2D/3D Wireless Ray Tracing Educational Land

Transcription

1 2D/3D Wireless Ray Tracing Educational Land A dissertation submitted to the University of Manchester for the degree of Master of Science by Research/Master of Enterprise in the Faculty of Engineering and Physical Sciences 2011 Mona Demaidi School of Computer Science

2 Contents List of figures... 4 List of tables... 7 Abstract... 8 Declaration... 9 Copyright Acknowledgment Chapter 1 Introduction Aims Hypothesis Chapter 2 Background Virtual Worlds Migrating from Second Life to OpenSimulator Education in Virtual Worlds Virtual worlds in comparison with e-learning systems Simulations in education Choosing the appropriate virtual world for educational purposes Electromagnetic signals Electromagnetic spectrum Decibels Antennas Free space propagation Reflection Refraction Scattering Absorption Diffraction Objects properties Multipath propagation Ray tracing

3 2.4 Ray tracers in virtual worlds Chapter summary Chapter 3: Design and Implementation Implementation language Scripts in OpenSim D/3D Wireless Ray Tracing Educational Land Frequency-wavelength converter tool Frequency-wavelength converter buttons Frequency-wavelength self test Frequency-wavelength information box Electromagnetic spectrum tool Electromagnetic spectrum sphere Electromagnetic spectrum coloured boxes Antennas tool Free space propagation laboratory The transmitter antenna The receiver antenna D/3D wireless Ray tracing laboratory The 2D/3D wireless ray tracing remote Control The transmitter antenna Determining the frequency and the transmission power Ray tracing Drawing the rays Send the stored information to rays Rays Obstacles Evolution and adaption Chapter 4: Results Overview Frequency-wavelength converter tool Frequency-wavelength self test Frequency-wavelength information box

4 4.3 Electromagnetic spectrum tool Antenna tool Free space propagation laboratory The transmitter antenna The receiver antenna D/3D wireless ray tracing laboratory The transmitter antenna Obstacles D/3D ray tracing simulation Evaluation Technical evaluation Educational evaluation Chapter 5 Conclusion Summary of contribution Further Work Short term enhancements Longer term enhancements Bibliography Appendix Appendix Appendix

5 List of figures Figure 1: Clicker tool presenting a quiz question to students Figure 2: Evaluation results for each student after the quiz ends Figure 3: Emitting signals in 2D Figure 4: Emitting signals in 3D Figure 5: Inventory associated with each avatar in Second Life Figure 6: (a) In-world content creation tools for modelling, (b) Scripting tool Figure 7: Box shows a welcome message when it is touched by an avatar Figure 8: Discussion forum in Moodle Figure 9: Classroom in Second Life Figure 10: A snapshot taken in AWEDU Figure 11: A snapshot taken in Wonderland Figure 12: A snapshot taken in Open Cobalt virtual environment Figure 13: Electromagnetic signal Figure 14: Electromagnetic spectrum Figure 15: Isotropic antenna Figure 16: Omni-directional antenna Figure 17: Directional antenna Figure 18: The radiation pattern of an Omni-directional antenna Figure 19: The radiation pattern of a Yagi antenna Figure 20: Reflection Figure 21: Refraction Figure 22: (a) Diffraction at the edge of an obstacle and (b) Fresnel zone Figure 23: Multipath propagation Figure 24: Screenshot form demo of Unreal 3 game engine Figure 25: Side view of the room used in 3D ray tracer Figure 26: (a) Reflection, (b) Diffraction, (c) Diffuse propagation Figure 27: Frequency-wavelength converter tool Figure 28: Frequency-wavelength converter button state diagram Figure 29: The self test questions format Figure 30: Calculator state chart Figure 31: Electromagnetic spectrum tool Figure 32: A 2.4 GHz directional Yagi antenna simulated in 4NEC Figure 33: Antenna tool Figure 34: Free Space propagation laboratory Figure 35: Transmitter antenna state chart Figure 36: The code responsible for calculating the path loss Figure 37: State chart of a sphere listening to the transmitting antenna Figure 38: The geometric origin of the inverse square law Figure 39: The intensity and distance inverse square relation Figure 40: The receiver antenna state chart

6 Figure 41: The 2D/3D wireless ray tracing laboratory Figure 42: Obstacles state chart Figure 43: Wireless ray tracing educational land Figure 44: The dialog box displayed in a wavelength to frequency conversion Figure 45: The wavelength of a 100 Hz frequency Figure 46: The self test in Frequency-wavelength converter tool Figure 47: The score presented to students after they finish the test Figure 48: The Notecard produced for the Frequency-wavelength converter tool Figure 49: The electromagnetic spectrum tool decided that 3000 Hz is within the VLF range.. 75 Figure 50: Isotropic antenna information displayed in a dialog box Figure 51: The billboard and the information box Figure 52: The dialog box displayed when the student touch the transmitter antenna Figure 53: The path loss chart for a 2.4 GHz and -10 dbw signal Figure 54: The details displayed by the transmitter antenna Figure 55: The path loss and the received power at the sphere position Figure 56: Intensity and distance square law relation at a 1 meter distance from Tx Figure 57: Intensity and distance square law relation at 2 meters distance from Tx Figure 58: Configure the sensitivity at the receiver antenna Figure 59: The received power is less than the receiver sensitivity Figure 60: The billboard and the information box Figure 61: Configure the frequency in the transmitter antenna Figure 62: A cement obstacle wall changed to become a wooden obstacle wall Figure 63: 2D ray tracing simulation environment Figure 64: Visualize one interaction with the surrounding environment Figure 65: Information displayed for each sphere in the incident ray Figure 66: Information displayed at the intersection point of wooden obstacle Figure 67: Information displayed at the intersection point of cement obstacle Figure 68: Information displayed for each sphere in the reflected ray from a wooden obstacle. 89 Figure 69: Information displayed for each sphere in the reflected ray from a cement obstacle.. 89 Figure 70: The 2D/3D Simulation environment to visualize the refracted rays Figure 71: (a) Incident ray (b) Refracted ray Figure 72: (a) Refraction angle for a wooden cuboid (b) Refraction angle for a cement cuboid 91 Figure 73: Three walled room with a floor and ceiling Figure 74: Buttons one and two are pressed to visualize one and two interactions Figure 75: The 3D ray tracer output Figure 76: Reflection from a ceiling cube obstacle in 3D Figure 77: Computational time and the number of interactions related to the emission angle Figure 78: Relationship between the emission angle and the computational time Figure 79: Emission angle relation with the number of one reflection and two reflections Figure 80: Rays produced at a 1 degree emission angle increment Figure 81: Rays produced at 2 degrees emission angle increment Figure 82: Intersection of a Line and a Sphere

7 Figure 83: Intersection of a Line and a plane Figure 84: Rays produced at 3 degrees emission angle increment Figure 85: Rays produced at 4 degrees emission angle increment Figure 86: Rays produced at 5 degrees emission angle increment Figure 87: Rays produced at 6 degrees emission angle increment Figure 88: Rays produced at 7 degrees emission angle increment Figure 89: Rays produced at 8 degrees emission angle increment Figure 90: Rays produced at 9 degrees emission angle increment Figure 91: Rays produced at 10 degrees emission angle increment

8 List of tables Table 1: Comparison between Second Life and OpenSimulator Table 2: Virtual world s features Table 3: Comparison between LSL and Non-LSL Table 4: Tasks performed by the buttons and the lights Table 5: Obstacle s name parts and the assigned value and objective of each part Table 6: The information displayed by intersection and ordinary spheres Table 7: Computational time and number of interactions for different emission angles

9 Abstract Technology has a great impact and influence on educational process in classroom environments. Students can use the advanced computing and telecommunication technologies, to access different types of information and to communicate with their teachers and colleagues using several types of media. Among the new emerging technologies are online three dimensional virtual worlds (3D VW s). This technology allows students to understand thoroughly and predict the physical phenomena, which require interactive simulations and laboratories that may be expensive, time consuming and dangerous. Simulations can help carry out virtual experiments but they are not very interactive, complex and slow. 3D VW s provide a natural interactive exploration environment, where individuals and groups can interact and learn. This project used the VW s technology to improve the learning experience for electrical engineers and physics students studying electromagnetic wireless systems. Instead of using textbooks, pictures, equations and paper examples to understand how signals propagate, signals are visualized in an interactive 3D virtual environment. In this research a Wireless Ray Tracing Educational Land(WRTEL) has been implemented in OpenSimulator[ 1 ] virtual world, to allow students to understand and visualize wireless signal propagation. The land consists of three main regions; in the first region, three educational tools have been implemented to introduce students to the wavelength, frequency, the electromagnetic spectrum and antennas. In the second region, a free space laboratory had been designed in the outer space to allow students to visualize line of sight signal propagation between the transmitter and the receiver antennas. In the third region, students are provided with a two and three dimensional ray tracing laboratory to create environments using obstacles made from different materials. Students will be able to visualize how signal behaviour (reflection, refraction, diffraction and scattering) is affected by the surrounding environment. Path loss calculations, received power, angle of incidence and many other values will be provided at any point in space until the signal is received by the receiver antenna. The transmitted wireless signals will be visualized by mapping them into the visual spectrum for display; this makes the invisible rays visible. A brief technical and educational evaluation indicated that the educational land was both usable and would support student learning activities in the laboratories. 8

10 Declaration No portion of the work referred to in the dissertation has been submitted in support of an application for another degree or qualification of this or any other university or other institute of learning. 9

11 Copyright The author of this dissertation (including any appendices and/or schedules to this dissertation) owns any copyright in it (the Copyright ) and s/he has given The University of Manchester the right to use such Copyright for any administrative, promotional, educational and/or teaching purposes. Copies of this dissertation, either in full or in extracts, may be made only in accordance with the regulations of the John Rylands University Library of Manchester. Details of these regulations may be obtained from the Librarian. This page must form part of any such copies made. The ownership of any patents, designs, trade marks and any and all other intellectual property rights except for the Copyright (the Intellectual Property Rights ) and any reproductions of copyright works, for example graphs and tables ( Reproductions ), which may be described in this dissertation, may not be owned by the author and may be owned by third parties. Such Intellectual Property Rights and Reproductions cannot and must not be made available for use without the prior written permission of the owner(s) of the relevant Intellectual Property Rights and/or Reproductions. Further information on the conditions under which disclosure, publication and exploitation of this dissertation, the Copyright and any Intellectual Property Rights and/or Reproductions described in it may take place is available from the Head of School of Computer Science. 10

12 Acknowledgment This thesis is the product of my Master research project, and would not have been possible without the support and the high quality learning resources provided by the educational stuff at the University of Manchester. I am sincerely and heartily grateful to my advisor, Dr Nicholas Filer, for the support and guidance he showed me throughout my dissertation writing. I am sure it would have not been possible without his help. Words fail me to express my appreciation to my family for their support, understanding and endless love, through my master s year. Lastly, I offer my regards to all of those who supported me in any respect during the completion of the project. 11

13 Chapter 1 Introduction Technology has a very important role in the classroom today and can be used to teach significant concepts in almost every subject area. Teachers use electronic presentations to integrate video, audio and images to their lecture notes. This helps them to provide students with a better understanding and improve the educational process. The youth of today know more about technology than any generation before them. They communicate with each other using various communication technologies such as the internet. Most students have profiles in different on-line social networks which they use to share thoughts and exchange knowledge. Web based education is their normal expectation. Students prefer to search for learning material where the information they need will be found instantly. Recent improvements in information and communication technologies such as powerful processors and broadband connections are available in most universities and schools. This has created the opportunity for developing several web 2.0[ 2, 3 ] based teaching tools which better meet students expectations. Students and teachers can use the World Wide Web (WWW)[ 4 ], to communicate with each other using live chat such as the Internet Relay Chat(IRC)[ 5 ]. E-learning systems provide students with 24 hour online access to educational materials. This plays an essential role in improving the educational process, especially when the subject discussed in the classroom is difficult to fully understand or large and couldn t be finished within the lecture s specified time. In other words, a face-to-face class conversation can be shifted to the e-learning systems where the students have instant feedback from their teachers and colleagues. Today the Moodle[ 6 ] and Blackboard[ 7 ] virtual learning environments (VLE) are integrated with VLE clickers, to provide students with instant feedback and continuous assessment[ 8 ]. These tools have been developed to facilitate learning in and out the classroom by using the VLE combined with a personal response system. It gives teachers the ability to ask questions, assess students using quizzes and get their responses instantly. Figure 1 shows a clicker tool presenting a quiz question to students. Students answer the question using the clicker, and the tool presents their feedback in a pie chart with pending and received answers. Figure 2 shows the evaluation results for each student after the quiz ends. 12

