Non-Taylor series based positioning method for location based services

Location Based Services (LBS) has gained increasing popularity in major cities. Due to blocking from man-made structures, the existing Global Positioning System (GPS) could not satisfy LBS applications, especially in street canyon and indoor surroundings. This has lead to the development of Assisted GPS (A-GPS) which can provide better service availability and accuracy gain. In the conventional positioning method, Taylor series expansion is applied to solve non-linear distance equations. This method requires an initial estimation of A-GPS receiver’s position. This paper investigates the positioning method for LBS based on hybrid E-OTD/GNSS. The proposed positioning method is non-Taylor series based. Therefore, it involves less complicated mathematical expansion and substitution. A flexible LBS positioning tool is developed which can generate position information in convenient way. It supports both Taylor series and non-Taylor series based positioning methods. The obtained results showed that the proposed non-Taylor series based positioning method can achieve better positioning accuracy

Multi-purpose TDM Component for GNSS

International audienceThis article proposes a Time-Division-Multiplexing (TDM) technique applied at PRN code level as a signal design solution able to cope with the provision of several functionalities in one signal component: the allocation of the signal to the different functionalities is made at PRN code level. The functionalities targeted in this article are low-complexity acquisition, fast Time-ToFirst-Fix Data (TTFFD), Security Code Authentication (SCA) and, additionally, non-coherent signal processing. The interest of using a TDM component signal design lays on the introduction of just one new component to reduce the complexity to be added to the legacy GNSS satellite payload and to the GNSS receiver. Moreover, a TDM signal design solution presents a great flexibility able to adapt the signal design to the different GNSS strategic directives. The TDM component is constituted of period blocks called short basic blocks and advanced blocks; the introduction of such blocks simplifies the TDM component processing by a GNSS receiver. The TDM component is divided first in a continuous stream of short basic blocks of 20ms, where the short basic blocks are used to provide a signal periodic structure for the acquisition functionality. Then, the short basic blocks are grouped in advanced blocks to provide the signal periodicity for fast TTFFD and SCA. The low-complexity acquisition functionality is provided by the first PRN codes of a short basic block: PRN codes are selected to have a low duration and are always at the same position inside the block. Code Shift Keying Modulation is used to provide the fast TTFFD and the SCA key delivery. An example of application on the Galileo E1 civil signals is presented with different target scenarios or type of users: lowcomplexity user, high performance – no TTFFD, high performance – TTFFD and high dynamics user

A New Cooperative PPP-RTK System with Enhanced Reliability in Challenging Environments

Compared to the traditional PPP-RTK methods, cooperative PPP-RTK methods provide expandable service coverage and eliminate the need for a conventional expensive data processing center and the establishment and maintenance of a permanently deployed network of dense GNSS reference stations. However, current cooperative PPP-RTK methods suffer from some major limitations. First, they require a long initialization period before the augmentation service can be made available from the reference stations, which decreases their usability in practical applications. Second, the inter-reference station baseline ambiguity resolution (AR) and regional atmospheric model, as presented in current state-of-art PPP-RTK and network RTK (NRTK) methods, are not utilized to improve the accuracy and service coverage of the network augmentation. Third, the positioning performance of current PPP-RTK methods would be significantly degraded in challenging environments due to multipath effects, non-line-of-sight (NLOS) errors, poor satellite visibility and geometry caused by severe signal blockages. Finally, current position domain or ambiguity domain partial ambiguity resolution (PAR) methods suffer from high false alarm and miss detection, particularly in challenging environments with poor satellite geometry and observations contaminated by NLOS effect, gross errors, biases, and high observation noise. This thesis proposed a new cooperative PPP-RTK positioning system, which offers significant improvements to provide fast-initialization, scalable coverage, and decentralized real-time kinematic precise positioning with enhanced reliability in challenging environments. The system is composed of three major components. The first component is a new cooperative PPP-RTK framework in which a scalable chain of cooperative static or moving reference stations, generates single reference station-derived or reference station network-derived state-space-representation (SSR) corrections for fast ambiguity resolution at surrounding user stations with no need for a conventional expensive data processing center. The second component is a new multi-feature support vector machine (SVM) signal classifier based weight scheme for GNSS measurements to improve the kinematic GNSS positioning accuracy in urban environments. The weight scheme is based on the identification of important features in GNSS data in urban environments and intelligent classification of line-of-sight (LOS) and NLOS signals. The third component is a new PAR method based on machine learning, which employs the combination of two support vector machine (SVM) to effectively identify and exclude bias sources from PAR without relying on satellite geometry. The prototype of the new PPP-RTK system is developed and substantially tested using publically available real-time SSR products from International GNSS Service (IGS) Real-Time Service (RTS)

