
In Long’s view, “All of the challenges ultimately come down to the antenna technology.
Advanced intelligent antenna solutions – including key breakthroughs such as multi-beam and lighter, more scalable digitally phased array antennas – are essential to ensuring that NTNs are not only economically viable, but also able to integrate seamlessly into terrestrial 5G networks,” he writes in the white paper on 5G and NTN.
–Technology maturity. Both 5G and higher performance non-terrestrial networks are in their early days—and being built separately from each other, as standalone businesses with their own models and business cases that don’t require the other. It will take some time, Long says, before 5G evolves to a level where integration with NTN makes sense—and perhaps by that time, HAPS-based services, and other new space-based ventures such as Starlink and perhaps Jeff Bezos’ Blue Origin, develop a level of maturity where it makes sense on the NTN side as well.
–Regulatory and legal challenges. As noted in a paper by Ericsson researchers, current terrestrial cellular networks are “typically deployed so that they provide coverage within a single country only, fulfilling the associated regulatory obligations for that specific country. Satellite-based radio systems may, however, cover multiple countries or cover international waters.” While satellite operators may be familiar with operating in such a landscape, this represents new territory for mobile network operators, in terms of both legal jurisdiction and operational practices on, for instance, which data collection, storage and protection practices they must follow, depending on where the company and/or the devices it serves are located.
Still, Long remains optimistic that the advantages of more integrated 5G and non-terrestrial networks—particularly in lower infrastructure costs—and the work of 3GPP will ultimately drive a hybrid terrestrial/NTN 5G network. That network, he says, “will provide a range of valuable new services for consumers and enterprise alike, and create new opportunities for just about everyone in the ecosystem.”
