Literature Review: Wireless Sensor Networks

CHAPTER 2

To complete this project, a lot of literature reviews have been done. These include many case studies from past to recent research and general understanding towards the theory behind each technology. Articles, journals, books, previous projects and internet have served as sources of literature reviews. Some major case studies are described below.

2.1.1 Case study 1

Case study towards paper “Integration of RFID into Wireless Sensor Networks: Architectures, Opportunities and Challenging Problems” (2006) [1]

In this paper, Lei Zhang and Zhi Wang propose three different forms of network architecture based on integration of RFID and wireless sensor network, The three architecture are Heterogeneous network, Distributed reduced functional sensor reader network, and Mini node network.

Heterogeneous network architecture uses 802.11b/Wi-Fi technology as its platform. In Physical layer, 802.11b/Wi-Fi uses the unlicensed 2.4 GHZ band and Discrete Sequence Spread Spectrum (DSSS) technique. Its maximum data rate can reach to 11 Mbps. In MAC sub-layer, 802.11b/Wi-Fi uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) scheme, which will improve the efficiency of network. This architecture is good for real-time operation but limited range.

Distributed reduced functional sensor reader network architecture uses ZigBee protocol as its platform. The reasons are ZigBee uses lower power consumption in physical layer and MAC layer, more reliable and low cost. This architecture is good for wide range but no real-time requirement.

The last architecture which is the Mini node network architecture uses IEEE 802.15.4/ZigBee standard protocol as its platform since there is little data flow and reduced cost. The mini node is actually the Mica nodes which allow communication between each mini node. This architecture is specially fit for industrial security and remote condition-based maintenance system,

Figure 2.1 below describe remote condition-based maintenance systems based on the application of Mini node network architecture. By using this architecture, the reader from the forklift will sense signal from each mini node and will move toward the signalled mini node to perform tasks like move rotating parts of a machine automatically.

Figure 2.1: Fork lift operation dispatching in a factory [1]

Case study 2

Case study on paper “Smart Home Mobile RFID-based Internet-Of-Things Systems and Service” (2008) [2]

Mohsen Darianian, Martin Peter Michael introduce a RFID reader system architecture for a home comprised of several readers in master slave architecture. The communication protocol between the readers and tags is based on RFID standard protocols like UHF. As shown in Figure2.2 below, the system consists of following reader components: Master Reader (MR), a number of Slave Readers (SR), and Mobile RFID (MRFID) Reader

The Master reader is a conventional powerful fixed reader with a direct fixed or wireless connection to the smart home server. It starts the read process of slave readers and power up passive tags for reading process. In addition, this master reader also acts as the so-called “RF Energy Generator” for mobile RFID reader so that the mobile RFID reader can have lower consumption of power.

The Slave reader acts as middleware for capturing tag ID information tags which are not accessible by the direct radio transmission of the master reader. Slave readers will be integrated in the home appliances. Since location of the slave readers is known by the system, it is good for localization of tags

As for the Mobile RFID reader, in this paper, it has been improved so that it does not consume a lot of energy. The mobile RFID reader will use the proposed architecture so-called “RF Energy Generator” to be powered up by master reader or slave reader. Thus, these mobile readers will act like passive readers.

In this paper, Mohsen Darianian, and Martin Peter Michael have apply the proposed system architecture as described above to create a smart home which apply wireless concepts along with RFID technologies for creating services almost everywhere in a house. It applications include control electrical appliances, home tele-monitoring, and give intelligent suggestions inside the house automatically and wirelessly.

Figure 2.2: Smart Home using RFID and WSN [2]

Case study 3

Case study on Paper “Bus Management System Using RFID in WSN” by Ben Ammar Hatem and Hamam Habib (2009) [3]

In this paper, intelligent bus tracking application applying integration of RFID and wireless sensor network technology to monitor whether the bus will be arriving on time, early or late inside the bus station is introduced.

The design approach is proposed. As shown in Figure 2.3, first, each bus will has its own UHF tag. Next, Entrance and exit doors will be equipped with an RFID reader, antennas and motion sensors. When a bus enters or exits the station, the RFID reader will send its identification to the central computer where the event is displayed on a Map. Finally, a software application on the control station keeps track of the entrance and the exit of buses and updates the displays related to those buses with useful information. The communication will be wireless using ZigBee protocol.

To execute this proposed architecture, they choose to use Ultra High Frequency generation 2 (UHF Gen2) RFID which operates between 860MHz to 960MHz bandwidth. UHF is better suited for reading tag attached to buses. It uses backscatter technique to communicate with the tag and provides higher read range compared to HF and LF technology. As for the antenna, they used Alien circular antenna to read RFID tags to improve orientation of reading. Two antennas are used in each gate, to communicate with tags. One is used for the emission of energy to the tag and the other receives energy back from the tag. The display is using the LCD and LED technologies.

By completing this proposed system, it is hope to provide a smart solution for managing the bus schedule in the bus stations and offering helpful information to passengers. Problems like under employment of buses fleet and long waiting time at the bus station can be minimised.

