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simulation of multiple input multiple output (MIMO)wireless system

By Carol Murphy,2014-06-04 10:56
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1 introduction 2 technical background 3 implementation of ray tracing 4 implementation of mimo simulator 5 results conflusions and further research

    DUBLIN CITY UNIVERSITY

    SCHOOL OF ELECTRONIC ENGINEERING

    Simulation of a Multiple Input Multiple Output

    (MIMO) wireless system

    John Fitzpatrick

    TC4

    52140938

    April 2004

    B.Eng

    IN

    Telecommunications Engineering

    Supervised by Dr. Conor Brennan

    Simulation of a MIMO wireless system John Fitzpatrick

    Acknowledgements

I would like to thank my supervisor Dr. Conor Brennan for his guidance, assistance and

approachability throughout this project. I would also like to thank John Diskin for his work

on the ray tracing program. Finally I would like to thank my parents and Laura for their

support throughout my project.

    Declaration I hereby declare that, except where otherwise indicated, this document is entirely my own

    work and has not been submitted in whole or in part to any other university.

Signed: ...................................................................... Date: ...............................

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    Simulation of a MIMO wireless system John Fitzpatrick

    Abstract

    This project explores the development of a multiple input multiple output (MIMO) simulator using ray tracing techniques. This project gives an overview of ray tracing techniques, beamforming, MIMO channel models and MIMO systems. It explains the ability of MIMO systems to offer significant capacity increases over traditional wireless systems, by exploiting the phenomenon of multipath. By modelling high frequency radio waves as travelling along localized linear trajectory paths, they can be approximated as rays, just as in optics.

    The radio environment is then represented using a ray tracing C++ program. I highlight some of the different approaches used to realize a MIMO system, the most important being the Singular Value Decomposition (SVD). I illustrate the development of the MIMO simulator, through explanations of the techniques and algorithms I developed and used. These algorithms model the system under ideal conditions with no noise distortions. I show the use of the MIMO simulator created, and investigate the MIMO channel. The results obtained show the affects of changing the different parameters of the system on the MIMO channel and the radio environment.

    Finally, in the conclusion, I discuss the future of MIMO systems and recommend further modifications, which could be made to the MIMO simulator, to create a more accurate and efficient system.

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    Simulation of a MIMO wireless system John Fitzpatrick

    Table Of Contents

CHAPTER 1 - INTRODUCTION ....................................................................................... 1

CHAPTER 2 - TECHNICAL BACKGROUND................................................................. 2

2.1 MULTIPATH .................................................................................................................... 3

2.2 RAY TRACING ................................................................................................................. 3

2.3 BEAMFORMING ............................................................................................................... 4

2.4 LINEAR ARRAYS.............................................................................................................. 6

2.5 MIMO ............................................................................................................................ 7

    2.5.1 MIMO Transmission............................................................................................... 8

    2.5.2 The MIMO Channel H............................................................................................ 9

    2.6 GAUSSIAN ELIMINATION............................................................................................... 10

    2.7 SINGULAR VALUE DECOMPOSITION (SVD) .................................................................. 12

CHAPTER 3 IMPLEMENTATION OF RAY TRACING .......................................... 13

3.1 RAY TRACING ............................................................................................................... 14

    3.1.2 The ray tracing program ...................................................................................... 14

    3.2 CONVERGENCE OF ORDER ............................................................................................. 26

CHAPTER 4 - IMPLEMENTATION OF MIMO SIMULATOR.................................. 30

    4.1 GAUSSIAN ELIMINATION............................................................................................... 30

4.2 SVD ............................................................................................................................. 33

    4.2.1 Operation of the SVD algorithm........................................................................... 33

    4.2.2 Matlab SVD .......................................................................................................... 35

4.3 FURTHER MODIFICATIONS TO THE RAY TRACING PROGRAM .......................................... 39

    4.4 PLOTTING THE RESULTS ................................................................................................ 40

    4.5 THE MIMO SIMLATOR ................................................................................................. 41

    4.5.1 MIMO simulator users guide................................................................................ 43

CHAPTER 5 RESULTS .................................................................................................. 46

    5.1 SVD IN FREESPACE ...................................................................................................... 46

