2D/3D Wireless Ray Tracing Educational Land...2D/3D Wireless Ray Tracing Educational Land A...
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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
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Contents
List of figures ............................................................................................................................. 4
List of tables ............................................................................................................................... 7
Abstract ...................................................................................................................................... 8
Declaration ................................................................................................................................. 9
Copyright .................................................................................................................................. 10
Acknowledgment ...................................................................................................................... 11
Chapter 1 Introduction .............................................................................................................. 12
1.1 Aims ........................................................................................................................ 16
1.2 Hypothesis ............................................................................................................... 17
Chapter 2 Background .............................................................................................................. 19
2.1 Virtual Worlds ............................................................................................................... 19
2.1.1 Migrating from Second Life to OpenSimulator........................................................ 19
2.2 Education in Virtual Worlds .......................................................................................... 22
2.2.1 Virtual worlds in comparison with e-learning systems ............................................. 23
2.2.2 Simulations in education ......................................................................................... 24
2.2.3 Choosing the appropriate virtual world for educational purposes ............................. 25
2.3 Electromagnetic signals ................................................................................................. 29
2.3.1 Electromagnetic spectrum ....................................................................................... 29
2.3.2 Decibels .................................................................................................................. 30
2.3.3 Antennas................................................................................................................. 30
2.3.4 Free space propagation............................................................................................ 33
2.3.5 Reflection ............................................................................................................... 34
2.3.6 Refraction ............................................................................................................... 35
2.3.7 Scattering ............................................................................................................... 36
2.3.8 Absorption .............................................................................................................. 36
2.3.9 Diffraction .............................................................................................................. 36
2.3.10 Objects properties ................................................................................................. 37
2.3.11 Multipath propagation ........................................................................................... 38
2.3.12 Ray tracing ........................................................................................................... 39
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2.4 Ray tracers in virtual worlds .......................................................................................... 40
2.5 Chapter summary .......................................................................................................... 42
Chapter 3: Design and Implementation ..................................................................................... 43
3.1 Implementation language ............................................................................................... 43
3.2 Scripts in OpenSim ........................................................................................................ 44
3.3 2D/3D Wireless Ray Tracing Educational Land ............................................................. 45
3.3.1 Frequency-wavelength converter tool ...................................................................... 46
3.3.1.1 Frequency-wavelength converter buttons .......................................................... 47
3.3.1.2 Frequency-wavelength self test......................................................................... 47
3.3.1.3 Frequency-wavelength information box ............................................................ 49
3.3.2 Electromagnetic spectrum tool ................................................................................ 49
3.3.2.1 Electromagnetic spectrum sphere ..................................................................... 50
3.3.2.2 Electromagnetic spectrum coloured boxes ........................................................ 50
3.3.3 Antennas tool .......................................................................................................... 51
3.3.4 Free space propagation laboratory ........................................................................... 53
3.3.4.1 The transmitter antenna .................................................................................... 54
3.3.4.2 The receiver antenna ........................................................................................ 58
3.3.5 2D/3D wireless Ray tracing laboratory .................................................................... 59
3.3.5.1 The 2D/3D wireless ray tracing remote Control ................................................ 60
3.3.5.2 The transmitter antenna .................................................................................... 62
3.3.5.2.1 Determining the frequency and the transmission power .............................. 62
3.3.5.2.2 Ray tracing ................................................................................................ 63
3.3.5.2.3 Drawing the rays ....................................................................................... 66
3.3.5.2.4 Send the stored information to rays ............................................................ 67
3.3.5.3 Rays ................................................................................................................. 67
3.3.5.4 Obstacles ......................................................................................................... 69
3.3.5.5 Evolution and adaption ..................................................................................... 70
Chapter 4: Results ..................................................................................................................... 71