14 Figure 1: Clicker tool presenting a quiz question to students[ 8 ] Figure 2: Evaluation results for each student after the quiz ends[ 8 ] 13

15 Undeniably, a student s physical presence inside a classroom is an essential part of the educational process. Therefore, Virtual worlds tend to provide users with a three dimensional environment filled with several objects. Users can explore the surrounding scenes by walking, swimming, flying and teleporting using a graphical representation called avatars[ 9, 10 ]. In contrast to the two dimensional VLE, existing virtual worlds support the sense of presence and active participation. Therefore, this means that students can interact and collaborate with each other to perform an educational task. Students can also experience inquiry based learning by simply wondering around the virtual learning world either freely or with some directions. Teachers and students could then perform practical experiments, which may be expensive or difficult to do in the real world in the Virtual World (VW). In addition, in the VW invisible phenomena can be made visible. For example magnetic fields can be visualized, and in this work electromagnetic (EM) signals are made visible. EM signals propagation and interactions between these signals and the surrounding environment is one of the phenomena which cannot be easily visualized within real classrooms and e-learning systems. Teachers and students find it difficult to perform any practical experiments to visualize the propagated signals in the real surrounding environment. For some cases, instruments can measure parameters such as signal strength at a given location, but this would take a long time to achieve these measurements everywhere, and to make the results visual and easy to use. As a result, students find it difficult to predict how signals propagate and interact with the surrounding environment. In the VW students should be able to visualize and understand the behaviour of the propagated signals (reflection, refraction, diffraction, and scattering) easily. In this project a two dimensional (2D) and three dimensional (3D) Wireless Ray Tracing Educational Land (WRTEL) is developed in an OpenSimulator virtual word[ 1 ]. WRTEL introduces students to several aspects; firstly, students will become familiar with the signal s wavelength and frequency properties. Secondly, they are introduced to the electromagnetic spectrum, to understand frequency ranges. Thirdly, students can 14

16 create, view and check 3D style antenna geometry structures and generate, display and/or compare near/far-field radiation patterns. Fourthly, students are provided with a simulated real free space propagation laboratory where the line of sight (LOS) signal between the transmitter and the receiver antennas is visualized. The laboratory which is shown in Figure 34 gives students the indication that the free space propagation occurs in a theoretical environment, where no interactions with the surrounding environment occurs, and only the LOS signal is received by the receiver antenna. Free space path loss and received power calculations are provided to students at each point along the LOS signal. Finally the main part in the WRTEL is the 2D and 3D wireless ray tracing laboratory. It allows students to visualize the propagated signals between the transmitter and the receiver antennas in 2D and 3D modes. As shown in Figure 3, in 2D mode signals are emitted from the transmitter antenna in an X-Y plane only and in 3D mode signals are emitted with the additional Z axis as shown in Figure 4. In the VW, students can create different environments and assign various materials to the obstacles presented in the scene, to visualize how the signal propagation behaviour is affected by the obstacles. Each time obstacles change in shape or material the results will change. Information about the path loss, received power, angle of incidence, refraction angle and many other values are provided to students. Figure 3: Emitting signals in 2D 15

17 Figure 4: Emitting signals in 3D According to a literature search, this kind of virtual educational land has not been implemented in virtual worlds before, and the research presented in the project appears to be unique on a world-wide basis. Subsequent use of the educational land will help us to gain more knowledge about the effectiveness of using virtual environments for teaching different physical phenomena. 1.1 Aims The WRTEL aims for the following: Allow students to understand signals wavelength and frequency properties. Enable students to understand the frequency ranges. Allow students to create, view and check 3D style antenna geometry structures and generate, display and/or compare near/far-field radiation patterns. Provide students with a free space propagation laboratory where the free space path loss term and the receiver antenna sensitivity are introduced. Enable students to visualize signals behaviour (reflection, refraction, diffraction and scattering) when obstacles with different materials and shapes are presented in the environment. Allow students to create different environments and assign various materials to the obstacles presented in the scene, to visualize how the signal 16

18 propagation behaviour is affected each time obstacles change in shape or material. Allow students to visualize the power loss after each interaction between the propagated signals and the surrounding environment. Provide students with a self test functionality which they can use to test their understanding. 1.2 Hypothesis In this research the invisible signal propagation are made visible using the VW technology. Students are able to visualize signal behaviour (reflection, refraction, diffraction and scattering) in 2D and 3D dimensions and information about each interaction between signals and the surrounding environment is displayed. In the future, experiments will show whether this technology is an effective teaching tool or not. But this project concentrates on the design and implementation of the system not its evaluation. 17

19 Dissertation Guide Chapter 2 contains the necessary background to understand this research, including background on virtual learning environments and education in virtual worlds, background on electromagnetic signals, free space propagation and ray tracing. Chapter 3 is about the design and implementation of the 2D and 3D wireless ray tracing educational land which is the focus of this research; it includes implementation issues that were met and how they were overcome. Chapter 4 describes the project results and a very brief technical and educational evaluation. Chapter 5 presents the project conclusion, and mentions the short- and longerterm enhancements which could be applied to the work presented in this project. 18

20 Chapter 2 Background This chapter contains the necessary background to understand this research. Section 2.1 includes a brief description on virtual worlds, education in virtual worlds, a comparison between virtual worlds and e-learning systems and a study about the most appropriate virtual world for educational purposes. In section 2.2 a background about electromagnetic signals, electromagnetic spectrum, antennas, free space propagation, multipath propagation and ray tracing is introduced. Finally section 2.3 includes a description about existing ray tracers in virtual worlds. 2.1 Virtual Worlds Virtual worlds like many computer games provide users with a 3D environment filled with several objects. Users can explore the surrounding scenes by walking, swimming, flying and teleporting[ 9, 10 ]. It is an Internet virtual community"[ 11 ], where people from all over the world interact with each other in real time using a graphical representation of themselves called avatars Migrating from Second Life to OpenSimulator Virtual worlds have been simulated in massively multiplayer online (MMO) games, which support thousands of users simultaneously[ 10 ]. MMO games had been created statically by the games producers, players have no privilege to modify or create contents while playing. Moreover, physical and interaction rules are predefined for each player; players are restricted to specific interactions at each state in the game and can t act freely[ 12 ]. For example the player has to shoot a specific target, in order to gain points and move to the next stage. It is obvious that the MMO focus was on providing users with games, where the scenario on how each player will move and interact with the surrounding environment is already known[ 12 ]. To allow users to interact freely and create their own contents, Second Life [ 13 ] was released by Linden Labs in Each avatar in Second Life[ 13 ] is associated with an inventory shown in Figure 5. It is a persistent personal repository used to store contents such as, clothes and buildings[ 10, 13 ]. 19

21 Figure 5: Inventory associated with each avatar in Second Life [1] Second Life[ 13 ] has become one of the most popular 3D virtual online worlds (over 16.8 million users in 2009)[ 14 ]. It provides users with a free networked multiuser environment, users log in using the Second Life Viewer client to communicate, socialize and interact with each other using the public chatting and messaging interface[ 15, 16 ]. Second Life[ 13 ] provides users with a graphical and scripting tool shown in Figure 6. The tool is used to create and manage their own contents[ 12 ]. It provides users with several primitive objects which are called prims including spheres, cones and cubes. It also allows users to control the behaviour of each object using scripts. Figure 7 represents a box, which is scripted to show a welcome message once it is touched by an avatar. Figure 6: (a) In-world content creation tools for modelling, (b) Scripting tool [ 15, 16 ] 20

22 Figure 7: Box shows a welcome message when it is touched by an avatar Even though Second Life[ 13 ] allows users to create and control their own in-world environments, it is not an open source project[ 10 ]. In 2007 OpenSimulator(OpenSim)[ 1 ] was developed under the Berkeley Software Distribution(BSD) license. It is an open source project which aims to provide users with an open and extensible platform. Virtual worlds within OpenSimulator[ 1 ] can run on users own servers rather than using Second Life s Linden Lab servers. Table 1 illustrates a comparison between OpenSimulator[ 1 ] and Second Life[ 13 ]. Table 1: Comparison between Second Life and OpenSimulator Second Life OpenSimulator Hosting Location Linden Labs Anywhere Hosting Costs Annual fee Free Server Closed Source Open Source Scripting LSL LSL, OSSL, C# Client Open Source Open Source 21

23 It is obvious that OpenSimulator[ 1 ] is much more suitable for implementing thy 2D/3D wireless ray tracing educational land than Second Life[ 13 ] due to the following: In Second Life[ 13 ], user s contents are hosted in Linden Lab servers and streamed to the client application, as a result, a fast low-latency internet connection and a reasonably fast computer system with a good quality graphics card is required for Second Life[ 13 ] to work successfully[ 10, 15 ]. On the contrary, contents in OpenSimulator[ 1 ] are hosted on the user s machines[ 10 ]. This allows more computation intensive tasks than the remote sources can do. Users within Second Life can t host their own land for free, they need to pay an annual rental fee to Linden Labs[ 10, 17 ]. On the other hand, OpenSimulator[ 1 ] server is open source and is available for free, users can host their lands and build their own environments without paying any rental fees. Second Life[ 13 ] uses Linden Scripting language (LSL)[ 18 ] as its only official scripting language. LSL scripts in Second Life[ 13 ] have a memory limit (code segment[ 19 ] plus data segment[ 19 ]). The memory consumption at the beginning was a full 16KB for all scripts, but later the memory allocation mechanism changed to a dynamic method that only allocates the needed memory, up to 64KB, by each script[ 15, 20 ]. Compared to Second Life, OpenSimulator[ 1 ] Supports several in-world script languages such as C#[ 21 ], LSL[ 18 ] and OpenSimulator scripting language (OSSL)[ 22 ]. 2.2 Education in Virtual Worlds Educators face new challenges which have not been experienced by teachers in the past. They are dealing with Net Generation [ 23, 24 ] students who have been raised in a computerized world, where online identities and virtual communication take place. This generation expects more interactive and engaging learning experiences which the universities cannot afford. In 2001 Prensky introduced the difference between two generations, the Digital natives who have been born in a digital world and grew up with video games and computers, and the Digital Immigrants who started using digital 22

24 technologies during their life time[ 23, 25 ]. Both generations interact with each other within the educational process, as the digital natives are usually taught by digital immigrants. Digital immigrants, who used to learn from books and communicate by phone, need to figure out how the digital natives think and try to communicate with them using different methods[ 23 ]. Students are in touch with technology in their everyday activities through computers, online networks and mobile phones. These students are known as community focused [ 25 ], as they participate in virtual communities to develop social relations and share interests[ 26 ]. Educational institutions are trying to catch up with all these technologies to satisfy the students needs by using e-learning systems and educational virtual worlds which integrate education with technology Virtual worlds in comparison with e-learning systems E-learning systems and virtual worlds have been used for educational purposes by many universities. Both of them had been evaluated to figure out how students get involved and interact with each other during educational tasks. E-learning systems such as Moodle[ 6 ] and Blackboard[ 7 ] lack the social presence and face to face interactions between students and teachers. Students manifest their presence through discussion forums, blogs and posting links or videos. Figure 8 shows the discussion forum in Moodle[ 6 ] e-learning system. 3D Virtual worlds tend to provide a much greater sense of presence; students are represented as avatars that interact in real time. Figure 9 shows a classroom in Second Life[ 13 ]. This provides the sense of social interaction which is missing in the e-learning systems[ 27 ]. Also the technology provided within virtual worlds contributes to the sense of social presence, as the user can hear a person who is standing close more clearly than a person who is far away[ 28 ]. It is clear that virtual worlds tend to provide students with an educational environment much closer to a real environment than e-learning systems. 23

