Energy Efficient Mechanisms For Wireless Sensor Networks

Wireless sensor network normally consists of a large number of distributed nodes that organize themselves into a multi-hop wireless network. Each node has one or more sensors, embedded processors and low-power radios, and is normally battery operated. Typically, these nodes coordinate to perform a common task. This network has a series of the strengths , for example: it can also be used for emergency search, disaster rescue, military applications , and so forth. Consequently, MSNs takes on widespread application foreground.The severe energy constraints and limited computing resources of the sensors, present major challenges for such a vision to become a reality. We can conclude the dissertation that "Having nodes enter sleep state as often and for as long as possible".In the dissertation we first study the S-MAC that combine the wireless sensor networks characteristic. S-MAC uses three novel techniques to reduce energy consumption and support self -configuration. To reduce energy consumption in listening to an idle channel, nodes periodically sleep. Neighboring nodes form virtual clusters to auto-synchronize on sleep schedules. Inspired by PAMAS, S-MAC also sets the radio to sleep during transmissions of other nodes. Unlike PAMAS, it only uses in-channel signaling. Finally, S-MAC applies message passing to reduce contention latency for sensor-network applications that require store-and-forward processing as data moves through the network. But being a MAC protocol containing fixed duty cycle, S-MAC's performance is not very good for the flow fluctuated with time and location. So the dissertation introduces an adaptive duty cycle in a novel way, that is, duty cycle adapt to the network flow automatically, using time out mechanism to decide the end of the active time dynamically, named as an adaptive Time out MAC. We provide the simulation of the two MAC comparing with CSMA/CA (not comprising duty cycle mechanism), the result show that the adaptive Time out MAC has more perfect performance in the scene of message rate fluctuant with time and location than S-MAC. In stochastically deployed sensor networks, the number of nodes is usually higher than if a deterministic deployment is used. The effort of the dissertation is the heuristics to select mutually exclusive set of sensor nodes that can completely cover the target or monitored area. By maximizing the cardinality of such mutually exclusive sets, we can prolong the sensor network lifetime significantly.