Automatic Vehicle Location (AVL)
Introduction
Automatic Vehicle Location (AVL) sometimes also referred to as Automatic Person Location (APL) is used to track and trace persons or vehicles using TETRA radios. Most TETRA radios are equipped with a integrated GPS receiver. The TETRA radio is able to determine its location and can send this information to the TETRA infrastructure were it can be forwarded to an end point which is in most cases a control room.
End user perspective
From the vehicle that is equipped with the TETRA radio or the person this is wearing the TETRA radio not much is noted on the radio itself. No interaction is needed. In most cases the GPS receiver is enabled when the radio is powered on. The benifit is for the dispatching centre that is now aware of the location of the vehicle or person. This information can be used to efficient dispatch the person or vehicle.
Technical
The TETRA radio needs to be equipped with a GPS receiver to be able to obtions its location. The locations is sent via a SDS or packet data to an AVL server. The AVL system may be a fixed host in the TETRA network or a server connected to the PEI of a TETRA radio. The radio needs be have the destination address (ISSI) of the AVL system pre-programmed. It is common that the TETRA radio sends the location message as a LIP (Location Information Protocol) to the AVLS server. The LIP protocol is an ETSI standardised protocol for location information. The control room(s) connect to the AVL server to obtain the location information of the TETRA mobile radios and display their locations on a map. The connection between the control room(s) and AVL server is usually a proprietary protocol.