What is NB-IoT?
NB-IoT (Narrowband IoT) is a 3GPP radio access technology standardised in Release 13, designed specifically for low-power, low-data-rate IoT applications. It uses a 200 kHz channel - a single LTE resource block - and is deployed by UK operators in three modes: in-band (within existing LTE spectrum), guard-band (in the LTE guard band) and standalone (in dedicated 200 kHz spectrum).
Key applications: smart metering (gas, electricity, water), asset tracking, environmental monitoring, smart city sensors and any device that sends small amounts of data infrequently and needs years of battery life.
NB-IoT deployment modes in the UK
| Mode | Description | UK operators |
|---|---|---|
| In-band | Occupies 1 resource block within LTE carrier | EE, Vodafone, O2 |
| Guard-band | Deployed in LTE guard band, minimal interference | EE, Vodafone |
| Standalone | Dedicated 200 kHz carrier, e.g. former GSM spectrum | Vodafone (limited) |
Coverage classes and what they mean
NB-IoT uses Coverage Extension (CE) to maintain connectivity at low signal levels by repeating transmissions multiple times.
| Coverage class | Mode | RSRP range | Repetitions | Impact |
|---|---|---|---|---|
| CE Mode A (Normal) | Standard | Above -100 dBm | None to low | Normal latency and battery usage |
| CE Mode A (Extended) | Extended | -100 to -114 dBm | Up to 32 | Higher latency, more battery consumption |
| CE Mode B | Deep coverage | -114 to -120 dBm | Up to 2048 | Very high latency, significant battery impact |
For battery-powered devices, operating in CE Mode B significantly reduces battery life. A device expected to last 10 years on a battery in normal coverage may only achieve 3-4 years in deep CE Mode B. If your NB-IoT deployment targets battery life as a design requirement, confirm coverage class at the install location.
NB-IoT vs LTE-M comparison
| Feature | NB-IoT | LTE-M (Cat-M) |
|---|---|---|
| Peak downlink | ~26 kbps | ~1 Mbps |
| Peak uplink | ~62 kbps | ~1 Mbps |
| MCL | 164 dB | 156 dB |
| Voice | No | Yes (VoLTE) |
| Mobility | Limited (no handover) | Full handover support |
| Power saving | PSM + eDRX | PSM + eDRX |
| Best for | Static, very low data rate | Mobile, moderate data rate |