Basic Principles of Satellite Navigation

Objectives By the end of this lesson you will be able to: Explain how a position can be worked out Identify the limitation of basic GPS Explain the principles of dead reckoning Identify what components are used in the car to dead reckon Next >

Basic Principles of Satellite Navigation Next >

WE ALL KNOW WHAT ITS MEANS TO GET LOST. Every car driver knows what it’s like to get lost, a trip to a holiday destination or driving to an unfamiliar town or city. Before you set off , you study your route on a map or street plan, during the journey you find your bearings by reading traffic signs, and noticing features of the landscape. WE ALL KNOW WHAT ITS MEANS TO GET LOST. Next >

Navigation involves locating the position of a car as well as determining the direction and distance of your destination and taking the necessary steps to reach that destination. Next >

2-D Trilateration Imagine you are somewhere in the United States and you are TOTALLY lost -- for whatever reason, you have absolutely no clue where you are. You could be anywhere on a circle around Boise that has a radius of 625 miles, like this. Next >

You ask somebody else where you are, and she says, "You are 690 miles from Minneapolis, Minnesota." Now you're getting somewhere. If you combine this information with the Boise information, you have two circles that intersect. You now know that you must be at one of these two intersection points, if you are 625 miles from Boise and 690 miles from Minneapolis. Next >

If a third person tells you that you are 615 miles from Tucson, Arizona, you can eliminate one of the possibilities, because the third circle will only intersect with one of these points. You now know exactly where you are --. I. Next >

This same concept works in three-dimensional space, as well, but you're dealing with spheres instead of circles. In the next section, we'll look at this type of trilateration Next >

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Satellite navigation enables the driver to travel from their starting point to their destination quickly, safely and comfortably without having to read maps. Next >

Switch for reverse lights System components Satellites GPS Receiver Triplex Antenna Navigation CD ROM ABS Sensor Radio Loudspeaker Next > Switch for reverse lights

The Global Positioning System The GPS system makes satellite navigation possible, the system was originally developed for the US military of defence. For military reasons the quality of the transmitted data for position finding was deliberately reduced for civilian use using a special procedure. Next >

The military version of the GPS system used a random number generator that “hashes” the radio signals containing the satellite data. The encrypted corrective data which is transmitted in parallel cannot be decoded by civilian receivers. For civilian used it is only possible to determine positions accurate to +/- 100 metres. This has now been lifted. Next >

The GPS system currently comprises of a total of 24 satellites which are evenly distributed over six orbits at an altitude of 20,000 kilometres, they each circle the earth once every 12 hours Next >

Each time the Radio Navigation System is switched on it attempts to receive a signal from the satellites. Signals from at least three satellites are required for an accurate position fixing, only then can the position of the receiver be calculated at any point on the earths service. Next >

The satellites radio an ID code, their position and a high-precision signal earthwards at intervals of one millisecond. The GPS receiver in the Radio Navigation System receives the satellites data and calculates how long the data transmission took by comparing the timing signal with its internal high precision clock. Next >

Reception & Interference. Reception interference may occur if the satellite transmitter does not have line of sight contact with the receiver. Next >

Multi-storey car parks, In the following situations the radio link may be interrupted or faulty: City Streets, Valleys, Tunnels, Multi-storey car parks, Next >

Dead Reckoning Navigation Next >

Dead Reckoning Navigation The system components of the Radio Navigation System increase the accuracy of position fixing. The navigation control unit calculates the route profile from the signal supplied by the ABS signal and the Angle of turn sensor. ABS Sensor. Angle of turn sensor. Next >

Dead-reckoning is the result of the interplay between these two sensors. The navigation control unit calculates the route profile with signal supplied by the angle of turn sensor and the ABS sensor, the control unit compares this with the street map stored on the CD ROM several times per second, this is known as “map matching”. Next >

How Vehicle Navigation Works The angle of turn sensor Next >

The angle of of turn sensor is located in the housing of the Radio Navigation System. Next >

Function of the angle turn sensor The angle of turn sensor is shaped like a tuning fork. The two legs of this element are designed as oscillating bodies. Next >

When the ignition is turned on, voltage is applied to the lower piezoelements. They begin to oscillate. Lower piezoelements V Next >

When the vehicle changes direction the so-called coriolis force acts on the legs of the sensor Lower piezoelements Next >

The flexure of the legs is transmitted to the upper piezoelements, which in turn generates a small voltage. V piezoelements Upper Next >

The navigation control unit can calculate the change in direction of travel from this voltage. piezoelements Upper O.3 MV

Because of the process of “map-matching” the accuracy of position fixing can be increased to +/- .5m in urban areas and +/- 5m on long straight roads or motorways. Next >

Navigation control unit Vehicle Navigation is the overall result of the inter-play between Sat Nav and dead reckoning navigation. Satellite GPS antenna Receiver Navigation Control unit Turn angle sensor ABS sensor CD-ROM Navigation control unit Vehicle Navigation Next >

How Vehicle Navigation Works The navigation control unit calculates the distance, the direction of travel, and the change of direction of travel,etc. Next >

How Vehicle Navigation Works Route recommendations are then output in the form of visual and audible messages Next >

How Vehicle Navigation Works During the trip the distance travelled is measured on the basis of the wheel speed pulses generated by the ABS wheel speed sensor and changes of direction sensed by the angle of turn sensor. N KM W E S Next >

How Vehicle Navigation Works The system continuously monitors whether the driver follows the route recommendations. Next >

How Vehicle Navigation Works The system tells the driver when he has deviated from the recommended route. Next >

How Vehicle Navigation Works If the driver stays on this route the system recalculates the distance to the destination. Next >

The angle of turn sensor records changes in the direction of travel to the left and right. 360 DEG’S Next >

The angle of turn sensor detects this rotational movement and informs the the navigation control unit. The navigation control unit then calculates the angle of the direction change. 360 DEG’S Next >

In order for to distinguish between forward and reverse the control unit will receive a signal from the reverse switch. 360 DEG’S Next >

The distance travelled is still required in order to calculate the curve radius, this is determined with the aid of the ABS wheel speed sensor. 360 DEG’S Next >

Are there any questions? Next >

Objectives By the end of this lesson you will be able to: Explain how a position can be worked out Identify the limitation of basic GPS Explain the principles of dead reckoning Identify what components are used in the car to dead reckon