INTRODUCTION
A sensor network is a structure comprised of sensing (measuring), computing, and communication elements which gives an administrator the ability to instrument, observe, react to events and phenomena in a specified environment. The administrator typically is a civil, governmental, commercial, industrial entity. The environment can be the physical world, a biological system, or an information technology framework. Network sensor systems are seen by observers as an important technology that will experience major deployment in the next few years for a plethora of applications, not the least being national security. Typical applications include, but are not limited to, data collection, monitoring, surveillance, and medical telemetry.
There are four basic components in a sensor network: (1) An assembly of distributed or localized sensors; (2) An interconnecting network (usually, but not always, wireless-based); (3) A central point of information clustering; and (4) A set of com4puting resources at the central point (or beyond) to handle data correlation, event trending, status querying, and data mining.
In this context, the sensing and computation nodes are considered part of the sensor network; in-fact, some of the computing may be done in the network itself. Because of the potentially large quantity of data collected, algorithmic methods for data management play an important role in sensor networks. The computation and communication infrastructure associated with sensor networks is often specific to this environment and rooted in the device- and application-based nature of these networks.
Background of Sensor Network Technology
Researchers see WSNs as an ‘‘exciting emerging domain of deeply networked systems of low-power wireless motes (The terms sensor node, wireless node, smart dust, mote, and COTS (commercial off the shelf) mote are used somewhat interchangeably; the most general terms, however, are sensor node and wireless node ) with a tiny amount of CPU and memory, and large federated networks for high-resolution sensing of the environment’’. Sensors in a WSN have a variety of purposes, functions, and capabilities.
The field is now advancing under the push of recent technological advances and the pull of a myriad of potential applications. Much less expensive WSNs are now being planned for novel applications in physical security, health care, and commerce. Sensor networking is a multidisciplinary area that involves, among others, radio and networking, signal processing, artificial intelligence, data- base management, systems architectures for operator-friendly infrastructure administration, resource optimization, power management algorithms, and platform technology (hardware and software, such as operating systems).
The near ubiquity of the Internet, the advancements in wireless and wireline communications technologies, the network build-out(particularly in the wireless case), the developments in IT (such as high-power processors, large random-access memory chips, digital signal processing, and grid computing), coupled with recent engineering advances, are in the aggregate opening the door to a new generation of low-cost sensors and actuators that are capable of achieving high-grade spatial and temporal Resolution.
Applications of Sensor Networks
Traditionally, sensor networks have been used in the context of high-end applications such as radiation and nuclear-threat detection systems, ‘‘over-the-horizon’’ weapon sensors for ships, biomedical applications, habitat sensing, and seismic monitoring. More recently, interest has focusing on networked biological and chemical sensors for national security applications; furthermore, evolving interest extends to direct consumer applications.
Military applications
- Monitoring friendly forces and equipment
- Military-theater or battle field surveillance
- Targeting
- Battle damage assessment
- Nuclear, biological, and chemical attack detection and more...
Environmental applications
- Microclimates
- Forest fire detection
- Flood detection
- Precision agriculture and more...
Health applications
- Remote monitoring of physiological data
- Tracking and monitoring doctors and patients inside a hospital
- Drug administration
- Elderly assistance and more...
Home applications
- Home automation
- Instrumented environment
- Automated meter reading and more...
Commercial applications
- Environmental control in industrial and office buildings
- Inventory control
- Vehicle tracking and detection
- Traffic flow surveillance and more...
Wireless sensors can be used where wireline systems cannot be deployed (e.g., a dangerous location or an area that might be contaminated with toxins or be subject to high temperatures). The rapid deployment, self-organization, and fault-tolerance characteristics of WSNs make them versatile for military command, control, communications, intelligence, surveillance, reconnaissance, and targeting systems Many of these features also make them ideal for national security.
