u-blox ANTARIS 4 - Acquisition


your position is our focus
4.4.6 How to change between protocols
1. Reconfiguringaportfromoneprotocoltoanotherisatwo-stepprocess.Firstofall,oneneedstoassignthe
oneachport.
4.5 Acquisition
At system power up the ANTARIS
®
4 GPS Software executes the initial acquisition code. This part of the GPS
Softwaredefinesthreedifferentstrategies:
• Coldstart
• Warmstart
• Hotstart
Dependingontheamountofvalidorbitalinformationavailable,thereceiverchoosesthefastestpossiblestartup
scenario.Beforethereceivercancalculateapositionfixitmustmust
acquireandtrackGPSsignals.
Acquisitionistheprocessof‘locking’ontothesignal.TheSVsearchandacquisitiontimehighlydependsonthe
hsignallevelsarepreferred.
Afteracquisition,the receiver willhave tosynchronize tothe datastream, anddownloadorbitdatafrom
the
ded.
gis Iforbitdatahasbeendownloaded
before,andthereceiveriscalculatingpositionfixes,itcancontinuetodosoevenwhenthesignallevelfalls
below
theminimumsignallevelthatwouldberequiredfordatadecoding.
preferred protocol(s) to a port. One port can handle several protocols at the same time (e.g. NMEA and
UBX).Bydefault,allportsareconfiguredforUBXandNMEAprotocol
soinmostcases,it’snotnecessaryto
changetheportsettingsatall(UBX-CFG-PRTor"PUBX,41"messages).
2. Activatecertainmessages
signallevel.Forbestperformancehig
50Bits/sdatastream.This canonlybedonedownto acertainsignallevel(~25-30dBHz).If thesignallevelfalls
below thatthreshold, downloadingdata is halted,and can onlybe resumedonce thesignal level is abovethe
threshold, again. A firstposition fix can only be achieved
if orbit data for a sufficient number of satellites has
beendeco
Trackin theprocessofmaintaininglockonapreviouslyacquiredsignal.
Minimum Acquisition Time
depends on Signal Level
Acquisition
Sync/
Confirm
Download
Ephemeris
Tracking
typ : 27 secs
18..36 secs
Start
Receiver
First
Position
Time
(TTFF)
C
hann
el
s
velMinimal Signal Le
Minimum Sync/ Download Level
~25.30 dBHz, continously
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Figure 73: GPS Signal Acquisition
4.5.1 Coldstart Strategy
InColdstart,thereceiversearchesallvalidSVnumbers,from1 to32,inapredefinedorder.AssoonasSVsare
found, they are transferred to tracking and ephemeris decoding starts. This process takes between 18 to 36
wi
Once
there tSVswithvalidephemeris,positionfixesarecalculatedandoutput.
seconds thgoodskyview,butcantakemuchlongerotherwise.
aresufficien
GPSModules-SystemIntegrationManual(SIM)(incl.ReferenceDesign) ReceiverDescription
GPS.G4-MS4-05007-A1
  Page 89