Principle
Navigation position calculation(Dead Reckoning) is used in scenarios where GNSS temporarily fails, such as in tunnels or under overpasses, by utilizing wheel speed pulses, steering angular velocity, or MEMS IMU integration to estimate displacement. Errors accumulate over time and need correction when GNSS is reacquired. High-end solutions combine map matching to jointly suppress drift.
Integration
Obtaining vehicle speed from the CAN bus requires parsing the vehicle's protocol; the installation angle and IMU calibration affect accuracy. Software algorithms on the module side and hardware synchronization are key.
Application
Insurance UBI, fleet management, and ETC path reconstruction all benefit; privacy design should limit storage of raw trajectories.
Sensor Fusion and Calibration
Dead Reckoning Accuracy depends on wheel speed pulse scaling, tire pressure, and slip detection. The IMU needs to compensate for gyro bias and accelerometer gravity components. Mounting angle errors will systematically amplify lateral drift, so production lines or after-sales should support a one-click calibration process. When fused with CAN, message delay and frame loss should be noted; when combined with GNSS, the Kalman filter state noise should adapt to vehicle speed and road conditions. In tunnels where magnetic interference exists, magnetometer assistance may fail and should degrade to a pure inertial plus wheel speed model.
Cellular Reporting and Compliance
When the vehicle module periodically uploads dead reckoning trajectories, it should also upload confidence levels and sensor health status. The cloud can perform anomalous driving detection and map matching. Storage and transmission must comply with personal and vehicle data security regulations and minimize collection of raw high-frequency IMU data. When performing OTA algorithm updates, ensure version compatibility and rollback to avoid entering an unverified state while driving. In cooperative scenarios with ETC or roadside RSUs, timestamp alignment and coordinate system unification are key.
Engineering Practice Supplement
Combine "Vehicle Dead Reckoning" with the full life cycle of the module: EVT stage verifies reference design and antenna schemes; DVT stage performs conducted/radiated scanning and thermal imaging; PVT stage solidifies calibration and test scripts. Before certification, verify target country regulations and operator registration requirements to avoid frequency band or SAR omissions. Production lines should retain golden sample comparisons and random inspection rules; after-sales should be able to trace software versions, calibration parameters, and key component batches by serial number. If the client requires remote maintenance, security upgrades, rollback, and emergency stop strategies must be designed simultaneously.
The longer the outage, the faster the reckoned error grows
Dead reckoning means that, during a short loss of satellite signal, wheel-speed pulses, yaw rate, or inertial sensors are integrated to keep the track continuous. It is a limited extrapolation, not another absolute position. The conditions are that the wheel-speed scale has been calibrated for the current tires, that the mounting angle is known, and that a new absolute position removes the integrated error once satellites return. The longer the outage, and the more speed and turns, the faster the cross-track error grows. If the set time passes with no satellite or map constraint, mark that segment as low confidence. Do not keep treating it as a lane-level position.
Vehicle speed taken from the vehicle bus has to be parsed from the specific message. Delay and lost frames make the integral miss a stretch of road. If gyro bias is not removed, the position still creeps while the vehicle is stopped. If the accelerometer has not removed gravity, a slope is counted as forward motion.
The old pulse scale cannot be reused after a tire change
Tire diameter, pressure, and slip all change the distance each pulse represents. Replacing tires in service without a new calibration is a common reason a track becomes systematically long or short. A small tilt in the mounting angle amplifies cross-track drift. Production or service needs a calibration on a level road, not a turntable standing in for the vehicle. The magnetic field in a tunnel can make magnetometer aiding fail. Degrade to wheel speed plus inertial sensors then. Do not keep folding compass heading into the solution.
Reports should carry confidence and sensor health, so the cloud knows which segment cannot be used to assign blame. The coordinate name must match the satellite points, or the correction shows a false jump; see coordinate systems in China. A slow cold start lengthens the time that must be reckoned. Getting assistance data is in A-GNSS. Raw high-rate inertial samples should not be uploaded for long. The track itself is enough to describe the trip.
A stopped vehicle can still creep forward
If gyro bias is not estimated, a stop is integrated into slow motion. A geofence that fires on that false displacement raises an alert that the vehicle left its parking spot by itself. Stationary detection should look at zero wheel speed and acceleration change together, freeze the position while stopped, and keep only the attitude estimate. The first segment after moving off again should be given a larger uncertainty. Do not keep the confidence from before the stop. Otherwise a short outage followed by recovery is misread as a position jump when the correction is applied.