Case study 4

Case study on paper “Intelligent Traffic Management System Base on WSN and RFID” by Lejiang Guo, Wei Fang, Guoshi Wang and Longsheng Zheng (2010) [4]

This paper introduces Intelligent Transportation System (ITS) base on RFID and WSN, and discusses the hardware and software design principles of the system. Figure 2.4 shows the ITS system architecture. It consists of Access and Terminal Layer, Application Processing Layer, and Data storage and access management. The Access and Terminal layer mainly completes information exchange between each subsystem of ITS. Application Processing Layer will be responsible for processing the information. And lastly the Data storage and access management will be the data management system for the ITS system.

As for the composition of the system, RFID tags and sensor nodes are used to keep stored in the monitoring area. RFID reader is used for the base station. At the same time, the sensor nodes send the data after its transfer to the local PC or remote network. RFID can be used for dereliction of duty as an intelligent base station device for RFID and data WSN systems Integration. In the network, the system consists of five types of facilities which are Base Station, Sensor nodes, RFID Tags, Device reader and Center Data Platform. Zigbee protocol is implemented in this system architecture. Figure 2.5 show how the sensor nodes are deployed and communicate to each other.

As for the data communication middleware, advanced web Service architecture is implemented. The reason is web service is the most advanced platform for distributed applications, by which it not only can achieve basic distributed application, but also improve fault tolerance. Messaging middleware is using XML format for the transmission of information. Geographic Information System (GIS) is also combined in the system. GIS is based on one of the technologies supported by Public Security Traffic Management GIS platform. GIS is used to process all information associated with visual processing, to provide simple and direct for visualization information interface.

By utilizing the application of ITS based on combination of RFID and WSN. The real-time traffic management system can provides the basis for efficient data monitoring. Second, the system uses the heterogeneous adaptive network architecture for road monitoring will provide a more flexible way, efficient, reliable system communication architecture for traffics management system

Case study 5

Case study on paper “Innovative Application of RFID Systems to Special Education Schools” by Shu-Hui Yang and Pao-Ann Hsiung (2010) [5]

In this paper, the uses of RFID system innovatively broaden. Application of innovative Radio Frequency Identification (RFID) systems has been incorporated to special education school campus to improve the teaching and learning and control process in special education schools.

For the Implementation Platform and Architecture, the main RFID campus system was implemented using the YesTurnkey technology, which includes four parts, namely front-end RFID middleware server, front-end RFID application server, backend database server, and backend RFID application server.

Front-end RFID Middleware Server consists of YesTurnkey Asset Tracking Manager which is a manager of all network resources that includes the set of active RFID readers installed on campus and RFID Processor DLL that processes RFID data. Front-end RFID Application Server is a server which used by the Type 1 (Direct-Connected) RFID scenario windows applications. Backend Database Server implemented the Microsoft SQL Server. And finally, Backend RFID Application Server: which manages the execution of two kinds of applications which are YesTurnkey WiNOC (Wired/Wireless Network Operations Center) Web Application and Type 2 (LAN-Based) RFID Scenario Web Application.

However, five of the innovative works are focused, including student temperature monitoring (STM), body weight monitoring (BWM), garbage disposal monitoring (GDM), mopping course recording (MCR), and campus visitor monitoring (CVM) by applying the RFID system technology. Basic operation for mopping course recording (MCR) system will be described below.

(Swab with the reader is moving across tag)

As shown in Figure 2.6, first, they patch up of a mobile pedestal, an artificial plastic floor with embedded passive RFID tags, and a real mop equipped with a Bluetooth passive RFID reader. The mobile pedestal carried a laptop for displaying the real time status of how a student is performing the cleaning job and a projector connected to the laptop, which could project a black, dark grey, light grey or white image on the artificial floor, which represented dirty, little clean, quite clean, and clean. By using this MCR, teacher can monitor these special education students so that the students will learn to complete their task better.

As can be seen, by using this RFID technology, outcomes shown above have truly give benefits not only to teacher but also the student. Research is still ongoing to include RFID technologies in teaching method and materials.

Summary of the case studies

Theories behind this project

This section explains general theory on the technologies involve in this project. The theory and technology involve include Wireless Sensor Network (WSN), Radio-frequency identification (RFID), Integration of WSN and RFID and Visual Basic Programming (VB).

2.2.1 Wireless Sensor Network (WSN)

A Wireless Sensor Network is a self-configuring network of small sensor nodes communicating among themselves using radio signals, and deployed in quantity to sense, monitor and understand the physical world such as temperature, pressure, humidity and more.

