Navigation Systems

Basic Description

Navigation systems help the driver of a vehicle to locate a particular destination and identify the best route for getting to that destination. Most automotive navigation systems use Global Positioning System (GPS) signals and electronic maps to identify the vehicle's current position relative to the desired destination. Portable navigation systems powered through the cigarette lighter or batteries, can be easily moved from vehicle to another. Built-in navigation systems have the advantage that they can access information about the vehicle's speed and direction to help navigate in situations where a GPS signal is temporarily blocked by buildings, traffic, foliage, etc.

Although the vast majority of automotive navigation systems rely on GPS signals, proximity beacons provide another form of radio-positioning. Proximity beacons are devices installed at key intersections and other strategic roadside locations that communicate their location along-with other information to receivers in passing vehicles via very short range radio, microwave or infrared signals. The reception of a proximity beacon signal provides an occasional basis for confirming vehicle position. One such system is described here.

Vehicle navigation systems generally offer the option of a top view (or bird's eye view) that shows the position of the vehicle on a traditional map; or a forward view that shows the road ahead as it would be viewed by the driver.

The diagram below illustrates the inputs and outputs associated with a navigation system that employs both GPS and proximity beacons.

Some navigation systems are integrated with real-time traffic information and emergency notifications that are transmitted to the vehicle wirelessly (e.g. at cell phone or FM radio frequencies).

The Global Positioning System

The U.S. military has 27 satellites orbiting the earth, 24 that are used for the GPS system and 3 as back-ups in case of a failure. They travel around the earth twice everyday and are arranged in such a way that at least 4 satellites are visible from any point on the earth at any time. To use GPS, a vehicle must have a GPS receiver. The GPS receiver has a pre-stored map or almanac of the position of each satellite (which is updated based on information sent out by the satellite). The GPS receiver finds its distance from one satellite. Now, the receiver might be at any point on the surface of a sphere (say, Sphere A) with a radius equal to the distance from this satellite. Now, if the receiver measures its distance from a second satellite, it obtains another sphere (say, Sphere B) of probable positions. Sphere A and Sphere B will intersect to form a locus of points that would be a circle. So, we now have a circle of probable positions. Now, the receiver does the same with a third satellite. The result is 3 spheres that will give only 2 possible locations of the GPS receiver. Only one of these two positions can be on earth.

The GPS satellite communicates with satellites by high-frequency, low-power radio signals. Radio signals travel at the speed of light and the GPS receiver measures the distance between itself and the satellite by finding the time taken for a radio signal to travel between the satellite and itself. However, to be able to measure this, the satellite and the receiver require extremely accurate clocks. The satellites have an atomic clock; most commercial receivers employ an ordinary quartz clock. The receiver measures incoming signals from 4 or more satellites, which is more information than necessary just to establish position. The additional information is used to update the receiver's quartz clock to maximize the accuracy of its position calculations.

Sensors

GPS receiver, gyrocompass, accelerometer, vehicle speed sensor

Actuators

Display

Data Communications

Control Unit Communication: Typically Control Area Network (CAN) Bus System

Manufacturers

Bosch, Continental, Dash, Delphi, Denso, Garmin, Kenwood, Lowrance, Magellan, Mio, Nextar, Pioneer, TomTom

For More Information

[1] Nissan's 'Smarter' Navigation System Assists with Safer, Greener Driving, Jeff Salton, gizmag.com, July 23, 2009.

[2] Automotive Navigation System, Wikipedia.

[3] Automotive Navigation Systems, Jennifer Suggitt, PC Today, Sep. 2005.

[4] Luxury-Car Navigation Systems: Best Bets, Kelsey Mays, Cars.com, Oct. 2, 2008.