3,854 research outputs found
Privacy in Inter-Vehicular Networks: Why simple pseudonym change is not enough
Inter-vehicle communication (IVC) systems disclose rich location information about vehicles. State-of-the-art security architectures are aware of the problem and provide privacy enhancing mechanisms, notably pseudonymous authentication. However, the granularity and the amount of location information IVC protocols divulge, enable an adversary that eavesdrops all traffic throughout an area, to reconstruct long traces of the whereabouts of the majority of vehicles within the same area. Our analysis in this paper confirms the existence of this kind of threat. As a result, it is questionable if strong location privacy is achievable in IVC systems against a powerful adversary.\u
GPS Carrier Tracking Loop Performance in the presence of Ionospheric Scintillations
The performance of several GPS carrier tracking loops
is evaluated using wideband GPS data recorded during
strong ionospheric scintillations. The aim of this study is
to determine the loop structures and parameters that enable
good phase tracking during the power fades and phase
dynamics induced by scintillations. Constant-bandwidth
and variable-bandwidth loops are studied using theoretical
models, simulation, and tests with actual GPS signals.
Constant-bandwidth loops with loop bandwidths near 15
Hz are shown to lose phase lock during scintillations. Use
of the decision-directed discriminator reduces the carrier
lock threshold by ∼1 dB relative to the arctangent and conventional Costas discriminators. A proposed variablebandwidth
loop based on a Kalman filter reduces the carrier
lock threshold by more than 7 dB compared to a 15-Hz
constant-bandwidth loop. The Kalman filter-based strategy
employs a soft-decision discriminator, explicitly models
the effects of receiver clock noise, and optimally adapts
the loop bandwidth to the carrier-to-noise ratio. In extensive
simulation and in tests using actual wideband GPS
data, the Kalman filter PLL demonstrates improved cycle
slip immunity relative to constant bandwidth PLLs.Aerospace Engineering and Engineering Mechanic
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Review of Unbiased FIR Filters, Smoothers, and Predictors for Polynomial Signals
Extracting an estimate of a slowly varying signal corrupted by noise is a common task. Examples can be found in industrial, scientific and biomedical instrumentation. Depending on the nature of the application the signal estimate is allowed to be a delayed estimate of the original signal or, in the other extreme, no delay is tolerated. These cases are commonly referred to as filtering, prediction, and smoothing depending on the amount of advance or lag between the input data set and the output data set. In this review paper we provide a comprehensive set of design and analysis tools for designing unbiased FIR filters, predictors, and smoothers for slowly varying signals, i.e. signals that can be modeled by low order polynomials. Explicit expressions of parameters needed in practical implementations are given. Real life examples are provided including cases where the method is extended to signals that are piecewise slowly varying. A critical view on recursive implementations of the algorithms is provided
Robust Gaussian Filtering using a Pseudo Measurement
Many sensors, such as range, sonar, radar, GPS and visual devices, produce
measurements which are contaminated by outliers. This problem can be addressed
by using fat-tailed sensor models, which account for the possibility of
outliers. Unfortunately, all estimation algorithms belonging to the family of
Gaussian filters (such as the widely-used extended Kalman filter and unscented
Kalman filter) are inherently incompatible with such fat-tailed sensor models.
The contribution of this paper is to show that any Gaussian filter can be made
compatible with fat-tailed sensor models by applying one simple change: Instead
of filtering with the physical measurement, we propose to filter with a pseudo
measurement obtained by applying a feature function to the physical
measurement. We derive such a feature function which is optimal under some
conditions. Simulation results show that the proposed method can effectively
handle measurement outliers and allows for robust filtering in both linear and
nonlinear systems
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