1. Overview of Ad-hoc & Sensor Networks

2. Overview
Wireless networks of smart sensors have become feasible for many applications because of technological advances in semiconductors, energy- efficient wireless communications, reduced power budgets for computational devices, development of novel sensing materials.
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3. These sensor outputs must be converted to digital data that can be processed by the CPU.
This transformation is performed by the analog to-digital converter (ADC).
Batteries or power sources could provide the wireless sensor node with power as indicated by the power supply component.
Although other wireless communication mechanisms are possible, most wireless sensor nodes use radio frequency (RF) transmissions. So the final component shown in the sensor node is the RF transceiver.
The entire sensor node is encapsulated in the appropriate packaging for the environment in which the sensor node will operate
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5. Overview of ad hoc networking
Ad hoc networking refers to a network with no fixed infrastructure (Perkins, 2000).
When the nodes are assumed to be capable of moving, either on their own or carried by their users, these networks are referred to as mobile ad hoc networks (MANETs).
Otherwise, these networks are simply ad hoc networks with fixed nodes but without a preexisting infrastructure.
The nodes that form the network rely on wireless communication to collaborate with each other.
The advantage of ad hoc networking is that the absence of a fixed infrastructure reduces the cost, complexity, and time required to deploy the network. On the other hand, the lack of a fixed infrastructure introduces challenges to using and maintaining ad hoc networks.
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6. Wireless sensor network tasks
Neighbor discovery
Self-organization or self-configuration
Sensing
Signal processing or sensor data processing
Data aggregation, storage, and caching
Target detection, target tracking, and target monitoring
Topology control for energy savings
Localization
Time synchronization
Routing
Medium access control
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7. Properties of an Ad Hoc Network
No preexisting infrastructure
By definition, ad hoc networks do not have any infrastructure.
The nodes in the network rely on wireless communication for information dissemination and gathering.
This obviates the expense of providing many resources and allows the use of ad hoc networks in remote environments.
the reduced cost of setting up and using such networks.
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8. Wireless sensor nodes generally need to communicate with base stations, which may be fixed nodes.
However, sensor nodes themselves do not tend to rely on any underlying infrastructure for performing their duties locally.
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9. Limited access to a base station
Ad hoc wireless sensor networks perform most of their functions without a base station.
A more powerful computer thus may function as a base station to act as a gateway to the Internet or other networks.
This base station would inject queries into the sensor network and accumulate and archive information generated by the sensors.
however, the ad hoc network would need to perform many tasks locally rather than relying heavily on the base station.
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10. There are several reasons why this is desirable.
Fundamentally, the cost of communicating with the base station could be a significant power drain on the nodes in the network.
Multi-hop communication from the sensors consumes power at each sensor along the path toward the base station.
Sending large amounts of data will exhaust the energy of nodes even more rapidly.
Another reason is that the sheer volume of information that can be generated by the sensor nodes could easily overwhelm the base station, especially for a large-scale sensor network.
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11. Power-limited devices
Sensor nodes or other computational devices that make up the ad hoc network exist in an environment that is assumed to be devoid of resources such as power.
In fact, because of the absence of any underlying infrastructure, power outlet generally are not available.
For this reason, devices that form the ad hoc network use either battery power or passive power sources, such as solar energy
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12. No centralized mechanisms
Since ad hoc networks do not have any underlying infrastructure and wireless communication is employed, centralized algorithms are not feasible.
The cost of transmitting data from all the nodes in the network to a central location becomes prohibitively expensive in terms of power usage.
In addition, there are the typical problems with scalability and fault tolerance because centralized algorithms suffer from being a single point for processing all the information.
Therefore, centralized processing of large volumes of data or data from a large number of nodes is impractical in most cases.
It is often more practical to perform some localized processing within the network, reducing the amount of data that must be delivered to the base station.
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13. Unique Features of Sensor Networks
Direct interaction with the physical world
Sensor nodes are designed to interact with the physical world and to perform computational tasks based on the information gathered from the surrounding environment.
