1996 soccer game in the Midwest, (Rick Dikeman image)

Nouméa ground station after the flood

A pencil and a coffee cup show the size of NASA’s teeny tiny PhoneSat

Bonus Hotspot: Naro Tartaruga AUV

Pacific lamprey spawning (photo by Jeremy Monroe, Fresh Waters Illustrated)

“Return of the Bucentaurn to the Molo on Ascension Day”, by (Giovanni Antonio Canal) Canaletto

The U.S. Naval Observatory Alternate Master Clock at 2nd Space Operations Squadron, Schriever AFB in Colorado. This photo was taken in January, 2006 during the addition of a leap second. The USNO master clocks control GPS timing. They are accurate to within one second every 20 million years (Satellites are so picky! Humans, on the other hand, just want to know if we’re too late for lunch) USAF photo by A1C Jason Ridder.

Detail of Compass/ BeiDou2 system diagram

Hotspot 6: Beluga A300 600ST

1. RESCUE DRONE
Noordwijk, Netherlands
√ Inspired by the refugee crisis, Dutch start-up Avy has been working on robust, long-duration drones capable of detecting people in distress and, if necessary, dropping life jackets, life buoys, food and medicine. The rescue drone can take off from a boat or the shore, carrying among other items, a cylinder that contains a large deployable rescue buoy, which not only can keep refugees afloat but indicates its location to boats in the vicinity.

1. RESCUE DRONE
Noordwijk, Netherlands
√ Inspired by the refugee crisis, Dutch start-up Avy has been working on robust, long-duration drones capable of detecting people in distress and, if necessary, dropping life jackets, life buoys, food and medicine. The rescue drone can take off from a boat or the shore, carrying among other items, a cylinder that contains a large deployable rescue buoy, which not only can keep refugees afloat but indicates its location to boats in the vicinity.

The Avy Rescue is especially tailored to operate in emergency conditions for performing life-saving missions in support of search and rescue and for the management of disaster relief. In order to operate in these demanding scenarios, the drone possesses a powerful and complete sensor and communication package as well as a sturdy construction and operational flexibility, according to the company. The company is currently based at ESA’s Business Incubation Centre in Noordwijk, receiving technical and business advice.

2. UBER FOR BIKES
China
√ Bike-sharing is not new in China, but Chinese startups — including leaders like Mobike and Ofo — have reinvented the concept to make it even more efficient and these services have become very popular. The premise is simple: pedestrians looking for a ride can open their smartphones, unlock a bike parked nearby, hop on, and pay a fee once they arrive at their destination.
These bike-sharing startups allow their vehicles to be placed anywhere in the city as engineers have developed GPS-based apps that allow people to find nearby bikes, and charge based on how much time riders spend on them. Many people have taken up bike-sharing as a replacement for the subway, or even walking.

Some of the same technologies used to start up these services are now being implemented to improve efficiency as well as fight off user abuse by using GPS tracking services to encourage rider responsibility. One bike-sharing service now includes an updated brake box that contains a mechanical lock compatible with the integrated GPS system in the updated app, allowing app users to lock/unlock the bicycle under three seconds.

3. TRUCK DRIVERS OUTSIDE THE TRUCK
California
√ Trucking is the backbone of the American economy, moving a majority of freight. California-based startup Starsky Robotics is working to make trucks autonomous on the highway and remote controlled by drivers for the first and last mile. The plan is for these trucks to take advantage of the evolving GPS and navigation technologies to make roads safer while giving drivers meaningful work close to their homes and families. Starsky Robotics is approaching the autonomous space with an eye on keeping drivers employed and improving their lives.

Starsky is not building a self-driving truck that removes the driver from the vehicle altogether. Instead, it is building a retrofit kit that it said will keep drivers employed, just not in the truck. Currently they’re testing vehicles in Michigan, Nevada and Florida with drivers in the cab, but the company hopes to remove drivers from the cab during testing later this year. A vehicle has already moved a 5,000-pound load 140 miles, with 120 of those miles driven autonomously. It has also been tested successfully in a local yard moving trailers without a driver in the vehicle. Starsky’s tech is also looking to make an impact now, by using components and techniques that are currently available at prices which are palatable to truck purchasers and manufacturers.

4. ROBORACERS
Paris, France
√ Roborace showed off its self-driving Robocar on the city streets of Formula E’s Paris ePrix on May 20, 2017. The Robocar is the first driverless car on the streets of Paris. The driverless race car performed a demonstration for the crowds at Les Invalides in the French capital and wowed the fans with a successful showcase of its autonomous capabilities. The demonstration saw the car negotiate its way around 14 turns of the 1.9-kilometer circuit without a human in the vehicle entirely self-driven by autonomous software.

The Robocar is designed by Daniel Simon, the automotive futurist who creates vehicles for Hollywood sci-fi blockbusters including Tron Legacy and Oblivion, It weighs 1000 kilograms and measures 4.8 meters long and 2 meters wide. It has four motors of 300 kilowatts each, a 540 killowatt battery and is capable of speeds more than 200 mph. The car uses a number of technologies to “drive” itself including 5 LiDARs, 2 radars, 18 ultrasonic sensors, 2 optical speed sensors, 6 AI cameras, GNSS positioning and is powered by Nvidia’s Drive PX2 brain, capable of up to 24 trillion A.I. operations per second to be programmed by teams’ software engineers using complex algorithms, according to Roborace. Roborace’s open A.I. platform allows companies to develop their own driverless software and push the limits in an extreme and safe environment. The series is designed to be a competition of intelligence so all teams will use the same “Robocar” to ensure all efforts will be focussed on advancing the software for everyday road cars to adopt.

The post GNSS Hotspots | June 2017 appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

Long-overdue approval of the request should be expedited by the FCC.

For several years the European Union (EU) has sought a waiver for its Galileo system from Federal Communications Commission (FCC) licensing requirements — the so-called Part 25 rule to operate in this country.

Long-overdue approval of the request should be expedited by the FCC.

The initial request, channeled through the U.S. State Department, came in October 2013. On January 30, 2015, the National Telecommunications and Information Administration (NTIA) asked the FCC to seek public comment on the EC’s waiver request and recommended granting the exemption to the Galileo system, which met NTIA’s criteria for such waivers.

Nearly two years passed before the FCC, on January 6, issued the public notice sought by NTIA. The comment period closed on March 23 and drew 18 responses, including replies to other submitters’ comments.

The Galileo exemption would apply to three frequencies, but it’s the swath of RF spectrum at 1559–1591 MHz, within which GPS military and civil signals also reside, that are primarily at issue. That GNSS E1/L1 spectrum adjoins a band (1525-1559 MHz) in which Ligado Networks, the successor of LightSquared Inc., would like to build a terrestrial broadband network that has been shown to interfere with many GPS receivers.

Comments made to the FCC strongly favored granting the exemption — with two exceptions. Inmarsat, an international satellite communications organization, raised concerns about out-of-band (OOB) interference from Galileo. Inmarsat and the EC subsequently issued a joint statement supporting a test campaign to assess the risk of OOB interference from Galileo E1 and agreed to mitigate such effects if they appeared.

The other negative response, predictably, came from Ligado Networks, which argued that the waiver should not be granted until after demonstrations that Galileo won’t interfere with Ligado’s proposed operations and that the addition of Galileo would not make user equipment more vulnerable to Ligado’s terrestrial transmissions. 

Given that Ligado’s broadcast power would be much stronger than Galileo’s, the company’s first objection seems rather disingenuous. As for the latter issue, Galileo E1 has long operated within the same frequency as GPS L1 and P(Y)-code and within the same receivers without any substantive problems. Moreover, as the EC pointed out, Galileo has transmitted the PRS signal since 2006 “without reports of interference to systems operating in the band below 1559 MHz.”

In contrast to the limited grounds for denying the Part 25 licensing exemption, several compelling arguments exist for granting it:

National Security. Use of Galileo can further protect critical U.S. infrastructure, such as the national electrical grid and civil aviation, and enhance military operations. In a report attached to the National Defense Authorization Act for Fiscal Year 2017, the U.S. House Armed Services Committee urged the FCC to quit fooling around and act on the waiver request.

Foreign Relations. The EU represents one of the United States’ oldest and closest allies, reflected in a 13-year-old agreement that established similarly designed binary offset carrier (BOC) waveforms as the basis for new civil signals at L1/E1: the GPS L1C and Galileo’s Open Service at E1. The U.S.-European relationship is going through a rough patch right now that could be smoothed by granting the Galileo exemption as soon as possible.

Emergency Services. Unauthorized signals cannot be used for official or regulated applications such as law enforcement or 911 services without FCC approval. The EC’s request received support from NENA, the national emergency number association, which argued that additional satellite signals from Galileo would significantly improve 911 services.

GNSS Market Growth. In bilateral and multilateral negotiations the United States has long argued for ensuring a “level playing field” in commercial markets that does not favor one GNSS system over another. Not granting the exemption risks tit-for-tat treatment of GPS by other nations with their own GNSS systems. 

GPS Protection/Backup. In 2010 the Obama administration adopted a space policy that said foreign GNSS services could be used “to augment and strengthen the resiliency of GPS.” Use of Galileo would aid detection of spoofing, improve interference rejection, and provide a needed GPS backup. It’s time for the FCC to move ahead and grant the Galileo request.

The post Get Galileo on Board appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

Airspace is subject to the territorial sovereignty of the respective underlying state, and that state can therefore exercise a level of discretion in prohibiting or conditioning activities in that area which is only limited by international obligations resting upon that state – for instance, following certain international aviation treaties. The only exception here concerns airspaces over international waters, for which the 1944 Chicago Convention provides a general solution regarding the regulation of aviation for safety purposes. In general, as a consequence the use of GNSS and their services in the context of aviation is dealt with by air law, national as well as international, as a body of law principally regulating activities in airspaces, national as well as international.

Outer space, by contrast, is defined as an area not subject as such to any territorial or quasi-territorial sovereignty, a virtual “global commons”, where the freedom of use and exploration is the baseline legal principle and such freedom can only be curtailed, at the international level, by applicable international (space) law. This principle has been codified in the 1967 Outer Space Treaty, to which all important spacefaring nations are party. The Outer Space Treaty at the same time provides for a first embryonic set of international obligations resting upon states which limit the baseline freedom of use and exploration, while several other space treaties as well as customary international law and more general treaties which impact outer space and space activities provide for further limitations. This is what is commonly labeled “space law”, a body of (in first instance international) rules addressing such space activities. Only at a secondary level, national law or (in the case of the European Union) EU law plays a role, partly in implementing and applying the international regime in a national respectively EU context.

