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Cellular IoT (NB-IoT and LTE-M) is proving to be the most successful LPWAN technology. According to IoT Analytics, outside of China (which skews the data due to a nationwide policy to adopt NB-IoT) LTE-M and NB-IoT will comprise some 58 percent of the 1.3 billion LPWAN IoT connections globally by 2027[1].
However, while 4G/LTE technology alone covers as much as 90 percent of the world’s population, once geographical coverage is considered, only about 15 percent of the Earth’s is serviced. Adding 2G/3G technologies increases coverage increases to 30-35 percent, but these are technologies that are facing sunsetting by as early as 2033, according to trade body, Mobile World [2].
It’s time for Non-Terrestrial Networks
The lack of global cellular IoT coverage restricts the operation of IoT devices in applications such as those monitoring critical infrastructure, safeguarding food production and livestock, or tracking shipments of valuable goods. Manufacturers of such IoT products face a tough challenge: how do they provide customers with uninterrupted global coverage in the absence of ubiquitous cellular IoT service?
- Read more: How cellular IoT can improve agricultural yield and the lives of farmers
- Read more: New cellular IoT SiPs power smaller, more efficient asset trackers
- Read more: Ensuring distribution network reliability in the age of renewable energy
One solution is the 3rd Generation Partnership Project’s (3GPP) Non-Terrestrial Network (NTN) technology. NTNs support NB-IoT via satellites rather than relying on cellular infrastructure. The technology is serviced by a satellite constellation, complemented by cellular IoT infrastructure where it is available. The result is access to global cellular networks that are accessed in a similar way to terrestrial LTE-M/NB-IoT networks.
3GPP NTN providers offer two equally important parts, the satellites replacing the cell towers, and the cellular core network. The core network allows NTN and terrestrial networks to seamlessly interact, enabling mobile IoT devices such as asset trackers to roam from a ground network to NTN, in the same way roaming occurs on today’s terrestrial networks.
Selecting the right NTN for an IoT application
Just like IoT applications, all 3GPP NTNs are not the same. At the basic level, NTNs split into three main categories defined by the type of satellites they use. The technology can be based on Geostationary Earth Orbit (GEO), Low Earth Orbit (LEO), or Medium Earth Orbit (MEO) satellites, although the latter is not commonly used for IoT applications.
A GEO satellite orbits the Earth at the same speed it rotates and therefore appears to be stationary in the sky over a particular region, from which it can cover as much as one third of the globe.
GEO satellites generally reflect the signals sent from an IoT device back to earth without any processing. The satellite is transparent to the IoT device and the communication is with a ‘cell tower’ on the ground. Data sent can reach a Cloud service while the NTN connection is active.
The high altitude (almost 36,000 km) and relatively low number of GEO satellites present challenges for the IoT device’s radio link budget reducing throughput compared with terrestrial networks. The PHY bit rates are typically 1-2 kbps, using a standard power class 3 (23 dBm) module and a 0 dBm antenna.
Due to this relatively low effective data rate, but real time connection to the core network, NTN GEO has mainly been used for urgent communication; for example, direct-to-device (D2D) services for mobile devices that need instant delivery of important messages.
LEO provides higher throughput
LEO satellites orbit the planet at 600-to-800 km. This eases the challenges on the IoT device radio link budgets and supports throughputs of 20-to-40 kbps, while using the same power class 3 module and antenna as that for GEO NTN. The higher effective data rates bring the extra advantage of reducing satellite connection time and therefore IoT device power consumption.
The downside of LEO NTN is that the satellites are orbiting the earth rapidly, taking only around 90 min for each orbit when at an altitude of 700 km. An individual LEO satellite is only in line-of-sight of the IoT device and the NTN core network for a few minutes per orbit.
Robust coverage demands a constellation of tens or even hundreds of satellites, and a backhaul infrastructure relaying data through the LEO constellation to reach earth stations in real time. Until that infrastructure is in place, a ‘store and forward’ architecture is being used. This arrangement retains data in a particular satellite until it can be relayed to another satellite or earth station. The result is discontinuous coverage making LEO NTN networks more suitable for use cases where collected data don’t require immediate attention from the Cloud.
In time, LEO NTN constellations will deploy more satellites reducing latency and enhancing coverage.
Compact SiP for NTN applications
Nordic has developed a low power, compact and integrated module for NTN applications. The nRF9151 SiP also supports NB-IoT, LTE-M, and DECT NR+. The SiP integrates a dedicated 64 MHz Arm Cortex-M33 programmable application processor, and 1 MB Flash plus 256 KB RAM memory.
Nordic has collaborated with several satellite network companies for early integration of NTN into its nRF9151 SiP. For example, Iridium Communications’ Iridium NTN Direct—which is said to be the “world’s first truly global NB-IoT service" and offers D2D among other applications—will be incorporated into the SiP as part of the 3GPP release 19 NTN roadmap.
Nordic is also working with Skylo, an NTN communications provider, in a strategic partnership to certify the nRF9151 on Skylo’s satellite network service, and has collaborations with Omnispace and Gatehouse Satcom, as well as Myriota to deliver end-to-end 5G NTN standards-based connectivity solutions for battery-constrained IoT applications.
With these hardware and satellite network developments underway it will not take long for NTN to be commercially available. That will enable users for the first time to track critical assets or vital infrastructure no matter where it’s situated on the planet.
References
- LPWAN market 2024: Licensed technologies boost their share among global 1.3 billion connections as LoRa leads outside China; https://iot-analytics.com/lpwan-market/
- 2G/3G Switch Off: What you need to know; https://www.mobileuk.org/2g-3g-switch-off
