Navigation System: Description and Operation

Navigation System

COMPONENT LOCATION









INTRODUCTION
The navigation system provides audible and visual route guidance information to enable the driver to reach a desired destination. The system allows the driver to choose the desired route using minor or major roads or motorways and the quickest or shortest route. Directions to hospitals, museums, monuments and hotels are also available. The computer uses map information stored on a DVD-ROM to determine the best route for the journey and provide the driver with details of directions and approaching junctions.
The navigation system is controlled from the integrated control panel and the Touch Screen Display (TSD). Control signals from the touch screen display are sent on the MOST ring to the navigation computer. The navigation computer uses a dedicated GVIF bus to transmit its video signals to the TSD.
Vehicles with navigation systems also incorporate additional traffic information systems. These are market dependant and are as follows:
- Japan-Voice recognition and VICS
- Europe-TMC
- NAS-No TMC, VICS or voice recognition











NAVIGATION COMPUTER
The navigation computer is located in the rear loadspace next to the battery.





The navigation computer incorporates the following:
- GPS receiver
- VICS receiver (Japan only)
- Traffic Message Channel (TMC) receiver
The navigation computer is connected to the MOST bus. The navigation computer generates its own graphics and transmits them to the TSD on a dedicated GVIF (Gigabyte video Interface) bus.
The navigation computer contains a solid state piezo gyro which measures the motion of the vehicle around its vertical axis. The gyro operates on the principle known as the Coriolis force. The Coriolis force is the force that appears to accelerate a body moving away from its rotational axis against the direction of rotation of the axis.
Using inputs from the ABS module, the GPS antenna and the gyro sensor, the computer calculates the vehicle's current position, direction and speed.
The navigation computer houses the DVD-ROM drive. The drive is used to read map data from region specific DVD's. The regions are as follows:
- Europe (3 discs)
- NAS (2 discs)
- Japan, Middle east and Australia (1disc)
A button, located adjacent to the DVD slot, is provided to eject the DVD from the unit. Prior to ejecting the disc the slot protection has to be slid to the side. If the ignition is on, or the Entertainment System is in 1-hour mode, one press of the button will eject the DVD.
The GPS receiver receives information from between 1 and 8 satellites at any one time. This information is received from the GPS antenna. The built in GPS receiver is used for calculating the position (i.e. Latitude, longitude and height), direction and speed.
The navigation computer uses non-volatile memory to store settings and configuration information when it is powered down. This process takes place just before the computer turns off.
For the Japanese market the navigation computer incorporates a VICS receiver. The VICS receiver, receives information from the beacon antenna in the center of the instrument panel and the electric FM antenna. The VICS system receiver allows the vehicle to receive information about traffic conditions from roadside transmitters and adjust the navigation instructions accordingly.
For ceratin European markets the navigation computer incorporates the Traffic Message Channel (TMC) receiver. The TMC receiver decodes TMC data. The navigation computer then displays this information on the TSD and also re-routes the navigation guidance around any traffic hold ups. The TMC data is received via the electric FM (frequency modulation) antenna via the antenna signal splitter.


TOUCH SCREEN DISPLAY (TSD)





The Touch Screen Display (TSD) is located in the center of the instrument panel. TSD is a touch sensitive 7 inch LCD (liquid crystal display) VGA screen containing 800 x 480 pixels in a 15:9 format. The TSD is connected to the Information and Entertainment system on the Media Oriented Systems Transport (MOST) ring. The MOST ring is a fibre optic communications data bus that allows high speed transfer of control instructions and audio around the system.
The TSD processes its own video for system operation but receives the navigation graphics from the navigation computer on a dedicated serial link called GVIF (Gigabit Video Interface).
The TSD is also the control interface for the following vehicle systems:
- Climate control
- Audio system
- Heated seats
- Customer programmable security features
- Cellular phone
- Vehicle settings
The TSD navigation control signals are sent on the MOST ring to the navigation computer,

GPS ANTENNA





The GPS (global positioning system) antenna is located in the rear liftgate spoiler. The GPS antenna is connected to the GPS computer by a single co-axial cable and passes signals from the GPS satellites to the navigation computers built in receiver for processing.
It is possible for the GPS antenna to lose the signal from the GPS satellites:
- In hilly or tree lined areas
- Built up areas with tall buildings
- In multi storey car parks
- In garages
- In tunnels
- In bridges
- During heavy rain or thunderstorms.
When the signal is lost the navigation computer will continue to give guidance using memory mapped data from the DVD (digital versatile disc) map until the signal is restored.

INFORMATION AND ENTERTAINMENT CONTROL MODULE





The Information and Entertainment Control Module (ICM) is located between the TSD and the IAM. The ICM is mounted in the vehicle using four M6 bolts.
The ICM is the gateway between the vehicle MS CAN bus and the Information and Entertainment system MOST bus.

INFORMATION AND ENTERTAINMENT CONTROL PANEL





The Information and Entertainment Control Panel is connected to the MS CAN bus. The ICP incorporates switches for audio system control, climate control hazard warning lamps and the navigation system. The navigation system is operated from the TSD via signals on the MOST ring. Hard switches on the ICP send CAN signals to the ICM which transfers signals to the relevant module on the MOST ring.

