1,720,959 research outputs found
Algorithms for Indoor Positioning Systems Using Ultra-Wideband Signals
No full textPositioning systems and techniques have attracted more and more attention in recent years, in particular with satellite navigation technology as a tremendous enabler, and developments in indoor navigation. The work presented in this thesis has been conducted within the research project: \HERE: indoor positioning based on UWB radio signals", which aims at developing an alternative solution to the indoor positioning problem, since the Global Navigation Satellite Systems (GNSSs), e.g. the Global Positioning System (GPS), generally can not provide reliable positioning services in indoor areas, due to strong signal attenuation and dense multipath e ects. The project focuses on range-based technologies, which are mainly composed of two parts: 1) ranging based on information such as Time of Arrival (ToA), Time Dierence of Arrival (TDoA) and Received Signal Strength (RSS); 2) positioning using the obtained ranging results. This four-year project has been carried out in a team composed of two Ph.D. candidates and two supervisors. As one of the Ph.D. candidates, the author of this thesis focuses on the positioning part of the project, with the main covered issues summarized as follows. Iterative Descent Methods The majority of existing systems, e.g. GPS, solve the positioning problem using Iterative Descent (ID) methods based on non-linear least-squares. Applying these ID methods for indoor positioning purpose faces the following three major problems: It is more dificult to obtain a good initial guess, which is critical for the ID methods to converge to the correct solution and converge faster. For on-earth satellite navigation applications, a good initial guess can be very easily obtained by choosing the Earth's center since the other (local) solution (if any) usually lies far in space. On the contrary, for indoor positioning, it is not as easy to obtain a good initial guess since the information on the user position is rather limited beforehand. In this thesis, we propose to use the so called direct methods or simply the geometric center of the seen transmitters, for initial guess. A thorough study of the existing direct methods is also given. The non-linear least-squares estimator is inherently biased, even with unbiased range measurements, since the expectation of the higher order terms in the final estimator is non-zero. This bias is generally negligible for GNSSs, with extremely large satelliteuser distance, but can be problematic for indoor applications with reduced geometric system scale. Based on an analysis of the bias due to nonlinearity, a scheme is proposed to test the significance of the bias. The corresponding work is validated with measurements obtained using UWB acoustic testbed. The iterative nature of the ID methods may be computationally too heavy for indoor applications, which usually require low power systems. Aiming at reducing the computational load of traditional iterative descent algorithms, a new framework is proposed for position estimation. The multidimensional non-linear localization problem is first transformed to a lower dimension and then solved iteratively. In three dimensional positioning systems, the achievable reduction on the amount of computation in each iteration is 67%. On the other hand, accurate positioning results can be obtained with this low-complexity framework, especially with TDoA measurements. Direct Methods In general, strict direct (non-iterative) least-squares solutions to nonlinear problems do not exist. However, with some assumptions or simplifications, direct least-squares positioning algorithms can be developed. In fact, there is a large number of direct methods documented in literature, scattered across the fields of radar, aerospace engineering, oceanic engineering, (acoustic) signal processing and wireless communications. Some of the documented methods are, surprisingly, identical, though the derivations are often greatly different. A deep study and a proper classification of the methods helps to achieve a better understanding, which is one of the central contributions of this thesis. It can be used to assist researchers and developers in the field to find the right choice for their applications. The direct methods provide simple to compute estimates, but they are suboptimal with the introduced simplifications. Based on the survey of the existing direct methods, a new non-iterative algorithm has been developed to improve the positioning accuracy. Theoretical proof is given that the method provides a better estimator in the sense that it corresponds to an equal or smaller value of the original least-squares objective function. It does so by exploiting two similar fully constrained models. Meanwhile, the non-iterative nature makes the algorithm attractive for low cost, low power applications. NLoS Identification/Mitigation It is widely known that the Non-Line of Sight (NLoS) effect is one of the main degraders for the position estimation accuracy. Hence, NLoS identification and mitigation is another important and hot subject regarding indoor positioning. A review of several existing NLoS identification