Lora-技术介绍

LoraAdvantageFeb,20142SemtechConfidentialAbitoftheory
Lora™isaproprietaryspreadspectrummodulationscheme,tradingdatarateagainstsensitivity.WorksmuchclosertotheShanontheoriticallimitBreaksthetraditionalimplemetnationlimitofFSKnarowbandsystems21kbps10kbps250kbps1MbpsDatarateSensitivity*-150dBm-100dBm-90dBm-125dBm*SensitivityisDatarateandBWdependantFeb,20143SemtechConfidentialAdvantages
Demodulatebelownoisefloor
BettersensitivitythanFSK(betterEb/No)
Morerobusttointerference,noise,andjamming
SimultaneousoccupationonasinglechannelifspreadingfactorisdifferentLoRaisaspreadspectrumbasedmodulationBenefitsofspreadspectrummodulations?Feb,20144SemtechConfidentialHowdifferentisLora™fromDSSS?
Lora™isdesignedforlowdataratescomparedtootherDSSSsystems(CDMA,Wifi…)
Lora™isusinghighspreadingfactorsallowinglargeprocessinggainsmoreorlesslikeGPStechnology
Lora™iscapableof«onthefly»demodulationAsopposedtotraditionnalDSSSsystemslikeGPSMakesLora™verysuitableforlowpoweroperation
Lora™isnonsensitivetofrequencyoffsetsBasic+/-30ppmcrystalissufficientformostapplicationsOthersystemsusinglongspreadingfactors(GPS..)dorequireveryprecisetimereference
Lora™isimplementedinasmartwayEntiredemodulationengineiscontainedin50KgatesFeb,20145SemtechConfidentialLoRaadvantagesvsFSK
15.4kFSKPHYvs.LoRa
SpreadingGainFSK:I/QbasebandprocessingrequiredtoachieveprocessinggainLoRa:Processinggaininherenttomodulationscheme
BlockingInterferenceFSK:Intoleranttoin-bandinterferersLoRa:Toleranttoblockinginterferers:50%blockerreducessensitivityby3dB
FrequencyToleranceNBFSK:willrequireTCXO/high-toleranceXTALand/orAFCLoRa:Frequencyoffsettolerant(±30ppmtypical)Feb,20146SemtechConfidentialQuicklookatSX1276/8LoraandFSK
LORA--NewtechnologybasedonspreadspectrumSX1276/8:SupportbothLORAmodulationandtraditional(G)FSK,OOKSi4438/CC1125:traditional(G)FSK,OOKonly
BriefComparisonofKeyperformanceFeb,20147SemtechConfidential10310410595100105110115120125130135140145bits/secsensitivity(dBm)Talkpoints1–sensitivityimprovementSX1276/8LORAIndustryBestinclassGFSKSX1276/8GFSKShannoncapacityboundary
SensitivityofSX1276/8isabout10dBbetterthanSi4438+TCXORangeTestincityenvironment–10dBmeansabout3times•SameTXpower(+17dBm)–470MHzAMRbandofChina•transmitterisplacedintheoffice•Similardata-rateFeb,20149SemtechConfidentialTalkpoints2–sensitivityVSfrequencytolerance9
SX1276/8LORA–NOTsensitivetofrequencytolerance-136dBm@500bps(BW125_SF11)sensitivitycanbeeasilyachievedwith+/-30ppmcrystalNOneedtouseTCXOwithBW=62.5KHz(dataratefrom150bpsto40kbps)
Si4438(G)FSK–verysensitivetofrequencytoleranceGenerally,tomakesuresensitivitydegradelessthan2dB,frequencytoleranceshouldbewithinFdev/4-124dBm@500bpssensitivityisNOTpossibleevenwith+/-1ppmTCXO!–considering200HZFdev,thisonlyexistintheLabbutNOTpossibleinrealworld!-114dBm@9.6kbpssensitivityat434/470MHzisachievedwith4.8KHzFdev,thisisonlyachievablewithbetterthan+/-5ppmcrystalorTCXO!BOMcostwillbehigh(needTCXO)to“achieve”declaredsensitivityTalkpoints3–immunitytointerference(G)FSKThermalnoisefloorWantedLORAsignalChannel25dBLORAistechnologyofspreadspectrum,itcanworkupto25dBbelowthenoisecomparedwithabout8dBabovenoiseforFSKBurstyinterfererstoleratedatarbitrarypowerwith3dBsensitivitydegradationif:•burstlengthhalfLORAsymbollength•interfererdutycycle50%Feb,201411SemtechConfidentialInterferenceImmunity
Co-channelinterferenceperformanceanderrorcorrectiongiveLoRalicensedbandQOS
MultiplechannelsandnetworkmanagementatserverallowforadditionaloradaptiveQOSfeaturesTalkpoints4–WORandCurrentConsumption•WOR(WakeonRadio)iswidelyusedforpowersavingwithwhichchipwillgotoreceivermodeperiodicallytodetectwhetherthereiswake-upsignal/preamble•SX1276/8haveaspecialCADmode–candetectwhetherthereisLORApreamble(withconfiguredparameters)inanultrashortslot–1.5~2symbolsonly•LORA:CADonlylastfor~2symbols(125KHz_SF7_CR4/5,5.47kbps,1symbol=1ms)FSK:withsamedata-rate,assume3bytespreambleforsyncanddetection–RXwindowneed5ms•batterylife(assumeWORonly)withLORAisabout3~4timesof(G)FSKTalkpoints5–Networking•longrangewithstarnetworkisrecommended•LORAcanre-usethesamefrequencywithdifferentSF,Concentratormultiplechannelreceivinginparallelincreasethecapacityofnetwork•wide-bandspreadspectrumtechnology—LORAissuitableformorevalueaddedapplications:rangingandlocalization•…Feb,201414SemtechConfidentialLoRaadvantagesvsDSSS
15.4kDSSSPHYvs.LoRa
ColdStartDSSS:acquisitiontimecanbeseveralsecondsathigherSFLoRa:twosymbolperiod
FrequencyToleranceDSSS:±2.5ppmLoRa:±30ppmtyp.
SpectralEfficiencyLoRaisspectrallymoreefficientthat15.4kDSSSLoRabettersensitivityonaSFperBWbasisLoratrueConstantEnvelopeModulation
Availability15.4kDSSS:Nosinglesiliconimplementationavailabletoday(onlyatsystemlevel)LoRa:Availabletoday(SX1272/SX1276/SX1278)
Cost15.4kDSSS:$$LoRaDSS:$Feb,201415SemtechConfidentialLoRavsOnRampDSSS
OnRampusesDSSontopofaBPSK/QPSKmodulation.Thishas2extremelyseveredrawbacks
1)PowerconsumptionissueThetransmitterrequiresanI/Qlinearmodulator(a1257likechip)withpoorefficiencycomparedtoasaturatedLORAtransmitter.This