WIRELESS SENSOR NETWORKS Speaker HsuanLing Weng Advisor Dr

WIRELESS SENSOR NETWORKS Speaker : Hsuan-Ling Weng Advisor : Dr. Kai-Wei Ke Date: 2015/03/11

Outline § Introduction § Sensor Networks Communication Architecture § Design Factors § Routing Protocols in WSN § Conclusion 2

Introduction § Recent advances in wireless communications and electronics have enabled the development of low-cost, low-power, multifunctional sensor nodes that are small in size and communicate untethered in short distances. § These tiny sensor nodes, which consist of sensing, data processing, and communicating components, leverage the idea of sensor networks. Sensor networks represent a significant improvement over traditional sensors. § The sensor networks can be used for various application areas (e. g. , health, military, home). 3

Sensor Networks Communication Architecture § The sensor nodes are usually scattered in a sensor field. Each of these scattered sensor nodes has the capabilities to collect data and route data back to the sink. Data are routed back to the sink by a multihop infrastructureless architecture through the sink. The sink may communicate with the task manager node via Internet or satellite. § The design of the sensor network is influenced by many factors, including fault tolerance, scalability, production costs, operating environment, sensor network topology, hardware constraints, transmission media, and power consumption. 4

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Design Factors - Fault Tolerance & Scalability § Fault Tolerance — Some sensor nodes may fail or be blocked due to lack of power, or have physical damage or environmental interference. The failure of sensor nodes should not affect the overall task of the sensor network. This is the reliability or fault tolerance issue. Fault tolerance is the ability to sustain sensor network functionalities without any interruption due to sensor node failures. § Scalability — The number of sensor nodes deployed in studying a phenomenon may be on the order of hundreds or thousands. Depending on the application, the number may reach an extreme value of millions. New schemes must be able to work with this number of nodes. They must also utilize the high density of the sensor networks. The density can range from few sensor nodes to few hundred sensor nodes in a region, which can be less than 10 m in diameter. 6

Design Factors - Production Costs § Production Costs — Since sensor networks consist of a large number of sensor nodes, the cost of a single node is very important to justify the overall cost of the network. If the cost of the network is more expensive than deploying traditional sensors, the sensor network is not costjustified. As a result, the cost of each sensor node has to be kept low. 7

Design Factors - Hardware Constraints § A sensor node is made up of four basic components, : a sensing unit, a processing unit, a transceiver unit, and a power unit. § Sensing units are usually composed of two subunits: sensors and analog-to-digital converters(ADCs). The analog signals produced by the sensors based on the observed phenomenon are converted to digital signals by the ADC, and then fed into the processing unit. § The processing unit, which is generally associated with a small storage unit, manages the procedures that make the sensor node collaborate with the other nodes to carry out the assigned sensing tasks. § A transceiver unit connects the node to the network. § One of the most important components of a sensor node is the power unit. Power units may be supported by power scavenging units such as solar cells. 8

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Design Factors - Hardware Constraints § They may also have additional application-dependent components such as a location finding system, power generator, and mobilizer. § Most of the sensor network outing techniques and sensing tasks require knowledge of location with high accuracy. Thus, it is common that a sensor node has a location finding system. § A mobilizer may sometimes be needed to move sensor nodes when it is required to carry out the assigned tasks. § All of these subunits may need to fit into a matchbox-sized module. The required size may be smaller than even a cubic centimeter, which is light enough to remain suspended in the air. Apart from size, there are some other stringent constraints for sensor nodes. These nodes must consume extremely low power, operate in high volumetric densities, have low production cost, be dispensable and autonomous, operate unattended, and be adaptive to the environment. 10

Design Factors - Sensor Network Topology § We examine issues related to topology maintenance and change in three phases: • Predeployment and deployment phase : Sensor nodes can be either thrown in as a mass or placed one by one in the sensor field. They can be deployed by dropping from a plane, delivered in an artillery shell, rocket, or missile, and placed one by either a human or a robot. • Post-deployment phase : After deployment, topology changes are due to change in sensor nodes’ position, reachability (due to jamming, noise, moving obstacles, etc. ), available energy, malfunctioning, and task details. • Redeployment of additional nodes phase : Additional sensor nodes can be redeployed at any time to replace malfunctioning nodes or due to changes in task dynamics. 11

