Location Systems for Ubiquitous ComputingIntroPhysical Position and Symbolic LocationAbsolute versus Relative positioningLocalized Location ComputationAccuracy and PrecisionScaleRecognitionLimitationsSlide 10Active BadgeActive BatCricketRADARMotionstar Magnetic TrackerEasy LivingSmart FloorEnhanced 911Future WorkChoosing a SystemLocation Systems for Ubiquitous ComputingJeffrey Hightower and Gaetano BorrielloIntroUbiquitous computinga person wanting to know where he was when he did a particular task Help rescue teams Customize environment based on location of user devices have already been developed what they sense and how they go about achieving it•physical attribute used •size•power usage•type of results obtainedPhysical Position and Symbolic LocationPhysical•GPS - 47°39´17’’ N by 122°18´23’’ WSymbolic•Abstract , relative to the position of a known object•Provide coarse grained location information•Derived from Physical-positioning systemsLinking real-time train positions to the reservation and ticketing database can locate a person on a trainAbsolute versus Relative positioningAbsolute location systems – GPS uses a universal reference grid•Two GPS receivers at the same position will show the same readingIn Relative Systems, each receiver has its own frame of reference•Devices that use a particular transmitter form a grid relative to that transmitter Absolute position can be transformed to a relative one – relative to another reference pointLocalized Location ComputationObject we are interested in computes its own location•Ensures privacy•Does not require the object to transmit information for external systems to locate itBurden on the object increases so it is better left to the external systemAccuracy and PrecisionDepend on the distribution of error and the density of elements •Overlapping levels of positioning systems to obtain fine grained location information•Coping dynamically with failures•Suitability for application at handScaleCoverage of system, the number of objects the system can locate per unit area per unit timeCommunication bandwidth is importantIncreasing infrastructureRecognition Recognition of located objects to carry out some action, like controlling the located device over the internetAssigning unique IDs to the located objectsCombine contextual informationLimitationsGPS does not work indoorsInterferenceCharacteristics of underlying technologiesActive BadgeActive BatCricketRADARMotionstar Magnetic TrackerEasy LivingSmart FloorEnhanced 911Active BadgeUses diffuse infrared technology - flooding an area with infra-red lightEach badge emits signal with unique id every 10 seconds that is received by a network of sensorsLocation is symbolic – restricted area like a roomRange of several meters Has difficulty in presence of sunlightActive BatInfers location based on time of flight of ultrasound pulseEach bat emits an ultrasound pulse with unique id to a grid of receiversAt the same instant a controller resets the receiverOrientation is calculated by analysis Distance is computed from the time interval between the reset and receiving the pulseAccurate to within 3cmPagingRequires large sensor infrastructureCricketfixed ultrasound emitters and mobile receiverstime gap to receive the signal is also set in the pulse to prevent reflected beamscomputation takes place at receiverdecentralized architecturefew centimeters of accuracy computational and power burdenRADARBased purely in software, building on standard RF wireless LAN technology Uses signal strength and signal to noise ratio from wireless devices Employs multiple base stations with overlapping coverage Requires wireless LAN support on objects being trackedGeneralization to multifloored buildings is a problemMotionstar Magnetic TrackerUses electromagnetic sensingAxial DC magnetic-field pulses are generatedPosition and orientation are found from by measuring the response on the three axesLess than 1mm spatial resolution and 0.1° orientationMust be within 1-3 meters of transmitterMotion capture for animationEasy LivingSystem to keep track of a room's occupants and devices Uses real-time 3D cameras to provide vision positioning measures location to roughly 10 cm on the ground plane, and it maintains the identity of people based on color histograms Difficult to maintain accuracy Aimed for a home environmentSmart FloorSystem for identifying people based on their footstep force profiles Does not need device or tag93% overall user recognition High cost factorEnhanced 911Locates any phone that makes a 911 callreported in most instances with an accuracy of 100 meters or lessCan be enhanced for use by cell phone usersIdentifying areas of traffic congestionFuture WorkIntegrating multiple systems•Overlapping levels off sensing •Increases accuracyAd Hoc Location sensing•Cluster of ad hoc objects•Relative or absolute•Correlation of multiple measurements•High scalabilityChoosing a SystemAccuracy based comparisonRepresenting error distributionsEvaluationDensity of elementsPrototyping using a simulatorQuake
View Full Document
Unlocking...