Overview of Wireless Sensor Network

A sensor network is a network that translates the physical parameters like humidity, temperature, pressure direction, etc. to a form that can be Sensor networks are integrated into various different devices as well as With the advances in wireless networking, Very Large Scale Integration (VLSI), Micro-Electro-Mechanical Systems (MEMS) developed. These networks are suitable for different applications like air microprocessors, a new generation of wireless sensor networks is being weathered sensing, national border monitoring, video surveillance, etc. applications, environmental applications, health care, process control.

Introduction To Microwave Engineering

What is a Wireless Sensor Network?

A wireless sensor network is a group of sensors used for humidity, pressure, temperature, sound pollution, wind speed, etc., organizing monitoring, and recording the environmental physical conditions like and embedded the data gathered at some central location.

  • A wireless sensor network provides a bridge between the physical world and The elements of a sensor network include:
  • A group of localized or distributed sensors.
  • A central location for clustering the data collected.
  • A group of computing resources at the central location.

A wireless sensor network is a network consisting of small sensor nodes that communicate amongst themselves with the help of radio signals and are deployed for sensing, understanding, and monitoring the physical world.

The wireless sensor networks demand in-network processing as data gathered is large in quantity.

 Background of Sensor Network Technology:

We know that the wireless sensor network is a network that comprises small sensor nodes for communication. The sensor node is the basic element of a wireless sensor network. Its function is to monitor or sense the physical parameters and process and communicate the data collected to nearby sensor nodes to form a network of sensor nodes referred to as Wireless Sensor Networks (WSN).

With advancements in sensing, computing, and different communication methodologies, tiny, low-power, and powerful sensor nodes have been developed. These networks have a small amount of CPU memory.

The wireless sensor networks have several applications ranging from smart homes, artificial intelligence, surveillance, vehicular and supply chain management applications.

Examples of previously used sensor networks are radar networks used for nationwide stations, air traffic control. However, these systems employ specialized computers as well as communication protocols and are expensive. This led the researchers to find less expensive and secure WSNS that need automation and are based on intelligent sensing. The WSNs are developed nowadays and are well planned.

Overview of Cellular Systems

The WSN architecture is similar to the 7 layer architecture used for the OSI model in computer networks. Each layer performs different functionalities In WSN there are four layers in the bottom namely the physical layer, data link There ar them. Those are done in hierarchical manners. layer, network layer, and transport layer. sensor size The function of these layers is to transfer the data from one node/system to another node/system.

osi model

 Nanoscale Above these layers is the upper layers and three cross planes, viz Task Management Plane, Mobility Management Plane, and the Power Management Plane.

All these together manage the network and the sensor nodes in such a manner so as to increase the overall efficiency of the WSN system. The physical layer converts the data to signals. The signal travel on the media. (i.e. wired or wireless).

The data link layer transfers data across a link between two systems that are directly connected. The network layer is responsible for linking, routing, internetworking, communicating between the systems that are not directly connected to each other.

The transport layer provides end-to-end connection data transfer between processes running in the nodes. The 4 bottom layers are communication-oriented. The upper layers are data / user-oriented. The data needs to be processed by these layers. Along with the data transfer, different management protocols are also performed. The nodes interact with each other, they collaborate ate with each other. As their size is small there are limited resources. To manage them there is a power management plan. It manages the power of the sensor node.

The mobility management plane manages and tracks the node as it moves. i.e. it handles the node mobility. The task management plane is for sensing the task management plane for sensing the task assigned to different areas of the sensor network.

There are various types of sensors. Hence it is very important to classify them. Table 4.13.1 shows the taxonomy (classification) of sensor nodes.

*(Please rotate the screen horizontally if you want to see this table full view on your smartphone)

Sensor size

Mobility

Power

Storage

capability

Sensor Mode

Sensor

protocols

Nanoscale

(<10-4 mm3)

Immobile at

deployment and semi-mobile post-deployment

--

Low end

and mid-range

processor

low-end

storage

Single

function

chemistry

biology

--

Microscale  (10-3 mm3)

Immobile at

deployment and fully-mobile post-deployment

105 hours, battery

Low-end

storage 64-bit high-end

processor

Single

function

physics

--

Ultrasmall

(10-2 mm3)

Semi-mobile

during

deployment and

immobile

post-deployment

104 hours, battery

Mid-range

storage

Multihop,

Mesh-hops

--

Very small

(10-1 mm3)

Semi-mobile

during

deployment and

also, post

deployment

103 hours, battery

Mid-range

storage

Multihop,

Mesh-hops

Static routing

Small

(100~1mm2)

Semi-mobile

during

deployment and

fully post-deployment

102 hours, battery

Mid-range

storage

Multimodal physics

QoS based dynamic routing

Medium (10mm3)

Fully mobile at

deployment,

immobile

postdeployment

100 hours, battery

Hing end storage

Multimodal

chemistry,

biology

physics

Location

based

dynamic

routing,

multihop

MAC

Large

(102 mm2)

Fully mobile

during

deployment and

immobile post

deployment

Sporadic

Hing end storage

High-end

multimodal

chemistry

biology

Hierarchical dynamic routing, multishot MAC

Very large (103 mm3)

Fully mobile

during

deployment and

immobile post

deployment

Continous

Hing end storage

High end

multi-modal

physics

MAC, multishop, dynamic data center routing


Thus, the wireless network system is small, battery-powered, static, supports multihop networking.

