Fig. 3: GPS systems require line of site between the car and the satellite – this can be problematic in cities
In-vehicle navigation systems offer significant benefits when connections are temporarily lost. With a dead-reckoning module, many navigation systems can still communicate over the vehicle’s CAN bus, getting velocity information from the speedometer and turning data from the steering wheel sensor. That lets the vehicle keep track of its position, even when satellite signals are lost while driving in a tunnel or urban canyon. It’s difficult to retain precision in these instances, but newer systems are monitoring more sensors to improve accuracy. Depending on the availability of these sensors in the car, different levels of enhanced positioning sensor support can be defined.
- In entry positioning, the dead reckoning is based on differential wheel speed (DWS), but this method has low accuracy. This level can be achieved by interpreting the sensor data of vehicle state, wheel ticks of all wheels and GNSS (or GPS).
- In standard positioning, the dead reckoning is based on the gyroscope (either head unit internal or built-in in the stabilization ECU). This level can be achieved with the sensors required for entry positioning and additionally odometer / wheel ticks and gyroscope (2D gyro).
- In premium positioning, the dead reckoning is based on the gyroscope with additionally ramp and wheel slip detection. This level can be achieved with the sensors required for standard positioning and additionally inclination, slip angle and accelerometer (3D gyro).
Carmakers can re-use the same software and sensor set on different vehicles and head units. In addition, gyroscope devices built into an ESP module are of higher quality than those used in the head unit due to safety reasons. It is possible to use this device as sensor source for the Enhanced Positioning module with