VICS BEACON ANTENNA (JAPAN ONLY)

VICS Beacon Antenna





The VICS beacon antenna is located on top of the instrument panel. The antenna receives infra red and RF signals from road side transmitters. The Antenna is connected to the navigation computer which incorporates a VICS receiver.

CONTROL DIAGRAM

NOTE:
A = Hardwired; D = High speed CAN bus; N = Medium speed CAN; P = MOST ring; Q = GVIF; T = Coaxial









PRINCIPLES OF OPERATION
The system used to calculate the current position of the vehicle is called the GPS (global positioning system). The system utilizes satellites which are owned by the United States Department of Defense (DoD). A total of 24 satellites orbit the earth every 12 hours at a height of 20,000 km (12500 miles), and between 5 and 11 of these satellites can be seen from a single point at any given time. The orbits are tilted to the earth's equator by 55 degrees to ensure coverage of polar regions. Each satellite transmits radio signals to provide information about the satellite position i.e. latitude, longitude, altitude, almanac data and an accurate time signal generated by an on-board atomic clock. Each satellite contains four atomic clocks.
The vehicle needs to receive data from at least four different satellites to give a three dimensional fix on its current position.
As the vehicle moves, this information is continually being updated. The computer determines which satellites are 'visible' to the system and their current position and relationship to each other. Using this information the computer can account for positional deviations of the satellites and compensate to enhance the accuracy of the navigation system.
The GPS (global positioning system) signal is also known as the Precision Positioning Signal (PPS).
PPS predictable accuracy is:
- 22 meters horizontal accuracy
- 27.7 meters vertical accuracy
- 200 nanoseconds time accuracy.
The navigation system provides computer generated audible and visual route guidance information to enable the driver to reach a desired destination. The system allows the driver to choose the desired route using minor or major roads or highways and the quickest or shortest route. Directions to hospitals, museums, monuments and hotels are also available. The computer uses map information stored on a DVD-ROM to determine the best route for the journey and provide the driver with details of directions and approaching junctions.
The navigation system receives GPS (global positioning system) information via the GPS antenna. The GPS signals are used by the navigation computer to calculate the vehicles position. Once the driver has input a desired destination the navigation computer can calculate a route, based on the drivers pre-determined preferences or the default settings in the navigation computer.
The navigation system is accessed by pressing the navigation soft key on the TSD.
Navigation is initiated by the driver inputting a destination. This can be achieved by:
- Entering in an address using the TSD.
- Entering a post code.
- Choosing a previous destination.
- Choosing a point of interest from the map disc database.
- Choosing the home location
- Choosing a memory stored location.
The driver is then guided to the destination by a scrolling map display and voice guidance. The display can be varied by scale and display type.
In addition to the standard navigation system there are two market dependant systems that supply extra information to the navigation system and the driver. These are:
- Traffic Message Channel (TMC)
- Vehicle Information and Communication System (VICS) (Japan only).

Traffic Message Channel (TMC)
The Traffic Message Channel (TMC) is a function of the FM (frequency modulation) Radio Data System (RDS). The system broadcasts real-time traffic and weather information. Data messages are received and decoded by the TMC receiver and passed onto the navigation system, which then delivers them via the navigation system interface. TMC messages can be filtered by the navigation computer so that only those relevant to the current journey are displayed, allowing the navigation system to offer dynamic route guidance - alerting the driver of a problem on the planned route and calculating an alternative route to avoid the incident. All TMC events on the map can be viewed not just the ones on the calculated route.
TMC traffic information systems conform to a global standard that has been adopted by traffic data gatherers, information service providers, broadcasters and vehicle/receiver manufacturers. TMC information is received via the normal FM (frequency modulation) radio antenna.
All TMC receivers use the same list of event codes, while the location database (on the map disc) contains both a country-specific set of location codes for the strategic European road network.
TMC traffic data is currently broadcast in many European countries.

Vehicle Information and Communication System (VICS)
The VICS system supplies the navigation computer with information to enable the navigation computer to re-route the navigation guidance or to inform the vehicle driver of traffic conditions in the vehicles vicinity. Information is provided to the system through three routes:
- RF transmission
- Infra-red transmission
- FM (frequency modulation) multiplex transmissions.
The RF transmissions are generally transmitted from road side beacons mainly on expressways. The information transmitted is as follows:
- Traffic congestion
- Travel time to next intersection
- Traffic conditions in surrounding areas and expressway turn offs
- Traffic accidents
- Speed limits
- Lane regulations
- Tire change
- Parking availability at expressway service areas and parking areas.
The Infra-Red transmissions are received by the beacon antenna mounted on the top of the instrument panel.
Infra-Red transmissions are transmitted from road side beacons on major trunk roads. The information transmitted is:
- Traffic congestion and travel time
- Traffic accidents
- Breakdowns
- Road works restrictions
- Parking availability.
FM (frequency modulation) transmissions are broadcast as part of the normal RDS FM (frequency modulation) transmission. Information transmitted is:
- Traffic congestion and travel time for wide areas
- Traffic accidents, road works, speed limits and lane restrictions for a wide area
- Parking availability information.
FM transmissions are received via the FM antenna and split from the normal FM transmissions by the FM signal splitter.