Analysis of the Galileo signal outage

By Fabio Dovis, A. Minetto, A. Nardin, Politecnico di Torino Department of Electronics and Telecommunications,
E. Falletti, D. Margaria, M. Nicola, M. Vannucchi, LINKS foundation

Following the issue by the Galileo Service Center of the Notice Advisory to Galileo Users (NAGU) reporting Service Outage for all the Galileo satellites, as curious Galileo users our team of researchers of the NavSAS group started an independent investigation of the received signals in space (SISs).

In fact, we observed that a commercial ublox EVK-M8T receiver, forced to use Galileo-only satellites, provided a “no-fix” indication. Three Galileo-enabled smartphones, the Xiaomi MI 8, Huawei P 10 and Samsung Galaxy S8, which use assistance from the cellular network, were also not providing a Galileo-based position solution, considering the Galileo satellites as “not usable.”

However, the investigation started exploiting our in-house developed software receiver NGene, that was used in the past for similar monitoring of the GNSS signals, for example at the time of the transmission of the first IOV Galileo satellites in 2012, and the transmission of anomalous GPS signals from SVN49 in 2009. Monitoring the Galileo SISs, which were usable until the day before, we found that they were still correctly trackable, with normal power levels and Doppler profiles within feasible limits.

At the time of the first analysis, seven satellites were visible in the sky over Torino, Italy. Figure 1 reports a screenshot of the positions computed by means of NGene between 07:14:54 and 07:24:54 UTC on July 15, plotted on Google Earth. The position estimated using the Galileo-only satellite or hybrid GPS-Galileo solutions (red dots) showed errors on the order of 500 meters or even more. The georeferenced antenna position is depicted by the green pin.

The monitoring of the status flags taken from the Galileo E1B I/NAV message showed that the SIS was marked as “healthy” for all the visible PRNs apart the number 14, which is known to be “not usable” for a long time. The Signal in Space Accuracy Index (SISA) was set to 109, which is an acceptable prediction of the minimum standard deviation of an overbound of the SIS error.

According to the Galileo Open Service, Service Definition Document (OS SDD, issued 1.1, May 2019), a SIS “Healthy” means that the SIS is expected to meet the Minimum Performance Level and “a navigation solution obtained with Galileo SIS is expected to meet the Minimum Performance Levels reported in the Galileo OS SDD only if receivers comply with the assumptions reported in Section 2.4, including the use of navigation parameters within their broadcast period.”

In fact, the document specifies that “The navigation solution is expected to meet the Minimum Performance Levels only if receivers do not use navigation parameters beyond their broadcast period. The maximum nominal broadcast period of a healthy navigation message data set is currently 4 hours.”

The check of the nominal broadcast period was bypassed in our software receiver, which is indented as a research tool and not a commercial product as the one mentioned above, so that we were still able to obtain a GPS + Galileo PVT solution, since this check looked to be the only discrimination factor to validate and thus exclude the computed solution.

On July 17, the SISA flag was changed to 255: according to the OS SDD, the accuracy status was “No Accuracy Prediction Available (NAPA).” This means that the status of the broadcast SIS must be intended as “Marginal.” In this condition the EVK-M8T restarted to provide Galileo-based fixes, while the Xiaomi Mi8 Pro smartphone still excluded the Galileo satellites from its PVT fix.

The analysis of the decoded Galileo navigation message led to the conclusion that ephemerides and clock correction data were last updated around 19:00 UTC of 1July 16. For example, PRN 3 and 15 changed Issue Of Data (IOD) from 958 to 17 at Galileo Signal Time TOW 241855, which corresponds to 19:01:25.

As a final check, we used external ephemerides to process the Galileo signals during the “system outage.” Figure 2 and Figure 3 show different navigation solutions obtained by processing a data collection taken on July 12 at 10.00 UTC (12.00 Local time). The purple dots indicate few fixes obtained by demodulating the navigation message transmitted by the Galileo satellites and show a remarkable bias with regard to the reference antenna location.

In Figure 3, the green dots are the navigation solution obtained correcting the satellites positions according to precise orbits data and clock drift provided by the IGS network. The fix is a simple code based Least Mean Square solution without smoothing of the pseudoranges.

The two results were obtained by processing the same satellites signals, thus proving that their quality was still sufficient to get an acceptable positioning solution during the Galileo service outage period. This brought us to the conclusion that, during the outage, only the ephemerides updates were affected by problems, while the other SIS components appeared sound and usable.

The NavSAS group is a joint team of researchers of Politecnico di Torino and LINKS Foundation. The full analysis of the outage can be found at www.navsas.eu.

About the Author: Allison Barwacz

Allison Barwacz is the digital media manager for North Coast Media (NCM). She completed her undergraduate degree at Ohio University where she received a Bachelor of Science in magazine journalism from the E.W. Scripps School of Journalism. She works across a number of digital platforms, which include creating e-newsletters, writing articles and posting across social media sites. She also creates content for NCM’s Pit & Quarry magazine, Portable Plants magazine and Geospatial Solutions. Her understanding of the ever-changing digital media world allows her to quickly grasp what a target audience desires and create content that is appealing and relevant for any client across any platform.

