• A transducer that converts a physical Phenomenon such as heat, light, sound, or motion into electrical or other signals that may be further manipulated by other apparatus.

• Sensor node: A basic unit in a sensor network, with on-board sensors, processor, memory, wireless modem, and power supply. It is often abbreviated as node. When a node has only a single sensor on board, the node is sometimes also referred to as a sensor, creating some confusion.

Network topology: A connectivity graph where nodes are sensor nodes and edges are communication links.

Routing: The process of determining a network path from a packet source node to its destination.

The estimation of the state of a physical entity such as a physical phenomenon or a sensor node from a set of measurements. Tracking produces a series of estimates over time.

sensors can improve signal-to-noise ratio (SNR) Increased energy efficiency in communications improved robustness and scalability. Energy Advantage

where r is the transmission distance and α is the RF attenuation exponent.

Environmental monitoring (e.g., traffic, habitat, security)

Industrial sensing and diagnostics (e.g., appliances, factory, supply chains)

Infrastructure protection (e.g., power grids, water distribution)

Battlefield awareness (e.g., multitarget tracking)

Context-aware computing (e.g., intelligent home, responsive environment)

Limited hardware: Each node has limited processing, storage,and communication capabilities, and limited energy supply and bandwidth.

Limited support for networking: The network is peer-to-peer, with a mesh topology and dynamic, mobile, and unreliable connectivity.

Limited support for software development: The tasks are typically real-time and massively distributed, involve dynamic collaboration among nodes, and must handle multiple competing events.

new mechanisms is the major challenge of the vision of wireless sensor networks.

Type of service : conventional communication network is

evident – it moves bits from one place to another. For a WSN, moving bits is only a means to an end, but not the actual purpose.

to provide meaningful information such a network are required, new

interfaces and new ways of thinking about the service of a network.

Quality of Service Closely related to the type of a network’s

service is the quality of that service usually coming from multimedia-type

applications – like bounded delay or minimum bandwidth are irrelevant when applications are tolerant to latency

delay is important when actuators are to be controlled in a real-time fashion by the sensor network.

The packet delivery ratio is an insufficient metric;

Fault tolerance Since nodes may run out of energy or

might be damaged or since the wireless communication

between two nodes can be permanently interrupted

To tolerate node failure, redundant deployment is necessary

Lifetime limited supply of energy (using batteries) WSN must operate at least for a given

mission time or as long as possible. A simple option is to use the time until

the first node fails (or runs out of energy) as the network lifetime.

Since a WSN might include a large number of nodes, the employed architectures and protocols must be able scale to these numbers.

In a WSN, the number of nodes per unit area – the density of the network – can vary considerably.

Different applications will have very different node densities.

the density also does not have to homogeneous in the entire network

nodes should be programmable, and their programming must be changeable during operation when new tasks become important.

Maintainability As both the environment of a WSN and

the WSN itself change (depleted batteries,failing nodes, new tasks), the system has to adapt.

It has to monitor its own health and status to change operational parameters or to

choose different trade-offs the network has to maintain itself

To realize these requirements, innovative mechanisms for a communication network have to be found, as well as new architectures, and protocol concepts.

Multihop wireless communication direct communication between a sender

and a receiver is faced with limitations. In particular,communication over long

distances is only possible using prohibitively high transmission power.

The use of intermediate nodes as relays can reduce the total required power.

so-called multihop communication will be a necessary ingredient.

To support long lifetimes, energy-efficient operation is a key technique.Options to look into include energy-efficient data transport between two nodes

Rather a design guideline than a proper mechanism, the principle of locality will have to be embraced extensively to ensure, in particular, scalability.

this will allow the network to scale to large numbers of nodes without having to rely on powerful processing at each single node.

Building such wireless sensor networks has only become possible with some fundamental advances in enabling technologies.

Smaller feature sizes in chips have driven down the power consumption of the basic components of a sensor node to a level that the constructions of WSNs can be contemplated

This is particularly relevant to microcontrollers and memory chips as such, but also, the radio modems,responsible for wireless communication, have become much more energy efficient.

Reduced chip size and improved energy efficiency is accompanied by reduced cost, which is necessary to make redundant deployment of nodes affordable.

This requires,depending on application, high capacity batteries that last for long times, that is, have only a negligible self-discharge rate, and that can efficiently provide small amounts of current.

sensor node also has a device for energy scavenging, recharging the battery with energy gathered from the environment – solar cells or vibration-based power generation are conceivable options.

Both batteries and energy scavenging are still objects of ongoing research.

The counterpart to the basic hardware technologies is software

the architecture of the operating system or runtime environment.

This software architecture on a single node has to be extended to a network architecture, where the division of tasks between nodes

how to design appropriate communication protocols.

A light bulb is hanging in the first floor of the room. There are three switches in the ground floor room. One of these switches belongs to that light bulb. The light bulb is not lit and the switches are in off state. There is only one chance to visit the room. How can it be determined which of these switch is connected to the light bulb.

Solution: First turn ON the first switch and leave it for few minutes. Then turn OFF the first switch and ON the second switch. Now enter the first floor room. If the light bulb is lit, the second switch must be connected to it. If it is not lit, it might the first or the third switch. Now touch the light bulb, it is hot it will be the connected to the first switch. Nor if it is cold, then it should be the third one.

Miss Anne has eleven kids in her class. She has a bowl containing eleven apples. Now Miss Anne want to divide the eleven apples to the kids, in such a way that a apple should remain in her bowl. How can Miss Anne do it?

Ten kids will get each one apple. The eleventh kid will get the apple with the bowl.

Dr.Will wants to operate for three different persons who were wounded. But he had only two surgical gloves. There is not any blood contact between the three persons. How can Dr.Will operate for the three people with two pair of surgical gloves?

Solution: First, Dr.Will wear both of the gloves, one above the other. He operate the first person. After finishing he remove the outer pair of gloves as inside out and place it in a tray. Then operate the second person. Now he will wear the first gloves as inside out above the second gloves. Operate the third person. At last he remove the gloves and dispose them.

Two fathers took their sons to a fruit stall. Each man and son bought an apple, But when they returned home, they had only 3 apples. They did not eat, lost, or thrown. How could this be possible?

Solution: There were only three people. Son, his father and his grandfather.