CS230 Project Mobility in Energy Harvesting Wireless Sensor Network Nga Dang, Henry Nguyen, Xiujuan Yi
What is our project? Motivation: Wireless Sensor Network - Sensor nodes are powered by batteries - High maintenance cost - Unreliability: network is disconnected when nodes are out of battery Energy Harvesting WSN - Powered by a centralized energy harvesting source whose energy is delivered to sensor nodes by robot - Advantage: + Green computing + Autonomous system + Low maintenance cost Energy Harvesting System Model Battery System Model
What have other groups done? Energy-Efficient Approaches in WSN – Hardware layer: energy-efficient circuit, redundant deployment _ Network layer: energy-efficient routing protocol and network topology _ Operating system: dynamic voltage scheduling, duty cycling _ Application layer: energy-efficient quality-aware data collection, multi-version applications Use robot mobility as data collector – Robot is scheduled to visit sensor nodes, collecting data in close range – Goal: prolong system’s lifetime reduce transmission energy for sensor nodes (shorter range) Find a shortest path to minimize travelling energy Avoid buffer flow at sensor node’s data buffer, deliver data in time Usually modeled as Travelling Salesman Problem with additional constraints Hardware layer Network layer Operating system Application
What have other groups done? (cont.) Use robot mobility as energy deliverer – Robot is equipped with a large capacity battery – Sensors’ nodes batteries are monitoring periodically – Every hour k nodes with least remaining energy are chosen and robot will visit and charge these nodes through wireless transfer – Prolong system lifetime by charging extra battery – Disadvantage: System lifetime extension is limited by robot’s battery capacity Maintenance cost: changing robot battery
How does our system work? Sensor Nodes Base Station Send Energy Requests Collect Energy Requests &Run algorithm to schedule charging activity Robot Send schedule to robot Execute plan: Visit nodes and recharge batteries Report charging status Sensor Nodes
The charging algorithm If the robot can’t visit all the node. - It should find the maximum subset of nodes it can visit and give the shortest path of that subset. Find a starting time satisfy both energy and timing constraints Input: Energy request queue: sensor deadline Input: Robot charging status Robot speed & power consumption & energy harvesting profile Travelling Salesman Problem Input to TSP: D[i]: Deadline of each sensor node C[i,j]: Time to travel from node i to node j W[i]: Waiting time at each node i to charge Output: A sequence of sensor nodes which robot had to visit
6:10 8:00 9:30 13:15 7:30 leave base station at 5:00 get back at 23:40 12:00 21:00 23: hour charging 1 hour 2 hours 1.5 hours 2 hours 4 hours 2 hours Charging algorithm example 0.5 hour charging