Nghiên cứu giải pháp nâng cao khả năng chống nhiễu cho các bộ thu định vị GNSS tiên tiến

s MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY NGUYEN DINH THUAN ROBUST SIGNAL PROCESSING TECHNIQUES FOR MODERN GNSS RECEIVERS Major: Computer Engineering Code No.: 9480106 COMPUTER ENGINEERING DISSERTATION SUPERVISORS: Assoc Prof Ta Hai Tung Prof Letizia Lo Presti Hanoi - 2019 STATEMENT OF ORIGINALITY AND AUTHENTICITY I confirm that my dissertation is an original and authentic piece of work written by myself The data, results in the thesis is reliable and has never been published by others I further confirm that I have fully referenced and acknowledged all material incorporated as secondary resources in accordance with the regulations Hanoi, SUPERVISORS PHD STUDENT PGS.TS Tạ Hải Tùng Nguyễn Đình Thuận Prof Letizia Lo Presti ACKNOWLEDGEMENTS I would like to express my gratitude to Hanoi University of Technology, Graduate School, School of Information and Communication Technology, Department of Computer Engineering and Politecnico di Torino, NavSaS group for creating favorable conditions for me to work and study I would like to express my special thanks to my supervisors, Assoc Ta Hai Tung and Prof Letizia Lo Presti The supervisors have always been helpful, giving great advice, scientific orientations so that I can develop and complete my research Sincerely thank the lecturers, colleagues in the Department of Computer Engineering, School of Information and Communication Technology, Hanoi University of Science and Technology where I work, study and carry out research projects for the enthusiastic in helping and encouraging me during the research With gratitude to teachers, scientists, colleagues and close friends for encouraging and supporting me in the research process Finally, I would like to express my deep gratitude to my family for encouraging me to overcome all obstacles to complete this thesis Nguyen Dinh Thuan TABLE OF CONTENTS STATEMENT OF ORIGINALITY AND AUTHENTICITY ACKNOWLEDGEMENTS TABLE OF CONTENTS LIST OF ACRONYMS LIST OF TABLES LIST OF NOTATIONS IN THIS THESIS ……………………………………….…9 LIST OF FIGURES 10 INTRODUCTION 13 FUNDAMENTAL BACKGROUND 18 1.1 GNSS positioning principle 18 1.2 History and development of GNSS 19 1.3 GNSS Threats 20 1.3.1 Multipath 21 1.3.2 Atmosphere 21 1.3.3 Interference 21 1.3.4 Spoofing 21 1.3.5 GNSS Segment errors 21 1.3.6 Cyber Attacks 22 1.4 1.4.1 Signal Conditioning and Sampling 22 1.4.2 Acquisition 23 1.4.3 Tracking and Data Demodulation 23 1.4.4 Positioning Computation 24 1.5 Countermeasures to GNSS Threats 25 1.5.1 Antenna array processing techniques 25 1.5.2 Frontend and Digital Signal Conditioning based techniques 28 1.5.3 Correlator/Tracking and PVT based techniques 29 1.6 GNSS Receiver Architecture 22 GNSS Simulator and effect of sampling frequency 30 ANTENNA ARRAY PROCESSINGS FOR GNSS RECEIVERS 33 2.1 2.1.1 Determining the samples difference 34 2.1.2 Determining the clock phase shift 35 2.2 Implementation a low-cost antenna array 39 2.3 Antenna array frontend verification 40 2.3.1 Phase difference between frontends 40 2.3.2 Carrier to noise ration improvement 41 2.4 The proposed solution for synchronizing separated antenna array element 33 Conclusion 42 GNSS SNAPSHOT PROCESSING TECHNIQUE FOR GNSS RECEIVERS 44 3.1 Proposed Design of GNSS Snapshot Receiver 44 3.1.1 GNSS Grabber 44 Implementation of GNSS Grabber 44 Firmware Architecture 45 3.2 3.2.1 GNSS signal acquisition 45 3.2.2 Combined Doppler and Snapshot Algorithm 48 3.3 Loosely coupled Snapshot GNSS/INS 53 3.4 Tightly coupled Snapshot GNSS/INS 60 3.5 Results 61 3.5.1 Standalone Snapshot GNSS Receiver 61 3.5.2 Snapshot GNSS/INS Integration 66 3.6 Server Software 45 Conclusion 68 GNSS SIGNAL SIMULATOR DESIGN AND IMPLEMENTATION 69 4.1 Modeling methodology 69 4.2 Overview of the modeling of antenna array signals in GNSS receivers 69 4.2.1 General model of the received signal in GNSS receivers 70 4.2.2 Interference 74 4.2.3 Multipath 75 4.2.4 Noise 76 4.3 Effect of sampling frequency and mitigation technique 76 4.3.1 Effect of sampling frequency on positioning performance 76 4.3.2 Implementation of