Unlike traditional opportunistic networks characterized by relatively very short connectivity period among mobile devices during their contacts, in this paper, we explicitly consider the underground/bus scenario where the inherited structured mobility pattern enforces more stable passenger behaviors. If with the aid of potential formation of Bluetooth-enabled multi-hop wireless networks, one can expect a type of new emerging applications for passengers on the move. In particular, we conducted a thorough experimental study on passenger dynamics and connectivities in Beijing Underground during peak hours, via building an information collection application in an Android-based smartphone. From the total of 41,806 records for 120 days, we have performed extensive analysis on a variety of statistics for the number of neighbors, the lifetime of the neighbors, the received signal strength indicator (RSSI) and its derived physical distance, flow speed of the nearby passengers, battery usage rate, etc. Then, we further prove our justification that Bluetooth is the perfect technology to build up a relatively small multi-hop wireless network with the network size of four nodes, and in particular it is applicable and may fundamentally drive new applications in an underground environment during the peak hour, where two notable examples are music album sharing and neighborhood gaming.
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