by Raghul Premkumar, Business Development/Applications Engineer, Anritsu Company
For the past decade, cellular IoT has extended low-power connectivity to places where conventional network economics could not justify the deployment of terrestrial infrastructure. Even so, roughly four-fifths of the earth’s surface remains beyond the useful range of a base station, including many locations where trackers, sensors, and monitors are expected to operate.
Until recently, reaching those areas required a separate proprietary satellite radio in addition to the cellular modem. Non-terrestrial networks (NTN) change that model by incorporating satellite access into the 5G standard, allowing the same modem to connect via satellite when no terrestrial cell is available. This application note examines what NR NTN requires of an IoT device and the components and test systems needed for verification, moving from the state of 3GPP standards and emerging use cases to the design challenges, test methods, and measurements that determine whether a device is ready for deployment.
Evolution Toward 5G NR-NTN
3GPP’s formal study of satellite integration with 5G began during Release 15, with study activities examining the use of NTNs as part of the 5G system. One, in the radio group, examined how 5G NR could be adapted for NTNs and produced technical report TR 38.811. The other study was in the services group and focused on the use of satellite access in 5G.
3GPP Release 16 continued to move momentum forward with a follow-up study. The IoT-specific branch took shape a bit later, when a study item on NB-IoT and eMTC support for NTNs was approved at the TSG-RAN meeting — at which “NTN for IoT” became its own line of development rather than simply a subset of the NR effort.
The work advanced significantly with 3GPP Release 17, frozen in March 2022, which standardized NTN support for 5G NR (NR-NTN) and IoT technologies such as NB-IoT and eMTC (IoT-NTN). The central challenge Release 17 addressed was timing and synchronization. Because the satellite and the “base station” are in motion, an IoT device must maintain timing and a stable frequency relative to a constantly shifting reference.
The adopted solution uses the UE’s Global Navigation Satellite System (GNSS) position, together with satellite ephemeris data — which describes where a satellite is expected to be at specific times — to pre-compensate for propagation delay and the Doppler effect before transmission. Because this kept changes to the air interface relatively modest, the existing NB-IoT and LTE-M ecosystem could be extended rather than replaced.
Why NTN for IoT?
IoT is particularly well suited to NTN because satellite links provide what many of these devices need without requiring the throughput or latency of a terrestrial base station. For example, a tracker typically sends small, infrequent, delay-tolerant messages, while the NB-IoT/Cat-technologies it already uses are designed for low signal-to-noise ratios (SNR), extended coverage, and low power consumption. By standardizing satellite access within 3GPP, NTN draws on established cellular chipsets and module supply chains.
Use Cases Benefiting From NTN
Remote asset tracking and massive IoT are expected to generate much of the traffic in the coming years. Shipping container and trailer tracking, fleet telematics, and heavy-equipment monitoring all involve routes that repeatedly move in and out of cellular coverage. A hybrid device can remain on the terrestrial network wherever service is available and fall back to satellite only when necessary, eliminating dead zones without requiring a second radio. Agriculture follows the same pattern, as soil and moisture sensors, weather stations, and livestock trackers often operate across such enormous amounts of land that no mobile operator can economically cover with towers.
Emergency and public-safety IoT applications also benefit from NTN because the incidents that create the greatest need for communications often occur where infrastructure is unavailable, damaged, or destroyed. Low-rate satellite messaging can provide a fallback path for alerts and telemetry when the ground network is down, while the same link can support command and control for unmanned aircraft operating beyond terrestrial coverage. In addition, offshore equipment and cargo spend much of their operating life outside the reach of terrestrial networks, making a standards-based 3GPP module more attractive than a proprietary terminal in cost and integration.
Challenges for Design Engineers
Engineers responsible for developing IoT devices have a multitude of challenges to overcome to ensure operation in these use cases. Three key factors are power efficiency, RF signal quality, and antennas.
Power Efficiency — The first design priority is efficient use of power because nearly every demand imposed by the link consumes energy. A tight link budget requires extensive repetition and low coding rates, which lengthens on-air time and increases the energy required per delivered bit well beyond the terrestrial case. GNSS acquisition adds a fixed cost to every transmission, and in a device that reports only a few times per day, a fix can dominate the daily energy budget. Sparse Low Earth Orbit (LEO) constellations and discontinuous coverage add another layer of complexity. Extended discontinuous reception (eDRX) and Power Saving Mode (PSM) are essential for achieving multi-year battery life, making the coordination of sleep schedules with satellite visibility a primary design consideration.
