AN IMPROVED INTERPOLATION METHOD FOR CHANNEL ESTIMATION IN AN ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING (OFDM) SYSTEM USING PILOT SIGNALS
AN IMPROVED INTERPOLATION METHOD FOR CHANNEL ESTIMATION IN AN ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING (OFDM) SYSTEM USING PILOT SIGNALS AHMED NOORI HUMMADI THESIS SUBMITTED IN FULFILMENT FOR THE DEGREE OF DOCTOR OF PHILOSOPHY FACULTY OF ENGINEERING AND BUILT ENVIRONMENT UNIVERSITI KEBANGSAAN MALAYSIA BANGI 2011 KAEDAH INTERPOLASI DIPERBAIKI BAGI PENGANGGARAN SALURAN DALAM SISTEM PEMULTIPLEKSAN PEMBAHAGIAN FREKUENSI ORTOGON MENGGUNAKAN ISYARAT PEMANDU AHMED NOORI HUMMADI TESIS YANG DIKEMUKAKAN UNTUK MEMPEROLEH IJAZAH DOKTOR FALSAFAH FAKULTI KEJURUTERAAN DAN ALAM BINA UNIVERSITI KEBANGSAAN MALAYSIA BANGI 2011 ii DECLARATION I hereby declare that the work in this thesis is my own except for quotations and summaries which have been duly acknowledged Date 5/10/2011 AHMED NOORI HUMMADI P43836 iii AKNOWLEDGMENTS Praise is to Allah Almighty for giving me the strength, patience and ability to complete this thesis I would like to thank my supervisor Professor Dr Mahamod Ismail for his thoughtful comments, guidance, attention and encouragement Thank you for the invaluable advice and assistance My Thanks go to my co-supervisor Professor Dr Mohd Alauddin Mohd Ali for her support and help My beloved family for all support, patience, understanding and being helpful throughout my study I give my deepest gratitude and sincerest love to my parents for their love and support through my entire life Special thank to my brother Muneer for his help to solve any problem floating on the surface with my employer I am grateful to all my colleagues, friends, staff, and lecturers in Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia and Hadhramout University of Science and Technology for their help and support at every step during this study I wish to extend my grateful appreciation to all those who have contributed directly and indirectly to the preparation of this study I would like to thank my best friend Mona Alsayigh for her assistance Not forgetting also, my examiners and all committee members for their helpful suggestions iv ABSTRACT Orthogonal Frequency Division Multiplexing (OFDM) system can achieve high data rates in mobile environment due to its robustness against the Inter Symbol Interference (ISI) Likewise, development of efficient receiver with proper channel estimation technique is crucial to ease the prediction of the received signal Pilot symbol assisted modulation introduced to achieve reliable channel estimation through transmitting pilot signals along with in OFDM symbol Moreover, interpolation method developed to estimate the channel samples and eliminates the effect of the fading channel from the received signals However, most of the interpolation techniques such as Linear, Cubic and Spline Cubic interpolation are irresistible against the noise while the conventional interpolation is not resilience The objective of this work is to propose a new improved interpolation technique which is more reliable and efficient for channel estimation in OFDM system based on pilot signal under fast varying and noisy channels The proposed interpolation is much simpler than other technique, such as Linear, Second Order Modulation, Spline, Time domain, and Lowpass interpolation; where it depends on two parameters which are the mean and variance of two adjacent pilot signals Furthermore, this type of interpolation can be modified to give more accurate estimation for the channel depending on two modification factors (β and ξ) The mathematical formulations have been derived based on linear interpolation technique and then validated using simulations The Mean Square Error (MSE) performance of the interpolation technique is then compared with other five