Signal Dragging: Effects of Terminal Movement on War-Driving in CDMA/WCDMA Networks

Daehyung JoMMLab., Seoul National University

LNCS 47180211

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Table of Contents 1. Introduction 2. What is Signal Dragging 3. Properties and Implications 5. Conclusion 4. Technical Reasons2

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IntroductionNetwork-based localization is essential for ubiquitous computing and LBSsAvailability of GPS is limitedResources for network-based localizationRSS, TOA, TDOACell-ID, antenna orientation and openingPopular RSS-based localization algorithmsPattern matching (PM) scene analysisCentroid family - laterationParticle filter Monte Carlo methodWar-drivingPractical signal information collection procedure3

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Signal Pattern DataSignal pattern is a series of [RSS, BS ID] pairsSignal pattern data obtained through war-drivingCDMA and WCDMA measurements in Seoul, KoreaWCDMA measurements in Seattle, USA

Measurement area in Seoul, Korea, 25 km24

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What is Signal DraggingA phenomenonA moving mobile terminal tends to retain signal information of old BSs than newly appearing BSsSum of BS vectors = reverse of moving directionBS vectors stemming fromthe terminal to BSSum of all receivedBS vectorsReverse of sum vectorActual moving direction5

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Signal Dragging in RealSignal dragging occurs in cellular networks when the terminal moves fast enough

In real circumstancesReverse of sum vector= Estimated direction vector6

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Signal Dragging Error Metric (SDEM)The average of angular difference between the actual user direction vector and the estimated direction vectorIf SDEM is less than 90 degreesSignal dragging has occurredmean 31.5 degreesmean 72.6 degreesSDEM distribution7

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Table of Contents 1. Introduction 2. What is Signal Dragging 3. Properties and Implications 5. Conclusion 4. Technical Reasons8

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Properties: Correlation with SpeedAs the terminal moves faster, the signal dragging becomes more notable

Compute the correlation coefficient between the terminals moving speed and (180SDEM)Correlation coefficient is 0.48 in a typical straight roadMean and deviation of the terminal speed in km/h is 31 and 12 each

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Properties: Direction ChangeEstimated direction arrows converge to the changed direction with some delayIncrease SDEM in curved areasWCDMA trajectory in Seoul, KoreaSDEM distribution10

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Properties: Arrangement of BSsThe arrangement of BSs and the geographical environment affects the efficacy of signal draggingFundamental factor to increase SDEMWCDMA trajectory in Seattle, USASEA11

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Direction and Arrangement TogetherSignal dragging is prevailing in both directionsWCDMA data sets in Seoul, Korea12

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Direction and Arrangement TogetherSignal dragging hardly occurs due to the uneven arrangement of BSsSignal pattern is different enough to affect the result of localization performanceCDMA data sets in Seoul, Korea13

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Implications: PMPM system compares pattern database or seed with users signal pattern or sampleSignal pattern can be different depending on the movement context in war-drivingDifferent PM resultsPotential hint for improvementConstruct pattern DB in diverse movement contexts95 percentile errors (m)14

Seed by SampleWCDMACDMAInitial by Initial97.8786.71Initial by Reverse202.80197.33Reverse by Reverse54.8674.58Reverse by Initial115.30271.21

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Implications: Centroid FamilyCentroid family algorithms do not compare signal patternsSimilar results on both directionsPotential hint for improvementCut out unnecessary BS signals if signal dragging prevails95 percentile errors (m)15

DataCentroidWeighted CentroidCell IDWCDMA initial325.37454.44462.85WCDMA reverse326.56427.62527.01CDMA initial2103.77412.15274.16CDMA reverse1623.28502.55335.13

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Implications: Direction EstimationThe way we calculate SDEM provides the estimation of moving directionUse only one time signal patternWe have drawn direction arrows based on the BS vectors stemming from GTNo big difference if we use the resulting position of localization instead of GT

SDEM mean (median)16

AreaGT basedWC based72.6 (64.0)73.9 (65.6)

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Why Signal Dragging OccursTechnical reasons why signal dragging occurs17

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ConclusionSignal DraggingA phenomenon showing a significant relationship between the signal pattern and the movement context of war-drivingNatural phenomenon due to the CDMA/WCDMA mechanism

Understanding Signal PatternPM results can be different depending on the movement context of war-drivingDirection context can be extracted naturally

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********The remaining parts are about the properties ..***********