and mitigation schemes is provided, and four new schemes are described, which are based on systematic positioning model hypothesis testing. The idea is to combine the statistics of timing- and RSS-based range measurements, and in the mean time exploit the fact that all collected measurements are related to the same unknown position. The four proposed schemes all use the combination of timing and RSS measurements because 1) the timing measurements are usually very accurate compared to RSS measurements, 2) the distributions of RSS measurements under LoS and NLoS conditions are well separated. The computational load of the schemes decreases as more simplifications are introduced, and the performance, however, is also degraded in general, except the case where most of the links are NLoS. Validation results show that, under full UWB signal bandwidth of 7.5 GHz, up to 99% correct decision rate can be achieved.Remote SensingAerospace Engineerin
Estimation of slack tide using GPS measurements on a buoy: A case study on buoy 18 in the Schelde Estuary
No full textIn this paper I present a novel method to determine the time of occurrence of tidal slack with a GPS receiver mounted on an anchored buoy commonly used to delineate shipping lanes in estuaries and tidal channels. Slack tide occurs when the tide changes direction from ebb to flood flow, or from flood to ebb. The determination of this point in time is not only useful for shipping and salvaging, it is also important information for calibrating tidal models, for determining the maximum salt intrusion and for the further refinement of the theory on tidal propagation. The accuracy of the timing is well within 10 minutes and the method - able to operate in real-time - is relatively cheap and easy to implement on a permanent basis or in short field campaigns.Geoscience and Remote SensingCivil Engineering and Geoscience
Moblie Rail Survey System: Een nauwkeurig en betrouwbaar systeem voor spoormetingen?
No full textGeomatics EngineeringAerospace Engineerin
The development of an autonomous GPS system to monitor tidal slack in estuaries
No full textRecently, a promising method for measuring tidal slack using GPS receivers attached to buoys has been tested. The next step is to build a wireless GPS system which conducts measurements continuous and real-time. This research primarily focuses on the development of the hardware of that GPS system. Secondly it focuses on modeling the buoy behavior and calculation algorithms for determining the moment of slack. A series of GPS measurements are conducted to test the accuracy and precision of candidate receivers. For the hardware a Waspmote-board and Meshlium router are chosen. Together they provide a complete solution for the GPS system, including GPS receiver. The solution combines adaptability with low costs. The module is made waterproof and solar powered. A buoy model is made with which data sets can be simulated to test the accuracy of the calculation algorithms. The sensitivity tests of the algorithms are performed with a Monte Carlo model. Clear differences in performance between high-end and common receivers are observed. EGNOS improves only the performance of the high-end receiver. The buoys have different behaviour, not all buoys can be modeled the same. Also a bias of up to 10 minutes is found for the calculation algorithms. In terms of sensitivity of the methods, there is a critical standard deviation for the GPS receiver for which the methods become unstable.With all tested GPS receivers the moment of tidal slack can be calculated with a deviation up to 15 minutes. The greatest improvement can be made in reducing the bias in the calculation methods.Water ResourcesWater ManagementCivil Engineering and Geoscience
GPS for structural health monitoring: A case study on the Basarab overpass cable-stayed bridge
No full textThe Basarab cable-stayed bridge is a newly built structure in Bucharest, Romania, which was inaugurated in June 2011. Before the oficial opening, in order to assure its qualification for trafic, it had to pass several loading tests with convoys of trucks and trams. For this, besides a priori evaluation using the Finite Element Method (FEM), levelling and acceleration measurements were made to identify vertical displacements, as well as vibration frequencies of the bridge. The three-day loading trial of the bridge represented a good opportunity for setting-up a GPS campaign for structural monitoring of the Basarab bridge. Taking advantage of the redundancy obtained via simultaneous multi-sensor measurements, it was possible to compare and validate the GPS estimated displacements with both FEM and levelling. Moreover, the dynamic behaviour of the bridge during a dynamic loading test was evaluated using a 20 Hz GPS observation rate and validated afterwards with vibration frequency estimates from acceleration time series. Along with simulations (FEM) and laboratory tests, the in situ monitoring of a structure has a particular importance in establishing the safety of a newly-built structure. Furthermore, in some cases permanent monitoring is needed for safety and economic reasons, especially for strategic structures such as dams and bridges. GPS technology can satisfy this request due to its real-time processing capability and thus it can be looked upon as a new and promising tool for dynamic evaluation of engineering structures. In this contribution we have also assessed the performance of GPS with regard to accuracy and false alarm probability demands for the continuous monitoring of the Basarab cable-stayed bridge.Geoscience & Remote SensingCivil Engineering and Geoscience
