无线传感器网络系列讲座 Lectures for Wireless Sensor Networks

1. 无线传感器网络系列讲座 Lectures for Wireless Sensor Networks 上海海事大学信息工程学院 2012年12月 WEI CHEN （陳慰） Department of Computer Science Tennessee State University

2. Outline of Lectures Lecture 1: Cross-Layered Design of Sensor Networks Lecture 2: Fundamentals of Wireless Communication and Ad-Hoc /Mobile /Sensor Networks Lecture 3: Networking Architecture, Routing Protocols and Algorithms Lecture 4: Resource Allocation and Optimization Lecture 5: Cryptography and Sensor Network Security Lecture 6: Cooperative Communication and Networking Lecture 7: Cognitive Radios and Sensor Networks

3. College of Engineering, Technology and Computer Science 和田研 Lecture 1 Cross-Layered Design of Wireless Sensor Networks – Network Architectures, Communication Protocols, and Routing Algorithms WEI CHEN （陳慰） July, 2006 Dept of Computer Science, TSU Center of Excellence in Battle Field Sensor Fusion, TSU & PSU

4. Lecture 1: Cross-Layered Design of Sensor Networks I. Fundamentals - Basics of Wireless Ad-Hoc Networks - Autonomous Systems - Communication Models and Algorithms II. Design of Wireless Sensor Networks - Reconfigurable Networking Architecture - Routing Protocol and Communication Algorithms - Network Self-Reconfiguration Algorithms - Sensor Network Deployment

5. I. Fundamentals What is A Wireless Ad-Hoc Network (AD-NET)? • An AD-NET is a self-managing system of cooperating mobile and/or stationary nodes connected by unreliable wireless links. • Each node operates not only as an end-system, but also as a router to process and forward application data. • Usually, the nodes are inexpensive and have limited computation and communication capability. They can be used to cover a large terrain and has great potential in civic and military applications. • Due to severe energy, environmental, timing constraints and dynamic topological changes, design a wireless AD-NET is a big challenge. A Wireless Ad-Hoc Network

6. Autonomous tracking in Sensor Network f /c Autonomous failure detecting & power re-assigning in Power supply network • Basics of A Wireless Ad-Hoc Network • There is no fixed communication infrastructures. • Tasks are self-organized without central control • Network is dense: control and communication overlap • Control and communication patterns are specific: one-to-many, many-to-one • Network topology is dynamic: topology self-reconfiguration is necessary

7. An Example of Wireless Sensor Network

8. How Can Distributed Systems Work Autonomously? (What are centralized/decentralized systems?) • Example • 50 kids are playing in a ground. How can they form a circle when their teacher asks them to do? • Condition 1: Each kid can see all other kids. • Condition 2: Each kid can see some kids. • Questions: In which case, will a circle be formed faster? • Observations: • More global information a node has, the easier the work will be done. • It is expensive to get global information form dynamic distributed systems

9. Nodes with different communication range Communication on Wireless AD-NETs Communication Model Directed Graph G=(V,E) V={nodes} E={edge (u,v): if node u can transmit data to node v}

10. Communication on Wireless AD-NETs – Continue Example of communication tasks :Broadcast Algorithm 1: Broadcast by flooding Each node v: if v received the message then transmit the message Source • How to solve collision problem? • -- using randomized algorithm: generate a random number k, transmit data at kth time slot. • It may need long time in a dense network !!!

11. Algorithm 2: Broadcasting using Euclidean Circle • Each node v: • if v received the message (u, x, d) then • if x is not v, then ignore the message. Otherwise, select a neighbor w whom v hasn’t sent the message to yet and transmit the message (v,w,d). If v has sent the message to all its neighbor, v sent the message (v, parent, d) • Forming a spanning tree T (Each node keeps • a neighbor list in T) • Transmitting data in depth-first style v (Sender, receiver, data) Source u • Observations: • It is a Deterministic algorithm: only one node transmits in one time slot. • Communication complexity: Totally 2(n-1) time slots with n nodes • It is expensive in a large scale of network!!!

12. 6 4 5 1 2 9 8 3 7 Communication on Wireless on AD-NETs – Continue Another example - How to get a neighbor list(suppose there is a global clock at each node) ? Algorithm: Building neighbor list by using Round Robin Each node v: Node v transmits its id at the time slot same as its id’s. • Observations: • Each node can have a neighbor list after n time-slot. • Synchronization is needed. • Questions: • How to get a neighbor list if the Ids of nodes are not numbered contiguously? • Counting problem: How to number n nodes from 1 to n? • Leader selection problem: how to select a leader?