sampling mitigation technique for GNSS Simulator 79 4.4 Performance verification 81 4.4.1 Verification of the simulated antenna array signals 81 4.4.2 Antenna distortion simulation 87 4.4.3 Verification of multipath simulation 89 4.5 Conclusion 90 CONCLUSIONS AND FUTURE WORKS 92 PUBLICATIONS 94 REFERENCES 96 LIST OF ACRONYMS Acronym Meaning ADC Analog to Digital Converter AGC Automatic Gain Control AWGN Additive White Gaussian Noise BB BaseBand BOC Binary Offset Carrier BPSK Binary Phase Shift Keying C/A Coarse/Acquisition C/N0 Carrier-to-Noise-Density Ratio CDC Conventional Differential Combination CDMA Code Division Multiple Access CRC Cyclic Redundancy Check CS Commercial Service DLL Delay Lock Loop DFT Discrete Fourier Transform DSP Digital Signal Processor EGNOS European Geostationary Navigation Overlay Service EU European Union FEC Forward Error Correction FFT Fast Fourier Transform FPGA Field Programmable Gate Array FOC Full Operational Capability GLONASS Global Orbiting Navigation Satellite System I Inphase IF Intermediate Frequency Q Quadrature PVT Position Velocity Time SDR Software Defined Radio LIST OF TABLES Table 3.1: Configuration of the GPS grabber 61 Table 3.2: Information of acquired satellites 63 Table 4.1: GNSS Simulator Features 81 Table 4.2: The coordinate of elements 82 Table 4.3: The direction of visible satellites 82 Table 4.4: The carrier phase relative to the first element of each satellite at the four elements of the array 83 Table 4.5: The simulation scenario 83 Table 4.6: Estimated carrier phase using the post-correlator beamforming tracking loop 86 LIST OF NOTATIONS IN THIS THESIS Notation Description 𝜏 Code phase 𝜌 Pseudo range Φ Carrier Phase 𝐶(𝑡) Spreading Code exp(𝑗2𝜋𝑓𝑡) Complex expression of in-phase and quadrature carrier component 𝐹𝑠 Sampling Frequency 𝐹𝐼𝐹 Intermediate Frequency 𝐷(𝜏) Discrimination Function 𝑐 Speed of light 𝐼(𝑡) In-phase tracking output 𝑄(𝑡) Quadrature tracking output E, L, P Early, Late, and Prompt branch of tracking stage 𝒘 Weight vector 𝑅 Cross correlation 𝜑 Latitude 𝜆 Longitude ℎ Height 𝑣 Velocity 𝑅𝑀 The radius of curvature 𝑅𝑁 The prime vertical radius expressed as attenuation For example, the situation of Figure 4.19 shows that the elements 1, 2, and are distorted with dB, -4 dB, -6 dB, and -8 dB, respectively in the region: 𝑅={ 30⁡deg ≤ 𝐴𝑧 ≤ 60⁡deg 45⁡deg ≤ 𝐸𝑙 ≤ 75⁡deg During the simulation experiment, the signal from the satellite PRN will impinge the antenna in the perturbed region two minutes after starting Element without distortion Element with -4dB in the distorted region (red) Element with -6dB in the distorted region (red) Element with -8dB in the distorted region (red) Figure 4.19: Element patterns utilized for simulation (East-North) By observing the signal to noise ratio (SNR) of the PRN in Figure 4.20, we can see that SNR decreases according to the degradation given in Figure 4.20 Figure 4.20: The C/N0 of the satellite PRN 88 4.4.3 Verification of multipath simulation In this section, the simulator is demonstrated the capability of simulating multipath signal with a complicated scenario The scenario is described as following steps Firstly, a multipath-free signal is generated The simulator configuration is the same as the setup described in section 3.1 However, for this verification, simulating the signal for a single array element is sufficient to evaluate the multipath effect on ranging errors Secondly, the second signal is generated with the presence of the multipath signals of the satellite PRN11 The multipath signals simulated can be expressed as follows: 𝑠𝑀𝑃 (𝑡) = 𝑠1 (𝑡) + 𝑠2 (𝑡) + ⋯ + 𝑠30 (𝑡) (4.21) where the multipath component 𝑠𝑚 (𝑡) is present during a certain time interval of 1.5 seconds 𝐴𝑠 𝐶(𝑡 − 𝜏𝑘 − 𝜏𝑀𝑃,𝑘 )𝐷(𝑡 − 𝜏𝑘 − 𝜏𝑀𝑃,𝑘 ) ×⁡ 𝑠𝑘 (𝑡) = exp (𝑗(2𝜋(𝑓𝐿1 + 𝑓𝑑 + 𝑓𝑀𝑃,𝑑 )𝑡 + 𝛷𝑘 + Φ𝑀𝑃,𝑘 )) { (4.22) when⁡1.5𝑘 ≤ 𝑡 ≤ 1.5(𝑘 + 1)⁡(seconds) 0⁡⁡⁡otherwise The terms in equation (21) are defined as in section 2.4 In [2], the authors confirmed that the ranging error caused by multipath is negligible when the multipath delay is above 1.5 chip-length Therefore, the multipath delays are set to vary from to 1.5 chip-length, the code