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DECODE: Exploiting Shadow Fading to DEtect COMoving Wireless DEvices
December 2009 (vol. 8 no. 12)
pp. 1663-1675
Gayathri Chandrasekaran, WINLAB, Technology Centre of New Jersery, Rutgers and The State University of New Jersey, North Brunswick
Mesut Ali Ergin, WINLAB, Technology Centre of New Jersery, Rutgers and The State University of New Jersey, North Brunswick
Marco Gruteser, WINLAB, Technology Centre of New Jersery, Rutgers and The State University of New Jersey, North Brunswick
Richard P. Martin, Rutgers University, Piscataway
Jie Yang, Stevens Institute of Technology, Hoboken
Yingying Chen, Stevens Institute of Technology, Hoboken
We present the DECODE technique to determine whether a set of transmitters are comoving, i.e., moving together in close proximity. Comovement information can find use in applications ranging from inventory tracking to social network sensing and to optimizing mobile device localization. The positioning errors from indoor RSS-based localization systems tend to be too large, making it difficult to detect whether two devices are moving together based on the interdevice distances. DECODE achieves accurate comovement detection by exploiting the correlations in positioning errors over time. DECODE can not only be implemented in the position space but also in the signal space where a correlation in shadow fading due to objects blocking the path between the transmitter and receiver exists. This technique requires no change in or cooperation from the tracked devices other than sporadic transmission of packets. Using experiments from an office environment, we show that DECODE can achieve near-perfect comovement detection at walking speed mobility using correlation coefficients computed over approximately 60-second time intervals. We further show that DECODE is generic and could accomplish detection for mixed mobile transmitters of different technologies (IEEE 802.11b/g and IEEE 802.15.4), and our results are not very sensitive to the frequency at which transmitters communicate.

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Index Terms:
Comovement, localization, Received Signal Strength Indicator (RSSI), shadow fading, correlation coefficient.
Gayathri Chandrasekaran, Mesut Ali Ergin, Marco Gruteser, Richard P. Martin, Jie Yang, Yingying Chen, "DECODE: Exploiting Shadow Fading to DEtect COMoving Wireless DEvices," IEEE Transactions on Mobile Computing, vol. 8, no. 12, pp. 1663-1675, Dec. 2009, doi:10.1109/TMC.2009.131
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