Wireless sensor network have been identified as one of the most important technologies for the 21stcentury. This seminar traces the history of research in sensor network over the past three decades. Technology trends that impact the development of sensor network are reviewed and new applications such as infrastructure security, habitat monitoring, and traffic control are presented. Technical challenges in sensor network development include network discovery, control and routing, collaborative signal and information processing, tasking and querying, and security.
The wireless sensor network that monitors the environmental conditions such as light, temperature, and humidity. This network is comprised of nodes called “motes” that form an ad-hoc network to transmit this data to a computer that function as a server. The server stores the data in a database where it can later be retrieved and analyzed via a web based interface. The network works successfully with an implementation of one sensor mote.
A wireless sensor network is a wireless network consisting of spatially distributed autonomous device using sensor to cooperatively monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants, at different locations. The development of wireless sensor network was originally mediated by military applications such as battlefield surveillance. However wireless sensor networks are now used in many civilian application areas, including environment and habitat monitoring, healthcare application, home automation, and traffic control.
The technological drive for smaller devices using less power with great functionality has created new potential applications in the sensor and data acquisition sectors. Low-power microcontrollers with RF transceivers and various digital and analog sensors allow a wireless, battery-operated network of sensor modules (“motes”) to acquire a wide range of data.
WIRELESS SENSOR NETWORK
A wireless sensor network is a group of specialized transducers with a communications infrastructure intended to monitor and record conditions at diverse locations. Commonly monitored parameters are temperature, humidity, pressure, wind direction and speed, illumination intensity, vibration intensity, sound intensity, power-line voltage, chemical concentrations, pollutant levels and vital body functions. A sensor network normally constitutes a wireless AD-HOC network.
The figure shows the complexity of wireless sensor networks, which generally consist of a data acquisition network and a data distribution network, monitored and controlled by a management center. The plethora of available technologies makes even the selection of PDABSC(Base Station Controller Preprocessing) BST Wireless Sensor Online monitoring Server transmitter Ship Sensor Online monitoring Server transmitter Ship, Monitoring Machine Monitoring Medical Monitoring Wireless Sensor Wireless Data Collection Networks Wireless(Wi-Fi 802.11 2.4GHzBlueToothCellular Network, -CDMA, GSM)Printer Wire land (Ethernet WLAN, Optical)Animal Monitoring Vehicle Monitoring Anywhere , any time to access Notebook Cellular Phone PC Wireless Sensor Networks Roving Human monitor Data Distribution Network Management Center(Database large storage, analysis). .
A sensor node is also known as a mote. 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.
There are two kinds of sensor nodes used in the sensor network. One is the normal sensor node deployed to sense the phenomena and the other is gateway node that interfaces sensor network to the external world.
The primary focus of wireless sensor network is the development of the Sensor Mote Network component. It is the component responsible for collecting and transmitting raw environmental data to the Server. There is also the potential for the motes to receive commands from the Server, although that functionality may not be
implemented in wireless sensor network. Uses for this feature would include the server based synchronization and wireless network reprogramming.
This sensor motes consists of two parts. The first is the sensor mote. The primary purpose of the sensor mote is to collect and transmit raw environmental data. When not doing this, it went into a low-power idle mode to conserve energy. Another aspect of the sensor motes involved AD-HOC networking and may be for multi-hop routing.
The gateway mote is the second part of the Sensor Mote Network. Its purpose is to serve as between the Server and the Sensor Mote Network and deliver all the data packets. In this both standard and gateway motes could be implemented on the same hardware and with the same software.
COMPONENTS OF SENSOR NODE
The main components of a sensor node are microcontroller, transceiver, external memory, power source and one or more sensors.
Sensor nodes make use of ISM band which gives free radio, huge spectrum allocation and global availability. The various choices of wireless transmission media are Radio frequency, Optical communication (Laser) and Infrared. Laser requires less energy, but needs line of sight for communication and also sensitive to atmospheric conditions. Infrared like laser, needs no antenna but is limited in its broadcasting capacity. Radio Frequency (RF) based communication is the most relevant that fits to most of the WSN applications. WSN use the communication frequencies between about 433 MHz and 2.4 GHz. The functionality of both transmitter and receiver are combined into a single device know as transceivers are used in sensor nodes.
From an energy perspective, the most relevant kinds of memory are on-chip memory of a microcontroller and flash memory off-chip RAM is used. The Flash memories are used due to its cost and storage capacity. Memory requirements are very much application dependent. Two categories of memory based on purpose of storage. a) User memory used for storing application related or personal data. b) Program memory used for programming the device.