25 Figure 8: Discussion forum in Moodle[ 6 ] Figure 9: Classroom in Second Life[ 13 ] Simulations in education Simulations are the first fundamental change to education since the textbook [ 29 ]. People learn best when they do things, and simulations help teachers in providing an exciting learning environment for students[ 29 ]. Simulations are generally used as a replacement for real life situations which are too dangerous or impractical to experience. Providing students with practical experience is a key concept in improving the learning 24

26 process, as it helps them to experiment, explore and expand their knowledge beyond the theoretical concepts. Simulations are categorized into three types, linear, cyclic and open-ended. Each one of them has its purpose and outcome[ 29 ]. Linear simulations like books have a beginning and ending, and even if the user chooses to simulate the content in different ways, the result at the end will be the same. Most of the e-learning systems are linear and include standard assessments and tests. Cyclical simulation is in arcade games where the outcome depends on the users speed and skill. This type of simulation is used to teach a specific skill. Open-ended simulation is considered to be good in developing strategies and skills which can be transferred to students. For example, in teaching someone how to drive a car, telling them to make the car move by stepping on the gas and make it stop by pressing the brake pedal is linear, but having them actually learn by doing is cyclical as it requires muscle memory[ 29 ]. Driving the car under real conditions so that users have various interactions of law, other drivers (both bad and good), weather conditions, manoeuvring the car, and navigating is open-ended[ 29 ]. Virtual worlds are open-ended simulations which will provide students with the next generation of e-learning. In contrast to cyclical simulation, open-ended is not goal oriented. It provides students with the freedom to move, create object and interact with other people[ 30 ]. Developing educational simulations is extremely challenging, as developers have to compete on budget with industry and with experienced game designers to develop a high quality simulation. So most of the educational simulations are likely to be of a lower quality than those in the marketplace. Virtual worlds solved these issues as they provide developers with a platform that is relatively fast and cost effective to design their virtual environments for learning and teaching[ 29 ]. 3D simulations can be implemented within these worlds to enhance experimental learning Choosing the appropriate virtual world for educational purposes Virtual world educational environments should be reusable, available and open source. In choosing the appropriate virtual world these aspects had been considered for Active worlds[ 31 ], Wonderland[ 32 ], Open Cobalt[ 33 ], Second Life[ 13 ] and OpenSimulator[ 1 ]. Table 2 illustrates the features of each virtual world[ 27 ]. 25

27 Table 2: Virtual world s features Active worlds Wonderland Croquet Cobalt Second Life OpenSimulator Open Source No Yes Yes No Yes Free client/server As guest/yes Yes/Yes Free peer As guest/no Yes/Yes Language C Java Smalltalk C++ C# Focus Education (AWEDU) Any Any Business Any capabilities Web browsing, voice chat, basic instant messaging Application sharing Easy content creation, uses scripts Active Worlds[ 31 ] focus on education, as it offers an educational community known as the Active Worlds Educational Universe (AWEDU)[ 31 ]. However, it is not an open source project; it lacks a lot of capabilities such as content creation and users need to pay a registration fee[ 27 ]. Figure 10 shows a snapshot taken in AWEDU[ 31 ]. Figure 10: A snapshot taken in AWEDU[ 31 ] 26

28 Wonderland[ 32 ] is an open source project. Although it supports many capabilities, it is still an early version (v0.5) and needs a lot of improvements. Figure 11 shows a snapshot taken in Wonderland[ 32 ]. Figure 11: A snapshot taken in Wonderland[ 32 ] Open Cobalt[ 33 ] project has been used by many universities such as the University of British Columbia. However, it is still an early version. Figure 12 shows a snap shot taken in Open Cobalt virtual environment[ 33 ]. Figure 12: A snapshot taken in Open Cobalt virtual environment[ 33 ] 27

29 Second Life[ 13 ] virtual world is the most popular among the presented virtual worlds. Although it has been used for educational purposes by many universities, it has a complex registration process especially when users are non adult members[ 27 ]. This causes a problem especially when the created educational environment considers non adult users. In our case the land is implemented for both adults and non adult users and simplifying the registration process is a requirement. OpenSimulator[ 1 ] is an open source virtual world which is highly compatible with Second Life[ 13 ]. Although it is in the alpha phase of development, it has been used by many universities and companies such as IBM and Microsoft[ 27 ]. OpenSimulator[ 1 ] allows non expert users to create contents easily and use text and voice communication facilities. It satisfies the educational purposes better than Second Life because it is open source and it has no age restrictions. Both adults and non adult users are provided with the same facilities. OpenSimulator[ 1 ] is also much easier to use than Cobalt[ 33 ] and Wonderland[ 32 ] as both of them are closer to API than virtual worlds[ 27 ]. Finally, Active Worlds have limited capabilities. In addition to the motivations discussed in section 2.1.1, the reasons above reinforce choosing OpenSimulator[ 1 ] as an implementation platform for the 2D/3D wireless ray tracing educational land. OpenSimulator[ 1 ] supports multiple users, which allows students from all over the world to meet at one place and engage in an innovative learning environment[ 10, 34 ]. It is possible to build 3D demonstration models in OpenSimulator[ 1 ], which provides students with supportive learning environments where several activities such as exploration, experimentation and dynamic feedback can be performed[ 35 ]. 28

30 2.3 Electromagnetic signals Electromagnetic signals are composed of both electric and magnetic fields, both of which oscillate perpendicular to each other in the direction of propagation as shown in Figure 13. Electromagnetic signal propagation has been described by Maxwell s equations[ 36 ], which state that electrical field is produced by changing the magnetic field, and the magnetic field is produced by changing the electrical field. As a result electromagnetic signals are able to self propagate[ 36 ]. Electromagnetic waves have a number of basic properties such as wavelength, frequency and speed. Figure 13: Electromagnetic signal Electromagnetic spectrum Electromagnetic signals cover a wide range of frequencies and wavelengths which is called the electromagnetic spectrum[ 37 ]. As shown in Figure 14 the spectrum consists of frequency ranges-bands for visible light, ultraviolet, infrared, X-rays and radio[ 38 ]. Each band has a particular frequency range, for example radio signals have a frequency range between 3Hz and 300 GHz. 29

31 Figure 14: Electromagnetic spectrum[ 38 ] Decibels In communication systems most of the units used to present the path loss, power, gain and sensitivity use Decibels (db) scaled relative units. For example, Decibels are used to measure the signals strength; it is a logarithmic ratio which is used to represent one power value to another[ 38 ]. A Decibel can have either a positive value (+db) which indicates power gain or a negative value (-db) which represents power loss. In addition to db units, dbm unit where m stands for milli is often used as a unit for transmission power and receiver sensitivity Antennas Antennas, are defined as an electrical conductor or system of conductors used for either radiating electromagnetic energy or for collecting it [ 39 ]. The transmitter antenna converts the electrical energy into electromagnetic energy and radiates it into the surrounding environment. On the other hand, the receiver antenna collects the radiated electromagnetic energy and converts it back to electrical energy[ 39 ]. 30

32 Figure 15: Isotropic antenna Figure 16: Omni-directional antenna [ 40 ] Figure 17: Directional antenna[ 40 ] 31

33 Antennas are characterised by their radiation pattern into isotropic, Omni-directional and directional antennas which are shown in Figures 15, 16 and 17 respectively[ 40 ]. A radiation pattern defines the variation of the power radiated by an antenna as a function of the direction away from the antenna[ 40 ]. The isotropic antenna is defined as a hypothetical lossless antenna having equal radiation in all directions [ 41 ]. It is a theoretical antenna which has a spherical radiation pattern and radiates the power equally in all directions. The Omni-directional antenna provides a 360 degree radiation pattern, where the power is radiated uniformly in all directions in one plane only and not in all planes as the isotropic antenna[ 40 ]. An example on Omni-directional antenna is a dipole shown in Figure 18[ 42 ]. The dipole has a circular radiation pattern in one field and a figure (8) pattern representing a doughnut shape. These types of antennas can be used in a small office environment to provide coverage for WLAN clients[ 42 ]. Figure 18: The radiation pattern of an Omni-directional antenna[ 42 ] The directional antennas focus the energy in one direction more than another, which results in an increase in the signal strength in the chosen direction. The signal strength is called the antenna gain and it is measured in decibels with respect to a dipole (dbd) or to the theoretical isotropic antenna (dbi)[ 40 ]. An example on the directional antennas is the Yagi antenna which is shown in Figure 19[ 42 ]. The antennas have a high gain, between 32

34 12 and 18 dbi and are best used for a point-to-point link over a distance, for example, between two buildings[ 42 ]. Figure 19: The radiation pattern of a Yagi antenna[ 42 ] Free space propagation Signals propagation through space, results in reducing the signal s strength over distance. This is known as the free space path loss and it is calculated using the following equation[ 43, 44 ]: Where is the path loss in, is the gain at the transmitter antenna, is the gain at the receiver antenna, d is the separation between the transmitter and the receiver in meters and is the frequency in hertz and is the velocity of propagation. 33

35 Different types of antennas have different gain values. If the antenna is isotropic, the energy will be radiated equally in all directions and the gain is one. This is introduced in the following equation where and values are one[ 43, 44 ]: The Free space propagation model can be used to find the received signal strength. In air, close to the ground there is a clear Line of sight (LOS) between the transmitter and the receiver antennas, the received power is predicted using the following Friis free space equation[ 43, 44 ]: Where is the received power and is the system loss factor which results from several causes of attenuation such as interactions with, for example ground reflections [ 43 ]. The Receiver antennas have particular power sensitivity. This means it can only detect and decode signals when the strength is above the sensitivity. If is less than the sensitivity the signals will be unusable[ 43 ] Reflection Reflection which is shown in Figure 20 occurs when a propagated signal in a medium encounters a border of another medium with different electrical properties. Some of the signal will be reflected and some is refracted. The signal s direction, amplitude and phase are affected on reflection[ 45 ]. 34

36 Figure 20: Reflection Refraction Refraction which is shown in Figure 21 occurs when a signal passes from one medium to another, for example from air to water. This means that Part of the signal is refracted and the rest is reflected, scattered or absorbed[ 45 ]. Refraction affects the signal s direction and phase which is tightly related to the objects materials refractive indexes which the signal encounters[ 45 ]. Figure 21: Refraction 35

37 2.3.7 Scattering Most surfaces are rough and irregular, as a result they are not totally reflective and when signals hit them, they will be scattered in all directions. In propagation, the roughness of a surface is tested via Rayleigh criteria (a heuristic) which define a critical height of a surface is protuberances for a given angle of incidence of a wave[ 44 ]: Rough surfaces have a minimum to maximum protuberance height greater than, smooth surfaces are less than. The path loss can be approximated by multiplying the flat surface reflection with the scattering loss factor, which is described by a Gaussian random protuberance height with a standard deviation representing the differences in height across a surface[ 44 ] Absorption Absorption is the most common Radio Frequency (RF) behaviour. Most materials absorb some of an RF signal to a varying degree[ 40 ]. For example brick and concrete walls will absorb a signal more significantly than a drywall[ 46 ]. Another example on absorption is the microwave oven. It transmits RF which is absorbed by water molecules and others in food. The absorbed energy is then converted to heat causing a rise in the temperature[ 47 ] Diffraction In diffraction signals can propagate even behind obstacles. Huygen's principal states that wavelets originating from all points on AB propagate into the shadow region, and the field at any point in the region will be the result of the interference of all these wave lets [ 43 ]. This shown in Figure 22a[ 43 ]. 36