When analyzing to what extent space law has an impact on GNSS, furthermore, we should realize that GNSS from an overarching legal perspective comprises five main elements: (1) ground stations controlling by way of (2) radio signals (3) the satellites launched into and then operating in outer space, emitting (4) the position, navigation and timing (PNT) signals allowing (5) relevant receivers to calculate positioning and navigation information. 

Elements (1) and (5) are not generally considered to be a subject which space law should regulate, as they fall completely within the sovereign jurisdiction of whatever state the ground stations respectively receivers find itself in. For the sake of simplicity, any receiver infrastructure in outer space is not further discussed in the contribution, whereas any similar receiver infrastructure in airspace is subsumed within the concept of receivers as it is legally subject to the same territorial jurisdiction (as further regulated internationally by air law).

Elements (2) and (4), which at least in part traverse outer space on their way to respectively back from the satellites, are effectively dealt with already by an international body of law dealing with all communications, not with space communications only; hence these will not be dealt with in any detail here.

For completeness’s sake, suffice it here to point to the International Telecommunication Union (ITU) which, in a legal sense, operates on the basis of the ITU Constitution, the ITU Convention, and whatever is the most recent version of the Radio Regulations, listed in Additional Resources near the end of this article. Once it had become clear that satellites could be integrated in the international infrastructure for communications in the late 1950s, it was agreed that the ITU presented the obvious forum to address these issues as it had since decades already addressed the issue of potential interference on the international level, by developing and implementing an elaborate system of coordination of frequency use. The ITU’s legal involvement with satellites, including GNSS, remains limited however to such coordination of frequencies and attendant orbits.

That leaves most prominently element (3) to be subject to space law. Following primarily from the aforementioned Outer Space Treaty and two of its successor treaties, the 1972 Liability Convention and the 1975 Registration Convention (See Additional Resources), the following fundamental legal rules and obligations would then arise which are of particular importance for GNSS.

Freedom of Use and Exploration for the Benefit of All Mankind
This principle notably emanates from Articles I and II of the Outer Space Treaty, and would generally include the use of satellites for positioning, timing and navigation purposes. The limits to this freedom under the Outer Space Treaty are fairly limited, and remain essentially confined to an obligation to comply with general international law as applicable (Article III, Outer Space Treaty, which specifically references the UN Charter), to undertake reasonable efforts to avoid harmful interference with other legitimate space activities (Article IX, Outer Space Treaty) and to share any relevant scientific information gathered in the context of operations with the world community (Article XI, Outer Space Treaty).

Conversely, it will be clear that GNSS actually contributes – at least in principle – to the benefits of space activities for all mankind, since it allows many activities on earth or in the airspaces above it to take place safer, quicker and more efficiently. This would apply in particular, of course, to the extent the GNSS signals would be openly and freely available – which currently is the case with GPS and GLONASS Standard Positioning Signals, whereas also BeiDou and Galileo plan to offer such openly and freely accessible signals. The only exceptions would be where GNSS would be used, for instance, for supporting the unlawful use of force, so as to violate Article III of the Outer Space Treaty. This would mainly refer to the use of force other than in the exercise of the right of self-defense (Article 51, UN Charter) or following a mandate of the UN Security Council (Article 42, UN Charter).

Responsibility of States for National Activities in Outer Space
This responsibility also pertains to the operation of GNSS satellites. If such satellites are involved in activities violating the rights of other states (such as referenced above), it will be the state or states as whose “national activities” these operations qualify, which will be held responsible under international law (Article VI, Outer Space Treaty). Such violations would then give rise to a requirement for the violating state(s) to remedy the situation and as appropriate apologize, punish responsible operators and/or provide assurances that such violations will not occur again. This is independent from the occurrence of actual damage, which may in addition give rise to obligations to compensate for such damage, even beyond the particular concept of liability dealt with below. Thus, the United States would be responsible for GPS operations, the Russian Federation for GLONASS operations, and the People’s Republic of China for BeiDou operations.

Since such state responsibility also pertains to satellite operations conducted by private operators, any future private operator of Galileo pursuant to a concession would also give rise to the responsibility of the state(s) as whose “national activities in outer space” such operations would qualify. The idea of having Galileo operated under a concession, as originally intended by the European Commission, turned out to be premature, but it cannot and is not excluded that in the future this may change.

While the EU is in the political and financial lead when it comes to Galileo, and the European Space Agency (ESA) has been the initial developer in a technical and operational sense, pursuant to Articles VI and XIII of the Outer Space Treaty such international responsibility ultimately rests with the member states, or at least with the member states which are involved specifically in the Galileo programs. To what extent the seat of the European GNSS Agency (GSA), the hosting of ground stations for the purpose of Galileo, or relative investments into Galileo might cause for specific responsibility of specific member states is an issue for internal considerations; any third state complaining about any perceived illegality of Galileo operations would in principle have the choice to address any such complaints against any of the EU and ESA member states.

Article VI of the Outer Space Treaty furthermore requires the “appropriate State” to ensure “authorization and continuing supervision” of non-governmental entities. As long as Galileo operations would remain the domain of the GSA, as an agency of the European Commission, Articles VI and XIII would allow the European Union to effectively exercise such control over Galileo operations. As soon as, however, a private concessionaire were to take over as operator, one or the other EU/ESA member state would have to step into the breach to ensure the aforementioned “authorization and continuing supervision”, even if in practice the EU/GSA could still be used as the “tool” to achieve that aim.

Liability of States for Physical Damage Caused by Space Objects
Pursuant to this principle, although following a different scheme of attribution based on fundamental involvement with the launch of the space objects concerned (namely that of the so-called “launching State” of the space object at issue; Article VII, Outer Space Treaty; Articles I, II & III, Liability Convention), states are not only responsible but also liable for physical damage caused by space objects. Such damage would then give rise to an obligation to compensate for the damage, which is fault-based only to the extent that damage is caused to other space objects (Articles II & III, Liability Convention) and is in principle without limit (Article XII).

In other words, if a GPS satellite would crash into another space object, the United States would be held liable for the damage caused thereby to the extent the crash would be considered its fault; if the damage by contrast would take place on earth or to aircraft in flight, the United States would be held liable without further ado. The same obviously would apply for the Russian Federation with respect to GLONASS and the People’s Republic of China with respect to BeiDou. 

It is important to note here, that damage is defined, following the general interpretation of the Liability Convention, as direct damage caused by physical impact, meaning that non-physical damage such as radio interference or indirect damage – an aircraft crashing as a consequence of erroneous GNSS information; loss of revenues due to interference – are not compensable. In the context of discussions within the International Civil Aviation Organization (ICAO), for instance, the United States has consistently denied any liability for damage which users of GPS signals or services could suffer due to their trust in those signals or services being unwarranted. Only exceptionally it has been claimed by authors that liability for signals and services emanating from GNSS satellites could be equated to “damage caused by the satellites”, and hence be subject to liability claims pursuant to the Liability Convention. In the US case, it has only been admitted that under particular circumstances liability claims against the US government could be entertained in US courts, to the extent that the Federal Tort Claims Act or Suits in Admiralty Acts might be invoked.

Victims of such types of damages should therefore seek compensation either under the heading of state responsibility as addressed above or in a private capacity in a relevant national court.

Again, international liability also applies for privately-owned and/or -operated GNSS systems; a possible future private concessionaire operating Galileo would thus only be held liable to the extent the states themselves liable would derogate such liability under the concession. While the Liability Convention in this respect offers intergovernmental organizations the opportunity to qualify as a state party to the Convention for practical purposes (Article XXII, Liability Convention), ESA has so far complied with the relevant conditions but not the EU. Even to the extent ESA would be held liable for damage caused by Galileo (due to its initial involvement in system launch and deployment), ultimately the burden of compensation would come to rest upon the ESA member states.

As for the EU, due to absence of its qualification pursuant to Article XXII of the Liability Convention as a de facto party to its regime, legally speaking it is an “invisible” entity. Asserting a claim for damage caused by Galileo and otherwise falling within the scope of the Liability Convention against the EU or the EC consequently would not be legally possible – instead, if the victim state(s) would not favor addressing ESA as per the aforementioned option, the only option left would be to address individual EU member states who could all, legally-technically speaking, be argued to be procuring states (Article I(c)(i), Liability Convention) of the Galileo satellite in question and hence liable.

At the same time, it should be noted that in the Galileo context a substantial element of the proposed package of paid services (as opposed to the open GPS services for which no liability could unequivocally be claimed) would be the inclusion of liability acceptance on the part of the operator. To the extent this approach were to become accepted, users who would rely on Galileo services which would then turn out to be erroneous (hence such reliance would in hindsight be unjustified) and as a consequence cause damage to third parties, would be able to derogate the relevant third-party claims to the Galileo operator. An example on point would be an aircraft crashing as a consequence of malfunctioning of a Galileo service: the derogation of liability would allow the airline to shift the burden of any third-party liability claim under applicable air law treaties ultimately to the Galileo operator.

Registration of Space Objects by States Involved in their Launching
Closely related to the international regime on liability summarized above, states are also required to register – at least in principle – the space objects for which they qualified as “launching State(s)”. This registration obligation is actually twofold. On the one hand, states need to register such space objects in a national register, the details of which are further left to the state of registry (Article II(1), Registration Convention). On the other hand, they are required to provide the United Nations with a specific set of data for the purpose of inclusion in the international register (Articles III, IV, Registration Convention).

Unfortunately, the latter obligation is qualified as “as soon as practicable” (Article IV(1), Registration Convention); coupled with the principled absence of an international monitoring organization, effectively this means that many satellites do not get registered at all (in particular if military in nature).

A further problem concerns the impossibility – at least formally, as per the Registration Convention, to “unregister” or “deregister” satellites. The assumption had simply been that satellites, once launched, would be owned and operated by their principal owner until their end-of-life, so the possibility of change of ownership in-orbit was never seriously contemplated.

Since the possibility of more than one state qualifying as a launching state is real, in view of the four alternative criteria for that, in relevant cases those states should determine which one of them is to fulfill the functions pursuant to the Registration Convention – double registration is legally speaking not possible (Article II(2), Registration Convention).

Clearly, following the above, the United States, the Russian Federation and the People’s Republic of China are required to register the satellites composing their respective GNSS. A final point of note concerns the fact that, while GPS, GLONASS and BeiDou are obviously multi-satellite systems, pursuant to the Registration Convention each individual launch carrying one or more satellites is registered individually – the main concern driving the registration regime was the launch phase as deemed the by far most risky and accident-prone. 