Near-term commercial applications include, but are not limited to, industrial and building wireless sensor networks, appliance control [lighting, and heating, ventilation, and air conditioning (HVAC)], automotive sensors and actuators, home automation and networking, automatic meter reading/load management, consumer electronics/entertainment, and asset management.
Commercial market segments include the following:
- Industrial monitoring and control
- Commercial building and control
- Process control
- Home automation
- Wireless automated meter reading (AMR) and load management (LM)
- Metropolitan operations(traffic, automatic tolls, fire, etc.)
- National security applications: chemical, biological, radiological, and nuclear wireless sensors
- Military sensors
- Environmental (land, air, sea) and agricultural wireless sensors.
BASIC OVERVIEW OF THE TECHNOLOGY
The provided a high-level description of the approach, issues, and technologies associated with WSNs. Some additional details are provided in this section from a generic perspective; many of these issues and concepts are then dis- cussed in greater detail in the chapters that follow. As we proceed, the reader should keep in mind that sensor networks deal with space and time: location, coverage, and data synchronization. Data are the intrinsic ‘‘currency’’ of a sensor network.
Instead of sending the raw data to the nodes responsible for the data fusion, nodes often use their processing abilities locally to carry out basic computations, and then transmit only a subset of the data and/or partially processed data. In a hierarchical processing architecture, processing occurs at consecutive tiers until the information about events of interest reaches the appropriate decision-making and/or administrative point.
Sensor nodes are almost invariably constrained in energy supply and radio channel transmission bandwidth; these constraints, in conjunction with a typical deployment of large number of sensor nodes, have posed a plethora of challenges to the design and management of WSNs. These challenges necessitate energy aware- ness at all layers of a communications protocol stack. Some of the key technology and standards elements that are relevant to sensor networks are as follows:
- Sensors
- Intrinsic functionality
- Signal processing
- Compression, forward error correction, encryption
- Control/actuation
- Clustering and in-network computation
- Self-assembly
- Wireless radio technologies
- Software-defined radios
- Transmission range
- Transmission impairments
- Modulation techniques
- Network topologies
TINY OS
Tiny OS (TinyOS is being developed by the University of California– Berkeley as an open-source software platform; the work is funded by DARPA and is undertaken in the context of the Network Embedded Systems Technology Research Project at UC–Berkeley in collaboration with the University of Virginia, Palo Alto Research Center, Ohio State University, and approximately 100 other organizations) Tiny DB (a query-processing system for extracting information from a network of Tiny OS sensors)
Software applications
Operating systems
Network software
Direct database connectivity software
Middleware software
Data management software
Basic Sensor Network Architectural Elements
In this section we briefly highlight the basic elements and design focus of sensor networks. These elements and design principles need to be placed in the context of the C1WSN sensor network environment, which is characterized by many (some- times all) of the following factors: large sensor population (e.g., 64,000 or more client units need to be supported by the system and by the addressing apparatus), large streams of data, incomplete/uncertain data, high potential node failure; high potential link failure (interference), electrical power limitations, processing power limitations, multi hop topology, lack of global knowledge about the network, and (often) limited administrative support for the network (C2WSNs have many of these same limitations, but not all).
Sensor network developments rely on advances in sensing, communication, and computing (data-handling algorithms, hardware, and software). As noted, to manage scarce WSN resources adequately, routing protocols for WSNs need to be energy-aware. Data-centric routing and in-network processing are important concepts that are associated intrinsically with sensor networks The end-to-end routing schemes that have been proposed in the literature for mobile ad hoc networks are not appropriate WSNs; data-centric technologies are needed that perform in-network aggregation of data to yield energy-efficient dissemination.
Challenges and Hurdles
For WSNs to become truly ubiquitous, a number of challenges and hurdles must be overcome. Challenges and limitations of wireless sensor networks include, but are not limited to, the following:
- Limited functional capabilities, including problems of size
- Power factors
- Node costs
- Environmental factors
- Transmission channel factors
- Topology management complexity and node distribution
- Standards versus proprietary solutions
- Scalability concerns.
