3.4 ASYNCHRONOUS SENSOR AREA COVERAGE
Ye et al. (2003) proposed probing environment and adaptive sleeping (PEAS), which is a localized threshold-based protocol for dynamically selecting an area-covering set in asynchronous sensor networks. Each sensor is assumed to have the same probing radius p and the same maximum CR, which is also the maximum SR. Initially, all nodes are sleeping and the sleep duration is an exponentially distributed random number. The protocol consists of two phases, probing environment and adaptive sleeping.
When a node A wakes up, it broadcasts a probing message using probing radius p. Any active node receiving the message (that is, active neighbor of A at distance up to p) will send back a reply message to the node. Node A decides to work continuously if it does not hear any reply message from neighbors (this means that there is no active neighbor within distance p of A). Once a sensor decides to be active, it continues to work until it depletes its energy. Otherwise, the node selects a new sleeping duration and goes back to sleep mode. It will wake up at a later predetermined time to reevaluate the decision. In adaptive sleeping phase, each active sensor measures the current accumulated wake-up rates of its sleeping neighbors. The measured rate is included in the reply message, which will be sent back to any probing neighbor. The probing node then adjusts its sleeping time accordingly, with the goal of having a relatively constant wake-up rate. ...