As for Europe, though similarly to the Liability Convention under the Registration Convention the possibility is open for an intergovernmental organization to become a “party” to the Convention for all practical purposes exists (Article VII, Registration Convention), again only ESA, not the EU has qualified as such. Any EU “register” of Galileo satellites, if ever contemplated, would not have any legal meaning pursuant to the Registration Convention; (Note that in an effort to provide as much relevant identification-related information to the general public, the UN Office for Outer Space Affairs will include any such information provided by the European Union in the international register between brackets, to distinguish it from information provided formally in accordance with the Registration Convention.) The absence moreover of a possibility to register such satellites in two or more states at the same time (Article II(2), registration Convention) also principally excludes such a register under the Convention. Galileo satellites, consequently, could be registered either by ESA or by any EU member state qualifying as the launching State. 

At least to the extent Galileo satellites are launched from Kourou on Ariane launchers, France would be the logical launching state, as the use of its territory and launch facilities for the launch would most unequivocally qualify it as a launching state – much more so than, for instance, Germany or Italy where the main control centers are hosted. In practice, as it turns out, ESA registered the GIOVE satellites in 2005 and 2008; the Galileo IOV and Galileo satellites launched from 2011 onwards, however, were not officially registered with the United Nations, also raising legal questions regarding jurisdiction and control at least under international law (Article VIII, Outer Space Treaty). For more details on this, see Additional Resources.

Mitigation of Space Debris
The issue of space debris is not yet formally dealt with by the space treaties in any relevant detail: the provision coming closest to addressing the issue concerns that which requires a state which “has reason to believe that an activity or experiment planned by it or its nationals in outer space (…) would cause potentially harmful interference with activities of other States Parties in the peaceful exploration and use of outer space, including the Moon and other celestial bodies” to “undertake appropriate international consultations before proceeding with any such activity or experiment” (Article IX, Outer Space Treaty). Vice versa as per the same Article, a state potentially victimized by such harmful interference may require consultations – yet there is not obligation not to create any space debris, let alone to clean up one’s own or indeed any space debris already out there. 

In that sense, the only remaining support coming directly from the space treaties of relevance here would be the inclusion of space debris in the concept of “space object”, which means that damage caused by space debris under the Liability Convention would give rise to compensation – on the assumption, of course, that the launching state of that space debris could (still) be identified.

Only recently legal developments have started to address the problem of space debris more profoundly. Partly in further elaboration of the aforementioned Article IX of the Outer Space Treaty, the major space agencies gathered together in the Inter-Agency Space Debris Coordination Committee (IADC) in 2002 drafted a first set of (legally non-binding) Space Debris Mitigation Guidelines, which has been further buttressed by a relevant set of UNCOPUS guidelines in 2010. Those guidelines may well develop into customary international law over the coming years, in particular as increasingly individual states licensing private operators include compliance with the guidelines in the conditions for being granted a license to undertake space activities in the first place – which is certainly binding upon those licensees. Of the countries concerned with GNSS, at least for the United States and the member states of ESA (which is a prominent member of the IADC) this holds true, which means such principles will also be applied at least to GPS- and Galileo-related launches.

In Conclusion
While it is clear that GNSS constitutes one of the most beneficial space operations and space-based applications, the legal regime pursuant to international space law remains fairly general and limited in its specific guidance of such operations and activities. Partly that is due to a general lack of political awareness of the relevance of compliance with such issues as registration and space debris, which would hopefully change as more and more terrestrial users become dependent upon satellite navigation services. Partly it is due to the remaining crucial impact of national sovereignty in this particular field of international law; the absence of sovereign control by other states than the GNSS operator states over the applications on their territory or within their airspace and the potential consequences in terms of liability understandably causes a considerable amount of hesitation in allowing to reap the full potential benefits of GNSS.

In Europe, with respect to Galileo, the legal situation is even more wanting. While ESA is able to register satellites and has actually done so with the first few launched, the leading position that the EU has increasingly taken in this respect has not yet translated into properly addressing such issues – neither have, probably as a consequence of the Union’s lead role, individual EU/ESA member states such as France, Germany or Italy. Thus, even at the level of the fairly succinct body of international space law, much still needs to be done to arrive at a proper legal framework properly implemented.

Additional Resources 
[1] Charter of the United Nations (UN Charter), San Francisco, done 26 June 1945, entered into force 24 October 1945; USTS 993; 24 UST 2225; 59 Stat. 1031; 145 UKTS 805; UKTS 1946 No. 67; Cmd. 6666 & 6711; CTS 1945 No. 7; ATS 1945 No. 1.
[2] Constitution of the International Telecommunication Union (ITU Constitution), Geneva, done 22 December 1992, entered into force 1 July 1994; 1825 UNTS 1; UKTS 1996 No. 24; Cm. 2539; ATS 1994 No. 28; Final Acts of the Additional Plenipotentiary Conference, Geneva, 1992 (1993), at 1.
[3] Convention of the International Telecommunication Union (ITU Convention), Geneva, done 22 December 1992, entered into force 1 July 1994; 1825 UNTS 1; UKTS 1996 No. 24; Cm. 2539; ATS 1994 No. 28; Final Acts of the Additional Plenipotentiary Conference, Geneva, 1992 (1993), at 71.
[4] Convention on International Liability for Damage Caused by Space Objects (Liability Convention), London/Moscow/Washington, done 29 March 1972, entered into force 1 September 1972; 961 UNTS 187; TIAS 7762; 24 UST 2389; UKTS 1974 No. 16; Cmnd. 5068; ATS 1975 No. 5; 10 ILM 965 (1971).
[5] Convention on Registration of Objects Launched into Outer Space (Registration Convention), New York, done 14 January 1975, entered into force 15 September 1976; 1023 UNTS 15; TIAS 8480; 28 UST 695; UKTS 1978 No. 70; Cmnd. 6256; ATS 1986 No. 5; 14 ILM 43 (1975).
[6] Radio Regulations Articles, Edition of 2016 (Radio Regulations).
[7] Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies (Outer Space Treaty), London/Moscow/Washington, done 27 January 1967, entered into force 10 October 1967; 610 UNTS 205; TIAS 6347; 18 UST 2410; UKTS 1968 No. 10; Cmnd. 3198; ATS 1967 No. 24; 6 ILM 386 (1967).
[8] United Nations Office of Outer Space Affairs; see here; search “Galileo”.

The post Space Law and GNSS appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

No longer consigned to predicting what might one day happen, the folks at the Galileo program can now look at and talk about what is happening right now, starting with initial services. To help us understand what’s going on, we enlisted no less than Matthias Petschke, Galileo Program Director at the European Commission (EC).

“Since the initial service declaration that took place on 15 December 2016,” Petschke told us, “the European Commission and the GSA [European GNSS Agency] have put together an extensive service provision, monitoring and reporting process.” 

Beyond the real-time operations of the system, he explained, the performance of Galileo services is being assessed a posteriori on a monthly basis.

“The data collected so far indicate an excellent level of performance,” Petschke said, “well within the performance levels published in the Galileo OS Service Definition Document. In fact, recent independent tests have confirmed that Galileo plus GPS already offers increased accuracy in urban areas over GPS alone.”

It would be hard to overstate the significance of what Petschke is reporting here. A system that for so long was considered by some to be on the verge of becoming the poster child for all that is wrong with the EU – among other things long, convoluted and often contentious decision-making processes – Galileo is finally, and in a very real and measurable way, a success story. The system currently counts 18 satellites in orbit, in various functional states, out of 30 planned.

Except…
We need to point out here that Petschke relayed his remarks to us some days before the first wide scale failure of Galileo services, an event that began on May 14, 2017. When Petschke made his remarks, they were still accurate and pertinent.

More on the service failure later. For now, let’s continue with the good news.

Petschke said the program plans to make public its performance reports on a quarterly basis through the European GNSS Service Center (GSC) website. The first report of this type, covering the first quarter of 2017, is expected in May.

“In parallel,” he said, “the GSA is setting up a fully independent performance monitoring capability, which will be hosted at the Galileo Reference Center (GRC) in the Netherlands. This independent performance monitoring will also include worldwide monitoring capabilities from various EU Member States and should be available as of July 2017.”

Before the failure of May 14, we knew that there had already been some less serious glitches affecting the initial service, but such was to be expected given the level of immaturity of the system, and we were not prepared to dwell on these. One of our sources in Brussels who prefers to remain anonymous did tell us at the time, “The initial services are an important milestone, and are injecting some sense of responsibility into the program.” Yes, the people who for so long were occupied with telling us why it wasn’t ready, are now at last proud owners of a functioning multi-billion-euro space system, and they’re getting a feel for how it handles.

In the Driver’s Seat
Actual hands-on operation of Galileo now falls to the newly designated Galileo Service Operator (GSOp). Working under a 10-year, 1.5-billion-euro contract (about $1.65 billion), Spaceopal is a joint venture between Italy’s Telespazio and the German Space Agency (DLR). After a long and complex tendering process that started in January 2015, Spaceopal and the GSA officially signed the GSOp contract last December, on the very day when initial services were launched.

Under GSA management, Spaceopal is charged with securing Galileo operations from two mission control centers (GCCs), one located in Germany and the other in Italy, and it is to provide user sup-port services through the European GNSS Service Centre (GSC) in Spain.

Spaceopal will manage the Galileo Data Distribution Network (GDDN) and provide integrated logistics support and maintenance for the entire space and ground infrastructure. Finally, the group will monitor system performance and otherwise support to the best of its ability the ongoing roll-out of Galileo infrastructure and associated launches.

Petschke told Inside GNSS, “The handover of operations from the current contractual set-up to the Galileo Service Operator is being conducted according to plan, following a series of milestones to verify readiness in a number of areas. The GSA has already put in place its own internal organization to fully oversee service delivery as of July 2017.”

To that end, the GSOp contract includes a set of clear and tangible key performance indicators (KPIs), against which the GSA will assess the work of the Spaceopal. 

In reality, there has been little anxiety to be felt over Spaceopal’s ability to do the job, the group having already served as the contractor for Galileo operations since 2010 under the Galileo Full Operational Capability (FOC) Operations Framework Contract. At the new GSOp contract signing ceremony in Prague, Spaceopal CEO Giuseppe Lenzo gave every impression of being up to the task, assuring the gathered happy dignitaries that his group is committed to continuing to support the deployment and completion of the Galileo system.

