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Search Results: 1 - 10 of 19121 matches for " Global Navigation Satel-lite Systems (GNSS) "
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Limited Bandwidths and Correlation Ambiguities: Do They Co-Exist in Galileo Receivers  [PDF]
Elena Simona Lohan
Positioning (POS) , 2011, DOI: 10.4236/pos.2011.21002
Abstract: Galileo is the Global Navigation Satellite System that Europe is building and it is planned to be operational in the next 3-5 years. Several Galileo signals use split-spectrum modulations, such as Composite Binary Offset Carrier (CBOC) modulation, which create correlation ambiguities when processed with large or infinite front-end bandwidths (i.e., in wideband receivers). The correlation ambiguities refer to the notches in the correlation shape (i.e., in the envelope of the correlation between incoming signal and reference modulated code) which happen within +/– 1 chip from the main peak. These correlation ambiguities affect adversely the detection probabilities in the code acquisition process and are usually dealt with by using some form of unambiguous processing (e.g., BPSK-like techniques, sideband processing, etc.). In some applications, such as mass-market applications, a narrowband Galileo receiver (i.e., with considerable front-end bandwidth limitation) is likely to be employed. The question addressed in this paper, which has not been answered before, is whether or not this bandwidth limitation can cope inherently with the ambiguities of the correlation function, to which extent, and which the best design options are in the acquisition process (e.g., in terms of time-bin step and ambiguity mitigation mechanisms).
The use of civilian-type GPS receivers by the military and their vulnerability to jamming
Andries F. Van Niekerk,Ludwig Combrinck
South African Journal of Science , 2012, DOI: 10.4102/sajs.v108i5/6.749
Abstract: We considered the impact of external influences on a GPS receiver and how these influences affect the capabilities of civilian-type GPS receivers. A standard commercial radio frequency signal generator and passive GPS antenna were used to test the sensitivity of GPS to intentional jamming; the possible effects of the terrain on the propagation of the jamming signal were also tested. It was found that the high sensitivity of GPS receivers and the low strength level of GPS satellite signals combine to make GPS receivers very vulnerable to intentional jamming or unintentional radio frequency interference. Terrain undulation was used to shield GPS antennas from the direct line-of-sight of the jamming antenna and this indicated that terrain characteristics can be used to mitigate the effects of jamming. These results illuminate the vulnerability of civilian-type GPS receivers to the possibility and the ease of disablement and establish the foundation for future work.
BeiDou Inter-Satellite-Type Bias Evaluation and Calibration for Mixed Receiver Attitude Determination
Nandakumaran Nadarajah,Peter J. G. Teunissen,Noor Raziq
Sensors , 2013, DOI: 10.3390/s130709435
Abstract: The Chinese BeiDou system (BDS), having different types of satellites, is an important addition to the ever growing system of Global Navigation Satellite Systems (GNSS). It consists of Geostationary Earth Orbit (GEO) satellites, Inclined Geosynchronous Satellite Orbit (IGSO) satellites and Medium Earth Orbit (MEO) satellites. This paper investigates the receiver-dependent bias between these satellite types, for which we coined the name “inter-satellite-type bias” (ISTB), and its impact on mixed receiver attitude determination. Assuming different receiver types may have different delays/biases for different satellite types, we model the differential ISTBs among three BeiDou satellite types and investigate their existence and their impact on mixed receiver attitude determination. Our analyses using the real data sets from Curtin’s GNSS array consisting of different types of BeiDou enabled receivers and series of zero-baseline experiments with BeiDou-enabled receivers reveal the existence of non-zero ISTBs between different BeiDou satellite types. We then analyse the impact of these biases on BeiDou-only attitude determination using the constrained (C-)LAMBDA method, which exploits the knowledge of baseline length. Results demonstrate that these biases could seriously affect the integer ambiguity resolution for attitude determination using mixed receiver types and that a priori correction of these biases will dramatically improve the success rate.
- , 2015, DOI: 10.11908/j.issn.0253-374x.2015.12.020
Abstract: 提出对流层去相关的实时动态定位(RTK)方法,有效降低单历元对流层参数与高程的相关性,实现对流层延迟与高程的有效分离,从而实现毫米级RTK定位.采用上海连续运行参考站(CORS)网的11条长度从23km到90km的基线,比较忽略对流层延迟与估计对流层延迟的单历元最小二乘解、动态卡尔曼滤波与对流层去相关4种RTK方法,重点分析对流层去相关RTK方法分离对流层参数与高程的效果,结果表明,对流层去相关方法在平面与高程方向定位精度均为毫米级,且高程相比平面精度更高.
