Navigation System: Description and Operation

Navigation System

COMPONENT LOCATION









OVERVIEW
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 highways with the option of three routes. Directions to hospitals, museums, monuments and hotels are also available. The computer uses map information stored on a DVD to determine the best route for the journey and provide the driver with details of directions and approaching junctions.
The navigation system is controlled by the driver from the touch screen display. Control signals from the touch screen display are sent on the Media Orientated System Transport (MOST) ring to the infotainment control module where they are then transmitted on the MOST ring to the navigation computer. The navigation computer uses a dedicated Gigabit Video Interface (GVIF) to transmit video signals to the touch screen display.
Vehicles with navigation systems also incorporate additional traffic information systems. These are market dependant and are as follows:
- Europe - Traffic Message Channel (TMC).
- Japan - Vehicle Information and Communication System (VICS).
- NAS - No additional system.

Navigation Computer





The navigation computer located under the right-hand front seat, houses the DVD drive that reads the map data from the region specific DVD. Access to the DVD slot is from the rear of the seat.
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.
Connected to the MOST bus, the navigation computer generates its own graphics and transmits them to the touch screen display on a dedicated Gigabyte Video Interface (GVIF) bus.
The navigation computer also incorporates the following:
- GPS receiver
- VICS receiver (Japan only)
- Traffic Message Channel (TMC) receiver
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 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.
To calculate the vehicle's current position, direction and speed, the navigation computer uses:
- speed signals transmitted on the high-speed CAN from the ABS module to the MOST ring,
- and signals transmitted from the GPS antenna and the gyro sensor.
For the Japanese market the navigation computer incorporates a VICS receiver. The VICS receiver, receives information from the VICS beacon antenna in the center of the instrument panel and the electric Frequency Modulation (FM) antenna. Using this information the VICS system monitors information regarding traffic conditions from roadside transmitters, and if necessary, adjusts the navigation instructions accordingly to avoid traffic congestion.
For certain 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 touch screen display and re-routes the navigation guidance system to avoid traffic congestion. The TMC data is received via the electric FM antenna.
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.

Touch Screen Display





The touch screen display is located in the center of the instrument panel and is the dedicated interface with the navigation system. The touch screen display does not operate any other vehicle systems. The screen is a touch sensitive 7 inch liquid crystal display (LCD) screen containing 800 x 480 pixels in a 15:9 format. The touch screen display is connected to the Information and Entertainment system on the MOST ring. The MOST ring is a fiber optic communications data bus that allows high speed transfer of control instructions and audio around the system.
The touch screen display processes its own video for system operation but receives the navigation graphics from the navigation computer on a dedicated serial link called Gigabit Video Interface (GVIF).
The touch screen display navigation control signals are sent on the MOST ring to the navigation computer.

GPS Antenna





The Global Positioning System (GPS) antenna is located on the rear of the vehicle's roof. The GPS antenna is connected to navigation computer by a single co-axial cable and passes signals from the GPS satellites to the navigation computer's 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 map until the signal is restored.
For additional information, refer to Antenna

VICS Beacon Antenna - Japan Only





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.
For additional information, refer to Antenna

Control Panel and Infotainment Control Module
The control panel incorporates switches for audio system and telephone control. The navigation system is operated from the touch display screen via signals on the MOST ring. Hard switches on the control panel send CAN signals to the infotainment control module which transfers signals to the relevant module on the MOST ring.
The infotainment control module is the gateway between the medium-speed CAN bus and the infotainment system MOST bus.
For additional information, refer to Audio System

Integrated Audio Module
Audio signals are sent on the MOST ring from the Integrated Audio Module to the amplifier.
For additional information, refer to Audio System

CONTROL DIAGRAM

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









PRINCIPLES OF OPERATION
The system used to calculate the current position of the vehicle is called the Global Positioning System (GPS). The system utilizes satellites which are owned by the United States Department of Defense. 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's position, for example the 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 Global Positioning System (GPS) 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 receives GPS information via the GPS antenna. The GPS signals are used by the navigation computer to calculate the vehicles position. Once the driver has entered a destination, the navigation computer can calculate a route, based on the driver's pre-determined preferences or the default settings in the navigation computer.
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 touch screen display.
Navigation is initiated by the driver entering a destination. This can be achieved by:
- Entering in an address using the touch screen display.
- 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 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) - Europe only.
- Vehicle Information and Communication System (VICS) - Japan only.

Traffic Message Channel (TMC)
The Traffic Message Channel (TMC) traffic data is currently broadcast in many European countries.
TMC is a function of the FM (frequency modulation) Radio Data System (RDS). The system broadcasts real-time traffic and weather information. TMC information is received via the normal FM radio antenna.
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.
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.

Vehicle Information and Communication System (VICS)
The Vehicle Information and Communication System (VICS) is broadcast in the Japanese market.
The VICS system supplies the navigation computer with information that enables the computer to inform the vehicle driver of traffic conditions in the vehicle's vicinity and calculate an alternative route if necessary. Information is transmitted to the navigation system through three routes:
1. Radio Frequency Transmission
Radio frequency transmission is generally transmitted from road side beacons mainly on highways. The information transmitted is as follows:
- Traffic congestion
- Travel time to next intersection
- Traffic conditions in surrounding areas and highway turn offs
- Traffic accidents
- Speed limits
- Lane regulations
- Tire change
- Parking availability at highway service areas and parking areas.
2. Infra-red Transmission.
Infra-red transmission is 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.
3. FM (frequency modulation) Transmissions.
FM (frequency modulation) transmissions are received via the FM antenna, broadcast as part of the normal RDS FM 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.