WN Operating Environment :

The sensor nodes in WN systems need to interact with the following resource

constraints.

  1. Communication: We know that the wireless network has a limited bandwidth, limited reliability, poor quality of service (e.g. high frame loss, high latency, high variance), service exposure (eg jamming, high bit error rates).
  2. Uncertainty in measured parameters: The signals that are detected may have intrinsic uncertainty i.e. the data may have noise or interference present or data may be inaccurate because of node malfunctioning.
  3. Computation: WNs have limited computing power and memory resources. This poses limitations on the algorithms that are executed on the sensor nodes and also the results that can be stored. Further developments have a goal to develop a distributed data management layer that will scale the computational power on the sensors and use methods that are available on the sensor nodes and do not require computation or centralization of data on the processing nodes.
  4. Power consumption: The WNs have a reserved supply of operating energy. designing WSNs and WNs.

The design requirements need to consider the following points while The WNs have limited power memory and computational capacity. The WNs should be deployed in a dense environment.

WNS need not have global addresses as they have a large number of sensors. Hence, the overhead required for supporting global addresses is Sensor protocols Hierarchical dynamic routing, multihop.

WNS needs data dissemination and routing methods. WNS need in-network processing, although the data is routed, aggregated, WNs must support rapid deployment for military and security applications. WNS can be susceptible to failure. Some of the WSNs need sensing systems with long shelf-life and are resilient environmentally.

WNS needs to adapt to changes frequently. The links used for communication can be expensive and more system infrastructure is required. The sensor availability, bandwidth may also be limited for supporting large links and high-capacity networks.

Wireless nodes arrays can be used in reconfigurable networks that operate at high speeds. The WNs systems intelligence should increase so that WSNs can be deployed widely with a low power consumption of the sensor nodes.

As the mobile travels over small distances, the instantaneously received signal strength will vary rapidly resulting in small-scale fading. This is because the received signal is the summation of signals from different directions.

As the mobile travels over long distances i.e. away from the transmitter and receiver, the average received signal strength will decrease. It is predicted with the help of large-scale propagation models. The average received power is found out by averaging the signal measurements.

The three basic propagation mechanisms in wireless communication systems are Reflection, Diffraction, and Scattering. The large-scale propagation models are based on the physics of reflection, diffraction, and scattering. These models predict the received power or path loss. Reflection takes place in electromagnetic wave propagation whenever the hits an object that has very large dimensions as compared to the wavelength of the propagating wave. The reflections take place from buildings, walls, and from the surface of the earth.

Diffraction takes place when the radio path between the transmitter and receiver is obstructed by a surface that has sharp edges. The secondary waves from the obstructing surface exist throughout the space and also behind the obstructed surface, resulting in the bending of waves. At high frequencies, diffraction depends on the geometry of the object and amplitude, phase, and polarization of the incident wave at the point of diffraction.

Medium Access Control Protocols

 Medium access control (MAC) is the first protocol above the physical layer (PHY) protocol. The basic task of MAC is to coordinate time among nodes which are Since the spectrum is restricted, the existing bandwidth for the communication transmitter and is also restricted.

Applications of RFID

Hence, access to this common spectrum should be controlled in such a way that all sensor nodes get an honest share of existing bandwidth and to be for power utilized efficiently. a separate set of protocols is needed to control the access to the shared spectrum.

The tasks get divided between MAC and logical link control (LLC). The MAC protocol decides the correct timing for a node to send data to access the shared spectrum to another node to set of multicast or broadcast nodes. Error control and flow control supported by L.L.C. Error control acknowledges the correct transmission of packets and it takes correct action in case packets are Application Upper layer lost.

Fundamentals of Wireless MAC Protocols :

As nodes in WSN are spatially distributed it becomes difficult to design In order to keep communication among all nodes, nodes can exchange the data using a communication channel. This multi-access channel problem rises the complexity of the access control protocol as a result overhead is needed to control access among competing sensor nodes.

Any data collected by any node on the network is as old as the time needed to propagate their channel. The trade-off between the efficiency of MAC and the overhead needed to control is the foundation of most of the access techniques for a common channel access network.

Energy efficiency :

A sensor node consists of more than one sensor, processors with restricted capability, and small range transceiver communication ability These sensor nodes are energized using batteries with short capacity. In standard WSN, nodes are often installed in unattended areas, it becomes difficult to replace or recharge the batteries of nodes.

Furthermore, energy scavenging to recharge batteries makes it complicated and volatile. These restrictions have a direct impact on node life and results, energy conservation as supreme importance in WSN to extend the node life. One way to minimize energy consumption at the node is to use a battery of low-power electronics.

Low Duty Cycle Protocols and Wake up Concepts :

periodic wakeup scheme
Low duty cycle protocols try to minimize more spending time in inactive States. These protocols minimize the communication activities of sensor nodes to a minimum. The sleep state is left in an ideal case when a node wishes to send or receive packets. Many protocols use periodic wakeup protocol. Such periodic wakeup protocols are available in many types. In this protocol, nodes spend their maximum time in the sleep mode and get up periodically to receive packets from other nodes.


Post a Comment

Previous Post Next Post