LTE-M, NB-IoT or LTE Cat 1: which cellular technology suits a battery-powered tracker?

All three are LTE, scaled differently. Cat 1 is ordinary LTE at modest speed: about 10 Mbit/s down and 5 Mbit/s up, with full mobility, and it works wherever LTE does. LTE-M (Cat M1) narrows the channel to 1.4 MHz, giving up to about 1 Mbit/s, and adds coverage enhancement and low-power features while keeping handover between cells. NB-IoT uses a 200 kHz carrier and delivers tens of kilobits per second in its first release, with the deepest coverage of the three, but it was designed for stationary devices: in its basic form there is no connected-mode handover, so a moving device has to reselect cells and re-establish its connection.

For something that moves, that last point effectively rules out NB-IoT as the only bearer.

Coverage and roaming should be checked before anything else, because they vary by country and operator. Some operators deployed LTE-M, some NB-IoT, some both, and roaming agreements for the two low-power technologies are less complete than for ordinary LTE. A tracker that crosses borders needs a SIM and a module that can fall back: many modules combine LTE-M and NB-IoT with 2G fallback, and Cat 1 modules roam on normal LTE networks.

Match the module's band variant to the regions you need, and confirm with the SIM provider which technologies are enabled on the subscription in each country. A module that supports a technology is of no use if the SIM is not allowed on it.

Power saving mode (PSM) is what gives long battery life. The device stays registered but switches the radio off completely and cannot be reached until it wakes. Two timers are negotiated with the network: the active timer T3324, the time the device stays reachable after finishing a transfer, and the periodic tracking area update timer T3412, the longest it may sleep before it must check in. They are requested with AT+CPSMS, and the network may grant different values from the ones you asked for, so read back what was granted.

eDRX is the middle ground: the device stays reachable but listens for paging only every so often, from seconds up to many minutes, requested with AT+CEDRXS. For a tracker that only sends on its own schedule, PSM fits. If you need to send it commands with a delay of a minute or so, use eDRX.

A rough energy budget shows what dominates. Suppose each report keeps the modem awake for 10 s at an average of 100 mA: that is 1 A·s, or about 0.28 mAh per report. Moving 8 hours a day with a report every 15 minutes is 32 reports, about 9 mAh per day. Sleeping in PSM at, say, 10 µA for the whole system adds only 0.24 mAh per day. A 5000 mAh pack would then last well over a year on paper.

Those figures are placeholders, so measure your own module with a current profiler. The awake time varies a lot with signal quality: in poor coverage the module repeats transmissions and stays on several times longer, and the GNSS receiver's time to first fix often costs more energy than the modem. Peak current is also lower for LTE-M and NB-IoT modules than the 2 A bursts of 2G; take the figure from the datasheet when sizing the battery and regulator.