38 (a) (b) Figure 22: (a) Diffraction at the edge of an obstacle and (b) Fresnel zone[ 43 ] Diffraction is explained via Fresnel zones, which provides alternative constructive and destructive interference that is equivalent to a phase difference of 90 degrees. Each Fresnel zone represents a region where secondary waves have a path length greater than the LOS path. It is important to keep the first Fresnel zone free of obstructions, in order to perform transmission under mainly free space conditions[ 43 ]. This is shown in Figure 22b Objects properties When a signal encounters an object in space, interactions between them occurs and the signals direction, phase and power is affected. The frequency of a signal has an influence on its behaviour. Most of the wireless data communication frequencies operate at the Non Line Of Sight (NLOS) range[ 45 ]. For example, the 2.4GHz frequency used by IEEE [ 48 ] is specifically planed to work for NLOS. This means that they can propagate through certain objects. Objects are composed from different materials which affects the radio waves differently[ 45 ]. For example, wood, bricks and glass have different influence on the electromagnetic waves. 37

39 A research had been done to determine the path loss experienced by frequencies larger than 2 GHz indicates that a typical suburban house results in a 9.1dB loss[ 45 ]. A stone building results in a 12.8dB loss and an aluminium sheet results in a 46dB loss[ 45 ]. Water tends to almost absorb the 2.4GHz wave completely[ 45 ]. Rain drops smaller than the wavelength of the encountered wave will absorb the signal; large raindrops will scatter the wave, which results in a decrease in the amplitude[ 45 ] Multipath propagation Multipath propagation occurs when the signal emitted from the transmitter propagates through several paths until it is received by the receiver antenna[ 43, 44 ]. It is an unavoidable phenomenon which depends on the surrounding environment, for example multipath propagation in a warehouse with metallic surfaces is more prominent than a normal office environment[ 49 ]. Multipath propagation results from signals reflection, refraction, diffraction, scattering and many other environmental effects[ 43, 44 ]. This is shown in Figure 23[ 40 ]. In order to track how the emitted signals direction, phase and power change until they reach the receiver antenna, ray tracing is used. Figure 23: Multipath propagation[ 40 ] 38

40 Ray tracing Ray tracing is based on geometrical optics (GO), where rays are traced out from a specific source in all directions. In graphics, ray tracing is used as a rendering method, which simulates reflection, refraction and shadows[ 50 ]. The light path is tracked from a specific source to compute each pixel in the rendered image. Virtual worlds use ray tracing to produce shadows, 3D lighting scenes, and to determine whether an object is in the camera s view and should be processed for rendering or not[ 51 ]. Figure 24 shows a rendered scene from the Unreal 3 game engine; where lighting and shadowing is introduced[ 52 ]. Figure 24: Screenshot form demo of Unreal 3 game engine[ 52 ] 39

41 In communication systems, ray tracers are used to predict signals propagation characteristics such as reflection, refraction, diffraction and scattering in indoor and outdoor environments[ 53, 54 ]. Several 2D and 3D ray tracers have been developed to find ray paths between the transmitter and the receiver antennas. Generally, ray tracers are implemented using two algorithms. The first one is known as ray launching and is a brute force technique[ 53, 55 ]. This approach is used to determine all the possible rays that propagate between the transmitter and the receiver antennas by emitting a large number of rays separated by a constant angle from the transmitter. According to [ 56 ] an angular separation of one degree will obtain reasonable coverage and computation time. Ray launching is very efficient computationally, since rays can be discarded if they exceeds a specific number of interactions (reflection, refraction, diffraction, and scattering) with the surrounding environment. The second algorithm is the point to point ray tracing. It has been introduced in [ 57, 58 ] to solve limitations presented by the ray launching algorithm. However exhaustive search of possible ray paths is required. Point ray tracing also requires computation of a visibility graph that contains all possible rays that could occur between the transmitter and receiver. 2.4 Ray tracers in virtual worlds Several ray tracers have been implemented within virtual worlds, such as the 3D ray tracer which has been developed by the University of Lancaster for Ultra Wideband (UWB) Channel Modelling[ 59 ]. The tool was designed using a 3D Game Studio tool to model the indoor virtual environment. It consists of a single room with a single transmitter and receiver antennas presented as a Tx and Rx the small yellow spheres in Figure 25. The room consists of objects with different materials and textures such as the walls, light and tables. 40

42 Mirror Tx Rx Light Table Figure 25: Side view of the room used in 3D ray tracer[ 59 ] Both reflection and refraction have been considered in the implementation of the ray tracer. The refraction occurs when the transmitted ray hits the mirror. When the ray hits the fronts or face of the mirror it splits into reflected and refracted rays, both of them are traced through for the reflections and refractions until they reach the receiver. Reflected and refracted rays which reach the receiver antenna are not visualized. The output of the ray tracer is a text file, which consists of the delay experienced by each ray that reaches the receiver successfully, and the distance covered by each ray in meters[ 59 ]. The second example on ray tracers is the interactive geometric sound propagation and rendering system[ 60 ], which is shown in Figure 26. The system is able to render sound in a dynamic manner, where the source, the listener, and obstacles can move. Propagated paths are between the source and the listener takes into account reflection, diffuse, refraction and edge diffraction[ 60 ]. (a) (b) (c) Figure 26: (a) Reflection, (b) Diffraction, (c) Diffuse propagation[ 60 ] 41

43 2.5 Chapter summary This chapter contains all the required information necessary and related to this research. A brief description of virtual worlds, education in virtual worlds and a comparison between virtual worlds and e-learning systems had been introduced and elaborated. OpenSimulator virtual world had been chosen as an implementation platform for the 2D/3D WRTEL, after a complete and comprehensive research and analysis of the existing educational virtual environments. In order to fully understand how the ray tracer in the WRTEL is implemented and what information is provided to students within this educational environment. This chapter introduced a brief description on the ray tracing implementation algorithms, signals behaviour (reflection, refraction, diffraction and scattering) and objects properties which affects signal propagation. 42

44 Chapter 3: Design and Implementation This chapter describes the design and implementation work undertaken in the wireless ray tracing educational land (WRTEL). The implementation language and scripts are briefly described in sections 3.1 and 3.2. The implementation of the wireless ray tracing educational land is explored in section Implementation language OpenSimulator[ 1 ] supports several in-world scripting languages which are used to control the behaviour of virtual objects and communicate with other objects and avatars[ 1, 22 ]. According to Table 3 [ 1, 10, 13, 18, 61 ] the in-world scripting languages in OpenSimulator[ 1 ] can be categorized to LSL[ 18 ] and Non-LSL[ 10 ]. LSL scripting language was originally developed for Second Life by Linden Labs, with over 300 library functions (functions start with ll) and different data types. ll functions in LSL have limitations; there are a lot of tasks that can t be performed by them. For example they don t support the teleport functionality and writing data on Notecards[ 15, 61 ]. To overcome this problem, OpenSimulator[ 1 ] has extended the implementation of ll functions by adding new functions which starts with os[ 1 ]. OpenSimulator[ 1 ] extensions to LSL[ 18 ] provide a layer on top of the LSL[ 15, 18 ] language, called the OpenSimulator Scripting Language (OSSL)[ 22 ]. The Non-LSL scripting languages such as; C#[ 21 ], J#[ 62 ] and VB.NET[ 63 ] provide users with richer data types and exceptions, which are not available in LSL[ 18 ], and allows them to create new methods. However, the in-world compiler faces problems in generating useful debugging information when an error occurs in the code[ 15 ]. In addition to that, not all functions in LSL are implemented in Non-LSL scripting languages, such as llgetlocalpos[ 64 ] which gets the position of a child object relative to its parent [ 65 ]. Finally, the Non-LSL scripting languages are not fully documented[ 10 ], which makes them very hard to use. For all the reasons mentioned above OSSL was used for writing the 2D/3D WRTEL scripts. 43

45 Table 3: Comparison between LSL and Non-LSL[ 1, 10, 13, 18, 61 ] LSL Non-LSL LSL OSSL C# J# VB.net Functionality ll-functions are limited in functionality.(no ll-functions Provides more functionality by extending LSL implementation and Allow the developer to create new functions has been written to teleport an agent or to write data to Notecards) adding new functions ( ll-functions+ OS functions) Data types Integer, Float, Vector, Rotation, Key, String, List Integer, Float, Vector, Rotation, Key, String, List Richer data types than LSL and OSSL such as (System.Collections.Generic. Dictionary) Documented yes yes No 3.2 Scripts in OpenSim LSL[ 18 ] and OSSL[ 22 ] are state-event driven scripting languages[ 66, 67 ]. Each script consists of functions, variables and at least one default state. States react in response to events which occur while the program is in that state. The system sends events to scripts such as collisions, movements and timers, and the scripts move from one state to another in response to events[ 61 ]. Scripts are associated to objects within OpenSimulator[ 1 ]. An object can be attached to more than one script and all of them execute simultaneously [ 61 ]. Scripts within objects are independent from each other; as a result public and private communication channels are used for data transfer and communication between different objects with the support of llwhisper[ 68 ], llsay[ 69 ] and lllisten[ 70 ] functions [ 61 ]. The public channel is dedicated to channel zero and it can be heard by Avatars in either ten meters range when llwhisper[ 68 ] function is used or twenty meters range when llsay[ 69 ] function is used[ 68, 69 ]. On the other hand, private channels are from 1 to [ 71 ], and they can only be heard by objects who are listening to the channel using lllisten[ 70 ] function and located in the appropriate 10 or 20 meters range[ 71 ]. 44

46 Scripts support a lot of functionalities which are related to the objects presented in the space. The main functionalities which have been widely used through the implementation of the 2D/3D wireless ray tracing educational land are: Object presence: llsensor[ 72 ] function is used to detect the objects presence, name, position and rotation within the 3D space[ 73 ]. Objects within OpenSimulator can be created as physical or non physical objects; the only difference between them is that physical objects are affected by gravity[ 72 ]. Objects are also classified as passive, active and scripted[ 72 ]. This classification is given as a parameter to the llsensor[ 72 ] function to determine which type of objects it should detect. For example if the parameter given to the llsensor[ 72 ] function is SCRIPTED the function will only detect non physical scripted objects. Object creation: Scripts support object creation using the llrezobject[ 74 ] function which creates a new object at a given position in the 3D space[ 74, 75 ]. Each of the dynamically created objects is assigned a specific position, rotation, velocity and could include scripts which will execute when the object is created within the 3D space[ 74 ] D/3D Wireless Ray Tracing Educational Land WRTEL designed and implemented in this project consists of three main regions. In the first region students will be made familiar with the signals frequency, signals wavelength, electromagnetic spectrum and antennas. The second region is the free space propagation laboratory, where signals do not interact with the surrounding environment and only the LOS signal is received by the receiver antenna. The laboratory is designed in outer space, to allow students to understand that free space propagation only occurs in a theoretical environment. The third region is the 2D/3D wireless ray tracing laboratory where students are able to track signals from the transmitter antenna until they are received by the receiver antenna. Each region is associated with an information box and self test questions; students can use information to learn about each region and also test their understanding at each stage during the learning process. To avoid redundancy the 45

47 design and implementation of the self test questions [ 76 ] and the information box [ 76 ] will only be discussed in sections and Students are free to start exploring and learning in any of the three regions, even though sign posts indications are given to help them learn about ray tracing in an incremental manner. The following sections describe how each region is designed and implemented Frequency-wavelength converter tool The Frequency-wavelength converter allows students to understand the relation between the signal s frequency and wavelength. It can be used to find the frequency when the wavelength is entered by students and vice-versa. The tool provided to students is shown is Figure 27. It consists of two white buttons which are used to determine whether the student wants to convert frequency to wavelength or vice-versa. The red Q letter[ 76 ] presents the student with a self test and a blue information box[ 76 ], which provides students with instructions about the tool usage and the equations used for conversion. The following sections describe how each part is designed and implemented. Figure 27: Frequency-wavelength converter tool 46

