3 Wireless Sensor Networks (WSN) A wireless sensor network is a collection of self-organized sensing nodes grouped in a network.A wireless sensor network (WSN) consists of spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, pressure, etc. and to cooperatively pass their data through the network to a main location.
4 Wireless Sensor Networks (WSN) A sensor node, also known as a mote, is a node in a wireless sensor network that is capable of performing some processing, gathering sensory information and communicating with other connected nodes in the network.
6 Wireless Sensor Networks (WSN) on the basis of mode of operation and type of intended applications, WSN can be broadly classified in to 2 categories: Proactive WSN: The sensor nodes periodically switch on their transmitters, sense the parameter, and transmit the data to the network. Reactive WSN: The sensor nodes react immediately to sudden and significant changes in the value of a sensed parameter.
7 WSN Functioning: Components: The main components of a sensor node are a microcontroller, transceiver, external memory, power source and one or more sensors.ControllerThe controller performs tasks, processes data and controls the functionality of other components in the sensor node.While the most common controller is a microcontroller, other alternatives that can be used as a controller are: a general purpose desktop microprocessor, digital signal processors, ect.A microcontroller is often used in many embedded systems such as sensor nodes because of its low cost, flexibility to connect to other devices, ease of programming, and low power consumption.
8 WSN Functioning: Components: Transceiver Sensor nodes often make use of ISM band, which gives free radio, spectrum allocation and global availability.The possible choices of wireless transmission media are radio frequency (RF), optical communication (laser) and infrared.Lasers require less energy , but need line-of-sight for communication and are sensitive to atmospheric conditions.Infrared, like lasers, needs no antenna but it is limited in its broadcasting capacity.Radio frequency-based communication is the most relevant that fits most of the WSN applications. WSNs tend to use license-free communication frequencies: 173, 433, 868, and 915 MHz; and 2.4 GHz.The functionality of both transmitter and receiver are combined into a single device known as a transceiver.
9 WSN Functioning: Components: External memory From an energy perspective, the most relevant kinds of memory are the on-chip memory of a microcontroller and Flash memory—off-chip RAM is rarely, if ever, used.Flash memories are used due to their cost and storage capacity. Memory requirements are very much application dependent.Components: Power sourceA wireless sensor node is a popular solution when it is difficult or impossible to run a mains supply to the sensor node.However, since the wireless sensor node is often placed in a hard-to-reach location, changing the battery regularly can be costly and inconvenient.The sensor node consumes power for sensing, communicating and data processing. More energy is required for data communication than any other process. The energy cost of transmitting 1 Kb a distance of 100 metres is approximately the same as that used for the execution of 3 million instructions by a 100 million instructions per second/W processor.
11 WSN: Operating System support in Sensor Devices As sensor nodes must be low power, their hardware design will tradeoff computation capabilities for lower power consumption.As such, the nodes will have limited processing power and memory resources.An operating system for sensor networks should deliver the required application services without using a significant amount of the computational resources available to the nodes.Typical embedded operating systems, such as TinyOS, VxWorks, QNX, OS-9, WinCE and Clinux provide a programming environment similar to those existing in traditional computers.
12 WSN: Operating System support in Sensor Devices TinyOS is based on an event driven programming model instead of multithreading. TinyOS programs are composed in to event handlers and tasks which run to completion semantics.When an external event occurs, such as an incoming packet or a sensor reading, TinyOS calls the appropriate event handler to handle the event.Both the TinyOS system and programs written for TinyOS are written in a special programming language called network embedded systems C (nesC).
13 WSN Characteristics: The main characteristics of a WSN include: Power consumption constrains for nodes using batteries or energy harvestingAbility to cope with node failuresMobility of nodesCommunication failuresHeterogeneity of nodesScalability to large scale of deploymentAbility to withstand harsh environmental conditionsEase of use
14 WSN Operations: Five stages: Planning Deployment Post Deployment Post Operation
15 WSN Design Process:The following issues should be considered during design of WSNRouting Protocol IssuesData DisseminationQuery ProcessingLocation and Management IssuesKey DistributionSecurity MeasuresMAC Protocol Issues.
16 Sensor Architecture Cluster Management: Low Energy Adaptive Clustering Hierarchy (LEACH) a clustered based protocol that minimizes energy dissipation in sensor networks.The purpose of LEACH is to randomly select sensor nodes as Cluster Heads (CHs), so the high energy dissipation in communicating with the base station is spread to all sensor nodes in the sensor network.The operation of LEACH is separated into 2 phases,The Setup PhaseThe Steady State Phase.
17 Sensor Architecture Cluster Management: Each setup phase consists of CH selection and cluster formation.Steady state phase consists of the data transmission.The duration of the steady state phase is longer than that of the setup phase to minimize the overhead.