Design Factors - Environment § Environment — Sensor nodes are densely deployed either very close or directly inside the phenomenon to be observed. Therefore, they usually work unattended in remote geographic areas. They may be working in the interior of large machinery, at the bottom of an ocean, in a biologically or chemically contaminated field, in a battlefield beyond the enemy lines, and in a home or large building. 12

Design Factors - Transmission Media § Transmission Media — In a multihop sensor network, communicating nodes are linked by a wireless medium. These links can be formed by radio, infrared, or optical media. To enable global operation of these networks, the chosen transmission medium must be available worldwide. § Much of the current hardware for sensor nodes is based on RF circuit design. The μAMPS wireless sensor node uses a Bluetooth-compatible 2. 4 GHz transceiver with an integrated frequency synthesizer. The low-power sensor device uses a single-channel RF transceiver operating at 916 MHz. The Wireless Integrated Network Sensors (WINS) architecture also uses radio links for communication. 13

Design Factors - Transmission Media § Another possible mode of internode communication in sensor networks is by infrared. Infrared communication is license-free and robust to interference from electrical devices. Infrared-based transceivers are cheaper and easier to build. Another interesting development is that of the Smart Dust mote, which is an autonomous sensing, computing, and communication system that uses the optical medium for transmission. Both infrared and optical require a line of sight between the sender and receiver. 14

Design Factors - Power Consumption § Power Consumption — The wireless sensor node, being a microelectronic device, can only be equipped with a limited power source (< 0. 5 Ah, 1. 2 V). In some application scenarios, replenishment of power resources might be impossible. Sensor node lifetime, therefore, shows a strong dependence on battery lifetime. In a multihop ad hoc sensor network, each node plays the dual role of data originator and data router. The malfunctioning of a few nodes can cause significant topological changes and might require rerouting of packets and reorganization of the network. Hence, power conservation and power management take on additional importance. It is for these reasons that researchers are currently focusing on the design of power-aware protocols and algorithms for sensor networks. § The main task of a sensor node in a sensor field is to detect events, perform quick local data processing, and then transmit the data. Power consumption can hence be divided into three domains: sensing, communication, and data processing. 15

Routing Protocols in WSN § Location-based Protocols: -MECN, SMECN, GAF, GEAR, Span, TBF, BVGF, Ge. Ra. F § Data-centric Protocols: - SPIN, Directed Diffusion, Rumor Routing, COUGAR, ACQUIRE, EAD § Hierarchical Protocols: -LEACH, PEGASIS, HEED, TEEN, APTEEN § Multipath-based Protocols: - Disjoint Paths, Braided paths, N-to-1 Multipath Discovery § Qo. S-based protocols: - SAR, SPEED, Energy-aware routing 16

Location-based Protocols § Sensor nodes are addressed by means of their locations. Location information for sensor nodes is required for sensor networks by most of the routing protocols to calculate the distance between two particular nodes so that energy consumption can be estimated. 17

Location-based Protocols - MECN § Minimum energy communication network (MECN) maintains a minimum energy network for wireless networks by utilizing low power GPS. § The main idea of MECN is to find a sub-network, which will have less number of nodes and require less power for transmission between any two particular nodes. In this way, global minimum power paths are found without considering all the nodes in the network. This is performed using a localized search for each node considering its relay region. 18

Data Centric Protocols § When the source sensors send their data to the sink, intermediate sensors can perform some form of aggregation on the data originating from multiple source sensors and send the aggregated data toward the sink. This process can result in energy savings because of less transmission required to send the data from the sources to the sink. 19

Data Centric Protocols - SPIN § SPIN(Sensor Protocols for Information via Negotiation) is a three-stage protocol as sensor nodes use three types of messages, ADV, REQ, and DATA, to communicate. ADV is used to advertise new data, REQ to request data, and DATA is the actual message itself. § The protocol starts when a SPIN node obtains new data it is willing to share. It does so by broadcasting an ADV message containing metadata. If a neighbor is interested in the data, it sends a REQ message for the DATA and the DATA is sent to this neighbor node. The neighbor sensor node then repeats this process with its neighbors. As a result, the entire sensor area will receive a copy of the data. 20

