Chapter 1
WIA-COMM-003 treats Vehicle-to-Everything (V2X) as one family of four modes, each aimed at a different kind of counterpart.
Safety traffic in V2V is connectionless. A vehicle transmits its Basic Safety Message (BSM) or Cooperative Awareness Message (CAM) periodically, at 10 Hz in the nominal case. There is no handshake and no acknowledgment, and every vehicle in range receives the message. A second class is event-triggered: emergency braking, collision warnings, lane-change notices and hazardous-location warnings. Nothing has to be negotiated before a warning can be sent.
The standard defines five core message types, each with its own rate and latency budget.
| Message | Frequency | Purpose | Latency |
|---|---|---|---|
| BSM | 10 Hz | Position, speed, heading | <10 ms |
| CAM | 1-10 Hz | Vehicle status | <100 ms |
| DENM | Event-driven | Hazard warnings | <10 ms |
| SPaT | 10 Hz | Traffic signal info | <100 ms |
| MAP | 1 Hz | Road geometry | <500 ms |
Three kinds of node take part. The On-Board Unit (OBU) sits in the vehicle and generates and processes messages. The Road Side Unit (RSU) broadcasts SPaT and MAP data, collects traffic data and relays V2V messages. Cloud services reach the vehicle through V2N. The specification draws the OBU as the hub that talks to peer OBUs, to RSUs, to pedestrians and to the network.
The stated philosophy is 弘益人間, "Benefit All Humanity": fewer traffic accidents, better flow, and safer autonomous transportation. This explains the standard's emphasis on latency budgets and broadcast reliability. A warning that arrives after the driver has already reacted has no value.
The architecture is layered from the top down.
Because the facilities and security layers sit above the access layer, the same message definitions can run over either radio.
DSRC uses 10 MHz channels at 5.9 GHz with OFDM modulation (BPSK through 64-QAM), giving 3-27 Mbps. Its MAC layer is CSMA/CA with no association step, supports broadcast and unicast, and applies EDCA for quality of service. Typical latency is 5-10 ms. Line-of-sight range reaches 1000 meters, falling to 300-500 meters in urban settings and 500-800 meters on highways.
LTE-V2X (Release 14) uses either the PC5 sidelink at 5.9 GHz or cellular bands through the Uu interface. In Mode 3 the network schedules transmissions through the eNodeB. In Mode 4 vehicles sense and schedule autonomously, so the service still works without cellular coverage. 5G NR-V2X (Release 16+) adds ultra-reliable low latency, an enhanced sidelink, network slicing support and data rates up to 1 Gbps.
The ITS band is 5.850-5.925 GHz in the US (75 MHz), 5.875-5.905 GHz in the EU (30 MHz) and 5.770-5.850 GHz in Japan (80 MHz). The channel plan reserves Channel 172 (5.860 GHz) as the safety-critical control channel, with service channels 174 through 184 in 10 MHz steps.
Channel 172: 5.860 GHz (Safety critical - CCH)
Channel 174: 5.870 GHz (Service channel)
...
Channel 184: 5.920 GHz (Service channel)Canonical envelopes use scaled integers rather than floating-point values. In the BSM, latitude and longitude are in tenths of a micro-degree, speed in 0.02 m/s units, heading in 0.0125-degree units and acceleration in 0.01 m/s². An abridged excerpt follows.
{
"messageType": "BSM",
"msgCount": 127,
"position": { "latitude": 37774900000, "longitude": -122419400000, "elevation": 100 },
"speed": 1800, // 0.02 m/s units (= 36 m/s = 65 km/h)
"heading": 18000, // 0.0125 degree units (= 225°)
"vehicleSize": { "width": 200, "length": 480 }
}The market splits between 802.11p-based DSRC and cellular C-V2X. The specification compares them without declaring a winner.
| Parameter | DSRC | LTE-V2X | 5G NR-V2X |
|---|---|---|---|
| Range | 300-1000 m | 500-1500 m | 1000-2000 m |
| Latency | 5-10 ms | 10-20 ms | 1-5 ms |
Spectrum policy differs by region. The same 5.9 GHz idea occupies 75 MHz in the US, 30 MHz in the EU and 80 MHz in Japan, at different offsets. A vehicle sold across regions therefore needs configurable radios, and application software must stay independent of the exact channel plan.