RF Signaling — The principal RF challenges are propagation delay, Doppler, and link budget. Satellites in geosynchronous orbit impose a round-trip delay of about 500 ms. LEO reduces that delay to tens of milliseconds but replaces it with rapidly changing Doppler and frequent handovers, which Geostationary Earth Orbit (GEO) satellites avoid because they hold a fixed position relative to the ground. A LEO satellite moving about 7.5 km/s can produce Doppler shifts of tens of kilohertz at L- and S-band, requiring Doppler pre-compensation based on satellite ephemeris and UE position information. The link budget remains tight in either orbit because satellites are constrained in power and bandwidth, slant-range path loss is high, and the device antenna is typically small and inefficient. As a result, UE design depends heavily on coverage-enhancement techniques and antenna efficiency to recover sufficient margin.
Antenna — Speaking of antennas, their design and form factor are major hurdles for engineers as they translate the link-budget problem into mechanical terms, since compact size and strong antenna performance tend to work against one another. NTN IoT operates in the mobile-satellite service spectrum, principally the L-band near 1.6 GHz and the S-band near 2 GHz, in bands n255 and n256. Because satellite links experience high free-space path loss and significant Doppler shift, antenna efficiency, frequency accuracy, and UE transmit performance become particularly important for maintaining reliable connectivity. Ku- and Ka-bands are generally reserved for VSAT terminals. At these margins, antenna efficiency and radiation pattern are extremely important. A tracker (or other IoT device) cannot assume a favorable orientation toward the satellite, and the combined behavior of the antenna, ground plane, and enclosure determines whether the device connects the link.
Test and Evaluation Solutions
Validating an NR NTN IoT device is difficult because the conditions that place it under the greatest stress are those the 3GPP standard was written to overcome. A static base-station emulator cannot be used to reproduce an accurate scenario because in the real world a satellite is moving, which creates long propagation delays, large and time-varying Doppler, and intermittent coverage. Consequently, a device can pass every static conformance test and still fail when exposed to an actual satellite link.
For these reasons, a test environment dedicated to NTN must factor:
Satellite Links — The first requirement is a channel environment that faithfully reproduces the satellite link. That means applying controlled propagation delay, Doppler shift, and data rate based on a defined orbital pass, along with appropriate path loss and fading, and then confirming that the device’s pre-compensation removes these effects. Verifying pre-compensation is equally important because an incorrect delay or frequency correction can place the transmission in the wrong time window or channel — an error that may remain invisible in a static test. For these reasons, a satellite channel emulator driven by an orbital profile is the recommended solution.
Signaling — The next challenge is signaling because a round trip of nearly 600 ms, once processing is included, disrupts procedures that terrestrial networks complete in milliseconds. Random access procedures must accommodate timing uncertainties and extended propagation delays far beyond terrestrial ranges and be exercised at those limits.
Hybrid Automatic Repeat Request (HARQ), an error-control method used in cellular networks, also requires waiting hundreds of milliseconds for feedback, which can stall the process. Consequently, NTN permits HARQ feedback to be disabled or to account for longer propagation delays and Radio Link Control (RLC) retransmission, defined as resending of missing or corrupted data in any cellular or IoT network.
Latency — Radio Resource Control (RRC) procedures that manage the control relationship between a device and the network, ephemeris-driven cell selection, and paging must also be tested under latency conditions. This requires a network emulator that can impose the delay and NTN-specific signaling conditions.
In LEO systems, the serving satellite’s location may change every few minutes, requiring the device to go through mobility procedures as link quality changes throughout a pass. Feeder-link switching and transitions between terrestrial networks (TN) and non-terrestrial networks (NTN) introduce additional mobility events, each creating an opportunity for the device to drop a session or fail to reacquire the network. As a result, link adaptation must be verified across the full SNR range of a pass from low-elevation acquisition through peak visibility and back again.
