Luận án Kỹ thuật xử lý tín hiệu mạnh cho máy thu GNSS hiện đại - Nguyễn Đình Thuận

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: 1. Ta Hai Tung 2. 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. Tạ Hải Tùng Nguyễn Đình Thuận Prof. Letizia Lo Presti 1 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 2 TABLE OF CONTENTS STATEMENT OF ORIGINALITY AND AUTHENTICITY. 2 TABLE OF CONTENTS.

3 LIST OF ACRONYMS. 6 LIST OF TABLES. 8 LIST OF FIGURES. GNSS positioning principle.

History and development of GNSS. GNSS Segment errors. GNSS Receiver Architecture. Signal Conditioning and Sampling.

Tracking and Data Demodulation. Countermeasures to GNSS Threats. Antenna array processing techniques. Frontend and Digital Signal Conditioning based techniques.

Correlator/Tracking and PVT based techniques. GNSS Simulator and effect of sampling frequency. GNSS SIGNAL SIMULATOR DESIGN AND IMPLEMENTATION. Overview of the modeling of antenna array signals in GNSS receivers.

General model of the received signal in GNSS receivers. Effect of sampling frequency on the positioning performance. Residual code phase estimation. Correlation output calculation.

Effect of sampling frequency on correlation shape and DLL discriminator function 42 2. Effect of the sampling frequency and the integration period selection. Effect on the presence of Doppler and local oscillator (LO) clock drift. Theoretical code tracking loop error estimate.

Theoretical results evaluation by simulated, and numerical models. Effect of Doppler and coherent integration period. Sampling Frequency Effect Mitigation Technique. Verification of the simulated antenna array signals.

Antenna distortion simulation. Verification of multipath simulation. ANTENNA ARRAY PROCESSINGS FOR GNSS RECEIVERS. The proposed solution for synchronizing separated antenna array element.

Determining the samples difference. Determining the clock phase shift. Implementation a low-cost antenna array. Antenna array frontend verification.

Phase difference between frontends. Carrier to noise ration improvement. GNSS SNAPSHOT PROCESSING TECHNIQUE FOR GNSS RECEIVERS. Proposed Design of GNSS Snapshot Receiver.

80 Implementation of GNSS Grabber. GNSS signal acquisition. Combined Doppler and Snapshot Algorithm. Loosely coupled Snapshot GNSS/INS.

Tightly coupled Snapshot GNSS/INS. Standalone Snapshot GNSS Receiver. Snapshot GNSS/INS Integration. 104 CONCLUSIONS AND FUTURE WORKS.

Correlation output calculation. Error analysis for coherent early minus late DLL. 117 5 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 6 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 7 LIST OF TABLES Table 2.1: GNSS Simulator Features .2: The coordinate of 4 elements .3: The direction of 6 visible satellites.4: The carrier phase relative to the first element of each satellite at the four elements of the array.5: The simulation scenario.6: Estimated carrier phase using the post-correlator beamforming tracking loop.1: Configuration of the GPS grabber .2: Information of acquired satellites. 99 8 LIST OF FIGURES Figure 1.1: Satellite navigation principle .2: Typical GNSS Threats .3: Signal conditioning and sampling stage.6: Transmission time estimation in GNSS receivers.7: Interference mitigation techniques in GNSS receivers .8: The traditional low-cost architecture of antenna array for GNSS applications 27 Figure 1.9: The correlation between 2 GPS signal grabbed by antenna array .10: Spectrum and histogram of GNSS signal in the absence of interference .11: Snapshot positioning architecture .1: Geometry of antenna array.2: The model of the received signal for a single antenna .3: GPS multi-antenna frontend.4: Flowchart of the simulator .5: Bandlimited Gaussian interference model .7: Effect of sampling frequency on the positioning performance .8: Residual code phases versus the number of samples per code chip with 4fc < fs < 5fc .9: Normalised correlator and EML discriminator functions for different sampling frequencies.

