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179 results on '"Lo, Sherman"'

1. Time Synchronization of TESLA-enabled GNSS Receivers

Author

Anderson, Jason, Lo, Sherman, and Walter, Todd

Subjects
Computer Science - Cryptography and Security
Abstract

As TESLA-enabled GNSS for authenticated positioning reaches ubiquity, receivers must use an onboard, GNSS-independent clock and carefully constructed time synchronization algorithms to assert the authenticity afforded. This work provides the necessary checks and synchronization protocols needed in the broadcast-only GNSS context. We provide proof of security for each of our algorithms under a delay-capable adversary. The algorithms included herein enable a GNSS receiver to use its onboard, GNSS-independent clock to determine whether a message arrived at the correct time, to determine whether its onboard, GNSS-independent clock is safe to use and when the clock will no longer be safe in the future due to predicted clock drift, and to resynchronize its onboard, GNSS-independent clock. Each algorithm is safe to use even when an adversary induces delays within the protocol. Moreover, we discuss the implications of GNSS authentication schemes that use two simultaneous TESLA instances of different authentication cadences. To a receiver implementer or standards author, this work provides the necessary implementation algorithms to assert security and provides a comprehensive guide on why these methods are required., Comment: 16 pages, 15 figures

Published
2024

2. High-resolution Probabilistic Precipitation Prediction for use in Climate Simulations

Author

Lo, Sherman, Watson, Peter, Dueben, Peter, and Dutta, Ritabrata

Subjects
Statistics - Computation, Statistics - Applications
Abstract

The accurate prediction of precipitation is important to allow for reliable warnings of flood or drought risk in a changing climate. However, to make trust-worthy predictions of precipitation, at a local scale, is one of the most difficult challenges for today's weather and climate models. This is because important features, such as individual clouds and high-resolution topography, cannot be resolved explicitly within simulations due to the significant computational cost of high-resolution simulations. Climate models are typically run at $\sim$50-100 km resolution which is insufficient to represent local precipitation events in satisfying detail. Here, we develop a method to make probabilistic precipitation predictions based on features that climate models can resolve well and that is not highly sensitive to the approximations used in individual models. To predict, we will use a temporal compound Poisson distribution dependent on the output of climate models at a location. We use the output of Earth System models at coarse resolution $\sim$50 km as input and train the statistical models towards precipitation observations over Wales at $\sim$10 km resolution. A Bayesian inferential scheme is provided so that the compound-Poisson model can be inferred using a Gibbs-within-Metropolis-Elliptic-Slice sampling scheme which enables us to quantify the uncertainty of our predictions. In addition, we use a Gaussian process regressor on the posterior samples of the model parameters, to infer a spatially coherent model and hence to produce spatially coherent rainfall prediction. We illustrate the prediction performance of our model by training over 5 years of the data up to 31st December 1999 and predicting precipitation for 20 years afterwards for Cardiff and Wales.

Published
2020

3. Characterisation of computed tomography noise in projection space with applications to additive manufacturing

Author

Lo, Sherman Edea

Subjects
670, QA Mathematics, TS Manufactures
Abstract

X-ray computed tomography can be used for defect detection in additive manufacturing. Typically, several x-ray projections of the product at hundreds of angles are used to reconstruct the object in 3D to look for any defects. The process can be time-consuming. This thesis aims to investigate if it is possible to conduct defect detection from a single projection to speed up the process. An additive manufacturing test sample was created with voids to see if they can be detected. The uncertainty of the projection was modelled using a compound Poisson distribution. This arises from x-ray photon arrivals being a Poisson process and each photon has random energy. This results in a linear relationship between the mean and variance of the grey values in the projection. Fitting of the compound Poisson distribution using the expectation maximisation algorithm was unsuccessful due to identifiability issues with the model. Instead, a gamma-distributed generalised linear model was fitted onto sample variance-mean data and used for variance prediction to quantify the uncertainty. Software, called aRTist, was used to simulate the projection and compared with the experimental projection in the face of uncertainty by treating each pixel as a hypothesis test. To overcome the imperfections of the simulation, the empirical null filter was used to cater for model misspecification so that sensible inference was achieved. This was done by locally normalising the test statistics using the mode. Voids with diameters in the order of millimetres were detectable. This thesis is a contribution to real-time quality control in additive manufacturing.

