Introduction to Distributed Networks Wireless Sensor Networks Rabie
Introduction to Distributed Networks Wireless Sensor Networks Rabie A. Ramadan, Ph. D Cairo University http: //rabieramadan. org rabie@rabieramadan. org 1
Web. Site l Website: • http: //rabieramadan. org/classes/2014/sensor/ 2
Class Format l l l Presentations by myself and others Assignments Survey on one of the following topics : • Topics • Survey Format • Prepare a presentation for your topic – some will be • • publically presented and others will be in private 4 persons per survey (effort should be equivalent to the number of persons) Not less than 6 pages 3
Textbooks l Some other materials will be provided 4
Introduction and Basic Concepts 5
Wireless Networks l l l Most of the traditional wireless networks occur over fixed infrastructure • Access points Many wireless protocols (heterogeneity problem) • Bluetooth, Wi. Fi, Wi. Max We need Seamless network • Connects everyone from his/her home to work, . . Katrina hurricane, 2006 Disasters may be a drive force for such networks 6
General Types of Wireless Networks l l Wireless Cellular Networks • First , Second, 2. 5 , third, and 4 th generations Wireless Ad Hoc Networks • Nodes function as host and router • Dynamic topology • Nodes may departure • Requires efficient routing protocols • Mobile Ad Hoc Networks (MANET) • Wireless Sensor Networks (WSN) 7
Wireless Sensor Networks 8
Definitions and Background l l Sensing: • Is a technique used to gather information about a physical object or process, including the occurrence of events (i. e. , changes in state such as a drop in temperature or pressure). Sensor: • • • An object performing such a sensing task Converts energy of the physical worlds into electrical signal. Sometimes named “Transducer” Transducer converts energy from one form to another. 9
Definitions and Background l Examples on remote sensors: • eyes: capture optical information (light) • ears: capture acoustic information (sound) • nose: captures olfactory information (smell) • skin: captures tactile information (shape, texture) 10
Sensing Task e. g. amplification, filtering, . . etc 11
An example of a sensor: Passive infrared PIR is a differential sensor: detects target as it crosses the “beams” produced by the optic
PIR signal: Amplitude Human 3 mph @ 10 m Car 20 -25 mph @ 25 m
What is a Smart Sensor Node? Sensing Unit Sensors Processing Unit Processor ADC Storage Power Unit Communication Unit Mobility Support Unit Location Finding Unit
Node’s Responsibilities l Data Collection l In-Network Analysis l Data Fusion l Decision Making 15
Sensors Classification Physical property to be monitored determines type of required sensor Type Examples Temperature Thermistors, thermocouples Pressure gauges, barometers, ionization gauges Optical Photodiodes, phototransistors, infrared sensors, CCD sensors Acoustic Piezoelectric resonators, microphones Mechanical Strain gauges, tactile sensors, capacitive diaphragms, piezoresistive cells Motion, vibration Accelerometers, mass air flow sensors Position GPS, ultrasound-based sensors, infrared-based sensors, inclinometers Electromagnetic Hall-effect sensors, magnetometers Chemical p. H sensors, electrochemical sensors, infrared gas sensors Humidity Capacitive and resistive sensors, hygrometers, MEMS-based humidity sensors Radiation Ionization detectors, Geiger-Mueller counters 16
Other Classifications l l Power supply: • active sensors require external power, i. e. , they emit energy (microwaves, light, sound) to trigger response or detect change in energy of transmitted signal (e. g. , electromagnetic proximity sensor) • passive sensors detect energy in the environment and derive their power from this energy input. Electrical phenomenon: • resistive sensors use changes in electrical resistivity (ρ) based on physical properties such as temperature • capacitive sensors use changes in capacitor dimensions or permittivity (ε) based on physical properties • inductive sensors rely on the principle of inductance (electromagnetic force is induced by fluctuating current) • piezoelectric sensors rely on materials (crystals, ceramics) that generate a displacement of charges in response to mechanical deformation
What is a sensor Network? Monitored field Sink Node Internet 18
Wireless Sensor Network (WSN) l l Multiple sensors (often hundreds or thousands) form a network to cooperatively monitor large or complex physical environments Acquired information is wirelessly communicated to a base station (BS), which propagates the information to remote devices for storage, analysis, and processing
History of WSN 20
History of Wireless Sensor Networks l l l DARPA: • Distributed Sensor Nets Workshop (1978) • Distributed Sensor Networks (DSN) program (early 1980 s) • Sensor Information Technology (Sens. IT) program UCLA and Rockwell Science Center • Wireless Integrated Network Sensors (WINS) • Low Power Wireless Integrated Microsensor (LWIM) (1996) UC-Berkeley • Smart Dust project (1999) • concept of “motes”: extremely small sensor nodes Berkeley Wireless Research Center (BWRC) • Pico. Radio project (2000) MIT • μAMPS (micro-Adaptive Multidomain Power-aware Sensors) (2005)
Sample Sensor Hardware: Berkeley motes 22
l l Communication and Computation Rene Mote • Communication = • Computation = 23
