1、Lora AdvantageFeb , 2014 2Semtech ConfidentialA bit of theory Lora is a proprietary spread spectrum modulation scheme, trading data rate against sensitivity.Works much closer to the Shanon theoritical limitBreaks the traditional implemetnation limit of FSK narow band systems 2= 62.5KHz (data rate fr
2、om 150bps to 40kbps )Si4438 (G)FSK very sensitive to frequency tolerance Generally, to make sure sensitivity degrade less than 2dB, frequency tolerance should be within Fdev/4-124dBm500bps sensitivity is NOT possible even with +/-1ppm TCXO! considering 200HZ Fdev, this only exist in the Lab but NOT
3、possible in real world !-114dBm9.6kbps sensitivity at 434/470MHz is achieved with 4.8KHz Fdev, this is only achievable with better than +/-5ppm crystal or TCXO!BOM cost will be high(need TCXO) to “achieve” declared sensitivityTalk points 3 immunity to interference(G)FSKThermal noise floorWanted LORA
4、 signalChannel25dBLORA is technology of spread spectrum, it can work up to 25dB below the noise compared with about 8dB above noise for FSK Bursty interferers tolerated at arbitrary power with 5ms battery life (assume WOR only) with LORA is about 34 times of (G)FSKTalk points 5 Networking long range
5、 with star network is recommended LORA can re-use the same frequency with different SF, Concentrator multiple channel receiving in parallelincrease the capacity of network wide-band spread spectrum technologyLORA is suitable for morevalue added applications : ranging and localization Feb , 2014 14Se
6、mtech ConfidentialLoRa advantages vs DSSS15.4k DSSS PHY vs. LoRaCold StartDSSS: acquisition time can be several seconds at higher SFLoRa : two symbol periodFrequency ToleranceDSSS: 2.5 ppmLoRa: 30 ppm typ.Spectral EfficiencyLoRa is spectrally more efficient that 15.4k DSSSLoRa better sensitivity on
7、a SF per BW basisLora true Constant Envelope ModulationAvailability15.4k DSSS: No single silicon implementation available today (only at system level)LoRa : Available today (SX1272 / SX1276/SX1278)Cost 15.4k DSSS: $LoRa DSS: $Feb , 2014 15Semtech ConfidentialLoRa vs OnRamp DSSSOnRamp uses DSS on top
8、 of a BPSK/QPSK modulation. This has 2 extremely severe drawbacks1) Power consumption issue The transmitter requires an I/Q linear modulator (a 1257 like chip) with poor efficiency compared to a saturated LORA transmitter. This is in essence the same problem than for OFDM or any non-constant envelop
9、e modulation . Because the average output power is not equal to the peak power, the PA cannot be used at its maximum efficiency but must be used with some back-off 99% of the time .2) On ramp is using long DSS spreading codesThis requires very precise frequency alignment of the TX & RX sides. This l
10、ocking and correlation takes a significant amount of time which degrades battery lifetime. Very large chip ( 700 Kgate) which makes end-node very expensive 30 sec cold startNode transmission schedule is fixed (not random) Complex protocol (sold by Onramp) Very power inefficient since Node needs to s
11、tay awake and then transmitting upon request with a non constant envelope modulation Parameter On ramp claim (web site) comment SX1272 Long rangecommentWireless Frequency 2.4 GHz Propagation 915/868 is better by a factor of 4868 -915 MHz 433- 950 available Bandwidth 1 MHz Fixed bandwidth limited num
12、ber of channels (80)User defined BW 100 KHz to 1 MHzModulation DSSS Proprietary ProprietaryTransmit power +30/+20 dBm +30 dBm AP+20/10 Enode+30/+20 dBm PA dependantReceiver sensitivity -142 dBm At 240 bps ! -139dBm 293 Bps at SF 12 125 KHz BWData rate 6 kbps AT 6 Kbps link margin sensitivity is -124
13、 dBm40 Kbps to 300 bpsLatency 3 sec (beaconperiod) Cold start - 30 sec 240 km Theory only Link margin 172dB Between AP at +30 dBm and receiver 172 dB Between AP at +30 dBm and receiverAverage power (sleep) 25w (enode) 72 W(node) 0.2 W typ at 25degCTypical Rx power 530 mW (enode) 300 mW(node) 32mWTyp