types of interpolation under Rayleigh fading channel using comb type channel estimation Simulations show that the proposed interpolation technique able to estimate the channel much better than other interpolation types for Signal to Noise Ratio (SNR) from dB to dB at MSE equal to 10-3 and as a result it is much robust against noise which reduces the accuracy of the estimated channel Furthermore, the channel estimation is then used to examine the effect of pilot estimation using different technique of estimation such as Least Square Error (LSE), Minimum Mean Square Error (MMSE) and Wavelet De-noising It is shown that pilot estimation give superior MSE performance in channel estimation by about 20 dB at low SNR Simulation also shows that SNR performance improved up to 10 dB comparing to other type of interpolation at BER equal to 10-3 Finally, the proposed method also performed well in the estimation of the channel over different Doppler frequencies and achieves higher OFDM system performances v ABSTRAK Sistem Pemultipleksan Pembahagian Frekuensi Ortogon (OFDM) dapat mencapai kadar data yang tinggi dalam persekitaran bergerak kerana ketahanannya terhadap Gangguan Antara Simbol (ISI) pembangunan penerima cekap dengan teknik penganggaran saluran yang tepat sangat penting untuk memudahkan ramalan isyarat yang diterima Pemodulatan terbantu simbol pandu diperkenalkan untuk mencapai penganggaran saluran yang bolehharap melalui penghantaran isyarat pandu bersamasama dengan simbol OFDM Selain itu, kaedah interpolasi dibangunkan untuk menganggarkan sampel saluran dan menghapuskan kesan pemudaran saluran daripada isyarat yang diterima Namun, sebahagian besar teknik interpolasi seperti interpolasi Lelurus, Kubik dan Kubik Spline tidak berupaya menahan kesan hingar sementara interpolasi konvensional tidak terkawal dan tidak anjal Tujuan penyelidikan ini adalah untuk mencadangkan suatu teknik interpolasi baru dipertingkatkan yang lebih bolehharap dan cekap untuk penganggaran saluran dalam sistem OFDM berdasarkan isyarat pandu dalam saluran berubah pantas dan berhingar Interpolasi yang dicadangkan adalah jauh lebih ringkas dari teknik yang lain, seperti interpolasi Lelurus, Pemodulatan Tertib Kedua, Spline, domain Masa, dan Lulus rendah, yang bergantung pada dua parameter iaitu dan varians dari dua isyarat pandu yang bersebelahan Selanjutnya, jenis interpolasi ini boleh diubahsuai untuk memberikan penganggaran yang lebih tepat untuk saluran bergantung pada dua faktor pengubahsuaian (β dan ξ) Formulasi matematik telah diterbitkan berdasarkan teknik interpolasi lelurus dan kemudian disahkan menggunakan simulasi Prestasi Ralat Ganda Dua Min (MSE) dari teknik interpolasi ini kemudian dibandingkan dengan lima jenis interpolasi yang lain dalam saluran pemudaran Rayleigh menggunakan penganggaran saluran jenis sikat Simulasi menunjukkan bahawa teknik interpolasi yang dicadangkan berupaya menganggarkan saluran jauh lebih baik berbanding jenis interpolasi yang lain untuk Nisbah Isyarat Terhadap Hingar (SNR) dari dB hingga dB pada MSE sebanyak 10-3 dan sebagai hasilnya teknik ini jauh lebih tahan terhadap hingar yang mengurangkan kejituan saluran dijangka Selanjutnya, penganggaran saluran ini kemudian digunakan untuk menguji kesan penganggaran pandu menggunakan teknik penganggaran yang berbeza seperti Ralat Ganda Dua Terkecil (LSE), Ralat Ganda Dua Min Minimum (MMSE) dan Wavelet De-noising ini menunjukkan bahawa penganggaran pandu memberikan prestasi MSE yang lebih tinggi dalam penganggaran saluran sekitar 20 dB pada SNR rendah Simulasi juga menunjukkan bahawa prestasi SNR dipertingkatkan sehingga 10 dB berbanding dengan jenis interpolasi lain pada BER sebanyak 10-3 Akhirnya, kaedah yang dicadangkan juga bertindak baik dalam menganggarkan saluran bagi frekuensi Doppler yang berbeza dan mencapai prestasi sistem OFDM