Sensing tasks are created and maintained in the bubblesensing system through the interaction of a number of virtual roles, where a given physical node can take on one or more virtual role based on its location, device capabilities (e.g., communication mode, sensor), user configuration (when and to what extent resources should be shared for the common good), device state (e.g., an ongoing phone call may preclude taking an audio sample for another application), and device environment (e.g., a picture taken inside the pocket may not be meaningful to the data consumer). In the bubble-sensing system, a task is a tuple (action, region, duration) The action can be any kind of sensing operation such as “take a photo”, or “record a sound/video clip”. The region is defined as the tuple (location, radius), where location is a point in a
coordinate system like GPS indicating the center of the region, and the radius defines the area of the region. We call this region of interest the “sensing bubble”. In the following, we describe each of the virtual roles (i.e., bubble creator, bubble anchor, sensing node, and bubble carrier) in the context of the major system operations: bubble creation, bubble maintenance, bubble restoration.
The bubble creator is the device whose user initiates thesensing request that leads to the creation of the sensing bubble. Generally speaking, there are two ways a bubble can becreated. In the first scenario, the creator is a mobile phone. The phone’s carrier moves to the location of interest and createsthe sensing task. In the second scenario, the creator is any entity that registers a task with the bubble server, but doesinteract with other nodes at the location of interest in support of the sensing. As the process flow for the second case is asubset of the first (c.f. bubble restoration in Section II-D), inthe following we omit any further explicit discussion of the second scenario.
Proceeding with a discussion of the first scenario, weassume the bubble creator is a mobile device at the location of interest with a short range radio for local peer interactions. The creator broadcasts the sensing task using its short range radio.If the user has enabled cellular data access to the backend bubble server, the creator also registers the task with the bubble server. If the creator has localization capability, it populates the region field of the task definition, and the sensing bubble is created with its center at this location. Otherwise, the region field of the task is left blank in the broadcast, and the sensing bubble is created with its center at the current location of the creator where the area of the bubble is determined by its radio transmission range. Note, that if the creator is not able to obtain a location estimate and register its task with the bubble server, it will not be possible to restore the bubble later
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