3 research outputs found
A STAP anti-interference technology with zero phase bias in wireless IoT systems based on high-precision positioning
Fog computing has been applied to the data processing for the Internet of Things (IoT) based on distributed high-precision Global Navigation Satellite Systems (GNSS). However, the space-time adaptive processing (STAP) interference suppression technology in the system will cause fog computing data deviation that includes carrier phase bias and pseudocode offset. An unbiased STAP technique is proposed to eliminate these deviations. First, it is analyzed that the carrier phase bias and pseudocode offset are caused by the non-linear phase response of the STAP equivalent filter. Then, a coefficient-constrained method based on practical engineering processing is proposed, which can eliminate these deviations by restricting the tap coefficients to be symmetrically equal around the center-tap. Moreover, by analyzing the coherent integral function of the pseudocode after filtering, the tap structure of STAP is modified to eliminate the group offset of the pseudocode without increasing the computational complexity and hardware resources. Finally, the unbiased performance and anti-interference performance of the system are verified by numerical and real data simulations
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Anti-Jam GPS Controlled Reception Pattern Antennas for Man-Portable Applications
Military GPS receivers provide crucial information to soldiers in the field, however, the performance of these devices is degraded by in band RF interference, making GPS susceptible to jamming. Anti-jam techniques for aircraft and vehicular platforms have been developed, but at present there is no system for dismounted soldiers. There is a need for an anti-jam system which meets the demands of a dismounted soldier and conforms to the size, weight, and power requirements of a portable device.
A controlled reception pattern antenna, or CRPA, is a potential solution for jammer mitigation. These devices work by steering reception pattern nulls toward the jammer direction, reducing the jammer power which reaches the GPS receiver. Prior CRPA realizations have been designed for use on vehicular and aircraft applications, however, these platforms do not suffer from the same limitations as a man-portable CRPA. Three considerations which are more pertinent for man-portable designs than prior work are (i) distributed antenna element positions and orientations dynamically change during use changing the reception pattern characteristics, (ii) the user is lower to the ground and moves through the environment meaning that multipath propagation can have a greater effect on CRPA performance, and (iii) the size weight and power constraints for a portable system limit the number of antenna elements reducing the degrees of freedom that can be used for cancellation.
To address these challenges, a framework for man-portable CRPA modeling is presented. This includes development of efficient modeling methods which enable investigations into element perturbations to address the dynamic orientation problem. These and other methods are presented in Chapter 3, along with a discussion of the relative strengths and weaknesses of each. Additionally, a mixed scattering channel model is applied to the CRPA reception patterns, combining diffuse and specular reflection in Chapter 4. Discussion of this model centers around the eigenvalues of the signal covariance matrix and the effect of coherence between multipath components. Following this, Chapter 5 examines the performance of polarimetric CRPAs and space-time adaptive processing for man-portable CRPAs with limited degrees of freedom
Multiple Antenna-based GPS Multipath Mitigation using Code Carrier Information
ํ์๋
ผ๋ฌธ (๋ฐ์ฌ)-- ์์ธ๋ํ๊ต ๋ํ์ : ์ ๊ธฐ๊ณตํ๋ถ, 2013. 8. ์ต์ง์.์ฌ๋ฌ ์์ฉ๋ถ์ผ์์ ์ ์ต๋์ GPS(Global Positioning System) ์์ ๊ธฐ๊ฐ ์ฌ์ฉ๋๊ณ ์์ง๋ง, GPS์ ๊ธฐ๋ฐ์ผ๋ก ํ๋ ์์น๊ธฐ๋ฐ ์๋น์ค(LBS: Location Based Services)์์๋ ์ฌ์ ํ ๋ค์ค๊ฒฝ๋ก ์ค์ฐจ์ ๊ฐ์ ์ ํ ๋ฐฉํด๊ฐ ๋ฐ์ํ๊ณ ์์ผ๋ฉฐ, ์ด๋ฌํ ์ค์ฐจ๋ค๋ก ์ธํ์ฌ ์๊ดํจ์์ ์๊ณก์ ๊ฑฐ๋ฆฌ ์ค์ฐจ๊ฐ ๋ฐ์์ ์ํฅ์ ๋ฏธ์น๊ณ ์๋ค. ์ด๋ฌํ ์ด์ ๋ก ์ธํ์ฌ GPS์ ์ด์ฉํ ํญ๋ฒ ์์คํ
์์์ ์์น ์ ํ๋ ํฅ์์ ์ํ์ฌ, ๋ค์ค๊ฒฝ๋ก ์ค์ฐจ๋ฅผ ํจ๊ณผ ์ ์ผ๋ก ์ค์ด๊ธฐ ์ํ ๊ฐ์ธํ๊ณ ํ์ค์ ์ธ ๋ฐฉ๋ฒ์ด ์๊ตฌ๋๋ค.
