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Sensor Network 教育部資通訊科技人才培育先導型計畫. 1.Introduction General Purpose  A wireless sensor network (WSN) is a wireless network using sensors to cooperatively.

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Presentation on theme: "Sensor Network 教育部資通訊科技人才培育先導型計畫. 1.Introduction General Purpose  A wireless sensor network (WSN) is a wireless network using sensors to cooperatively."— Presentation transcript:

1 Sensor Network 教育部資通訊科技人才培育先導型計畫

2 1.Introduction General Purpose  A wireless sensor network (WSN) is a wireless network using sensors to cooperatively monitor physical or environmental conditions  The development of wireless sensor networks was originally motivated by military applications.  Wireless sensor networks are now used in many wide-range application areas.

3 1.Introduction Typical Sensor Network sensor Center Relay node Relay node Data gathering Data transmitting processing

4 sensor characteristics  Wireless sensors are small devices that gather information.  Pressure, Humidity, Temperature  Speed, Location  Wireless sensors have some characteristics:  Low power  Small size  Low cost

5 sensor network characteristics  Primary Function  Sample the environment for sensory information  Propagate data back to the infrastructure  Traffic pattern in sensor network  Low activity in a long period  Bursting data in short time  Highly correlated traffic

6 sensors categories  Sensors can be classified into two categories:  Ordinary Sensors  Data gathering  Ordinary Sensors require external circuitry to perform some dedicated tasks like data analyzing.  Smart Sensors  Data gathering and processing  Smart Sensors have internal circuitry to perform dedicated tasks.

7 2.MAC for Sensor Network Sources of Energy Wastage  The major sources of energy wastage are:  Collisions  Overhearing  Control packet overhead  Idle listening  Achieving good scalability and collision avoidance capability is necessary.

8 2.MAC for Sensor Network S-MAC  Sensor-MAC (S-MAC): Medium Access Control for Wireless Sensor Networks  S-MAC is a medium-access control (MAC) protocol designed for wireless sensor networks.  Sensor networks are deployed in an ad hoc fashion, with individual nodes remaining largely inactive for long periods of time, but then becoming suddenly active when something is detected.

9 2.MAC for Sensor Network S-MAC  These characteristics of sensor networks and applications motivate a MAC that is different from traditional wireless MACs such as IEEE in almost every way  Energy conservation and self-configuration are primary goals.  Per-node fairness and latency are less important.

10 2.MAC for Sensor Network Three techniques in S-MAC  S-MAC uses three techniques to reduce energy consumption.  Nodes go to sleep periodically.  Nearby nodes form virtual clusters to synchronize their wake-up and sleep periods to keep the control packet overhead of the network low.  Message passing is used to reduce the contention latency and control overhead.

11 3. Challenges  Challenges:  1. Energy Efficiency:  Power consumptions are crucial to wireless sensor network applications because sensor nodes are not connected to any energy source.  Energy efficiency is a dominant consideration no matter what the problem is.  Sensor nodes only have a small and finite source of energy. Many solutions, both hardware and software related, have been proposed to optimize energy usage.

12 3. Challenges  2. Ad hoc deployment:  Most sensor nodes are deployed in regions which have no infrastructure.  We must cope with the changes of connectivity and distribution.  3. Unattended operation:  Generally, once sensors are deployed, there is no human intervention for a long time.  Sensor network must reconfigure by itself when certain errors occur.

13 3. Challenges  4. Dynamic changes:  As changes of connectivity due to addition of more nodes or failure of nodes, Sensor network must be able to adapt itself to changing connectivity.

14 4.Coverage  Coverage can be classified into three types:  Area coverage  deployment of sensors to cover a given area  Point coverage  deployment of sensors to cover a set of points  Barrier coverage  The goal is to minimize the probability of undetected penetration through the barrier.  To find a path in a region  For any point on the path, the distance to the closest sensor is minimized.

15 4.Coverage Area coverage  Area coverage  deployment of sensors to cover a given area

16 4.Coverage Point coverage  Point coverage  deployment of sensors to cover a set of points

17 4.Coverage Point coverage  Barrier coverage  To find a path from A to B  For any point on the path, the distance to the closest sensor is minimized. A B

18 5.Localization  In sensor networks, nodes are deployed without priori knowledge about their locations.  Estimating spatial-coordinates of the node is referred to as localization.

19 5.Localization Categories  Localization can be classified into two categories:  Fine-grained  Based on timing / signal strength  Coarse-grained  Based on proximity

20 6.Routing Categories  Routing protocols can be divided into two types.  Proactive routing protocol  Proactive routing protocol maintain consistent updated routing information between all nodes.  To update routing table periodically.  Reactive routing protocol  Routes are created only when they are needed.

21 6.Routing Three types in sensor network  Because of the energy constrained nature of sensor networks, conventional routing protocols have many limitations when being applied to sensor networks.  Three types of routing protocol in sensor network:  Data-centric  Hierarchical  Location-based

22 6.Routing Data-centric  Data-centric:  Managers broadcast a Query message to the network.  If a sensor observes some events related to the Query message, it sends the data to the data center.  Data aggregation: sensor1 sensor2 Relay node1 Data Center Data A

23 6.Routing Hierarchical  Hierarchical: Low Energy Adaptive Clustering Hierarchy (LEACH)  LEACH is a two-tier protocol.  Cluster head  Cluster member  Every node runs a random algorithm periodically to decide its identity. (cluster head or not)

24 6.Routing Hierarchical  LEACH  All cluster heads broadcast Advertisement (ADV) message and other nodes decide which cluster they belong to according the strength of ADV message.  Cluster members only send data to their cluster head. Then, cluster heads reply data to Sinks.

25 6.Routing Location-based  Location-based: Geographic Adaptive Fidelity (GAF)  GAF divides the network into several virtual grids.  For adjacent virtual grids A and B, every node in A can directly connect with every node in B.  In GAF, every node has three types of status:  Active  Discovery  Sleep


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