13. Application Layer Task Management Transport Layer Mobility Management Power Management Network Layer Data Link Layer Physical Layer II. Design of Wireless Sensor Networks (WSNs) Basics of AD-Net Design Issues in WSNs • Medium Access Control (MAC) • Routing • Multi-casting • Network Self-organization • Security • Energy Management • Query/Addressing • Scalability • Deployment Methods • Quality of Service Cross-layer control Sensor Node Protocol Stack

14. Overall Networking Process Application Layer n o l i o t c a o c Presentation Layer i t l o p r p P Correlation-based Communication Layer A Session Layer Transport Layer (end-to-end transfer of message) l o c Network Layer (Transfer of packets across network) o t o r P t r o Data Link Layer (Transfer of blocks across a link) p s n a r T Physical Layer Wireless Ad-Hoc Model ISO/OSI Reference Model

15. Embed Network into Nodes

16. Correlation-based Communication Layer Fusion-Oriented Application Layer Communication Tasks System Maintenance Tasks Broadcasting Global Synchronization Network Reconfiguration Multicasting Hierarchical Communication Routing Protocols / Highest Level Lowest Level Structured (Hierarchical) Communication Network Static/Dynamic Grained-Clustering Physical Layer (Flat Communication Network)

17. Communication System RF Transceiver Power System Power tracking unit Sensor System Control and computing System Micro controller Sensor array System timers Data memory Architecture of Sensor Nodes Data path • Tradeoffs between power consumption, bandwidth, and latency • Interrelationship between transmission rates, processor speed and power consumption. • Interface between an application and its communication protocols

18. Types of Nodes in Sensor Networks • Homogeneous Sensor Network • Uniform sensor nodes & sink nodes • No base station • (2) Heterogeneous Sensor Network • Sensing nodes, processing nodes, mobile nodes, sink nodes • Mixed with base station • Wireless Stands • IEEE 802.11 (Wi-Fi): Mainly used for the access between wireless devices and base stations. Possible for the access between wireless devices. • IEEE 802.15 (based on Bluetooth): Used forAd-hoc network without base station.

19. Comparison between standards 54 Mbps 802.11(a,g) 5-11 Mbps 802.11b 1 Mbps 802.15 384 Kbps UMTS/WCDMA,CDMA2000 56 Kbps IS-95 CDMA, GSM Indoor 10-30 m Outdoor 50-200 m Mid range 200m-4km Long range 5Km-20Km standard Frequency (unlicensed) Data rate MAC Protocol 802.11b 2.3-2.485 GHz Up to 11 Mbps Random access CSMA/CA 802.11a 5.1-5.8 GHz Up to 54 Mbps Same as above 802.11g 2.4-2.485 GHz Up to 54 Mbps Same as above 802.15(based on Bluetooth) 2.4 GHz Up to 1 Mbps TDM CSMA/CA CAMA/CA: carrier sense multiple access with collision avoidance TDM: time division multiplexing

20. Communication Unit Application control MAC (Media access control ) protocol Protocol processing Synchronizer Channel coding RF transceiver Transmission power control

21. 802.15.4 The physical layer (PHY) PHY manages the physical RFtransceiver and performs channel selection and energy and signal management functions. It operates on one of three possible unlicensed frequency bands: 868.0-868.6 MHz: Europe, allows one communication channel (2003, 2006) 902-928 MHz: North America, up to ten channels (2003), extended to thirty (2006) 2400-2483.5 MHz: worldwide use, up to sixteen channels (2003, 2006) The medium access control (MAC) enables the transmission of MAC frames through the use of the physical channel. Besides the data service, it offers a management interface and itself manages access to the physical channel and network beaconing. It also controls frame validation, guarantees time slots and handles node associations. Finally, it offers hook points for secure services.

22. View of WSN at Different Level

23. Networking Architecture/Topology • Flat architecture • Completely decentralized • Large communication overlap • Difficult to select local control and data aggregation point • Almost impossible to organize a real-time application • Easy (Cheap) for topology management • Cluster-based (Hierarchical) architecture • Centralized control in local and decentralized control in global • Easy for schedule a routing without or with less overlap • Easy to select local control and data aggregation point • Expensive for topology management

24. MAC takes care collision problem but needs time and energy! e.g., Broadcast storm problem Design of Networking Architecture Flat and Structured AD-Nets Flat (unstructured) Network Cluster-based (structured) Network

25. Broadcast on A Cluster-Based Network s

26. Local way (cluster) Highway (Back bone) Sink Flat and Structured Sensor Network: An Example Primary sensor node Communicable sensor node

27. head cluster • Trade-offs in Network Architecture • Balance between communication and network self-organization Flat (unstructured) Network Architecture – Complete decentralized control Cluster-Based Network Architecture – Combining the centralized control in local with the decentralized control in global Observations: Control architecture and communication protocols should support both (time and energy) efficient autonomous distributed control and communication and easy network self-organization. So far, control/communication and network reconfiguration are considered separately !