14、ical Tx power 1400 mW(enode)20dBm750 mW(node) 170mW 17dBmOperating voltage 2.6 -5.5 v (enode) Low voltage not an option 1.8 to 3.6vAdaptative yes Yes Variable bandwidth, variable sensitivity, variable data rateCost of solution (cost per chip based) X 5 (market input )SOC with Very large chip (On ram
15、p and Maxxim 2830 radio) X 1 Mass market compatible chip few Sq mm2Second source On ramp provides chip set No second source One radio (Maxxim) IP availableConcentrator Multi channel Non YesOnRamp Versus LoRa Feb , 2014 17Semtech ConfidentialIoT Technology Comparison Parameter LoRa Sigfox LTEMFreq 43
16、3/470-510M868M, 902-928M433/470-510M868M, 902-928MLTE BandDatarate 300bps-100kbps 100bps (fixed EU)600bps (fixed USA)20kbpsTX current low low highRX current low (10-12mA) low (10-13mA) moderate (20-30mA)Full 2-Way yes No yesInterference immunitygood (Spread-spectrum w/ FEC)bad (narrow band BPSK)mode
17、rateScalability for capacityyes no ?Localization potentially yes no noMobile/Nomadic NodesYes / Yes No / Yes No / YesComments GW low cost and silicon in productionGW is complex and expensiveDevelopment just startingFeb , 2014 18Semtech ConfidentialLoRa vs Sigfox in North America 900MHzFeature LoRa S
18、igfox CommentMobility 100 km/h No Sigfox requires a 1 second stationary channel so nothing in the path can change eitherPayload 46 Bytes 12 Bytes User data, both have device IDs, etc.Network Sync Not RequiredNot RequiredLink Budget (EU) 156 dB 290 bps156 dB 100 bpsLink Sensitivity(US)-132dBm 970 bps
19、-126dBm 600 bpsLimit of messages per dayNone 140 Up to 10 minute delay for Sigfoxalarms?Max Data Rate 5 Kbps (Upstream)600 bpsFeb , 2014 19Semtech ConfidentialSnapshot of key Metrics RANGE: Cell Range x2 with LoRa (6dB better sensitivity for 30% higher datarate) CAPACITY: 1 LoRa GW has 19 times more
20、 capacity (300k end points at 1 message/hour) Sigfox capacity grows slower than Gateway density. Reality is GW will likely need to be replaced. LoRa capacity grows faster than Gateway density A true DOWNLINKwith LoRaenabling a TRUE Security & Authentication & Configurability: Sigfox downlink very li
21、mited (no broadcast and only for acknowledge) LoRa enables broadcast and individual control at low latencyX2 in Cell radiusLower Cost LoRa GatewayLatencyLoRa SigfoxUplink 0 0 to 10mnDownlink Acknowledge 1sec no downlink dataDownlink Control 10secFeb , 2014 20Semtech ConfidentialLora Modem fits in a
22、Semtech chip Long Range +20 dBm output power, programmable in 1 dB steps -138dBm sensitivity 169 MHz 1020 MHz frequency range w/ 60Hz resolutionLow Current9.3mA RX FSK10mA RX Lora100nA SleepFast wake-up: 100us Sleep to RX/TXRobust Links-12dBm IIP3 69dB adjacent channel rejectionJamming resistantSimu
23、ltaneous channel receptionLow System CostTCXO not required (20-30ppm XTAL)SAW not requiredEliminates repeatersL or ad em odF SK d em odL or am odF SK m odReference document1. AN1200.22 Lora Modulation Basic2. AN1200.13 SX1272/3/6/7/8 Lora modem design guideLoRa Power Consumption and Timing calculati
24、onFeb , 2014 23Semtech ConfidentialSpread SpectrumBW = 125kHzBW = 250kHzBW = 500kHzTechnical information about LoRaFeb , 2014 24Semtech ConfidentialDesigning With LoRaLink BudgetData RateSymbol RateChip RateFeb , 2014 25Semtech ConfidentialDesigning With LoRaLink BudgetData RateBandwidthchips/secChi
25、p RateFeb , 2014 26Semtech ConfidentialForward Error CorrectionLink BudgetData RateSpreading FactorBit Rate:Feb , 2014 27Semtech ConfidentialLoRa Frame LayerLora Packet - Explicit Header ModeHeader is encoded with CR 4 (4/8) payload length : 8bits coding rate : 3 bits CRC enabled 1 bit Reserved 3 bi
26、ts header CRC : 6bitsLora Packet Implicit Header ModeFeb , 2014 28Semtech ConfidentialLoRa in detailsSupported SF are:SF6, SF7, SF8, SF9, SF10, SF11, SF12Supported BW are:7.8kHz, 10.4kHz, 15.6kHz, 20.8kHz, 31.2kHz, 41.7kHz, 62.5kHz, 125kHz, 250kHz, 500kHzSupported CR are:CR1 (4/5), CR2 (4/6), CR3 (4/7) and CR4 (4/8)ISM Frequency Bands:169MHz434MHz470MHz868MHz915MHzPowerFrom -2dBm to 20dBm (PA Boost only, 14dBm on RFO)Feb , 2014 29Semtech ConfidentialLoRa Calculator: Link EngineeringFeb , 2014 30Semtech ConfidentialLoRa Operating Mode