delay is set as follows: 𝜏𝑀𝑃,𝑘 = 𝑘 ∗ 0.05⁡(chip − lengths), 𝑘 = ̅̅̅̅̅̅̅ .30 (4.23) The Doppler shift and carrier phase due to multipath is set to: Φ𝑀𝑃,𝑘 = 𝑘𝜋, 𝑓𝑀𝑃,𝑑 = 0, 𝑘 = ̅̅̅̅̅̅̅ .30 𝑘 = ̅̅̅̅̅̅̅ .30 (4.24) (4.25) Afterward, the generated signals are processed using the AKOS software receiver with onechip in the correlator spacing The comparison of the multipath-free pseudorange and multipath-affected pseudorange of the simulation conducted is shown in Figure 4.21 89 Figure 4.21: Multipath error Clearly, the multipath errors (black) are similar to the theoretical multipath error envelope (red) The result validates the capacity of simulating multipath with a complicated scenario of the simulator It is worth to note that the computation complexity for generating a satellite is O(n) but n is huge (16368000 for 16.368MHz in sampling frequency for example) 4.5 Conclusion This This chapter presented a modeling methodology for simulating reliable GNSS signals taking into account the effect of the sampling frequency Thanks to SDR technology, the architecture is very flexible to adopt other systems without any change In particular, the input of the synthesizer block in this design include data stream, spreading code, carrier frequency and Doppler shift that are also parameter used to distinguish between systems Moreover, the effect of sampling frequency on the performance of both simulator and receiver was first considered in this work The obtained results show that the value of the sampling frequency is one parameter that needs to be considered during the simulation Besides generating IF digitalized signal, the simulator also shows that it is capable of generating RF data to feed commercial receivers with high reliability These verification experiments were conducted with a commercial receiver to confirm the capability of the simulator to correctly produce signals for validating various algorithms including interference mitigation and array signal processing 90 The predominant limitation of the present simulator is its low speed in generating the signals In the future, this aspect will be improved by using advanced programming techniques Besides, the simulator is in progress to be able to include other constellations The results of this study have been published in journals (10,11) and conferences (1,4) 91 CONCLUSIONS AND FUTURE WORKS The content of this thesis aims to investigate the potentials and challenges of robust techniques in modern GNSS receivers under emerging threats Through the investigation of properties of modern GNSS receivers, some improvement its performance is presented In this thesis, the works devoted to improving modern GNSS receivers are the main contributions, which can be summarized as follows: Design and implementation of a software-based GNSS simulator (Chapter 2): A complete theory and implementation of a GNSS simulator which is capable of simulating antenna array signals The block diagrams, theoretical and practical analyses of all stages in the simulator are provided especially the sampling frequency The performance evaluation results prove that the generated signals are reliable like live sky signals Testing with multiple frontends will be the future work of this section Antenna array processing for GNSS Receivers (Chapter 3): The proposed technique allows us to deploy a low-cost antenna array and overcome existing limitations This technique that allows extending the antenna elements theoretically to infinite is proposed for the first time in this thesis The technique is proved suitable for low-cost antenna array frontends GNSS Snapshot Processing Technique (Chapter 4): The multi-GNSS snapshot receiver along with INS integration is proposed Such receiver is proved to be suitable for working with discontinuous GNSS signal due to interference Besides the achievement, we also presented the limitations of our solutions, which need further efforts to be solved In array processing techniques, the proposed synchronization technique is very time-consuming Therefore, it is not suitable for real-time deployment In snapshot positioning technique, the navigation message of the