TTS: a two-tiered scheduling mechanism for energy conservation in wireless sensor networks

In this paper, we present a two-tiered scheduling approach for effective energy conservation in wireless sensor networks. The effectiveness of this mechanism relies on dynamically updated two-tiered scheduling architecture. We aim to prolong network lifetime, while preserving the major requirements of wireless sensor networks: coverage and connectivity. In this approach, sensors are periodically scheduled into sleep in two phases using weighted greedy algorithms that can be deployed either centralised or distributed. First, we establish a coverage-tier by selecting a set of sensors that fully covers the sensing field. Thus, sensors that are not selected for the coverage-tier, are put into sleep immediately. However, the coverage-tier sensors do not necessarily stay active all the time when events are not reported. Therefore, a second tier, called connectivity-tier, is formed to deliver data traffic to a sink node. Thus sensors, essential to coverage-tier but not in connectivity-tier may periodically sleep and become active only for sending new sensing measurement and receiving queries from the sink to preserve coverage for energy savings. In addition, periodically rotating the coverage and connectivity tiers is performed in order to maximise network lifetime and achieve fairness of energy consumption. Through extensive simulations in ns2, we demonstrate that the two-tier scheduling can reduce average energy consumption up to 40% while balancing the residual energy of sensors.