NB-IoT

NB-IoT (Narrowband Internet of Things) is a cellular radio technology for low-power IoT devices that send small amounts of data infrequently, such as meters, sensors and simple trackers. Standardized by 3GPP in Release 13, it uses a narrow 180 kHz channel to reach deep indoor and underground locations while letting devices run for years on a battery.

Key characteristics

Characteristic	NB-IoT
Channel bandwidth	180 kHz, the width of one LTE resource block
Deployment	Standalone, in an LTE guard band, or inside an LTE carrier
Data rate	Tens of kbps with Cat-NB1; higher with Cat-NB2 from Release 14
Coverage	Designed for a maximum coupling loss of 164 dB, about 20 dB beyond legacy GPRS
Mobility	Limited — no connected-mode handover; devices reselect cells while idle
Voice	Not supported
Power saving	PSM and eDRX

How NB-IoT behaves in practice

Much of NB-IoT’s coverage comes from repetitions: in poor conditions, the network and device repeat each transmission many times. That extends reach but increases latency and energy per message, so a device at the cell edge may take seconds to deliver a packet that would take milliseconds on LTE.

Battery life relies on PSM (Power Saving Mode, introduced in 3GPP Release 12) and eDRX (extended discontinuous reception), which let a device sleep for long periods while staying registered. The trade-off is reachability: a sleeping device cannot receive downlink data until it wakes. The GSMA Mobile IoT Deployment Guide gives recommendations on these timers.

Deployment and roaming

NB-IoT is not deployed everywhere, and roaming support is less mature than for LTE: many roaming agreements cover LTE and LTE-M but not NB-IoT. Devices that must work across borders often use LTE-M with NB-IoT as a secondary option, or the reverse, depending on target markets. Networks may also handle the APN and data delivery differently for NB-IoT, including non-IP data options.

Why it matters for testing

NB-IoT failures are often subtle: attach rejects because NB-IoT is not in the roaming agreement, long attach times at the cell edge, or power-saving timers the network overrides. Testing must force NB-IoT specifically and measure attach time and round-trip latency, not just success. SimCheck.ai’s IoT (MQTT) quick test attaches on LTE-M or NB-IoT and measures an MQTT publish/subscribe round trip — see NB-IoT vs LTE-M testing.