A Real-Time Capable Software-Defined Receiver Using GPU for Adaptive Anti-Jam GPS Sensors

Due to their weak received signal power, Global Positioning System (GPS) signals are vulnerable to radio frequency interference. Adaptive beam and null steering of the gain pattern of a GPS antenna array can significantly increase the resistance of GPS sensors to signal interference and jamming. Since adaptive array processing requires intensive computational power, beamsteering GPS receivers were usually implemented using hardware such as field-programmable gate arrays (FPGAs). However, a software implementation using general-purpose processors is much more desirable because of its flexibility and cost effectiveness. This paper presents a GPS software-defined radio (SDR) with adaptive beamsteering capability for anti-jam applications. The GPS SDR design is based on an optimized desktop parallel processing architecture using a quad-core Central Processing Unit (CPU) coupled with a new generation Graphics Processing Unit (GPU) having massively parallel processors. This GPS SDR demonstrates sufficient computational capability to support a four-element antenna array and future GPS L5 signal processing in real time. After providing the details of our design and optimization schemes for future GPU-based GPS SDR developments, the jamming resistance of our GPS SDR under synthetic wideband jamming is presented. Since the GPS SDR uses commercial-off-the-shelf hardware and processors, it can be easily adopted in civil GPS applications requiring anti-jam capabilities

Assessment of Measurement Distortions in GNSS Antenna Array Space-Time Processing

Antenna array processing techniques are studied in GNSS as effective tools to mitigate interference in spatial and spatiotemporal domains. However, without specific considerations, the array processing results in biases and distortions in the cross-ambiguity function (CAF) of the ranging codes. In space-time processing (STP) the CAF misshaping can happen due to the combined effect of space-time processing and the unintentional signal attenuation by filtering. This paper focuses on characterizing these degradations for different controlled signal scenarios and for live data from an antenna array. The antenna array simulation method introduced in this paper enables one to perform accurate analyses in the field of STP. The effects of relative placement of the interference source with respect to the desired signal direction are shown using overall measurement errors and profile of the signal strength. Analyses of contributions from each source of distortion are conducted individually and collectively. Effects of distortions on GNSS pseudorange errors and position errors are compared for blind, semi-distortionless, and distortionless beamforming methods. The results from characterization can be useful for designing low distortion filters that are especially important for high accuracy GNSS applications in challenging environments

