CricketCricket GoalsFeaturesCricket: Private location-supportFinding the distanceSlide 6Slide 7Location EstimationMultiple BeaconsSolutionBounding Stray Signal InterferenceSlide 13Bounding stray signal interferenceProblem: Closest Beacon May Not Reflect Correct SpaceCorrect Beacon PlacementImplementationCricket v1 PrototypeCricket Beacon LEDsCricket Beacon AntennasListener LEDsSoftware ComponentscricketdCricket Listener OutputSpeed of SoundSo where are you?So whre are you?Two beaconsOrientationHardware DesignMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial CricketTutorial on using cricket location systemMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 2Cricket GoalsResearch prototypebuild and then evaluateUseful mainly indoor environmentswalls, ceilings not too farRecognize spaces, not just physical positiongood boundary detection is importantdoors, floors, etc.Preserve user’s privacyBig-brother can be a botheruser has choice to reveal locationMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 3FeaturesDistributed architectureNo wired infrastructureEasy deployment (no satellites)Low maintenance Users are not trackedListeners are passiveLarge number of listeners w/o interferenceIntegrates with a wide range of resource discovery systemsMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial Cricket: Private location-supportBeaconListenerspace = “a1”space = “a2”Pick nearest to infer spaceNo central beacon control or location databasePassive Listeners + Active BeaconsMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 5Finding the distance distance = speed * timewant to find the distancewe know the speedHow do we figure out time?Radar: measure round-trip timecannot use it as it violates some goalsMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 6Finding the distanceSynchronized clocksreceiver knows exactly when transmitter sent signalhow about sending signal first to sync clocks and then 2nd signal?MIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 7Finding the distanceUse two different speed signalsboth start at same time d = s1 * t1 d = s2 * t2 We measure delay: m = t1 - t2 t2 = m * s1/(s2 - s1) d = m * s2 s1 /(s2 - s1)MIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 8Location Estimation• Distance estimation via coupled RF and ultrasonic signals– Beacons send information on the RF channel with concurrent ultrasonic pulseRF infoBeaconListenerUltrasound(pulse)MIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 10Multiple Beacons• Beacon transmissions are uncoordinated• Ultrasonic signals reflect heavily• Ultrasonic signals are pulses (no data)These make the correlation problem hard and can lead to incorrect distance estimatesBeacon ABeacon BtRF B RF A US BUS AIncorrect distanceListenerMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 11SolutionCarrier-sense + randomized transmissionreduce chance of concurrent beaconsBounding stray signal interferenceenvelop all ultrasonic signals with RFListener inference algorithmProcessing distance samples to estimate locationMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 12Bounding Stray Signal Interference• Engineer RF range to be larger than ultrasonic range– Ensures that if listener can hear ultrasound, corresponding RF will also be heardtRF A US AMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 13Bounding Stray Signal InterferencetS/br/v (max)S = size of space advertisementb = RF bit rater = ultrasound rangev = velocity of ultrasound (RF transmission time) (Max. RF-US separation at the listener)S rb v• No “unaccompanied” ultrasonic signal can be valid!MIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 14Bounding stray signal interference• Envelop ultrasound by RF• Interfering ultrasound causes RF signals to collide• Listener does a block parity error check– The reading is discarded...tRF A US ARF B US BMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 15Problem: Closest Beacon May Not Reflect Correct SpaceI am atBRoom A Room BMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 16Correct Beacon PlacementRoom A Room Bx xI am atA• Position beacons to detect the boundary• Multiple Beacons per space are possibleMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 17Implementation• Cricket beacon and listenerMicro-controllerRFUSMicro-controllerRFUSRS232MIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 18Cricket v1 PrototypeUltrasonicsensorRF antennaRF module (rcv)AtmelprocessorListener BeaconRF module (xmit)RS232i/fMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 20Cricket Beacon LEDsDebug Switch = UPGreen LED = TransmitRed LED = Carried SensedDebug Switch = DownGreen LED = Every 5th transmissionAt StartupLEDs flash version numberRed on, Green flash count = Major #Green on, Red flash count = Minor #Power SwitchUp = OnPowerSwitchOnOfDebug SwitchBeacon IDMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 21Cricket Beacon AntennasReceive AntennaFor sensing transmission of other beaconsTransmit AntennaLimit transmission distanceShould not touch ultrasoundShould not cover receive antennaTransmit antennaReceive antennaMIT 6.893; SMA 5508 Spring 2004 Larry Rudolph Lecture Cricket tutorial 22Listener LEDsGreen FlashReceived valid RF and ultrasoundRed Flash OnceReceived Radio, but not ultrasoundRed+Green FlashRF Error (e.g., parity error)Red and Green always onListener not working
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