๋ค์ค๊ฒฝ๋ก๋ GPS ์ ํธ๊ฐ ์ฅ์ ๋ฌผ์ ์ํด ๋ฐ์ฌ๋ ํ์ ๋์ด ์์ ๊ธฐ์ ๋์ฐฉํ ๋ ์ ์ผ์ด๋๋ค. ๊ฐ์๊ฒฝ๋ก ์ ํธ์ ๊ฒฐํฉ๋ ๋ค์ค๊ฒฝ๋ก ์ ํธ๋ GPS ์์ ๊ธฐ์ ์๊ดํจ์์ ๋ณํ์ ์ผ์ผํค๋ฉฐ ๊ถ๊ทน์ ์ผ๋ก ์ฐจ๋ณํจ์์ ์ํฅ์ ๋ฏธ์น๋ฏ๋ก ๊ฑฐ๋ฆฌ์ค์ฐจ๋ฅผ ๋ฐ์์ํจ๋ค. ๊ทธ๋ฌ๋ฏ๋ก ๋ค์ค๊ฒฝ๋ก ์ค์ฐจ๋ ์์ฑํญ๋ฒ ์์คํ
์์์ ์์น์ ํ๋ ํฅ์์ ์ํด ํด๊ฒฐ ๋์ด์ผ ๋ ๋ฌธ์ ๋ก ์์ ์ด ๋์ด์๋ค.
์ต๊ทผ์๋ ์ด๋ฌํ ์ ํ ๊ฐ์ญ์ ํธ๋ฅผ ์ค์ด๊ธฐ ์ํ์ฌ ๋ค์ค๊ฐ์ ์ํ
๋(Multiple Antenna)๋ฅผ ์ด์ฉํ๋ ๋ฐฉ๋ฒ์ด GPS ํญ๋ฒ ์์คํ
์์ ์ด์ฉ๋๊ณ ์๋ค. ํ ์์ ์์, ๋ค์ค๊ฐ์ ์ํ
๋๋ฅผ ์ฌ์ฉํ๋ ์์ฉ๋ถ์ผ๋ ์ฃผ๋ก ํ์ ์ ์ธ ์ฐ๊ตฌ ๋ฐ ๋ณต์กํ ๊ตฐ์ฌ์ฉ ์ฐ๊ตฌ๋ก ์ฃผ๋ก ์งํ ๋์๋ค. ๊ทธ๋ฌ๋ ์ํ
๋ ์ ์ ๋ฐฉ๋ฒ ๋ฐ ์ ๊ธฐ์ ์์คํ
์ ๊ธ๊ฒฉํ ๋ฐ์ ์ผ๋ก ์ธํด ์ด์ ์ ํ๋์จ์ด ๋ฐ ์ํ์จ์ด์ ์ธ ๋ฌธ์ ๋ฅผ ์ฝ๊ฒ ํด๊ฒฐ ๋จ์ ๋ฐ๋ผ ๊ฐ๊น์ด ๋ฏธ๋์๋ ๋ค์ค ์ํ
๋ ๊ธฐ๋ฐ์ ์์ ๊ธฐ๊ฐ ๋ฏผ๊ฐ ์์ฉ๋ถ์ผ๋ก ํ๋ ๋ ๊ฒ์ผ๋ก ์์์ด ๋๋ค. ๋ํ ์ํ
๋ ์์ ๊ธฐ RF๋จ์ ์ํํ๋ก ์ธํ์ฌ ๋ค์ค ์ํ
๋ ์์คํ
์์์ ์ํ
๋ ํฌ๊ธฐ ๋ฌธ์ ์ ๋ํ ํด๊ฒฐ ๊ฐ๋ฅํ๋ค.