PRS Included
Of the various services promised over the years by the Galileo program, the Public Regulated Service (PRS) always seemed the least likely to get off the ground without a hitch, among the doubters, that is.

And yet, speaking at the Munich Satellite Navigation Summit earlier this year, Christoph Kautz, European Commission Galileo and EGNOS Deputy Head of Unit, was able to remind participants that the PRS was indeed among the Galileo initial services declared last December.

The PRS comprises a dedicated, authenticated and encrypted service for governmental authorized users in areas such as public safety and security, critical infrastructure, and defense.

Speaking at the same event in Munich, GSA PRS Manager Charles Villie described the PRS as an encrypted navigation service designed to be more resistant to jamming, involuntary interference and spoofing, “…offering continuity of service, including higher availability of the signal in space and providing an independent authenticated position, velocity and timing service.”

The main task now is to make the transition to exploitation, Kautz said. And the EC, he added, is looking forward to full deployment of the Galileo constellation by 2020, working in concert with the relevant ground system elements, including the Galileo Security Monitoring Center (GSMC) near Paris and the Competent PRS authorities (CPAs) that need to be established in Member States in order to access and control the use of the PRS within their borders.

Kautz made no mention of the putative back-up GSMC supposed to have been located in the UK, the country whose status within the program has been thrown up in the air in the wake of its decision to leave the European Union. But then no one within the Galileo program, not even Kautz, is volunteering any substantive thinking of any kind on that most embarrassing of issues. The one and only official response to all questions Brexit is “we don’t know yet”.

Kautz went on to argue that, following the publication of the EU’s Space Strategy in 2016, it is likely that the range of security-related space applications will increase in the future, and there could therefore [hopefully] be an increased demand for the more secure and robust PRS service.

Meanwhile, a majority of the EU European Member States have now established their CPAs, and a number of non-EU countries have expressed interest in using the service. Negotiations on that last score are being held tightly under wraps.

Villie insisted: “Today all PRS functionalities are available. The whole infrastructure is functional and operational and authorized users can test their procedures for real and can check PRS functionalities themselves.”

PRS receiver concepts have already been developed and validated under a battery of pilot projects funded by the EU’s Horizon 2020 program.

As for user acceptance, Villie said, that is going to depend plainly and simply on whether or not the PRS can prove its worth. A range of testing and demonstration activities is being carried out through 2017.

So, these are still very early days for the PRS, but some users appear to be sold already. Speaking on behalf of the German CPA, Lukas Schmid of the German Transport Ministry said he saw many potential applications for the PRS within the police and security services. As an example, he said, server-based Galileo PRS solutions for authenticated positioning and timing that are available today could significantly simplify the tracking of tagged terrorist suspects.

He also described the “Hali Berlin” project under which traffic lights were synchronized for emergency vehicles, with the PRS helping to secure the application. The procedure greatly reduced the time it took for emergency vehicles to get to incidents while also reducing the number of accidents involving those vehicles. Schmid said further joint test activities between Germany, Belgium and other Member States are slated. Also, proclaiming the potential benefits of the PRS was Colonel Philippe Bertrand, head of the French CPA, which is now also part of an organization that will ensure the interoperability of Galileo PRS with military GPS for the French Ministry of Defense.

During 2016, the French CPA along with the French MoD and the French Space Agency (CNES) undertook in-depth PRS validation activities, including monitoring and security tests. Bertrand told participants at the Munich event, “It is very clear that the PRS’ navigation performance is really very good and very interesting.”

Much like Villie though, Bertrand said he thought that large numbers of users will only come if the PRS lives up to its pledges, e.g., gaining full operational capability by 2020 and providing the promised very high level of security.

For his part, Petschke is confident the PRS will come through: “The PRS is already in its initial service phase and the Galileo program is committed to achieving the objective of full operational capability by the end of 2020.”

On the Other Hand
Petschke said that while the PRS is definitely alive and kicking, the equally-anticipated Galileo Commercial Service (CS) is still a ways off: “The first signal transmissions for the Commercial Service should take place late in 2018.”

The CS has seen its ups and downs and it was glaringly though not unexpectedly absent from the package of initial services launched in December. The service has been described as encrypted and accurate to the nearest centimeter, allowing for the development of applications for professional or commercial use owing to improved performance and data with greater added value than that obtained through the open service.

We have it on good authority that an invitation to tender for the pre-selection phase of the CS service provider is likely to be issued by the end of this year. So, the CS is still a going concern, but users will have to wait a while longer to get a feel for what it can do.

Still No Getting Away From….
Clearly a major source of disappointment, both inside and outside the program, continues to be the affair of the failed Galileo satellite onboard clocks. But not to harp on the issue, as we do believe there is reasonable potential benefit to be gained by bringing to light certain observations.

Readers will remember the failure of a number of Galileo onboard clocks, as revealed by European Space Agency Director General Johan-Dietrich Woerner last January. At that time, he said, nine of the 72 orbiting clocks had failed – three rubidium clocks and six passive hydrogen maser [PHM] clocks. One additional PHM clock had failed, but had been successfully restarted.

And, Woerner told reporters, the decision to use the Italian-produced clocks was part of a larger European “political” strategy. “This discussion of Galileo as a whole was a strategic decision,” he said. “We wanted to have an autonomous European solution for satellite navigation and so to have these systems based on European technology was a clear political decision.”

He and others have made clear since then that the clock failures, while indeed troubling, have had no effect on the operational integrity of the Galileo system.

Most recently, Petschke told us, “The ESA-led investigation has significantly progressed and should be able to confirm a resolution plan that contains the risks in the weeks to come.”

The fact that a resolution plan is still in progress, four months after the problem was revealed, is neither disquieting nor reassuring. If the plan does not surface within the cited weeks, that will be disquieting.

“This plan would include both a refurbishment program for the next satellites to be launched and operational procedures for the satellites in orbit. The next launch is planned to take place in December this year,” Petschke said.

One anonymous source in Brussels told us, “The clock problem is being resolved. The rubidium clocks will all need retrofitting, but this will have little or no impact on the launch schedule.

Galileo Goes Off
Having been fair in giving the Galileo program the credit it is due, and we do believe it is due much credit, we feel equally minded to record its failures. The following Notice Advisory for Galileo Users (NAGU) was issued on 15 May 2017, announcing such a failure beginning on 14 May.

“EVENT DESCRIPTION: NAVIGATION MESSAGES NOT REFRESHED FOR ALL SATELLITES SINCE 2017-05-14 15:50 UTC UNTIL FURTHER NOTICE.”

During the event, one individual who is close to the program spoke of disappointment over a complete failure after just five months of initial services.

Another inside source told us the failure involved one part of the Galileo ground segment, nothing to do with the onboard clocks.

While the failure notice was still in effect, an ESA spokesperson confirmed to us, “A hardware equipment malfunction in the ground segment affected the functioning of the Galileo system. As a result the navigation message for all satellites has not been refreshed since 15:50 on 14/05/2017. The cause of the malfunction has been identified, the equipment concerned has been replaced and the recovery of the services to their nominal levels has started.”

On May 17, three days after the beginning of the event, the follow-up NAGU appeared:

“EVENT DESCRIPTION: CONDITIONS LEADING TO NAVIGATION MESSAGES NOT TIMELY REFRESHED FOR ALL SATELLITES HAVE CONCLUDED.”

During the length of the event, there was no tentative recovery date given. Some very hard questions are now being asked, both within and without the Galileo program. Here are just a few such questions that have been suggested to us:

1) Is the Galileo technical infrastructure mature enough to provide committed services?

2) Have the European Commission, the GSA and the ESA invested enough in the organizational aspects of Galileo, including logistics, and considered with due attention the meaning and implied responsibilities of service provision?

3) Is it clear to all of them what the difference is between developing a technology, procuring and integrating a system, operating a system and providing services continuously and reliably?

We will be watching and asking these questions of the responsible agencies as the Galileo program moves forward.

Also, we are asked to imagine where we would be if GPS were to suddenly announce a complete service failure, with no recovery date given. Various unpleasant epithets immediately come to mind. As far as we know, this has never happened to GPS, however some problems have occurred in GPS operations over the years, including the Jan. 26, 2016, software upload that adversely affected the GPS system time/UTC offset information in the navigation message and caused a lot of problems for users. See the article here.

We have also been reminded of certain outspoken claims regarding Galileo’s eventual superiority to GPS (and we know there are voices expressing at every opportunity a deep and abiding respect for the immeasurable hard work and dedication that has made GPS, GLONASS and BeiDou what they are today).

All are eager to see an improved and strengthened Galileo, but there is also a perceived need to shake up the establishment, to encourage heightened diligence and, in some cases, a little humility.

In the end, this latest event could serve the maturing Galileo program well. But that will depend on how the relevant parties respond, starting now.

The post Galileo in the Here and Now appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

Motivation and Background

Motivation and Background
GNSS technology has become a crucial component for modern society. One of the major factors that impacts the performance of GNSS at high latitudes and equatorial areas is ionospheric scintillation. Ionospheric scintillation is usually manifested by rapid and random fluctuations in signal amplitude and carrier phase (see S. Basu et alia (2002) and Y. Jiao and Y.T. Morton (2015) in Additional Resources near the end of this article). During severe ionospheric scintillation, deep amplitude fading and high carrier dynamics may result in increased carrier tracking loop errors, carrier phase cycle slips, and potential loss of lock of signals. (see S. Skone et alia (2001) and J. Seo et alia (2011), Additional Resources). As a result, there is a need to monitor and detect ionospheric scintillation, to gain an understanding of the signal characteristics during scintillation, and to develop robust receiver algorithms that can mitigate scintillation effects.

The motivation for this project was initiated by the need to effectively and efficiently collect sufficient volume of high quality, real scintillation data for the purpose of analyzing and characterizing the ionospheric scintillation phenomena. Since 2011, the authors’ research group has been developing multi-GNSS data collection systems to capture scintillation signals by deploying these systems at various locations known to be susceptible to scintillation activities around the world (see Y. Morton et alia (2015)). Figure 1 (see figure at the top of this article) shows the locations of the established and planned data collection sites. Some of the data collection systems are equipped with devices to collect raw intermediate-frequency (IF) samples during scintillation for post-processing. This capability is especially important when commercial ionospheric scintillation monitoring (ISM) receivers are unable to maintain lock of the signals or are incorrectly estimating signal parameters during strong scintillation. A caveat of IF data collection is that it requires an enormous storage space due to the high sampling rate. Therefore, an effective scintillation detector is needed to automatically and accurately detect scintillation events and trigger the IF data collection process. The detector is also useful for researchers to sort out scintillation events collected by continuously operating ISM receivers for analysis.

