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

GF82.61-P-2010CW Position Finding And Destination-oriented Navigation, Function
- with CODE (527) COMAND APS with single DVD drive (with navigation)
- with CODE (512) COMAND APS with DVD changer

Function requirements for Global Positioning System (GPS)
position finding
^ "Circuit 30 ON" status.
^ The Cockpit Management and Data System (COMAND) is authorized and working correctly.
^ No errors in the GPS antenna system.
^ Signals 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
^ Destination-oriented navigation through driving lane recommendations
^ Map function

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. A vital precondition is the synchronicity of the clocks in the satellites and in 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
GPS signals are received by the GPS receiver integrated into the COMAND controller unit (A40/3), directly from the multifunction antenna (A28/11). The GPS signals are used by the COMAND controller 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.

General information on basic position finding
Basic position finding runs parallel to GPS position finding. For basic position finding the COMAND controller unit 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 COMAND controller unit requires signals from the following components:
^ 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 COMAND controller unit, 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 wheel speed signals are received by the COMAND controller unit from the listed rpm sensors 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 turn rate sensor (gyro sensor) data in the COMAND controller unit are forwarded within the COMAND controller unit.

The data about the direction of travel (forwards or backwards) is received by the COMAND controller unit in the following way:
^ Front SAM control unit with fuse and relay module
^ Interior CAN

After this the COMAND controller unit uses the distance traveled, the vehicle alignment and the direction of travel to calculate the vehicle position (degree of longitude and degree of latitude) at any given time.
The steering angle signal is read in by the control unit for the steering column module (N80), and forwarded over the chassis CAN to the front SAM control unit with fuse and relay module and over the interior CAN to the COMAND controller unit.

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 instances the deviation is automatically corrected by the COMAND controller unit's integrated navigation processor upon reception of GPS data.

Calibration
Wheel calibration is necessary following a tire change. To this end, the tire size, and coding, whether new (tread depth approx. 5 to 10 mm) or used tires (tread depth approx. 3 to 5 mm) are mounted have to be entered. The entry is made using STAR DIAGNOSIS or directly on the COMAND controller unit. 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.

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 route calculation
Under "Own selection", the following stretches can be excluded from the route calculation:
^ Highway
^ Ferries and vehicle transport
^ Tunnel

For vehicles except code (494) USA version, additional stretches can be excluded from the route calculation:
^ Toll road
^ Roads requiring toll stickers

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 on the map and this information is then relayed acoustically -"Route 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 signal reaches the following speakers over discrete lines.
^ Left front door speaker (H4/1)
^ Right front door speaker (H4/2)
^ Center instrument panel speaker (H4/27)

For vehicles except code (810) Sound system, voice output takes place directly over the COMAND controller unit through discrete lines at the following speakers:
^ Left front door speaker
^ Right front door speaker
^ Center instrument panel speaker

The signals for destination-oriented navigation visual display (map navigation) are generated by the COMAND controller unit and forwarded over a low voltage differential signaling (LVDS) line to the Audio/COMAND display (A40/8). The Audio/COMAND display switch-on request is generated by the COMAND controller unit over the telematics CAN.

General information on dynamic route guidance (for vehicles except code (494) USA version)
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. If necessary, a message that the route should be changed is output via the vehicle speaker.

Function sequence for dynamic route guidance (for vehicles except code (494) USA version)
The FM receiver in the COMAND controller unit receives the traffic messages from the antenna amplifier for the rear window FM antenna (A2/19) and forwards them to the traffic data recorder in the COMAND controller unit. The traffic messages are stored in the traffic data recorder of the COMAND controller unit and made available to the integrated navigation processor. The voice output for dynamic route guidance is placed on the MOST ring 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.

Destination-oriented navigation through driving lane recommendations
For certain turnoff situations on multiple-land exit points (e.g. freeway intersection) driving lane recommendations are shown in the bottom line. Along with a turnoff recommendation, the distance to the actual turnoff point is also displayed by means of a bar graph.

The lanes have arrows assigned to them, which indicate on which lane the destination can be reached or the best way to reach it. The following colors are valid for representation on the Audio/ COMAND display:
Midnight blue: The best or recommended lane.
Light blue: The lane is correct, but a lane change will soon be required.
Gray: This lane will not take you to the destination.

The instrument cluster (A1) only displays the midnight blue arrows.

Map function
Map display is always controlled by the COMAND controller unit. The following display functions are supported:
^ Destination-oriented navigation map
^ positioning map
^ Route map
^ Scrollable map
^ Destination entry map