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

1

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

2

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

3

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

4

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

5

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

6

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

7

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

8

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.

9

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.

10

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.

11

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.

12

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.

13

Figure 1: Clicker tool presenting a quiz question to students[8]

Figure 2: Evaluation results for each student after the quiz ends[8]

14

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

15

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

16

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

17

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.

18

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.

19

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

].

20

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

]

21

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

22

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

23

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.

77

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