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375 results on '"WALTER, TODD"'

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

5. 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

10. IONOSPHERIC CORRECTIONS FOR PRECISE POINT POSITIONING: How Good Are They?

Author

Langley, Richard B., Walter, Todd, Blanch, Juan, De Groot, Lance, and Norman, Laura

Subjects
Ionosphere, Business, Telecommunications industry, Stanford University, Glonass (Artificial satellite)
Abstract

Hexagon is investigating the utility of applying ionospheric corrections to decrease the overall convergence time of the precise point positioning (PPP) filter. Stanford University has conducted several analyses on the [...]

Published
2021

12. IMPROVING ARAIM: An Approach Using Precise Point Positioning

Author

Phelts, R. Eric, Gunning, Kazuma, Blanch, Juan, and Walter, Todd

Subjects
Telecommunications equipment, Software, Cellular transmission equipment, Software quality, Telecommunications equipment, Business, Telecommunications industry, Stanford University
Abstract

Advanced Receiver Autonomous Integrity Monitoring (ARAIM) is implemented using solution separation in positioning and navigation software. Solution separation computations presume one or more GNSS satellites may be faulty, and they [...]

Published
2020

13. Self-Predictions and Depressive Realism in Future Life Events.

Author

Walter, Todd J.

Abstract

Research has demonstrated that depressed people lack the optimistic bias evidenced by nondepressed persons and that the former may be more realistic in predicting the outcome of future events (depressive realism hypothesis). This study assesses the depressive realism hypothesis by comparing the accuracy of depressed and nondepressed people's self-predictions of a series of life events. One hundred college students (75 females) answered the Beck Depression Inventory and then made self-predictions about a series of future life events. Results indicate that depressed persons made significantly more pessimistic predictions than nondepressed subjects. Depressed persons were more accurate than nondepressed ones for pessimistic judgments while the latter were more accurate on optimistic judgments. No mediating factors such as event controllability and base rate were found for prediction accuracy. One possible explanation for the finding that depressives are more accurate than nondepressed subject in predicting undesirable events is that nondepressed persons may be more apt to avoid undesirable outcomes whereas depressed individuals may not elude these. Included are two tables which summarize the data and a copy of the Life Events Questionnaire. (RJM)

Published
1993

14. Voice Identification: Levels-of-Processing and the Relationship between Prior Description Accuracy and Recognition Accuracy.

Author

Walter, Todd J.

Abstract

A study examined whether a person's ability to accurately identify a voice is influenced by factors similar to those proposed by the Supreme Court for eyewitness identification accuracy. In particular, the Supreme Court has suggested that a person's prior description accuracy of a suspect, degree of attention to a suspect, and confidence in identifying a suspect, are reliable predictors for accurately identifying a suspect. Subjects, 18 males and 42 females from an undergraduate psychology course or volunteers from the local community, listed to a voice and later described the voice on a speech characteristic checklist. Later they were asked to identify the voice from a lineup and denote how certain they were of their choice. Results indicated no relationship between voice description accuracy and identification accuracy, or between degree of confidence and identification accuracy. Moreover, depth of processing had no effect on description accuracy, identification accuracy, or the relationship between the two. Future "earwitness" research should: employ a voice lineup in which the target voice is either present or absent; use longer retention delay between target presentation and voice identification; and develop a valid descriptive measure. (Contains 21 references, 2 tables, and 1 figure of data. The voice description checklist is attached.) (RS)

Published
1992

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