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Non-terrestrial networks (NTNs) are able to significantly extend coverage by moving from a terrestrial infrastructure to hybrid space. However, Keysight Technologies highlights the challenges that can threaten the successful deployment of these networks.
We’ve all experienced our mobile phones not having service. If we are not connected to Wi-Fi and move too far away from our network’s base station, which is a terrestrial infrastructure, connection is lost.
However, this is about to change with the advent of 5G non-terrestrial networks (NTNs).
NTNs refer to a constellation of satellites or high-altitude platforms (HAPs) that function as relays, extending the coverage and capacity of terrestrial 5G networks.
These networks present many benefits such as extended coverage, low latency, high throughput and spectrum sharing. As such, there is much hype over the commercial possibilities of 5G NTN.
Potential 5G NTN use cases for military and government include coverage for forward battlefields or focused special operations. NTNs could also provide coverage to restore communications in disaster areas experiencing widespread infrastructure outages. Among transportation use cases, NTNs support logistic in-transit tracking for long-haul trucking routes, rail lines and maritime shipping lanes.
However, there are numerous challenges to consider when deploying NTN networks. Nancy Friedrich of Keysight Technologies, a US company that provides electronic design and test solutions, points out the five key challenges.
More data, crowded spectrum
The hybrid 5G NTN provides obvious advantages as well as challenges. Handheld or vehicle-based user equipment tends to demand high volumes of data for video and mapping services. Additionally, sensor applications may connect user equipment with lower data rates.
Delivering the required volumes of data means leveraging 5G signalling fundamentals for 5G NTN, including mmWave carrier frequencies and complex modulation in wide bandwidths.
5G spectrum is already tightly allocated in terrestrial networks, and an onslaught of tens of thousands of lower-Earth orbit (LEO) satellites and geostationary Earth orbit (GEO), medium-Earth orbit (MEO) and high-altitude platform systems (HAPS) platforms soon operating in 5G NTNs will add to the spectrum crowding.
The space environment
Space is the foremost challenge for NTNs. Once deployed, equipment is inaccessible. In addition, systems must operate in an extremely harsh environment with extreme temperatures and radiation.
For successful performance, systems also need to provide consistent power generation and storage. For all of these aspects, satellite system providers need to balance risk versus cost across the lifetime of the operation.
Size, weight, power and cost
Another concern is the physical limits of placing high-frequency radio frequency (RF) and computing resources in the sky. Size, weight, power and cost (SWaP-C) become issues when moving away from the GEO system into more compact LEO satellites and HAPS platforms, and payloads must transform accordingly.
On the plus side, placing more satellites into service with smaller payloads and shorter life cycles is now feasible and cost-effective. A 5G NTN might consist of a group of satellites working together in various orbits.
Connecting in motion
5G NTNs put some things, or perhaps everything in the network, in constant motion. Satellite and HAPS movements factor into connection set-up, signal quality and handovers.
Parameters previously fixed or confined in a small range in a 5G terrestrial network suddenly become wide-ranging variables in a 5G NTN. Tracking areas, bulk delays, Doppler shifts, signal-to-noise ratios (SNRs) and more elements take on dynamic characteristics.
The payload question
The introduction of 5G NTNs disrupts the traditional 5G terrestrial network architecture and opens up a paradigm shift in connectivity.
Many alternatives exist for satellites and HAPS, some with multiple satellites in the chain scattered across miles of sky. The choice between transparent or regenerative payloads can completely change how the network organises and the resulting signal routing.
With LEO satellites in motion, remember that all timing relationships are dynamic. At stake is the quality of service (QoS) user experience, primarily due to variable delays and complex handovers that can result in dropped connections.
Platform kinematics rapidly alter 5G NTN channel behaviour, and staging fast-moving platforms in the proper orientation long enough to gather detailed physical measurements is not an option. However, simulations can account for complex orbital paths and decompose real-time motion into precise detail with time-correlated analysis.
To overcome these challenges and advance the next NTN wave, rather than relying on physical testing alone, successful deployments will require the use of virtual simulation, emulation and digital twin technology using RF system measurement science.
Accurate multi-domain simulation of a 5G NTN link depends on four elements: an authentic representation of complex digital modulation in a 5G waveform with real-world effects, a complete model of satellite kinematics, robust modelling of RF system signal processing and a time-correlated view of 5G protocol decoding. The critical goal is validating performance in a simulation before deployment of orbital hardware.
