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RESILIENT TIMING IS KEY

  • Published
  • DAF T3

Dr. Khanh D. Pham, a Supervisory Principal Aerospace Engineer at the Air Force Research Laboratory (AFRL), has been making waves in the satellite communication (SATCOM) industry with his groundbreaking patents. These patents focus on improving satellite communication network management architectures and integrating hybrid terrestrial and SATCOM solutions. Dr. Pham's research is a game-changer for the future of SATCOM and has the potential to revolutionize the industry.

As the matter of fact, timekeeping is an important capability required of any local SATCOM systems that expect to achieve and maintain high rates of data transmission. Acquiring reliable local reference time for extended periods when Positioning, Navigation, and Timing (PNT) services expected from Global Navigation Satellite Systems (GNSS) are denied, especially over a broad area is of concern. Back in 2019, Dr. Pham explored the concept of attaining an advantage in delivering and sharing local reference time in operationally degraded environments through network connectivity and friendly collaboration with advantage assets. One of necessary parts of this basic science discovery was the ability of the assets to reach out and share their timing references with disadvantage assets operating within degraded environments.

Dr. Pham's first patent, "Systems and Methods of Resilient Clock Synchronization in Presence of Faults (US Patent #11,509,451)," tackles the challenge of resilient clock synchronization when faults occur. It introduces a new approach which entails a hierarchical, open architecture and processes providing network aided multi-way time transfer for asynchronous time synchronization between at least one reference clock and its radio frequency (RF) subnetwork of neighboring clocks. A reference clock performs its resilient clock steering operation to its RF subnetwork of neighboring clocks that is enabled by random transmit and receive selection, iterative power control, and guaranteed synchronization link closures. Upon receiving the time-sharing signal from the reference clocks, the neighboring clocks obtain their local situation awareness of reference time phases of respective disagreements for time synchronization errors and convergent rates. Self-direct and autonomy at the neighboring clocks are capable of dynamic adjustments of clocks based on cluster phase offsets between the reference and its neighboring clocks via a pursuit-evasion graphical game, thereby synchronizing time between the reference clock and its subnetwork of neighboring clocks.

It introduces an innovative method to create clock steering protocols for resilient timekeeping systems. These systems are resistant to inaccurate timing signals sent to remote time distribution networks, ensuring accurate and reliable timing even when facing faults and disruptions. This invention promises a future with dependable timing signals, regardless of potential issues.

For example, let’s say that a car's time is incorrect and the driver needs help figuring out the correct time. They signal for help and another person responds with the unified time. Both clocks are now synchronized. How does the driver know that the information that was received is correct? What if the person sending the information is an adversary?

The patent's algorithm can detect and decide whether the data from a neighbor should be accepted or not, helping to refine the data and determine the intent of the person providing the information. This feature allows for control over the help received from external sources, making it relevant to social sciences.

Then Dr. Pham went on to further realize that there was a need for multi-domain collaborative navigation between manned/unmanned platforms and warfighters. He therefore led a national innovative ecosystem consisted of AFRL, Navy and high-tech small business - Intelligent Fusion Technology, Inc. where a much-needed framework of enhanced two-way time transfer (TWTT) was developed to achieve high-precision, e.g., ~100 pico-seconds, time synchronization of multiple distributed radio frequency sources located on UASs in a GPS-denied environment. The proposed Enhanced Multi-Way Time Transfer relaxes two conditions of traditional TWTT: (i) The time at which the time-based signal is transmitted is the same for both Transmit and Receive sides, and (ii) Propagation delay of the time signal must be the same in both directions. In-lab simulation and demonstration results were obtained for the use case where an unmanned aerial system (UAS) with access to GNSS signals or simply high-quality reference time was able to share that local timescale over tactical data links to improve timing assurance for disadvantage platforms in contested environments. His vision for future high precision time synchronization among UASs options led to the second patent, “Methods and Systems for Time Synchronization Among Unmanned Aerial Systems”.

Dr. Pham's contributions to resilient time transfer and synchronization requirements, research successes and, engineering challenges have created a valuable platform for idea exchanges and future opportunities for the timing and synchronization industry. His vision and leadership have helped small businesses, academia, and government program offices collaborate on developing resilient PNT enterprise for agile operations in the Space Development Agency and US Space Force warfighters.

By translating technical requirements and findings into small business opportunities, Dr. Pham aims to further develop and mature the concept, creating a technology incubator. With the help of America’s Seed Funds, the technology can mature and potentially be deployed in the field, providing a valuable resource for the DoD.