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Optimism around the potential to capitalize on advancements in satellite technology is out of this world.
In our last post on this topic, we covered Apple’s move to bring satellite tech to the masses with iPhone 14 and other advancements for the growing LEO NTN market. Increasingly, telecom is exploring opportunities to connect devices and land-based networks directly to satellites. This includes leveraging non-terrestrial networks (NTNs) to provide cellular service to the underserved and rural locations where it has not previously been realistic to provide connectivity.
Standards are now in place to bring low earth orbit (LEO) satellites into the 5G cellular network. While capabilities are evolving at a feverish pace, these advancements will not be without technical and commercial challenges.
Satellite direct-to-phone service
Traditionally, connecting to a satellite required an expensive, specialized satellite phone. This has limited the market opportunity to people and businesses with specific use case requirements and the budget to support them.
Lately, we’ve seen heightened focus on the viability of satellite direct-to-phone service. 3GPP Release 17 standards now support direct connection between 5G cellphones and satellites. Effectively, satellites are becoming part of the 5G network.
In another positive step, the 3GPP has identified a set of 5G frequency ranges in the n256 and n255 bands to allow future 5G handsets to stay connected using both terrestrial mobile networks and non-terrestrial satellite networks around the globe. The current first generation of LEO satellites is using frequency bands Ku (between 12 and 18GHz) and Ka (between 27 and 40GHz). These high-frequency bands support higher data throughput, higher bandwidth, smaller antennas, narrower beams, and greater security than traditional satellite bands operating below 12GHz.
The new bands are more susceptible to weather damage and rain fade, though exposure can be reduced by amending the ground station design and signal modulation.
Commercial challenges for LEO
The new standards are essential and exciting to have, however the business dynamics of NTNs are challenging. A big question is how to commercialize the opportunity to use LEO satellites as part of 5G.
The business case must offset the expense of launching and maintaining satellites against the revenue-generating coverage footprint.
The reality is that about 71 percent of the world is ocean. Granted, access by ships is required, but it is a small piece of the business opportunity, and the revenues are unlikely to offset satellite costs. The remaining 29 percent of earth is land-based with highly competitive markets where the largest demand and budgets exists.
Service providers are wrestling with use cases and where to provide coverage as they seek paths to phone-to-satellite service profitability.
3GPP standards set the stage
From a 5G mobile broadband perspective, the 3GPP standardization of non-terrestrial networks is important. Release R15 had a number of study items on deployment scenarios and R16 studied non-terrestrial network architectures.
Major progress was made in R17, which is now frozen. R17 includes the first standards for direct-to-phone as well as low power consumption connections for remote enterprise IoT devices. R17 provided specifications for using the satellite as a relay point, communicating with the cellphone and the terrestrial 5G gateway, which then communicates with the base station. This is called the “transparent model” where the satellite acts as a relay node, changing the frequency carrier of the uplink RF signal, then filtering and amplifying it before transmission via the downlink. In this case, the waveform of the signal repeated by the transparent payload is not changed.
In late 2023, R18 will include specifications for a base station or Open RAN to be hosted on the satellite. This is called the regenerative model which transforms and amplifies the uplink RF signal before transmitting it on the downlink. Further, the signal transformation involves the full digital processing of the signal, such as demodulation, decoding, re-encoding, remodulation and filtering.
NTN challenges to be addressed
These are important developments, however space is an incredibly complex working environment in which to work. You can’t just send a technician in a flying truck to fix a problem (well, maybe one day). For now, this puts a magnifying glass on the importance of validating satellite functions in labs on the ground before launching them to space.
For now, this puts a magnifying glass on the importance of validating satellite functions in labs on the ground before launching them to space.
Despite closer proximity than satellite constellations before them, technical challenges arise given how far LEOs are from Earth. Several technology and performance challenges must be considered and evaluated through NTN test plans:
Technical challenges:
Signaling delays and fluctuations, and timing variations due to altitude
Large doppler shifts due to moving at thousands of miles per hour
Signal degradations due to weather, atmospheric conditions, path loss, and shadowing
Interference and security attacks since signals are weaker
Line of sight challenges
Timing and synchronization issues
Performance challenges:
Providing seamless coverage and connectivity during handover to terrestrial network or another LEO satellite as it passes by
Cell stability
Capacity
Latency (delay) and jitter (consistent latency)
Throughput (speed)
End-to-end quality of voice, video, data, and emergency services
Testing is essential for success
New ideas that improve the NTN business case are coming to light daily. One is doubling LEO satellite payloads to include GPS/GNSS services currently deployed on medium earth orbit (MEO) satellites. Because of larger distance from Earth, MEOs have the disadvantage of weaker signals, which can be more easily spoofed.
The industry is evaluating two models:
A relay model that relays and amplifies the PNT signals from MEO orbiting constellations like Galileo. This strengthens Earth-delivered signals, supports faster position fixes and accommodates rapid two-way authentication checks to enhance security.
Direct from LEO PNT service where the LEO satellites could be either a trusted primary source of PNT or used for resilience.
NTN is complex, with many challenges to be addressed. Creating and executing a comprehensive test plan that assures NTN’s capabilities on the ground, before launch, is essential for success.
Learn more about testing in this space with Spirent Vertex and from our white paper Testing Satellite Communications for 5G Networks.