48 Frequency-wavelength converter buttons The white buttons which are represented in Figure 27 are responsible for converting the values inserted by students in the chat box. The touched button determines whether the conversion is from frequency to wavelength or vice-versa. Figure 28 shows the state diagram for a button listening to the inserted value in the chat box. Figure 28: Frequency-wavelength converter button state diagram The touched button colour changes from white to yellow and a dialog box with instructions on where to insert the data is presented on the screen. After the student views the instructions, the button listens to the value inserted in the chat box using lllisten[ 70 ] function. Finally, the equation with the converted result is shown to students in a dialog box Frequency-wavelength self test Students can use the self test which is presented as a Q red letter[ 76 ] in Figure 27, to evaluate their understanding of the frequency-wavelength relation. Though a teacher may impose the test on the student, the self test is not a system requirement; students are free to assess their understanding. To start the self test students should touch the Q red letter[ 76 ], which presents the multiple choice questions in dialog boxes. After the student answers each question, a 47

49 dialog box with an explanation of whether the answer is correct or wrong appears on the screen. At the end of the test students will receive their score. It is possible for students to repeat the test many times. Questions in the self test can be changed and updated easily, as they are stored in the self test object s Notecard and not hard coded in the script. The format of the stored questions is shown in Figure 29. Figure 29: The self test questions format New questions can be added by inserting the question mark symbol (?) at the beginning of each question and a hash symbol (#) at the end. Different choices should start with the star symbol (*) and the right answer is specified by the exclamation symbol (!). Both (+) and (-) symbols are used to display a message in the dialog box to help students to access whether their answers are correct or not. Questions in the self test include mathematical calculations, which is sometimes hard for students to predict without using a calculator. To overcome this problem an in-world calculator which had been implemented by Totems Gufler is used[ 77 ]. The calculator keeps on listening to the student chat box, if a mathematical equation with an equal symbol (=) is inserted in the chat box, the calculator will be triggered and the answer 48

50 will be displayed on the screen using the llsay[ 69 ] function. The calculator supports multiplication, division, addition and subtraction and many other physical operations. The student can use the answer displayed on the screen and chose the right answer in the multiple choice questions. Figure 30 shows the state diagram of the calculator. Figure 30: Calculator state chart Frequency-wavelength information box The blue information box shown in Figure 27 is responsible for giving the students instruction on how to use the tool. It provides them with the mathematical equations used with a brief description about each variable included in the equation. When students touch the box, instructions will be shown in a Notecard form Electromagnetic spectrum tool The electromagnetic spectrum tool will provide students with information about different types of electromagnetic radiation such as radio, microwave and visible light. Students will be made familiar with the range of frequencies and the practical usage of each type. The tool which is shown in Figure 31 consists of coloured boxes and a yellow sphere. The following sections describe how the boxes and the sphere are designed and implemented. 49

51 Figure 31: Electromagnetic spectrum tool Electromagnetic spectrum sphere Students use the public chat for many things such as, to socialize with each other and calculate mathematical equations to answer the test questions. To dedicate the public chat for the electromagnetic spectrum tool and allow students to insert different ranges of frequencies, the yellow sphere which is shown in Figure 31 is used. It is responsible for starting the electromagnetic spectrum tool. When the student touches the sphere the sphere sends a command to the coloured boxes using the private communication channels, to start responding to student s inserted frequency in the chat box Electromagnetic spectrum coloured boxes The coloured boxes in the electromagnetic spectrum represent the types of electromagnetic radiation. Each box is responsible for listening to the student s inserted frequency in the chat box and providing them with a full description about each frequency using the in-world loading web pages facility. 50

52 Figure 31 shows that boxes are located between specific frequencies ranges. Each box listens to the chat channel in order to receive the inserted frequency. Once the frequency is received, the box determines whether it is in its range or not. If the received frequency is in the box s range, the box will become bigger in size and touchable. Students can touch the box to start viewing information about the inserted frequency. Each box is currently associated with a specific web page which can be loaded using the llloadurl[ 78 ]function. Students can browse the web page and get all the information they need Antennas tool Signal propagation depends on the transmitter and the receiver antennas types. Students should be able to create, view and check 3D style antenna geometry structures and generate, display and/or compare near/far-field radiation patterns. Several antenna modellers such as the 4NEC2 antenna modeller[ 79, 80 ] had been developed, to allow users to create and view 2D and 3D style antenna geometry structures. 4NEC2 is antenna simulation software, where users can design different types of antennas. Figure 32 shows a 2.4 GHz directional Yagi antenna simulated in 4NEC2[ 81 ]. Figure 32: A 2.4 GHz directional Yagi antenna simulated in 4NEC2[ 81 ] 51

53 Allowing students to create and generate different types of antenna using the antenna tool in WRTEL will help them to understand how the propagation differs when different kinds of antennas are used. Students can create their antenna and use it in both the free space propagation and the 2D/3D wireless ray tracing laboratories. Due to the shortness of time, the antenna tool only provides students with information about different types of antennas, and the theoretical isotropic antenna is used in both the free space propagation and the 2D/3D wireless ray tracing laboratories. Extension to use different types of antennas is left as a further work. The implemented antenna tool introduces students to different kinds of antennas used in wireless communication systems. Students will be able to distinguish between the isotropic antenna, Omni-directional antenna and the directional antenna. The tool which is shown in Figure 33 consists of three white buttons, each one of them presents one of the antenna kinds. Students can touch one of the provided buttons to display information about the gain and the transmission power of the chosen antenna. Figure 33: Antenna tool 52

54 3.3.4 Free space propagation laboratory The Free space propagation laboratory exists in the second region of the WRTEL. In this practical experiment laboratory students will become familiar with free space propagation and the free space path loss terms. The laboratory exists in the outer space to give students an indication that the LOS free space propagation occurs in a theoretical environment where signals do not interact with the surrounding environment and only the LOS signal is received by the receiver antenna. For example there is no reflection. Within the laboratory students are able to visualize the free space electromagnetic waves (for instance, light, radio, and microwave) and realise that the power of electromagnetic waves is proportional to the inverse of the distance from the transmitter antenna. Calculations of the free space path loss, the transmission power, and the received power are provided to students at each point along the LOS path between the transmitter and the receiver antennas. Figure 34: Free Space propagation laboratory 53

55 The laboratory shown in Figure 34 consists of two white spheres which represent the transmitter and the receiver antennas. Students can leave the laboratory and return to earth using the window which is the teleporter to the real world. In the following sections details about the design and implementation of each component in the laboratory is provided The transmitter antenna The transmitter antenna is responsible for emitting signals with a specific frequency and transmission power to the surrounding environment. Both the frequency and the transmission power have default values which can be changed by students. Figure 35 shows the state diagram of the transmitter antenna. Figure 35: Transmitter antenna state chart Students start the configuration process by touching the antenna, which fires the touch_start[ 82 ] event. The event produces a dialog box that allows students to set the frequency and the transmission power. The antenna listens to the student s value inserted in the chat box using the lllisten[ 70 ] function. Students have to insert the value within a specific time; this is achieved using the llsettimerevent (TIMEOUT)[ 83 ] 54

56 function. If the system reaches TIMEOUT before the student enters the value, the configuration process starts all over again. In order to visualize the free space propagated signals and calculate the free space path loss between the transmitter and the receiver antennas, the transmitter antenna has to determine the receiver antenna position in space using the llsensor[ 72 ] function. The llsensor[ 72 ] function fires the sensor[ 84 ] event when the receiver antenna is found. The sensor event stores the receiver position which is used to draw the LOS path between the transmitter and the receiver antennas and to calculate the free space path loss. Figure 36 shows the code snippet which is responsible for calculating the power path loss. The equation presented in the code is derived from the free space propagation equation 2 presented in section See Appendix 1 for the full conversion details. Figure 36: The code responsible for calculating the path loss The LOS path is created using the llrezobject[ 74 ] function which creates spheres dynamically on the path between the transmitter and receiver the antennas. Students are also able to visualize the propagation path loss using the 2D charts. Charts are created using the Google API chart tool[ 85 ]. The transmitter calculates the path loss between the transmitter and the receiver for each meter, and produces the chart URL which will be loaded on the screen using llloadurl[ 78 ] function. The propagated signals shown in Figure 34 present the LOS path between the transmitter and receiver antennas. The LOS path consists of spheres which change their colours in response to the propagation path power loss. Each sphere on the path can be touched by students to give them details about the propagation loss and the received 55

57 power at that point. Figure 37 shows the state diagram of a sphere listening to the transmitting antenna to receive the transmitter antenna position, frequency and transmission power. Figure 37: State chart of a sphere listening to the transmitting antenna Each sphere listens to the transmitter antenna using lllisten[ 70 ] function and calculates the received power and the free space propagation loss. Both the path loss and received power calculations are done using the free space propagation equation 2 and the received power equation 3 presented in the free space propagation section The yellow sphere with a square hollow shown in Figure 34, represent the inverse square relation of radiation intensity with distance from the radiation source. When the student emits the ray, the sphere scale in size and so do the square to enable students to visualize how the intensity from an isotropic source with a radiating power P changes when the distance increases. Figure 38 shows that the intensity from an isotropic source, radiating power P, is equal to the radiated power per unit surface area[ 86, 87, 88 ]. Since the surface area of a sphere is given by A = 4 πr 2, then the intensity I is given by I=P/ (4 π R 2 )[ 87 ]. 56

58 Figure 38: The geometric origin of the inverse square law Figure 39: The intensity and distance inverse square relation In the free space propagation laboratory the yellow sphere scales in size until it reaches the receiver antenna. Figure 39 shows the intensity and distance relation displayed at a 1 meter distance from the transmitter antenna; it also shows the square hollow which will become bigger in size when the distance increases. The intensity and distance relation is presented on the top of the sphere using llsettext[ 89 ] function. 57

59 The receiver antenna The receiver antenna which is presented as a white sphere in Figure 34 is responsible for receiving the transmitted signal. It listens to the transmitter antenna to receive the transmission power, transmitter position and frequency which will be used to calculate the received power at the receiver antenna. The receiver antenna introduces students to the sensitivity parameter which allows them to understand that the received signal should be above the sensitivity level to generate a detectable output signal. When the receiver receives the signal it calculates the received power to determine whether the received power is less or more than the sensitivity level. If the received power is lower than the sensitivity level the receiver sphere colour changes from white to red. Figure 40 shows the receiver antenna state chart. Figure 40: The receiver antenna state chart The sensitivity parameter is configurable; students can change it by touching the receiver antenna and inserting the sensitivity value in the chat box. This allows students 58

60 to try different sensitivity values and see whether the emitted signal will be considered or discarded by the receiver antenna. Having configurable frequency, power and sensitivity parameters in both the transmitter and receiver antennas gives the student the ability to test different scenarios D/3D wireless Ray tracing laboratory The third main region in the WRTEL is the 2D/3D wireless Ray tracing laboratory. After students are introduced to signal frequency, wave length, electromagnetic spectrum, antennas and free space propagation, the 2D/3D ray tracing laboratory allows them to understand how the propagated signals behaviour is affected by the obstacles present in the surrounding environment. The laboratory allows students to visualize the LOS, reflected and refracted propagating signals. Students are also provided with information about each emitted ray such as; the angle of incidence, the refraction angle and the power remaining after each interaction between rays and the surrounding environment. The 2D/3D wireless ray tracing laboratory, seen in Figure 41 provides students with a default environment which consist of two perpendicular cuboids with a floor cuboid and two white spheres. The cuboids represent the obstacles and the spheres represent the transmitter and the receiver antennas. The laboratory supports spherical and cuboid obstacles, which students can use to change the surrounding environment dynamically by adding and removing them and changing their location, size and material. The following sections describe the design and the implementation of each component in the laboratory. 59

61 Figure 41: The 2D/3D wireless ray tracing laboratory The 2D/3D wireless ray tracing remote Control The wireless ray tracing laboratory is controlled by the remote control component which is shown in Figure 41. The remote control consists of thirteen buttons and eight spherical white lights. Table 4 illustrates the tasks performed by the buttons and the lights. Students use the remote control to control the whole ray tracing and visualization in the laboratory. They can create several environments using cuboid and spherical obstacles and touch the Ray Trace Button to start ray tracing. Depending on the surrounding environment, a large number of interactions could occur between the emitted signals and the obstacles in the scene. To facilitate the visualization of these interactions, components 2 to 9 (shown in Table 4) in the remote control were created. Students can decide how many interactions they want to visualize by touching the components. The 2D Ray Tracing Button and 3D Ray Tracing Button buttons are created to enable students to decide whether they want to visualize the propagated signals in X-Y dimensions or full 3D. 60