Instead of forcing a single choice, the standard describes hybrid deployment. Dual-mode devices carry both DSRC and C-V2X. A message translation layer bridges them, technology selection depends on availability, and handover protocols govern transitions. This lets deployments proceed before the market settles.
Different parties supply different parts of the system. Vehicle makers supply OBUs. Road operators install RSUs at signalized intersections. Network operators and cloud providers host V2N services such as traffic management, remote monitoring and over-the-air updates. The shared message formats let each party deploy independently.
The formats also follow regional conventions. The BSM and SPaT come from SAE J2735, while the CAM (ETSI EN 302 637-2) and DENM (ETSI EN 302 637-3) come from ETSI. Carrying both families in one standard is what lets a single implementation interoperate with infrastructure on either side of the Atlantic.
The core V2V application computes time-to-collision from shared position and speed. For two vehicles, TTC = (d - L₁ - L₂) / (v₁ - v₂), where d is the distance between them, L₁ and L₂ are the vehicle lengths and v₁, v₂ are their speeds. The reference algorithm discards targets whose heading differs by more than 45 degrees or that are not closing.
if relative_speed <= 0:
return None # Target moving away or same speed
ttc = (distance - ego_vehicle.length) / relative_speed
if ttc < 1.5:
return {'level': 'CRITICAL', 'action': 'BRAKE', 'ttc': ttc}| TTC | Level | Response |
|---|---|---|
| < 1.5 s | CRITICAL | Immediate brake |
| < 2.5 s | HIGH | Warning and prepare brake |
| < 4.0 s | MEDIUM | Visual/audio warning |
| otherwise | LOW | Monitoring |
The blind-spot zone extends 0.5 m to 3.0 m from the vehicle side, from the B-pillar to 2 m behind the vehicle, at an angle of 90° ± 30°. The right side mirrors the left. A warning fires when a vehicle is detected in the zone, the turn signal is activated and lateral acceleration is observed. Combining these three signals keeps parked or passing traffic from triggering needless alerts.
At intersections the RSU broadcasts SPaT (signal phase and timing) and MAP (intersection geometry). A vehicle that knows which lane it is in and when the light changes can advise the driver on speed. The SDK exposes this through a subscription to a signal identifier, delivering the current phase and time remaining.
Cooperative driving extends the same messaging to coordinated maneuvers. The CLI illustrates platoon formation with a leader, a vehicle cap and a spacing target, for example wia-comm-003 platoon --mode leader --max-vehicles 5 --spacing 10m. Close spacing is only safe when the lead vehicle's braking reaches followers faster than a human could react.
WIA-COMM-003 does not reinvent wire formats. It references IEEE 802.11p for DSRC, SAE J2735 for the BSM, and ETSI EN 302 637-2 and EN 302 637-3 for the CAM and DENM. It adds a canonical JSON envelope, an API surface and the performance requirements that go with them.
The specification states that latency, packet rate and range requirements "constrain valid encodings." An implementation is therefore judged against the per-message budgets, not only against field layout. The BSM and DENM must stay under 10 ms. The CAM and SPaT budget is 100 ms, and MAP is allowed 500 ms.
A DENM carries its own validity rules in the management container. An actionID of originating station plus sequence number identifies the event. relevanceDistance and relevanceTrafficDirection limit who should care, validityDuration (seconds) says how long the event holds, and transmissionInterval (ms) sets the repetition rate. The situation container pairs a causeCode such as "collision" with a subCauseCode such as "chainCollision" and a severity.
