Trail-based Location Service In Wireless Sensor Networks

In wireless sensor networks(WSN),when events of interest are detected,the sensor nodes should generate a packet including the event report and transmit it to the sink nodes.The sink nodes are equipment or personnel with intelligent terminals.When the sink nodes are mobile nodes,their current locations are usually unavailable for the sensor nodes.How to transmit the packet to the mobile sink nodes becomes a challenging issue.Location service is a popular solution to solve mobility problem of sink nodes.In location service,some sensor nodes are selected as location servers to connect sensor nodes and sink nodes.However,a sink node has to frequently update its location information to the location servers to guarantee that sensor nodes can obtain its newest location from location servers.In event-driven networks,the packet is transmitted only when an event is detected.When the frequency of events is relatively low,most location updates of the sink node are unnecessary and hence results in much waste of energy consumption.To solve the problem of energy waste in location services,we propose the algorithm named trail-based location service(TLS)in this paper.The basic idea is that when the sink node is moving,it can leave a trail which consists of multiple footprints.When a footprint is discovered during packet transmission,the packet can chase along the trail to capture the actor.The introduction of trail information can prolong the period of location updates in location services.Therefore,the overhead in update phase can be reduced.Specifically,the major contributions of this paper are given as follows.1.Since the trail information is the foundation of TLS,we first design a strategy to maintain the trail with low overhead to decrease the energy price resulting from the introduction of the trail.Then we derive the conditions to guarantee the connectivity of the trail.The connectivity of transmission path can guarantee the deliver rate of TLS.2.TLS can be separated into three phases:update phase,search phase and chase phase.In update phase,the sink node makes location update and footprint update respectively with corresponding periods.In search phase,the source node generates the packet and transmits it to location servers.Then the packet is transmitted to a footprint from location servers.In chase phase,the packet is transmitted along the trail to capture the actor.Theoretical analysis and simulation results show that through prolonging the period of location updates,TLS can significantly reduce energy consumption.3.Considering the transmission features in event-driven scenarios,we combine the trail information with ERS,which is more suitable when the frequency of events is relatively low and propose the algorithm named trail-based search(TS).By increasing the probability of discovering a target,TS can decrease the search attempts in ERS and hence reduce energy consumption and search delay.4.The introduction of trail information results in non-trivial transmission redundancy in chase phase.Therefore,we propose the redundancy reduction scheme,which use trail information to make the packet locally select relay node at each step.The redundancy reduction scheme can eliminate transmission redundancy and hence promote energy efficiency.