62 Table 4: Tasks performed by the buttons and the lights Component number Component behaviour Component Name Task Command sent to the receiver antenna 1 Push Ray Trace Button 2 Toggle One Interaction Button 3 Toggle Two Interactions Button 4 Toggle Three Interactions Button 5 Toggle Four Interactions Button 6 Toggle Five Interactions Button 7 Toggle Six Interactions Button 8 Toggle Seven Interactions Button 9 Toggle Eight Interactions Button Starts ray tracing Select all rays with one interaction Select all rays with two interaction Select all rays with three reflections Select all rays with four interaction Select all rays with five interaction Select all rays with six interaction Select all rays with seven interaction Select all rays with eight interaction 10 Toggle LOS Button Draws the Los ray between the transmitter and the receiver antennas 11 Push Draw Rays Button 12 Push 2D Ray Tracing Button 13 Push 3D Ray Tracing Button 14 Toggle Eight spherical lights Draws all the selected rays Emit Rays from the transmitter antenna in X and Y dimensions Emit Rays from the transmitter antenna in X, Y, Z dimensions The eight lights colours change from white to green to represent the number of interactions between rays and the surrounding environment llsay(raytracechannel, RayTrace ) llsay(onechannel, One ) llsay(twochannel, Two ) llsay(threechannel, Three ) llsay(fourchannel, Four ) llsay(fivechannel, Five ) llsay(sixchannel, Six ) llsay(sevenchannel, Seven ) llsay(eightchannel, Eight ) llsay(loschannel, LOS ) llsay(drawchannel, Draw ) llsay(2dchannel, 2DRayTracing ) llsay(2dchannel, 3DRayTracing )

63 After the ray tracing simulation, the lights colours on the remote control change from white to green to determine the number of reflections or refractions generated by the ray tracer. Students can use the light indications to decide what reflections and refractions they want to visualize. For example, after running the ray tracer light one and light two colours changed from white to green. This means that one interaction and two interactions between the rays and the surrounding environment had occurred. Students can then visualize the one interaction or two interactions or a combination of both one interaction and two interactions The transmitter antenna The white sphere which is shown in Figure 41 represents the transmitter antenna. At the idle state the transmitter antenna keeps on listening to the remote control component. When one of the commands which are presented in Table 4 is received using lllisten[ 70 ] function, the transmitter starts performing the specified task. The transmitter antenna in the laboratory is responsible for the following Determining the frequency and the transmission power The refractive index of various materials in the laboratory depends on the operating frequency of the transmitted signal and the transmission power, if one of these parameters changes, the refractive index changes. In this laboratory signal propagation experiment is performed according to a study, which has been done on the effects of wall parameters on wireless propagation at 900 MHz and 2.4 GHz frequencies and 44 dbm transmission power[ 90 ]. Three different wall materials (wood, cement, and iron) were used and the refractive index for each material was calculated. Table 5 includes the refractive index value for each material[ 90 ]. In the 2D/3D wireless ray tracing laboratory the transmitter frequency is set to 2.4 GHz at the idle state. Students can change the frequency by touching the transmitter which produces a dialog on the screen with a 2.4 GHz and a 900MHz frequency choice. The student s choice is used for future ray tracing until a further change is made. 62

64 Ray tracing The most important virtual world information needed during ray tracing is about the obstacles in the surrounding environment, such as the obstacle s position, rotation, name and bounding box which are accessed using the lldetectedpos[ 91 ], lldetectedrot[ 92 ], lldetectedname[ 93 ], llgetboundingbox[ 94 ] functions respectively. Each obstacle s material should also be detected and used in ray tracing, as it affects the propagation of signals and the whole ray tracing calculations such as; the path loss and the received power at the receiver antenna. OpenSimulator[ 1 ] does not provide users with information about the materials obstacles represent; the only way to distinguish between them is using different textures drawn on the obstacles surfaces. To overcome this problem each obstacle name in the laboratory consists of three main parts, the object s shape, the object s material and refractive index. Table 5 illustrates the objective of each part and the values that can be assigned to them. Thus, an obstacle has shape X, material Y and refractive index Z. This will be discussed in much more details in the rays ( ), obstacles ( ) and evolution and adaption ( ) sections. Table 5: Obstacle s name parts and the assigned value and objective of each part Shape Obstacle s name parts Rx Tx Assigned values Cuboid Sphere objective Represents the receiver antenna in the environment Represents the transmitter antenna in the environment Represents the Cuboid obstacles in the environment Represents the sphere obstacles in the environment Material Wood Cement Iron Could be assigned to the cubic and spherical obstacles shapes. Provides students with information about the obstacles materials that rays intersect with. Refractive index 4 (Wood) 1.8 (Cement) 14 (Iron) Each material is assigned to a specific refractive index, which will be used in several calculations such as the refraction angle. *Note: Tx and Rx shapes do not include the material and the refractive index parts in their names 63

65 When students touch the ray tracing button, the transmitter receives the RayTrace command and starts sensing the surrounding environment using the llsensor[ 72 ] function which triggers the sensor[ 84 ] event. Within the sensor[ 84 ] event all the information about the obstacles is stored and ray tracing starts. Students can determine whether they want to do ray tracing in 2D or 3D mode using the 2D and the 3D Ray Tracing Buttons. The transmitter emits the rays according to the selected ray tracing mode. If students chose the 2D mode, rays will be emitted in the X and Y dimensions, otherwise rays are emitted in X, Y and Z dimensions. Different values can be assigned to the emission angle in X- Y and Y-Z planes. Decreasing the emission angle increases the computation time and the number of interactions between rays and the surrounding environment. To provide students with a reasonable number of interactions in a reasonable computation time the emission angle in 2D mode is set to seven degrees in the X-Y plane and to 45 degrees for both X-Y plane and Y-Z plane in 3D mode. The emission angle in both modes can be changed. Ray tracing is implemented in OSSL[ 22 ] using the brute force method. The Ray tracer supports up to eight reflections and four refractions. Each emitted ray from the transmitter antenna is traced in a specified direction. If no intersection between the obstacles and the ray occurs, the ray will be discarded and a new ray will be emitted and traced. Once an intersection has occurred, the ray splits into a reflected ray and a refracted ray and a check is made to determine if one of the rays is received by the receiver antenna. The implementation supports two types of intersections; the line sphere intersection method and the line-plane intersection method (see Appendix 2 for more details). When a ray hits an obstacle and an intersection occurs, the ray tracer checks the obstacle name to determine the shape as illustrated in Table 5. If the objects shape is Rx or Sphere the line sphere intersection method will be used. Otherwise the line-plane intersection method is used. 64

66 During ray tracing detailed information about each ray received by the receiver antenna is calculated and stored. The information includes: The number of reflections and refractions the ray is involved in until it reaches the receiver. The intersection points with obstacles. The incident and the refraction angles of each reflected and refracted ray with the obstacles it encounters. The Material of each obstacle the ray intersects with. The refractive index of each obstacle the ray intersects with until it reaches the receiver. The reflection coefficient. The refraction coefficient. The return loss. Several calculations are done to obtain the specified information above; the incident angles are calculated using the ray s intersection point and the surface normal of the obstacle. The refraction angles are calculated using Snells law[ 95 ], which is presented in the following equation: = (5) and are the angles of incidence and refraction respectively. is the index of refraction of the medium the ray is leaving and is the index of refraction of the medium the ray is entering. The reflection and refraction coefficients are calculated using the following equations[ 90 ]: 65

67 and are the reflection coefficient and the refraction coefficient respectively, and and are incident and refraction angles respectively. Finally the return loss is calculated using the following equation[ 96 ]: is the return loss in, is the incident power and is the reflected power. The averaged reflected power is assumed to be the free space value for the unfolded path length (d1,.., dn) multiplied by the reflection coefficient where dn is the distance of the reflected nth rays. This is shown in the following equation[ 90 ]: When the ray tracing is done, all the information is stored and the transmitter sends the number of reflections and refractions to the remote control. In response to that, the remote control changes the light colours from white to green, so that students know the number of interactions in the simulation Drawing the rays The transmitter antenna is responsible for drawing the rays that are received by the receiver antenna. It listens to the remote control component to receive the drawing commands and start drawing. Drawing commands are classified into three types; the first type is a collection of commands received from components one to eight, which are illustrated in Table 4. The commands determine the number of reflections and refractions the students want to visualize. The second type is the Draw command which is send by the Draw Rays Button, the command draws all the rays with the specified number of reflections and 66

68 refractions determined by the first set of commands above. The third type is the LOS command which is sent by the LOS Button. When the transmitter receives the command the LOS rays between the transmitter and the receiver antennas will be drawn. Rays are drawn using the llrezobject[ 74 ] function, which uses the detailed information stored about rays to determine where the rays should be visualized between the transmitter and the receiver antennas Send the stored information to rays After the rays between the transmitter and the receiver antennas are drawn, the transmitter sends the detailed information stored to each ray. The information sent includes the ray tracing stored information in addition to the frequency and the transmission power Rays Rays are the most fundamental objects in the simulation. They represent the behaviour of the propagated signals in the environment. Each ray in the simulation is identified by a unique identifier and consists of a number of spherical objects, to allow students to gain information at points along the ray. Rays are created dynamically for each ray tracing simulation. Assigning an identical unique identifier to each spherical object as is assigned to the ray itself was an essential requirement, because spheres within a ray should receive the same information from the transmitter antenna. This raised an implementation issue, since OpenSimulator[ 1 ] assigns a randomly unique identifier for each object created in the scene. To solve this problem a unique identifier was declared in the code and sent instantly to each created sphere in the ray until the ray is complete (no more spheres will be created within the ray). The spherical objects listen to the transmitter antenna to receive the ray tracing information, such as the transmission power and the transmitter antenna position appended with the same unique identifier as was sent to each spherical object. When the data is received, each spherical object compares its own unique identifier with the identifier sent with the data; if it is the same the sphere stores the information. 67

69 Spheres start processing the received information in the following manner: The intersection point: This will improve the visualization of rays in the scene, by allowing students to distinguish the points of intersections with the surrounding environment. The received intersection point is used to determine whether the sphere is an intersection sphere or not. When the sphere receives the intersection point data, a comparison between the received intersection point and the spheres position is made. If the sphere s position is the same as the intersection point, the sphere is treated as an intersection sphere and it scales in size and changes its colour to red, otherwise the sphere will remain the same and it is called an ordinary sphere. Students can touch both the intersection and ordinary spheres to view information. The intersection sphere display much more data than ordinary spheres in the ray. Table 6 shows the information displayed by the intersection and the ordinary spheres. The transmission power and frequency: they are used by both the intersection and ordinary spheres to calculate the path loss and the received power at the spheres position in space. The material and refractive index: They are used by the intersection sphere to display information about the obstacles materials and refractive indices. The reflection and refraction coefficients: they are used by the intersection sphere to calculate the power loss after each reflection and refraction. The incidence and refraction angles: they are used by both the intersection and ordinary spheres to display the angles of incidence and refraction of each ray. Table 6: The information displayed by intersection and ordinary spheres Information Displayed Intersection Sphere Ordinary Sphere Incident angle refraction angle Material Refractive Index Reflection coefficient refraction coefficient Return loss Path Loss Received Power 68

