Network Computing Laboratory

Radio Interferometric GeolocationRadio Interferometric Geolocation

Miklos Maroti, Peter Volgesi, Sebestyen Dora Branislav Kusy, Gyorgy Balogh, Andras NadasKaroly Molnar, Akos Ledeczi (Vanderbilt Univ.)

2006. 11. 07. Tue.Presentor : Kim, Chanho

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ContentsContents

One Line SummaryIntroductionRIPS (Radio Interferometric Positioning System)

Source of ErrorImplementation IssuesRange CalculationLocalization

ExperimentConclusion

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One Line SummaryOne Line Summary

Introduce novel ranging technique (RIPS) for wireless sensor networks using application of the interference signal

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IntroductionIntroduction

Many application of the WSN require individual nodes’ locationState of Art

Ultrasound method, Ultrasonic method, …Limitation : cannot have adequate accuracy , acceptable range at the same time / work in 2D only

Radio Interferometry High accuracy, long rangeWork in 3D environment

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IntroductionIntroduction

TermsRanging: determine distances between nodesLocalization: find physical 3-D locations of nodesInterference: superposition of two or more waves resulting in a new wave patternInterferometry: cross-correlates a signal from a single source recorded by 2 observers, used in geodesy, astronomy, …

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RIPS RIPS (Radio Interferometric Positioning System)(Radio Interferometric Positioning System)

RIPSno processing power to correlate high freq radio signals in WSN

utilize two transmitters to produce low frequency interference signal directly

Feasible on the highly resource constrained

Achieve high accuracy

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RIPS RIPS (Radio Interferometric Positioning System)(Radio Interferometric Positioning System)

Phase Offset

Caculate dABCD

Localization

CentralLocalizationAlgorithm

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Interferometric PositioningInterferometric Positioning

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Sources of ErrorSources of Error

Carrier Frequency InaccuracyCarrier Frequency Drift and Phase NoiseMultipath effectsAntenna OrientationRSSI measurement delay jitterRSSI Signal-to-Noise RatioSignal Processing ErrorTime Synchronization Error

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RIPS implementation StepsRIPS implementation Steps

1. Selecting a pair of transmitters & scheduling2. Calibration of the radios of senders3. Transmission of a pure sine wave4. Analysis of the RSSI samples of the interference signal at

each of the receivers5. Calculation of the actual dABCD range from the measured rel

ative phase offset6. Localization algorithm

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RIPS Implementation Issue RIPS Implementation Issue (1/2)(1/2)

Radio ChipChipcon CC1000 (433MHz)

Time SynchronizationCrucial Operation : sampling of the RSSI signal (need to be aligned microseconds precision)Using external Synchronization protocol

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RIPS Implementation Issue RIPS Implementation Issue (2/2)(2/2)

TuningTo measure interference accurately

Implement a frequency tuning algorithm

Frequency & Phase estimationRSSI values need to be processed on the motes

SchedulingHigh Level Scheduling

Responsible for selecting the pair of transmitters

Should minimize the number of interference measurement

Low Level Scheduling : Coordinates the activities of the two transmitters and multiple

Frequency tuning algorithm, phase offset estimation requires proper timing

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Range CalculationRange Calculation

Final dABCD = the solution with the minimum error value

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LocalizationLocalization

Use an optimization method based on genetic algorithms (GA)Goal : find the relative positions of the nodesRequirement for this algorithm

Given a set of nodes with unknown locationsA set ‘M’ of dABCD ranges

OutputA node placement represented by a vector of (x,y,z) coordinates

Using genetic operators to fix the error of solutionCrossing overMutations

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ExperimentsExperiments

Setup16 sensor nodes

Area : 18 x 18 meter

3 anchor points

Compare with high resolution DFT-based tone parameter estimation

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ExperimentsExperiments

Error Distribution of all the ranges Calculating dABCD

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ExperimentsExperiments

Error distribution of LocalizationAverage : 3cm

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ConclusionConclusion

Introduce RIPS (Radio Interferometric Position System) which is the novel ranging technique for wireless sensor networks

Achieve high accuracy, long range simultaneouslySupport 3D localization, does not require extra HW or calibration

Key Ideathe application of interference signal