Most previous scintillation monitoring and detection methods were based on commonly used indicators such as the amplitude and carrier phase scintillation indices (e.g. S₄ and σ_ϕ), and their probability density functions (PDFs) (see W. Fu et alia (1999), S. Taylor et alia (2012) and D.V. Ratnam et alia (2015), Additional Resources). These indicators are the so-called lower-order moments of the scintillation statistics derived from standard deviations of signal parameters around their nominal trends. Abnormalities in these lower-order moments due to scintillation are often indistinguishable from other effects such as multipath and interference. In addition, these previous scintillation detection methods are usually based on traditional Neyman-Pearson detection theory (S.M. Kay (1998), Additional Resources) in which certain PDFs (e.g. Gaussian) under different hypotheses have to be assumed before training and detection. For these reasons, it is difficult for these previous detectors to have reasonable false alarm rates and missed event detection rates.

While missing event detection will clearly lead to missed opportunities to study potential interesting cases, a high false alarm rate will result in the data collection system capturing events that are not of interest to the researcher and lead to wasted storage space and analysis time. 

To overcome the above problems, we have developed a new automatic scintillation detection technique using a machine learning algorithm, called support vector machine (SVM) (see articles from Y. Jiao et alia (2017, 2016 and 2017), Additional Resources). The SVM algorithm is based on the Structural Risk Minimization (SRM) principle, which seeks the boundary with the greatest separation of the two classes in the data samples (see S. Haykin, (2009), Additional Resources). The data samples are transformed into high-dimensional space, where the data will reveal features that could not be captured by lower-order moments of the signal statistics. Moreover, unlike algorithms based on the traditional Empirical Risk Minimization (ERM) (e.g. minimum square error, least squares, and least mean squares), which uses empirical PDFs of the signals to minimize the error between the desired output and the actual output (see again S. Haykin, (2009), the SVM algorithm does not have to assume the PDFs for signals under different hypotheses. Finally, the SVM algorithm can further transfer the data samples that are not originally linearly separable into even higher dimensional space where they may be linearly separable.

The basic concept of SVM is shown in Figure 2 (see figure at the top of this article). Given a training data set 

{x_p; d_p}^P_p=1 

where x_p ∈ ℝ^N is the p^th input sample, d_p = ±1 represents the desired label for two classes. If the classes are linearly separable in ℝ^N, then the discriminant function g(x) = w^Tx + b exists such that 

x_p ∈ C₁ → g(x_p) ≥ 1, then d_p = +1     (1) 

x_p ∈ C₀ → g(x_p) ≤ 1, then d_p = −1     (2)  

The margin of separation between the two classes can then be derived as 

Equation (3) (See inset photo, above right, for equations 3 & 4)

In the SVM algorithm, the goal is to maximize this margin of separation, subject to equations (1) and (2). As a result, the Lagrangian cost function in SVM can be constructed as follows: 

Equation (4) 

where α_p’s are the Lagrangian multipliers.

The further development of SVM techniques is mainly established on the solution of equation (4). For detailed mathematical descriptions and derivations, the readers are referred to Y. Jiao et alia (2017) and S. Haykin, (2009). 

In this article, we summarize the findings reported in Y. Jiao et alia (2017, 2016 and 2017), Additional Resources, which used a large volume of real scintillation data collected from stations in the northern auroral and equatorial areas to train and test the SVM-based amplitude and phase scintillation detectors. The performance of the detectors will be mainly reviewed, including validation accuracy, testing performance on novel data, and concurrent amplitude and phase scintillation detection performance using similar SVM techniques using data from equatorial regions.

Training and Validation 
All the training data was collected by commercial ISM receivers, which output 50 hertz signal intensity and 100 hertz phase measurements. Only GPS L1C/A data is used in this article with an elevation mask of 30˚ to reduce multipath effect. For amplitude scintillation detection, a total of 46 hours of data consisting of 15 segments from Ascension Island and Hong Kong are selected for training. For phase scintillation detection, a total of 28 hours of data consisting of 30 segments from Gakona, Alaska are used for training (Figure 3). The training data are partitioned into three-minute blocks. Empirical class labels are assigned to the training data based on manual inspection of the values of amplitude scintillation index S₄ and phase scintillation index σ_ϕ within each block (examples shown in Fig. 2). Only two class labels are assigned: 0 for non-scintillation data, and 1 for scintillation data. More detailed information of the training data set is listed in Y. Jiao et alia (2016 and 2017), Additional Resources.

The content of the training vector for a three-minute data block is listed in Table 1. The first entry in a column training vector is the class label assigned manually. The second and third entries are the maximum and the average S₄/σ_ϕ index values within the block. To test the impact of the index values on the performance of the SVM detectors, the second and third entries can be turned on or off in the training. The rest of the entries in the training vector are power spectrum densities (PSD) for different frequencies obtained from performing short-time Fourier Transform (STFT) on raw signal intensity and detrended phase measurements for amplitude and phase scintillation detection, respectively. 

Validation can be performed using the training data and the manually-assigned class labels. The validation methods used for amplitude and phase scintillation detection are 25% hold-out validation and 5-fold cross-validation, respectively, as described by S. Haykin, (2009). In 25% hold-out validation, 75% of the training data is selected randomly to train the detector, while the rest is reserved for validation. In 5-fold cross-validation, the training data is randomly portioned into five subsets of equal sizes. One out of the five subsets is retained as the validation data to test the model that is trained by the remaining four subsets. Then, this cross-validation process is repeated five times, so that each of the subsets is used exactly once as the validation data set. The final validation performance is an average of the five validation results. The latter validation method is more suitable for a small training data set. 

The performance of the amplitude and phase scintillation detectors is evaluated in terms of the overall accuracy, and the true positive rate (TPR) and the false positive rate (FPR) of the operating point as listed in Table 2. TPR and FPR are also commonly referred to as “hit rate” and “false alarm rate”, respectively.

They describe the probability of categorizing a target (e.g., a scintillation event) as present when it is truly present or truly absent. In general, the higher the TPR or the lower the FPR is, the better the performance of the detector is. In this study, there are four variations of the detector implementation: the S/σ_4ϕ  features (2^nd and 3^rd entries) are either included or excluded in the training vectors; and the SVM algorithm is either linear SVM or medium Gaussian kernel SVM with a kernel scale of 9.1.

Table 2 shows that both the SVM amplitude detector and phase detector have good performances. Compared to the phase scintillation detector, the general performance of the amplitude scintillation detector seems to be slightly better with a higher overall accuracy and lower FPR. The four variations of either detector show comparable performance. This indicates that non-scintillation and scintillation events are almost linearly separable in the high-dimensional space, and excluding index features from the training vectors does not influence the validation performance of the amplitude or phase scintillation detector. 

Test Performance on Novel Data
To test the generalization capability of the SVM scintillation detectors, several segments of novel data from the training data sites and from other data sites are used. Figure 4 and Figure 5 show test results of the SVM amplitude and phase scintillation detectors using novel data from the training data sites (subplots (a)) and sites not involved in training (subplots (b)). Only the linear SVM technique is used for testing as it shows similar performance to the medium Gaussian SVM in the validation, and is easier to implement.

Results in Figure 4 and Figure 5 show that all the SVM detectors are able to capture strong scintillation events. However, for phase scintillation detection, the SVM detector trained with σ_ϕ features show obvious miss-detection of medium to weak scintillation events, while the detector trained without σ_ϕ features seem to have no problem in detecting weak to strong scintillation. This phenomenon shows that the absolute values of S₄ and σ_ϕ indices alone are not reliable indicators of scintillation activity. For phase scintillation, higher dimension features such as the spectral contents may offer a more reliable means to distinguish scintillation from other activities that impact phase measurements. This is the main reason why a machining learning-based approach that exploits the high-dimensional features can outperform traditional Neyman-Pearson detectors which are solely based on assumed models of low-order statistics such as scintillation indices. 

In addition, Figure 4 and Figure 5 demonstrate that the linear SVM detectors trained without S₄/σ_ϕ features have good generalization capabilities, as they are effective on novel data taken at different locations from the training data sites.

Concurrent Phase and Amplitude Scintillation Detection at Low Latitudes
Other than the stand-alone performance of the amplitude and phase scintillation detectors, it is also interesting to investigate the relationships in SVM detector performances for both amplitude and phase scintillation on the same data set from low latitude areas, where the strongest scintillation events tend to occur. Unlike high-latitude scintillation, which is dominated by phase scintillation, scintillation observed in the low-latitude area often features concurrent amplitude fading and rapid phase fluctuations (see articles from Y. Jiao et alia (2015 and 2013), Additional Resources). Using the data from low-latitude stations, we are able to investigate this feature of low-latitude scintillation from the perspective of detection performance. To ensure that we make a reasonable comparison, the linear SVM detectors trained without S₄/σ_ϕ features are used for amplitude scintillation detection and phase scintillation detection, respectively.

Figure 6 shows results for concurrent amplitude and phase scintillation detection using SVM on novel data from Hong Kong, Jicamarca (Peru), and Singapore. The results show that the SVM phase scintillation detector trained with data from Gakona, AK can effectively operate on data from the low-latitude area. This indicates that the higher dimensional features in phase scintillation are similar in high and low latitude events.

Based on visual inspection of the values of S₄ and σ_ϕ indices in Figure 6, the two indices are highly correlated at low latitudes. However, amplitude scintillation and phase scintillation detections are not concurrent. Results show that amplitude scintillation appears to be detected more often than phase scintillation. 

To further quantify the relationship between concurrent amplitude and phase scintillation detection, Figure 7a plots the percentage of positive phase scintillation detection during positive amplitude scintillation, with respect to different amplitude scintillation levels represented by the mean S₄ values within its three-minute block. The data used for these statistics are 15 segments of novel data with total length of 53 hours from Hong Kong, Jicamarca, and Singapore. Figure 7a shows that the percentage of phase scintillation detection increases as the amplitude scintillation level becomes stronger. When the average S₄ index within a block exceeds 0.3, a concurrent phase scintillation event will definitely be detected if an amplitude scintillation event is detected. A reverse study has also been conducted and the results are shown in Figure 7b where a positive phase scintillation detection is nearly always accompanied by a positive amplitude scintillation detection.