4.1 Overview ....................................................................................................................... 71
4.2 Frequency-wavelength converter tool ............................................................................ 72
4.2.1 Frequency-wavelength self test ............................................................................... 73
4.2.2 Frequency-wavelength information box .................................................................. 74
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4.3 Electromagnetic spectrum tool ....................................................................................... 75
4.4 Antenna tool .................................................................................................................. 75
4.5 Free space propagation laboratory.................................................................................. 76
4.5.1 The transmitter antenna ........................................................................................... 77
4.5.2 The receiver antenna ............................................................................................... 82
4.6 2D/3D wireless ray tracing laboratory ............................................................................ 83
4.6.1 The transmitter antenna ........................................................................................... 83
4.6.2 Obstacles ................................................................................................................ 84
4.6.3 2D/3D ray tracing simulation .................................................................................. 85
4.7 Evaluation ..................................................................................................................... 94
4.7.1 Technical evaluation ............................................................................................... 94
4.7.2 Educational evaluation ............................................................................................ 99
Chapter 5 Conclusion .............................................................................................................. 101
5.1 Summary of contribution ............................................................................................. 101
5.2 Further Work ............................................................................................................... 102
5.2.1 Short term enhancements ...................................................................................... 102
5.2.2 Longer term enhancements ................................................................................... 102
Bibliography ........................................................................................................................... 103
Appendix 1 ............................................................................................................................. 110
Appendix 2 ............................................................................................................................. 111
Appendix 3 ............................................................................................................................. 113
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List of figures
Figure 1: Clicker tool presenting a quiz question to students .................................................... 13
Figure 2: Evaluation results for each student after the quiz ends............................................... 13
Figure 3: Emitting signals in 2D .............................................................................................. 15
Figure 4: Emitting signals in 3D .............................................................................................. 16
Figure 5: Inventory associated with each avatar in Second Life ............................................... 20
Figure 6: (a) In-world content creation tools for modelling, (b) Scripting tool ......................... 20
Figure 7: Box shows a welcome message when it is touched by an avatar ................................ 21
Figure 8: Discussion forum in Moodle..................................................................................... 24
Figure 9: Classroom in Second Life ......................................................................................... 24
Figure 10: A snapshot taken in AWEDU ................................................................................. 26
Figure 11: A snapshot taken in Wonderland ............................................................................ 27
Figure 12: A snapshot taken in Open Cobalt virtual environment ............................................. 27
Figure 13: Electromagnetic signal ........................................................................................... 29
Figure 14: Electromagnetic spectrum ...................................................................................... 30
Figure 15: Isotropic antenna .................................................................................................... 31
Figure 16: Omni-directional antenna ...................................................................................... 31
Figure 17: Directional antenna ................................................................................................ 31
Figure 18: The radiation pattern of an Omni-directional antenna .............................................. 32
Figure 19: The radiation pattern of a Yagi antenna .................................................................. 33
Figure 20: Reflection............................................................................................................... 35
Figure 21: Refraction .............................................................................................................. 35
Figure 22: (a) Diffraction at the edge of an obstacle and (b) Fresnel zone ................................ 37
Figure 23: Multipath propagation ............................................................................................ 38
Figure 24: Screenshot form demo of Unreal 3 game engine ..................................................... 39
Figure 25: Side view of the room used in 3D ray tracer............................................................ 41
Figure 26: (a) Reflection, (b) Diffraction, (c) Diffuse propagation ........................................... 41
Figure 27: Frequency-wavelength converter tool ..................................................................... 46
Figure 28: Frequency-wavelength converter button state diagram ............................................ 47
Figure 29: The self test questions format ................................................................................. 48
Figure 30: Calculator state chart .............................................................................................. 49
Figure 31: Electromagnetic spectrum tool................................................................................ 50
Figure 32: A 2.4 GHz directional Yagi antenna simulated in 4NEC2 ....................................... 51
Figure 33: Antenna tool ........................................................................................................... 52
Figure 34: Free Space propagation laboratory .......................................................................... 53
