BASHIR AHMED SIDDIQUI SIMULINK-BASED ACQUISITION UNIT FOR GALILEO E1 CBOC MODULATED SIGNALS MASTER OF SCIENCE THESIS Examiners: Docent Simona Lohan M.Sc. Danai Skournetou Examiners and topic approved in the Computing and Electrical Engineering Faculty Council meeting on 4th November, 2009 Abstract TAMPERE UNIVERSITY OF TECHNOLOGY Degree Program in Information Technology, Department of Communication Engineering Siddiqui, Bashir Ahmed: Simulink-Based Acquisition Unit for Galileo E1 CBOC Modulated Signals Master of Science Thesis, 78 Pages March 2010 Examiners: Dr. Docent Elena-Simona Lohan and M.Sc. Danai Skournetou Funding: Academy of Finland and EU FP7-funded project Galileo Ready Advanced Mass Market Receiver (GRAMMAR) Keywords: Galileo, Acquisition, Composite Binary Offset Carrier (CBOC), E1 band, Simulink At the moment, Global Positioning System (GPS) is the only positioning system with global coverage. Currently, there are efforts to modernize GPS with the aim of improving its performance. Meanwhile, Europe is developing its own satellite positioning system, GALILEO. In order to provide interoperability with GPS and globally available navigational systems, new modulation techniques have been introduced. Multiplexed Binary-Offset-Carrier (MBOC) modulated signals are the main candidates for the future Galileo Open Services (OS) and modernized GPS L1C signals. Spreading waveforms corresponding to pilot and data components can be formed in a number of ways, including Composite Binary Offset Carrier (CBOC) and Time- Multiplexed Binary Offset Carrier (TMBOC). CBOC is considered here because CBOC has been selected for Galileo E1 OS signals in the most recent Galileo SIS-ICD of 2008 [1]. This new composition of E1 signal allows different techniques for acquiring the signal, i.e. data-only channel, pilot-only channel and joint data and pilot channel. The ABSTRACT iii MBOC(6,1,1/11) power spectral density (PSD) has better performance than SinBOC(1,1) power spectral density because it is a mixture of BOC(1,1) spectrum and BOC(6,1) spectrum. MBOC modulation schemes also bring new challenges due to additional side lobes in the envelope of the Autocorrelation Function (ACF) compared with the traditional BPSK modulation used in the basic GPS signals, which make the signal acquisition process challenging. In order to deal with the side lobes, the steps ‘∆t ’ for searching the time-bin search space should be chosen carefully. bin The goal of this thesis has been to develop an acquisition unit based on CBOC reference code and analyze the performance of new acquisition unit in terms of acquisition performance because MBOC signal has better power spectral density compared to SinBOC(1,1) signal. A brief study about the choice of the time-bin step ‘∆t ’ for bin searching the time-frequency window has been studied. Three different strategies have been used to acquire the signal and results are presented for each approach. The switching architecture model has introduced in the transmitter part which operates at dual frequency are also addressed under the scope of this thesis. The simulations are carried out with an own developed Simulink model for Galileo OS E1 signals, based on the most recent Galileo Signal-in-Space Interface Control Documentation. Conclusions are drawn with respect to the performance deterioration of a reference SinBOC(1,1) receiver compared to a reference CBOC receiver, and also with respect to different techniques used for acquiring the signal. Comparisons between the infinite bandwidth (theoretical case, typically used in literature) and a limited front-end filter bandwidth of 3 MHz (double-sided bandwidth) are also made. The choice of significant detection threshold in order to detect the signal properly and the performance degradation of the CBOC reference receiver when using switching architecture model in terms of detection probability are also presented. Preface The research work reported in this thesis has been carried out during the years 2009- 2010 at the Department of Communications Engineering, Tampere University of Technology, Finland. The work has been supported by the Academy of Finland-funded project “Digital Processing Algorithms for Indoor Positioning Systems” and the EU FP7-funded project under grant agreement number 227890 “Galileo Ready Advanced Mass Market Receiver (GRAMMAR)”. I would like to extend my profound gratitude to my supervisors Prof. Markku Renfors and Dr. Simona Lohan for their enthusiastic encouragement, valuable guidance, constant support and patience during the whole working period, and providing me the opportunity to work on a stimulating research topic. I am sincerely grateful to M.Sc. Danai Skournetou for her fruitful technical discussion, helpful comments and infinite tolerance with the incomplete draft of this thesis. I am also thankful to M.Sc. Muhammad Zahid and Zhang Jie for their friendly and generous support during the research work. I am profoundly grateful to all of my friends from Tampere for creating such a cheerful and unforgettable time together. Last but not least, I wish to express my deep gratitude and warmest thanks to my parents, brother and sisters for their unconditional support, endless love and encouragement during my studies. Tampere, March 2010. Bashir Ahmed Siddiqui Table of Contents Abstract ii Preface iv Table of Contents v List of Acronyms viii List of Symbols x 1. Introduction 1 1.1 Motivation and Background ............................................................................ 1 1.2 Thesis Objectives ............................................................................................ 4 1.3 Thesis Contributions ....................................................................................... 4 1.4 Thesis Outline ................................................................................................. 4 2. Emerging Galileo System and CBOC Modulation 6 2.1 Introduction to Galileo System ........................................................................ 6 2.1.1. Galileo System Overview .......................................................................... 7 2.1.2. Galileo Signal Characteristics .................................................................... 8 2.2 BOC Modulation ........................................................................................... 11 2.3 MBOC Modulation ....................................................................................... 14 2.3.1. TMBOC Implementation ......................................................................... 16 2.3.2. CBOC Definition and Implementation ..................................................... 16 2.4 Why CBOC ................................................................................................... 19 2.5 E1 Signal Description .................................................................................... 20 2.5.1. Logic Level ............................................................................................. 