Global Positioning System (GPS)
from the difference between local time and the time the satellite signals were sent (this distance is called psuedoorange). The locations of the satellites are decoded from their radio signals and a database internal to the receiver. This process yields the location of the receiver. Getting positioning information from fewer than four satellites, using imprecise time, using satellites too closely positioned together, or using satellites too close to the Earth’s curve will yield inaccurate data.
The GPS data is then transmitted to a central location which uses a tracking application to compile information about location, movement rates, and other pertinent data.
Note: Depending on the location of the satellites in relation to the modem’s location and how many signals are being received, the
PinPoint-E Supported Protocols
The PinPoint‐E supports three different GPS reporting protocols.
Remote Access Protocol (RAP)
The Remote Access Protocol (RAP) is a proprietary binary message format developed by Sierra Wireless AirLink Solutions. RAP was originally designed to work specifically with AirLink Tracking System (ATS), but other 3rd party appli‐ cations have been developed to take advantage of the RAP messaging format.
In the original RAP, a PinPoint line modem uses the UDP (User
Datagram Protocol) to communicate with the host server.
In RAP‐based AVL, each PinPoint line device sends its command status and responses to the Host server and the Host sends commands to one or more PinPoint line devices. For reliability, the Host expects each command to be acknowl‐ edged within a time‐out period. If the acknowledgement packet (ACK) is not received within the time‐out period, the Host will retransmit the command.
The RAP messages are in Hex and are referred to by their message ID. Reports can include GPS data alone, as well as GPS data with the date and time, radio frequency data, and state changes of I/O as well as sending reports based on power states.
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