yang tinggi vi TABLE OF CONTENTS Page DECELARATION ii ACKNOWLEDGEMENTS iii ABSTRACT iv ABSTRAK v TABLE OF CONTENTS vi LIST OF TABLES x LIST OF FIGURES xi LIST OF SYMBOLS AND ABBREVIATIONS xvi CHAPTER I INTRODUCTION 1.1 Introduction 1.2 OFDM System 1.3 Problem Statement 1.4 Objective and Scope 10 1.5 Methodology 11 1.6 Thesis Contribution 12 1.7 Thesis Organization 12 CHAPTER II LITERATURE REVIEW 2.1 Introduction 14 2.2 An Overview Of The Multiple Access Scheme 15 2.3 Modulation 19 2.4 Phase Shift Keying 20 2.5 The Basics Of OFDM 23 2.6 Multi-Path Fading Channel 24 2.7 2.6.1 Binary Phase Shift Keying 2.6.2 Mobile Channel Model OFDM Channel Estemation 25 26 29 2.7.1 2.7.2 29 31 Least Square (LS) Estimation Minimum Mean Square Error (MMSE) Estimation vii 2.8 Channel Equalization Using Wavelet Denoising 32 2.9 2.8.1 Discrete Wavelet Transform (DWT) 2.8.2 Wavelet Denoising 2.8.3 Wavelet Selection 2.8.4 Threshold Selection for Wavelet Denoising 2.8.4.1 VisuShrink 2.8.4.2 SureShrink 2.8.4.3 BaysShrink 2.8.5 Level of Decomposition Introduction For Interpolation 33 34 35 36 37 37 38 38 39 2.10 Interpolation Defenition And Methods 40 2.11 2.10.1 Linear Interpolation 2.10.2 Polynomial interpolation 2.10.3 Cubic-Spline Interpolation Error Correction Code 40 41 42 44 2.12 Trellis Coded Modulation (TCM) 45 2.13 Viterbi Algorithm 50 CHAPTER III CHANNEL ESTIMATION USING PILOT SIGNAL 3.1 Introduction 52 3.2 OFDM system 53 3.3 Pilot Sample Arrangment 54 3.4 Alnuaimy-Mahamod Interpolation 56 3.4.1 3.4.2 3.4.3 3.4.4 3.4.5 57 58 59 64 67 Formulation β and ξ Factors Samples Interpolation Alnuaimy-Mahamod Interpolation Implementation Summary CHAPTER IV MODULATION BASED CHANNEL ESTIMATION 4.1 Introduction 70 4.2 OFDM System Model 71 4.2.1 4.2.2 71 72 Transmitter Structure Receiver Structure 4.3 Channel Estimation 73 4.4 Alnuaimy-Mahamod Interpolation 76 4.5 Computer Simulation 77 4.6 Simulation 78 4.6.1 β and ξ Factor Values 78 viii 4.7 Results and Discussion 80 4.8 Coded OFDM System Model 92 4.9 COFDM Simulation 94 4.9.1 96 Simulation Results 4.10 Summary CHAPTER V PILOT SIGNAL CORRECTION OF ESTIMATION 5.1 Introduction 104 5.2 OFDM System Model With Channel Estimation Block 105 5.3 Channel Estimation 106 5.3.1 5.3.2 5.3.3 106 107 109 Channel Extraction Pilot Estimation Channel Interpolation 102 5.4 Simulation CHAPTER VI CONCLUSION AND FUTURE WORK 6.1 Conclusion 116 6.1.1 117 6.2 Pilot Channel Estimation Recommendations For Future Work REFERENCES 109 118 120 APPENDICES A Alnuaimy-Mahamod Interpolation Derivation 129 B Optimum Channel Interpolation 132 C List Of Publication 134 x LIST OF TABLES Table No Page 2.1 Main parameters of WLAN communication systems 15 2.2 The Advantages and drawbacks of different multiple access 18 schemes 3.1 RMSE for Alnuaimy-Mahamod interpolation with the original 67 point over different parameter of β and ξ factors 4.1 The OFDM system Parameter 79 4.2 The OFDM systems performance based on BPSK Modulation 81 4.3 The OFDM systems performance based on QPSK Modulation 83 4.4 The OFDM systems performance based on DBPSK Modulation 85 4.5 The OFDM systems performance based on DQPSK Modulation 87 4.6 The OFDM systems performance based on 16-QAM Modulation 90 4.7 The COFDM system Parameter 95 ... performance for channel estimation based Alnuaimy-Mahamod 112 interpolation using different techniques of pilot estimation with and without wavelet denoising 5.7 MSE performance for channel estimation. .. different interpolation 113 technique using LS technique for pilot estimation combined with wavelet denoising 5.8 MSE performance for channel estimation based different interpolation 114 technique using. .. Prestasi Ralat Ganda Dua Min (MSE) dari teknik interpolasi ini kemudian dibandingkan dengan lima jenis interpolasi yang lain dalam saluran pemudaran Rayleigh menggunakan penganggaran saluran jenis sikat