Definition
4G (Fourth Generation) is a fourth-generation mobile communication technology based on LTE, providing high bandwidth and low latency, widely used in IoT video backhaul, remote monitoring, connected vehicles, and other scenarios.
Technical architecture
4G is based on the LTE (Long Term Evolution) standard, using OFDMA for downlink and SC-FDMA for uplink multiple access technology, supporting both FDD and TDD duplex modes. LTE-Advanced introduces carrier aggregation (CA) and higher-order MIMO, with a theoretical downlink peak of up to 1 Gbps. Main global frequency bands include B1/B3/B5/B7/B8/B20, with B1/B3/B5/B8 being primary in China. Modules need to support multiple bands to adapt to different operator networks.
IoT Application Scenarios
4G modules are widely used in the Internet of Things (IoT) field: video surveillance and smart cameras transmit high-definition images via 4G; vehicle OBD and T-Box enable remote diagnostics and OTA upgrades for connected vehicles; industrial gateways and DTUs collect on-site data and upload it to the cloud; devices that require real-time connectivity, such as shared bikes, EV charging stations, and vending machines, all rely on stable 4G connections. Compared with 5G, 4G modules have lower costs and better power efficiency, offering a clear cost-performance advantage in medium-speed scenarios.
Collaboration with 5G
Currently, 4G and 5G networks coexist. Most 5G modules support 4G fallback, automatically switching to 4G when 5G coverage is insufficient, ensuring business continuity. Different speed levels such as LTE Cat.1, Cat.4, and Cat.6 meet differentiated requirements from low power consumption to high bandwidth, complementing NB-IoT and jointly supporting full-scenario coverage of IoT.
Engineering Practice Supplement
Regarding "4G," it is recommended to distinguish between real-time control links and non-real-time telemetry links in the architecture: control and interlock should preferably form a local closed loop, using cellular for monitoring, configuration, and OTA. The cloud platform side should drive optimization with observability metrics (connection duration, message delay distribution, failure codes, reconnection reasons), rather than just checking "connectivity." Document delivery includes interface specifications, error code tables, extreme operating conditions, and known limitations; test delivery includes test cases, data, and conclusions, facilitating third-party re-testing or audit.
How category rates map to the traffic model
On a module, 4G starts with the terminal category, not a vague claim of broadband. The category limits modulation order, uplink and downlink peaks, and whether several carriers can be used at once. Video backhaul, intersection snapshots, and full firmware downloads need sustained throughput, so choose a higher category and confirm that the target cell has actually enabled it. Environmental sensors, location tags, and payment terminals mostly send short messages; a lower category is a better fit, and the RF front end, cooling, and standby current are easier to contain. Writing a handset browsing experience into an IoT specification tends to break both the power budget and the finished-product test.
Before deployment, write down the bands, duplex mode, and roaming footprint. Public cellular, private networks, and cross-border SIMs land on different bands, and a band missing from the hardware list cannot be turned on later in software. If downlink must arrive within a few seconds, idle sleep cannot be stretched very long. Switch inputs, emergency stops, and interlocks stay on the device; cellular carries monitoring, parameter delivery, and upgrades. The SIM profile should also state whether the service is packet data only or also uses SMS wake-up. Declaring an unused voice capability can drag attach through unrelated signaling, which in the field looks like data that comes and goes.
Why locking a band can still fail
Locking the band without checking the access point name is the most common false fault. The radio has registered, but no address is assigned, and the application keeps restarting the module. Another class of fault is the antenna: a transmit level copied from the evaluation board into a tighter enclosure raises reflections, the power amplifier backs off on its own, and the rate falls without a disconnect in the log. A metal cavity, a longer feeder, and assembly with the cover on all make the lab curve miss the field. When cell reselection bounces, look at the antenna environment and the neighbor list before suspecting the core network.
When the plan is exhausted or throttled, the module still attaches repeatedly. If the application has no separate error code for arrears or rate limiting, repair is steered toward replacing hardware. After RF calibration data changes with firmware, remeasure conducted power on the target band; do not assume the old table is still valid. When a higher peak is required, first check that the carrier aggregation combination is in the specification. A data-only terminal must also confirm that the packet session will not be briefly suspended by voice fallback.