Esri’s Jesse Smith discusses how the U.S. Coast Guard’s International Ice Patrol is using Esri’s ArcGIS Enterprise platform to improve marine safety at the 2019 Esri User Conference in San Diego. Currently, the organization is using the platform to map, observe and track icebergs.

Jeremy Kirkendall, senior GIS administrator for NASA’s Disaster Program, gives GPS World an overview of the program at the 2019 Esri User Conference in San Diego. Watch this video to find out how satellite imagery produced by the program helps with disaster response efforts.

Galileo Initial Services have now been restored, according to a statement released on July 18 by the European GNSS Agency (GSA).

“Commercial users can already see signs of recovery of the Galileo navigation and timing services. . . although some fluctuations may be experienced until further notice.”

After a signal outage that began on July 11, efforts to restore services reportedly found a malfunction in the calculation of time and orbit predictions (ephemeris).

Why the error affected both Precise Timing Facilities (PTFs) within the Galileo ground control system, at Fucino in Italy and Oberpfaffenhoffen in Germany, has not been explained. System redundancy in the form of such doubled facilities was meant to prevent such breakdowns.

The GSA statement continues:

“Galileo Initial Services have now been restored. Commercial users can already see signs of recovery of the Galileo navigation and timing services, although some fluctuations may be experienced until further notice.

“The technical incident originated by an equipment malfunction in the Galileo ground infrastructure, affecting the calculation of time and orbit predictions, and which are used to compute the navigation message. The malfunction affected different elements on the ground facilities.

“A team composed of GSA experts, industry, ESA and Commission, worked together 24/7 to address the incident. The team is monitoring the quality of Galileo services to restore Galileo timing and navigation services at their nominal levels.

“We will set an Independent Inquiry Board to identify the root causes of the major incident. This will allow the Commission, as the programme manager, together with the EU Agency GSA to draw lessons for the management of an operational system with several millions of users worldwide.”

The full statement, including links to previously issued Notices to Galileo Users (NAGUs) is available here on the GSA website.

High-precision GPS/INS receiver is now available with a single-antenna option for faster integration, lighter weight and lower power consumption.

Septentrio’s GPS/INS receiver is now available with a single-antenna option. The single-antenna receiver brings the possibility of robust centimeter positioning and 3D attitude (heading, roll, pitch), while keeping weight and power consumption to a minimum. For Septentrio customers, this means simplified integration as well as increased operation time and productivity.

Septentrio centimeter-level positioning is based on multi-frequency, multi-constellation GNSS (GPS, GLONASS, Galileo, BeiDou, QZSS) technology. AsteRx-i S combines GNSS and an industry-grade inertial measurement unit (IMU) to deliver precise positioning together with 3D attitude and coasting functionality.

Septentrio’s unique GNSS/IMU integration algorithm enables continuous positioning in difficult environments such as near high structures, under foliage or during short GNSS outages (this is referred to as coasting or dead reckoning).

This makes AsteRx-i S a suitable positioning solution for robotics, autonomous vehicles and logistics. Previously available only as a dual-antenna product, AsteRx-i S is now available with either a single- or a dual-antenna option.

“By strengthening our GPS/INS integration portfolio we continue building upon our strategy of bringing reliable precise positioning together with 3D attitude to challenging industrial environments such as container parks or tree plantations,” said Danilo Sabbatini, product manager at Septentrio.

“AsteRx-i S has now become even more versatile with the support of both single and dual antenna operations on the same hardware platform,” Sabbatini said. “With the single-antenna AsteRx-i S delivers accurate 3D attitude in small-size applications where weight and power consumption are critical, while the dual antenna option is still the best solution for applications requiring short initialization time.”

Small, light, low power. The single-antenna AsteRx-i S requires minimal space which makes it suitable for robotic devices looking for small and light precise positioning solutions. Since only one antenna is required, there is less weight and lower power consumption, resulting in extended battery life. The dual antenna AsteRx-i S, on the other hand, is the best solution for devices requiring quick heading initialization and devices with prolonged static operation.

Advanced Interference Mitigation. AsteRx-i S comes with built-in Advanced Interference Mitigation (AIM+) technology. In robotic devices neighboring electronics can emit electromagnetic radiation which interfere with GNSS signals. AIM+ offers protection against such interference resulting in faster set-up times and robust continuous operation. A built-in power spectrum plot allows users to analyze interference, helping locate its source and mitigating it.

By offering both single and dual antenna options, Septentrio is now able to better accommodate specific needs of their customers interested in a GNSS/INS solution.

