Energy management in sensor networks is crucial to prolong the network lifetime. Though existing sleep scheduling algorithms save energy, they lead to a large increase in end-to-end latency. We propose a new Sleep schedule (Q-MAC) for Query based sensor networks that provides minimum end-to-end latency with energy efficient data transmission.Whenever there is no query, the radios of the nodes sleep more using a static schedule. Whenever a query is initiated, the sleep schedule is changed dynamically. Based on the destination's location and packet transmission time, we predict the data arrival time and retain the radio of a particular node, which has forwarded the query packet, in the active state until the data packets are forwarded. Since our dynamic schedule alters the active period of the intermediate nodes in advance by predicting the packet arrival time, data is transmitted to the sink with low end-to-end latency.The objectives of our protocol are to (1) minimize the end-to-end latency by alerting the intermediate nodes in advance using the dynamic schedule (2) reduce energy consumption by activating the neighbor nodes only when packets (query and data) are transmitted. Simulation results show that Q-MAC performs better than S-MAC by reducing the latency up to 80% with minimum energy consumption.

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Target tracking sensor networks monitor and track the movement of a target object. Energy management in these sensor networks is crucial to prolong the network lifetime. We propose a new protocol EST (Energy saving Schedule for Target tracking sensor networks) that provides a dynamic sleep schedule for the radios such that maximum energy is saved without affecting the sensors' activities. When there is no target, the communication modules of sensor nodes are put into sleep using a static schedule, except the border nodes. Interior nodes do not perform the sensing activity in the surveillance state. If a target arrives, the sleep schedule for the radios is changed dynamically in order to send the arrival message to neighboring sensors. By receiving the arrival message, the sleeping neighbor nodes start sensing. The objectives of our protocol are to (1) balance the lifetime of all the sensor nodes in the network to increase the network lifetime (2) reduce the energy consumption by activating the sensors only when the target arrives in that region. Simulation results show that EST provides a significant amount of energy savings and potentially increases the network lifetime by 25% more than S-MAC at low load.

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