We present the DECODE technique to determine from a remote receiver whether a set of transmitters are co-moving, i.e., moving together in close proximity. Co-movement information can find use in applications ranging from inventory tracking, to social network sensing, and to optimizing mobile device localization. DECODE detects comoving transmitters by identifying correlations in communication signal strength due to shadow fading. Unlike localization systems, it can operate using measurements

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... m only a single receiver. It requires no changes 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.