2024 BEITC Update: ATSC 3.0 Broadcast Positioning Systems

Move over, WWV and GPS. New information about Broadcast Positioning Systems presented at BEITC 2024 provides insight into work on a crucial, common view OTA, highly precision, public time reference that ATSC 3.0 broadcasters can easily provide.

The following story summarizes five technical papers presented at the 2024 NAB Show BEITC sessions most relevant to BPS. All credit for the information and graphics belongs to NAB.

The “ATSC 3.0 Broadcast Positioning System (BPS) Seminar Outcomes – Humber College B²C Lab, Toronto, Canada” paper reported on a one-day conference which took place in Toronto, Canada in November 2023. The conference theme was the Broadcast Positioning System (BPS), proposed by the broadcasting community as an alternative to GPS in the event GPS service is lost.

One speaker was Patrick Diamond, Ph. D. who is with Diamond Consulting in Ayer MA, and a member of NASA Space Based Position Navigation & Timing Advisory Board. In his BEIT session Diamond outlined how BPS-enabled ATSC 3.0 TV stations can evolve into a self-synchronizing mesh network for position and timing signals at a minimal cost. Diamond first introduced BPS in a 2023 BEITC paper. NAB CTO Sam Matheny also spoke about collaborative support behind BPS.

“Transmitting Time and Frequency Data by Using Broadcast TV Signals Observed in Common-View” was presented by Judah Levine with the Time and Frequency Division National Institute of Standards and Technology, and Christine Hackman, Advanced Space PNT Branch of the Naval Research Laboratory. The presentation was a study of using "common broadcast TV signals" at two sites receiving the same signal from the same transmitter.

The Time and Frequency Division of the National Institute of Standards and Technology (NIST) maintains a primary ensemble of atomic clocks at the NIST laboratories in Boulder, Colorado, and secondary clock ensembles at NIST in Gaithersburg, Maryland and at the NIST radio stations WWV and WWVB near Fort Collins, Colorado. The clocks in the ensembles are cesium frequency standards and hydrogen masers. The UTC(NIST) time scale is kept within ±3 ns of Coordinated Universal Time (UTC) computed by the International Bureau of Weights and Measures (BIPM) in Paris. The secondary ensembles are kept within ±15 ns of the primary clock ensemble by frequency adjustments as needed, typically every few weeks.

The geometrical path delay over a 30 km path in a vacuum is 90 µs, so that a time service designed to provide microsecond-level accuracy over this distance must apply a correction to the received data of the order of 1% of the geometrical path delay. The study concluded that urban multipath and atmospheric refractivity can vary the theoretical delay.

“ATSC 3.0 Broadcast Positioning System (BPS) Mesh Network” was presented by Mark T. Corl with Triveni Digital, Vladimir Anishchenko with Avateq Corp., Francisco Girela Lopez with Safran Electronics and Defense, and Tariq Mondal with NAB.

Within the ATSC 3.0 preamble lie essential fields, including timestamps and a reference point marking the commencement of the bootstrap signal.

Within the ATSC 3.0 preamble lie essential fields, including timestamps and a reference point marking the commencement of the bootstrap signal.

The preamble of an ATSC 3.0 frame carries the bootstrap emission timestamp. If this timestamp is accurate, a receiver can synchronize its clock using the ATSC 3.0 signal. The ATSC 3.0 signal can carry data, and the location of the transmission antenna can be sent with the signal. Armed with the precise bootstrap emission time and the location of the antenna, a receiver at a known location can maintain a very accurate clock.

The prototype BPS Synchronizer system was described at NAB BEITC in 2023. The 2024 BEITC paper describes the Phase 2 BPS Synchronizer in great technical detail. The intention of the new design was:

  1. Meet the Phase II project technical requirements in full.
  2. Provide more flexibility for development, verification and debugging the synchronization chain and its components at all levels.
  3. Expose a set of standard interfaces for off-the-shelf available instrumental hardware - PCIe cards for additional NICs, PTP, I/O, Timing, GPS (if required).
  4. Deliver a versatile platform suitable for potential application related to the BPS and not limited to the time synchronization task

The takeaway from the session is that the Phase 2 BPS Synchronizer remains 100% compliant with the ATSC 3.0 standard. The paper concluded that an independent mesh network of ATSC 3.0 TV transmitters can be used to provide highly accurate, traceable time across multiple frequencies covering the continental United States.

