NTN: The New Frontier of Communications

The new frontier of ubiquitous and resilient cellular coverage lies beyond the boundaries of the Earth: Non-terrestrial networks (NTNs), or wireless communication systems that operate in space, are expected to provide larger coverage and resilience, and enable applications requiring always-on connectivity such as IoT and autonomous driving. Whether it’s connecting regions experiencing natural disaster, assisting farmers in rural settings or ensuring uninterrupted communication for shipping containers, NTN technology is paving the way for a more connected and intelligent future.

Early services integrating satellite-based cellular networks such as emergency texting are expected to enter the mainstream in 2024 and 2025. It is essential to test NTNs before they are deployed into space to ensure their reliability, consistency and stability, but the road to ubiquitous coverage isn’t without its challenges. In a recent webinar with RCR Wireless, we explored strategies for seamless satellite-based cellular technology.

Standardization Helps NTNs Evolve and Grow

With 6G, there will be convergence between terrestrial and non-terrestrial networks. 3GPP is leading the charge to standardize NTNs to open the door to broader adoption and usage of satellite technology. Standardization ensures that the same NR and NB-IOT protocols/specifications across the stack (PHY & Higher Layers) are the same for NR NTN and IoT NTN respectively. For example, the minimum bandwidth for NB-IoT NTN is 200 kHz and the minimum bandwidth for NR NTN is 5 MHz – the same bandwidths used for terrestrial networks.

There are two main NTN architectures as defined by 3GPP: regenerative and transparent payload architecture. In recent years, architectures are beginning to flex, with variations including the addition of UPF on the satellite and DU / CU split on different satellites. In this dynamic environment, standardization is critical to the continued growth and adoption of NTNs. In addition, as new studies and detailed specification work are implemented, these standards will continue to evolve.

A good example is standardization for the management of UE location. 3GPP currently specifies that a UE supporting NTN must have a valid GNSS position and knowledge of the base station location before connecting to the cell. The UE will use these locations to calculate the time delay between itself and the base station, which is then used to automatically correct the delay for its uplink transmissions.

In Rel-17, a UE can be requested to report its location to the network via the UE Assistance Information. The challenge is that a rogue UE may report incorrect information. Rel-18 proposes a network function to independently verify the reported UE location, which in turn fulfils regulatory requirements such as lawful intercept, emergency calls, public warning systems and more.

Rel-19 will formalize the Regenerative Architecture, introduce further optimizations for Uplink Transmissions, and introduce Store and Forward techniques to enhance communications using sparse satellite constellations.

The proliferation of diverse pricing structures among satellite companies is impeding the widespread adoption of IoT / utilities. This necessitates negotiations between end-device manufacturers and utility firms across numerous pricing models. 3GPP standardization is a step in the right direction to alleviating this problem. A unified technology stack provides the opportunity to achieve truly global roaming using non-proprietary end-devices, which will in turn help to streamline the pricing models.

Testing to Ensure Space-Ready Networks

If NTNs are to be used for mission critical communications, it is essential that they are reliable and stable before they are launched into space. There are numerous challenges to address:

• Physics: propagation delays, Doppler, link budgets, timing
• Mobility: fast-moving satellites in NGSO constellations which may result in RACH storms due to UE handovers
• Seamless integration with Terrestrial Networks: SMO & NIC (NTN Intelligent Controller) enhancements to cope with NTNs
• Integration with Non-3GPP NTN Networks: utilizing a unified Core for both 3GPP and non-3GPP UEs
• Security: Large geographical coverage areas which cross-country boundaries

Testing is critical to ensure the continuity and reliability of service. VIAVI provides expertise in 5G RAN technology to address these challenges in a lab environment. Our leading solutions in RAN Test are already being delivered to satellite manufacturers to validate communication prior to space launch. Our solutions are designed to handle the improvements in 3GPP standards (Rel 17 and beyond).

For RAN Test, VIAVI TM500 UE emulation supports full 3GPP protocol including Doppler and delay pre-compensation. TeraVM RIC Test supports RIC/NIC Test while TeraVM Core Test emulates full RAN scenarios at scale. When deployed with the CMX500 Mobile Radio Communication Tester from Rohde & Schwarz, the TM500 EU Emulator provides the unmatched diversity of emulation scenarios needed to create a viable NTN-NR digital twin testbed in the lab.

Collaboration is Key

The vision of NTNs has ushered in an increased collaboration between industry, academia, applied research institutions, as well as governments and regulators. The private sector has an opportunity to assist regulators in keeping pace with technological advancements with valuable input on EPFD limits and spectrum allocation. Because the scale of planning, deploying and maintaining satellite constellations is larger than most individual organizations can manage, increased collaboration is essential for success.