Compare NB-IoT and LTE-M for cellular IoT applications

NB-IoT (Narrowband IoT, 3GPP Cat-NB1/NB2) and LTE-M (LTE for Machines, 3GPP Cat-M1) are both cellular LPWAN technologies designed for IoT, but they occupy different design points. NB-IoT uses a narrow 200 kHz channel bandwidth, delivers peak data rates of roughly 60 kbps downlink and 30 kbps uplink (Cat-NB1), and is optimized for stationary devices that send very small payloads infrequently — think smart meters, soil moisture sensors, and parking spot detectors. LTE-M uses a wider 1.4 MHz bandwidth, delivers peak rates of approximately 1 Mbps in both directions, supports voice (VoLTE) and full mobility with cell handover, and targets devices that need moderate throughput and movement — wearables, asset trackers, connected health devices, and point-of-sale terminals.

The power and coverage tradeoffs are nuanced. Both technologies support PSM (Power Saving Mode) and eDRX (extended Discontinuous Reception), which allow the modem to enter deep sleep for minutes to hours between scheduled paging windows, reducing average current to single-digit microamps. In PSM, the device is unreachable from the network until it wakes — acceptable for sensors that only report data, problematic for devices that need to receive commands. NB-IoT achieves deeper coverage (up to 20 dB better link budget than LTE, reaching underground basements and deep indoor locations) through extreme repetition of transmissions, but at the cost of higher latency (seconds to tens of seconds for data delivery). LTE-M has lower latency (10-100 ms typical), supports handover between cells (essential for moving assets), and enables real-time applications like voice calls.

The selection criteria in practice: choose NB-IoT for stationary, ultra-low-power devices with tiny payloads and no real-time requirements, especially in challenging coverage environments. Choose LTE-M for mobile assets, devices that need faster data rates, lower latency, or bidirectional communication, and applications where the device must be reachable by the network. Cost differences are narrowing but NB-IoT modules tend to be slightly cheaper. Both require a cellular subscription, which adds per-device monthly cost (typically $0.50-$2 for IoT plans). A key interview point: NB-IoT does not support handover, so a device moving between cells must re-attach, causing connection drops and increased power consumption — this makes NB-IoT unsuitable for vehicle tracking or anything that moves faster than walking speed.