6,324 research outputs found
Multipath and interference errors reduction in gps using antenna arrays
The Global Positioning System (GPS) is a worldwide satellite based positioning system that provides any user with
tridimensional position, speed and time information. The measured pseudorange is affected by the multipath propagation,
which probably is the major source of errors for high precision systems. After a presentation of the GPS and the basic
techniques employed to perform pseudorange measurements, the influence of the multipath components on the pseudorange
measurement is explained. Like every system the GPS is also exposed to the errors that can be caused by the interferences,
and a lot of civil applications need robust receivers to interferences for reasons of safety. In this paper some signal array
processing techniques for reducing the code measurement errors due to the multipath propagation and the interferences are
presented. Firstly, a non-adaptive beamforming is used. Secondly, a variant of the MUSIC and the maximum likelihood
estimator can be used to estimate the DOA of the reflections and the interferences, and then a weight vector that removes
these signals is calculated. In the third place, a beamforming with temporal reference is presented; the reference is not the
GPS signal itself, but the output of a matched filter to the code. An interesting feature of the proposed techniques is that they
can be applied to an array of arbitrary geometry.Peer ReviewedPostprint (published version
Cramer-Rao bounds in the estimation of time of arrival in fading channels
This paper computes the Cramer-Rao bounds for the time of arrival estimation in a multipath Rice and Rayleigh fading scenario, conditioned to the previous estimation of a set of propagation channels, since these channel estimates (correlation between received signal and the pilot sequence) are sufficient statistics in the estimation of delays. Furthermore, channel estimation is a constitutive block in receivers, so we can take advantage of this information to improve timing estimation by using time and space diversity. The received signal is modeled as coming from a scattering environment that disperses the signal both in space and time. Spatial scattering is modeled with a Gaussian distribution and temporal dispersion as an exponential random variable. The impact of the sampling rate, the roll-off factor, the spatial and temporal correlation among channel estimates, the number of channel estimates, and the use of multiple sensors in the antenna at the receiver is studied and related to the mobile subscriber positioning issue. To our knowledge, this model is the only one of its kind as a result of the relationship between the space-time diversity and the accuracy of the timing estimation.Peer ReviewedPostprint (published version
Maximum likelihood estimation of position in GNSS
In this letter, we obtain the Maximum Likelihood
Estimator of position in the framework of Global Navigation
Satellite Systems. This theoretical result is the basis of a completely
different approach to the positioning problem, in contrast
to the conventional two-steps position estimation, consisting
of estimating the synchronization parameters of the in-view
satellites and then performing a position estimation with that
information. To the authors’ knowledge, this is a novel approach
which copes with signal fading and it mitigates multipath and
jamming interferences. Besides, the concept of Position–based
Synchronization is introduced, which states that synchronization
parameters can be recovered from a user position estimation. We
provide computer simulation results showing the robustness of
the proposed approach in fading multipath channels. The Root
Mean Square Error performance of the proposed algorithm is
compared to those achieved with state-of-the-art synchronization
techniques. A Sequential Monte–Carlo based method is used to
deal with the multivariate optimization problem resulting from
the ML solution in an iterative way.Peer Reviewe
Review on Sparse-Based Multipath Estimation and Mitigation: Intense Solution to Counteract the Effects in Software GPS Receivers
Multipath is the major concern in GPS receivers that fade the actual GPS signal causes positioning error up to 10 m so special care need to be taken to mitigate the multipath effects. Numerous methods like hardware based antenna arrays technique, receiver based narrow correlator receiver, double -delta discriminator, Adaptive Multipath Estimator, Wavelet Transformation and Particle filter, Kalman filter based post receiver methods etc. used to resolve the problem. But some of the methods can only reduce code multipath error but not effective in eliminating carrier multipath error. Most of these techniques are based on the assumption that the Line-of-Sight (LOS) signal is stronger than the Non-Line of-Sight (NLOS) signals. However, in the scenarios where the LOS signal is weaker than the composite multipath signal, this approach may result in a bias in code tracking. In this chapter, different types of multipath mitigation and its limitation are described. The recent development in sparse signal processing based blind channel estimation is investigated to compensate the multipath error. The Rayleigh and Rician fading model with different multipath parameters are simulated to test the urban scenario. The inverse problem of finding the GPS signal is addressed based on the deconvolution approach. To solve linear inverse problems, the suitable kind of appropriate objective function has been formulated to find the signal of interest. By exploiting this methods, the signal is observed and the carrier and code tracking loop parameters are computed with minimal error
Collective unambiguous positioning with high-order BOC signals
© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The unambiguous estimation of high-order BOC signals in harsh propagation conditions is still an open problem in the literature. This paper proposes to overcome the limitations observed in state-of-the-art unambiguous estimation techniques based on the application of existing direct positioning techniques and the exploitation of the spatial diversity introduced by arrays of antennas. In particular, the ambiguity problem is solved as a multiple-input multiple-output (MIMO) estimation problem in the position domain.Peer ReviewedPostprint (author's final draft
Use of Navigation Beacons to Support Lunar Vehicle Operations
To support a wide variety of lunar missions in a condensed regime, solutions are needed outside of the use of Earth-based orbit determination. This research presents an alternate approach to in-situ navigation through the use of beacons, similar to that used on Earth as well as under technology development efforts. An overview of the current state of navigation aids included as well as discussion of the Lunar Node 1 payload being built at NASA/Marshall Space Flight Center. Expected navigation results of this beacon payload for planned operation from the lunar surface are provided. Applications of navigation beacons to multiple stages of the proposed human lunar landing architecture are given, with initial analysis showing performance gains from the use of this technology. This work provides a starting point for continued analysis and design, laying out the foundation of how navigation beacons can be incorporated into the architecture to enable continued analysis, design, and future expanded capability
Radio Frequency Interference Impact Assessment on Global Navigation Satellite Systems
The Institute for the Protection and Security of the Citizen of the EC Joint Research Centre (IPSC-JRC) has been mandated to perform a study on the Radio Frequency (RF) threat against telecommunications and ICT control systems. This study is divided into two parts. The rst part concerns the assessment of high energy radio frequency (HERF) threats, where the focus is on the generation of electromagnetic pulses (EMP), the development of corresponding devices and the possible impact on ICT and power distribution systems. The second part of the study concerns radio frequency interference (RFI) with regard to global navigation satellite systems (GNSS). This document contributes to the second part and contains a detailed literature study disclosing the weaknesses of GNSS systems. Whereas the HERF analysis only concerns intentional interference issues, this study on GNSS also takes into account unintentional interference, enlarging the spectrum of plausible interference scenarios.JRC.DG.G.6-Security technology assessmen
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