Definition
C-V2X (Cellular V2X) is a V2X communication technology based on 4G LTE-V2X (R14/R15) and 5G NR-V2X (R16+), standardized by 3GPP. C-V2X supports two communication modes: PC5 direct communication (vehicle-to-vehicle, vehicle-to-RSU direct, without base station) and Uu cellular communication (interaction via base station with cloud and other vehicles).
Compared with DSRC (802.11p), C-V2X has advantages such as wide coverage, low latency, evolution to 5G, and coordination with cellular networks, making it the mainstream technology path for intelligent connected vehicles. IoT SIM cards provide cellular connectivity for the Uu mode of C-V2X, supporting remote diagnostics, OTA upgrades, cloud collaboration, and high-precision map distribution.
Technical Features
C-V2X supports message types such as BSM (Basic Safety Message), SPAT (Signal Phase), MAP (Map data), and RSI (Roadside Information). 5G NR-V2X further supports enhanced scenarios like cooperative lane change and platooning. Both OBU (On-Board Unit) and RSU (Roadside Unit) need to be networked, with RSU accessing the cloud platform via wired or wireless means.
Use Cases
C-V2X is applied in intelligent connected demonstration zones, smart highways, smart transportation, and autonomous driving tests. Typical applications include traffic signal information push (GLOSA), blind spot warning, intersection collision warning, green wave passage, remote driving, and high-precision map updates. SimtoLink provides vehicle IoT SIM cards, dedicated APN, data plans, and connected vehicle solutions for C-V2X OBU and RSU.
Do not mix Uu bearer tests with PC5 direct tests
In C-V2X the IoT SIM appears only on the Uu side. An onboard unit or a roadside unit reaches the cloud through a base station, carrying diagnostics, map increments, a cloud copy of signal-phase data, and operations data. PC5 is the direct link between vehicles, or between a vehicle and the roadside. It does not pass through the IoT SIM, and it does not pass through the operator core’s user plane. Mixing the delay, loss, and faults of the two interfaces into one “connected-vehicle online rate” makes a direct-link problem look like a data-plan problem, or an unpaid SIM look like a failed intersection collision warning. Record them apart: whether a direct message left the air interface, whether the Uu bearer completed attach and the service connection, and whether the cloud received a record that corresponds to the direct event.
The conditions are that the module, the roadside equipment, and the live network all support the release being claimed, and that the SIM subscription allows the access technology and access point. If a roadside unit uses cellular rather than fiber to reach the cloud, the antenna must not be blocked by the signal pole and the metal cabinet, and the SIM should stay on that intersection’s asset so it can be compared with the MAP and the signal-controller phase. A vehicle SIM has to tolerate frequent cell reselection. After a service connection drops it should resume an unfinished map or log, but a reconnect storm must not affect local handling of direct safety messages. Remote driving or a high-definition map download needs far more bandwidth and continuity than a periodic heartbeat. The plan and QoS should be assessed on their own, not opened as “a few megabytes of diagnostic log per day.” Before a route is opened across regions, check that roaming limits and the access point work on the visited network.
A common error is to treat a vehicle position received in the cloud as proof that the direct link works. Position reporting uses Uu. The cloud does not know whether another vehicle at the intersection received the basic safety message. Another error is an unpaid or stopped SIM in the roadside unit. Signal phase cannot reach the cloud, while the direct link between vehicle and roadside may still work, and operations marks the whole intersection offline. A lab test on a fixed cell can pass, then handovers on the road break Uu, a remote configuration arrives halfway, and the terminal sits on unknown parameters. Acceptance should shield the direct antenna and the cellular antenna separately, and the alarm text should say which interface failed. The shared language of the standard release is described under 3GPP. The onboard unit boundary is described under OBU.
Intersection acceptance should record direct-message transmission and arrival of the cloud copy as two tables, not one green light. An unpaid roadside SIM, an antenna blocked by a cabinet door, or a changed platform address should display as a Uu fault, and the note should say whether direct forwarding is still happening locally. When an onboard unit crosses cities, confirm that the visited network still allows the original access point before discussing whether the map can update. Store map increments apart from safety-message logs. A failed map download must not clear the direct-link configuration already in use locally. If a parameter write drops halfway, the device should keep the version from before the write and report “incomplete,” not boot into an unknown combination. After a static lab test passes, retest Uu service continuity on a stretch that includes cell handover. If “intersection online” in the operations report comes only from a heartbeat, the note should say it does not mean a collision-warning message reached the neighboring vehicle.
The first check after a roadside unit powers up is the alarm for the direct radio and the alarm for the cellular radio, not only the platform icon. A cloud copy of signal phase should carry the phase source’s time. If it disagrees with the direct phase the vehicle received, separate which path is late before deciding whether it can be used for a green wave. After a vehicle SIM is replaced, cancel or migrate unfinished map tasks. The new SIM must not keep using the old vehicle’s task id. On an ordinary road outside a demonstration zone, with no roadside unit, information on Uu must not be described as if direct collision warning were already available. Write the software version, the SIM’s access technology, and the intersection id into the same acceptance record. Without all three, a later fault cannot be told apart as a version rollback or a stopped SIM.