A Data Collection Strategy For Mobile Base Stations In Wireless Sensor Networks

Wireless sensor networks connect people and the physical world.They are the way that people aware and monitor the physical world.They have gained lots of concerns because they can be used for a wide range of applications.Thousands of cheap sensor deployed in monitoring filed can collaborate to monitor environment,detect anomaly intrusion,track object and etc.As autonomous networks which are hard to maintain,saving energy as much as possible is the primary goal of sensor networks while the tasks can be performed.Low duty cycle technology let nodes sleep as much as possible.It can prolong the lifetime of wireless sensor networks.However,this leads to increasing network latency.Because nodes wakeup in turn in low duty cycle networks,broadcast data will be less efficient.By adding mobile nodes in wireless sensor networks,the hops from source node to base station can be reduced effectively.It can improve the network connectivity,reduce costs,increase network reliability and be energy efficiency.But due to the speed of mobile node much less than the data transmission speed in wireless network,it may increase transmission delay.It will be unable to meet the demands of real time tasks.Based on the above,this paper introduces mobile sink in low duty cycle wireless sensor networks.It gives a new method to collect data by mobile sink to reduce transmission delay and save energy of nods.In routine tasks,sensors only wake up when sink approaches them.Sink choose moving path based on its speed and buffer size of sensors.Optimization objective is to minimize total hops of data packets.We analysis the optimal route of sink with different data collection ratio and moving speed.When events happened in network,we set duty cycle to meet the requirement of delay.Sink catch the event message quickly and move to the hotspot to decrease relay message in network.This can achieve balance of energy consumption and transmission delay.When expanding to multi sinks,we analysis the situation of looking network as a whole and network fragments.In routine tasks,these tow have little difference in performance.While emergencies,scheduling sinks simultaneously is hard and not easy to perform in practice.With network fragments,events only influence the fragments and sinks around its area.The result of simulation by OPNET shows that the protocol can reduce transmission data in the network and prolong the network lifetime with single mobile sink.