Figure 35: Transmitter antenna state chart ............................................................................... 54
Figure 36: The code responsible for calculating the path loss ................................................... 55
Figure 37: State chart of a sphere listening to the transmitting antenna ..................................... 56
Figure 38: The geometric origin of the inverse square law ....................................................... 57
Figure 39: The intensity and distance inverse square relation ................................................... 57
Figure 40: The receiver antenna state chart .............................................................................. 58
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Figure 41: The 2D/3D wireless ray tracing laboratory .............................................................. 60
Figure 42: Obstacles state chart ............................................................................................... 69
Figure 43: Wireless ray tracing educational land ...................................................................... 71
Figure 44: The dialog box displayed in a wavelength to frequency conversion ......................... 72
Figure 45: The wavelength of a 100 Hz frequency ................................................................... 72
Figure 46: The self test in Frequency-wavelength converter tool .............................................. 73
Figure 47: The score presented to students after they finish the test ......................................... 73
Figure 48: The Notecard produced for the Frequency-wavelength converter tool ..................... 74
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 .......................................... 76
Figure 51: The billboard and the information box .................................................................... 77
Figure 52: The dialog box displayed when the student touch the transmitter antenna................ 78
Figure 53: The path loss chart for a 2.4 GHz and -10 dBW signal ............................................ 78
Figure 54: The details displayed by the transmitter antenna ..................................................... 79
Figure 55: The path loss and the received power at the sphere position .................................... 80
Figure 56: Intensity and distance square law relation at a 1 meter distance from Tx ................. 81
Figure 57: Intensity and distance square law relation at 2 meters distance from Tx .................. 81
Figure 58: Configure the sensitivity at the receiver antenna ..................................................... 82
Figure 59: The received power is less than the receiver sensitivity ........................................... 82
Figure 60: The billboard and the information box .................................................................... 83
Figure 61: Configure the frequency in the transmitter antenna ................................................. 84
Figure 62: A cement obstacle wall changed to become a wooden obstacle wall........................ 84
Figure 63: 2D ray tracing simulation environment ................................................................... 85
Figure 64: Visualize one interaction with the surrounding environment ................................... 86
Figure 65: Information displayed for each sphere in the incident ray ........................................ 87
Figure 66: Information displayed at the intersection point of wooden obstacle ......................... 88
Figure 67: Information displayed at the intersection point of cement obstacle .......................... 88
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 ......................... 90
Figure 71: (a) Incident ray (b) Refracted ray ............................................................................ 90
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 ............................................................ 92
Figure 74: Buttons one and two are pressed to visualize one and two interactions .................... 92
Figure 75: The 3D ray tracer output ......................................................................................... 93
Figure 76: Reflection from a ceiling cube obstacle in 3D ......................................................... 94
Figure 77: Computational time and the number of interactions related to the emission angle .... 96
Figure 78: Relationship between the emission angle and the computational time ..................... 96
Figure 79: Emission angle relation with the number of one reflection and two reflections ........ 97
Figure 80: Rays produced at a 1 degree emission angle increment ........................................... 98
Figure 81: Rays produced at 2 degrees emission angle increment............................................. 98
Figure 82: Intersection of a Line and a Sphere ....................................................................... 111
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Figure 83: Intersection of a Line and a plane ........................................................................ 112
Figure 84: Rays produced at 3 degrees emission angle increment........................................... 113
Figure 85: Rays produced at 4 degrees emission angle increment........................................... 113
Figure 86: Rays produced at 5 degrees emission angle increment........................................... 114
Figure 87: Rays produced at 6 degrees emission angle increment........................................... 114
Figure 88: Rays produced at 7 degrees emission angle increment........................................... 115
Figure 89: Rays produced at 8 degrees emission angle increment........................................... 115
Figure 90: Rays produced at 9 degrees emission angle increment........................................... 116
Figure 91: Rays produced at 10 degrees emission angle increment......................................... 116
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List of tables
Table 1: Comparison between Second Life and OpenSimulator ............................................... 21
Table 2: Virtual world‟s features ............................................................................................. 26
Table 3: Comparison between LSL and Non-LSL................................................................... 44
Table 4: Tasks performed by the buttons and the lights ............................................................ 61
Table 5: Obstacle‟s name parts and the assigned value and objective of each part .................... 63
Table 6: The information displayed by intersection and ordinary spheres ................................. 68
Table 7: Computational time and number of interactions for different emission angles ............ 95
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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.
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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.
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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.
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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.
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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.
