The Analysis Of Lifetime Wireless Sensor Network

Published Date: 02 Nov 2017

The advancement in last decade in electronics & communication, computer science and information technology domain has resulted in the new computing and communication era, known as Wireless Sensor Networks. . In the past the wired sensors were implemented in limited applications in industries. However, wireless implementation makes the wide deployment of sensor nodes more feasible than before. There has been much research regarding the great potential capabilities of wireless sensor networks (WSNs) in applications such as environmental monitoring, habitat study, military surveillance in the battlefield and home automation. With sharp decreases in cost and tangible improvements in storage and processing capabilities of sensor nodes, the integrated presence of sensor nodes in human everyday-life, as the connector of the physical environment with virtual digital world, will be dominant in near future. This paper survey Wireless Sensor Networks (WSN) and their technologies, routing and applications.

KEYWORDS

Sensor networks, virtual coordinates ad hoc routing.

INTRODUCTION.

Wireless Sensor Networks (WSNs) are unrecognized communication structure that uses a large number of self capable devices, sensor nodes, to form a network. Each node in a WSN is capable of sensing the surroundings, processing locally the information and sending it to one or more number of destinations through a wireless link. Wireless sensor nodes or sensors are hardware devices that are small in size, use low energy, function in high densities, are autonomous and operate unattended, and are adaptive to the environment. The continual analog signal obtained from the sensors is converted by an analog-to-digital converter into digitized signal and sent to controllers for further processing.

Sensors can be passive omni-directional, passive narrow-beam or active sensors. Sensors that sense the data and do not process them are known as passive sensors. The energy needed to magnify the analog signal is self generated. Sensors which can give the direction of measurement are categorized into narrow-beam sensors. Omni-directional sensors do not specify the concerned direction in measurements. However, active sensors dynamically probe the surroundings and uninterrupted supply of energy is needed.

WSN Architecture

The architecture of WSN varies for a individual sensor node and the entire network. Energy efficiency, size reduction and minimum cost are the main concern for sensor node architecture.

The figure 1[1] shows the functional block diagram of a sensor node.

Figure 1: Block diagram of WSN [1]

A wireless sensor node or node is also known as mote and is made up of the following four functional components: sensing unit, processing unit, transceiver, and power unit.

Sensing Unit

It consists of an array of sensors that can measure the physical characteristics of its environment.

Processing Unit

A sensor node uses a microcontroller which performs task, processes information and controls the working of other parts in the sensor node. Since a microcontroller is characterized by its small price, ease to attach other devices, simplicity of programming, and low power utilization, they are used in sensor nodes. Memory requirements depend on application type.

Transceiver

Transceiver is used to send and receive messages wirelessly. The functionality of both transmitter and receiver are combined into a single device known as a transceiver. In WSN any node has to "converse" with other nodes. Nodes are constrained by limited energy. A transceiver must provide an adequate balance between a low data rate and small energy consumption. This enables the node to live for an extended period of time.

Sensor nodes generally make use of ISM band, which gives free radio, spectrum allotment and universal accessibility. Wireless transmission medium can be radio frequency (RF), optical communication (laser) and infrared. Lasers need line-of-sight for communication and are susceptible to atmospheric conditions. But energy requirement is less for optical communication. Infrared transmission has limited broadcasting capacity but similar to laser communication antenna is not required. However, in majority of WSN applications, communication through radio is used. The license-free communication frequencies of 173, 433, 868, and 915 MHz and 2.4 GHz is ideal for radio communication in most cases since it is not limited by line of sight. The current technology allows implementation of low-power radio. Sensor nodes must do in-network processing as much as possible because of the energy consumption of the transceiver which is far greater than the energy consumption of the microcontroller.

After the appearance in 2003 of the, Most sensor nodes use transceivers for low-rate wireless personal area networks (PANs) that comply with the IEEE 802.15.4 standard introduced in the year 2003. Transceivers lack unique identifiers. The operational states of transceiver are transmitting, receiving, idling, and sleeping. Energy consumption for transceivers in idle mode and receive mode is generally almost equal. Hence the transceiver is shut down and not left in the idling mode when it is not communicating; otherwise considerable amount of energy will be wasted when switching from sleep mode to transmit or receive mode.

Power source

Energy required for all components of a WSN is obtained from a power supply. Since the wireless sensor node is frequently positioned in an unfriendly locality, changing the battery regularly can be expensive and problematic. The energy consumption in sensor node is required for sensing, communicating and data processing. Communication of information needs more energy than any other process. The main source of energy in sensor node is from power stored in batteries or capacitors. Present sensors are able to renew their energy from solar sources, heat differences, or pulsation etc.

Operating Systems for WSN

WSNs consist of many minute networked devices that can communicate. Operating systems are the basis of the sensor node architecture. The requirements of operating system architecture in WSNs are:

very small trace,

very little overhead, and,

very small power consumption.