    5.2 NUMBER OF ELEMENTS IN AN ARRAY............................................................................ 49

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    Simulation of a MIMO wireless system John Fitzpatrick

5.3 DIELECTRIC PARAMETERS AND CORRIDOR MODEL ........................................................ 51

CHAPTER 6 - CONCLUSIONS AND FURTHER RESEARCH................................... 55

Matlab code for Beamforming....................................................................................... 58

C++ Gaussian Elimination Code.................................................................................. 60

Matlab Singular Value Decomposition (SVD) Code..................................................... 64

Matlab mimo Code...................................................................................................... 66

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    Simulation of a MIMO wireless system John Fitzpatrick

    Table of Figures

FIGURE 2-1 MULTIPATH ENVIRONMENT ........................................................................ 3

    FIGURE 2-2 SIMO SYSTEM............................................................................................. 5

    FIGURE 2-3 LINEAR BEAMFORMING ARRAY................................................................... 6 FIGURE 2-4 BEAMFORMING ............................................................................................ 7

    FIGURE 2-5 THREE ELEMENT MIMO SYSTEM................................................................. 8 FIGURE 2-6 DATA TRANSMISSION IN MIMO SYSTEMS ................................................... 8 FIGURE 3-1 BUILDING STRUCTURE ............................................................................... 15

    FIGURE 3-2 OBLONG (WALL) ....................................................................................... 16

    FIGURE 3-3 FACE .......................................................................................................... 17

    FIGURE 3-4 RAY NODES ............................................................................................... 19

    FIGURE 3-5 DIRECT RAY .............................................................................................. 20

    FIGURE 3-6 FIRST ORDER IMAGE.................................................................................. 21

    FIGURE 3-7 FINDING REFLECTION POINTS .................................................................... 22

    FIGURE 3-8 FINDING THE REFLECTION POINT................................................................ 25 FIGURE 3-9 SAMPLE POINTS FOR CONVERGENCE .......................................................... 27 FIGURE 3-10 CONVERGENCE GRAPH, BLUE =1ST, RED =2ND, GREEN 3RD ORDER ........... 27

    FIGURE 3-11 2D PLOT OF 4TH ORDER ROOM WITH 6 WALLS ......................................... 28 FIGURE 3-12 3D PLOT OF 4TH ORDER ROOM WITH 6 WALLS ......................................... 29 FIGURE 4-1 SCREENSHOT OF GAUSSIAN ELIMINATION PROGRAM................................. 32 FIGURE 4-2 SCREENSHOT OF C++ SVD PROGRAM ....................................................... 34 FIGURE 4-3 SCREENSHOT OF RAY TRACING PROGRAM .................................................. 43 FIGURE 4-4 SCREENSHOT PLEASE ENTER ORDER ...................................................... 43 FIGURE 4-5 SCREENSHOT PLEASE RUN MYSVD ...................................................... 44 FIGURE 4-6 SCREENSHOT PLEASE RUN MIMO‟“ ......................................................... 44 FIGURE 4-7 RESULT OF RAY TRACING PROGRAM, TX ANTENNA IN FREESPACE............. 45

    FIGURE 4-8 RESULT OF RAY TRACING PROGRAM, RX ANTENNA IN FREESPACE ............ 45

    FIGURE 5-1 TX FREESPACE ANTENNA GAIN PLOT ......................................................... 46 FIGURE 5-2 RX FREESPACE ANTENNA GAIN PLOT ......................................................... 47 FIGURE 5-3 TX FREESPACE ANTENNA GAIN PLOT WITH ANTENNA SHIFTED UP ............. 48

    FIGURE 5-4 RX FREESPACE ANTENNA GAIN PLOT WITH ANTENNA SHIFTED UP ............. 48

    FIGURE 5-5 3 ELEMENT ANTENNA ARRAY ..................................................................... 49

    FIGURE 5-6 5 ELEMENT ANTENNA ARRAY ..................................................................... 50

    FIGURE 5-7 7 ELEMENT ANTENNA ARRAY ..................................................................... 50

    FIGURE 5-8 TX CORRIDOR MODEL ................................................................................ 52

    FIGURE 5-9 RX CORRIDOR MODEL................................................................................ 52

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    Simulation of a MIMO wireless system John Fitzpatrick

