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 significantly better, but still far from all.
Cellular coverage is hence far less ubiquitous for IoT products that may need to operate almost anywhere, monitoring critical infrastructure, safeguard food production and life stock, 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 enables 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 cell towers. 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 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 roaming on other terrestrial networks today. 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, you 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
Geo synchronous, and the subset Geo stationary, 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 therefore 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 generally reflect the signals sent from your IoT device back to earth without any processing. The satellite will therefore be transparent to your device and communication happens 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 still 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 seen in terrestrial networks. The PHY layer (on air) bit rates you can expect in GEO NTN is 1-2 kbps, using a standard power class 3 (23 dBm) module and a 0 dBm antenna.
Note that it is the same NB-IoT protocol mechanisms that are used to maintain a stable NTN GEO connection as is used to extend coverage in a terrestrial network. NTN GEO throughput and power consumption will therefore be similar to an cellular 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 have so far mainly been used for emergency communication. The main use case being 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 needs to be acted upon.
LEO Satellites
Low Earth Orbit (LEO) satellites, used by multiple emerging 3GPP NTN networks, are much closer to Earth at 600-800 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, using the same power class 3 module and antenna.
The higher effective data rates substantially reduce time in connection with a satellite that again reduced the power consumption. The power profile of an IoT device using a LEO connection, will hence be comparable to a cat. NB1 or medium/poor NB2 coverage in a terrestrial network, .
However, due to the lower altitude, LEO satellites are orbiting the Earth much faster than GEO, ~90min @ 700 km. An individual LEO satellite will therefore only be overhead a given location for a few minutes per orbit. The same is true for how often a LEO satellites are in view of an earth station, enabling communication with the NTN core network.
This means that the few satellites and simple transparent architecture used in GEO networks won’t work in LEO. To provide continuous, global coverage you will need a constellation of several 10’s to 100’s of satellites, and a backhaul relaying data through the LEO constellation to reach earth stations in real time. Until then a 'store and forward' architecture is used.
In store and forward the satellite takes on the role of an eNB manages the connection with the IoT devices and store the data in the satellite until it can relay the data to another satellite or earth station. While the 3GPP NTN LEO constellations are deployed, an IoT device will hence experience discontinuous coverage, meaning there isn’t always a satellite overhead, as well as longer delays end to end (device - cloud). With the much lower power consumption pr. connection, LEO networks are ideal for use cases where collected data don’t require immediate attention from the cloud/system side.
As LEO constellations deploy more satellites, the time gaps in network availability as well as the end to end latency will go down and you get to a continuous, global and low latency service for your 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 |
nRF9151
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nRF9151 SiP
Low power SiP for cellular IoT and DECT NR+
700-2200 MHz LTE band support
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