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

Signal Dragging : Effects of Terminal Movement on War-Driving in CDMA/WCDMA Networks. Daehyung Jo MMLab., Seoul National University LNCS 47180211. Table of Contents. 1. Introduction. 2. What is Signal Dragging. 3. Properties and Implications. 4. Technical Reasons.

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

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  1. Signal Dragging: Effects of Terminal Movement on War-Driving in CDMA/WCDMA Networks Daehyung Jo MMLab., Seoul National University LNCS 47180211

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

  3. Introduction • Network-based localization is essential for ubiquitous computing and LBSs • Availability of GPS is limited • Resources for network-based localization • RSS, TOA, TDOA • Cell-ID, antenna orientation and opening • Popular RSS-based localization algorithms • Pattern matching (PM) – scene analysis • Centroid family - lateration • Particle filter – Monte Carlo method • War-driving • Practical signal information collection procedure 3

  4. Signal Pattern Data Measurement area in Seoul, Korea, 25 km2 • Signal pattern is a series of [RSS, BS ID] pairs • Signal pattern data obtained through war-driving • CDMA and WCDMA measurements in Seoul, Korea • WCDMA measurements in Seattle, USA 4

  5. What is Signal Dragging Actual moving direction BS vectors stemming from the terminal to BS Sum of all received BS vectors Reverse of sum vector • A phenomenon • A moving mobile terminal tends to retain signal information of old BSs than newly appearing BSs • Sum of BS vectors = reverse of moving direction 5

  6. Signal Dragging in Real In real circumstances Reverse of sum vector = Estimated direction vector • Signal dragging occurs in cellular networks when the terminal moves fast enough 6

  7. Signal Dragging Error Metric (SDEM) SDEM distribution mean 31.5 degrees mean 72.6 degrees • The average of angular difference between the actual user direction vector and the estimated direction vector • If SDEM is less than 90 degrees • Signal dragging has occurred 7

  8. Table of Contents 1. Introduction 2. What is Signal Dragging 3. Properties and Implications 4. Technical Reasons 5. Conclusion 8

  9. Properties: Correlation with Speed • As the terminal moves faster, the signal dragging becomes more notable • Compute the correlation coefficient between the terminal’s moving speed and (180−SDEM) • Correlation coefficient is 0.48 in a typical straight road • Mean and deviation of the terminal speed in km/h is 31 and 12 each 9

  10. Properties: Direction Change SDEM distribution WCDMA trajectory in Seoul, Korea • Estimated direction arrows converge to the changed direction with some delay • Increase SDEM in curved areas 10

  11. Properties: Arrangement of BSs SEA WCDMA trajectory in Seattle, USA • The arrangement of BSs and the geographical environment affects the efficacy of signal dragging • Fundamental factor to increase SDEM 11

  12. Direction and Arrangement Together Reverse direction Initial direction WCDMA data sets in Seoul, Korea Signal dragging is prevailing in both directions 12

  13. Direction and Arrangement Together Initial direction Reverse direction • Signal dragging hardly occurs due to the uneven arrangement of BSs • Signal pattern is different enough to affect the result of localization performance CDMA data sets in Seoul, Korea 13

  14. Implications: PM 95 percentile errors (m) • PM system compares pattern database or seed with user’s signal pattern or sample • Signal pattern can be different depending on the movement context in war-driving • Different PM results • Potential hint for improvement • Construct pattern DB in diverse movement contexts 14

  15. Implications: Centroid Family 95 percentile errors (m) • Centroid family algorithms do not compare signal patterns • Similar results on both directions • Potential hint for improvement • Cut out unnecessary BS signals if signal dragging prevails 15

  16. Implications: Direction Estimation SDEM mean (median) • The way we calculate SDEM provides the estimation of moving direction • Use only one time signal pattern • We have drawn direction arrows based on the BS vectors stemming from GT • No big difference if we use the resulting position of localization instead of GT 16

  17. Synchronization Pilot set management Idle mode • Synchronization to • newly found BS is • difficult • Pilot signal broadcast • every 26.66 ms • Multipath fading • becomes severe • when moving fast • Pilot channels are • managed by 4 sets • in CDMA • Keep old pilot channel • information longer • Lower its set priority • level when its RSS • is weakened • Operational characteristic • of slotted/DRX mode • Terminal in an idle mode • wakes up periodically • to save its power • Updates its signal pattern • with relatively long • interval Why Signal Dragging Occurs Technical reasons why signal dragging occurs 17

  18. Signal Dragging A phenomenon showing a significant relationship between the signal pattern and the movement context of war-driving Natural phenomenon due to the CDMA/WCDMA mechanism Understanding Signal Pattern PM results can be different depending on the movement context of war-driving Direction context can be extracted naturally Conclusion 18

  19. Thank You ! Questions and Comments?

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