센티미터 급 광역 보강항법 시스템의 반송파 위상 기반 보정정보 생성 알고리즘에 관한 연구

학위논문(박사)--서울대학교 대학원 :공과대학 기계항공공학부,2020. 2. 기창돈.Recently, the demand for high-precision navigation systems for centimeter-level service has been growing rapidly for various Global Navigation Satellite System (GNSS) applications. The network Real-Time Kinematic (RTK) is one of the candidate solution to provide high-accuracy position to user in real-time. However, the network RTK requires a lot of reference stations for nationwide service. Furthermore, it requires high-speed data-link for broadcasting their scalar-type corrections. This dissertation proposed a new concept of satellite augmentation system called Compact Wide-Area RTK, which provides centimeter-level positioning service on national or continental scales to overcoming the limitation of the legacy network RTK methods. Using the wide-area network of multiple reference stations whose distance is 200~1,000 km, the proposed system generates three types of carrier-phase-based corrections: satellite orbit corrections, satellite code/phase clock (CPC) corrections, tropospheric corrections. Through the strategy of separating the scalar-type corrections of network RTK into vector forms of each error component, it is enable to expand network RTK coverage to continental scale using a similar number of reference stations as legacy meter-level Satellite-Based Augmentation System (SBAS). Furthermore, it is possible to broadcast their corrections over a wide-area using geosynchronous (GEO) satellite with extremely low-speed datalink of 250 bps likewise of legacy SBAS. To sum up, the proposed system can improve position accuracy by centimeter-level while maintaining the hardware infrastructure of the meter-level legacy SBAS. This study mainly discussed on the overall system architecture and core algorithms for generating satellite CPC corrections and tropospheric corrections. This study proposed a new Three-Carrier Ambiguity Resolution (TCAR) algorithm using ionosphere-free combinations to correctly solve the integer ambiguity in wide-area without any ionospheric corrections. The satellite CPC corrections are calculated based on multiple stations for superior and robust performance under communication delay and outage. The proposed algorithm dramatically reduced the latency compensation errors and message amounts with compare to conventional RTK protocols. The tropospheric corrections of the compact wide-area RTK system are computed using GPS-estimated precise tropospheric delay and weather data based model together. The proposed algorithm adopts spherical harmonics function to significantly reduce the message amounts and required number of GPS reference stations than the network RTK and Precise Point Positioning-RTK (PPP-RTK), while accurately modeling the spatial characteristic of tropospheric delay with weather data together. In order to evaluate the user domain performance of the compact wide-area RTK system, this study conducted the feasibility test on mid-west and south USA using actual GPS measurements. As a result, the 95% horizontal position error is about 1.9 cm and the 