Due to the resource constraints in WSN hardware platform, the main aim while selecting and designing operating systems for WSN is to reduce memory size and system overheads. According to [2] and [3] three classifications of operating system architectures are described for wireless sensor nodes. They are monolithic, modular/micro and virtual machine.

TinyOS[4] is one of the first operating system specially designed for WSNs. TinyOS has a component-based structure which enables swift improvement and realization along with minimizing code size necessary due to sever memory constraints in WSNs. Component library of TinyOS allows further modification for custom application. TinyOS is an open source OS based on an event-driven programming model.

Contiki [5] The Contiki is another operating system for WSN. Like TinyOS, its kernel is event-driven and on a per-application basis can perform multithreading. Contiki can support IPv4 and IPv6 type of IP communication.

SOS (SOS Embedded Operating System) [6] is an event-driven OS that follows a more dynamic position on the design field. Loadable modules support is one of the key features of SOS.

LiteOS [7] is an open source, interactive operating system designed for WSNs. LiteOS, like Unix, has tools that allows operation on one or more WSNs. Applications can be developed for nodes and can be distributed wirelessly to sensor nodes.

According to [3], [8], [9] and [10] there are a total of thirty nine operating systems identified for WSNs.

Topologies for WSN

In WSN the position of the nodes is known after the deployment of sensors. The topology architecture for WSN is dependent upon quantity and rate of data to be sent, transmission distance, power requirements, mobility and surroundings. Three types of network topology architecture are popularly used for wireless sensor networks. They are:

Star topology: A star topology is a single-hop system. Each node connects directly to a gateway. . All sensor nodes are the same and the base station serves to communicate information. Star topology is characterized by low power consumption and is restricted by the transmission distance of radio.

Cluster tree topology: Each node connects to a node higher in the tree and then to the gateway, and data is routed from the lowest node on the tree to the gateway.

Mesh topology: Mesh topologies are multi-hop systems where all nodes can connect to multiple nodes in the system and pass data through the most reliable path available. The nodes can pass information to any node in the network without the interference of the Base Station. A mesh network is more dependable and extremely fault tolerant. Mesh topology consumes more power than star topology.

Lifecycle of WSN

The lifecycle of a WSN can be distinguished into four stages [7]. They are:

Planning WSNs The planning stage is the first stage of the life cycle. This is necessary for achieving the purpose of creating a WSN. The survey of the deployment region is carried out for identification of the locations before the placement of the sensors. Deployment WSNs In the deployment stage, sensor nodes repeatedly send their connection status along with the path to the Base Station.

Monitoring WSNs This stage is concerned with the analysis of the information provided by the network sensors.

Controlling WSNs This stage is used for controlling the WSN by sending instructions from the Base Station. The instructions can include commands to sensors such as stop sending messages, change the frequency of message transfer or restart the entire network etc.

Planning and deployment stage is usually concerned by researchers whereas the end users are more concerned in monitoring and controlling the WSN.

Routing in WSN

Routing is a process of determining a path between source and destination for data transmission. Routing in WSN is very challenging due to the inbuilt characteristics that make out these networks from other wireless networks like mobile ad hoc networks or cellular networks. In WSN the routing protocols [11] [12] are application specific, data centric, capable of aggregating data and capable of optimizing energy consumption. The important characteristics of a good routing protocol for WSN are simplicity, energy awareness, adaptability and scalability due to limited energy supply, limited computation power, limited memory and limited bandwidth of WSN [13][14][15]. WSNs are intended to achieve data communication along with measures to extend the lifetime of the network. The demanding factors affecting the design of routing protocol in WSNs is summarized below:

Node deployment: In WSNs node deployment is dependent upon the purpose and environment. The performance of the routing protocols in WSNs is influenced by node deployment, particularly in the energy requirement. Nodes can be deployed either manually or in a self-organizing fashion classified as manual or random deployment method respectively. Nodes deployment is also distinguished according to the mobility of sensor nodes. If the nodes are passively moved by external forces, they are called passive nodes. Active nodes can actively look for concerned areas.

Network dynamics: The coverage and connectivity of WSN is affected by the dynamic characteristics of Base Station or sensor node. As connectivity among sensor nodes change, stability and route decision becomes one of the demanding issues. If the base station and sensor nodes are moving, the problem is more complicated.

Energy Conservation: While creating a WSN, energy conservation factor has an effect in the selection of routes [16] [17] [18]. In many cases, multi-hop communication conserves energy of sensor nodes compared to one hop communication and hence resulting in increase in life of WSN. However a problem arises in case of the forwarding nodes fast energy drainage in comparison to the nodes at the last layer in multi hop communication, hierarchical communication. Multi-hoping is involved with significant overhead due to network management and medium access control.

Fault Tolerance: The sensor node failure should not influence the working of WSN. Network need to work even when some of the sensor nodes fail.

Scalability: The sensors in the deployed area vary in number. Also many sensor nodes may not be functional due to power drainage, physical damage etc. creating holes in the existing WSN. Design of WSN must support scalability.