The troposphere decorrelation method was proposed, which can effectively decrease the correlation of tropospheric parameter and height of single epoch, thus realizing the efficient decouple of height and tropospheric delay and then the millimeter RTK (real time kinematic) results. In this paper, we evaluate the performance of 4 RTK methods by using 11 baselines with baseline lengths from 23 km to 90 km from Shanghai Continuously Operation Reference Station (CORS) network, including the single epoch least squares solutions with and without tropospheric delays, the kinematic Kalman filtering solution and the troposphere decorrelation solution. We highlight the analysis of RTK performance from the troposphere decorrelation method. The numerical experiments indicate that the millimeter accuracies can be obtained for all three coordinate components in the RTK solutions by the troposphere decorrelation method
End-User Attitudes towards Location-Based Services and Future Mobile Wireless Devices: The Students’ Perspective
Elena-Simona Lohan,Alexandru Rusu-Casandra,Oana Cramariuc,Ion Marghescu,Bogdan Cramariuc
Information , 2011, DOI: 10.3390/info2030426
Abstract: Nowadays, location-enabled mobile phones are becoming more and more widespread. Various players in the mobile business forecast that, in the future, a significant part of total wireless revenue will come from Location-Based Services (LBS). An LBS system extracts information about the user’s geographical location and provides services based on the positioning information. A successful LBS service should create value for the end-user, by satisfying some of the users’ needs or wants, and at the same time preserving the key factors of the mobile wireless device, such as low costs, low battery consumption, and small size. From many users’ perspectives, location services and mobile location capabilities are still rather poorly known and poorly understood. The aim of this research is to investigate users’ views on the LBS, their requirements in terms of mobile device characteristics, their concerns in terms of privacy and usability, and their opinion on LBS applications that might increase the social wellbeing in the future wireless world. Our research is based on two surveys performed among 105 students (average student age: 24 years) from two European technical universities. The survey questions were intended to solicit the youngsters’ views on present and future technological trends and on their perceived needs and wishes regarding Location-Based Services, with the aim of obtaining a better understanding of designer constraints when building a location receiver and generating new ideas related to potential future killer LBS applications.
A Novel Tool for the Determination of Tropopause Heights by Using GNSS Radio Occultation Data  [PDF]
Francesco Vespe, Rosa Pacione, Elisa Rosciano
Atmospheric and Climate Sciences (ACS) , 2017, DOI: 10.4236/acs.2017.73022
Abstract: The tropopause is a transitional layer between the troposphere and the stratosphere. The exchange of chemical constituents of the atmosphere (namely masses of air, water vapor, trace gases etc.) and energy between the troposphere and the stratosphere occurs through this layer. We suppose that just exchanges that are taking place at the tropopause heights are strongly influenced by the Global Change forcing. For this reason it is particularly urgent to accumulate temporal data the most accurate possible and with a certain continuity series to understand comprehensively what is happening to our climate. It is well known that Radio Occultation technique applied using Global Navigations Satellite Systems (GNSS-RO) is a powerful tool to detect the tropopause heights. It can be done working on the level 2 data provided by GNSS-RO payload: i.e. atmospheric profiles of pressure and temperature. We propose to measure tropopause using GNSS-RO level 1 data; i.e. the bending angles (BA) of the GNSS signal through the atmosphere. We fit the BA profiles applying in the integral relationship of BA as refractivity profile of background the Hopfield dry model of atmosphere which depends on the fourth degree of the height above the Earth. Through the layers in which tropopause is contained, the residuals between the background model and the observed BA have an anomalous trend. The residuals in this zone form anomalous non-gaussian bumps that we have exploited just to determine the relevant parameters of the tropopause. Such bumps are due to the wrong theoretical assumption made by Hopfield for the re-construction of the dry refractivity that the temperature lapse rate of the atmosphere is constant. But we know that the definition of tropopause according the World Meteorological Organization (WMO) is just the height where a sudden change of the temperature lapse rate usually occurs. Thus in the present work we have determined tropopause heights with new algorithms which exploit the bumps occurring along the BA profiles achieved by GNSS-RO. We have used the huge amount of data provided by several space missions devoted to GNSS-RO (namely COSMIC, METOP, etc.) for tuning the algorithms, performed a validation and provided a robust statistical soundness. The same GNSS-RO observations are helpful also to reconstruct the Mapping Function commonly applied in geodetic applications. Global mapping functions built with GNSS-RO and their evolution in time can be an interesting parameter helpful for climate investigations as well.
An Integrated Air Data / GPS Navigation System for Helicopters  [PDF]
Taner Mutlu, Chingiz Hajiyev
Positioning (POS) , 2011, DOI: 10.4236/pos.2011.22010
Abstract: In this study, the integration of two navigation systems Air Data System (ADS) and Global Positioning System (GPS) was aimed. ADS is a widely used navigation system which measures static and total air pressure and the air temperature. ADS has high sampling frequency and poor accuracy, on the other hand, another navigation system GPS has high accuracy compared to ADS but lower sampling frequency.Kalman Filter is used to integrate and minimize the errors of the two navigation systems. By this integration a navigation system with high sampling frequency and high accuracy is aimed. Another object is to calculate the wind speed with high accuracy.
