MULTIUSER DETECTION FOR CDMA SYSTEM - .MULTIUSER DETECTION FOR CDMA SYSTEM ... conventional CDMA

  • View
    223

  • Download
    0

Embed Size (px)

Text of MULTIUSER DETECTION FOR CDMA SYSTEM - .MULTIUSER DETECTION FOR CDMA SYSTEM ... conventional CDMA

  • 1

    pg. 1

    MULTIUSER DETECTION FOR CDMA SYSTEM

    A THESIS SUBMITTED IN PARTIAL FULLFILLMENT OF THE REQUIREMENTS

    FOR THE DEGREE OF BACHELOR OF TECHNOLOGY

    By

    VARUN SAHAY

    Roll No: 107EC006

    DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

    NATIONAL INSTITUTE OF TECHNOLOGY

    ROURKELA

    2011

  • 2

    pg. 2

    MULTIUSER DETECTION FOR CDMA SYSTEM

    A THESIS SUBMITTED IN PARTIAL FULLFILLMENT OF THE REQUIREMENTS

    FOR THE DEGREE OF BACHELOR OF TECHNOLOGY

    By

    VARUN SAHAY

    Roll No: 107EC006

    DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

    NATIONAL INSTITUTE OF TECHNOLOGY

    ROURKELA

    2011

  • 3

    pg. 3

    MULTIUSER DETECTION FOR CDMA SYSTEM

    A THESIS SUBMITTED IN PARTIAL FULLFILLMENT OF THE REQUIREMENTS

    FOR THE DEGREE OF BACHELOR OF TECHNOLOGY

    By

    VARUN SAHAY

    Roll No: 107EC006

    Under the Guidance of-

    Prof. POONAM SINGH

    DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

    NATIONAL INSTITUTE OF TECHNOLOGY

    ROURKELA

    2011

  • 4

    pg. 4

    NATIONAL INSTITUTE OF TECHNOLOGY

    ROURKELA 2011

    CERTIFICATE

    This is to certify that the thesis entitled, MULTIUSER DETECTION FOR CDMA

    SYSTEM submitted by Mr. VARUN SAHAY in partial fulfillment of the requirements of the

    award of Bachelor of Technology Degree in Electronics and Communication Engineering at the

    National Institute of Technology, Rourkela is an authentic work carried out by him under my

    supervision and guidance.

    To the best of my knowledge, the matter embodied in the thesis has not been submitted to any

    other university or institute for the award of any Degree or Diploma.

    Date: 15.5.2011

    Prof. Poonam Singh

    Department of Electronics and

    Communication Engineering.

    National Institute of Technology

    Rourkela 769008

  • 5

    pg. 5

    ACKNOWLEDGEMENTS

    With deep regards and profound respect, I avail this opportunity to express my deep sense of

    gratitude and indebtedness to Prof. Poonam Singh, Department of Electronics and

    Communication Engineering, N I T Rourkela for providing me the present topic and for her

    superb guidance, and all the invaluable suggestions. I thank her for all the constructive

    feedbacks provided by her during my work. Whenever I did the analysis wrong, she always

    remained calm and guided me to the correct path and always supported me as the best mentor.

    I am grateful to her.

    I am grateful to Prof. S.K. Patra, Head of the Department of Electronics and Communication

    Engineering for allowing us to make use of the facilities available in the department to carry

    out the project successfully.

    The staff members of the Department of Electronics and Communication Engineering were

    very helpful during the research work and I would like to thank them for that.

    And at last but not the least, my thanks and love to all my buddies who always stood up to me

    and shone like the light at the end of a tunnel.

    15th

    May 2011 Varun Sahay (107EC006)

  • 6

    pg. 6

    Abstract

    Multiple access interference (MAI) limits the capacity of Direct Sequence Code Division

    Multiple Access (DS-CDMA) systems. In CDMA systems MAI is considered as additive

    noise and a matched filter bank is employed. Traditionally, multiuser detectorsa code-

    matched and a multiuser linear filterare used which increases the complexity of the system

    due to its nature of operation. Multiuser detection is an approach which uses both these filters

    for the optimization. However, the main drawback of the optimal multiuser detection is one

    of complexity so that suboptimal approaches are being sought. Much of the present research

    is aimed at finding an appropriate tradeoff between complexity and performance. These

    suboptimal techniques have linear and non-linear algorithms. In this work, we introduce

    Successive Interference Cancellation (SIC) which is a nonlinear suboptimal method of MUD

    and is based upon successively subtracting off the strongest remaining signal. Further

    analysis is to be carried out and simulations to be done for better understanding of SIC.

