TTS: A Two-Tiered Scheduling Algorithm for Effective Energy Conservation in Wireless Sensor Networks

In this paper, we present a two-tiered scheduling scheme that provides effective energy conservation in wireless sensor networks. The effectiveness of this scheme 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 to sleep in two phases using weighted greedy algorithms. First, we establish a coverage-tier by selecting a set of sensors that covers the sensing field in order to provide fully monitoring of entire field. Sensors that are not selected for the coverage-tier, are put into sleep immediately. Then, a second tier, called connectivity-tier, is formed on top of the coverage-tier to forward the data traffic to 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 query from the sink to preserve coverage. By this way, we may allow more nodes to sleep with different sleeping behaviors, i.e., continuous sleep or periodic sleep/active. Moreover, fair energy consumption among sensors is achieved by periodically rotating the coverage and connectivity tiers. 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.