18 Sensor Architecture Cluster Management: The setup phase procedure is as follows:At the beginning of each round, each node advertises its probability to the CH, to all other nodes.Nodes with higher probabilities are chosen as the CHs.CHs broadcast an advertisement message (ADV) using CSMA MAC protocol.Based on the signal strength, each non-CH node determines its CH for this round.Each non-CH transmits a join-request message (join-REQ) back to its chosen CH using a CSMA MAC protocol.CH node sets up a time division multiple access (TDMA) schedule for data transmission coordination with in the cluster.
19 Sensor Architecture Cluster Management: The steady state phase procedure for data transmission is as follows:TDMA schedule is used to send data from node-to-head cluster.Head cluster aggregates the data received from node to cluster.Communication is via direct sequence spread spectrum (DSSS) and each cluster uses a unique spreading code to reduce inter-cluster-interference.Data are sent from the CH nodes to the BS using a fixed spreading code and CSMA.After a certain period of time spent on the steady state phase, the network goes into the setup phase again enters another round of selecting CHs.
22 Wireless Mess Networks Characteristics:WMN support ad-hoc networking, and have the capability of self-forming, self-healing, and self-organization.WMNs are multihop wireless, but with a wireless infrastructure/backbone provided by mesh routers.Mesh routers have minimal mobility and perform dedicated routing and configuration which significantly decreases the load of mesh clients and other end nodes.Mobility of end nodes in supported easily through the wireless infrastructure.Mesh routers integrate heterogeneous network, including both wired and wireless networks.WMNs are not stand alone and need to be compatible and interoperable with other wireless networks.
23 WMN Design: Internet Wireless Client Mesh Router with Gateway/ Bridge WiredClientWireless Mesh Backbone
24 Wireless Mess Networks Issues in WMNs:Physical Layer Issues.MAC Sub Layer Issues.Network Layer Issues.Transport Layer Issues.
25 Wireless Mess Networks Issues in WMNs: Physical Layer Issues:IEEE Mesh Networks-- peak load is 11 Mbps (802.11b).-- 54 Mbps (802.11a).-- Researchers interested to increase the speed of Wi-Fi by 10 to 20 times.IEEE Mesh Networksa is based on multiband Orthogonal frequency-division multiplexing(OFDM), that uses ultra wide band(UWB) to reach up to 480 Mbps.-- a direct sequence UWB (DS-UWB) claims up to 1.3 Gbps.IEEE Mesh Networksoperates in the 1066 GHz band and requires line of sight towers.-- The a extension uses lower frequency of 211 GHz, enabling non line of sight connections.-- to allow consumers to connect to the internet while moving at vehicular speed, e is used.
26 Wireless Mess Networks Issues in WMNs: MAC Sub Layer Issues:MAC layer is concerned with more than One Hop (OH) communication in WMN. MAC layer works for multipoint to multipoint and network self organization.Differences between the MAC in WMN and other types of networks are,MAC for WMNs is concerned with more than OH communication.MAC distributive, needs to be collaborative, and works for multipoint to multipoint communication.Self organization of the network is needed for better collaboration between neighboring nodes and nodes in multi-hop distances.Mobility is low but still affects the performance of MAC.
27 Wireless Mess Networks Issues in WMNs: Network Layer Issues:WMN is tightly integrated with the Internet and IP.Routing protocols for WMN are different from those in wired network.Multipath Routing-- for better load balancing.-- high fault tolerance.-- complexity (drawback).Multiradio Routing-- focuses on maximizing throughput rather than mobility or minimizing energy.-- shortest path routing algorithms are used.-- NIC is replaced with Multiradio NIC.-- for multiradio WMN, multiradio link quality source routing (MR-LQSR) is used.Hierarchical Routing
28 Wireless Mess Networks Issues in WMNs: Transport Layer Issues:The WMN use single channel for data transfer and control, and these are multi-hop networks.packet loses at higher bit rates.the hidden node and exposed node causes transmission failure.TCP is not suitable, because client moves across the network.UDP alone can not guarantee the delivery of packets.Real-Time Protocol (RTP) is used along with UDP.
30 Computational GridsA computational grid is a loose network of computers linked to perform grid computing.A large computational task is divided up among individual machines, which run calculations in parallel and then return results to the original computer. These individual machines are nodes in the network.Computational grids are often more cost effective than supercomputer of equal computing power.
31 Computational Grids Grid Features: Computational grids are used to solve the problems in engineering, science and commerce.Provides transparent access to remote resources.Enable resource sharing.Reduce execution time for data processing applications.Allow on-demand aggregation of resources at multiple sites.Provides access to remote database and software.
32 Computational Grids Issues in Grid Construction Design: For data grids:The ability to integrate multiple distributed, heterogeneous, and independently managed data sources.The ability to provide efficient data transfer mechanisms to provide data where the computation will take place.The ability to provide necessary data discovery mechanism, which allow the user to find data based on characteristics of data.The capability to implement data encryption and integrity checks to ensure that data is transported across the network in a secure fashion.The ability to provide the backup/restore mechanism and policies necessary to prevent data loss and minimize unplanned downtime across the grid.