    FIGURE 5-10 TX CORRIDOR MODEL, INCREASED DIELECTRIC PARAMETERS ................. 53 FIGURE 5-11 RX CORRIDOR MODEL, INCREASED DIELECTRIC PARAMETERS ................. 54

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    Simulation of a MIMO wireless system John Fitzpatrick

    Chapter 1 - Introduction

    In the modern era of communications, the ability to send large volumes of data is crucial.

    With the increasing use of wireless LAN technology and third generation mobile telephony

    systems, the demand for data services has never been greater. The bandwidth of wireless

    communication systems is often limited by the cost of the radio spectrum required. Any

    increase in bit rate, which can be realised without increasing the bandwidth, makes the

    system more spectrally efficient and less costly. Traditional wireless communication

    systems have been made more spectrally efficient through the use of clever coding

    techniques and algorithms. However, the fundamental bandwidth limitation does not change.

    Multiple Input Multiple Output (MIMO) communication systems have been an increasingly

    hot topic of research over the past eight years, due to their ability to greatly increase spectral

efficiencies.

    As opposed to traditional wireless systems, in which there is one transmitting and one

    receiving antenna, MIMO systems use arrays of multiple antennas at both ends of the

    communication link, all operating at the same frequency at the same time. This introduces

    spatial diversity into the system, which can be used to tackle the problem of multipath. In

    wireless communications system, such as point to point radio links, radio waves do not

    simply propagate from the transmit antenna to the receive antenna. Rather they bounce and

    scatter off objects, this effect is known as multipath. This effect is regarded as an

    impediment to the accurate transmission of data in traditional wireless links. MIMO systems

    exploit multipath by using the rich scattering environment to increase the spectral efficiency

of the wireless system.

    The modelling of radio waves on a large scale can be very complex. There is however, a

    simplification. At high frequencies radio waves can be approximated as travelling along

    localized paths. This is similar to the geometrical treatment of light rays in optics. Using ray

tracing methods, complex radio environments can be modelled.

    The use of numerical techniques is crucial to the operation of MIMO systems. Algorithms

    and signal processing at both ends of a MIMO wireless link are crucial to encode and

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    Simulation of a MIMO wireless system John Fitzpatrick

decode the data. The most important numerical method in MIMO systems is Singular Value

Decomposition (SVD). This allows the complex path, which exists between transmitter and

receiver to be analysed and simplified.

By combining the above techniques it was the aim of this project to develop a fully

operational MIMO simulator. The simulator needed to model indoor radio environments and

be easy to use.

    Chapter 2 - Technical Background

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    Simulation of a MIMO wireless system John Fitzpatrick

    In wireless communications system, such as point to point radio links, radio waves do not

    simply propagate from the transmit antenna to the receive antenna. Rather they bounce and

    scatter off objects. This effect is known as multipath. When the radio waves strike an object

    in the environment, they scatter randomly as can be seen in figure 2.1. This is also known as

    independent Rayleigh scattering. The red line shows the direct propagation path, whereas

    the many blue lines show the multiple propagation paths produced by multipath.

    Figure 2-1 MultiPath Environment

2.1 Multipath

    Multipath results in multiple copies of the same transmitted signal arriving at the receiver, at

    different times. As they arrive at different times they have varying phase delays, which can

    result in scattered signals combining destructively at the receiver producing destructive

    interference and fading. To carry out any simulation, the multipath environment needs to be

modelled. This is done using ray tracing.

2.2 Ray tracing

    The radio environment was modelled using ray tracing. Ray tracing was initially developed

    in the field of computer graphics to produce photorealistic computer generated images. Ray

    tracing operates by calculating the path taken by a ray of light from a light source to the

    point of interest. At frequencies greater than approximately 900MHz, radio waves can be

    described as travelling along localized ray paths (i.e. approximately a straight line). The

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