Interoperability — Perhaps the least forgiving requirement is interoperability, because NTN isn’t a single network. Services run across multiple constellations and operators, so a device that works perfectly on one network may not behave the same way on another. Additionally, an operator can layer its own requirements on top of the 3GPP baseline, so the device must satisfy the targeted release and the operator’s acceptance criteria. Hybrid operation — where a single-subscription device moves seamlessly between terrestrial cellular coverage and satellite coverage based on network availability using whichever is available — adds another challenge. Devices must be validated in both domains and throughout the handoff between them. This is why conformance testing alone won’t suffice. Carrier acceptance and cross-network testing are essential.
Key Measurements to Verify Device Design
Four measurements — transmit power and modulation accuracy, spectral emissions, receiver sensitivity and throughput, and Block Error Rate (BLER) — determine whether a UE is fit for deployment. Each corresponds to a failure mode that NTN makes more likely. Throughput and link reliability must be measured at the low SNR that defines the NTN operating point, with an emphasis on BLER and sustained throughput under heavy repetition rather than peak data rate. Establishing that margin requires precise control of signal level, and the passive components in the test path can matter as much as the instruments themselves.
- Transmit Power & Modulation Accuracy: Measures Error Vector Magnitude (EVM) and output power to ensure linear transmitter behavior under high-peak-to-average power ratio (PAPR) OFDM signals.
- Spectral Emissions: Verifies Adjacent Channel Leakage Ratio (ACLR) and Spectrum Emission Mask (SEM) to prevent out-of-band interference.
- Receiver Sensitivity and Throughput: Evaluates minimum input level performance and demodulation under low Signal-to-Interference-plus-Noise Ratio (SINR) conditions typical of space-to-ground links.
- BLER: Characterizes link quality and data recovery under degraded channel environments.
Latency and timing performance combine fixed propagation delay with the accuracy of the device’s timing advance and synchronization. Testing must determine whether pre-compensation places each transmission in the correct window and whether end-to-end latency remains within the application’s limit after the entire path is considered. In addition, power consumption must be characterized across every operating state because battery life is determined by the interaction between them rather than by a single figure. Active transmit current under repetition, the energy required for GNSS acquisition, and sleep current in eDRX and PSM all contribute to the total. A credible estimate requires measurement of the actual duty cycle imposed by the satellite-visibility schedule.
End-to-end validation confirms the behavior of the complete chain, from the device through the satellite, gateway, and core network to the application server. Emulation provides controlled access to the RF and protocol layers, while live over-the-air (OTA) testing verifies operation against an actual constellation. Ultimately, message-delivery reliability across the entire path and over an extended period is the measurement most likely to predict field performance.
Testing Solutions for NR NTN
Given the dynamics associated with NR NTN, test solutions must have specific measurement capability. The Radio Communication Test Station MT8000A supports test conditions that comply with 3GPP Release 17 and simulates propagation delay and Doppler shift in 5G NR NTN environments. The tester introduces controlled propagation delay conditions so engineers can verify that a 5G NR NTN device maintains synchronization and protocol performance under satellite-like conditions. Doppler frequency offset, Doppler rate of change, and frequency tracking behavior can be simulated, so engineers can verify that the device can acquire the NTN signal, maintain a 5G NR connection, and correct frequency errors over time.
The Signalling Tester Base Station Simulator MD8430A is for data session testing. It supports Layer 1, Layer 2, and Layer 3 protocol verification. For NB-IoT devices, where multi-year battery life is an important design consideration, the MD8430A can be used to verify power-saving features, such as PSM and eDRX. The MD8430A also supports baseband fading to emulate different radio propagation conditions by applying 3GPP-defined channel models, enabling device performance to be evaluated under controlled multipath and fading environments. NB-IoT NTN GEO testing is supported to measure propagation delay and satellite link behavior.
NB-IoT uses techniques, such as repetition and narrowband operation, to extend coverage. The MD8430A can test device behavior under challenging channel conditions to verify that a module maintains communication at weak signal levels.
Conclusion
NR NTN brings satellite access into the same standards framework, silicon ecosystem, and increasingly the same subscription model as terrestrial cellular networks. The remaining constraint on adoption is no longer whether the technology can work, but whether UE will operate reliably on a specific network under conditions that arise only when the satellite is moving and the round trip is long.
Reproducing those conditions requires NTN-capable test platforms, including Anritsu’s MT8000A for NR device RF and protocol testing and MD8430A for NB-IoT signaling and terrestrial-to-satellite roaming. These solutions distinguish UE that passes conformance from devices that will perform reliably in the field — and that is where the engineering effort must be concentrated.