120 20130-101a
GeminiG3 – 700MHz User Manual
32
4.7.4.3 GPS
►
AAVL
The “Autonomous Automatic Vehicle Location” (AAVL) feature adds the ability for GPS-equipped
GeminiG3 units to initiate "Here I am" position message transmissions. AAVL allows the system de-
signer to specify the maximum distance or the time interval between position reports:
If the vehicle moves more than a specified distance since its last report, a new position report will be
generated.
If no report has been sent for a specified amount of time, a new position report will be generated.
AAVL inhibits excessive transmission of reports to prevent network overload.
The “Dynamic Bandwidth Allocation” (DBA) protocol’s “Out Of Band” (OOB) mechanism is used to
deliver these “Automatic Vehicle Location” (AVL) reports.
Figure 25 - GPS - AAVL
Item
Description
MDBR (*2 meters)
MDBR – (Maximum Distance Between Reports)
Distance interval - the vehicle sends a position update each time it has moved this
distance (unless the minimum time interval has not yet elapsed).
The mobile firmware saves the last-transmitted position, and compares it with the
current (latest OOB update) position.
MTBR (*10 seconds)
This parameter controls the “Maximum Time interval between position Reports”.
Thus, the vehicle will send a position update every time “this interval has elapsed”
guaranteeing delivery of position reports at least this often. Data traffic and ACKs
will generate additional reports at shorter intervals.
MRI (*10 seconds)
At most, the vehicle sends a position update every time this interval, in seconds,
has elapsed.
The main purpose of the MRI parameter is to protect the network from being over-
loaded by excessive AVL reporting from one or a few mobiles.