The stack includes a security layer for authentication and encryption, and the SDK takes a securityLevel setting. The tension is built into the use case: safety requires broadcasting position and heading many times per second, while privacy requires that those broadcasts not become a tracking tool. The standard lists privacy protection among its security goals, and implementations should treat vehicle identifiers with care.
Budgets are only useful if they can be verified. The CLI provides wia-comm-003 measure-latency --target VEH-789 --count 100 to sample round-trip behavior against a peer. It also provides test-rsu to check a roadside connection. Repeated sampling matters because tail latency, not the average, decides whether a collision warning arrives in time.
The TypeScript SDK (@wia/comm-003) centers on a V2XCommunication object configured with a vehicle identifier, a radio technology and a security level.
const v2x = new V2XCommunication({
vehicleId: 'VEH-123456',
technology: 'C-V2X',
securityLevel: 'high',
frequency: 5900 // MHz
});A BSM is built as a V2VMessage with position, speed (km/h), heading (degrees), acceleration and timestamp, then sent with sendV2V. Reception is callback-based through onV2V, and detectCollisionRisk can be called inside the handler. Note that the SDK takes human-friendly units, while the wire format uses the scaled integers shown earlier.
For V2I, subscribeToInfrastructure('SIGNAL-001', ...) delivers SPaT data with a phase and the time remaining. A higher-level path is also available: broadcastPosition sends position updates, and onHazardWarning reports a warning with a type and distance. Applications can use the high-level calls and leave message encoding to the SDK.
start launches the service with a chosen technology and frequency.send-bsm transmits a test message.monitor filters traffic, for example by type V2V and collision-warning.test-rsu checks a roadside unit.measure-latency samples delay to a target.platoon forms a platoon.Several details deserve care.
5G NR-V2X lowers the latency range to 1-5 ms and reaches 99.9% reliability at 500 m, against 98% for LTE-V2X. Network slicing would let safety traffic keep reserved capacity on shared cellular infrastructure. The access-layer abstraction in the standard means upgrading the radio need not change application code.
The Collective Perception Message (CPM) belongs to the V2V branch alongside CAM and DENM. Instead of reporting only its own state, a vehicle shares what its sensors detect, which helps vehicles see road users that are not transmitting. As this spreads, the awareness picture shifts from self-reports to shared sensing.
V2N is the least latency-sensitive mode and the broadest. It covers cloud traffic management, remote monitoring and OTA updates. These services complement direct links, since cloud-scale information such as congestion can inform the local, millisecond-scale decisions.
V2P covers pedestrian detection, cyclist awareness and emergency vehicle warning. The open challenge is device-side: a pedestrian's phone or wearable must transmit often enough to be useful without exhausting its battery or exposing its owner's location.
Platooning and coordinated maneuvers are the near-term form of cooperative driving. Full autonomy will depend on the same primitives: shared intent through path prediction, hazard notices through DENM and intersection knowledge through SPaT and MAP.
V2X in WIA-COMM-003 is a set of four modes (V2V, V2I, V2P, V2N) built on periodic broadcast and event-driven warnings. A layered stack runs over two radio families, DSRC and C-V2X, in the 5.9 GHz band, and the messages are the BSM, CAM, DENM, SPaT and MAP.
Latency budgets drive the design. Safety messages must arrive in under 10 ms, while map and signal data can tolerate more. The TTC thresholds of 1.5, 2.5 and 4.0 seconds turn these budgets into driver and vehicle actions.
Because spectrum plans and message families differ by region, the standard favors dual-mode devices, translation and handover. The same configurable approach applies to security level and frequency in the SDK.
A new implementer should begin with the BSM envelope and its scaled units, then add the CAM and DENM, then SPaT and MAP. Next comes the V2V collision logic, followed by the RSU-facing V2I calls. The CLI latency and RSU tests help verify each step.
This chapter treated the messages mostly as black boxes with rates and budgets. The next chapter opens them up field by field: the BSM Part I and Part II contents, the CAM containers, the DENM management and situation blocks, and the SPaT structure. It shows how each value is encoded and why the units are scaled as they are.