LTE Cat 1 vs Cat 4 vs NB-IoT

Downlink (DL) means network to device, as in a firmware download. Uplink (UL) means device to network, as in an image upload. A high downlink number does not answer an uplink requirement.

Swipe the table to compare all three technologies.

Cat 1 and Cat 4 figures are maximum rates, illustrated by Quectel EC21 and EC25 documentation; they are not expected application throughput. Antenna and NB-IoT mobility distinctions are covered by u-blox and ETSI. [1] [2] [3] [4]

Cat 1 bis is not LTE-M, and it is not a slower Cat 1

Cat 1 bis keeps the Cat 1 rate class while using one receive path. Conventional Cat 1 uses receive diversity. Removing that second path can simplify the antenna design, but it changes the receive-side trade-off. Validate the intended Cat 1 bis module in the final enclosure; do not turn a two-antenna Cat 1 design into Cat 1 bis simply by leaving a connector unused. [3]

Cat 4's downlink MIMO and Cat 1's receive diversity are not interchangeable concepts. Ask for the manufacturer's reference layout, required antenna ports and ground-clearance rules rather than specifying only “one antenna” or “two antennas.”

LTE-M commonly refers to Cat M1, not Cat 1. It belongs on a separate shortlist when low power and mobility both matter and the target operator supports it. For NB-IoT, NB1 is associated with Release 13 and NB2 with Release 14 enhancements; the label alone does not establish a usable transfer rate. [5]

A small daily data total can hide a difficult update

A 500-byte report every 15 minutes produces 96 reports, or 48,000 bytes of application payload per day. That is only 48 kB in decimal units. It excludes protocol overhead, acknowledgments, security handshakes and retransmissions.

Now add a 2 MB firmware package. Its delivery window may be more demanding than the normal reporting workload. Document four separate items: routine reports, alarm bursts, remote commands and maintenance transfers. Include the largest burst, not just the monthly data allowance.

Use measured application throughput in the required direction. Category peaks omit important constraints such as cell loading, radio conditions and the host interface. If the host cannot feed the modem quickly enough, a faster radio category does not remove that bottleneck.

Make the update recoverable. Decide how the device resumes a partial transfer, verifies the image and recovers after a power loss. A smaller delta update can change the traffic budget, but its availability depends on your firmware architecture, not the cellular category.

A device that can send an alarm may still miss an incoming command

Write two different timing requirements: sensor event to server acknowledgment, and server command to device action. They are not equivalent when the modem sleeps.

In power saving mode (PSM), a device remains registered but is not listening for paging. It can wake for a local uplink event or a scheduled network update; the server cannot simply page it awake during PSM. Extended discontinuous reception (eDRX) instead provides periodic paging opportunities, trading energy for reachability. Inspect the settings actually granted by the network. [7]

A Cat 4 label does not create a deterministic control channel either. Safety-related actions need an appropriate local fail-safe design and a validated communication architecture, not an assumed public-network response time.

Battery life is a charge budget, not an NB-IoT feature

If a product has 3,000 mAh of usable battery capacity and a five-year target, its entire average-current budget is:

“Usable” matters: available capacity depends on the battery, temperature, aging, cutoff voltage and load profile. Peak radio current can also cause a brownout even when the average-current calculation looks acceptable.

What happens when reports become four times more frequent?

For an illustrative budget, not a module measurement, assume each complete communication event uses 100 mA for five seconds: 0.139 mAh per event. Add a 10 µA background load for 24 hours, or 0.24 mAh per day.

This simplified arithmetic is not predicted service life. The full-day background term conservatively overlaps the active periods. No extra allowances are included for retries, no-service searches, self-discharge or unexpected events; 3,000 mAh is assumed already usable.

Measure charge per successful transaction at the battery input. Include wake-up, registration when needed, the application exchange and the return to sleep. Repeat with weak signal, a cold battery, failed acknowledgments, a network outage and queued reports after recovery. A tiny sleep-current figure cannot describe these events.

A public field test shows why the network belongs in the power budget

For your own pilot, keep a record for each sample: location and enclosure, module order code, firmware, SIM/operator, radio measurements, delivered payload, transaction charge, completion time and failure reason. Keep the spread of results, not only the average. A design that works at most sites can still miss the product's service target at the difficult ones.

Coverage, mobility and roaming are separate questions

A phone's LTE signal is not an NB-IoT acceptance test

Confirm the operator's service for the actual country and site, then test the selected module, SIM and antenna together. Indoor placement, a metal enclosure and antenna detuning can change the result.

NB-IoT coverage enhancement can use repetition to support difficult links. That can also extend delivery time and increase energy per completed message. Stronger link reach does not automatically mean better battery life. [9]

Do not replace these checks with a universal “works underground” claim. The installation is part of the radio system.

Movement between reports is not continuous connected mobility

ETSI TS 136 300 V18.3.0 lists handover among functions not supported by NB-IoT. Idle cell reselection and subsequent reconnection are different from keeping an active session through conventional LTE handover. [4]

An asset that moves, stops and then sends a short report may have a different requirement from a vehicle that must keep exchanging data along a route. For the latter, start the evaluation with Cat 1/Cat 1 bis, or Cat 4 if the traffic justifies it; also evaluate LTE-M where its capabilities and operator support fit.

Roaming is a service question, not a yes/no category slogan

Do not assume NB-IoT roaming is impossible, or that a globally advertised SIM guarantees it. Ask which destination networks are accessible, which radio technologies and features are enabled, and what restrictions apply to the deployment. GSMA's deployment guidance treats interoperability and roaming as implementation considerations. [9]

Repeat the same discipline for Cat 1 and Cat 4. Matching frequency bands is necessary, but it does not by itself establish certification, service access or the expected lifetime of a commercial network offering.

Three application scenarios — and what changes the shortlist

The following are illustrative design scenarios, not reported YURUNOX projects or customer results.

Buy an exact module configuration, not just “Cat 1”

A shared category or similar footprint does not make two modules drop-in replacements. Pin functions, supply peaks, interfaces, antenna connections, AT commands and firmware behavior can differ. A module approval also does not automatically satisfy every requirement for the final product.

Even within a family, features vary. Quectel's EC25 documentation, for example, describes optional VoLTE and data-only variants. If voice is required, verify the exact variant, firmware, operator provisioning and service support; do not infer voice from “LTE.” [2]

What to include in a module RFQ

For a Quectel-based shortlist, see YURUNOX's Quectel sourcing page. Review the quality-assurance information and purchasing process alongside your engineering acceptance criteria.

Validate before locking the production BOM

1. Write pass/fail limits first. Define message success rate, command deadline, update time, daily charge and recovery behavior for the product's intended service.
2. Freeze the test configuration. Record module order code, firmware, SIM, APN, operator, antenna and enclosure. A development kit with a different configuration is not the final design.
3. Exercise the difficult conditions. Test weak signal, temperature limits, low battery, movement where relevant, and recovery after service loss. Include retries and queued traffic.
4. Review distributions and failures. Compare completion-time and charge distributions, unsuccessful transactions and recovery time. Run a representative pilot before accepting a production substitution.