Infact, these nodes are often referred to as smart sensor nodes because they combine both sensing functions with digital logic, which allows for some intelligent processing of the readings obtained from the on-chip sensor(s).
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14. The ability of sensors to measure physical, chemical, biologic, and other types of properties of the environment provides novel opportunities for computing systems, as well as imposing unique requirements on the implementation of protocols.
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15. Usually special-purpose devices
Sensor nodes are expected to be low-cost computing devices.
Many different types of sensors have been developed, including thermal sensors, magnetic sensors, vibration sensors, chemical sensors, biologic sensors, light sensors, and acoustic sensors.
For all these reasons, it is expected that these nodes will be customized for a specific application rather than functioning as a general purpose computational device.
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16. The memory in a sensor node makes it possible to install different programs, so a single sensor could be used for multiple applications.
Although it is possible to update the software in a node even after it has been deployed, the overhead of transmitting new code and installing it may limit the viability of this option.
it seems likely that sensor networks will be used as special-purpose systems, where a single task is assigned to the sensors, and this task does not change significantly during the lifetime of the sensor network.
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17. Very limited resources: Wireless sensor nodes obviously have limited communication bandwidth because of the need to share the wireless medium among many sensor nodes.
However, these nodes have other severe limitations because of the anticipated low cost of sensor nodes.
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18. Operate without a human interface
Sensor nodes have a small form factor. One reason is to reduce the cost.
Another reason for limiting the form factor is to increase the opportunities where the sensors can be placed. By making the sensors small and unobtrusive, more applications become viable.
A third reason is that security may necessitate that these nodes be hidden or at least hard to find.
Making the sensors small decreases the chances of detecting them.
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19. Specialized routing patterns
Routing in the Internet is designed around the principle that any two hosts can communicate with each other.
Sending an from one user to another is an example of such communication. In a wireless sensor network, on the other hand, routing has a much more predictable pattern.
Other than messages exchanged among neighboring sensors, most of the traffic in the network is between a base station and a sensor node
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20. Military applications
Several military applications have been identified.
One is the tracking of enemy troop movements.
Another military application is the use of sensors to detect the use of biologic or chemical weapons.
A third example of military applications that benefits from wireless sensor networks is improved battlefield communications.
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21. Medical applications
Sensor nodes also are being envisioned as medical devices that could be implanted within or reside on the body and perform tasks.
A few examples include glucose monitors for diabetic patients, artificial retinal and cortical implants for the visually impaired, heart monitors and a vital statistics repository
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22. Sensors used for medical applications also have unique requirements.
First, these sensors must be safe and biocompatible so that they continue to function inside the body and do not cause damage to the surrounding tissues.
Finally, patient confidentiality must be maintained so that unauthorized personnel cannot extract sensor readings from the sensors.
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23. Industrial applications
Low-cost sensor nodes could be attached to equipment to monitor performance or attached to parts as they move through the shop floor.
By tracking parts through the manufacturing plant, inefficiencies in plant process flow could be recognized more quickly, rush orders could be expedited more easily, and customer queries could be answered faster and with more accuracy. .
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24. A third example is the use of wireless sensors for inventory tracking.
Similar interest has been expressed by Wal- Mart to require all its suppliers to place RFID tags on all merchandise.
A third example is the use of wireless sensors for inventory tracking.
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25. Environmental applications
Because of the scope of the problems, wireless sensor networks also are being proposed and tested for environmental concerns.
For example,tracking the nesting habits of seabirds requires monitoring a large geographic region without a human presence.
Another option is attaching the sensors directly to large mammals. This allows the monitoring of their behavior and over a large area. The sensors can exchange information when two animals are near each other, so that the researchers can obtain readings from more animals over time.
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26. Water quality monitoring in general may be useful for determining when streams and beaches are contaminated with bacteria or other harmful pollutants.
River current.
The flow of currents in a river depends in part on the quantities and temperatures of water flowing from and into different tributaries
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