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Wireless networks - Lecture 34: Wireless sensor networks. The main topics covered in this chapter include: introduction to WSN; applications of WSN; factors influencing performance of WSN; architecture and communication protocols; challenges in WSNs;...
Wireless Networks Lecture 34 Wireless Sensor Networks Part I Dr Ghalib A Shah Outline Introduction to WSN Applications of WSN Factors Influencing Performance of WSN ► Power consumption, fault tolerance, scalability, topology, cost Architecture and Communication Protocols Challenges in WSNs Last Lecture Review Motivation ► TCP Variants ► ► Slow start Fast Retransmit/Recovery (TCP Reno) Issues in Heterogeneous Wireless Networks ► Fixed-end systems, fixed wired network, window-based, slow-start, loss-based congestion control BER, Bandwidth, variable RTT, Mobility, Power TCP Schemes for Wireless ► ► ► ► ► Revolve around distinguishing congestion loss, error loss, delay bounds, dup Acks Pure Link-level Approaches (FEC/ARQ) Soft-state Transport Layer Caching Approaches (SNOOP) Soft-state Cross Layer Signalling Approaches (ECN, EBSN, ELN, ATCP) Hard-state Transport Layer Approaches (I-TCP, Mobile TCP) Introduction to WSNs A sensor network is composed of a large number of sensor nodes, which are densely deployed either inside the phenomenon or very close to it Features: ► ► ► ► Random deployment Self-organizing Cooperative capabilities Local computation What is a Sensor ? Sensor is a small sized, low power, low cost, Micro-ElectroMechanical Systems (MEMS) which is capable of sensing, computing and communicating Processor Speed MHz Flash 512K bytes SRAM 8k bytes Radio Frequency 916 MHz/ 2.4 GHz (ISM) Data Rate 40 Kbits/Sec (Max) Radio Range 100 feet Power x AA batteries Open Experimental Platform Telos 4/04 Robust Low Power 250kbps Easy to use Services Networking TinyOS WeC 99 “Smart Rock” Rene 11/00 Dot 9/01 Small microcontroller kB code 512 B data Simple, low-power radio 10 kbps ASK Designed for experimentation EEPROM (32 KB) -sensor boards Simple sensors -power boards Demonstrate scale Mica 1/02 Mica2 12/02 38.4kbps radio FSK NEST open exp Platform 128 kB code, kB data 40kbps OOK/ASK radio 512 kB Flash Commercial Off The Shelf Components (COTS) Spec 6/03 “Mote on a chip” Introduction Sensor networks VS ad hoc networks: Scalability ► Deployment ► Sensor nodes mainly use broadcast, most ad hoc networks are based on p2p Power Limitation ► The topology of a sensor network changes very frequently? Communication Paradigm ► Sensor nodes are prone to failures Highly Dynamic topology ► Sensor nodes are densely deployed Failure Rate ► The number of nodes in a sensor network can be several orders of magnitude higher than the nodes in an ad hoc network Sensor nodes are limited in power, computational capacities and memory Unique IDs ► Sensor nodes may not have global ID Applications of sensor networks temperature humidity vehicular movement lightning condition pressure soil makeup noise levels the presence or absence of certain kinds of objects Applications of sensor networks (Cntd.) Military applic atio ns ► ► ► ► ► Monitoring friendly forces, equipment and ammunition Battlefield surveillance Reconnaissance of opposing forces and terrain Battle damage assessment Nuclear, biological and chemical attack detection and reconnaissance Environmental applications ► ► ► ► Forest fire detection Biocomplexity mapping of the environment Flood detection Precision agriculture Applications of sensor networks (Cntd.) Health applications ► Telemonitoring of human physiological data ► Tracking and monitoring patients and doctors inside a hospital ► Drug administration in hospitals Home applications ► Home automation ► Smart environment 10 Communication architecture of sensor networks 17 Communication architecture of sensor networks 18 Protocol Stack Power Management Plan ► ► Mobility Management Plan ► Turning off the receiver after a msg is received from neighbor in order to avoid getting duplicate msg and conserving energy Informing neighbor nodes during low battery power The mobility management plane detects and registers the movement of sensor nodes, so a route back to the user is always maintained, and the sensor nodes can keep track of who are their neighbor sensor nodes Task Management Plan ► The task management plane