95% vertical position error is 7.0 cm after the integer ambiguity is correctly fixed using GPS-only signals. The user ambiguity resolution takes about 2 minutes, and success-fix rate is about 100 % when stable tropospheric condition. In conclusion, the compact wide-area RTK system can provide centimeter-level positioning service to wide-area coverage with extremely low-speed data link via GEO satellite. We hope that this new system will consider as candidate solution for nationwide centimeter-level service such as satellite augmentation system of the Korea Positioning System (KPS).최근 자율주행자동차, 무인 드론 배송, 충돌 회피, 무인트랙터를 이용한 스마트 무인 경작 등 위성항법시스템(GNSS, Global Navigation Satellite System)을 사용하는 다양한 응용분야에서 수 cm 수준의 정밀 위치 정보에 대한 요구가 급격히 증가하고 있다. 본 학위논문에서는 1 m 급의 정확하고 신뢰성 높은 위치 서비스를 제공하는 기존의 정지궤도위성 기반 광역 보강항법 시스템(SBAS, Satellite-Based Augmentation System)의 기준국 인프라를 유지하면서 항법 성능을 수 cm 수준으로 향상시키기 위해 반송파 위상 기반의 초정밀 보정정보 생성 알고리즘에 관한 연구를 수행하였다. 실시간 정밀 측위(RTK, Real-Time Kinematic)는 반송파 위상 측정치에 포함된 미지정수를 정확하게 결정하여 수 cm 수준의 정밀 항법 서비스를 가능하게 하는 대표적인 기법이다. 그 중에서도 약 50~70 km 간격으로 분포된 다수의 기준국 정보를 활용하는 Network RTK 기법은 동적 사용자의 빠르고 정확한 위치 결정이 가능한 인프라로서 주목받고 있다. 하지만 스칼라 형태로 구성된 Network RTK 보정정보는 각 기준국 별로 관측된 위성 수에 따라 생성이 되기 때문에 보정 데이터 량이 상당히 방대하다. 메시지 전송에 필요한 데이터 량이 많을수록 고속의 통신 환경을 필요로 하며, 메시지 시간 지연이나 통신 단절에 매우 취약한 문제를 가지고 있다. 또한 스칼라 형태의 보정정보는 사용자와 기준국 간의 거리가 멀어질수록 보정 오차가 크게 발생하기 때문에 대륙 혹은 나라 규모의 광역에서 서비스하기 위해서는 수십~수백 개 이상의 기준국 인프라 구축이 필수적이다. 예를 들어, SBAS가 한반도 지역 서비스를 위해 5~7개의 기준국이 필요한 반면 Network RTK는 90~100개의 기준국이 필요하다. 즉 Network RTK는 시스템 구축 및 유지 비용이 SBAS 대비 약 15배 정도 많이 들게 된다. 본 논문에서는 기존 Network RTK의 문제점을 해결하기 위한 방법으로 대륙 급 광범위한 영역에서 실시간으로 cm급 초정밀 위치결정 서비스 제공이 가능한 Compact Wide-Area RTK 라는 새로운 개념의 광역보강항법시스템 아키텍처를 제안하였다. Compact Wide-Area RTK는 약 200~1,000 km 간격으로 넓게 분포된 기준국 네트워크를 활용하여 반송파 위상 기반의 정밀한 위성 궤도 보정정보, 위성 Code/Phase 시계 보정정보, 대류층 보정정보를 생성하는 시스템이다. 기존 스칼라 형태의 Network RTK 보정정보 대신 오차 요소 별 벡터 형태의 정밀 보정정보를 생성함으로써 데이터 량을 획기적으로 절감하고 서비스 영역을 확장할 수 있다. 최종적으로 SBAS와 마찬가지로 250 bps의 저속 통신 링크를 가진 정지궤도위성을 통해 광역으로 보정정보 방송이 가능하다. 본 논문에서는 3가지 보정정보 중 위성 Code/Phase 시계 보정정보와 대류층 보정정보 생성을 위한 핵심 알고리즘에 대해 중점적으로 연구하였다. 반송파 위상 기반의 정밀 보정정보 생성을 위해서는 먼저 미지정수를 정확하게 결정해야 한다. 본 논문에서는 삼중 주파수 반송파 위상 측정치의 무-전리층 조합을 활용하여 전리층 보정정보 없이도 정확하게 미지정수 결정 가능한 새로운 방법을 제안하였다. 위성 Code/Phase 시계 보정정보는 통신 지연 및 고장 시 우수하고 강건한 성능을 위해 다중 기준국의 모든 측정치를 활용하여 추정된다. 이 때 각 기준국 별 서로 다른 미지정수 때문에 발생하는 문제는 앞서 정확하게 결정된 기준국 간 이중차분 된 미지정수를 활용하여 수준을 조정하는 과정을 통해 해결이 가능하다. 그 결과 생성된 위성 Code/Phase 보정정보 메시지의 크기, 변화율, 잡음 수준이 크게 개선되었고, 통신 지연 시 오차 보상 성능이 기존 RTK 프로토콜 보다 99% 향상 됨을 확인하였다. 대류층 보정정보는 적은 수의 기준국 만을 활용하여 정확하게 대류층을 모델링하기 위해 자동 기상관측시스템으로부터 수집한 기상 정보를 추가로 활용하여 생성된다. 본 논문에서는 GNSS 기준국 네트워크로부터 정밀하게 추정된 반송파 위상 기반 수직 대류층 지연과 기상정보 기반으로 모델링 된 수직 대류층 지연을 함께 활용할 수 있는 새로운 알고리즘을 제안하였다. 구면조화함수를 사용하여 Network RTK 및 PPP-RTK 보다 필요한 메시지 양과 기준국 수를 크게 감소시키면서도 RMS 2 cm 수준으로 정확한 보정정보 생성이 가능함을 확인하였다. 본 논문에서 제안한 Compact Wide-Area RTK 시스템의 항법 성능을 검증하기 위해 미국 동부 지역 6개 기준국의 실측 GPS 데이터를 활용하여 테스트를 수행하였다. 그 결과 제안한 시스템은 미지정수 결정 이후 사용자의 95% 수평 위치 오차 1.9 cm, 95% 수직 위치 오차 7.0 cm 로 위치를 정확하게 결정하였다. 사용자 미지정수 결정 성능은 대류층 안정 상태에서 약 2분 내로 100% 의 성공률을 가진다. 