Position finding and destination-oriented navigation, function

General information

The position finding and destination-oriented navigation function is divided into the following subareas:

 General information concerning global positioning system (GPS) position finding

 GPS position finding, function

 General information concerning basic position finding

 Basic position finding, function

 Recalibration

 General information on route calculation

 Destination-oriented navigation through voice output, function

 General information on dynamic route guidance

 Dynamic route guidance, function

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Function requirements

 "Circuit 30 ON" status.

 The Auto pilot system (APS) is working correctly.

 No errors in the GPS antenna system.

 Signals are available from at least 3 GPS satellites.

 Communication with the ESP control unit (N47-5) is free of faults.

 The trip destination has been entered.

 Route calculation done.

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General information on GPS position finding

The GPS is a satellite-based positioning system. It is available worldwide. The GPS satellites permanently transmit time and position data (longitude and latitude). GPS position finding is irretrievable after vehicle transport (e.g. by train or ferry or after towing). A new GPS position (after interruption of the satellite reception) can take several minutes (up to 20 minutes when the equipment is commissioned).

The accuracy of the position finding and the actual calculation is essentially based on the measurement of the runtimes of the signals transmitted synchronously by the various satellites. An important prerequisite is the synchronicity of the clocks of the satellites and the receiver. To this end the receiver is equipped with an automatic time correction, which in turn is made possible with the aid of the satellite signals.

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Function sequence for GPS position finding

The GPS signals are received by the GPS receiver, which is integrated into the radio control panel and navigation unit (A2/56), directly by the GPS antenna (A2/49a2). The GPS signals are used by the radio control panel and navigation unit to calculate the current vehicle position (receiver). In addition, the vehicle's direction of travel is determined with the aid of the sequence of the locations calculated with GPS.

 Possible problems in GPS signal reception

Since GPS operates in the giga hertz (GHz) range (microwaves) and the signals are weak, reception interference can occur as a result of the following events:

- Atmospheric interference, e.g. inclement weather, water vapor, fog

- Multi-path reception due to signal reflections, e.g. from building walls

- Signal blocking, e.g. in built-over areas and in tunnels, through high-rise buildings, trees

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General information on basic position finding

Basic position finding runs parallel to GPS position finding. The radio control panel and navigation unit requires the following data for basic position finding:

- Wheel speed signals

- Distance traveled data

- Vehicle alignment (cardinal points)

- Direction of travel data (forwards or backwards)

Basic position finding function sequence

The radio control panel and navigation unit requires signals from the listed components for basic position finding:

- Left front rpm sensor (L6/1), right front rpm sensor (L6/2), left rear rpm sensor (L6/3), right rear rpm sensor (L6/4), for recording the wheel speed signals in the ESP control unit

- The turn rate sensor (gyro sensor), integrated into the radio control panel and navigation unit, to determine the vehicle alignment (cardinal points)

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- ESP control unit, for recording data on the direction of travel

The radio control panel and navigation unit receives the wheel speed signals from the listed rpm sensors via the following path:

- Direct line

- ESP control unit

- Controller Area Network bus Class C (engine compartment) (CAN-C)

- Central gateway control unit (N93)

- Controller area network bus, class B (interior compartment) (CAN B)

The data of the turn rate sensor (gyro sensor) integrated into the radio control panel and navigation unit is internally forwarded in the radio control panel and navigation unit.

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The data about the direction of travel (forwards or backwards) is received by the radio control panel and navigation unit via the following path:

- Direct line

- ESP control unit

- CAN-C

- Central gateway control unit

- CAN-B

After this the radio control panel and navigation unit uses the distance traveled, the vehicle alignment and the direction of travel to calculate the current vehicle position (degree of longitude and degree of latitude).

The radio control panel and navigation unit receives the steering angle signal from the steering angle sensor (N49) via the following path:

- Steering column tube module (N80)

- CAN-C

- Central gateway control unit

- CAN-B

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 The basic position finding calculation is carried out approx. once per second.

 Error during position finding

Backward roll with "circuit 15 OFF" (ignition switched off), any transport of the vehicle as well as driving in multi-level car parks or underground garages with circular entrances or exits can falsify the basic position finding. In such an event, the deviation is then automatically corrected by the navigation processor integrated into the radio control panel and navigation unit.

Recalibration

Because of the tire abrasion, a constant recalibration of the tire circumference is required. It is carried out automatically and uses the difference between the calculated and actually traveled distance between 2 turning points calculated with the aid of map-based position finding.

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General information on route calculation

Under "Own selection", the following stretches can be excluded from the route calculation:

- Freeway

- Toll road

- Roads requiring toll stickers

- Ferries and vehicle transport

- Tunnels

Route calculation is accomplished using the options set to the best possible extent. If observance of the options is not possible, then the options set are ignored for the sections in question and a message is displayed and signaled audibly. The set criteria and options can be displayed and changed at any time. After a successful calculation, the route is displayed by arrow pictograms and there is an acoustic information output stating "the route is calculated".

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Function sequence for destination-oriented navigation through voice output

The integrated navigation processor continuously compares the route calculation data with the position finding data and uses the data to deduce measures for further destination-oriented navigation. The voice output for destination-oriented navigation is sent to the Media Oriented System Transport (MOST) and then amplified in the amplifier for sound system (N40/3), with code 810 Sound system.

The audio signals reach the following speakers via direct lines:

- Left front door speaker group (H4/1)

- Right front door speaker group (H4/2)

- Center cockpit speaker (centerfill) (H4/27)

 On vehicles without code (810) Sound system, the voice output is performed via the radio control panel and navigation unit using direct lines to the speakers:

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General information on dynamic route guidance

The current traffic situation is taken into consideration in the dynamic route guidance. The incoming information concerning the traffic situation can be received by the radio data system/Traffic Message Channel (RDS/TMC) function via ultra-short wave (FM). The information on the current traffic situation is emitted by a specially equipped broadcasting corporation on an area-related basis via FM. A suitable FM/RDS transmitter must be tuned in. The traffic data recorder decodes the traffic information and forwards it internally to the navigation processor upon request. The navigation processor makes the decision whether the route should be changed.

Function sequence for dynamic route guidance

The FM receiver of the radio control panel and navigation unit receives the traffic messages from the left antenna amplifier module (A2/64) and the right antenna amplifier module (A2/65) (model 211.2 only) and relays it to the traffic data recorder in the radio control panel

and navigation unit.

The traffic messages are stored in the traffic data recorder of the radio control panel and navigation unit and made available to the integrated navigation processor. The voice output for dynamic route guidance is sent to the MOST and then amplified in the sound system amplifier control unit, with code 810 Sound system. The audio signals reach the following speakers via direct lines:

- Left front door speaker group (H4/1)

- Right front door speaker group (H4/2)

- Center cockpit speaker (centerfill) (H4/27)