They are classified according to electrochemical material used for electrode such as NiCd (nickel-cadmium), NiZn (nickel-zinc), Nimh (nickel metal hydride), and Lithium-Ion. Current sensors are developed which are able to renew their energy from solar, thermo generator, or vibration energy. Two major power saving policies used are Dynamic Power Management (DPM) and Dynamic Voltage Scaling (DVS). DPM takes care of shutting down parts of sensor node which are not currently used or active. DVS scheme varies the power levels depending on the non-deterministic workload.
Sensors are hardware devices that produce measurable response to a change in a physical condition like temperature and pressure. Sensors sense or measure physical data of the area to be monitored. The continual analog signal sensed by the sensors is digitized by an Analog-to-digital converter and sent to controllers for further processing. Characteristics and requirements of Sensor node should be small size, consume extremely low energy, operate in high volumetric densities, are autonomous and operate unattended, and be adaptive to the environment. As wireless sensor nodes are micro-electronic sensor device, can only be equipped with a limited power source of less than 0.5 v and 1.2 V.
WIRELESS SENSOR AD-HOC NETWORK
With the coming availability of low cost, short range radios along with the advances in wireless networking, it is expected that wireless ad hoc sensor network will become commonly deployed. In the sensor network, each node may be equipped with a variety of sensors, such as acoustic, seismic, infrared, still/motion video camera, etc Each node may have sufficient processing power to make a decision, and it will be able to broadcast this decision to the other nodes in the cluster. One node may act as the cluster master, and it may also contain a longer range radio using a protocol such as IEEE 802.11 or Bluetooth. The basic goals of a wireless AD-HOC sensor network generally depend upon the application, but the following tasks are common to many networks:
1: Determine the value of some parameter at a given location: In an environmental network, one might one to know the temperature, atmospheric pressure, amount of sunlight, and relative humidity at a number of locations. This example shows that a given sensor node may be connected to different types of sensors, each with a different sampling rate and range of allowed values.
2: Detect the occurrence of events of interest and estimate parameters of the detected event or events: In the traffic sensor network, one would like to detect vehicle moving through an intersection and estimate the speed and direction of the vehicle.
3: Classify a detected object: Is a vehicle in a traffic sensor networks a car, a mini-van, a light truck, a bus, etc.
4: Track an object: In a military sensor network, track an enemy tank as it moves through the area covered by the network.
WIRELESS SENSOR NETWORK TOPOLOGIES
As wireless sensors become real commodities on the market. The three classic network topologies 1) Point-to-point, (2) Multidrop, and (3) web.
Point to Point Network
In point-to-point network topologies, each sensor node requires a separate twisted shielded–pair wire connection. The cost is high, configuration management is difficult, and nearly all the information processing is done by the host.
These systems are the most reliable because there is only one single point of failure in the topology the host itself. You can improve the system by adding redundant hosts, but wiring two hosts can be a problem.
The standards allow multiple readout circuits if the standard loads are used at each readout. Problems can arise if readout devices load the circuit beyond its capability, but most designers are familiar with the limitations and are sufficiently careful.
Complete wireless local area network(LAN) were implemented using this technique. These were successful in the office environment but didn’t fare as well in factories. Many designers implemented remote data acquisition systems with this topology by using a data concentrator in the field to feed the data to a radio transmitter for transmission to the hosts, where the signals were demultiplexed into the original sensor signals.
Multi drop Network
In a multi drop topology, all nodes are potentially connected to all other nodes. Connectivity among a large collection of sensors gets complex because all nodes must have a connection to all other nodes. Some connections can be eliminated by using repeaters and routers to make virtual connections. The World Wide Web is a good example of this topology. Multidrop buses began to appear in the late 70s and early 80s. One of these, Modbus from Modicon (Schneider Auto mation, North Andover, Massa chusetts), led the way into the industrial sphere, followed by several proprietary and open buses (e.g., the Manufacturing Automation Protocol).
The emergence of intelligent sensors and microcomputers capable of operating in industrial environments irrevocably changed the sensor network landscape. Multi drop network (buses) reduced the number of wires required to connect field devices to the host, but they also introduced another single point of failure the cable. Several suppliers of industrial-grade products offered redundant cabling designs, but these came with an increase in complexity.
An architecture consisting of a decoder for each channel and a direct-sequence spread-spectrum receiver can perform simultaneous sampling because the same baseband signal goes to each decoder. But the decoders represent a significant cost, power, and size limitation.
The introduction of Ethernet in the mid-80s was a landmark in standardization, if not technological innovation. A group of large companies agreed that the future computer networking required an open interconnect standard that would allow multiple-vendor systems to work together with minimal difficulty.