본 논문에서 제안한 시스템이 향후 한국형 위성항법 시스템(KPS, Korean Positioning System)의 전국 단위 센티미터 급 서비스를 위한 알고리즘으로 활용되기를 기대한다.CHAPTER 1. Introduction 1 1.1 Motivation and Purpose 1 1.2 Former Research 4 1.3 Outline of the Dissertation 7 1.4 Contributions 8 CHAPTER 2. Overview of GNSS Augmentation System 11 2.1 GNSS Measurements 11 2.2 GNSS Error Sources 14 2.2.1 Traditional GNSS Error Sources 14 2.2.2 Special GNSS Error Sources 21 2.2.3 Summary 28 2.3 GNSS Augmentation System 29 2.3.1 Satellite-Based Augmentation System (SBAS) 29 2.3.2 Real-Time Kinematic (RTK) 32 2.3.3 Precise Point Positioning (PPP) 36 2.3.4 Summary 40 CHAPTER 3. Compact Wide-Area RTK System Architecture 43 3.1 Compact Wide-Area RTK Architecture 43 3.1.1 WARTK Reference Station (WRS) 48 3.1.2 WARTK Processing Facility (WPF) 51 3.1.3 WARTK User 58 3.2 Ambiguity Resolution and Validation Algorithms of Compact Wide-Area RTK System 59 3.2.1 Basic Theory of Ambiguity Resolution and Validation 60 3.2.2 A New Ambiguity Resolution Algorithms for Multi-Frequency Signals 65 3.2.3 Extra-Wide-Lane (EWL) Ambiguity Resolution 69 3.2.4 Wide-Lane (WL) Ambiguity Resolution 71 3.2.5 Narrow-Lane (NL) Ambiguity Resolution 78 3.3 Compact Wide-Area RTK Corrections 83 3.3.1 Satellite Orbit Corrections 86 3.3.2 Satellite Code/Phase Clock (CPC) Corrections 88 3.3.3 Tropospheric Corrections 89 3.3.4 Message Design for GEO Broadcasting 90 CHAPTER 4. Code/Phase Clock (CPC) Correction Generation Algorithm 93 4.1 Former Research of RTK Correction Protocol 93 4.1.1 Observation Based RTK Data Protocol 93 4.1.2 Correction Based RTK Data Protocol 95 4.1.3 Compact RTK Protocol 96 4.2 Satellite CPC Correction Generation Algorithm 100 4.2.1 Temporal Decorrelation Error Reduced Methods 102 4.2.2 Ambiguity Level Adjustment 105 4.2.3 Receiver Clock Synchronization 107 4.2.4 Averaging Filter of Satellite CPC Correction 108 4.2.5 Ambiguity Re-Initialization and Message Generation 109 4.3 Correction Performance Analysis Results 111 4.3.1 Feasibility Test Environments 111 4.3.2 Comparison of RTK Correction Protocol 113 4.3.3 Latency Compensation Performance Analysis 116 4.3.4 Message Data Bandwidth Analysis 119 CHAPTER 5. Tropospheric Correction Generation Algorithm 123 5.1 Former Research of Tropospheric Correction 123 5.1.1 Tropospheric Corrections for SBAS 124 5.1.2 Tropospheric Corrections of Network RTK 126 5.1.3 Tropospheric Corrections of PPP-RTK 130 5.2 Tropospheric Correction Generation Algorithm 136 5.2.1 ZWD Estimation Using Carrier-Phase Observations 138 5.2.2 ZWD Measurements Using Weather Data 142 5.2.3 Correction Generation Using Spherical Harmonics 149 5.2.4 Correction Applying Method for User 157 5.3 Correction Performance Analysis Results 159 5.3.1 Feasibility Test Environments 159 5.3.2 Zenith Correction Domain Analysis 161 5.3.3 Message Data Bandwidth Analysis 168 CHAPTER 6. Compact Wide-Area RTK User Test Results 169 6.1 Compact Wide-Area RTK User Process 169 6.2 User Performance Test Results 173 6.2.1 Feasibility Test Environments 173 6.2.2 User Range Domain Analysis 176 6.2.3 User Ambiguity Domain Analysis 182 6.2.4 User Position Domain Analysis 184 CHAPTER 7. Conclusions 189 Bibliography 193 초 록 207Docto

