Non-Terrestrial Networks Have Bright Future but Face Limitations

Non-terrestrial networks (NTNs) will expand the reach of cellular networks, which is increasingly important when 95% of the U.S. population has abandoned landline phones, David Witkowski, co-chair of the Deployment Working Group at IEEE Future Networks, said during an RCR Wireless webinar Tuesday. Last month, FCC commissioners approved a supplemental coverage from space framework, facilitating carriers working with satellite operators on converged networks (see 2403150045).

Almost 3 billion people are unconnected worldwide and women are 30%-50% less likely to use the internet, Witkowski said. That’s “a problem we need to solve.” Even in industrial nations like the U.S., wireless coverage remains problematic in rural areas and “NTN fills that gap,” he said. Witkowski noted that texting 911 is more effective than calling, especially in areas where a natural disaster has struck.

Challenges remain, Witkowski said. “Let’s be realistic, space is hard -- it is expensive to put something into orbit,” he said: It takes a lot of resources, effort and technology, and you can’t do upgrades. Once a system is in orbit, it can’t be changed. Wireless from space is difficult with significant free-space path loss, Witkowski said. A mobile phone doesn’t have a good antenna or a large aperture, and it’s “not going to get a lot of gain," he said. Satellite communications will require lots of power, which is a drain on the phone’s battery, he said. There’s also the “hidden node problem, meaning that two ground stations can’t talk to each other simultaneously.”

Carriers must understand the costs and limitations of satellite communications and that performance is “necessarily limited by the physics,” Witkowski said. The wireless industry tends to oversell technology, he argued. “We were promised a lot in 5G, and it still isn’t there,” Witkowski said. On satellite, “we need to be careful in setting expectations -- this is not broadband from space, at least not yet,” he said.

As the 3rd Generation Partnership Project standardizes NTNs as part of 5G, the “picture, though complex, is showing the vision of where things are going,” said Obilor Nwamadi, senior product manager at Viavi Solutions, a test measurement company. NTNs and cellular networks will converge under 6G and future 3GPP releases, he said. What 3GPP is aiming for is being able to match the throughput of up to 200 Mbps that Starlink is doing now, he said.

Nwambi said he grew up in Nigeria, and cellphones were the only way to communicate in the area where he lived. The only TV was satellite TV. “There will be convergence of non-terrestrial networks with terrestrial networks, and everything in between,” he said.

The physics of communicating with space and propagation delays are among the biggest challenges, Nwambi said. “The delays are very large compared to terrestrial networks,” he said. In low earth orbit constellations, “the satellites are moving really quickly.” Security will also be an issue, he said: “In classic terrestrial, you have a base station in a fixed location” while satellites are moving, which opens possibilities for spoofing and jamming, he said.

Consumers don’t want to think about how they’re connecting to a satellite network and wireless carriers don’t want to deal with all the problems that arise, said Parthsarathi Trivedi, CEO of Skylo, which offers NTN services to terrestrial providers. NTN solves not just “macro holes in coverage,” in places like Death Valley, California, but coverage gaps that occur in parts of built-up areas covered by wireless networks, he said.

Carriers are already offering services allowing text messaging through NTNs, Trivedi said, which will be “very key for the adoption of NTN, at scale, in the consumer market.” Another growth area will be using satellite communications for SOS calls from remote areas, he said. IoT devices can also be upgraded, which “opens up a whole range across container tracking [and] supply chain” uses, he said. Skylo is hearing interest from mining companies, farmers and oil-and-gas producers, he said: “We find that we’re getting a lot of traction from companies that are doing cattle tracking … as well as on-ground sensors for agriculture.”

When it comes to video streaming and other high bandwidth applications, the question is “how much are you willing to pay for it?” Trivedi said: “That is not something that anybody [on the panel] is talking about.” A limiting factor is spectrum “and satellite will never reach the kind of reuse that you can get terrestrially as it relates to spectrum,” he said. Wi-Fi will always make the most sense inside a building and cellular in a city, he said. Skylo stresses to carriers that their customers should always use a terrestrial network when it’s available, he said.