A Study On Wireless Sensor Networks Information Technology Essay
Wireless sensor networks are an area in which rapid research and development is going on. Wireless sensor networks now became part and parcel of many applications such as disaster management, health care applications, temperature and humidity monitoring, pollution monitoring, supply chain management, body area networks, medical and diagnostic applications etc. From a decade, research in sensor networks resulted in tremendous growth in its hardware, software solutions with high quality and low cost. The research includes development of compact hardware which consumes low power which leads to low cost, innovation of efficient routing algorithms, overcoming security problems by providing counter measures, building reliable applications such as interfacing sensors to cyber infrastructure. This paper discusses state of the art status of wireless sensor networks, sensor web - cyber infrastructure for wireless sensor networks, research issues and challenges.
Sensor networks become part of various fields such as Military, Emergency Situations like Fire and Hazardous gasses, Chemical detection, Disaster management, Observation of Biological changes, Medical and Health applications, In Automotives for pressure calculations, speed calculations, Temperature monitoring, Humidity monitoring, Home networks - Home Appliances, location monitoring etc. Sensor networks are collection of autonomous stationary or arbitrary sensor nodes or motes, which communicate information gathered by sensing the environment via hop-by-hop using wireless links . Wireless Adhoc Networks can be categorized in to Mobile Adhoc networks and sensor networks. However there exist several differences between them. The differences in view of their features were shown in Table 1. While designing the sensor applications choice of selecting a sensor node depends on the requirements, communication protocols, and constraints of the application undertaken. The functional requirements of sensor applications would be
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Application must consume minimum power.
Application must be compact.
Application must use QoS (Quality of Service) routing protocols.
Application must use energy efficient communication protocols.
Application must be accurate.
Application must be easy to deploy.
Based on the requirements, communication support provided by the sensor nodes, node design is vital in sensor
SENSOR NETWORKS Vs MANETS
Just to collect information
Designed for distributed computing
No global ID for sensor nodes
Exists global ID
Cheaper in cost
High compared to sensor nodes
Higher than Sensor Nodes
Higher than Sensor Nodes
Can be in large volume (Hundreds
applications. Nodes used in sensor networks can be of two types :
Full Functional Devices (FFDs) contains complete set of services, supports two way communications.
Reduced Functional Devices (RFDs) contains only limited set of services, support one way communication.
Sensor applications can be classified in to two categories based on data gathered by the sensor nodes.
Applications based on Event Detection in this sensor node will deploy especially to detect the events and sends the binary information back to the base station. Sensor nodes deployed for fire detection, quake detection, harmful gas or chemical detection are some of the examples of this kind.
Applications based on Spatial Process Estimation in this sensor nodes are deployed for estimating given areas physical phenomenon in a distributed manner and report back to the base station. These sensor nodes are usually non stationary and collects information in consolidated way. Atmosphere pressure or humidity estimation in a given geographical area is examples of this kind.
Organization of the papers is as follows. Section II provides components and architectural aspects of sensor nodes,
FIGURE 1: SINGLE SINK AND MULTI SINK SCENARIO
section III discusses protocol stack in WSN, section IV contains localization and synchronization concepts in WSN, Security issues and counter measures are described in section V. We describe multimedia Sensor networks, a class of wireless sensor networks in section VI. In section VII, we present various simulation tools and environments used for WSN. Section VIII discusses the concepts of sensor web. And finally section IX provides a road map of safety regulations in WSN and ongoing research projects, followed by conclusions.
