User Guide

Global Positioning System (GPS)
Rev 3.0B Feb.08 84
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 X may encounter “GPS drift”. The PinPoint X may report it is
in a location a few feet from its actual location because it does not
employ differential GPS.
PinPoint X Supported Protocols
ThePinPointX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ap pli
‐
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.