Modeling wide-area tropospheric delay corrections for fast PPP ambiguity resolution

The performance of precise point positioning (PPP) has been significantly improved thanks to the continuous improvements in satellite orbit, clock, and ambiguity resolution (AR) technologies, but the convergence speed remains a limiting factor in real-time PPP applications. To improve the PPP precision and convergence time, tropospheric delays from a regional network can be modeled to provide precise correction for users. We focus on the precise modeling of zenith wet delay (ZWD) over a wide area with large altitude variations for improving PPP-AR. By exploiting the water vapor exponential vertical decrease, we develop a modified optimal fitting coefficients (MOFC) model based on the traditional optimal fitting coefficients (OFC) model. The proposed MOFC model provides a precision better than 1.5 cm under sparse inter-station distances over the Europe region, with a significant improvement of 70% for high-altitude stations compared to the OFC model. The MOFC model with different densities of reference stations is further evaluated in GPS and Galileo kinematic PPP-AR solutions. Compared to the PPP-AR solutions without tropospheric delay augmentation, the positioning precision of those with 100-km inter-station spacing MOFC and OFC is improved by 25.7% and 17.8%, respectively, and the corresponding time to first fix (TTFF) is improved by 36.9% and 33.0% in the high-altitude areas. On the other hand, the OFC model only slightly improves the TTFF and positioning accuracy when using the 200 km inter-station spacing modeling and even degrades the positioning for high-altitude stations, whereas using the MOFC model, the PPP-AR solutions always improve. Moreover, the positioning precision improvement of MOFC compared with OFC is about 22.1%, 21.7%, and 25.7% for the Galileo-only, GPS-only, and GPS + Galileo PPP-AR solutions, respectively

Snapshot Estimation Algorithms for GNSS Mass-Market Receivers

This thesis resumes the PhD program carried out in the signal processing, satellite positioning and telecommunication fields, within the Navigation, Signal Analysis and Simulation (NavSAS) group, Department of Electronics and Telecommunications (DET) of Politecnico di Torino, in the period going from January 2012 to December 2014. The main topic of the PhD activity is represented by Global Navigation Satellite System (GNSS) receivers core technologies. In particular, it deals with the design, development, test and performance assessment of innovative architectures, techniques, and algorithms for Global Positioning System (GPS) and Galileo receivers, both professional high performance and commercial mass-market. GPS, and in general GNSSs are radio-communication infrastructures, aimed to enable a generic user to compute Position, Velocity and Time (PVT). The signals transmitted by a constellation of satellites are processed by an electronic device, performing trilateration with respect to the satellites, taken as reference points. At least 4 satellites are required to be in Line of Sight (LOS) with the receiver, so as to obtain 4 different signals and to solve the 4 navigation unknowns: latitude, longitude, height and time. Since their first appearance, in the early seventies, GNSS chipsets and devices are gaining a fundamental role in most applications of everyday life, and their global market continues to grow rapidly. In 25 years, GNSS receivers became extremely used worldwide, not only for positioning and navigation purposes, but also for time synchronization, thus spanning an unlimited range of applications, from commercial to scientific, from military to recreational. GNSS mass-market receivers are extremely widespread, produced in very high volume—hundreds of millions just for smartphones and tablets—and sold at a limited price. This variety of applications and possibilities represents the main reason of the continuous growth of the GNSS field: in fact, new systems are emerging beside GPS, such as GLONASS, currently operational and in expansion, Galileo and Beidou. With the latest trends of multi-constellation receivers, the positioning accuracy can greatly improve, as well as its robustness, availability, reliability, but at the expense of a greater complexity and power consumption

