The Importance of being resilient: Challenges with GNSS in COVID-19 times

John Fischer is a leading industry authority in PNT and GNSS technologies, and serves as the VP of Advanced R&D for Orolia, the world leader in Resilient PN

If we have learned anything from the pandemic of 2020, it is that we can take nothing for granted. Global commerce, social interactions, events both public and private, and our collective health all came into question and were disrupted. Few had mitigation plans for this rare but inevitable event, and even those who did endured hardships in some ways. Each country and community experienced it in its own unique way, but we all experienced it collectively as one world. We have all become more resilient, and similarly, Resilient PNT continues to evolve. At Orolia, we were fortunate that, as a global company, we were already well setup for teleconferencing and working remotely. As a provider of critical infrastructure and defense solutions, our customers still needed our systems, and we were fortunate to be in a position to deliver without interruption.

So, we look back on the year in gratitude, for the measures taken to address the crisis and for the progress made in the PNT industry despite the crisis. This was a year for Science. As we write this, multiple COVID vaccines are being distributed to millions daily, after being formulated and tested in an astounding record time. This represents a major milestone in our understandings of both the human genome and that of all living organisms. History may record this time as one of the pillars upon which the mass extinction of our species was prevented, along with long term solutions to battle climate change, and a fuller understanding of space through exploration.

Regarding space exploration, we made a quantum leap in the practicality of moving mass beyond the restrictive atmosphere and into orbit. The cost of launching a satellite is less than one tenth of what it was just a few years ago, and the miniaturization of satellites (cubesats or nanosats) allows for launching dozens at a time in a single payload. A record number of satellites were launched with a particular emphasis on Low Earth Orbit (LEO) for communications networks. Most GNSS satellites are in Mid Earth Orbit (MEO), approximately 20,000 km above the earth, where LEO orbits are approximately 1,000 km or less. This closer proximity gives them the advantage of much stronger signals at the earth’s surface. Even though these new constellations are primarily for communications, since they are using wideband channels, it is easy to add a precise time feature to them and therefore use them for a PNT purpose too, as an alternative or to augment GNSS. So why weren’t the original GNSS satellites placed in LEO orbit? Because at MEO a single satellite covers the entire earth whereas at LEO it only covers a small patch. So, you need hundreds of LEO satellites to do the same job as a couple of dozen MEO satellites. However, this will no longer be a problem as LEO constellations with several hundreds and even thousands of satellites are being planned. The next few years will see a major augmentation of GNSS with LEO PNT.

This is not to say that GNSS has no future. All the major constellations are nearly fully populated now and are close to full operation. Galileo (European Union) and Beidou (China) are nearing completion of their constellations with the launch of just a few more satellites. India’s NavIC regional system is fully populated with seven satellites as is Japan’s QZSS with four. Both the USA’s GPS and Russia’s GLONASS constellations are undergoing a refresh with the launches of their GPS III and GLONASS K CDMA respective satellites. Accuracies continue to improve with meter level precision as the norm and the centimeter level obtained via RTK and PPP. So far, the Galileo constellation is proving to be the most accurate of all, with the precision of the most stable spacebased atomic clocks in their satellites. The political strain among various countries over the past year has not been manifested in the GNSS community, as all of these nations continue to cooperate and work towards interoperability. Multi- Frequency, Multi-Constellation (MFMC) receivers are commercially available today because of all these countries worked hard to devise innovative ways for their signals to share spectrum together. We hope this cooperation continues.

Back on earth, PNT progress is also being made. In the USA, an Executive Order was issued in February 2020 for federal agencies to establish guidelines and recommendations for Resilient PNT for all critical infrastructure in the nation. Orolia participated in this initiative, and one of the outcomes was to establish a uniform framework for defining PNT systems and their levels of resiliency. This important definition will avoid confusion and give clarity to both vendors and customers alike. Other nations are making progress establishing national precise timing infrastructures – for example, in both the UK and India the National Physics Laboratories are creating networks to distribute precise time throughout the country, sourced from stable atomic clocks.

2020 also brought us a breakthrough milestone in secure networking time with the release of RFC 8915, Network Time Security. For years, attempts to provide reliable, effective, but practical authentication for time distribution went unfulfilled until this specification established a sound algorithm. We expect this standard to be widely accepted for NTP and work is underway now for adaptations so it can be used for PTP. This release was preceded by two other major precise time networking specifications published in late 2019: IEEE 1588-2019 v3 and RFC 8633 NTP Best Current Practices. With these three specifications, we now have a solid foundation to build ubiquitous precise timing networks for use by all.

