Introduction to Non-Terrestrial Networks (NTN)
Non-Terrestrial Networks with nRF9151
You select cellular technology because of the ubiquitous access to network infrastructure around the globe. While it is true that 4G/LTE technology alone covers as much as 90% of the world’s population, if you look at total geographical coverage instead, only about 15% of the earth’s surface is covered by LTE. If you also include older 2G/3G technologies, coverage increases to 30-35%, which is better but still far from all.
Cellular coverage is hence far less ubiquitous for IoT products that may need to operate almost anywhere, monitor critical infrastructure, safeguard food production and livestock, or track shipments of valuable goods. Adding the fact that many regions are sunsetting 2G networks, a wide range of IoT products are facing a tough question: What technology should they adopt for coming product generations?
This is where 3GPP Non-Terrestrial Networks (3GPP NTN), along with the terrestrial 4G/5G IoT technologies LTE-M and NB-IoT, can revolutionize your ability to deploy your IoT products where they are needed.
How do I access 3GPP NTN?
Whether your product is stationary in a remote location, or roaming across vast areas lacking needed coverage, 3GPP Non-Terrestrial Networks enable you to keep track of your assets and stay updated, wherever they are.
But what is 3GPP NTN actually? Put simply, it is NB-IoT via satellite instead of a cell tower. The introduction of 3GPP NTN means that you now have several new cellular networks you can access in a similar way to terrestrial LTE-M/NB-IoT networks.
3GPP NTN providers offer two equally important parts, the satellites replacing cell towers, as well as a cellular core network. The core network part means that NTN and terrestrial networks can interact, enabling your devices to roam from your home network to a non-terrestrial network, in the same way as roaming on other terrestrial networks today. So, ask your current connectivity provider, MNO or MVNO, what their plans for 3GPP NTN services are.
Which NTN to choose?
All 3GPP NTN are not the same, and neither are IoT applications. Which non-terrestrial network will be right for you depends entirely on your use cases and critical design criteria. At the top level, we can split non-terrestrial networks into two main categories by the type of satellites they use: GEO (Geo synchronous/stationary Earth Orbit) or LEO (Low Earth Orbit).
GEO Satellites
Geosynchronous, and the subset Geostationary, satellites orbit at the same speed as Earth due to the large distance (almost 36 000 km) from the Earth's surface. A GEO satellite will appear stationary in the sky over a region able to cover as much as 1/3 of the globe. This again means that the satellite is always available for your device and also always in sight of an earth station located in the same region. GEO satellites reflect the signals sent from your IoT device back to earth without any processing.
The satellite will be transparent to your device and communication flows between your device and an eNB or ‘cell tower’ also on the ground. Data sent can therefore reach your cloud service while the NTN connection is active.
The high altitude (almost 36,000 km) and low number of GEO satellites means that an IoT device must manage a tough link budget and the network capacity will be below the typical capacity seen in terrestrial networks. The PHY layer (on air) bit rates you can expect in GEO NTN are 1-2 kbps.
Note that it is the same NB-IoT protocol mechanisms that are used to maintain a stable NTN GEO connection as are used to extend coverage in a terrestrial network. NTN GEO throughput and power consumption will therefore be similar to what you see in an IoT device operating at the edge of coverage in a terrestrial NB-IoT network.
Due to the relatively low effective data rate, but real time connection to the core network, NTN GEO has so far mainly been used for emergency communication. The main use case is direct-to-device (D2D) services for mobile devices and other use cases that need instant delivery of important messaging.
With more services coming, this is now broadening to IoT use cases which often also have very limited need of data, but have important messaging where constant coverage and relatively low latency is a must-have.
NTN GEO is hence the choice where you have low amounts of data (bytes/day) or high importance messages like alarms that need to be acted upon.
LEO Satellites
Low Earth Orbit (LEO) satellites, used by multiple emerging 3GPP NTN networks, are much closer to Earth at 200-1500 km. This improves the link budget for your IoT device, allowing more flexibility in antenna designs and higher data rates, up to 20-40 kbps.
Power consumption and connection time with a satellite can be substantially reduced, and again, the protocol mechanisms are the same as for terrestrial networks. The power profile of an IoT device using a LEO connection will be similar to one with medium/low coverage in a terrestrial network.
Due to the lower altitude, LEO satellites are orbiting the Earth much faster (~90min @ 700 km) so one LEO satellite will only be overhead at a given location for a few minutes per pass. The same is true for how often individual LEO satellites are in view of an earth station and can send data back to Earth.
This means that the few satellites and simple reflector approach from GEO won’t work for LEO, and to provide the continuous, global coverage you will need a substantial network of satellites and a back haul that forwards data through a mesh network between the satellites.
Now initially, 3GPP LEO NTN satellites constellations consist of relatively few satellites. In such networks, a 'store and forward' architecture is used where data is temporarily stored in a satellite until they can connect with other satellites through a mesh network or directly to earth stations. This method offers IoT device power efficient, albeit delayed, device-to-cloud communication. This is ideal for all types of IoT devices and use cases that are tracking and collecting data that do not require an immediate response.
As the LEO constellations deploy more satellites, the time gaps in networking services will close, the end to end latency will go down and you will get global, real-time, low latency services for IoT devices.
Non-Terrestrial Network providers
Nordic Semiconductor is working with multiple providers to offer our customers commercial options for their NTN deployments.
| Press release with Iridium | Press release with Skylo | Press release with Myriota |
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