balances and schedules the sensing tasks given to a specific region Not all sensor nodes in that region are required to perform the sensing task at the same time As a result, some sensor nodes perform the task more than the others depending on their power level 19 Communication architecture of sensor networks Application layer ► An application layer management protocol makes the hardware and software of the lower layers transparent to the sensor network management applications ► Sensor management protocol (SMP) ► Task assignment and data advertisement protocol (TADAP) ► Sensor query and data dissemination protocol (SQDDP) Transport layer ► This layer is especially needed when the system is planned to be accessed through Internet or other external networks ► No attempt thus far to propose a scheme or to discuss the issues related to the transport layer of a sensor network in literature 20 Communication architecture of sensor networks Network layer Power efficiency is always an important consideration Sensor networks are mostly data centric Data aggregation is useful only when it does not hinder the collaborative effort of the sensor nodes An ideal sensor network has attribute-based addressing and location awareness 21 Communication architecture of sensor networks •Maximum available power (PA) route: Route 2 •Minimum energy (ME) route: Route 1 •Minimum hop (MH) route: Route 3 •Maximum minimum PA node route: Route 3 •Minimum longest edge route: Route 1 22 Communication architecture of sensor networks Data aggregation 23 Communication architecture of sensor networks Data link layer ► The data link layer is responsible for the medium access and error control It ensures reliable point-to-point and point-tomultipoint connections in a communication network Medium access control ► Creation of the network infrastructure ► Fairly and efficiently share communication resources between sensor nodes Power saving modes of operation ► Operation in a power saving mode is energy efficient only if the time spent in that mode is greater than a certain threshold 24 Communication architecture of sensor networks Error control Forward Error Correction (FEC) Automatic Repeat Request (ARQ) Simple error control codes with low-complexity encoding and decoding might present the best solutions for sensor networks 25 Challenges in WSN Cross-layer approach: A Grand Challenge ► Traditio nal laye re d appro ac h is no t s uitable fo r WS Ns ► Go o d fo r de s ig n, abs trac tio n & de bug g ing ► Bad fo r e ne rg y e ffic ie nc y, o ve rhe ad & pe rfo rmanc e 26 How to realize mapping? User/Applications Requirements ► Arch & Topology or Communication Protocols ► E.g reliability ? 27 Research Directions Topology Control Coverage Data Aggregation Temporal/Spatial Correlation Localization / Synchronization Energy Efficient Data Dissemination QoS Framework Network Monitoring and Management How to integrate WSNs into NGWI ? 28 Simulation for Sensor Networks Simulation provides : Controlled , Reproducible testing environment Cost – effective alternative Means to explore and improve design space 29 TinyOS The role of any operating system (OS) is to promote development of reliable application software by providing a convenient and safe abstraction of hardware resources Wireless sensor networks (WSNs) are embedded but general-purpose, supporting a variety of applications, incorporating heterogeneous components, and capable of rapid deployment in new environments An open-source development environment ► A programming language and model (NesC) TOSSIM for simulating TinyOS TinyDB for Sensor DB in TinyOS 30 Summary Introduction to WSN Applications of WSN Factors Influencing Performance of WSN Architecture and Communication Protocols Challenges in WSNs 31 ... Introduction Sensor networks VS ad hoc networks: Scalability ► Deployment ► Sensor nodes mainly use broadcast, most ad hoc networks are based on p2p Power Limitation ► The topology of a sensor. .. Link-level Approaches (FEC/ARQ) Soft-state Transport Layer Caching Approaches (SNOOP) Soft-state Cross Layer Signalling Approaches (ECN, EBSN, ELN, ATCP) Hard-state Transport Layer Approaches (I-TCP,... microcontroller kB code 512 B data Simple, low-power radio 10 kbps ASK Designed for experimentation EEPROM (32 KB) -sensor boards Simple sensors -power boards Demonstrate scale Mica 1/02 Mica2