22 2.5.2. Received Power Levels on Ground .......................................................... 23 3. Delay-Doppler Acquisition of Galileo Signals 24 3.1 Signal Acquisition ......................................................................................... 24 3.1.1. Correlation .............................................................................................. 25 SIMULINK-BASED ACQUISITION UNIT FOR GALILEO E1 CBOC MODULATED SIGNALS vi 3.1.2. Search Space ........................................................................................... 26 3.1.3. Search Strategy ........................................................................................ 28 3.1.3.1 Serial Search ........................................................................................ 28 3.1.3.2 Fully Parallel Search ............................................................................ 28 3.1.3.3 Hybrid Search ...................................................................................... 29 3.1.4. Detection Threshold ................................................................................ 29 3.2 Detection and False Alarm Probabilities ........................................................ 30 3.3 Standard Methods of Acquisition .................................................................. 30 3.3.1. Ambiguous Acquisition ........................................................................... 31 3.3.2. Unambiguous Acquisition ....................................................................... 31 4. Simulink Model for Galileo Signal Acquisition 33 4.1 Description of the Simulink Model ................................................................ 34 4.1.1. Transmitter Block .................................................................................... 34 4.1.2. Channel ................................................................................................... 36 4.1.3. Acquisition Block .................................................................................... 37 4.1.4. Tracking Block ........................................................................................ 39 4.2 Modified Acquisition Block .......................................................................... 39 4.2.1. CBOC Based Acquisition Unit ................................................................ 39 4.2.2. Variable time-bin Step ............................................................................. 40 4.2.3. Choice of the time-bin Size ...................................................................... 41 4.2.4. Switching Architecture Studies ................................................................ 42 5. Simulink-Based Simulation Results 45 5.1 Performance Measures in Simulation ............................................................ 45 5.2 Detection Probability with Certain Threshold ................................................ 46 5.3 Comparison Between SinBOC(1,1) and CBOC Reference Receiver .............. 48 5.4 Data-Pilot Combinations for BOC Reference Receiver .................................. 51 5.4.1. Data-Pilot Combinations for CBOC Reference Receiver .......................... 53 5.4.2. Comparison between BOC and CBOC Reference Receiver ..................... 55 5.4.3. Choice of the Weighting Factor ............................................................... 57 5.5 Detection Probability Versus time-bin Step ................................................... 57 5.6 Acquisition with Limited Bandwidth ............................................................. 58 5.7 Impact of the Threshold ................................................................................ 59 5.8 Switching Architecture Simulation Results .................................................... 60 TABLE OF CONTENTS vii 6. Matlab-Based Simulation Results 62 6.1 Difference between Matlab and Simulink Model ........................................... 62 6.2 Simulation Parameters ................................................................................... 64 6.3 Comparison of SinBOC(1,1) and CBOC Reception ....................................... 64 6.4 Comparison of Data-only, Pilot-only and Joint Data-pilot Processing with BOC Reference Receiver ............................................................................................... 65 6.5 Comparison of Data-only, Pilot-only and Joint Data-pilot Processing with CBOC Reference Receiver ................................................................................... 67 6.6 Impact of Acquisition Threshold ................................................................... 68 6.7 Impact of Maximum Delay Error .................................................................. 69 6.8 Normalized ACFs of Reference BOC and CBOC Receiver ........................... 69 7. Conclusion and Futher Research Issues 71 7.1 Conclusions .................................................................................................. 71 7.2 Future Work .................................................................................................. 73 References 74 List of Acronyms ACF Autocorrelation Function AltBOC Alternative BOC ARNS Aeronautical Radio Navigation Services AWGN Additive White Gaussian Noise B&F Betz & Fishman BOC Binary Offset Carrier BPSK Binary Phase Shift Keying C/A Coarse/Acquisition CBOC Composite BOC CDMA Code Division Multiple Access CFAR Constant False Alarm Rate CNR Carrier-to-Noise Ratio CS Commercial Services DoD Department of Defense ESA European Space Agency FFT Fast Fourier Transform GLONASS GLobal Orbital NAvigation Satellite System GNSS Global Navigation Satellite System GPS Global Positioning System I & D Integrate and Dump LIST OF SYMBOLS ix LOS Line-Of-Sight MBOC Multiplexed BOC MEE Mean Error Envelope OS Open Services PDF Probability Density Function PRN Pseudo Random Number PRS Public-Regulated-Services PSD Power Spectral Density RHCP Right-Hand Circular Polarization RNSS Radio Navigation Satellite Services RMSE Root Mean Squared Error SAR Search-And-Rescue-services SB Side Band SinBOC Sine BOC SIS-ICD Signal In Space Interface Control Document SoL Safety-of-Life-services STF Galileo Signal Task Force SV Satellite Vehicle TMBOC Time Multiplexed BOC UAL Unsuppressed Adjacent Lobes SIMULINK-BASED ACQUISITION UNIT FOR GALILEO E1 CBOC MODULATED SIGNALS x List of Symbols ∆ Mean Absolute Error ∆f Frequency Bin Length bin ∆t Time Bin Length bin (cid:1) τ Estimated LOS Delay Error LOS τ True LOS Delay Error LOS τ Channel Delay Introduced by i-th Path i τ Channel Delay σ2 Variance γ Detection Threshold δ(t) Dirac Pulse N BOC Modulation Order for SinBOC(1,1) BOC1 N BOC Modulation Order for SinBOC(6,1) BOC2 Nc Coherent Integration Length in Code Epochs (or ms) Nnc Non-Coherent Integration Length in Blocks Ns Oversampling Factor P Detection Probability d P False Alarm Probability fa S Spreading Factor F T Chip Period; 1/ fc c T Symbol Period sym