GF82.61-P-2010CWA Position Finding and Destination-Oriented Navigation, Function

GF82.61-P-2010CWA Position Finding And Destination-oriented Navigation, Function
- with CODE (511) Audio 50 APS with DVD changer
- with CODE (525) MB Audio 50 APS radio

Function requirements
^ "Circuit 30 ON" status.
^ Auto pilot system (APS) is authorized and operating free of faults.
^ No fault in Global Positioning System GPS antenna system.
^ Signals are available from at least 3 GPS satellites.
^ Communication with the Electronic Stability Program control unit (N30/4) is free of faults.
^ The trip destination has been entered.
^ Route calculation done.

The position finding and destination-oriented navigation function is divided into the following subareas:
^ GPS position finding
^ Basic position finding
^ Calibration
^ Destination-oriented navigation through voice output
^ Dynamic route guidance

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, 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

Function sequence for GPS position finding
The GPS signals are received by the GPS receiver, which is integrated into the radio with auto pilot system (A2/56), directly from the multifunction antenna (A28/11). From the GPS signals, the radio with auto pilot system then calculates the current position of the vehicle (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

General information on basic position finding
Basic position finding runs parallel to GPS position finding. For basic position finding, the radio with auto pilot system requires the following information:
^ Wheel speed signals
^ Distance traveled data
^ Vehicle alignment (cardinal points)
^ The data for the direction of travel (forward or reverse)

Basic position finding function sequence
For basic position finding, the radio with auto pilot system requires signals from the components listed:
^ Left front axle rpm sensor (L6/1), right front axle rpm sensor (L6/2), left rear axle rpm sensor (L6/3), right rear axle rpm sensor (L6/4), for detecting the wheel speed signals
^ Electronic Stability Program control unit
^ Turn rate sensor (gyro sensor), integrated into the radio with auto pilot system, for determining the vehicle orientation (compass direction)
^ Front SAM control unit with fuse and relay module (N10/1), for detecting data about the direction of travel
^ Steering angle sensor (N49), for detecting the steering angle signals

The radio with auto pilot system receives the wheel speed signals from the rpm sensors listed in the following way:
^ Discrete line
^ Electronic Stability Program control unit
^ Chassis CAN
^ Front SAM control unit with fuse and relay module
^ Interior CAN

The data from the turn rate sensor (gyro sensor) integrated into the radio with auto pilot system is forwarded internally in the radio with auto pilot system.
The data about the direction of travel (forwards or backwards) is received by the radio with auto pilot system in the following way:
^ Front SAM control unit with fuse and relay module
^ Interior CAN

Then, in the radio with auto pilot system, the instantaneous vehicle position (degree of longitude/latitude) is calculated from the travel distance covered and taking into consideration the vehicle orientation as well as the direction of travel.

The steering angle signal is read in by the steering column module control unit (N80) via the chassis CAN to the front SAM control unit with fuse and relay module and via the interior CAN to the radio with auto pilot system.

Calculation of the basic position finding takes approx. 1/s.

Error during position finding
Basic position finding is falsified when a vehicle rolls backwards with "circuit 15 OFF" (ignition switched off) or if it is transported somewhere. In both cases, when the GPS data are received, the deviation is automatically corrected by the navigation processor integrated in the radio with auto pilot system.

Calibration
Wheel calibration is necessary following a tire change. To this end, it is necessary to enter the tire size, e.g. 225/060/016 and the
coding as to whether new (depth of tread approx. 5 to 10 mm) or used tires (depth of tread approx. 3 to 5 mm) have been fitted. The entry is made via STAR DIAGNOSIS or directly at the radio with auto pilot system. A special calibration journey is not required.

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.

General information on route calculation
Under "Own selection", the following stretches can be excluded from the route calculation:
^ Highway
^ Toll road
^ Roads requiring toll stickers
^ Ferries and vehicle transport
^ Tunnel

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".

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 placed on the Media Oriented System Transport (MOST) and then amplified in the sound system amplifier control unit (N40/3) (with code (810) Sound system). The audio signals reach the following speakers via discrete lines:
^ Left front door speaker (H4/1)
^ Right front door speaker (H4/2)
^ Center dashboard speaker (H4/27)

In vehicles except code (810) Sound system, the voice output takes place on discrete lines via the radio with auto pilot system to the following speakers:
^ Left front door speaker
^ Right front door speaker
^ Center instrument panel speaker

The signals are generated by the radio with auto pilot system for visually depicting destination-oriented navigation (map navigation) and transmitted over a low voltage differential signaling (LVDS) line to the Audio/COMAND display (A40/8). The switch-on request for the Audio/COMAND display comes from the radio with auto pilot system via the telematics CAN.

General information on dynamic route guidance
The current traffic situation is taken into consideration in the dynamic route guidance. The incoming information on the traffic situation can be received by the radio data system/Traffic Message Channel (RDS/TMC) function via FM radio. The information on the current traffic situation is sent out 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 in the radio with auto pilot system receives the traffic reports from the rear window antenna FM antenna amplifier (A2/19) and forwards them to the traffic data recorder in the radio with auto pilot system. The traffic reports are stored in the traffic data recorder of the radio with auto pilot system and made available to the integrated navigation processor. The voice output for dynamic route guidance is placed on the MOST and then amplified in the sound system amplifier control unit (with code (810) Sound system). The audio signal reaches the speaker system via discrete lines.

In vehicles except code (810) Sound system, the voice output is processed and amplified within the radio with auto pilot system. The audio signal reaches the speaker system via discrete lines.