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Advances in automotive navigation systems

28 Apr 2015  | Oliver Jesorsky

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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 stabilisation 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 highest location accuracy.

Furthermore, the dead reckoning module requires calibration. The calibration depends on both sensor hardware and software configuration (even firmware changes affect the positioning quality). It is possible to manage several calibration files during runtime, according to the vehicle model and sensor configuration. When GNSS (GPS) is available, sensor data is being monitored and automatically calibrated.

However, that means there's more data to process. Fusing inputs from various sensors into a single determinant for distance requires an understanding of network latency and other factors. Data coming from one input may not be synchronised with information from faster sensors. Controllers must have some information on latency and other parameters that impact performance. Most of the networked signals don't have time stamps, so it's difficult to combine them without a good understanding of many aspects of the full vehicle system.

Where do I want to go?
Most drivers don't really care whether their navigation system is using this type of dead-reckoning information or the longitude and latitude data transmitted by GPS satellites. Instead, they're interested in finding addresses, restaurants, stores and businesses. Navigation systems must link addresses and point-of-interest information to the desired longitude and latitude, and then figure out the best way to get there.

This is a somewhat subjective task that's becoming more complex as technology advances. The best route can be the shortest, the fastest, or the least expensive. Picking a route is a challenging task that must be done quickly for drivers who don't expect to wait before they step on the accelerator and start their journey.

The calculations that determine the best route must include factors like speed limits, one-way streets and turn regulations, including rules that change during rush hours. Average wait times for traffic signals and stop signs must be factored in.

All calculations are based on an intelligent, multi-layer routing algorithm. For very long routes, the system may rely on a supra-layer that only includes motorways or major roads for route calculation. Map files are compiled in a way that the country tiles can be arranged according to available storage space. This allows seamless navigation across country borders and map tiles. For a wrong turn or at deviations, the routing algorithm performs an instant re-routing. Due to a distance-based background routing algorithm the re-routing doesn't take longer than a fraction of a second. The routing algorithm defines an area around the current car position and calculates all possible routes that lead to the destination inside this area. If the car moves along the route and approaches the border of the defined area, a new area with all possible routes is calculated in the background. If the car leaves the route, a new route is immediately available, because one of the pre-calculated routes can be taken from the defined area. A new area with all possible routes is calculated in the background. This way, the navigation software can immediately provide a new route with minimal calculation time.

As the car moves, a bounding rectangle is constantly updated to cover the area from the current position to the destination. This bounding rectangle can be used to create a view that shows the driver the route from the current position to the destination. For example, you can have a split screen, with manoeuvre arrows on the first screen and a route overview given by the bounding rectangle on the second screen. Parts of the route can be excluded from the route calculation. This feature is particularly useful for detours or closed roads. Excluded parts can be defined by specifying a bounding rectangle (all roads inside the rectangle are blocked) or by selecting a route segment. For time-restricted roads, the navigation provides a horizon-based routing. Within a defined horizon along the route, the route calculation checks if a time-restricted road will be reached in time. If the time restriction will be violated, the routing automatically calculates a new route.

Drivers may alter their requirements depending on conditions. On a rainy day, for example, a driver may want to take a different route than normal. Data about another major condition, traffic, is becoming more readily available as navigation systems evolve. It's no longer rare for navigation systems to process real-time traffic data.

Navigation systems today can adjust the route calculation dynamically according to traffic events, such as non-moving traffic, queuing traffic, slow traffic, accident, slippery road, snow on road, and many other situations. Traffic events are displayed on the map. Additionally, traffic events can be announced acoustically. An automatic re-routing module uses all events on the route to recalculate the directions.

Figure 1: Navigation systems today can adjust the route calculation dynamically according to traffic events.

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