๊ทธ๋ฌ๋ฏ๋ก ๋ณธ ๋
ผ๋ฌธ์์๋ ๋ค์ค GPS ์ํ
๋๋ฅผ ์ด์ฉํ์ฌ GPS ํญ๋ฒ์์์ ์ ํ ๊ฐ์ญ ๋ฐ ๋ค์ค๊ฒฝ๋ก ์ค์ฐจ ๊ฐ์์ ๋ํ ์ฐ๊ตฌ๋ฅผ ๋ชฉ์ ์ผ๋ก ํ๋ค. ๋ณธ ์ฐ๊ตฌ๋ ๊ฐํ ์ ํ ๊ฐ์ญ ๋ฐ ๋ค์ค๊ฒฝ๋ก ์ ํธ์ ๋ํ์ฌ ๊ณต๊ฐ ์ฒ๋ฆฌ ๊ธฐ๋ฒ์ ์ ์ฉํ๋ค. ์ ์๋ ์๋ก์ด ๋ฐฉ๋ฒ์ ๋ค์ค ์ํ
๋๋ฅผ ๊ธฐ๋ฐ์ ์ฝ๋ ์ผ๋ฆฌ์ด ์ ๋ณด๋ฅผ ์ด์ฉํ ๊ณต๊ฐ์ฒ๋ฆฌ ๊ธฐ๋ฒ์ผ๋ก ์ ํ ๊ฐ์ญ ๋ฐ ๋ค์ค๊ฒฝ๋ก ์ค์ฐจ๋ฅผ ์ํ์ํค๋ฉฐ, ๋ํ ๋นํ์ฑ ๊ธฐ๋ฒ์ ์ด์ฉํ์ฌ ์ ํธ ๋ ์ก์ ๋น์จ์ ์ต๋๋ก ํ๋ค. ์ ์๋ ์ฑ๋ฅ์ ๊ฒ์ฆํ๊ธฐ ์ํ์ฌ ์ํํธ์จ์ด GPS ์์ ๊ธฐ๋ฅผ ์ฌ์ฉ๋๋ค. ์ํํธ์จ์ด GPS ์์ ๊ธฐ๋ฅผ ์ด์ฉํ ์ ํธ์ฒ๋ฆฌ ๊ธฐ๋ฒ์ ์๋ก์ด ์ฅ๋น์ ์ ํํ ๋ฐ GPS ์ ํธ ๋ถ์์ ์ฅ์ ์ ๊ฐ์ง๊ณ ์๋ค. ๋ํ GPS ์๊ณ ๋ฆฌ์ฆ ๋ถ์ ๋ฐ ์์ ๊ธฐ ์ฑ๋ฅ ํฅ์ ๊ฒ์ฆ ๋ฑ ์ฌ๋ฌ ์ฐ๊ตฌ๋ถ์ผ์์ ๋๋ฆฌ ์ด์ฉ๋๊ณ ์๋ค.
๋ณธ ๋
ผ๋ฌธ์์๋ ์ ์๋ ๋ฐฉ๋ฒ์ ์ฑ๋ฅ ๊ฒ์ฆ์ ์ํ์ฌ ์ปดํจํฐ ์๋ฎฌ๋ ์ด์
๋ฐ ๊ฐ๊ณต IF ๋ฐ์ดํฐ๋ฅผ ์ด์ฉํ ์ํํธ์จ์ด ์์ ๊ธฐ ๊ฒฐ๊ณผ๋ฅผ ์ ์ํ๋ค. ๊ทธ ๊ฒฐ๊ณผ ์ ์๋ ๋ฐฉ๋ฒ์ ์ ํ ๊ฐ์ญ ๋ฐ ๋ค์ค๊ฒฝ๋ก ์ค์ฐจ ๊ฐ์์ ๊ฐ์ธํ๋ฉฐ, GPS ํญ๋ฒ์์คํ
์์์ ์์น์ ํ๋ ํฅ์์ ๊ฐ๋ฅ์ฑ์ ๋ณด์ฌ์ค๋ค. ๊ทธ๋ก๋ฏ๋ก ์ ์๋ ๋ฐฉ๋ฒ์ ์ฐจ๋ ํญ๋ฒ ์์ฉ๋ถ์ผ์์ ๋ฐฉํด์ ํธ ๊ฐ์์ ์ฌ์ฉ๋ ๊ฒ์ผ๋ก ์์๋๋ค.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