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Figure 1: Clicker tool presenting a quiz question to students[8]
Figure 2: Evaluation results for each student after the quiz ends[8]
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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
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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
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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
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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.
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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 longer-
term enhancements which could be applied to the work presented in this project.
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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.
2.1.1 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 2003. 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
].
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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
]
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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
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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
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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.
2.2.1 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.
24
Figure 8: Discussion forum in Moodle[6]
Figure 9: Classroom in Second Life[13
]
2.2.2 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
25
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.
2.2.3 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
].
26
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
]
27
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
]
28
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
].
29
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
2.3.1 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.
30
Figure 14: Electromagnetic spectrum[38
]
2.3.2 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.
2.3.3 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
].
31
Figure 15: Isotropic antenna
Figure 16: Omni-directional antenna [40
]
Figure 17: Directional antenna[40
]
32
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
33
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
]
2.3.4 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.
34
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
].
2.3.5 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
].
35
Figure 20: Reflection
2.3.6 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
36
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
].
2.3.8 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
].
2.3.9 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
].
37
(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.
2.3.10 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 802.11[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.
38
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
].
2.3.11 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
]
39
2.3.12 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
]
40
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.
41
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
]
Mirror
Table
Light Rx
Tx
42
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.
43
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 3.3.
3.1 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.
44
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
has been written to teleport an
agent or to write data to
Notecards)
Provides more functionality by
extending LSL implementation and
adding new functions
( ll-functions+ OS functions)
Allow the developer to create
new 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
2147483648[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
].
45
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
].
3.3 2D/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
46
design and implementation of the self test questions [76
] and the information box [76
]
will only be discussed in sections 3.3.1.2 and 3.3.1.3.
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.
3.3.1 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
47
3.3.1.1 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.
3.3.1.2 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
48
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
49
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
3.3.1.3 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.
3.3.2 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.
50
Figure 31: Electromagnetic spectrum tool
3.3.2.1 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.
3.3.2.2 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.
51
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.
3.3.3 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
]
52
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
53
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
54
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.
3.3.4.1 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
]
55
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 2.3.4. 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
56
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 2.3.4.
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 πR2, then the intensity I is given by I=P/ (4 π
R2)[
87].
57
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.
58
3.3.4.2 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
59
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.
3.3.5 2D/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.
60
Figure 41: The 2D/3D wireless ray tracing laboratory
3.3.5.1 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.
61
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
Starts ray tracing llSay(RayTraceChannel,”RayTrace”)
2 Toggle One Interaction
Button
Select all rays with one
interaction
llSay(OneChannel,” One“)
3 Toggle Two
Interactions
Button
Select all rays with two
interaction
llSay(TwoChannel,” Two“)
4 Toggle Three
Interactions
Button
Select all rays with
three reflections
llSay(ThreeChannel,”Three“)
5 Toggle Four
Interactions
Button
Select all rays with
four interaction
llSay(FourChannel,” Four“)
6 Toggle Five
Interactions
Button
Select all rays with five
interaction
llSay(FiveChannel,” Five“)
7 Toggle Six Interactions
Button
Select all rays with six
interaction
llSay(SixChannel,” Six“)
8 Toggle Seven
Interactions
Button
Select all rays with
seven interaction
llSay(SevenChannel,” Seven “)
9 Toggle Eight
Interactions
Button
Select all rays with
eight interaction
llSay(EightChannel,” Eight“)
10 Toggle LOS Button Draws the Los ray between the transmitter
and the receiver
antennas
llSay(LosChannel, ”LOS“)
11 Push Draw Rays
Button
Draws all the selected
rays
llSay(DrawChannel,” Draw“)
12 Push 2D Ray Tracing
Button
Emit Rays from the
transmitter antenna in
X and Y dimensions
llSay(2DChannel, “2DRayTracing”)
13 Push 3D Ray Tracing
Button
Emit Rays from the
transmitter antenna in
X, Y, Z dimensions
llSay(2DChannel, “3DRayTracing”)
14 Toggle Eight spherical
lights
The eight lights colours
change from white to
green to represent the number of interactions
between rays and the
surrounding
environment
-------------------
62
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.