The use of global navigation satellite systems for deformation analysis of the Dargovskych hrdinov housing estate
Pavel Kuku?ka,Slavomír Labant,Gabriel Weiss
Acta Montanistica Slovaca , 2011,
Abstract: In this paper, the deformation analysis of the Dargovskych hrdinov housing estate using global navigation satellite systemsis described. Theoretically, it deals with the reasons of formation of slope deformations, the ways of their measurement, and withthe recent development and availability of GNSS. Particular attention is paid to the description of the deformation analysis technique,beginning with working out the project, locating by the GNSS, up to processing and testing of the deformation network. The practicalpart is based on the theoretical knowledge and describes the measurement procedure, the equipment used, working methodologyand testing of the bonding network. Based on the results obtained by the deformation analysis, the paper offers information aboutthe recent condition of the investigated area.
New Passive Instruments Developed for Ocean Monitoring at the Remote Sensing Lab—Universitat Politècnica de Catalunya
Adriano Camps,Xavier Bosch-Lluis,Isaac Ramos-Perez,Juan F. Marchán-Hernández,Nereida Rodríguez,Enric Valencia,Jose M. Tarongi,Albert Aguasca,René Acevo
Sensors , 2009, DOI: 10.3390/s91210171
Abstract: Lack of frequent and global observations from space is currently a limiting factor in many Earth Observation (EO) missions. Two potential techniques that have been proposed nowadays are: (1) the use of satellite constellations, and (2) the use of Global Navigation Satellite Signals (GNSS) as signals of opportunity (no transmitter required). Reflectometry using GNSS opportunity signals (GNSS-R) was originally proposed in 1993 by Martin-Neira (ESA-ESTEC) for altimetry applications, but later its use for wind speed determination has been proposed, and more recently to perform the sea state correction required in sea surface salinity retrievals by means of L-band microwave radiometry (TB). At present, two EO space-borne missions are currently planned to be launched in the near future: (1) ESA’s SMOS mission, using a Y-shaped synthetic aperture radiometer, launch date November 2nd, 2009, and (2) NASA-CONAE AQUARIUS/SAC-D mission, using a three beam push-broom radiometer. In the SMOS mission, the multi-angle observation capabilities allow to simultaneously retrieve not only the surface salinity, but also the surface temperature and an “effective” wind speed that minimizes the differences between observations and models. In AQUARIUS, an L-band scatterometer measuring the radar backscatter (σ0) will be used to perform the necessary sea state corrections. However, none of these approaches are fully satisfactory, since the effective wind speed captures some sea surface roughness effects, at the expense of introducing another variable to be retrieved, and on the other hand the plots (TB-σ0) present a large scattering. In 2003, the Passive Advance Unit for ocean monitoring (PAU) project was proposed to the European Science Foundation in the frame of the EUropean Young Investigator Awards (EURYI) to test the feasibility of GNSS-R over the sea surface to make sea state measurements and perform the correction of the L-band brightness temperature. This paper: (1) provides an overview of the Physics of the L-band radiometric and GNSS reflectometric observations over the ocean, (2) describes the instrumentation that has been (is being) developed in the frame of the EURYI-funded PAU project, (3) the ground-based measurements carried out so far, and their interpretation in view of placing a GNSS-reflectometer as secondary payload in future SMOS follow-on missions.
GNSS spoofing detection based on uncultivated wolf pack algorithm
Sun Minhong, , Shao Zhangyi, Bao Jianrong, Yu Xutao
- , 2017, DOI: 10.3969/j.issn.1003-7985.2017.01.001
Abstract: In order to solve the problem that the global navigation satellite system(GNSS)receivers can hardly detect the GNSS spoofing when they are deceived by a spoofer, a model-based approach for the identification of the GNSS spoofing is proposed. First, a Hammerstein model is applied to model the spoofer/GNSS transmitter and the wireless channel. Then, a novel method based on the uncultivated wolf pack algorithm(UWPA)is proposed to estimate the model parameters. Taking the estimated model parameters as a feature vector, the identification of the spoofing is realized by comparing the Euclidean distance between the feature vectors. Simulations verify the effectiveness and the robustness of the proposed method.The results show that, compared with the other identification algorithms, such as least square(LS), the iterative method and the bat-inspired algorithm(BA), although the UWPA has a little more time-complexity than the LS and the BA algorithm, it has better estimation precision of the model parameters and higher identification rate of the GNSS spoofing, even for relative low signal-to-noise ratios.
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