Multiple Antenna-based GPS Multipath Mitigation using Code Carrier Information

학위논문 (박사)-- 서울대학교 대학원 : 전기공학부, 2013. 8. 최진영.여러 응용분야에서 수 억대의 GPS(Global Positioning System) 수신기가 사용되고 있지만, GPS을 기반으로 하는 위치기반 서비스(LBS: Location Based Services)에서는 여전히 다중경로 오차와 같은 전파 방해가 발생하고 있으며, 이러한 오차들로 인하여 상관함수의 왜곡은 거리 오차가 발생에 영향을 미치고 있다. 이러한 이유로 인하여 GPS을 이용한 항법 시스템에서의 위치 정확도 향상을 위하여, 다중경로 오차를 효과 적으로 줄이기 위한 강인하고 현실적인 방법이 요구된다. 다중경로는 GPS 신호가 장애물에 의해 반사나 회절 되어 수신기에 도착할 때 잘 일어난다. 가시경로 신호에 결합된 다중경로 신호는 GPS 수신기의 상관함수의 변형을 일으키며 궁극적으로 차별함수에 영향을 미치므로 거리오차를 발생시킨다. 그러므로 다중경로 오차는 위성항법 시스템에서의 위치정확도 향상을 위해 해결 되어야 될 문제로 쟁점이 되어왔다. 최근에는 이러한 전파 간섭신호를 줄이기 위하여 다중개의 안테나(Multiple Antenna)를 이용하는 방법이 GPS 항법 시스템에서 이용되고 있다. 현 시점에서, 다중개의 안테나를 사용하는 응용분야는 주로 학술적인 연구 및 복잡한 군사용 연구로 주로 진행 되었다. 그러나 안테나 제작 방법 및 전기적 시스템의 급격한 발전으로 인해 이전의 하드웨어 및 소프웨어적인 문제를 쉽게 해결 됨에 따라 가까운 미래에는 다중 안테나 기반의 수신기가 민간 상용분야로 확대 될 것으로 예상이 된다. 또한 안테나 수신기 RF단의 소형화로 인하여 다중 안테나 시스템에서의 안테나 크기 문제점 또한 해결 가능하다. 그러므로 본 논문에서는 다중 GPS 안테나를 이용하여 GPS 항법에서의 전파 간섭 및 다중경로 오차 감쇄에 대한 연구를 목적으로 한다. 본 연구는 강한 전파 간섭 및 다중경로 신호에 대하여 공간 처리 기법을 적용한다. 제안된 새로운 방법은 다중 안테나를 기반의 코드 케리어 정보를 이용한 공간처리 기법으로 전파 간섭 및 다중경로 오차를 완화시키며, 또한 빔형성 기법을 이용하여 신호 대 잡음 비율을 최대로 한다. 제안된 성능을 검증하기 위하여 소프트웨어 GPS 수신기를 사용된다. 소프트웨어 GPS 수신기를 이용한 신호처리 기법은 새로운 장비의 제품화 및 GPS 신호 분석에 장점을 가지고 있다. 또한 GPS 알고리즘 분석 및 수신기 성능 향상 검증 등 여러 연구분야에서 널리 이용되고 있다. 본 논문에서는 제안된 방법의 성능 검증을 위하여 컴퓨터 시뮬레이션 및 가공 IF 데이터를 이용한 소프트웨어 수신기 결과를 제시한다. 그 결과 제안된 방법은 전파 간섭 및 다중경로 오차 감쇄에 강인하며, GPS 항법시스템에서의 위치정확도 향상에 가능성을 보여준다. 그로므로 제안된 방법은 차량 항법 응용분야에서 방해신호 감쇄에 사용될 것으로 예상된다.Although hundreds of millions of receivers are used all around the world, the performance of location-based services(LBS) provided by GPS is still compromised by interference which includes unintentional distortion of correlation function due to multipath propagation. For this reason, the requirement for proper mitigation techniques becomes crucial in GPS receivers for robust, accurate, and reliable positioning. Multipath propagation can easily occur when environmental features cause combinations of reflected and diffracted replica signals to arrive at the receiving antenna. These signals which are combined with the original line-of-sight (LOS) signal can cause distortion of the receiver correlation function and ultimately distortion of the discrimination functionhence, errors in range estimation occur. Therefore, multipath error in the satellite navigation system to improve location accuracy is an important issue to be addressed. Recently, interference mitigation techniques utilizing multiple antennas have gained significant attention in GPS navigation systems. Although at the time of this dissertation, employing multiple antennas in GPS applications is mostly limited to academic research and possibly complicated military applications, it is expected that in the near future, antenna array-based receivers will also become widespread in civilian commercial markets. Rapid advances in antenna design technology and electronic systems make previously challenging problems in hardware and software easier to solve. Furthermore, due to the significant effort devoted to miniaturization of RF front-ends and antennas, the size of antenna array based receivers will no longer be a problem. Given the above, this dissertation investigates multiple antenna-based GPS the interference suppression and multipath mitigation. Firstly, a modified spatial processing technique is proposed that is capable of mitigating both high power interference and coherent and correlated GPS multipath signals. The use of spatial-temporal processing for GPS multipath mitigation is studied. A new method utilizing code carrier information based on multiple antennas is proposed to deal with highly correlated multipath components and to increase the signal to noise ratio of the beamformer by synthesizing antenna array processing. In order to verify the proposed method, a software defined GPS receiver is used. Software-based GPS signal processing technique has already produced benefits for prototyping new equipment and analyzing GPS signal quality. Not only do such receivers provide an excellent research tool for GPS algorithm verification, they also improve GPS receiver performance in a wide range of conditions. In this dissertation, the enhancement of the proposed method is presented in terms of the simulations and software defined GPS receiver using simulated IF data. From the result, the proposed method is robust to interference suppression, and multipath mitigation, and shows a strong possibility for use in improving location accuracy. Thus, this method can be employed to mitigate interference signals in vehicular navigation applications.Contents Abstract i Acknowledgements iv Contents v List of Figures x List of Tables xiv Chapter 1.Introduction 1 1.1 Introduction 1 1.2 Background and Motivation 2 1.2.1 Strong Narrowband and Wideband Interference 6 1.2.2 Multipath 7 1.3 Antenna Array Processing in GPS 11 1.3.1 Interference Suppression 11 1.3.2 Multipath Mitigation 13 1.4 Software-Defined GPS Receiver 15 1.5 Objective and Contribution 17 1.6 Dissertation Outline 18 Chapter 2. Global Positioning System 21 2.1 GPS System Overview 21 2.2 Basic Concept of GSP 25 2.3 Determining Satellite to User 28 2.4 Calculation of User Position 33 2.5 GPS Error Sources 40 2.5.1 Receiver Clock Bias 41 2.5.2 Satellite Clock Bias 42 2.5.3 Atmospheric Delay 43 2.5.4 Ephemeris Delay 46 2.5.5 Multipath Error 47 2.5.6 Receiver Noise 55 2.6 Summary 55 Chapter 3. Antenna Array Processing and Beamforming 56 3.1 Background on Antenna Arrays and Beamformers 56 3.1.1 Signal Model 59 3.2 Conventional Optimum Beamformers 69 3.2.1 Minimum Variance Distortionless Response Beamformer 69 3.2.2 Maximum Likelihood Estimator 71 3.2.3 Maximum Signal to Noise Interference Ratio Beamformer 72 3.2.4 Minimum Power Distortionless Response Beamformer 75 3.2.5 Linear Constrained Minimum Variance and Linear Constrained Minimum Power Beamformers 76 3.2.6 Eigenvector Beamformer 77 3.3 Space-Time Processing 81 3.4 Array Calibration 85 3.5 Summary 86 Chapter 4. Multipath Mitigation using Code-Carrier Information 87 4.1 Introduction 87 4.2 Interference Suppression and Multipath Mitigation 88 4.2.1 Signal Model 88 4.2.2 Interference Suppression by Subspace Projection 90 4.2.3 Multipath Mitigation by Subspace Projection 93 4.3 Determination of Multipath Satellites using Code-carrier Information 95 4.4 MSR Beamformer 100 4.5 Simulation Results 102 4.5.1 Subspace Projection and Beamforming 102 4.5.2 Performance Comparison 109 4.6 Summary 111 Chapter 5. Performance Verification using Software-Defined GPS Receiver 113 5.1 Introduction 113 5.2 Software-Defined GPS Receiver Methodology 114 5.2.1 Software-Defined GPS Receiver Signals 115 5.2.2 Software-Defined GPS Receiver Modules 116 5.3 Architecture of Software-Defined GPS Receiver 120 5.3.1 GPS Signal Generation 120 5.3.2 Interference Signal Generation 124 5.3.1 Front-End Signal Processing 125 5.4 Experimental Results 126 5.3.1 Static Environments 128 5.3.2 Dynamic Environments 133 5.5 Summary 136 Chapter 6. Conclusions and Future Work 138 6.1 Conclusions 138 6.2 Future Work 139 Bibliography 142 Appendix 168 Abstract in Korean 170 Acknowledgments 173Docto