The above relationships indicate that at low latitudes, an amplitude scintillation detector alone is sufficient to detect scintillation activities. Low level amplitude scintillation may not be accompanied by noticeable phase scintillation. However, all phase scintillations are associated with amplitude scintillations. This observation is important for low-latitude scintillation monitoring because signal intensity measurements are more reliable than phase measurements at low latitudes. For high latitudes, phase scintillation detector is needed because phase scintillation is the dominating activity as described by Y. Jiao and Y.T. Morton (2015).

Summary and Conclusions
This article introduces a SVM-based machine learning algorithm for autonomous ionospheric amplitude and phase scintillation detection on GPS signals. The input of the detectors is the PSD of the raw signal intensity and the detrended phase measurements. Instead of having to acquire knowledge of the PDFs of the signals, the machine learning algorithm learns the different high-dimensional features for non-scintillation and scintillation events from the training data, and automatically generates a discriminative hyperplane to optimally separate the two classes with the maximum separation space. 

The trained SVM amplitude and phase scintillation detectors were evaluated in validation and testing, which demonstrate good validation performance and generalization capability in testing. A summary of the findings and conclusions in this work is recapitulated below:

• The overall accuracies in the validation are around 98% and 92% for the SVM amplitude scintillation detector and phase scintillation detector, respectively.
• Linear and medium Gaussian kernel SVM perform similarly for scintillation detection.
• Excluding S₄/σ_ϕ features in the training vector does not affect the validation performance.
• Testing on novel data reveals miss-detection of weak to moderate phase scintillation events using the SVM phase detector trained with σ_ϕ features. This result shows that phase scintillation index values may not be a good indicator of the scintillation activity. Future development of the phase scintillation detector should mainly be based on features in the frequency domain, instead of the absolute values of phase fluctuations.
• The SVM detectors can be expanded to work for data from other sites not involved in training. 
• The detection of amplitude and phase scintillation may not be simultaneous with similarly implemented SVM detection techniques. At low latitudes, whenever phase scintillation is detected, it is almost certain that amplitude scintillation will be detected at the same time. On the other hand, when amplitude scintillation is detected, phase scintillation may not be simultaneously detected but the likelihood increases as scintillation intensifies.

Acknowledgement
The data collection systems are developed, assembled, and managed by CSU GPS Lab engineers Steve Taylor and Harrison Bourne. The authors wish to thank Dr. Don Hampton at the University Alaska Fairbanks, Mr. Marty Karjala at HAARP, Mr. Kevin Abnett at Poker Flat Research Range, Dr. Ding Yu Heh at the Nanyang Technological University, Dr. Marco Milla at the Jicamarca Radio Observatory, and Dr. Zhizhao Liu at the Hong Kong Polytechnic University for their support and hosting of the GNSS data collection systems. Dr. Todd Pedersen from Air Force Research Laboratory at Kirkland AFB helped to collect the GNSS scintillation data on Ascension Island. Jicamarca Radio Observatory is a facility of the Instituto Geofisico del Peru operated with support from NSF grant AGS-0905448 through Cornell University. Ms. Yu Jiao’s work is funded through a startup grant from Colorado State University and a grant from AFOSR (FA9550-14-1-0265). The data collection systems were deployed with funding support from AFRL (FA8650-08-D-1451), AFOSR (FA9550-10-1-0346), the Consortium of Ohio Universities on Navigation and Timekeeping (COUNT), and NSF (AGS-1428042).

Note: The methodologies and results presented in this article are based on materials presented in articles by Y. Jiao et alia (2017, 2016 and 2017), Additional Resources.

Additional Resources
[1] S. Basu, K.M. Groves, S. Basu and P. Sultana, “Specification and forcasting of scintillations in communication and navigation links: current status and future plans,” J. Atmo. Solar-Terr. Phy., vol. 64, no. 16, pp. 1745-1754, Nov. 2002. 
[2] S. Haykin, Neural networks and learning machines, 3rd ed., Upper Saddle River, NJ: Pearson Education Inc., 2009
[3] W. Fu, S. Han, C. Rizos, M. Knight and A. Finn, “Real-time ionospheric scintillation monitoring,” in Proc. ION GPS, Nashville, TN, 1999. 
[4] Y. Jiao and Y.T. Morton, “Comparison of the effect of high-latitude and equatorial ionospheric scintilltaion on GPS signals during the maximum of solar cycle 24,” Radio Sci., vol. 50, no. 9, pp. 886-903, Sept. 2015.
[5] Y. Jiao, J.J. Hall and Y.T. Morton, “Automatic equatorial GPS amplitude scintillation detection using machine learning,” IEEE Trans. Trans. Aerosp. Electron. Syst., 2017.
[6] Y. Jiao, J.J. Hall and Y.T. Morton, “Performance evaluations of an equatorial GPS amplitude scintillation detector using a machine learning algorithm,” in Proc. ION GNSS+ 2016, Portland, OR, 2016.
[7] Y. Jiao, J. J. Hall and Y.T. Morton, “Performance evaluation of an automatic GPS ionospheric phase scintillation detector using a machine learning algorithm,” NAVIGATION, Journal of the Institute of Navigation, 2017.
[8] Y. Jiao, Y.T. Morton, S. Taylor and W. Pelgrum, “Characterization of high latitude ionospheric scintillation of GPS signals,” Radio Sci., vol. 48, no. 6, pp. 698-708, Dec. 2013.
[9] S.M. Kay, Fundamentals of statistical signal processing: Detection theory, vol. 2, Upper Saddle River, NJ: Prentice-Hall, 1998.
[10] Y. Morton, Y. Jiao and S. Taylor, “High-latitude and equatorial ionospheric scintillation based on an event-driven multi-GNSS data collection system,” in Proc. Ionospheric Effects Sym., Alexandria, VA, 2015
[11] D.V. Ratnam, G. Sivavaraprasad and J. Lee, “Automatic ionospheric scintillation detector for global navigation satellite system receivers,” IET Radar Sonar Navig., vol. 9, no. 6, pp. 702-711, 2015.
[12] J. Seo, T. Walter and P. Enge, “Availability impact on GPS aviation due to strong ionospheric scintillation,” IEEE Trans. Aerosp. Electron. Syst., vol. 47, no. 3, pp. 1963-1973, 2011.
[13] S. Skone, K. Knudsen and M. de Jong, “Limitations of GPS receiver tracking performance under ionospheric scintillation conditions,” Phys. Chem. Earth (A), vol. 26, no. 6-8, pp. 613-621, 2001.
[14] S. Taylor, Y. Morton, Y. Jiao, J. Triplett and W. Pelgrum, “An improved ionosphere scintillation event detection and automatic trigger for GNSS data collection systems,” in Proc. ION ITM, Newport Beach, CA, 2012.

The post Automatic GPS Ionospheric Amplitude and Phase Scintillation Detectors appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

Recent changes in financial market regulations, as well a growing demand from traders and service providers for more accurate time, have driven the development of commercial time services with sub-microsecond precision. Several National Metrology Institutes (NMI), including NRC, are currently offering or are developing such services (as described by M. Lombardi et alia and P. Tavella et alia in Additional Resources near the end of this article). The NMIs’ advantages in providing time services are their expertise in time transfer and metrology, and the authority they have in their respective countries for the realization and dissemination of official time.

Most NMI’s contribute to the production of Coordinated Universal Time (UTC) through regular reporting of their timescales to the Bureau International des Poids et Mesures (BIPM). While UTC is a post-processed, paper timescale, each contributing laboratory produces its own version of UTC, represented by UTC(k), which it disseminates in real time. Regular reports from the BIPM to the contributing laboratories of the offsets between UTC and UTC(k) provide traceability of the UTC(k) timescales to UTC. Over decades, NMIs have perfected the methods and tools for the highest accuracy time synchronization. Now this knowledge is being adapted to services for government, industry and military applications. 

NRC has developed a Remote Clock product (NRC-RC) that disseminates time traceable to UTC(NRC) with sub-microsecond precision. The NRC-RC provides superior-accuracy time to its client’s system that guarantees traceability down to the end users’ devices. The service is robust, reliable, and secure. Based on a high quality local oscillator and GPS for time transfer, the remote clock is continuously monitored and adjusted to UTC(NRC) to ensure traceability and minimize vulnerability to GPS signal jamming and spoofing.

Results and Discussion
The NRC-RC configuration consists of a high quality rubidium (Rb) frequency standard, a GPS receiver, a time interval counter, a control computer, and several auxiliary components. Such systems are installed at the remote client site, and at the NRC main laboratory. The NRC-RC output signals consist of a one pulse per second (1PPS) signal, representing UTC(NRC-RC), and a timestamp provided in one of the standard NTP or PTP servers ASCII formats. An additional sine signal output at 5 or 10 megahertz, syntonized to UTC(NRC-RC), is also available. 

Several measurements are performed at each NRC-RC with periods ranging from seconds to minutes. The time offset of the NRC-RC Rb standard 1PPS is measured against the 1PPS from GPS time as derived from the receiver, [Rb – GPS]. The GPS receiver data of the time offset between the receiver time (its 1PPS) and the time from each satellite, GPSsd is also recorded. Similar setup is installed at the NRC main laboratory where the Rb 1PPS signal offset from UTC(NRC), [UTC(NCR) – Rb], is also measured.

Every few minutes, the data acquired at the NRC main laboratory (local, subscript L) is transferred to the RC site (remote, subscript R) where time and frequency transfer calculations and UTC(NRC-RC) timescale adjustments are made. The time transfer between NRC-RC and UTC(NRC), [RCR – UTC(NRC)], is shown in Equation 1. It consists of all these measurement results and also contains the common view comparison of the GPS data. It includes a term equal to the average offset of GPS time from receiver time for each satellite that is visible simultaneously at NRC and at the remote site, [GPSsd_R – GPSsd_L]. The common view method effectively removes the GPS timescale from the equation. By comparing the offset information collected, the Rb frequency and 1PPS are adjusted to keep UTC(NRC-RC) time at the remote site within a few nanoseconds of UTC(NRC). Calibration offset value, D, is added to compensate for static cable and instrumentation delays. 