GNSS-based receiver autonomous integrity monitoring for aircraft navigation
No full textNowadays, GNSS-based navigation is moving more and more to critical applications. Global Navigation Satellite Systems (GNSS), which in the past used to be represented by the American GPS and the Russian GLONASS are now growing in number and performance. The European systemGalileo and the Chinese systemBeidou are being deployed, while GPS and GLONASS are being modernized. The availability of a larger number of satellites to provide measurements, together with a new frequency dedicated to civil use, are strongly increasing the application potential of GNSS technology. To be used in aviation, in particular during critical phases of flight as approach and landing, satellite navigation shall provide a very high level of service. Correctness—within tight bounds—of the position solution, shall be guaranteed to extremely high levels of probability. In operating an aircraft, the risk for so-called HazardouslyMisleading Information (HMI) due to the navigation systemis typically budgeted at the 10−7 to 10−9 level. These extremely tight requirements constitute a guarantee of safety, which is called integrity. More formally, integrity is about the trust that a user can have in the navigation service (and more specifically, the indicated position information). The trust is measured by the probability of HMI (or integrity risk), which is the probability that the position error exceeds a certain tolerance, without being detected and an Alert being raised in time.Commonly, a distinction is made between system-level integrity and user-level integrity. At system level, integrity is monitored directly by the GNSS control segment and can be monitored by additional external augmentation systems. At user level, integrity is monitored directly by the user via statistical methods. This dissertation focuses on user-level integrity monitoring, also called Receiver Autonomous IntegrityMonitoring (RAIM). In a RAIM method, integrity ismonitored by exploiting the redundancy of theGNSS signals as collected at the receiver. Calculations are performed within the user equipment itself to check the measurements’ consistency. RAIM computations are possible as long as a number of satelliteslarger than the minimumnecessary for a position fix (four in case of single constellation) is visible.RAIM algorithms have been investigated since the late 1980s, starting with publications by Lee, Brown and Brenner. As main representative and reference of the first generation RAIM algorithms we cite the Weighted RAIM algorithm, also referred to as Least-Squares-Residuals (LS) RAIM, proposed by Walter and Enge. This algorithm is still in use today, typically implemented in aviation grade GPS receivers, to provide low-precision lateral integrity only. As of today no RAIM implementation exists for any application requiring integrity in the vertical plane (i.e. precision approaches), which has more stringent certification requirements. To serve this scope second generation RAIMalgorithms are nowbeing developed and tested, as for instance the Advanced RAIM(ARAIM), proposed by the Stanford group.Different approaches being around show that the community has not reached convergence on the subject of integrity of GNSS for aviation yet, especially on RAIM. The Least Squares residuals RAIM, was the staple of the first generation RAIM: its algorithmwas found to be not completely flawless from a theoretical point of view and is not designed to deal with a multi-constellation system. The ARAIM is currently being tested but has not reached yet a definitive shape and has not fully convinced the community because of its high computational load, its convoluted structure and supposed approximations. New alternative approaches are also being proposed.This dissertation offers to the community a critical review of the most popular RAIM algorithms currently available or under development (in particular LS RAIMand ARAIM), and highlights their major strengths and shortcomings. Furthermore it reviews the DIA procedure, a well-established method for gross error detection in geodesy developed by TU Delft, and proposes its application to the RAIMproblem. A connection is made fromthe DIA concept of reliability to integrity risk and a method to evaluate RAIM performance parameters (False Alarm and HMI rates) for a multi-step exclusion/adaptation procedure is proposed (by means of the concept of worst-case bias). The study performed shows the viability ofthe DIA procedure as an alternative RAIMprocedure, and its competitive performance compared to the algorithms currently in use or under development in aviation (LS RAIM and ARAIM). Simulation results show that in several scenarios the DIA method performs significantly better than the others. Points of