SENSOR NODE TECHNOLOGY
A WSN consists of a group of dispersed sensors (motes) that have the responsibility of covering a geographic area in terms of some measured parameter (also known as the measure and); alter- natively, a sensor supports a point-to-point link in which the ‘‘reader’’ end is attached to a wire line network (e.g., a stationary tag reader sensing a mobile tag).
Sensor nodes have wireless communication capabilities and some logic for signal processing, topology management (if and where applicable), and transmission handling (including digital encoding and possibly encryption and/or forward error correction).
Some sensor applications also support e-money purchases at point-of-sale locations such as from soft-drink machines, kiosks, gas stations, and checkout counters. The basic functionality of a WN generally depends on the application, but the following requirements are typical.
Determine the value of a parameter at a given location. For example, in an environment-oriented WSN, one might need to know the temperature, atmospheric pressure, amount of sunlight, and the relative humidity at a number of locations. Detect the occurrence of events of interest and estimate the parameters of the events. For example, in a traffic-oriented WSN, one would like to detect a vehicle moving through an intersection and estimate the speed and direction of the vehicle.
Track an object: For example, in a military WSN, track an enemy tank as it moves through the geographic area covered by the network.
Power: An appropriate energy infrastructure or supply is necessary to support operation from a few hours to months or years (depending on the application).
Computational logic and storage: These are used to handle onboard data processing and manipulation, transient and short-term storage, encryption, forward error correction (FEC), digital modulation, and digital transmission. WNs have computational requirements typically ranging from an 8-bit microcontroller to a 64-bit microprocessor. Storage requirements typically range from 0.01 to 100 gigabytes(GB).
Hardware and Software
Related to WN design, the following functionality typically needs to be supported: intrinsic node functionality; signal processing, including digital signal processing (e.g., FFT/DCT), compression, forward error correction, and encryption; control and actuation; clustering and in-network computation; self-assembly; communication; routing and forwarding; and connectivity management.
To support this functionality; the hardware components of a WN include the sensing and actuation unit (single element or array), the processing unit, the communication unit, the power unit, and other application-dependent units shows hardware and software components of a typical sensing node have four basic hardware subsystems:
Sensor transducer(s): The interface between the environment and the WN is thesensor.Basicenvironmentalsensorsinclude,butarenotlimitedto,acceleration, humidity, light, magnetic flux, temperature, pressure, and sound.
Communication: WNs must have the ability to communicate either inC1WSN arrangements (mesh-based systems with multi hop radio connectivity among or between WNs, utilizing dynamic routing in both the wireless and wire line portions of the network), and/or in C2WSN arrangements (point-to-point or multipoint-to- point systems generally with single-hop radio connectivity to WNs, utilizing static routing over the wireless network with only one route from the WNs to the companion terrestrial or wire line forwarding node).
Sensor nodes have to deal with the following resource constraints:
Power consumption: Almost invariably, WNs have a limited supply of operating energy; it follows that energy conservation is a key system design consideration.
Communication: The wireless network usually has limited bandwidth; the networks may be forced to utilize a noisy channel; and the communication channel may be relegated to an unprotected frequency band. The implications are limited reliability, poor quality of service (e.g. high latency, high variance, high frame loss), and security exposure (e.g., denial of service, jamming, interference, high bit-error rates).
Computation: WNs typically have limited computing power and memory resources. The implications are restrictions on the types of data-processing algorithms that can run on a sensor node. This also limits the scope and volume of intermediate results that can be stored in the WNs. Research aims at developing a distributed data management layer that scales with the growth of sensor interconnectivity and computational power on the sensors.
Uncertainty in measured parameters: Signals that have been often have various detected or collected degrees of intrinsic uncertainty. Desired data may be commingled with noise and/or interference from the environment. Node malfunction could collect and/or forward inaccurate data.
I tried my best to explain the basics of Wireless Sensor Network and related concepts. I hope you will like it. 😊