Wireless sensor networks: a survey

1. Wireless sensor networks: a survey 周紹恩 指導教授:柯開維

2. Outline • Introduction • Sensor networks applications • Factors influencing sensor network design • Sensor networks communication architecture • Routing protocols • Conclusion & Future work

3. Introduction • A sensor network is composed of a large number of sensor nodes • densely deployed either inside the phenomenon or very close to it • Sensor networks represent a significant improvement • Sensors can be positioned far from the actual phenomenon • Several sensors that perform only sensing can be deployed

5. What’s different with Ad hoc? • Sensor nodes are densely deployed • Sensor nodes are prone to failures • The number of sensor nodes in a sensor network can be several orders of magnitude higher than the nodes in an ad hoc network • The topology of a sensor network changes very frequently

6. Sensor networks applications • Sensor networks may consist of many different types of sensors such as: • Temperature • Pressure • Noise levels • Seismic • The concept of micro-sensing and wireless connection of these nodes promise many new application areas • Health • Military • Home and other commercial areas

9. Military applications • Monitoring friendly forces, equipment and ammunition • Battlefield surveillance • Reconnaissance of opposing forces and terrain • Targeting • Battle damage assessment • Nuclear, biological and chemical attack detection and reconnaissance

11. Factors influencing • Fault tolerance is the ability to sustain sensor network functionalities without any interruption due to sensor node failures • Physical damage • Environmental interference • Lack of power • Note that protocols and algorithms may be designed to address the level of fault tolerance required by the sensor networks • deployed in a house • deployed in a battlefield

12. Scalability • the number of nodes in a region can be used to indicate the node density • The node density depends on the application in which the sensor nodes are deployed • For machine diagnosis application, the node density is around 300 sensor nodes in a 5x5 region • vehicle tracking application is around 10 sensor nodes per region • The density will be extremely high when a person normally containing hundreds of sensor nodes • eye glasses, clothing, shoes, watch, jewelry, and human body…..

13. Production costs • the cost of a single node is very important • Since the sensor networks consist of a large number of sensor nodes • As a result, the cost of each sensor node has to be kept low • Bluetooth radio system to be less than 10$ • PicoNode is targeted to be less than 1$ • The cost of a sensor node should be much less than 1$ in order for the sensor network • Note that a sensor node also has some additional units such as sensing and processing units • As a result, the cost of a sensor node is a very challenging issue

14. Hardware constraints • A sensor node is made up of four basic components: • sensing unit • processing unit • transceiver unit • power unit • They may also have application dependent additional components such as: • location finding system • mobilizer • power generator

16. Hardware constraints • All of these subunits may need to fit into a matchbox-sized module • Apart from the size, there are also some other stringent constraints for sensor nodes: • consume extremely low power • operate in high volumetric densities • have low production cost and be dispensable • be autonomous and operate unattended • be adaptive to the environment

17. Power consumption • Sensor node lifetime dependence on battery lifetime • Limited power source • Replenishment of power resources • might be impossible • power conservation and power management take on additional importance • In other mobile ad hoc network ? • Maybe important but not primary • Can be replace by user

18. Power consumption • Power consumption can be divided into three domains • Sensing • Communication • Data processing • Sensing • varies with the nature of applications • Sporadic sensing might consume lesser power than constant event monitoring • complexity of event detection

19. Power consumption • sensor node expends maximum energy in data communication • Data transmission • Data reception • Data processing • Energy expenditure in data processing is much less compared to data communication • the energy cost of transmitting 1 KB a distance of 100 m • same as that for executing 3 million instructions

20. Communication architecture • sensor nodes are usually scattered in a sensor field • Each sensor nodes has the capabilities : • collect data • route data back to the sink and the end users

22. Routing protocol • Power efficiency • Data-centric protocols • Flooding and gossiping • Sensor protocols for information via negotiation (SPIN) • Directed Diffusion • Hierarchical protocols • LEACH • Network flow and QoS-aware protocols • SAR

24. Routing protocol • Sensor networks are mostly data centric • In data-centric routing, the interest dissemination is performed to assign the sensing tasks to the sensor nodes • There are two approaches used for interest dissemination: • Sinks broadcast the interest • sensor nodes broadcast an advertisement for the available data

25. Data-centric protocols • Flooding: • each node receiving a data or management packet repeats it by broadcasting • unless a maximum number of hops for the packet is reached • the destination of the packet is the node itself • However, it has several deficiencies: • Implosion • Overlap • Resource blindness

26. A • ..... B

28. Gossiping • A derivation of flooding • nodes do not broadcast but send the incoming packets to a randomly selected neighbor • randomly selected neighborsend the data • Although this approach avoid the implosion problem • by just having one copy of a message at any node • it takes long time to propagate the message to all sensor nodes

29. Data aggregation • solve the implosion and overlap problems • Data coming from multiple sensor nodes are aggregated • as if they are about the same attribute of the phenomenon • when they reach the same routing node on the way back to the sink • Data aggregation can be perceived as a set of automated methods of combining the data that comes from many sensor nodes into a set of meaningful information

31. SPIN • Sensor protocols for information via negotiation • The protocols are designed based on two basic ideas: • sensor nodes operate more efficiently • conserve energy by sending data that describe the sensor data instead of sending the whole data • SPIN has three types of messages: • ADV • REQ • DATA

33. Directed Diffusion • queries the sensors in an on demand basis by using attribute-value pairs for the data • Each sensor node then stores the interest entry in its cache • timestamp field • gradient field • However, Directed Diffusion cannot be applied to all sensor network applications • The applications that require continuous data delivery to the sink will not work efficiently • since it is based on a query-driven data delivery model

37. LEACH • Low-energy adaptive clustering hierarchy • minimizes energy dissipation in sensor networks • Randomly select sensor nodes as cluster-heads • The cluster head task is to manage communication among member nodes of the cluster, data processing, and relay processed sensed data to the Base Station

39. SAR • Sequential assignment routing • The SAR algorithm creates multiple trees where the root of each tree is an one hop neighbor from the sink • The SAR algorithm selects the path based on : • Energy resources • Additive QoSmetric • packet’s priority level

42. Conclusion & Future work • The flexibility, fault tolerance, high sensing fidelity, low-cost and rapid deployment characteristics of sensor networks create many new and exciting application areas for remote sensing. • In the future, this wide range of application areas will make sensor networks an integral part of our lives

43. Refference • I.F. Akyildiz et al., Wireless sensor networks: a survey, Computer Networks 38 (4) (2002) 393–422 • Kemal Akkaya, Mohamed Younis, A survey on routing protocols for wireless sensor networks, Ad hoc networks, 2005 - Elsevier • I.F. Akyildiz, W. Su, A power aware enhanced routing (PAER) protocol for sensor networks, Georgia Tech Technical Report, January 2002, submitted for publication. • C. Intanagonwiwat, R. Govindan, D. Estrin, Directed diffusion: a scalable and robust communication paradigm for sensor networks, Proceedings of the ACM Mobi-Com’00, Boston, MA, 2000, pp. 56–67