improvement are nevertheless individuated, also in the DIA, and recommendations are given for the development of the RAIMof the future.In particular, as a result of the algorithms review and the simulation results, it is concluded that all RAIM algorithms discussed, including the DIA procedure, have room for improvement. Both ARAIM and DIA show safe performance (i.e. risk is never larger than required/announced), but some of the approximations employed in ARAIM seem rather conservative and its exclusionmechanismseems not particularly effective. At the sametimealso the DIA exclusion mechanismdoes not appear to performoptimally, fromthe integrity maximization point of view. From a reliability analysis point of view — i.e. prior computation of the probability of HMI (PHMI) based on the satellite geometry alone — the DIA performs better than ARAIM, i.e. can guarantee higher availability (and higher continuity in a faulty scenario). On the other hand one of the mainweaknesses of the RAIMalgorithms analyzed is the Exclusion (or Adaptation) mechanism. Both ARAIM and DIA procedures recognize that in many geometries—given a requirement on the continuity—attempting exclusion introduces more risk than just declaring Alert. This suggests that further investigation is required to develop a more robust and reliable exclusion method for integrity
Time Delay Estimation Based on Multi-band Multi-carrier Signal in Multipath Environments
No full textThe matched filter is the most common approach for time delay estimation and ranging in positioning systems. The accuracy is mainly determined by the signal bandwidth and multipath propagation condition. Instead of occupying an enormous signal bandwidth, aggregating multiple signal bands, which are transmitted either simultaneously or sequentially from the same transmitter, can still provide a very high time resolution due to its large virtual signal bandwidth. This paper discusses time delay estimation based on multiband signals, considering precision, range ambiguity and resistance to multipath. Combining carrier phases from different bands, which are physically not perturbed by a sampling frequency offset, can also mitigate the bias of time delay estimation due to the sampling frequency error. Simulation results show that using two groups of multiband signals, which are sparsely placed in the signal spectrum, can significantly improve the accuracy of time delay estimation in the presence of multipath and sampling frequency offset.Accepted Author ManuscriptMathematical Geodesy and PositioningSignal Processing System
Sparse Signal Bands Selection for Precise Time-based Ranging in Terrestrial Positioning
No full textTime-based ranging accuracy is inversely proportional to the signal bandwidth. A larger the signal bandwidth leads to a higher accuracy of time delay estimation, but more complex hardware is needed. Alternatively, we explore the idea of using multiple narrow signal bands (e.g., 10 MHz of each) to create a large virtual signal bandwidth, which maintains the spectral efficiency but largely improves the ranging accuracy. Considering the impact of multipath, the propagation delay of the LoS path is computed from the estimated channel impulse response (CIR). In this paper, we propose an approach to sparsely select signal bands for ranging and positioning based on convex optimization. The Cramér-Rao lower bound (CRLB) for the propagation delay and gain estimators, as a performance criterion, is employed in the constraint of the optimization. The CRLB is derived in a two-path channel, so that the accuracy and the correlation between the LoS path and the reflection are taken into account. Experiments are conducted in a laboratory environment to illustrate the proposed signal design methodology dedicated for ranging with a sub-decimeter accuracy.Accepted Author ManuscriptMathematical Geodesy and PositioningSignal Processing System
Positioning based on OFDM signals through phase measurements
No full textHigh accuracy terrestrial radio positioning systems, as a complement to a global navigation satellite system (GNSS), are attracting significant attention from academia and industry. This article investigates the feasibility of positioning based on carrier phase measurements of orthogonal frequency division multiplexing (OFDM) signals. Generally, the carrier phase cannot be obtained from a baseband central carrier (i.e., direct current (DC) subcarrier) of OFDM signals, so we derived the carrier phase by calculating the average phase from two symmetrically located pilot sub-carriers. The sampling clock error and the timing synchronization error, which often occur in practice, can be cancelled by measuring the phase difference between two symmetrically located sub-carriers. The presented approach is simulated for a positioning system based on IEEE 802.11p Wireless LAN. Due to the presence of an initial carrier phase offset, the integer carrier phase ambiguity can, as expected, not be properly resolved. Although we can only obtain a 'float' solution from the observation model, the position accuracy can still achieve decimetre level.Mathematical Geodesy and PositioningSignal Processing System
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