Wireless Sensor Networks By Ravi Kumar Dasari EECE 505 Term Project
Contents • Introduction • Applications of WSN • Sensor Nodes and Network • Various Routing Algorithms in WSN • SPIN Routing • Simulation using SNetSim • Conclusions
What are WSN? • Large number of heterogeneous Sensor devices spread over a large field. • Wireless sensing + Data Networking. Group of sensors linked by wireless media to perform distributed sensing tasks
Applications of WSN • Military, Environmental, Health (Scanning), Space, Exploration, Vehicular Movement, Mechanical stress levels on attached objects etc.
Sensor Network and Nodes • Network Channels: User nodes or gateways and onward transmission to other network. • Sensor channels: Communicates among sensor nodes and targets. • Sensor Network has three types of Nodes * Sensor nodes: Monitor immediate environment * Target Nodes: Generates various stimuli for sensor nodes. * User Nodes: Client and Administration of Sensor Networks.
Sense Phenomena Process Data Communicate Data Sensor Node
Challenges in WSN’s • Energy • Computation • Communication • Scalability • Fault Tolerance • Power Consumption
Routing in WSN They can be divided into two main categories • Address Centric: Finding shortest path between pairs of addressable end-nodes. • Data Centric : Finding routes from multiple sources to a single sink, allowing data aggregation.
Address Centric Source 2 Source 1 C A B Sink
Data Centric Source 2 Source 1 C A B – aggregates data from 1 & 2
Various Routing Protocols • Classic Flooding • Gossiping • Ideal Dissemination • SPIN
B D G C A E F Classing Flooding • Send data to all neighbors.
Classic Flooding Problems A • Implosion Problem: A starts by flooding its data to all of its neighbors. Two copies of the data eventually end at node D. The system wastes energy and bandwidth. • Overlap Problem: Two sensors cover an overlapping graphic region. When the sensors flood their data to node, the Node receives two copies of the Data. • Resource Blinding: Resources do not modify their activities based on the amount of energy they have. C B D
Gossiping A • Gossiping is an alternative to the classic flooding approach that uses randomization to conserve energy. • At every step each node only forwards data on to one neighbor, which it selects randomly. After node D receives the data, it must forward the data back to sender (B), otherwise the data would never reach node C B C D
Ideal Dissemination A a c • Ideal Dissemination of observed data a and c. Each node in the figure is marked with its initial data and boxed number represent the order in which data is disseminated. In Ideal dissemination both implosion caused by B and C’s common neighbor and overlap caused by A and C’s overlapping initial data item do not occur. a,c B C c a D
SPIN: Sensor Protocols for Information Negotiation • One of the most dominant form of routing in the wireless sensor networks. • Name data, using meta-data • Meta Data for each sensor data • Same senor data -> same meta-data • Different sensor data -> different meta-data • Size of meta-data << Size of actual data • Uses three types of messages: • ADV – advertise data • REQ – request for data • DATA – data message, contains actual sensor data
SPIN1 : Three way handshaking protocol. ADV, REQ, DATA. Each sensor node has resource manager Keeps track of resource consumption Applications probe the manager before any activity Cut down activity to save energy SPIN2 : energy constraint Adds energy-conservative heuristic to the SPIN1 protocol. Node initiates three stage protocol, only if it has enough energy to complete it. If below energy threshold, node can still receive messages, cannot send/recv DATA messages SPIN1 and SPIN2
If node B had its own data, it could aggregate this with the data of node A and advertise.
Simulators available for WSN • JavaSim: Easy to use, very modular but no wireless support. • GlomoSim: Specific for wireless networks, layer architecture, but too robust to be used for small networks. • NS-2: Supports wireless simulations, lots of good documentation, But difficult to use, we need to create separate modules for each protocol. • SNetSim: New simulation software, mainly for event driven conditions, simple and easy to use, can create our own protocols.
SNetSim • SNetSim is a event-driven simulation software running on Windows based operating systems. Developed at Naval Science and Engineering Institute (Turkey)
Conclusions • SPIN is simple to implement compared with other protocols. • SPIN seems to be the best protocol. It is better than flooding because it overcomes data implosion and overlap. • More energy-efficient than flooding or gossiping while distributing data at the same rate or faster than either of these protocols. • These is no redundant data sent through the network.
Reference • SNetSim Software from http://www.dho.edu.tr/enstitunet/snetsim/index.htm • Routing Issues from http://www.rystal.uta.edu/~kumar/cse6392/termpapers/Kalyani_paper.pdf • SPIN issues from http://www.r2.cs.ucla.edu/seapahn/papers/sensor_nets.pdf