FLAMINGO – Fulfilling enhanced location accuracy in the mass-market through initial GalileO services

This paper discusses FLAMINGO, an initiative that will provide a high accuracy positioning service to be used by mass market applications. The status and future for the initiative are discussed, the required accuracies and other location parameters are described, and the target applications are identified. Finally, the currently achieved accuracies from today’s Smartphones are assessed and presented. FLAMINGO (Fulfilling enhanced Location Accuracy in the Mass-market through Initial GalileO services), part funded through the European GNSS Agency, is a collaborative venture comprising NSL (as lead organization), Telespazio France, University of Nottingham, Rokubun, Thales Alenia Space France, VVA, BQ, ECLEXYS and Blue Dot Solutions. The initiative is developing the infrastructure, solutions and services to enable the use of accurate and precise GNSS within the mass-market, thereby operating predominantly in an urban environment. Whilst mass-market receivers are yet to achieve accuracies below one metre for standard positioning, the introduction of Android raw GNSS measurements and the Broadcom dual frequency chipset (BCM47755), has presented the devices such an opportunity. FLAMINGO will enable and demonstrate the future of high accuracy positioning and navigation information on mass-market devices such as smartphones and Internet of Things (IoT) devices by producing a service delivering accuracies of 50cm (at 95%) and better, employing multi-constellation, PPP and RTK mechanisms, power consumption optimisation techniques. Whereas the Galileo High Accuracy Service targets 10cm precision within professional markets, FLAMINGO targets 30-50cm precision in the mass-market consumer markets. By targeting accuracies of a few decimetres, a range of improved and new applications in diverse market sectors are introduced. These sectors include, but are not limited to, mapping and GIS, autonomous vehicles, AR environments, mobile-location based gaming and people tracking. To obtain such high accuracies with mass market devices, FLAMINGO must overcome several challenges which are technical, operational and environmental. This includes the hardware capabilities of most mass-market devices, where components such as antennas and processors are prioritised for other purposes. We demonstrate that, despite these challenges, FLAMINGO has the potential to meet the accuracy required. Tests with the current Smartphones that provide access to multi-constellation raw measurements (the dual frequency Xiaomi Mi 8 and single frequency Samsung S8 and Huawei P10) demonstrate significant improvements to the PVT solution when processing using both RTK and PPP techniques

Link-Layer Coding for GNSS Navigation Messages

In this paper, we face the problem of ensuring reliability of Global Navigation Satellite Systems (GNSSs) in harsh channel conditions, where obstacles and scatter cause long outage events that cannot be counteracted with channel coding only. Our novel approach, stemming from information-theoretic considerations, is based on link-layer coding (LLC). LLC allows us to significantly improve the efficiency in terms of time-to-first-fix with respect to current operational GNSSs, which adopt carousel transmission. First, we investigate the maximum theoretical LLC gain under different Land Mobile Satellite channel conditions. Then, some practical LLC coding schemes, namely, fountain codes and a novel low-density parity-check plus low-rate repetition coding, are proposed and tested in realistic single-satellite and multi-satellite Land Mobile Satellite scenarios, considering the Galileo I/NAV message as study case. Simulation results show that our designed schemes largely improve on carousel transmission and achieve near-optimal performance with limited increase in complexity. Also, back-compatibility of LLC is assessed with respect to present-time GNSS specifications. © 2018 Institute of Navigation