snapshot receiver is still based on the public navigation message from server In simplistic spoofing attack, the receiver can detect the inconsistent position between the previous epochs and current epoch However, in sophisticated spoofing attack, the information is insufficient to verify the current position of the receiver The above analysis motivates our future works to address those problems, namely: Adaptive antenna array processing with the low-cost antenna array: The proposed technique needs a performance improvement in terms of processing time Moreover, the achievement in the thesis is a preliminary result It needs more efforts to implement and benchmark its performance in various environments GNSS Snapshot Processing Technique: A further investigation in sophisticated spoofing attack is needed Based on that result, we will propose an effective method to mitigate such kind of spoofing In conclusion, in this dissertation we have proposed our solutions for addressing the existing limitations in antenna array and in snapshot positioning techniques However, there are some 92 existing limitations in our works which require more efforts to be solved Achievements and challenges motive us to continue our work in this research area 93 PUBLICATIONS [1] Thuan Nguyen Dinh, Ta Hai Tung, and Lo Presti Letizia (2015) "A software based multi-IF output simulator." Proceedings of the International Symposium of GNSS (ISGNSS), Kyoto, Japan 2015 (Scholarship Awarded Paper) [2] Hai Tung Ta, Thuan Nguyen Dinh, Gianluca Falco, Nicola Linty, Calogero Cristodaro, Rodrigo Romero, and Fabio Dovis "Performance Assessment of the New L2C CNAV GPS Signal." Proceedings of the International Symposium of GNSS (IS-GNSS), Kyoto, Japan 2015 [3] Nguyen, Thuan D., Vinh T Tuan, Tung H Ta, and Letizia Lo Presti (2016) "An ultralow-cost antenna array frontend for GNSS application." International Global Navigation Satellite Systems (IGNSS) [4] Vinh T Tran, Nagaraj C Shivaramaiah, Thuan D Nguyen, Andrew G Dempster (2016) “The effect of sampling frequency and front-end bandwidth on the DLL code tracking performance” Proceedings of International Global Navigation Satellite Systems Society Symposium IGNSS [5] Thuan Nguyen Dinh, Vinh Duong Hoang, Trung Ngo Lam: “Performace Evaluation of GPS Snapshot Positioning under Ionospheric Scintillation Effect” PROCEEDINGS OF AUN/SEED-NET REGIONAL CONFERENCE ON COMPUTER AND INFORMATION ENGINEERING 2016, Yangon, Myanmar, October 3-4, 2016 [6] Thuan Dinh Nguyen, Vinh La The (2017, October) “A novel design of low power consumption GPS positioning solution based on snapshot technique” In Advanced Technologies for Communications (ATC), 2017 International Conference on (pp 285290) IEEE [7] Tran, Vinh Tuan, Andrew Graham Dempster, Thuan Dinh Nguyen, and Nagaraj Channarayapatna Shivaramaiah "A Dynamically Configurable Decimator for a GNSS Baseband Receiver." IEEE Transactions on Aerospace and Electronic Systems 53, no (2017): 296-309 (SCI) [8] Nguyen Hong Lam, Nguyen Dinh Thuan, La The Vinh (2016) “Performance evaluation of the tightly coupled GPS/INS integration with different constraints”, Journal of Science and Technology, Section on Information and Communication Technology [9] Thuan Nguyen Dinh, Tung Hai Ta, Vinh La The, Lan Nguyen Thi Hoang (2017) “A Novel Method for the Use of Carrier Smoothing in the Loosely Coupled GPS/INS Integration” Journal of Science & Technology 120 (2017) 140-146 [10] Vinh Tran Tuan, Shivaramaiah NC, Thuan Nguyen Dinh, Glennon EP, Dempster AG “GNSS receiver implementations to mitigate the effects of commensurate sampling frequencies on DLL code tracking” GPS Solutions 2018 Jan 1;22(1):24 (SCIE) [11] Tran, Vinh T., Nagaraj C Shivaramaiah, Thuan D Nguyen, Joon W Cheong, Eamonn P Glennon, and Andrew G Dempster "Generalised Theory on the Effects of Sampling 94 Frequency on GNSS Code Tracking." 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Basically, GNSS positioning is based... software for post-processing to estimate PVT of the GNSS grabber 3.1.1 GNSS Grabber Implementation of GNSS Grabber The architecture of our GNSS grabber is shown in Figure 3.1 In particular, MAX2769