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 802.11 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