Choosing a radio technology

A cellular IoT device connects with one or more radio technologies, set by the module inside it. That choice is hard to change after the device ships, so decide it early. It decides how much data the device can send, how long a battery lasts, whether it works on the move and which countries it can roam in.

The main options

• LTE-M is a low-power version of 4G. It suits trackers, meters and wearables that send modest amounts of data, may move around and need long battery life. It can carry voice calls where the operator supports it.
• NB-IoT can use less power and reaches deeper indoors and underground. It suits fixed sensors that send small messages now and then. It is slow, does not suit moving devices, and fewer networks offer it to roaming devices.
• LTE Cat-1 is ordinary 4G at modest speed. It is widely available, including when roaming, and suits devices that need more data or a steady connection, such as alarm panels, payment terminals and routers.
• LTE Cat-1 bis is Cat-1 with a single antenna, which makes the device smaller and cheaper. It runs on the same 4G networks.
• 5G RedCap is a lighter version of 5G for devices such as cameras and industrial gateways. It needs a 5G standalone network, and only a small number of operators have launched it so far.

How to decide

Start with what the device does. If it sends small readings and runs on a battery, LTE-M or NB-IoT is usually the right fit. If it moves, or must work in many countries, LTE-M is usually the safer of the two. If it needs more data, works on mains power or must connect in as many places as possible, Cat-1 or Cat-1 bis is the usual choice. Video and other high-volume uses need full 4G, or 5G.

Many modules support both LTE-M and NB-IoT. That gives a device more ways to connect, but each network still has to support the technology and allow roaming on it.

Why not 2G or 3G

2G and 3G networks are being switched off around the world, usually 3G first. See 2G and 3G switch-off for dates by country. A new device built for 2G or 3G may lose service within its working life.

The table below shows the technologies each DataSIM SIM profile supports.

The candidates

For a new cellular IoT device the realistic choices are LTE-M, NB-IoT, LTE Cat-1, LTE Cat-1 bis and 5G RedCap. The device’s capability is set by the UE category it declares, defined for LTE in TS 36.306 and for NR in TS 38.306.

• LTE-M (Cat-M1, Release 13; Cat-M2, Release 14). A 1.4 MHz narrowband within an LTE carrier for M1, up to 5 MHz for M2, with coverage enhancement by repetition. See LTE-M.
• NB-IoT (Cat-NB1, Release 13; Cat-NB2, Release 14). A 180 kHz carrier, half-duplex, with deeper coverage enhancement and no connected-mode handover in Release 13. See NB-IoT.
• LTE Cat-1 (Release 8). Standard LTE at the lowest original category, with two receive antennas.
• LTE Cat-1 bis (Release 13). The same data capability as Cat-1 with one receive antenna. TS 36.306 notes that a Cat-1 bis device is only required to support one receive antenna, although it also indicates Category 1 for compatibility with older networks.
• 5G RedCap (Release 17) and eRedCap (Release 18). NR devices with reduced capability, defined in TS 38.306 clauses 4.2.21 and 4.2.22.

Comparison

Peak figures come from the transport block sizes in TS 36.306. For LTE categories with a 1 ms TTI, bits per TTI convert directly to a peak rate. For LTE-M and NB-IoT, half-duplex operation (required on NB-IoT, common on LTE-M) and scheduling gaps keep real throughput well below the transport block figure, and on NB-IoT one transport block spans several milliseconds.

Release 14 added an optional larger LTE-M uplink transport block of 2,984 bits, and Release 17 a 1,736-bit downlink block and 16QAM for NB2 (4,968 bits downlink). The RedCap figure depends on bandwidth, receive branches and modulation. 3GPP and GSA quote about 226 Mbit/s downlink and 120 Mbit/s uplink as peaks for Release 17 RedCap, and a cap of about 10 Mbit/s in each direction for eRedCap. RedCap devices have one transmit branch and support no carrier aggregation or dual connectivity, and eRedCap does not operate in FR2.

Cost classes are relative and move with volumes.

LTE-M or NB-IoT, which should I use?

• Battery device, small payloads, may move or roam. LTE-M. It hands over in connected mode, supports PSM and eDRX, and has wider roaming than NB-IoT.
• Fixed device, very small payloads, deep indoor or underground. NB-IoT, where the networks in your target countries offer it and allow roaming on it. Its coverage margin comes from repetition, which costs time and energy.
• Mains or larger battery, moderate data, broad coverage. Cat-1 bis, or Cat-1 where the extra receive antenna improves reception. Both connect wherever LTE data roaming is in place. GSMA warns that Cat-1 and Cat-1 bis may not outlast 4G, while LTE-M and NB-IoT carry on inside 5G. Cat-1 bis also has a weaker link budget than Cat-1, because it has one receive antenna.
• Higher throughput, 5G-only roadmap. RedCap, where 5G standalone is deployed. GSA counted 42 operators in 27 countries investing in RedCap in April 2026, with commercial eRedCap expected from 2026. Coverage and roaming for 5G standalone remain far narrower than for LTE.

Many modules combine LTE-M and NB-IoT, which lets a device use whichever a network offers. Each network must still support the technology and the roaming agreement must include it.

When you need more

Use LTE Cat-4 or above, or full 5G, for video, large file transfers or uplink above a few Mbit/s. Cat-4 carries up to 150,752 bits per TTI downlink with two layers and 51,024 bits uplink, about 150 Mbit/s and 51 Mbit/s. Cat-4 needs two receive antennas.

2G and 3G

2G and 3G are not a basis for new devices. Operators worldwide are closing them, usually 3G first: the United States, Australia and Singapore have closed 3G, most of Europe has too, and most European operators that have set 2G dates have put them between 2027 and 2030, though France closed 2G in 2026 and many operators have yet to set one. In the UK the operators have committed to close both by 2033 at the latest. A device with a life of ten years or more should be designed for LTE or 5G from the start. See 2G and 3G switch-off for dates by country.

Practical points for IoT

• Check each target country for the technology, not just the operator. An operator can offer LTE roaming and no LTE-M or NB-IoT roaming.
• Log the access technology each device actually uses (reported by AT+CEREG).
• Test PSM and eDRX values on each network. The network decides what it grants.
• Plan the antenna with the category. Cat-1 needs two receive antennas, while Cat-1 bis, LTE-M and NB-IoT need one.