Commercial Effort l l l Crossbow (www. xbow. com), Sensoria (www. sensoria. com), Worldsens (http: //worldsens. citi. insa-lyon. fr), Dust Networks (http: //www. dustnetworks. com ), and Ember Corporation (http: //www. ember. com ). 24
Challenges and Constraints l Energy • Sensors powered through batteries • • sometimes impossible to do. Mission time may depend on the type of application (e. g. battlefield monitoring – hours or days) Node’s layers must be designed carefully. 25
Wireless Range Controls the Network Topology Routing in multihop network is a challenge Relay node may aggregate the data 26
Medium Access Control layer (MAC) l l l Responsible for providing sensor nodes with access to the wireless channel. Responsible of Contention free Transmission. MAC protocols have to be contention free as well as energy efficient. • Contention free requires listening to the wireless • channel all the time Energy efficient requires turning off the radio 27
Network Layer l l l Responsible for finding routes from a sensor node to the base station Route characteristics such as length (e. g. , in terms of number of hops), required transmission power, and available energy on relay nodes Determine the energy overheads of multi-hop communication and try to avoid it. 28
Operating System l Energy affects the O. S. design : • Small memory footprint, • Efficient switching between tasks • security mechanisms 29
Challenges and Constraints l Self-Management • Sensors usually deployed in harsh environment. • There is no pre-infrastructure setup. • Once deployed, must operate without human • intervention Sensor nodes must be self-managing in that • They configure themselves, • Operate and collaborate with other nodes, • Adapt to failures, changes in the environment, 30
A self-managing Network l l Self-organization • A network’s ability to adapt configuration parameters based on system and Environmental state. Self-optimization • A device’s ability to monitor and optimize the use of its own system resources Self-protection • Allows a device to recognize and protect itself from intrusions and attacks Self-healing • Allows sensor nodes to discover, identify, and react to network disruptions. 31
Ad Hoc Deployment l Deterministic Vs. Ad Hoc Deployment 32
Challenges and Constraints l Wireless Networking • Transmission Media • Sensors use wireless medium • Suffer from the same problems that wireless networks suffer from • Fading • High error rate 33
Challenges and Constraints l Wireless Networking • Communication ranges are always short • It is required for the network to be highly connected • Routing paths will be long • What about critical applications where delay is not acceptable ? • Qo. S will be an issue 34
Challenges and Constraints l Wireless Networking • Sensing Range • Very small • Nodes might be close to each other • Data Redundancy • Coverage Problem 35
Challenges and Constraints l Decentralized Management l Security • Requires Distributed Algorithms • Overhead might be imposed • Exposed to malicious intrusions and attacks due to • • unattendance characteristics. denial-of-service jamming attack 36
In Network Processing 37
Enable Data Base Like Operations 38
Network Characteristics l l l l l Dense Node Deployment Battery-Powered Sensors Sever Energy , Computation , and Storage Constraints Self Configurable Application Specific Unreliable Sensor Nodes Frequent Topology Change No Global Identifications Many-to-One Traffic pattern ( multiple sources to a single Sink node) Data Redundancy 39
Design Issues l l l Fault Tolerance • • Large number of nodes already deployed or Nodes do the same job. If one fails , the network still working because its neighbor monitors the same phenomenon. Mobility • Helps nodes to reorganize themselves in case of a failure of any of the nodes Attribute-Based Addressing • • Addresses are composed of group of attribute-value pairs Ex. < temp > 35, location = area A>
Design issues l l l Location Awareness • Nodes’ data reporting is associated with location Priority Based Reporting • Nodes should adapt to the drastic changes in the environment Query Handling • • • The sink node / user should be able to query the network The response should be routed to the originator We might have multiple sinks in the network
Traditional networks Vs. wireless sensor networks Traditional Networks Wireless Sensor Networks General-purpose design; serving many applications Single-purpose design; serving one specific application Typical primary design concerns are network performance and latencies; energy is not a primary concern Energy is the main constraint in the design of all node and network components Networks are designed and engineered according to plans Deployment, network structure, and resource use are often ad-hoc (without planning) Devices and networks operate in controlled and mild environments Sensor networks often operate in environments with harsh conditions Maintenance and repair are common and networks are typically easy to access Physical access to sensor nodes is often difficult or even impossible Component failure is addressed through maintenance and repair Component failure is expected and addressed in the design of the network Obtaining global network knowledge is typically feasible and centralized management is possible Most decisions are made localized without the support of a central manager 42
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