Published
2020

6. MONITORING GNSS INTERFERENCE AND SPOOFING: A Low-Cost Approach

Author

Taleghani, Leila, Rothmaier, Fabian, Chen, Yu-Hsuan, Lo, Sherman, Walter, Todd, Akos, Dennis, and Gattis, Benon Granite

Subjects
Communications equipment, Cellular transmission equipment, Telecommunications equipment, Business, Telecommunications industry, University of Colorado, Stanford University
Abstract

GNSS signals are extremely low power by the time they reach users on Earth and are easily overwhelmed by nearby terrestrial signals. Such signals can interfere with a user's ability [...]

Published
2022

11. Authentication of Satellite-Based Augmentation Systems with Over-the-Air Rekeying Schemes.

Author

Anderson, Jason, Lo, Sherman, Neish, Andrew, and Walter, Todd

Subjects
*DIGITAL signatures, *ELLIPTIC curves
Abstract

Here we delineate a complete satellite-based augmentation system (SBAS) authentication scheme, including over-the-air rekeying (OTAR), that uses the elliptic curve digital signature algorithm (ECDSA) and timed efficient stream loss-tolerant authentication (TESLA) without the quadrature (Q) channel. This scheme appends two new message types to the SBAS scheduler without overburdening the message schedule. We have taken special care to ensure that our scheme (1) meets the appropriate security requirements needed to prevent and deter spoofing; (2) is compatible with existing cryptographic standards; (3) is flexible, expandable, and future-proof to different cryptographic and implementation schemes; and (4) is backward compatible with legacy receivers. The scheme accommodates a diverse set of features, including authenticating core-constellation ephemerides. We discuss the SBAS provider and receiver machine state and its startup, including its use by aircraft that traverse differing SBAS coverage areas. We tested our scheme with existing SBAS simulation and analysis tools and found that it had negligible effects on current SBAS availability and continuity requirements. [ABSTRACT FROM AUTHOR]

Published
2023
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18. poLCAParallel

Author

Lo, Sherman

Abstract

The library poLCAParallel reimplements poLCA and its bootstrap log-likelihood ratio test in C++. This was done using Rcpp and RcppArmadillo which allows C++ code to interact with R. Additional notes include: - The code uses Armadillo for linear algebra - Multiple repetitions are done in parallel using for multi-thread programming and to prevent data races - Response probabilities are reordered to increase cache efficiency - Use of std::map for the chi-squared calculations

Published
2023
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25. Secure Location Verification : A Security Analysis of GPS Signal Authentication

Author

Becker, Georg T., Lo, Sherman C., De Lorenzo, David S., Enge, Per K., Paar, Christof, Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Doug, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, Foresti, Sara, editor, and Jajodia, Sushil, editor

Published
2010
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32. Antenna pilots UAV

Author

Perkins, Adrien, Dressel, Louis, Lo, Sherman, and Enge, Per

Subjects
Drone aircraft, Vehicles, Remotely piloted, Antennas (Electronics), Business, Telecommunications industry
Abstract

A JAMMER-HUNTING UAV employs a radio frequency (RF) detection system and a navigation control scheme. The RF detection component uses a directional antenna and the unmanned aerial vehicle's (UAV's) ability [...]

Published
2016

41. Jammer hunting with a UAV

Author

Spicer, James, Perkins, Adrien, Dressel, Louis, James, Mark, Chen, Yu-Hsuan, Lo, Sherman, De Lorenzo, David S., and Enge, Per

Subjects
Drone aircraft, Vehicles, Remotely piloted, Hunting, Business, Telecommunications industry
Abstract

A fully autonomous, unmanned aerial vehicle (UAV)-based system for locating GPS jammers, currently under development, seeks to localize a jammer to within 30 meters in less than 15 minutes in [...]

Published
2015

50. Loran data modulation: extensions and examples

Author

Lo, Sherman C., Peterson, Benjamin B., Enge, Per K., and Swaszek, Peter

Subjects
Electronic data processing -- Methods, Modulation (Electronics) -- Methods, Loran -- Design and construction, Aerospace and defense industries, Business, Computers, Electronics, Electronics and electrical industries
Abstract

Loran has provided navigation service since 1958. Though not originally designed with data broadcast capabilities, Loran's versatility has enabled data to be broadcast with great benefits. Research in the last two decades has resulted in a tremendous increase in the data capacity of Loran thereby increasing its utility. Currently, a modernized Loran is being evaluated for its capability to backup GPS and data modulation is an integral part of this Loran design. This paper details some recent Loran modulation designs and ideas.

Published
2007

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