  • 7

    pg. 7

    CONTENTS

    Page no. Acknowledgements 5

    Abstract 6

    Contents 7-8

    List of Figures 9

    List of Tables 10

    CHAPTER-1 Introduction

    1.1 What is CDMA? 11

    1.2 Multiuser Detection (MUD) 12

    1.2.1 MUD Concepts and Techniques 12

    1.2.2 MUD Algorithms 15

    1.2.3 Optimum Multiuser Detection 16

    1.2.4 Linear Multiuser Detection 16

    1.3 Successive Interference Cancellation 19

    CHAPTER-2 Experimental Work

    2.1 First Program 21

    2.1.1 Algorithm 21

    2.1.2 MATLAB Program 21

    2.1.3 Output of the first program 24

    2.2 Second Program 25

    2.2.1 Algorithm 25

    2.2.2 MATLAB Program 25

    2.2.3 Output of the second program 29

  • 8

    pg. 8

    CONTENTS

    Page no. 2.3 Third (Final) Program 30

    2.3.1 Algorithm 30

    2.3.2 MATLAB Program 31

    2.3.3 Output of the final program 37

    CHAPTER-3 Conclusions & Future Work 39

    References 40

  • 9

    pg. 9

    LIST OF FIGURES

    S. no. Figure nos. Title of Figure Page no.

    1 Fig. 1.1 A schematic comparison of FDMA, TDMA, and CDMA multiple-

    access techniques.

    11

    2 Fig. 1.2 CDMA Uplink 13

    3 Fig. 1.3 CDMA Channel Model 14

    4 Fig. 1.4 Flowchart for MUD Algorithms 15

    5 Fig. 1.5 Spectral Efficiency vs. System Loading at Eb/N0 = 10 dB 18

    6 Fig. 1.6 Large K Spectral Efficiencies with optimum K/N 18

    7 Fig. 1.7 Block diagram of Successive Interference Cancellation 19

    8 Fig. 2.1 (ts) (WHEN ERROR=0) i.e SNR=100 24

    9 Fig. 2.2 (rss) (WHEN ERROR=0) i.e SNR=100 24

    10 Fig. 2.3 (ts) (WHEN ERROR=18) i.e SNR=10 24

    11 Fig. 2.4 (rss) (WHEN ERROR=18) i.e SNR=10 24

    12 Fig. 2.5 Plot of SNR (x-axis) vs. BER (y-axis) for 6 different users 29

    13 Fig. 2.6 1st Run of BER VS Number of Users 37

    14 Fig. 2.7 2nd

    Run of BER VS Number of Users 37

    15 Fig. 2.8 BER VS Number of Users 38

  • 10

    pg. 10

    LIST OF TABLES

    S. no. Table nos. Title of Table Page no.

    1 Table 2.1 Input from six different CDMA users and plotting the BER 29

  • 11

    pg. 11

    INTRODUCTION

    1.1 What is CDMA?

    CDMA stands for Code Division Multiple Access. It is a digital cellular technology that uses

    spread-spectrum technique means it works by digitizing multiple conversations. It is

    developed by Qualcomm, Inc. and standardized by the Telecommunications Industry

    Association (TIA) as an Interim Standard (IS-95). In this several users share the share the

    same physical medium i.e. same frequency band at same time.

    In CDMA every communicator will be allocated the entire spectrum all of the time. It uses

    codes to identify connection. A conventional DS/CDMA system treats each user separately as

    a signal, with other users considered as noise or MAI multiple access interference. All users

    interfere with all other users and the interferences add to cause performance degradation. The

    near/far problem is serious and tight power control, with attendant complexity is needed to

    combat it. All users in a CDMA system interfere with each other. Potentially significant

    capacity increases and near/far resistance can theoretically be achieved if the negative effect

    CHAPTER-1

    Fig. 1.1 A schematic comparison of FDMA, TDMA, and CDMA multiple-access

    techniques.

  • 12

    pg. 12

    that each user has on others can be canceled. A solution to the shortcomings of the

    conventional CDMA system is Multiuser Detection in which all users are considered as

    signals for each other.

    1.2 Multiuser Detection (MUD)

    Because all users are considered as signals for each other, therefore, instead of users

    interfering with each other, they are all being used for their mutual benefit by joint detection.

    The multiuser