Publications

This paper establishes a fundamental theory of secure clock synchronization. Accurate clock synchronization is the backbone of systems managing power distribution, financial transactions, telecommunication operations, database services, etc. Some clock synchronization (time transfer) systems, such as the Global Navigation Satellite Systems (GNSS), are based on one-way communication from a master to a slave clock. Others, such as the Network Transport Protocol (NTP), and the IEEE 1588 Precision Time Protocol (PTP), involve two-way communication between the master and slave. This paper shows that all one-way time transfer protocols are vulnerable to replay attacks that can potentially compromise timing information. A set of conditions for secure two-way clock synchronization is proposed and proved to be necessary and sufficient. It is shown that IEEE 1588 PTP, although a two-way synchronization protocol, is not compliant with these conditions, and is therefore insecure. Requirements for secure IEEE 1588 PTP are proposed, and a second example protocol is offered to illustrate the range of compliant systems.

Cite and download the paper:
Lakshay Narula and Todd E. Humphreys, "Requirements for Secure Clock Synchronization," October 2017 preprint of paper submitted for review.

 

Dr. Humphreys presented at an Institute of Navigation conference between September 27th - 29th, 2017.

Download the slides (pptx).

Dr. Humphreys presented at an Institute of Navigation conference between September 27th - 29th, 2017.

Download the slides (pptx).

Dr. Humphreys presented at an Institute of Navigation conference between September 27th - 29th, 2017.

Download the slides (pptx).

This paper investigates the effectiveness of multipath-decorrelating antenna motion in reducing the initialization time of Global Navigation Satellite System (GNSS) receivers employing low-cost single-frequency antennas for carrier-phase differential GNSS (CDGNSS) positioning. Fast initialization times with low-cost antennas will encourage the expansion of CDGNSS into the mass market, bringing the benefits of globally-referenced centimeter-accurate positioning to many consumer applications, such as augmented reality and autonomous vehicles, that have so far been hampered by the several-meter-level errors of traditional GNSS positioning. Poor multipath suppression common to low-cost antennas results in large and strongly time-correlated phase errors when a receiver is static. Such errors can result in the CDGNSS initialization time, the so-called time to ambiguity resolution (TAR), extending to hundreds of seconds—many times longer than for higher- cost survey-grade antennas, which have substantially better multipath suppression. This paper demonstrates that TAR can be significantly reduced through gentle wavelength-scale random antenna motion. Such motion acts to decrease the correlation time of the multipath-induced phase errors. A priori knowledge of the motion profile is shown to further reduce TAR, with the reduction more pronounced as the initialization scenario is more challenging.

Cite and download the paper:
K. M. Pesyna, Jr., T. Novlan, C. Zhang, R. W. Heath, Jr., and T. E. Humphreys, "Exploiting antenna motion for faster initialization of centimeter-accurate GNSS positioning with low-cost antennas," IEEE Transactions on Aerospace and Electronic Systems, vol. 3, Aug. 2017

 

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