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Sierra Wireless 20070914 Cell Phone User Manual

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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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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