With tariffs, trade wars and sanctions ruling the day, how is a self-respecting UAS manufacturer supposed to make a buck? And to whom are the manufacturers of defense UAS able to sell their wares?

To NATO and other friendly countries, comes the ready answer, but there may still be a problem selling drones with armaments and offensive capabilities. Another layer of governmental review could swing into action when a company wants to sell to friendly countries like Saudi Arabia or perhaps to allies within the old Russian USSR block.

Last year, General Atomics lost sales to Saudi Arabia and the United Arab Emirates (UAE) for Predators and/or Reapers, large-bodied medium-altitude, long-endurance unmanned aircraft systems (or MALES). The deal went instead to a competing Chinese outfit. General Atomics complained bitterly about the loss of this business, which it blamed on restrictive U.S. export rules. The Administration responded by apparently loosening the regulations, in fact easing the way for most international sales. In response, it is possible that UAV manufacturers have also undertaken some changes which make U.S. drones even more competitive for export.

Business matters appear to have improved significantly. In May this year, the State Department actually used emergency provisions within the Arms Control Act to bypass Congressional review of a proposed sale to Saudi Arabia, UAE and Jordan of a package of Insitu Blackjack drones and launchers, worth $80 million.

The competition for world-wide sales of U.S. UAS products is increasingly tough, especially against Chinese suppliers with equivalent or perhaps less capable mil-spec drones. Hence the export rule changes which now appear to be working in the right direction.

Chinese Drones in the U.S.

Meanwhile, in an effort to accommodate U.S. concerns about the potential for user data somehow “leaking” to DJI — the Chinese supplier of almost 75% of U.S. drone purchases — DJI has implemented a “Government Edition” which apparently addresses the risk of data loss.

When US-based 3D Robotics stopped supplying 3DR Solo drones, the Interior Department found itself in a bind, as it had already bought hundreds of these devices for its inspection/surveillance operations. As the department searched for a new source for UAVs, it came to the conclusion that U.S. supplied drones were much less capable or up to ten times more expensive than equivalent DJI units. So they began working with DJI to solve the issue with potential data loss, and went on to test the results extensively

Working with the U.S. Interior Department for over 18 months, DJI has equipped drones and their controllers with modified hardware and custom software that ensure that the drones only operate in local data mode: information collected in flight is stored on the UAV alone and must be manually downloaded after flight. The drone is actually loaded with custom software by the user prior to flight to ensure this mode of data collection.

Even with these modifications, for now the use of DJI drones is still restricted to non-sensitive applications.

USAF/Kratos XQ-58A

Kratos is working with the U.S. Air Force to develop a jet-powered UAV system that can fly alongside manned fighter aircraft to multiply their effectiveness. At much lower cost than manned aircraft, the concept appears to be that more risk can be taken with the ‘loyal wingman’ UAVs to not only support the mission of the attack aircraft, but to also keep it safe.

We reported earlier on the XQ-58A after its first flight in March of this year. Now the Valkyrie is back in the flight test program with its second flight lasting 71 minutes over the Yuma test range on June 11. In the long- erm, it is hoped that both ground controllers and flight crew would operate these extensively autonomous drones.

A parallel “Skyborg” program is also underway to develop the hardware and artificial intelligence software capability to enable this type of drone to fly and fight alongside manned aircraft.

In conclusion, trade wars and tariffs aside, let’s hope that good UAV products can still make headway on their merits alone.

Trimble’s Stephanie Michaud discusses the company’s SiteVision augmented reality system at the 2019 Esri User Conference in San Diego. According to the company, SiteVision uses Trimble’s Catalyst softGNSS receiver, combined with Google ARCore technology, to produce a handheld high accuracy outdoor augmented reality system.

What is the biggest safety challenge for autonomous vehicles?

“Sharing the road with human drivers.  Optimized safe driving algorithms are compromised to mesh with the human’s natural level of risk taking. But this reduces safety, delaying acceptance — a real conundrum. Now, if we could just eliminate the humans…”
John Fischer
Orolia

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“When AI systems can deal with 99.9% of situations, the challenge will be keeping the passenger engaged to take over quickly when the 0.1% happens. Imagine a truck in front with a load coming loose. Which one would you trust?”
Julian Thomas
Racelogic

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Members of the EAB

Tony Agresta
Nearmap

Miguel Amor
Hexagon Positioning Intelligence

Thibault Bonnevie
SBG Systems

Alison Brown
NAVSYS Corporation

Ismael Colomina
GeoNumerics

Clem Driscoll
C.J. Driscoll & Associates

John Fischer
Orolia

Ellen Hall
Spirent Federal Systems

Jules McNeff
Overlook Systems Technologies, Inc.

Terry Moore
University of Nottingham

Bradford W. Parkinson
Stanford Center for Position, Navigation and Time

Jean-Marie Sleewaegen
Septentrio

Michael Swiek
GPS Alliance

Julian Thomas
Racelogic Ltd.

Greg Turetzky
Consultant