Energy-efficient interference-free link scheduling in wireless sensor networks

Wireless sensor networks (WSNs) consist of thousands of tiny, inexpensive and lowpower sensor nodes that perform collaborative tasks and organize themselves into multihop networks. These sensor nodes are deployed over a given area, including both the terrestrial and underwater environments. Consequently, WSNs can be divided into terrestrial wireless sensor networks (TWSNs) and underwater wireless sensor networks (UWSNs). In this thesis, we mainly focus on the design of energy-efficient interferencefree link schedulings in WSNs. In a link scheduling, each transmission link is assigned a set of time slots such that it can transmit without interferences. In TWSNs, sensor nodes use radio waves to communicate, and the major source of energy wastage is the idle listening state in the radio modules. To reduce the energy consumption, sensors are generally scheduled to sleep when the radio is not in use. In a traditional sleep scheduling, however, sensors have to start up numerous times in a period, and thus consume extra energy due to the state transitions (e.g. from the sleep state to the listening state or transmitting state). We first identify a novel energy-efficient interference-free link scheduling problem called contiguous link scheduling, in which links incident to one node are scheduled together to obtain consecutive time slots so that the node needs to start up only once to monitor the channel in a period. We prove that the problem is NP-complete, and propose efficient centralized and distributed algorithms that use time slots at most a constant factor of the optimum in both homogeneous and