The promise of the web topology (i.e., when all nodes are connected all the time) had to wait until vendors developed a way to interconnect nodes without the required wiring connections. A network of any appreciable size becomes infeasible if all wires must be connected specifically for the network. Early star topologies were successful as long as the star wasn’t too large. The World Wide Web illustrates what is possible, though, if you can use wiring that is already in place. The telephone network provides the available connectivity in most parts of the country, although at less than suitable speeds in many locations.
The advantages of web connectivity for sensor networks become clear as the level of intelligence in each sensor increases. Cooperating sensors can form a temporary configuration that provides sufficient capacity to replace the host. Self-hosting networks then become self-configuring and finally, years from now, perhaps even self-aware. But several problems remain and are the topic of significant research, such as size and power consumption reduction, throughput and performance during transmissions, and algorithms for allocating priorities and authority.
In a wireless web network, individual nodes have the potential of being constantly connected (physically) with many other nodes in the network. How the network is configured at any instant becomes a matter of how the software configures it. In a code division multiple access (CDMA) network, the radios can receive all channels at once.
1. Limited power it can harvest or store.
2. Ability to cope with environmental conditions.
3. Mobility of nodes.
4. Dynamic network topology.
5. Ability to cope with nodes failures.
6. Communication failure.
7. Ease of use.
8. Scalability to large scale of deployment.
APPLICATIONS OF WIRELESS SENSOR NETWORK
Various applications are:-Environmental and habitat monitoring, Traffic control, Infrastructure security and industrial sensing.
Environmental and Habitat Monitoring
Environment and habitat monitoring is a natural candidate for applying sensor networks, since the variables to be monitored, e.g., temperature, are usually distributed over a large region. Environmental sensors are used to study vegetation response to climatic trends and diseases, and acoustic and imaging sensors can identify, track, and measure the population of birds and other species. The communication network connecting the sensors operates at different speeds.
Sensor networks have been used for vehicle traffic monitoring and control for quite a while. Most traffic intersections have either overhead or buried sensors to detect vehicles and control traffic lights. Furthermore, video cameras are frequently used to monitor road segments with heavy traffic, with the video sent to human operators at central locations. However, these sensors and the communication network that connect them are costly; thus, traffic monitoring is generally limited to a few critical points. Inexpensive wireless ad hoc will completely change the landscape of traffic monitoring and control.
Another more radical concept has the sensors attached to each vehicle. As the vehicles pass each, they exchange summary information that may be generated by ground sensors. These summaries propagate from vehicle and can be used by drivers to avoid traffic jams and plan alternative routes
Sensor networks can be used for infrastructure security and counter terrorism applications. Critical buildings and facilities such as power plants and communication centers have to be protected from potential terrorists. Networks of video, acoustic, and other sensors can be deployed around these facilities. These sensors provide early detection of possible threats. Improved coverage and detection and a reduced false alarm rate can be achieved by fusing the data from multiple sensors. Even though fixed sensors connected by a fixed communication network protect most facilities, wireless and ad hoc networks can provide more flexibility and additional coverage when needed. Sensor networks can also be used to detect biological, chemical, and nuclear attacks.
Commercial industry has long been interested in sensing as a means of lowering cost and improving machine (and perhaps user) performance and maintainability. Monitoring machine “health” through determinate on of vibration or wear and lubrication and the insertion of sensors into regions inaccessible by humans.
ADVANTAGES AND DISADVANTAGES
1. It avoids lot of wiring.
2. It can accommodate new devices at any time.
3. It’s flexible to go through physical partitions.
4. It can be accessed through a centralized monitor.
1. It’s damn easy for hackers to hack it as we can’t control propagation of waves.
2. Comparatively low speed of communication.
3. Gets distracted by various elements like Blue-tooth.
4. It is a costly.
There are a number of future extensions for this wireless sensor network.
A few are: Expand the sensor mote network by adding more motes. This would allow the development and testing of advanced network-layer functions, such as multi-hop routing. By creating a new hardware design that integrates with the sensors and power hardware on a single-board another interesting feature can be developed or adopt a standard expandable plug-in sensor interface in both hardware and software. In researching alternative energy sources to extend mote battery life. Possibilities include solar cells and rechargeable batteries.
Wireless sensor networks are getting smaller and faster, increasing their
potential applications in commercial, industrial, and residential environments.
Wireless Sensor Network, as implemented, represents one commercial application. However, the limit of applications depends only upon the sensors used and the interpretation of the data obtained. As the technology improves and new low-power digital sensors become more readily available, motes will increase functionality without increasing power consumption and will expand the wireless sensing market.
1. Reserch paper by F.L.Lewis in Texas Associate Director for Research
Head, Advanced Controls, Sensors, and MEMS Group
Automation and Robotics Research Institute
3. http://en.wikipedia.org/wiki/wireless sensor network.