28. Comprehensively Design AD-Nets • Clustering architecture which support the functionalities • for both of communication and network self-organization. • Design efficient algorithms for network self-organization • Design efficient algorithms for key control and communication functions

29. head cluster backbone gateway cluster Architecture Self-Clustering/ Reconfiguration Self-Clustering • When self-clustering finished, each node has 1-hop information: • In a cluster, head knows members’ ids, and members know head’s id. • In backbone, each backbone node knows its neighbors in the backbone. • Each node knows its neighbors’ ids.

30. (1) Node move-in Self-reconfiguration • Nodes may get out of or turn back to the network because of running out of battery or being recharged. Want to join

31. Want to join

32. Want to move out (2) Node move-Out Backbone is re-built !!! Backbone is broken!!!

33. (1) Broadcasting Routing Protocols and Communication Algorithms (i) Broadcast via depth-first-search of backbone Euclid circuit traveling s

34. cluster head gateway node cluster Using time division scheme to avoid collision pure cluster member 2 1 1 depth i depth i+1 v (ii) Broadcast via collision-free flooding (power saving and robust)

35. cluster head gateway node cluster (2)Multicast pure cluster member • Outline of Algorithm • Self-building group-backbone tree for each group • One to many: broadcasting on group-backbone tree

36. Summary (Assuming the size of one packet is 280 bytes and transmitting speed is 1 MB/second) Notations n: number of nodes; d: number of neighbors, |T|: size of the backbone tree T; |C|: the number of clusters; h: height of the backbone tree; h’: height of the multicast backbone tree g; D: maximum degree in the network

37. Sensor board + wireless module Crossbow Sensor Network Deployment for Research Integration Research Focus A network of Crossbow mote that can detect and track vehicles fast enough so that the base station can activate the camera systems before the vehicles close to the building.

38. Technical Approach Sensing and Networking – Sensor Selection 570 520 470 420 370 320 270 1 3 5 7 9 10:54 10:55 10:56 10:57 10:58 10:59 11:00 11:01 11:02 11:03 11:04 10:54 10:55 10:56 10:57 10:58 10:59 11:00 11:01 11:02 11:03 11:04 11 13 15 17 19 21 • Acceleration Sensor– Doesn’t work • Magnet sensor– range 11m • Acoustic sensor– range 8.89 m to 17.78 m sensitive to vehicle speed and background noise Time (sec)

39. Technical Approach Sensing and Networking – Sensor Deployment DEPLOYMENT 1 Cost optimal for vehicle detection by using poles 110 m 122.5 m • 4 sensor boards • 10 wireless modules • longest path = 7 • distance between poles = 45 – 50 m • Transmission range = 43m • Sensing range = 11m Gateway

40. Technical Approach Sensing and Networking – Sensor Deployment DEPLOYMENT 2 Cost optimal for vehicle detection without poles 110 m 122.5 m • 4 sensor boards • 20 wireless modules • longest path = 13 • Transmission Rage = 43m • Sensing range = 11m If latency < 1 second, listening > 12 times/s Network lifetime = wireless mote lifetime = 99 hours < 5days even no one vehicle passing through! Gateway

41. Technical Approach Sensing and Networking – Sensor Deployment DEPLOYMENT 3 Cost optimal for vehicle tracking • 25 sensor boards • 25 wireless modules • longest path = 9 • Transmission Rage = 43m • Sensing range = 11m gateway

42. Technical Approach Sensing and Networking – Sensor Deployment DEPLOYMENT 4 Longer network lifetime with redundancy 2 < 29 m < 18.5m cluster cluster 22m • 24 sensor boards • 32 wireless modules gateway

43. Technical Approach Sensing and Networking – Sensor Deployment DEPLOYMENT 5 Longer network lifetime with redundancy 4 cluster cluster gateway

44. Homework/Assignment • What are wireless ad-hoc/mobile/sensor networks? • What are the challenge for the networks of low cost and small-sized sensor nodes? • What are the differences between a centralized system and a distributed system? • How to get a neighbor list if the Ids of nodes are not numbered contiguously? • Counting problem: How to number n nodes from 1 to n? • Leader selection problem: how to select a leader?