Production Costs: The general requirement is to keep the cost of a sensor node to be minimum.

Hardware Constraint: Since the requirement of WSNs is low energy, low computational capacity and low communicational range, it becomes one of the important design issues related to power saving, quality of service etc. All subunits of sensor node, that is sensing, processing, communication, power, location finding system and mobilize, must consume very low power [19] and be contained within a very small range. MAC layer may be designed in to synchronize the wake and sleep time with application requirement.

Sensor network topology: It must be maintained regardless of very high node density. Maintaining the topology in the mobile scenario becomes one of the important and necessary issues.

Environment: Nodes should be operating in inaccessible location because of hostile environment.

Transmission Media: Generally, transmission media is wireless (RF or Infrared), which is affected by fading and high error rate and affect the operation of WSNs.

Data delivery models: Data delivery may be categorized in to following: event driven, query-driven, reactive, proactive, hybrid. Choosing one data delivery model is basically requirement of the application of the WSNs.

Quality of Service (QoS): Quality service required by the application is dependent upon the life time, data consistency, energy efficiency, position knowledge, collaborative-processing, etc. The choice of routing protocols for a particular purpose is influenced by the QoS factors.

Security: WSNs may communicate with sensitive information and operate in unfriendly surroundings. Hence security concerns needs to be addressed while designing the routing protocols for WSN.

Node capabilities: A sensor node can be committed to a particular special work such as relaying, sensing and aggregation, depending on the requirement. Engaging all the three functionalities simultaneously on a node may result in quickly drainage of the energy at that node.

Data aggregation/fusion: In order to effectively use the limited energy available, computation costs which are much smaller than the communications cost, is utilized to minimize the amount of information that actually has to be sent [20], [21]. Data aggregation/fusion helps in reducing number of communications by using some aggregate functions like suppression (eliminating duplicates), min, max and average. The clustering protocol supports in-network aggregation which is used to aggregate information from various sensors and to summarize that information before communicating and passing it on to the other nodes. This increases the life span of WSNs.

Byte Overhead [22]: The total number of bytes in the routing control messages in order to determine a routing path to the Base Station is called byte overhead. In case of flooding the byte overhead specifies the total number of bytes in the extra messages flooded throughout the network. The bytes transferred along the path from the starting node to the base station are not considered as overhead.

Applications of WSN

Wireless Sensor Network is being used in wide range of applications that extensively differ in needs and characteristics [23]. WSNs can be applied extensively in areas such as environment monitoring and tracking, calamity assistance, crisis operation, home networks, detecting chemical/biological /radiological /nuclear/explosive material, monitoring patents and elderly people, asset and warehouse management, building monitoring and control, fleet monitoring, military battlefield awareness and surveillance, security and surveillance, environmental monitoring, pipeline corrosion monitoring, homeland security, monitoring conditions of buildings and bridges, process management, machine health monitoring, healthcare applications, home automation, traffic control, etc.

The table 1 below lists applications of WSNs in different areas.

Area

Applications

Military

• Military site alertness [24].

• Detection of enemy movements on land or sea [25].

• Battleground surveillances[26]

Emergency

situations

• Calamity management [27].

• Fire/water detectors.[ 25]

• Harmful chemical level and fires [28].

Physical world

• Ecological monitoring [29].

• Habitual monitoring [29].

• Examination of biological and artificial systems [29].

• Marginal Farming.

Medical and health

• Sensors for blood flow, respiratory rate, ECG (electrocardiogram), pulse oxymeter, blood pressure and oxygen measurement [30].

• Monitoring people’s location and health condition.

Industry

• Factory process control and industrial automation [24].

• Monitoring and control of industrial equipment [28].

• Machine health monitoring [31].

Home networks

• Home appliances, location awareness (blue tooth).

• Person locator.

Automotive

• Tire pressure monitoring [28, 32].

• Active mobility [33].

• Coordinated vehicle tracking [24].

Area monitoring

• Detecting enemy intrusion [24]

• Geo-fencing of gas or oil pipelines [25].

• Detecting the presence of vehicles [24].

8. Conclusion

This paper carries out a survey on Wireless Sensor Networks (WSN) based on their technologies, routing and applications. WSNs comprises of a miniature sensor nodes with capabilities of sensing, computation, and wireless communications. All systems, processes and communication protocols for sensors and sensor networks must minimize power consumption. The small requirement of power for sensor nodes makes the design of energy-efficient communication protocol necessary. Routing protocols are primarily application specific. They network architecture also influences the design of routing techniques. In comparison with the traditional Mobile Ad hoc Network, WSNs have different characteristics and poses different design challenges.

The flexibility, fault tolerance, high sensing dependability, low cost, and swift deployment characteristics of sensor networks have made their use in many new applications such as artificial intelligence, remote sensing etc. The possible applications for wireless sensor networks can be as diverse as the human body where they may monitor the circulation system. In the future, WSN is being considered to help in exploration of planets.