3.3.5.2 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.
3.3.5.2.1 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.
63
3.3.5.2.2 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
(3.3.5.3), obstacles (3.3.5.4) and evolution and adaption (3.3.5.5) sections.
Table 5: Obstacle’s name parts and the assigned value and objective of each part
Obstacle’s name
parts
Assigned
values
objective
Shape
Rx
Tx
Cuboid
Sphere
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
64
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.
65
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
]:
66
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.
3.3.5.2.3 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
67
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.
3.3.5.2.4 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.
3.3.5.3 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.
68
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
69
3.3.5.4 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.
70
3.3.5.5 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.
71
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
72
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
73
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
74
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 Frequency-
wavelength 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
75
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.
76
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 51.
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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 51.
4.5.1 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.
78
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
y
79
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.
80
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.
81
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
82
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 2.3.4 was
-30.000,034 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
83
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
4.6.1 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.
84
Figure 61: Configure the frequency in the transmitter antenna
4.6.2 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
85
4.6.3 2D/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
86
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.
87
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.
88
Figure 66: Information displayed at the intersection point of wooden obstacle
Figure 67: Information displayed at the intersection point of cement obstacle
89
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
90
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
91
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 4.905 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 10.953
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.
92
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
93
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 75.
94
Figure 76: Reflection from a ceiling cube obstacle in 3D
4.7 Evaluation
The 2D/3D WRTEL had been evaluated technically and educationally. Section 4.7.1
presents an efficiency test of the ray tracer algorithm implemented in the 2D/3D
wireless ray tracing laboratory. Section 4.7.2 presents an educational evaluation for the
tools and the laboratories implemented.
4.7.1 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.
95
Table 7: Computational time and number of interactions for different emission angles
Emission angle
(degrees)
Ray tracing Computational time
(Seconds)
Number of interactions
1 145.712,334 Rays with one reflection : 15
Rays with two reflections : 6
2 58.025,319 Rays with one reflection : 7
Rays with two reflections : 3
3 38.814,220 Rays with one reflection : 5
Rays with two reflections : 2
4 38.369,801 Rays with one reflection : 3
Rays with two reflections : 1
5 31.283,789 Rays with one reflection : 3
Rays with two reflections : 1
6 26.779,532 Rays with one reflection : 3
Rays with two reflections : 1
7 22.402,281 Rays with one reflection : 2
Rays with two reflections : 1
8 19.374,108 Rays with one reflection : 2
Rays with two reflections : 0
9 19.201,098 Rays with one reflection : 2
Rays with two reflections : 0
10 19.396,109 Rays with one reflection : 2
Rays with two reflections : 0
96
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 145.712,334 seconds and with ten degrees emission angle the
time is 19.396,109 seconds.
Figure 78: Relationship between the emission angle and the computational time
97
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
98
Figure 80: Rays produced at a 1 degree emission angle increment
Figure 81: Rays produced at 2 degrees emission angle increment
99
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.
4.7.2 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”.
100
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.
101
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.
102
5.2 Further Work
5.2.1 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/far-
field 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 3.3.5.4 it was mentioned that the 2D/3D ray tracing laboratory supports
cuboids and spherical obstacles. Supporting more sophisticated obstacles shapes will
provide further enhancements.
5.2.2 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.
103
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110
Appendix 1
Deriving from
Is similar to:
For is in MHz, in meters :
For c= :
111
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 P1 (x1,y1,z1) and P2 (x2,y2,z2)
Or in each coordinate:
A sphere centred at P3 (x3, y3, z3) with radius r is described by[100
]:
Substituting the equation of the line into the sphere gives the following quadratic
equation[100
]:
112
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
].
113
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
114
Figure 86: Rays produced at 5 degrees emission angle increment
Figure 87: Rays produced at 6 degrees emission angle increment
115
Figure 88: Rays produced at 7 degrees emission angle increment
Figure 89: Rays produced at 8 degrees emission angle increment
116
Figure 90: Rays produced at 9 degrees emission angle increment
Figure 91: Rays produced at 10 degrees emission angle increment