70 Obstacles Using obstacles with different materials and different refractive indices will help students to visualize how the propagated signal s direction, refraction angle and power loss calculations are affected by interactions with materials. As mentioned in Table 5 obstacles in the 2D/3D wireless ray tracing laboratory are either cuboids or spheres and can have wood, cement or iron material. By default, obstacles in the environment have a wooden material and a touch me text is assigned to them using the llsettext [ 89 ] function. Students can touch each obstacle and assign different materials to them. A dialog box appears on the screen and allows student to choose the material. Figure 42 shows the state diagram of the obstacle configuration. Figure 42: Obstacles state chart When students decide which material they want to use for the obstacle, the obstacle name changes to include the new assigned material and the specified refractive index. 69

71 Evolution and adaption Obstacles in the 2D/3D wireless ray tracing laboratory can be added and removed dynamically. Students can create any object in the environment using the graphical tool and convert it to an obstacle which can be considered by the ray tracer. The conversion is done by assigning one of the specified names to the created object: shape:cuboid ^RefIndex:4^material:wood shape:sphere^refindex:4^material:wood It is obvious that the obstacle name consists of three parts shape, refractive Index and material. The shape part depends on the created object. Ideally students should assign the right shape value to the created object s name, to improve the ray tracing accuracy in determining the intersection point with obstacles. If students create a cuboid object the shape part of its name should be assigned to a cuboid, and if they created a sphere object the shape part of its name should be assigned to a sphere. Both the refractive index and the material parts can be assigned to any valid value. When the ray tracing starts the object will then be considered as an obstacle in the environment. If a student entered an invalid object value, the ray tracer will ignore the created object. 70

72 Chapter 4: Results This chapter describes the output of the design and the implementation of the 2D/3D wireless ray tracing educational land. Section 4.1 presents an overview of the three main regions in the wireless educational land. Sections 4.2, 4.3, 4.4, 4.5 and 4.6 describe the output of each part. Section 4.7 represents a technical and educational evaluation of the 2D/3D wireless ray tracing laboratory. 4.1 Overview The wireless ray tracing educational land consists of region A, region B and region C shown in Figure 43. Region A contains the frequency-wavelength converter tool, the electromagnetic spectrum tool and the antenna tool. The free space propagation laboratory exists in region B and the 2D/3D wireless ray tracing laboratory is presented in region C. The land has no restriction on what, where and when students should start or stop learning in any of the regions. This helps because students have different educational backgrounds and can choose to start leaning in any of the regions. Figure 43: Wireless ray tracing educational land 71

73 4.2 Frequency-wavelength converter tool In the frequency-wavelength converter region, students decide whether they want to do frequency-wave length conversion or vice-versa. Figure 44 shows a student who decides to do wavelength-frequency conversion. After he touched the button a dialog box with instructions appears on the screen. Figure 44: The dialog box displayed in a wavelength to frequency conversion After the student enters the value 100 for frequency in the chat box, the tool produces the wavelength which is 3,000,000 m in a dialog box shown in Figure 45. Some details of the calculations are also shown. Figure 45: The wavelength of a 100 Hz frequency 72

74 4.2.1 Frequency-wavelength self test Students can decide whether they want to perform the self test or not. Figure 46 shows the test produced in the dialog boxes after a student decided to do the test and touched the red Q letter. If the student answers the question correctly a dialog box with a correct text will be displayed on the screen. Otherwise the dialog box will inform the student about the correct answer. At the end of the test a score dialog will be displayed as shown in Figure 47. Figure 46: The self test in Frequency-wavelength converter tool Figure 47: The score presented to students after they finish the test 73

75 4.2.2 Frequency-wavelength information box An information box is presented in region A, region B and region C to provide students with information and instructions in the form of a Notecard. Figure 48 shows the Notecard produced when the student touches the information box for the Frequencywavelength converter tool in region A. The Notecard shows the equations used and the instructions that help students to use the tool in an appropriate way. Figure 48: The Notecard produced for the Frequency-wavelength converter tool 74

76 4.3 Electromagnetic spectrum tool To start using the electromagnetic spectrum tool, a student has to touch the yellow start sphere and then enters the frequency which they want to know details about in Hertz (Hz) in the chat box. Figure 49 shows a student who entered 3000 Hz in the chat box, the tool determined that the frequency is within the very low frequency (VLF) range. After the range is determined the cube which includes the range scales in size, this is presented in the Figure as a red cube. Students can touch the cube and see some web information about the chosen frequency. Figure 49: The electromagnetic spectrum tool decided that 3000 Hz is within the VLF range 4.4 Antenna tool The antenna tool allows students to view information about isotropic, Omni-directional and directional antennas in a dialog box. Figure 50 shows the isotropic antenna information displayed in a dialog box, when the isotropic antenna button is touched by students. Students can use the scroll bar in the dialog box to display the information. 75

77 Figure 50: Isotropic antenna information displayed in a dialog box 4.5 Free space propagation laboratory When students enter the wireless educational land, they can start the free space propagation experiment by teleporting using the teleporter object placed in region A shown as a red square in Figure 43. The Free space propagation laboratory is placed at region B shown in Figure 43. When a student reaches the free space propagation laboratory area, a billboard which briefly describes the purpose and the actions that can be performed is found. In addition to the billboard an information box with all the equations used and the calculations done in the experiment is also placed in region B. This is shown in Figure

78 Figure 51: The billboard and the information box In the free space propagation experiment the transmitter and the receiver antennas in the laboratory are placed by default at the positions labelled F and G in Figure 43. Students can move the antennas and change their position in the laboratory. Students can leave the laboratory by using the window teleporter shown in Figure The transmitter antenna At the beginning of the experiment, the transmitter antenna is assigned a default frequency and transmission power value of 2.4 GHz and -10 dbw respectively. Students have to touch the transmitter to change the default values and configure the transmitter in the way they prefer. When Students touch the transmitter antenna the dialog box shown in Figure 52 will be displayed on the screen. 77

79 y Figure 52: The dialog box displayed when the student touch the transmitter antenna If a student decides to change the frequency or the transmission power, they have to press the button and insert the required value in the chat box. The transmitter antenna helps students to visualize the path loss using charts or by emitting the rays toward the receiver antenna. Figure 53 shows the chart produced after the student used the default 2.4 GHz frequency and -10 dbw transmission power values. The receiver antenna is 10 meters away from the transmitter antenna. The chart shows the signals path loss at each meter between the transmitter and receiver antennas. Figure 53: The path loss chart for a 2.4 GHz and -10 dbw signal 78

80 Students can also choose to emit the LOS ray (see Figure 55) between the transmitter and the receiver antennas by pressing the Emit Rays choice in the dialog box shown in Figure 52. When the transmitter antenna emits the LOS ray a dialog with the details shown in Figure 54 is displayed on the screen. Figure 54: The details displayed by the transmitter antenna The details include the transmitted frequency, the wavelength, the gain of the transmitter and receiver antennas, the distance between them, the transmission power and the free space path loss. Each sphere in the drown LOS ray s representation can be touched by students to produce a dialog box on the screen, which includes details about the path loss and the received power at the sphere s position; this is shown in Figure 55. The path loss and the received power had been calculated for the sphere surrounded by the orange ellipse when the transmission power was -10 dbw. 79

81 Figure 55: The path loss and the received power at the sphere position In addition to the drawn emitted LOS ray, a yellow sphere shown in Figures 56 and 57 will scale inclemently in size after the student presses the Emit Rays choice in the dialog box shown in Figure 52. Figures 56 and 57 show the intensity and distance square law relation at a 1 meter and 2 meters distance from the transmitter antenna. Students can visualize the relation until the yellow sphere hits the receiver antenna. 80

82 Figure 56: Intensity and distance square law relation at a 1 meter distance from Tx Figure 57: Intensity and distance square law relation at 2 meters distance from Tx 81

83 4.5.2 The receiver antenna The receiver antenna has a default -30dBm sensitivity value, which can be configured. Students can touch the receiver to see the current sensitivity, which is shown in Figure 58 and change it by inserting the required sensitivity value in the chat box. Figure 59 shows the receiver colour changed from white to red, after the student used a 2.4 GHz frequency, -60 dbw transmission power and -30 dbm sensitivity. The received power at the receiver antenna, which is calculated using equation 3 in section was ,034 dbm. This indicates that the received power at the receiver antenna is less than the sensitivity and the received signal is ignored, as it is not enough for the receiver to work with. Figure 58: Configure the sensitivity at the receiver antenna Figure 59: The received power is less than the receiver sensitivity 82

84 4.6 2D/3D wireless ray tracing laboratory The 2D/3D wireless ray tracing laboratory is placed in region C shown in Figure 43. When a student enters the laboratory area, a billboard which briefly describes the purpose and the actions that can be performed is found. Also an information box with all the equations used and the calculations done in the experiment is placed in the area. The billboard and the information box are shown in Figure 60. Figure 60: The billboard and the information box The transmitter antenna In the 2D/3D wireless ray tracing laboratory the transmitter antenna frequency can currently either be configured as 2.4 GHz or 900 MHz. Figure 61 shows the dialog box displayed when the student touches the transmitter antenna to change the frequency. 83

85 Figure 61: Configure the frequency in the transmitter antenna Obstacles Obstacles in the environment can be created, moved, resized and assigned to different materials with different wireless properties. Students touch the obstacle and a dialog appears currently with cement, wood and iron as the material choices. Figure 62a shows a cement cuboid obstacle changed to become a wooden cuboid obstacle in Figure 62b. Students can change the materials dynamically; they could also add new materials with specific refractive indices which depend on the operating frequency and the transmission power. (a) (b) Figure 62: A cement obstacle wall changed to become a wooden obstacle wall 84

86 D/3D ray tracing simulation Students can decide whether they want to perform a 2D or 3D ray tracing. In the 2D ray tracing, the student starts the ray tracing simulation either by pressing the 2D button on the remote control (see Figure 63) or by pressing the Ray trace Button which defaults to 2D ray tracing mode. When the student presses the Ray trace button, ray tracing starts and some of the lights on the remote control change from white to green, to indicate the number of interactions between the rays emitted and obstacles in the environment. Figure 63 shows a 2D ray tracing with a seven degrees emission angle in the X-Y plane, which had been performed at a frequency of 2.4 GHz and 44 dbm transmission power. The two green lights indicate that one and two interactions occurred between the transmitted rays and the obstacles in the environment. After that, the student decided to visualize all rays with one interaction that had occurred in the environment by pressing the one button in the remote control. This is shown in Figure 64. Figure 63: 2D ray tracing simulation environment 85

87 Figure 64: Visualize one interaction with the surrounding environment The pressed button sends a command to the transmitter antenna to draw all the rays with one interaction. Figure 65 shows that there are two reflected rays produced from the wooden cuboid obstacles in the current environment. It also presents the information displayed when the student touched one of the incident rays. The incident ray presented in the Figure has a 19 degrees angle of incidence which occurs when the ray hits the wooden cuboid obstacle. Calculations of the received power and the path loss for the touched sphere are also introduced in the dialog box. By changing the frequency and performing ray tracing again, students will be able to understand how the calculations change in response to the operating frequency. 86

88 Figure 65: Information displayed for each sphere in the incident ray During the simulation the student changed the wooden cuboid obstacle shown in Figure 65 into a cement cuboid obstacle to visualize how the path loss, received power, reflection coefficient, refraction coefficient and reflection loss depends on the obstacles material in the environment. The incident ray path loss calculations for both obstacles are the same; the difference between them becomes clear at the intersection point and the reflected ray. Figures 66 and 67 show that each material has a different refractive index, as a result the reflection coefficient, refraction coefficient and reflection loss calculations are not the same. Figures 68 and 69 show how the power loss after reflection differs between the wooden and cement obstacles. Students can change the obstacles dynamically and visualize how the interactions between rays and obstacles depend on what the obstacles are made of. 87

89 Figure 66: Information displayed at the intersection point of wooden obstacle Figure 67: Information displayed at the intersection point of cement obstacle 88

90 Figure 68: Information displayed for each sphere in the reflected ray from a wooden obstacle Figure 69: Information displayed for each sphere in the reflected ray from a cement obstacle 89