[RC_R – UTC(NRC)] = [Rb_R – GPS_R] + [GPSsd_R – GPSsd_L] – [Rb_L – GPS_L] – [UTC(NRC) – Rb_L] +D      [1]

The measurement results for [Rb_R − GPS_R], [Rb_L – GPS_L] and [UTC(NRC) – Rb_L] are shown in Figure 1 (a), (b) and (c) (see inset photo, above right, for all figures), respectively. The “local” implementation of NRC-RC does not apply the time transfer information ([GPSsd_R – GPSsd_L] − [Rb_L – GPS_L] − [UTC(NRC) – Rb_L]) to the Rb disciplining, effectively keeping it locked to the GPS signal with a time constant of tens of seconds. As a result, the [Rb_L – GPS_L] measurement shows a straight line behavior, with short-term noise, as can be seen in Fig. 1(b). The fluctuations in [UTC(NRC) – Rb_L] shown in Fig. 1(c) are due to the GPS time signal variation with respect to UTC(NRC). Except for differences in short-term noise, Fig. 1(d) clearly shows that [Rb − GPS_R] is equivalent to [UTC(NRC) − Rb_R] in the intermediate and the long term. Since Rb_L is equivalent to GPS_L (Fig 1(b)), and as it clearly follows from Equation 1, Rb_L is locked to UTC(NRC). Therefore, UTC(NRC-RC) that is derived from Rb_R 1PPS follows UTC(NRC). In Fig. 1(d) we also show for comparison hydrogen maser, HM, offset from UTC(NRC) to demonstrate the noise characteristics of the UTC(NRC) signal and the measurement system.

In order to achieve time transfer accuracy within a few nanoseconds with respect to UTC(NRC), we calibrate internal delays for each individual component of the NRC-RC system, such as the 1PPS distribution system, the Time Interval Counter, and the GPS receiver 1PPS output. For GPS receivers it is important to use one standard configuration for all receivers at different NRC-RC sites to ensure optimal common view noise cancellation. Ideally the NRC-RC system should be calibrated with the GPS antenna that is used on site, but this is not always feasible due to specific site circumstances and accessibility issues. In these cases, in order to achieve the best uncertainty, the GPS output signal should be calibrated using time transfer with a traveling caesium frequency standard (Cs). Using regular performance Cs we achieved time transfer uncertainty with a remote NRC-RC site of under ±10 nanoseconds.

One important parameter for a remote time dissemination system is its hold over time. We use a high quality rubidium oscillator and we adjust its magnetic field setting to control the frequency and keep it close to UTC(NRC). When, for any technical reason, the GPS signal or the time transfer information from the NRC main lab is unavailable or deemed unreliable by the NRC-RC algorithm, the Rb oscillator is allowed to free run for a period of time determined by its stability and the level of drift in UTC(NRC-RC) that is acceptable for the application.

Another contributor to the overall uncertainty of the NRC-RC time signal is the accuracy and the reproducibility of the GPS receiver self-survey position. We tested both the NRC-RC holdover and the signal stability over several cycles of NRC-RC GPS receiver resetting. We used the NRC-RC.001 unit, connected to a small antenna, collocated with UTC(NRC). This way the NRC-RC.001 signal accuracy can be evaluated with lowest uncertainty. Figure 2 shows the results for [UTC(NRC) − NRC-RC.001] offset measured with the time interval counter. The hold over periods for each self-survey cycle lasted for 10,000 seconds. The offset level change due to the variation in the GPS receiver-determined antenna position is well under ±5 nanoseconds. During the holdover intervals the Rb oscillator inside NRC-RC.001 was free running and as it can be seen from the figure, the offset of NRC-RC.001 never exceeded ±80 nanoseconds.

The corresponding Rb phase drift rate of ±30 nanoseconds/hour will be improved in the next upgrade to NRC-RC where additional fine scale adjustments of the Rb magnetic field will be implemented. 

The NRC-RC system can be used in a stationary setup or as a traveling calibration system. If the system needs to be restarted, it is important that the initialization time required to bring the system operating parameters within the specification range is short. If the site location has not been surveyed before and the GPS antenna coordinates are not known, several hours may be required by the GPS receiver used in the NRC-RC system to complete the self-survey and obtain accurate antenna coordinates. We analyzed the receiver performance after the cold start and measured its 1PPS output signal offset from UTC(NRC). The results are shown in Figure 3. The GPS time 1PPS signal offset from UTC NRC is less than ±10 nanoseconds of its fully surveyed value within one minute after start up. The site survey by the GPS receiver is completed after approximately 10,000 seconds. It results in an improved signal-to-noise ratio as can be seen in the plot, but does not affect the time offset measurements significantly.

Another important contributor to the start-up process is the Rb standard. Its frequency and 1PPS signal output time have to be adjusted based on the time transfer information. It is important to bring the frequency of the Rb close to UTC(NRC) as fast as possible, because it directly impacts the holdover time of the unit. In Figure 4 we show the Rb 1PPS signal offset from GPS receiver time and from the reference Cs standard following Rb start up. The Rb was restarted at MJD = 57764.778 and the corresponding spike can be seen in the [Rb_R − GPS_R] data shown in Fig. 4(a). The [CS − Rb_R] data, shown in Fig. 4(b) that is being collected every 10 minutes doesn’t show any phase jumps indicating immediate recovery of accurate time by the Rb after the start up. The curve shown in Fig. 4(c) represents the Rb frequency adjustment values. It can be seen that the frequency adjustment algorithm takes only three steps to bring the Rb frequency to a stable value, in the current implementation of the Rb control algorithm. In the future we plan to modify the Rb control algorithm to shorten the frequency adjustment period after Rb start up to just a few minutes.

For reliable and secure operation of the NRC-RC system we introduced watchdog monitoring of critical system parameters such as system temperature, power levels, equipment health and others. Alerts and notifications are generated by the watchdog and, in some cases when the algorithm detects a major problem with data and deems the output signal quality and accuracy unreliable, the output time signals from NRC-RC are stopped to prevent the dissemination of inaccurate time.

NRC-RC reduces the vulnerability of time dissemination to GPS signal jamming and spoofing. One of the important watchdog process functions is to detect GPS signal jamming or other malfunction and stop the GPS data from being used for time transfer until the interference stops. Due to the long holdover times allowed by the NRC-RC performance, as was shown in Figure 2, the NRC-RC has high tolerance to GPS signal jamming.

In many cases the NRC-RC system has to be installed at an unmanned facility. For this reason it is important to have the full control of the remote system integral parts for power cycling, configuration parameters adjustment, data logging and environmental monitoring. We implemented a web-based interface for easy control and monitoring. Two tabs from the web interface are shown in Figure 5.

Conclusion
We have developed an affordable reliable secure system that disseminates traceable time with uncertainties in tens of nanosecond range.

Careful calibration of the NRC-RC system and time transfer uncertainties allow for long holdover times. With the rubidium oscillator that we selected for this product, 95% guaranteed uncertainty is less than ±200 nanoseconds for eight hours of autonomous operation. Smaller uncertainty or longer holdover times can be achieved with higher quality and more expensive atomic standards. The control systems integrated in the RC algorithm alert the client and NRC staff if any system disruptions or anomalies occur. Events, such as GPS signal degradation, loss of Ethernet connectivity, changes in the SNR level that can be caused by jamming or spoofing, etc., are all communicated via alerts such as email messages, flashing lights or other notifications.

The NRC-RC system is able to take pre-programmed corrective measures based on severity of the problem. The auxiliary systems of the NRC-RC provide: a timecode signal that, along with 1PPS, can be used as a stratum-0 clock for the local NTP or PTP network; a monitoring and alert system for traceable time dissemination across a local network; system operation watchdog processes; and other technical and support services to ensure system security and reliability. Future upgrades include upgrades to system hardware and software to allow time transfer via GLONASS and Galileo GNSS systems.

Several NRC-RC systems can be installed at the client site to improve redundancy and reliability and reduce uncertainty within the system. Each system provides timecode, 1PPS, and frequency (e.g. 10 megahertz) signals traceable to UTC(NRC), UTC and SI Proper Time Frequency. The use of the NRC-RC with each grandmaster of the client’s PTP network, along with the continuous monitoring and analysis of the PTP performance of their clients’ clocks, ensures the quality of the local network systems and provides the necessary evidence to demonstrate time synchronization to UTC for regulatory purposes, while guaranteeing sub-microsecond accuracy across the client’s network and globally between different networks around the world.

Acknowledgement
This article is based in large part on a paper presented at the ION PTTI 2017 conference, January 30-February 2, 2017 in Monterey, California.

Additional Resources
[1] Lombardi, M., A. Novick, G. Neville-Neil, and B. Cooke. “Accurate, traceable, and verifiable time synchronization for world financial markets.” Journal of research of the National Institute of Standards and Technology 121 (2016): 436-463.
[2] Tavella, P., I. Sesia, G. Cerretto, G. Signorile, D. Calonico, E. Cantoni, C. De Stefano, V. Formichella, R. Costa, P. Cerabolini, L. Rotiroti, A. Simonetti, A. Colombo, P. Defraigne, N Ozdemir, M. Gandara, P. L. Puech, V. Hamoniaux, E. Varriale, Q. Morante, T. Widomski, J. Kaczmarek, J. Uzycki, K. Borgulski, P. Olbrysz, J. Kowalski, A. Cernigliaro, F. Fiasca, A. Perucca, A. Samperi, V. Dhiri, E. Giulianini, M. T. Veiga, T. Suárez, M. Mangiantini, A. E. Wallin, L. Galleani, D. Hindley. “The Horizon 2020 DEMETRA project: DEMonstrator of EGNSS services based on Time Reference Architecture.” Metrology for Aerospace (MetroAeroSpace), 2015 IEEE. IEEE, 2015.

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Working Papers explore the technical and scientific themes that underpin GNSS programs and applications. This regular column is coordinated by Prof. Dr.-Ing. Günter Hein, head of Europe’s Galileo Operations and Evolution.

Working Papers explore the technical and scientific themes that underpin GNSS programs and applications. This regular column is coordinated by Prof. Dr.-Ing. Günter Hein, head of Europe’s Galileo Operations and Evolution.

Generation and transmission of faked GNSS signals – so-called spoofing – poses a major threat to GNSS. Spoofing has received considerable attention in recent years, but conclusive assessments or proven countermeasures have still not been found. This article summarizes experience gained while conducting real-world spoofing attacks, with one or two transmission antennas. They were conducted using a modified GNSS radio-frequency (RF) signal generator. A reliable countermeasure against spoofing is direction-of-arrival discrimination and this was realized using a rotating GNSS antenna employing synthetic aperture processing and an adaptive beamforming algorithm. This GNSS receiver/antenna system not only increases the resilience of GNSS reference networks, which are otherwise very vulnerable against sophisticated spoofing attacks, but also allows us to localize the spoofer with high accuracy. It also provides an excellent tool for studying GNSS signal reflections.