Figure 2.7: WSN Sensor Node

2.2.1.1 Wireless Sensor Network (WSN) Topology

Wireless sensor network topology show how each sensor node inside a wireless network are connected. Some of the WSN topologies are like star, mesh and cluster/tree. They are shown Figure 2.8 below. Basic WSN topology is the star topology in which each node maintains a single, direct communication path with the gateway. To increase wireless coverage, cluster/tree topology can be used although it increases complexity. Finally, although network latency may be experienced, mesh topology is especially good in increase network reliability. [6]

Figure 2.8: WSN network topologies

2.2.1.2 Wireless Sensor Network (WSN) components

A wireless sensor network may consist of the following components: power supply, microcontroller, wireless communication, sensor, local storage, and real time clock systems. Some components may be optional and are depend on the function purpose. The main idea is that the sensors are connected to a tiny computer that coordinates the measurement, pre-processes, stores and delivers the information.

Wireless Sensor Network (WSN) characteristics

This section describes the behavior or the uniqueness of wireless sensor network. Some of them are: harvest or store limited power, Able to withstand harsh environmental conditions, able to adapt with node breakdown, nodes mobility, dynamic network topology, heterogeneity of nodes, large scale of deployment, unattended operation, and lastly, node capacity is scalable and only limited by bandwidth of gateway node.

Wireless Sensor Network (WSN) protocols

There are a lot of wireless sensor network protocols in market nowadays. Some of the well- known WSN protocols are Bluetooth, WiFiZone, IEEE and ZigBee. Choosing the wrong protocol may cause severe inefficiency and prevent the WSN to accomplish user need. The protocol will affect energy dissipation, system cost, Latency and Security. Thus, it is very important to choose the best protocol for a system as it strongly impact on system performance.

Wireless Sensor Network (WSN) platform

Wireless sensor network platform basically include the hardware design, modular design, smart sensor interface, software design, and operating system. The hardware designs include super node, simple node and gateway. All these design have to follow several standardized specification developed by IEEE, Internet Engineering Task Force, and International Society of Automation. Modular design has to be flexible and expandable for various applications. Smart sensor interface has to equipped with plug and play modules. Important topics to be considered in software design include security, mobility and middleware which allow communication between software and hardware. And finally, operating system has to be compatible with TinyOS as TinyOS allows easy establishment to wireless sensor network.

Radio-frequency identification (RFID)

RFID is a means of identifying a person or object using radio frequency transmission. Mainly, RFID consists of three parts which are reader, tag and also host computer. There are also various types of reader and tags depend on their uses.

Figure below show basic operation of a RFID system. First, to read data for tag, tag is move and enter RF field of reader through antenna. Then, RF signal from antenna will power the tag to allow the tag to transmit its ID and data back. Reader will then capture the data and send them to the computer for displaying.

To write data to the tags, we just write the data into the computer, and the reader will take the data from the computer and transmits them into the tag via the antenna.

Figure 2.9: Basic Operations of RFID

2.2.2.1 RFID reader

RFID reader is also called as RFID interrogator and it is used to read/write data from/to tags. It can operate on single or multiple frequencies, and perform anti-collision processing. There is also a hybrid RFID reader which can read bar code. There are mainly three types of RFID reader which are fixed, hand-held and mobile reader. Each reader has their own uniqueness.

RFID reader consists of components like receiver, transmitter, oscillator, controller/processor and input/output port. The receiver holds an amplifier and a demodulator. Transmitter has a modulator and power amplifier. Oscillator is used to provide carrier signal to modulator and a reference signal to demodulator circuits. Then, the controller/processor will perform data processing and communicates with external network. And lastly, input/output port is connected to the antenna.

2.2.2.2 RFID tag

RFID tag consists of RFID chip, antenna and power source.

RFID chip consists of modulation circuitry, control circuitry, processor and memory. Modulation circuitry can change the signal from reader to include data to be transmitted back to the reader. Control circuitry control internal function under the command of processor. Processor interpret signal from reader and control memory storage with retrieval. And memory serves as writable and non-writable data storage.

Antenna is only used by Ultra high frequency and Microwave frequency tags. Low frequency and High frequency tags will use induction coils.

As for power sources, the tags can be divided into three types which are active tags, semi-passive tags and passive tags. Active tags have internal power source. Passive tags draw power from reader. And Semi-passive tags are battery-assisted but communicated by drawing power from reader.

Integration of WSN and RFID

Wireless sensor network (WSN) is used to sense and monitor various parameters in the environment while RFID is used to detect presence, location and identification of objects. By integrating these two technologies, they will provide a significant improvement on monitoring application. The basic idea of integration of WSN with RFID is to connect the RFID reader to an RF transceiver, which has routing function and can forward information to and from other readers wirelessly. RFID will act as a ‘sensor’ in the WSN. With combination of RFID and WSN, monitoring and tracking application can be done not only outdoor but indoor also (with obstacle). The coverage can also be improved depends on the specification of WSN platform used.

Visual Basic Programming (VB)

Visual Basic is a programming language and environment developed by Microsoft which is based on the BASIC language. Visual Basic is commonly used to develop graphical user interface. Visual Basic was one of the first products to provide a graphical programming environment for developing user interfaces. Since it uses graphical programming environment, we can be sure to increase the efficiency in design the graphical user interface.