“Leveraging Traditional GNSS Time Servers for Resiliency and Interoperability in Broadcast Positioning System (BPS)” was presented by Francisco Girela Lopez with Safran Electronics and Defense, Mark T. Corl with Triveni Digital, and Alexander Babakhanov with Avateq Corp.

In 2021, the U.S. Department of Transportation (USDOT) released the Complementary Positioning, Navigation, and Timing (CPNT) and GPS Backup Technologies Demonstration Final Report to Congress. Complementary Positioning Navigation and Timing (CPNT) technologies are becoming increasingly important as GNSS systems facing different vulnerabilities such as jamming, spoofing, and signal degradation. CPNT systems can strengthen, augment, and replace GNSS systems when needed and could be an interesting alternative to provide highly available systems on sovereign soil.

A PNT layered defense refers to a strategy that involves the use of multiple technologies and capabilities to ensure reliable and accurate PNT information in GNSS-challenged or denied environments.

A PNT layered defense refers to a strategy that involves the use of multiple technologies and capabilities to ensure reliable and accurate PNT information in GNSS-challenged or denied environments.

Traditional GNSS time servers support multi-GNSS synchronization including GPS, Galileo, GLONASS, BeiDou and QZSS, GPS jamming and spoofing detection options, a wide variety of available input/output signals and high bandwidth network synchronization protocols like NTP and IEEE1588 (PTP) Master/Slave over Ethernet. These features can be combined with Inter-Tower Synchronization in Broadcast Positioning Systems for resilient operation, interoperability with existing systems and for time measurement and accuracy monitoring while minimizing the time to market for deploying such systems. The synergy of ATSC 3.0 BPS technology with GNSS provides an additional level of resiliency and reliability for a national-wide PNT system.

“PNT and ZTA for Timing and Synchronization in Broadcast” by Rick Knea with Oscilloquartz SE. Knea’s paper evaluates the vulnerabilities inherent in existing time sources and explores potential solutions to safeguard critical infrastructure, such as Positioning, Navigation, and Timing (PNT), and Zero Trust architectures (ZTA). ZTA is becoming the base standard to guarantee the highest degree of security to modern computer networks.

The TV broadcast industry began using timestamps for editing videotape in the 1960s, before SMPTE standardized timecode. Today, TV stations rely on time stamps during content generation, processing, distribution, and building security, and that timing is often based on GPS. The recent development and use of small GPS jamming devices has had an impact on GPS. It is not illegal to possess a GPS jamming device, but it is illegal to use it.

GPS satellites orbit about 20,000 km above the earth’s surface. By the time the PNT signal arrives at a rooftop GPS antenna it is approximately -125 dBm, which is a very low signal level and very susceptible to jamming and spoofing.

GPS satellites orbit about 20,000 km above the earth’s surface. By the time the PNT signal arrives at a rooftop GPS antenna it is approximately -125 dBm, which is a very low signal level and very susceptible to jamming and spoofing.

On February 12, 2020, President Trump signed Federal Executive Order 13905. Its intent is to safeguard the national and economic security of the United States by addressing disruptions to PNT services, such as GPS jamming. Jamming can disrupt broadcast TV signal distribution, content acquisition, live event coverage, emergency alerts and advertising schedules. A resilient and assured PNT solution compliant with Executive Order 13905 consists of 3 main areas of remedial action:

  1. A single or multi-band antenna with an anti-jamming design provides the ability to process PNT signals from one or more GNSS constellations as well as decrease the potential of jamming.
  2. Hardware with the ability to process GPS/GNSS/LEO PNT signals is a start but processing multiple PTP inputs as well as Enhanced Primary Reference Timing Clock (ePRTC) and 1PPS timing signals provides the best resiliency and redundancy.
  3. Management software that provides centralized multi-technology control for the distribution and assurance of frequency, phase and time synchronization, as well as providing jamming and spoofing detection.

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