GPS是怎样工作的-简单易懂的介绍

1、HowGPSWorksOutline•WhatisGPS•HowGPSworks•HowGPScodeswork•WhyIuseGPSformyresearchHowdoyouusethesesatellitestocalculateyourposition?TheGlobalPositioningSystemisaconstellationof31satellitesthatisusedtocalculateyourposition.Insteadofsatellites,letsusetransmittersontheground.GrandJunctionsendsasignaltoRadon’sGPS.Whatkindofsignal?GrandJunctionTransmitterRadoninBoulderitputsthetimeonthesignal.Forthistowork,we’llneedforboththetransmitterandRadontohaveclocks.GPSWhenRadon’sGPSreceivergetsthesignal,hecomp。

2、aresthetimeonthesignalwiththetimeonhisclock.So,aGPSsignaltellsyouhowfaryouarefromthetransmitter.TimeDifference(inseconds)*2.99792458108meters/second=Distance(inmeters)IfthedistancefromtheGPStransmitteris250miles,thatmeansyouaresomewhereonacircleofradius250miles.Nowadda2ndtransmitterinFt.Collins.AndathirdtransmitterinPuebloRadonisattheintersectionofthe3circlesThisonlyworksif:•Youknowwherethetransmittersare.•GPSsignalsalsotransmitthesatellitelocations.•Everyonehasgoodclocks.•TheGPSsatelliteshaveve。

3、rygoodclocks.AGPSusercanusea4thsignaltopiggy-backontotheGPSsatelliteclocks.•Andyoucantellthetransmittersapart.•Thesignalsaremadeinawaysothatyoucantellwhichtransmittersentthem.•Forrealproblems,weusetheintersectionofthreespheres,notthreecircles.IntersectingSpheresButonly1pointisontheEarthWhenGPSreceivesasignal•Itcomparesthatsignalwithalltheknowncodes(therearecurrently37).•Thereceiverdetermineswhichsatelliteitis.•Itdecodesthetiminginformation,multipliesbythespeedoflighttofindtheradiusofthesphere.•O。

4、nceithasdonethatfor3satellites,itcandeterminethelocation.HowdoGPSsignalssendallthisinformation?•Theyusecodes!Binarycodes.•Eachsatellitehasadifferentcode.00001000101001110000111001001000100001000101011000111101110010101101100111101011001011001010011001111110110011110010011001101000111000100100010110001011011100000011011001000100010110100010100100000001111100011000101111101111110011011100101101111000111111010100101000010101001110000110100111011000111101111100001111111111010010010010011001110101011。

5、11100001000101101001111110000100110111100111000110110101101101010000101101001010001010010001110011100010100101110101110101010000010110111001101100110100000000000111011101100011011010101011011000111000110011001111101011111001110101010000011111100100101000000111010001111011010010110110000010010010011000011011000011110111011100011011101101001110010001101010100001101101001011100101111111110110001110000001101110001100000010000000010000011010100010101111011000111011010001100101011111001111010000000110。

6、11110011001110101111000001111011001000100101011100000000100001010101001111101100111011011111100101111000100110101Forexample,herearethefirst1000numbersofthecodeforsatellite11001111011101000100110111111111011110010110111101100110111110101010001111101100011000100110011010000100000101111111000010000110101101011101011010011000001101000011000101010110010001001000001100000111100001110100000111001001110110000000101100111100010010101011111010100111100101111101100101000101110000100111000011111011101011101。

7、01101100111100100110101110010001101101111101100110101110000111010111000110001111000001000111011011100010000011010011001001110000100010111000100100011011111000111010101001100000000110011110011101010000100100011100101010100111001011011111001111111001101001110110011101100101001010011001010111011100111000110111100110000010100011110011011110110011110100110111010011100110101010110100000101110001110001110101100011110001001010011101010110000110001000110010101110011000011111000001111100010010001101000101。

8、000101001001000110000110010000011000110001010000110110010110100110011000101101110011110010001010010100011110011101100001111101100101Thisisthecodeforsatellite6Strategy•FirstweneedtolearnhowGPScreatesthesecodes•Thenweneedtocomeupwithawaytoquicklytellthecodesapart.Howdoyoucreatecodes?•Youusebinaryadditionrules.•0+0=0•1+0=1•0+1=1•1+1=10(butonlyusethelastbit,0)•GPSuses“shiftregisters.”•Themoreshiftregistersyouhave,themorecomplicatedyoucanmakeyourcode.Register1Register2Register3Code111-Startwithall1’s。

9、inyourshiftregistersAddRegister1andRegister3Theanswer0goesintoRegister1andeverythingshiftstotheright.Hereisanexamplewith3shiftregistersForthisexample,1+1=10==0ResultinginRegister1Register2Register3Code111-0111Next0+1=1Register1Register2Register3Code111-01111011After2N-1steps(Nisthenumberofregisters),thecoderepeatsRegister1Register2Register3Code111-0111101101010010100111001110For3shiftregisters,thecoderepeatsafter7steps.RealGPS•Uses10shiftregisters.•Theyadddifferentregisterstoproducethecodesfordi。

10、fferentsatellites.•Satellite1uses2and6.•Satellite2uses3and7,andsoon.•A10-shiftregistercoderepeatsafter210-1,or1023.Howdoyoucomparecodes?100111101110100010011011111111101000010001010011100001110010010001Everytimethenumbersagree,add1.Everytimethenumbersdisagree,subtract1.Thisexample:2differentsatellites10011110111010001001101111111111100001000101001110000111001001000114agree11disagreeTotalscore:3Perfectagreementwouldbe35011000101010110010001001000001100000111100001100010101011001000100100000110000。