II - COMPONENTS AND ARCHITECTURE OF SENSOR NETWORKS
Wireless sensor networks compose of sensor nodes (which are said to be source devices), base stations or gate ways (which are said to be sink devices). In sensor networks projects, sensors are deployed in large number in certain geographical area with out intervention of human beings. Because of this, sensor nodes must communicate themselves; pass the information among themselves with in the radio range of the nodes. Hence, sensor nodes are not only used for sensing but also used for communication, for which every node should support sensing and communication. Sensor node may take the help of neighboring nodes to pass on the sensed data to based station. This model is said to be multi hop (multi sink) routing model. In single hop routing (single sink) model, sensor node directly sends the sensed data to the base station. Sensor nodes are low capacity devices consists of limited processing capacity and limited resource, hence performs limited task. Sensor nodes sense the data and send to the base station in binary format. Base stations or gate ways are high capacity devices contains high processing capacity and long battery life than sensor nodes. Base stations receive the data and perform the data aggregation, which deals with processing and summarizing the received data from the sensor nodes in the network. Base stations will acts as an interface between the sensor nodes and out side world such as World Wide Web. Figure 1 depicts the scenario. The radio range used in the sensor nodes depends on the sensor network application to be deployed and type
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FIGURE 2: SENSOR NODE ARCHITECURE
of wireless standard used. Most commonly used wireless standards include IEEE 802.11a/b/g WLAN standards operated under several frequency bands (868MHz, 2.5GHz, and 5GHz) are mostly used for higher date transmission rate (preferably for multimedia sensors and at base stations). For short range communication IEEE 802.15.4 Zig Bee standard operated under 868MHz, 915MHz, 2.4GHz ISM (Industrial, Scientific and Medical) band are best suitable (preferable for sensor nodes).
Basically sensor nodes are embedded with transducer, analog to digital converter, CPU (possibly a microcontroller), communication division, and power supply (possibly rechargeable battery). Figure 2 illustrates the node architecture. Sensor system can be broadly categorized into three subsystems - sensing subsystem, processing subsystem, and communication subsystem.
Sensing subsystem consists of sensors and analog to digital converters. In sensing subsystem sensors continuously sense the required object or environment (e.g temperature, humidity, light etc) and send the sensed data to analog to digital converter. The converted digital form will be use by processing subsystem.
Processing subsystem composes of CPU and memory unit. Microcontroller, DSP (Digital Signal Processor), ASIC (Application Specific Integrated Circuits), and FPGA (Field Programmable Gate Arrays) can be used in place of processing subsystem. Choosing a processing subsystem depends on the nature of work carried out by the sensor node. Sensor applications like house hold appliances, toys, engaged with limited computation, will make use of microcontrollers. DSPs are special form of microprocessors, support complex calculations and are more accurate than microcontrollers. A multimedia sensor which captures audio and video may make use of DSP. Because, processing audio and video involves complex processing and require accuracy. Some times sensor node designer may customize the circuit according to the design requirements. Usage of customized processors will lead in to ASIC. FPGAs are more flexible and at the same time more complex in design. FPGAs offer more bandwidth than DSPs. FPGAs are more preferable in the systems where parallel processing is required.
Communication subsystem consists of a low power radio for transmitting the data to the other sensor nodes. All the subsystems are connected to a battery. To save power consumption sensor nodes will turn off radio and other subsystems and go to sleep mode. Sensor node will become active whenever an event occurs or timer expires.
Processing in sensor networks will carry out in distributed fashion. In distributed computing, every node contains its own clock and settings. While maintaining clock, one significant component in processing sensor networks is time synchronization. Clock or time generation depends on the oscillator, which is a part of processing sub system. Base station processes the data depending upon the data generated time. For example, in temperature monitoring system, three sensors S1, S2, and S3 sends the data to the base station at their own time t1, t2 and t3 respectively. Base station collects data and process according to clock time of the sensors, such as S1 (t1) < S2 (t2) < S3 (t3). So, Clock of every node must be accurate to obtain optimal results. However, due to the deployment of sensor nodes in harsh environments where human intervention is not present, time synchronization is a typical issue. Factors such as environment, energy, wireless medium, and mobility will greatly challenge the time synchronization. Improper time synchronization affects the data consistency, concurrency, security, and routing mechanisms.
Wide range of ready made nodes are developed by manufactures, research and education communities. A practitioner need not develop the nodes from scratch, instead they can purchase ready made nodes and can program according to the requirements. Some of them are : AVID Director, BTnode, EnRoute family, EyesIFX, JN5121, MeshScape, MICAx family, Scatter node, SensiNet, Smart Tags, SunSPOT, Tmote Sky, Wavefront. However, technological changes are observing in hardware design, factors like power consumption, capacity to work on low voltages, long battery life, cost, reliability, quality of service in hardware, security became open issues in hardware.
FIGURE 3: PROTOCOL STACK
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