Results are obtained by correlating the incoming signal with various local generated replica signals that have the time delay from−Tc to Tc with step = 10-2Tc.10: Correlation shapes for 1 ms integration with various sampling frequencies .11: Ambiguous synchronization between a local PRN code and two different incoming analog signals of the same PRN sequence, but with slightly differing code phase offset.12: Correlation shapes and their errors with respect to the ideal correlation at a sampling frequency fs =16.3676 MHz using various coherent integration periods .13: Representation of code tracking loop [54] .14: DLL jitter versus different sampling frequencies (step= fc) for a GPS L1 C/A with C/N0=40 dB-Hz, BL=0.5 Hz, T=1 ms, and fixed BW βr = 2fc.15: Upper bound and lower bound of the DLL jitter versus different sampling frequencies (step = 5∗10-2 fc) for a GPS L1 C/A with C/N0=45 dB-Hz, BL=0.5 Hz, T=1 ms, and βr = fs .16: Mean values of two error bounds σs1 and σs2 versus different sampling frequencies (step = 10-1 fc) for a GPS L1 C/A with C/N0=45 dB-Hz, BL=0.5 Hz, T=1 ms, and βr = fs .17: DLL tracking error comparison among the simulated, numerical and theoretical models (step = 10-1 fc) for a GPS L1 C/A with T=1 ms, and βr = fs.18: DLL tracking error versus Doppler frequencies fD for different integration periods T when the sampling frequency is an integer multiple of the nominal code rate (ns=4), in which the blue dotted lines indicate the typical Doppler range.19: DLL tracking error versus integration periods T. GPS L1 C/A is used with fs = 4.092 MHz (ns=4), C/N0=40 dB-Hz, BL=0.5 Hz, T=1 ms, and βr = fs .20: DLL tracking error versus Doppler frequencies fD for different integration periods T when the sampling frequency is a non-integer multiple of the nominal code rate.21: Code chip selection versus jitter values with M=4, where Triangle, circle, and diamond dots indicate samples belonging to (k−1)th, kth , and (k+1)th chips, respectively.22: Correlator shapes versus different jitter techniques for GPS L1 C/A signal, where τ runs in the range [−Tc,Tc] with step interval =10−3Tc, fs=4.092 MHz, fD = 0 Hz, βr = fs and θNCO(0) = 0.23: Pseudo-code algorithm that can be used to implement jittering solution on SDR receiver .24: The results after applying the mitigation technique .25: Antenna array configuration .26: Post-correlator beamforming receiver architecture [30] .27: Scatter diagram of the tracking output of the satellite PRN01 at 4 elements .28: Estimated position of elements (East-North) .29: Estimated position of elements (Up) .30: Element patterns utilized for simulation (East-North) .31: The C/N0 of the satellite PRN 1 .1: The architecture of antenna array based GNSS receiver .2: Time difference between 2 elements .4: The architecture of the system to determine the phase offset .5: The impact of clock phase shift .6: The loop filter using for estimating the clock drift .7: The estimated frequency shift using the loop filter.8: The scatter plot of the signal after mitigating clock phase shift .9: The 3-elements antenna array frontend modified from turner RTL2832Us .10: The setup of the verification of the frontend using a GPS simulator .11: Tracking output of satellites in view .12: 𝑪/𝑵𝟎 of the satellite PRN 09 for the received signal at every element and beamed signal .1: The architecture of the GNSS grabber .2: The flowchart of the grabber firmware .3: Acquisition search space.4: Probability of Detection w.5: FFT-based acquisition .6: Snapshot solution diagram .7: Traditional loosely-coupled GPS/INS integration .9: Tightly-coupled integration scheme .10: The prototype of GNSS grabber.11: Acquisition result of the grabbed signal .12: The position converged after 7 iterations .13: The positioning accuracy of the proposed solution .14: Power consumption comparison of our proposed solution and Ublox LEA 6T .15: The experiment setup .16: GNSS Snapshot/INS integration result .17: Positioning performance between GNSS Snapshot and GNSS Snapshot/INS Integration. 103 12 INTRODUCTION Nowadays, GNSS receivers have become core components in many applications ranging from vehicle navigation to unmanned vehicle guidance, from location-based services to environment monitoring. Besides providing position information for many applications, GNSS services also provide a highly precise timescale for synchronizing systems such as telecommunication and network.

Hence, the performance of GNSS which have considerable influence on the operation of these services must be guaranteed. In [1] a list of four parameters of GNSS performance is reported: accuracy, availability, continuity, and integrity. Recently, the accuracy of GNSS has been significantly improved with the development of new navigation systems (Galileo-European system and BEIDOU-Chinese system) and the modernization of the existing navigation systems GPS and GLONASS. However, GNSS services are seriously being threatened by the emergence of jamming and spoofing threats.

Because GNSS signals are buried under ambient noise, the signals and services of GNSS systems are highly sensitive to interference such as radio frequency interference, jamming and spoofing; meanwhile, the quality of such services is not guaranteed to the conventional users. Technically, the GNSS signal is transmitted from satellites away from Earth (about 20.000 km), so when it comes to receivers, the signal power is smaller than the background noise about 1024 times (26dB) [2]. Therefore, any source of interference (jammer, digital terrestrial communication systems, ionosphere scintillation) may reduce the quality of the received signal, which in turn can disable the operation of the receiver. In addition, because the GNSS systems are often under the management of military based organizations [3] [4] [5], the open services (e., GPS L1 C/A, Beidou B1, GLONASS L1OF) are provided to users without any guarantee of their reliability and continuity.

However, ensuring reliable and continuous position and time information is essential in modern GNSS receivers. To meet these requirements, receivers must make use of advanced techniques to detect and mitigate interferences so that they can provide the requested continuous position and time information. These techniques are called “interference mitigation techniques”. In recent studies [6] [7] reflecting the state of the art, interference mitigation techniques can be classified according to the position of the algorithm within the processing stages of GNSS receiver chain.

In short, they are classified into three groups namely antenna array processing techniques, frontend and digital signal conditioning-based techniques, and correlator/tracking and PVT based techniques Antenna array signal processing technique: A popular method for robust GNSS receiver performance consists in using multiple physical antenna elements which constitute a so- called antenna array.