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Hierarchical Protocols § Clustering is an energy-efficient communication protocol that can be used by the sensors to report their sensed data to the sink. § The main aim of hierarchical routing is to efficiently maintain the energy consumption of sensor nodes by involving them in multi-hop communication within a particular cluster and by performing data aggregation and fusion in order to decrease the number of transmitted messages to the sink. § Cluster formation is typically based on the energy reserve of sensors and sensor’s proximity to the cluster head. 22

Hierarchical Protocols - LEACH § Low-energy adaptive clustering hierarchy (LEACH) is one of the most popular hierarchical routing protocol for wireless sensor networks. In LEACH , formation of clusters of the sensor nodes are done on the received signal strength. § LEACH uses local cluster heads as routers to the sink. The transmission of data is done only through these cluster heads rather than all the sensor nodes in the network. This will save energy as only cluster heads are responsible for transmission of data towards sink. § These cluster heads change randomly over time depending on energy dissipation of the sensor nodes. This decision is made by the node choosing a random number between 0 and 1. The node becomes a cluster head for the current round if the number is less than the threshold given below: 23

Hierarchical Protocols - LEACH § Where p is the desired percentage of cluster heads (e. g. 0. 05), r is the current round, and G is the set of nodes that have not been cluster heads in the last 1/p rounds. § LEACH is completely distributed and it does not require global knowledge of network. LEACH uses single-hop routing where each node can transmit directly to the cluster-head and the sink. Therefore, it is not applicable networks which are deployed in large regions. Furthermore, the idea of dynamic clustering brings extra overhead, e. g. cluster head changes, advertisements etc. , which may cause the increase in energy consumption. 24

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Multipath-based Protocols § Considering data transmission between source sensors and the sink, there are two routing paradigms: single-path routing and multipath routing. In single-path routing, each source sensor sends its data to the sink via the shortest path. In multipath routing, each source sensor finds the first k shortest paths to the sink and divides its load evenly among these paths. 26

Multipath-based Protocols - Disjoint Paths § Protocol that helps finds a small number of alternate paths that have no sensor in common with each other and with the primary path. In sensor disjoint path routing, the primary path is best available whereas the alternate paths are less desirable as they have longer latency. The disjoint makes those alternate paths independent of the primary path. 27

Network flow and Qo. S-aware protocols § Although most of the routing protocols proposed for sensor networks fit our classification, some pursue somewhat different approach such as network flow and Qo. S. In some approaches, route setup is modeled and solved as a network flow problem. Qo. S-aware protocols consider end to end delay requirements while setting up the paths in the sensor network. 28

Network flow and Qo. S-aware protocols - SAR § Sequential Assignment Routing (SAR) is the first routing protocol which concentrates more on the energy efficiency and QOS factors. It creates multiple paths from the nodes to the sink to help in achieving a more energy efficient structure. It also maximizes the fault tolerance of the network. § The SAR protocol creates trees rooted at one-hop neighbors of the sink while considering Qo. S metric, energy resource on each path and priority level of each packet. These created trees are used to find multiple paths from sink to sensors. While selecting one of the paths among these multiple paths, energy resources and Qo. S on the path is considered. Routing table consistency between downstream and upstream on each path is enforced for failure recovery. 29

Network flow and Qo. S-aware protocols - SAR § Any local failure causes an automatic path restoration procedure locally. SAR offers less power consumption than the minimum-energy metric algorithm, which focuses only the energy consumption of each packet without considering its priority. SAR ensures fault-tolerance and easy recovery but the protocol suffers from the overhead of maintaining the tables and states at each sensor node especially when the number of nodes is huge. 30

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References § [1] I. F. Akyildiz, W. Su, Y. Sankarasubramaniam, and E. Cyirci, “A Survey on Sensor Networks”, IEEE Communications Magazine, vol. 40, no. 8, Aug. 2002, pp. 102 -114 § [2] Deepak Goyal, and Malay Ranjan Tripathy, “Routing Protocols in Wireless Sensor Networks: A Survey”, Advanced Computing & Communication Technologies (ACCT), 2012 Second International Conference on, pp. 474 -480, 7 -8 Jan. 2012. § [3] Savita Lonare, and Gayatri Wahane “A Survey on Energy Efficient Routing Protocols in Wireless Sensor Network”, Computing, Communications and Networking Technologies (ICCCNT), 2013 Fourth International Conference on, pp. 1 -5, 4 -6 July 2013. 33

Thanks for listening 34