Definition
V2X (Vehicle to Everything) covers V2V (vehicle-to-vehicle), V2I (vehicle-to-infrastructure), V2N (vehicle-to-network), and V2P (vehicle-to-pedestrian) communication modes. C-V2X is based on cellular technology, including LTE-V2X (PC5 direct communication + Uu cellular) and 5G NR-V2X. It supports low latency (<20ms), high reliability (99.999%), and high throughput V2X applications, making it a key enabling technology for intelligent driving, collaborative autonomous driving, and smart transportation.
Communication Types and Scenarios
- V2V: Direct vehicle-to-vehicle connection (PC5/Sidelink), broadcasting BSM (Basic Safety Message), collaborative perception, enabling collision warning and cooperative adaptive cruise control (CACC)
- V2I: Communication between vehicles and roadside units (RSU), acquiring traffic light status, road conditions, and speed limit information, supporting traffic light optimization and blind spot warning
- V2N: Accessing the cloud through the cellular Uu interface to obtain high-precision maps, remote diagnostics, OTA updates, and fleet management
- V2P: Communication between pedestrian devices (mobile phones, wearable devices) and vehicles, supporting pedestrian collision warnings
C-V2X Technology Roadmap
LTE-V2X uses PC5 direct communication (licensed-exempt spectrum 5.9GHz) complemented by Uu cellular; 5G NR-V2X enhances Sidelink capabilities, supporting wider bandwidth, higher throughput, and lower latency. V2X has extremely high QoS requirements, requiring priority scheduling and differentiated services to ensure the safety-related messages. Compared with DSRC (802.11p), C-V2X has better non-line-of-sight performance and an evolution path.
Typical Use Cases
V2X is applied in forward collision warning, blind spot warning, intersection assistance, traffic light passing, green wave travel, remote driving, platooning, and more. Vehicle network T-Box and OBU (On-Board Unit) access V2N through cellular IoT SIM cards to achieve remote vehicle monitoring, OTA, and fleet management; V2V/V2I requires modules that support PC5 direct communication.
SimtoLink provides IoT SIM cards and connectivity solutions for connected car customers, supporting V2N access for in-vehicle terminals such as T-Box and OBU. Vehicles communicate with cloud platforms via cellular networks to achieve remote diagnostics, OTA upgrades, fleet management, location tracking, and more. SimtoLink can configure private APN, static IP, and QoS policies according to customer needs, ensuring high reliability and low latency for connected car services; in V2V/V2I scenarios, SimtoLink can assist customers in selecting modules supporting C-V2X PC5.
Direct Link and Cellular Backhaul Use Two Radios
V2X splits communication between a vehicle and the objects around it. Safety messages from vehicle to vehicle, vehicle to roadside, and vehicle to pedestrian can be broadcast on the PC5 direct link, without passing through a base station, so an oncoming vehicle can receive them even with no cellular coverage. Vehicle-to-network uses the Uu air interface, enters the cloud through a base station, and carries maps, diagnostics, fleet dispatch, and upgrade packages. The radio, the subscription, and the failures of the two links are completely different. The direct link works in an agreed ITS band and needs a module, an antenna, and a resource pool that the region allows for PC5. A cellular SIM only proves that Uu can attach. A direct message received by a roadside unit does not automatically appear in the enterprise APN, unless the roadside unit itself uploads it again.
The messages do not age the same way. A safety broadcast is meant to be received nearby within a very short time. A stale position is more dangerous than no message, so the retransmission count cannot be increased the way a file transfer would be. The cloud path can tolerate a longer round trip and is used for management that is not immediate. Stuffing both kinds of message into the same MQTT topic lets the cloud queue drag down the delay the direct link requires.
Safety Messages Need a Direct-Link Module and a Priority
Remote monitoring, tracks, and upgrades that use only a cellular SIM are V2N. They do not need PC5. Intersection collision warning, vehicle-to-vehicle coordination, or exchanging position when there is no network does require the direct link, and the roadside unit and the other vehicle have to use the same generation of the protocol and the same resource pool. 5G direct and LTE direct do not interwork automatically. A high-reliability class also has to place the matching service in high-priority scheduling on the network side. Congestion control on the direct link is done by the resource pool and by a limit on the sending rate. It is not an APN rate cap.
A vehicle crosses cells at high speed. The V2N session has to survive handover. An anchor chosen too far away adds delay. When the vehicle leaves the country or changes operator, the direct-link band may no longer allow transmission. Cellular roaming can be available and still cannot replace permission to use the direct link. Tell the cellular antenna and the direct-link antenna apart. Under a metal roof, or blocked by luggage, the link budget is not the bench test.
Cellular Online Is Taken to Mean the Direct Link Is Usable
The most common mistake is a platform that sees the T-Box online and concludes that vehicle-to-vehicle safety messages are already open. Online only means Uu and the SIM are normal. The direct link may have no antenna fitted, no resource pool configured, or local rules that do not allow transmission. Surrounding vehicles receive nothing. Another case is to judge a safety service by public-network delay and to treat the cloud round trip as the vehicle-to-vehicle delay. The numbers differ by a whole path. Someone also sends large video packets on the direct link, fills the resource pool, and the short safety broadcasts then fail in collisions.
Test the two sides separately. For the direct link, see whether nearby devices receive the broadcast, and record delay and loss. For cellular, see attach, handover, and arrival in the cloud. Do not close a failure on one side with a success on the other. If the module prints only cellular registration state, find the direct-link counters separately. Otherwise the acceptance sheet writes the two links as one item.
When the direct-link antenna is blocked by the metal roof or by luggage, the receive distance on the bench does not represent the distance on the road. A healthy cellular antenna only shows that backhaul is usable. Continuing to resend a safety broadcast after it has expired can make surrounding vehicles use a stale position, which is more dangerous than sending once less. Cut the retransmission count to the lifetime of the message. After the direct-link resource pool is occupied by large packets, collisions among short safety messages rise, while cloud video is still smooth. The two tests have to record the receiver, the delay, and the loss cause separately. Platform online status cannot stand in for whether a surrounding vehicle received the message. Permission to transmit on the direct-link band also differs by region. On a road section where it is not permitted, direct-link transmission should stop.