Another advancement in the timing world was the proliferation of PTP High Accuracy or what is known as White Rabbit technology. Formerly just a niche technology mostly used in scientific applications like the CERN Hadron Collider, this method of combining synchronous Ethernet with PTP timing is gaining mainstream acceptance to provide nanosecond and even subnanosecond accuracy across LANs.

Atomic clock technology took a quantum leap forward in 2020 with the next generation Mini Rubidium. Packaged as a standard OCXO component, it consumes much less power than a typical OCXO but with over one hundred times the stability; and over ten times the stability of the first generation of chip scale atomic clocks.

In aviation, the growth of Unmanned Airborne Vehicles (UAVs) continued unabated, increasing demand for accurate and reliable PNT in small Size, Weight and Power (SWAP) packages. The combination of GNSS and other signals of opportunity for navigation, with the continued advances of Inertial Measurement Unit (IMU) technology has brought precise PNT to mission payloads for exceptional performance in Intelligence, Surveillance and Reconnaissance (ISR) applications.

Another milestone this year in aviation was the first successful flight test of a Search and Rescue (SAR) Emergency Locator Transmitter with Distressed Tracking capability (ELT-DT). As a result of the loss of flight MH370 several years ago, the industry has decided to expand the capability of the ELT beacon onboard every aircraft to transmit not only when a crash has occurred, but also when it is in distress so it may be located and rescue actions initiated during the flight. There is no doubt this initiative will save more lives in the future.

Awareness of the vulnerabilities of GNSS’ weak signal to easy jamming along with the fact that its open, unencrypted signal standards are susceptible to spoofing has led to increased vulnerability testing of all critical GNSS systems. As the threats become more sophisticated, the defenses must be too. However, before any defensive measure can be devised, one first needs to evaluate the weak points in the system. This is where advanced GNSS simulation test equipment comes in, and advances in the capability and affordability of these simulators, especially softwarebased ones, were significant in 2020.

On the frontline of defense for Interference Detection and Mitigation (IDM) are CRPA antennas. Controlled Radiation Pattern Antennas will steer the GNSS receiver’s antenna beams to track the satellite signals and away from the interference sources. 2020 saw advances in the affordability and practicality of these devices, which previously had only been used in high-end, expensive military applications. New GNSS receivers with narrowband interference cancellers became more common this year, with software features which at least detect and warn of GNSS jamming and spoofing so a user can avoid using a corrupted PVT solution and instead use alternative navigation means.

Another outcome last year from the growing awareness of GNSS vulnerabilities was the recognition that no one solution will be the “magic bullet” to address the challenge. It will take a combination of several alternative techniques, so towards this end, the Open PNT Industry Alliance (www.openpnt.org) was established to strengthen economic and national security by supporting government efforts to accelerate the implementation of backup PNT capabilities for critical infrastructure. This alliance is expected to focus the collective ingenuity of the PNT industry to help create technologically advanced, commercially viable and sustainable long-term solutions for resilient PNT.

One of the many sources for alternative PNT will be the 5G network. Release 16 was finalized in 2020 and it established performance goals for more accurate PNT from its signals, taking the first steps towards accuracy which could rival our current GNSS meter-level performance. Look for further evolutions in the coming years. We can also expect growing resilience in PNT coming from Machine Learning and Artificial Intelligence (ML/ AI) techniques. As processing power, memory size and network connectivity bandwidth continue to grow and become cheaper and more ubiquitous, we can expect to see AI in our mobile systems in a few years. One area showing promise is crowd-sourced positioning: a mobile user can infer its position based on incomplete information from many other nodes on its network, many of which know their positions to varying degrees of accuracy. There are still many possibilities for PNT advancement in the near future.

Though most of us are glad 2020 has now passed, we did learn (or re-learn) many important things. We learned that paying attention to boring, mundane essentials like wearing a mask to stay healthy and washing hands to prevent the spread of the virus can make a huge difference in our survival. We learned not to take important things for granted – our family, our friends, our health. We also learned the importance of being resilient – in our societies and in the global economy, by being prepared for disruptions, adapting to changes and taking preventative measures. These were lessons in both life and in the world of PNT.