User talk:Scprajapati37

1. Wireless Sensor Network:
A wireless sensor network (WSN) is a network that is made of hundreds or thousands of sensor nodes which are deployed in an environment with the capabilities of sensing, wireless communications and computations (i.e. collecting and disseminating environmental data). These spatially distributed autonomous devices cooperatively monitor physical and environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants, at different locations. Each node typically consists of the four components: sensor unit, central processing unit (CPU), power unit, and communication unit. They are assigned with different tasks.

2.1 Fault Tolerance:
Some sensor nodes may fail due to lack of power, have physical damage or environmental interference. The failure of sensor nodes should not affect the overall task of the sensor network. Fault tolerance is the ability to sustain sensor network functionalities without any interruption due to sensor node failures.

2.2 Scalability:
The number of sensor nodes deployed in the sensing area may be in the order of hundreds, Thousands or more and routing schemes must be scalable to different network sizes.

2.3 Low Power Consumption:
Since sensor nodes are powered by battery and it is often very difficult or even impossible to charge or recharge their batteries, it is crucial to reduce the power consumption of sensor nodes so that the lifetime of the sensor nodes, as well as the whole network is prolonged.

2.4 Data Aggregation:
Sensor nodes might generate significant redundant data; similar packets from multiple nodes can be aggregated so that the number of transmissions would be reduced. As computation would be less energy consuming than communication, substantial energy savings can be obtained through data aggregation.

2.5 Limited hardware resources:
In addition to limited energy capacity, sensor nodes have also limited processing and storage capacities, and thus can only perform limited computational functionalities. These hardware constraints present many challenges in software development and network protocol design for sensor networks, which must consider not only the energy constraint in sensor nodes, but also the processing and storage capacities of sensor nodes

3. Low-energy adaptive clustering hierarchy (LEACH):
LEACH is the first and most popular energy-efficient hierarchical clustering algorithm for WSNs that was proposed for reducing power consumption. Hierarchical approach breaks the network into clustered layers. Nodes are grouped into clusters with a cluster head that has the responsibility of routing from the cluster to the other cluster heads or base stations. The clustering task is rotated among the nodes, based on duration. Direct communication is used by each cluster head (CH) to forward the data to the base station (BS).

It uses clusters to prolong the life of the wireless sensor network. LEACH uses a randomize rotation of high-energy CH position rather than selecting in static manner, to give a chance to all sensors to act as CHs and avoid the battery depletion of an individual sensor and dieing quickly.

The operation of LEACH is divided into rounds having two phases each namely:

 * 1) a setup phase to organize the network into clusters, CH advertisement, and transmission schedule creation
 * 2) a steady-state phase for data aggregation, compression, and transmission to the sink.

Its advantages such as reduced control messages, bandwidth reusability, enhanced resource allocation, improved power control and lest wastage of energy.




 * 1) Minimizing the communication cost between sensors and their cluster heads
 * 2) Turning off non-head nodes as much as possible.


 * Drawbacks of LEACH:


 * 1) LEACH uses single-hop routing where each node can transmit directly to the cluster-head and the sink. Therefore, it is not applicable to networks deployed in large regions.
 * 2) LEACH uses dynamic clustering, which brings extra overhead, e.g. head changes, advertisements etc., which may diminish the gain in energy consumption.
 * 3) The nodes on the route a hot spot to the sink could drain their power fast. This problem is known as "hot spot" problem.

4. Power-Efficient Gathering in Sensor Information Systems (PEGASIS):
PEGASIS is an extension of the LEACH protocol, which forms chains from sensor nodes so that each node transmits and receives from a neighbor and only one node is selected from that chain to transmit to the base station (sink). The data is gathered and moves from node to node, aggregated and eventually sent to the base station. The chain construction is performed in a greedy way. Unlike LEACH, PEGASIS avoids cluster formation and uses only one node in a chain to transmit to the BS (sink) instead of using multiple nodes. In PEGASIS routing protocol, the construction phase assumes that all the sensors have global knowledge about the network, particularly, the positions of the sensors, and use a greedy approach. When a sensor fails or dies due to low battery power, the chain is constructed using the same greedy approach by bypassing the failed sensor. In each round, a randomly chosen sensor node from the chain will transmit the aggregated data to the BS, thus reducing the per round energy expenditure compared to LEACH. Simulation results showed that PEGASIS is able to increase the lifetime of the network twice as much the lifetime of the network under the LEACH protocol. Such performance gain is achieved through the elimination of the overhead caused by dynamic cluster formation in LEACH and through decreasing the number of transmissions and reception by using data aggregation. Although the clustering overhead is avoided, PEGASIS still requires dynamic topology adjustment since a sensor node needs to know about energy status of its neighbors in order to know where to route its data. Such topology adjustment can introduce significant overhead especially for highly utilized network.

5. Sensor Protocols for Information via Negotiation (SPIN):
The SPIN protocols are resource aware and resource adaptive. The sensors running the SPIN protocols are able to compute the energy consumption required to compute, send, and receive data over the network.


 * SPIN is designed based on two basic ideas:


 * 1) To operate efficiently and to conserve energy by sending metadata (i.e., sending data about sensor data instead of sending the whole data that sensor nodes already have or need to obtain),
 * 2) Nodes in a network must be aware of changes in their own energy resources and adapt to these changes to extend the operating lifetime of the system.


 * SPIN has three types of messages, namely, ADV, REQ, and DATA:

When a node has data to send, it advertises via broadcasting this message containing meta-data (i.e., descriptor) to all nodes in the network.
 * 1) ADV:

An interested node sends this message when it wishes to receive some data.
 * 1) REQ:

Data message contains the actual sensor data along with meta-data header.
 * 1) DATA:

SPIN enables the sensors to negotiate with each other before any data dissemination can occur in order to avoid injecting non-useful and redundant information in the network.

SPIN uses meta-data as the descriptors of the data that the sensors want to disseminate. The notion of meta-data avoids the occurrence of overlap given sensors can name the interesting portion of the data they want to get. It may be noted here that the size of the meta-data should definitely be less than that of the corresponding sensor data.

Each sensor is aware of its resource consumption with the help of its own resource manager that is probed by the application before any data processing or transmission. This helps the sensors to monitor and adapt to any change in their own resources. SPIN is a data-centric routing protocol where the sensor nodes send ADV message via broadcasting for the data they have and wait for REQ messages from interested sinks or nodes.


 * It has its own drawbacks:
 * 1) SPIN is not scalable,
 * 2) If the sink is interested in too many events, this could make the sensor nodes around it deplete their energy,
 * 3) SPIN's data advertisement technique cannot guarantee the delivery of data if the interested nodes are far away from the source node and the nodes in between are not interested in that data.

7. Conclusion:
One of the main challenges in the design of routing protocols for WSNs is energy efficiency due to the energy resources of sensors. The ultimate objective behind the routing protocol design is to keep the sensors operating for as long as possible, thus extending the network lifetime. Therefore, routing protocols designed for WSNs should be as energy efficient as possible to prolong the lifetime of individual sensors, and hence the network lifetime.