91 After the student visualized the reflected rays and realized how the power calculations depend on types of obstacles in the environment, the student changed the environment in Figure 63 to visualize the refracted rays. In the new environment a wooden obstacle which is called cuboid obstacle is placed between the transmitter antenna Tx and the receiver antenna Rx. The new 2D/3D ray tracing simulation environment is shown in Figure 70. Figure 70: The 2D/3D Simulation environment to visualize the refracted rays Figures 71a and 71b show how the emitted ray from the transmitter antenna hits the wooden obstacle which is a cuboid obstacle and get refracted as it passes into and out of the obstacle. Students can visualize the incident rays, refracted rays and the intersection points which are shown as red spheres in Figures 71a and 71a respectively. (a) (b) Figure 71: (a) Incident ray (b) Refracted ray 90

92 Students can visualize how the refraction angle for the emitted rays depends on the refractive index of the obstacles materials. When the student touches the intersection point, information about the refraction angle is displayed in a dialog box. Figures 72a and 72b show the difference between two types of materials (wooden, cement) when assigned to the cuboid obstacle in Figure 70. (a) (b) Figure 72: (a) Refraction angle for a wooden cuboid (b) Refraction angle for a cement cuboid When the cuboid obstacle had been assigned to a wooden material with a refractive index equals to 4, one ray was refracted and received by the receiver antenna and the refraction angle was approximately degrees. On the other hand, when a cement material with a refractive index equals to 1.8 was used, one ray was refracted and received by the receiver antenna and the refraction angle was approximately degrees. Students can also visualize the interactions between the rays and the surrounding environment in 3D by pressing the 3D button and then the Ray trace Button on the remote control. To visualize the difference between 2D and 3D simulation, the environment in Figure 63 had been used with some modifications shown in Figure 73. The new environment consists of a three walled wooden cuboid obstacles with ceiling and floor cuboids. 91

93 Figure 73: Three walled room with a floor and ceiling The 3D ray tracing is performed using a 45 degrees increment in the emission angle in the X-Y plane, and a 45 degrees increment in the Y-Z plane. These values are used, to decrease the number of interactions between the emitted rays and the surrounding environment. Consequently, simplifies the visualization of the produced rays in this simulation. After the student started ray tracing, the lights on the remote control indicated that one, two and three interactions between the transmitted rays and the surrounding environment occur. Students choose to visualize one and two interactions by pressing number one and two buttons on the remote control as shown in Figure 74. Figure 74: Buttons one and two are pressed to visualize one and two interactions 92

94 Figure 75 shows that the ray tracer produced one ray with one interaction and two rays with two interactions. The one interaction ray results from a ray which hits the floor obstacle and then get reflected and received by the receiver antenna. One of the two interaction rays results from the emitted ray which hits the floor obstacle and gets reflected, and then the reflected ray hits the second obstacle and gets reflected again. It is obvious that the ray was affected twice by reflection until it reached the receiver antenna. The second ray with two interactions hits the obstacle and gets reflected, and then the reflected ray hits the ceiling obstacle and gets reflected again. Figure 75: The 3D ray tracer output Within the laboratory students are free to change the Tx and Rx antennas positions. Figure 76 shows a Tx and Rx antennas whose positions is different from the Tx and Rx antennas in Figure

95 Figure 76: Reflection from a ceiling cube obstacle in 3D 4.7 Evaluation The 2D/3D WRTEL had been evaluated technically and educationally. Section presents an efficiency test of the ray tracer algorithm implemented in the 2D/3D wireless ray tracing laboratory. Section presents an educational evaluation for the tools and the laboratories implemented Technical evaluation The ray tracer algorithm implemented in the 2D/3D wireless ray tracing laboratory was executed for ten times in the environment shown in Figure 63. Each time the emission angle of rays was increased by 1 degree. Table 7 and Figure 77 show the computational time and the number of interactions related to the emission angle when using WRTEL on an HP G62 notebook with an Intel Core i3 processor, 3 gigabytes RAM and a 320 gigabytes hard disk drive. The emission angle is determining the increment between emitted rays from the transmitter. The large this increment is the less likely the system is to find rays that reach the target receivers. Smaller values mean that many more rays are traced.this improves the chances of reaching the receiver but also requires lots more computation. 94

96 Table 7: Computational time and number of interactions for different emission angles Emission angle (degrees) Ray tracing Computational time (Seconds) Number of interactions ,334 Rays with one reflection : 15 Rays with two reflections : ,319 Rays with one reflection : 7 Rays with two reflections : ,220 Rays with one reflection : 5 Rays with two reflections : ,801 Rays with one reflection : 3 Rays with two reflections : ,789 Rays with one reflection : 3 Rays with two reflections : ,532 Rays with one reflection : 3 Rays with two reflections : ,281 Rays with one reflection : 2 Rays with two reflections : ,108 Rays with one reflection : 2 Rays with two reflections : ,098 Rays with one reflection : 2 Rays with two reflections : ,109 Rays with one reflection : 2 Rays with two reflections : 0 95

97 Figure 77: Computational time and the number of interactions related to the emission angle Figure 78 shows the relationship between the emission angle in degrees and the ray tracing computational time in seconds. It can be shown that the computational time increases when the emission angle decreases, for example when the emission angle is one degree the time is ,334 seconds and with ten degrees emission angle the time is ,109 seconds. Figure 78: Relationship between the emission angle and the computational time 96

98 Figure 79 shows that the number of rays with one reflection and two reflections that are found increases when the emission angle decreases. The largest number of rays with one reflection and two reflections occur at a 1 degree emission angle increment, and the number starts to decrease until it reaches two rays with one reflection and zero rays with two reflections at a 10 degrees emission angle increment. Figures 80 and 81 show the number of rays received by the receiver antenna at a 1 degree and 2 degrees emission angles. See Appendix 3 for all the rays produced when the emission angle changes from 3 degrees to 10 degrees. Figure 79: Emission angle relation with the number of one reflection and two reflections 97

99 Figure 80: Rays produced at a 1 degree emission angle increment Figure 81: Rays produced at 2 degrees emission angle increment 98

100 As the emission angle decreases interactions with the environment becomes much more complex and the ray tracing computation time increases. Also the computation time depends on the complexity of the environment. In this evaluation the environment consists of two obstacles only, when the number of obstacles increases the computation time will increase. Finally the system used to run the ray tracing algorithm within the OpenSimulator virtual world affects the computational time. Due to the shortage of time this performance evaluation was performed in only one environment and one system Educational evaluation The WRTEL had been informally evaluated by its author (myself), and it is usable, works correctly and achieve the WRTEL aims introduced in section 1.1. To further check the WRTEL usability, the land was introduced to a limited number of users [n=2].of course, this is a small number of users to test the efficiency of the educational land implemented, but the time available was a practical limitation. Both of the users reported that the educational land is useful and introduces the basic concepts that the user needs to know before starting the ray tracing experiment. However, one of the users was an electrical engineer (person A), who already knows about ray tracing and used virtual worlds for entertainment. The other was an optician (person B) who knows about rays behaviour (reflection, refraction, diffraction, and scattering) and had never used virtual worlds. Person A observed that The design of the laboratories provides users with the required information and the outer space environment in the free space propagation laboratory is interesting and gives the indication that free space propagation occurs in a theoretical environment. Additionally A observed The calculations provided in both the free space and the 2D/3D wireless ray tracing laboratories are useful and giving users the ability to change the environment in the 2D/3D ray tracing laboratory enables them to learn by playing with the surrounding environment and experimenting the results. 99

101 Person B observed that It is interesting how the rays in the 2D/3D ray tracing laboratory are visualized. Additionally B observed I really do like the remote control idea and I think providing students with such a facility will allow them to visualize simple and complex interactions with the surrounding environment. The WRTEL is both usable and engaging, and should serve its pedagogic purposes. However, further testing with electrical engineers and physics students is needed in order to fine tune the system. 100

102 Chapter 5 Conclusion 5.1 Summary of contribution In conventional learning environments students face challenges in understanding how signals propagate and interact with the surrounding environment. It is difficult for them to predict how signals behaviours (reflection, refraction, diffraction and scattering) are affected by the obstacles geometry, construction and position in space. It is also computationally expensive causing long delays to recalculate the path loss, received power and many other calculations related to signal behaviour each time something in the environment changes. The main aim of this project is to allow students to visualize signal propagation behaviours in different environments. Calculations are done dynamically and introduced to students at each point in space. The project provided students with a 2D/3D wireless ray tracing educational land to learn different aspects related to signals and signals propagation. The land consists of three main regions, in the first region students are provided with a wavelength-frequency converter tool, electromagnetic tool, antennas tool. This provides them with the basic information to start learning about free space propagation and signal ray tracing. In the second region a free space propagation laboratory had been implemented to provide students with the simplest form of the path loss and received power calculations. Students can change the operating frequency, transmission power and the receiver sensitivity dynamically and visualize how the signal propagation is affected. Finally in the third region the 2D and 3D ray tracing laboratory had been implemented. Students can change the environment dynamically and assign different materials to obstacles and visualize how signal propagation, power calculations, incident and refraction angles are affected. 101

103 5.2 Further Work Short term enhancements Several short term enhancements could be applied to the WRTEL. The antenna tool which exists in region B could be improved to allow students to create, view and check 3D style antenna geometry structures and generate, display and/or compare near/farfield radiation patterns. In the 2D/3D wireless ray tracing educational land students perform the free space propagation and the 2D /3D ray tracing experiments using isotropic antennas. An obvious enhancement would be to allow students to use several types of antennas such as the Omni-directional and directional antennas to visualize how signals propagation and interaction with the surrounding environment is affected. A third enhancement would be by improving the reflection and refraction ray tracing algorithm to include diffraction and scattering behaviours. In section it was mentioned that the 2D/3D ray tracing laboratory supports cuboids and spherical obstacles. Supporting more sophisticated obstacles shapes will provide further enhancements Longer term enhancements In the 2D/3D ray tracing laboratory rays interact only with the obstacles created within the in-world building tool. Land and avatars interactions with the propagated signals had been ignored due to the shortage of time. An obvious enhancement to the project would be to consider both of them, so that students can have a more realistic feeling about the whole ray tracing phenomena. OpenSimualtor LSL functions supports taking the land into consideration. llgroundslope[ 97 ]and llgroundnormal[ 98 ]determine the ground slope and the normal vector at specific positions in space. land_collision[ 99 ] event is also fired when an object hits the land and returns the point of intersection. 102

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111 Appendix 1 Deriving from Is similar to: For is in MHz, in meters : For c= : 110

112 Appendix 2 In this appendix both the line-sphere and line-plane intersections are described. Line-Sphere intersection[ 100 ]: Figure 82: Intersection of a Line and a Sphere[ 100 ] Points P on a the line are defined by two points P 1 (x 1,y 1,z 1 ) and P 2 (x 2,y 2,z 2 ) Or in each coordinate: A sphere centred at P 3 (x 3, y 3, z 3 ) with radius r is described by[ 100 ]: Substituting the equation of the line into the sphere gives the following quadratic equation[ 100 ]: 111

113 Where[ 100 ]: The solution to this quadratic is described by[ 100 ]: The exact behaviour is determined by the expression within the square root.if this is less than 0 then the line does not intersect the sphere. If it equals 0 then the line is a tangent to the sphere intersecting it at one point, namely at u = -b/2a. If it is greater than 0 the line intersects the sphere at two points. Line-Plane intersection: Figure 83: Intersection of a Line and a plane [ 101 ] To find whether the line intersects with the plane or not, the dot product between I which is the line vector and N which is the surface normal vector is found. If the dot product is greater than, or equal to, zero then the line does not intersect the plane. Otherwise an intersection occurs[ 101 ]. 112

114 Appendix 3 Rays produced when the emission angle changes from 3 degrees to 10 degrees. Figure 84: Rays produced at 3 degrees emission angle increment Figure 85: Rays produced at 4 degrees emission angle increment 113

115 Figure 86: Rays produced at 5 degrees emission angle increment Figure 87: Rays produced at 6 degrees emission angle increment 114

116 Figure 88: Rays produced at 7 degrees emission angle increment Figure 89: Rays produced at 8 degrees emission angle increment 115