Today many applications rely on GNSS and the number is continuously growing. Some of these applications also incorporate GNSS reference station data to improve their navigation solution. Misleading or degrading a GNSS navigation solution can have serious harmful impacts, especially when thinking about Safety-of-Life services. GNSS spoofing is an intentional attack on a GNSS receiver to mislead or degrade the navigation solution. Spoofing is considered as a serious threat, especially when spoofing GNSS reference stations that distribute their degraded or falsified correction data to many GNSS users.

Whereas the position of a reference station (and its time) is typically well known and cannot be spoofed, a sophisticated spoofing attack may induce multipath like effects or ionospheric-like effects on the measured pseudoranges and carrier phases. This attack will degrade the performance of the reference station and the service relying upon it. These spoofing signals do not require a high signal power and thus may be well below the line-of-sight signal power. They are thus very difficult to detect as standard methods like signal-quality-monitoring, C/N₀ monitoring, or a time series analysis still see the line-of-sight signal as the main contribution (see R. T. Ioannides et alia in Additional Resources). Direction of arrival (DoA) estimation, addressed in this article, efficiently detects these attacks by making use of a synthetic antenna aperture and advanced detection and mitigation techniques.

We first describe our spoofing equipment and confirm that advanced spoofing attacks require considerable effort as a number of technical difficulties must be solved. The next section describes the rotating GNSS antenna plus receiver to detect and mitigate the spoofing attack. Finally, results from various spoofing attacks are presented and analyzed.

Degrees of Spoofer Fidelity and Predictability of the Navigation Message 
A GNSS signal spoofer can be realized with various degrees of fidelity. In the simplest case, a GNSS signal is recorded and played back using commercial record and replay systems. In that case, one may also speak of a meaconing attack and the target receiver will see the position of the recorded signal. More sophistication is achieved if a GNSS RF simulator transmits a GNSS signal over air. This already allows for inducing an arbitrary position and time on the target receiver. Linking the spoofed position and time to the true position and time (in order to make the attack less obvious) requires further technology. Whereas the position link is easily established, if the true position of the target is known, time requires synchronizing the signal generator to the true GNSS time and frequency. This requires that a dedicated GNSS receiver provide a pulse-per-second (PPS) output to the spoofer signal generator. Even more sophistication is required if the spoofer attempts to broadcast an identical navigation message as the satellites. This will render the spoofing signal even less distinguishable from the true signal. As the message needs to be broadcast in real-time by the spoofer, it is necessary to predict the message, as a data link from the data message capturing receiver to the spoofer will always have some latency.

To better understand the predictability of the navigation message for GPS C/A and Galileo Open Service (OS), we note that the respective interface control documents specify the message structure for those data fields which are actually used for navigation. Those fields can be recorded by a dedicated receiver and can be predicted into the future. The prediction is valid as long as the content of the data fields (e.g., the Kepler elements) does not change. Changes after an upload from the ground control segment occur every few hours. There are other fields in the navigation message which are not specified in the interface control document. They are usually called spare or reserved fields. The extent to which these can be predicted has been assessed within a short experiment.

As the first and most important signal, the GPS C/A signal is considered. The GPS C/A message structure includes parity bits, telemetry, and handover words. A full-frame of the navigation message has a duration of 12.5 minutes and is subdivided into 25 pages. Each page has five subframes. It is straightforward to extrapolate the navigation data bits. Only the telemetry and handover word must be updated to reflect the current sent time, and this requires the recalculation of the parity bits. The content and definition of the reserved bits is not known. They are contained in Subframes 1, 4, and 5, with most of them in Subframe 4.

We tracked eight GPS C/A signals over 2,099 seconds starting on November 28, 2013 at 09:10:49 and logged the reserved bits. Tables 1 and 2 provide the statistics. The field “Bit” indicates the location of the bits within the subframe. The field “Cnt” is the number of occurrences of the specific pattern in that location. The field “Val” is the pattern in hexadecimal notation. The field “PRNs” lists the satellites that broadcast the listed pattern. The number of occurrences includes all satellites. First, Table 1 shows the occurrence within Subframe 1. For example, bits 91-113 showed mostly the content 0x1326fe for all PRNs over the whole duration, but for PRN9 the content 0x1726fe was also broadcast. For Subframe 5, the situation is similar (see Table 2). The bits in page 25 (=SV-Id 51) are different for two different sets of PRNs but did not change during the experiment.

The situation for Subframe 4 is more complex. This subframe has a different content for each page and this also applies for the reserved bits. The statistics for the whole duration show that most of the reserved bits repeat, but exceptions occur. For example, in the page with SV-Id 57 or 62, bits 271-292 change. If the duration of the statistics is shortened, then the reserved bits remain constant. We conclude that the GPS C/A navigation message can be predicted with a very good likelihood to guess the correct navigation data bits. Occasional changes (when ephemeris data is uploaded or changes occur in the reserved bits), however, cannot be foreseen.

As a second important case, the Galileo I/NAV message as used for E1 OS has been experimentally analyzed for broadcast status as of November 2013. The structure of the I/NAV message is more complex than that of the GPS C/A navigation message. The message period is 720 seconds (called a frame) and is subdivided into subframes with 30-second duration and pages with two-second duration. Each page has an even and odd part, with a duration of one second. The overhead of the messages includes the sync pattern, tail bits, and a cyclic-redundancy-check (CRC). The message is convolutional encoded and interleaved. The odd page part contains reserved bits, spare bits, and search-and-rescue (SAR) bits, which are potentially not predictable. Furthermore, the data content is not defined for Word type 0. The presence of alert pages complicates the structure and predictability.

Using exactly the same experiment as before, the Galileo I/NAV message content was analyzed. Results are obviously very preliminary as the data content of I/NAV may and will most likely change during the later phase of Galileo operation. Table 3 shows that Word 0 was broadcast frequently but always had the same data content of alternating zeros and ones. Furthermore, we found that the 40 bits of the “Reserved 1” field of the odd page contained 0x0, the 24 bits (22-bit SAR plus 2 spare bits) contained 0xaaaaa9, and the 8 bits of the “Reserved 2” field contained 0xfd. It should also be noted that during the experiment, no alert page was broadcast.

Real-World Spoofing Test Setup
The spoofing setup used within this work for the real-world tests consists of an RF constellation simulator operated in a dedicated spoofing mode. The simulator is frequency synchronized via a rubidium atomic clock. Time synchronization to the true GNSS signals is achieved via a separate GNSS receiver. In general, the setup is similar to the one used by T. E. Humphreys et alia, but in our case a field-programmable-gate-array (FPGA) based constellation simulator has been used to generate the signals. Figure 1 (see inset photo, above right) shows the principal setup as a block diagram and its realization.

The spoofer calibration GNSS receiver delivers demodulated navigation data symbols. Those symbols are collected over a certain time and are then predicted for GPS C/A to allow real-time transmission of the true symbols. The Galileo spoofing was done on the pilot (E1C) only, and in this case no prediction is necessary. The spoofing mode allows for the application of position/velocity and time/time drift offsets to the true target position, velocity, and time (PVT).

The setup was installed in a 19 inch rack in the laboratory with a 20 meter RF cable to the transmit antenna on the roof. The complete setup with all RF cables (signal-in-space (SIS) antenna to transmit antenna) was calibrated with a test receiver connected to the RF output of the signal simulator for the exact delay between the PPS of the rubidium clock and the PPS of the test receiver receiving the spoofing signal. The determined offset was configured in the spoofing mode setup of the RF simulator for compensation. To further compensate for the free space loss, 55 decibel amplifiers were connected to the RF output to provide margin in addition to the simulator internal amplifier.

The tests were performed on the IFEN premises in Poing, Germany. Respective transmission permission was granted and proper measures ensured that the spoofing signal was weak enough. The transmit antenna was installed on the roof pointing to the receivers under tests (one static and one rotating antenna receiver) placed on the parking deck. On the other side of the roof, outside the effects of the spoofing signal, a second static and a second rotating antenna receiver used as reference were installed and were running throughout the experimentations. Figure 2 (see inset photo, above right) shows the setup with views from and to the parking deck.

The setup was used in a test campaign lasting several days to perform the following spoofing attacks:

• Position spoofing by introducing a velocity after initial multipath spoofing to take over the receiver.
• Time spoofing by introducing a time drift after initial multipath spoofing to take over the receiver.
• Multipath spoofing without any offset to the truth position and time.

Furthermore, with an additional transmit antenna, the azimuth angular resolution for spoofer signal detection was determined. Therefore, the spoofing signal was split at the RF level and transmitted over two transmit antennas with an angle of around 30 degrees to the test receiver. While the first transmit antenna was kept static, the other transmit antenna was gradually repositioned and moved step by step nearer to the static first transmitter until they were both side by side.

At the beginning of each measurement day a brief calibration and verification of the test setup was performed to achieve the same signal propagation conditions for the whole measurement campaign. This was necessary due to severe fading effects. Fading effects in spoofing occur among all involved signals. They include the direct satellite and spoofing signal as well as reflections of these signals from the ground. These effects occurred especially on the static reference receiver with significant C/N₀ variations for nearly identical placement of the antennas. By moving the reference receiver antenna slightly, these effects have been increased or decreased. Figure 3 (see inset photo, above right) shows the fading effect for the multipath spoofing scenario on the static reference receiver. Due to misalignment of the phase of the spoofing signal with respect to the direct LOS signal, signal reflections occur, especially for low elevation transmitted signals. Constructive and destructive signal effects can be observed as shown in the figure and are caused by the increasing drift of the spoofer oscillator. In order to reduce the fading effects (between the spoofing signal and its ground reflection) a ground plane with approximately 40-centimeter diameter was placed below the receiving antenna. This reduced the impact of ground multipath from the spoofing signal and decreased the fading amplitude; overall the experiments were then more repeatable.

Spoofing Mitigation Via Direction of Arrival Discrimination
Spoofing signals can be easily distinguished from true GNSS signals if the DoA can be estimated. Spoofing signals will most likely come from a ground based transmitter (thus arriving at a low elevation to the target receiver) and the DoA will be identical for all signals. DoA is of course different for each true satellite signal. DoA estimation can be done with a proper GNSS receiver plus antenna, provided that multiple antenna elements are used within a phased array system (see R. T. Ioannides et alia). An alternative approach is to use a synthetic aperture GNSS antenna exploiting the antenna motion to combine GNSS signals received at different spatial locations to optimize a certain performance criterion. Like phased array antennas, the synthetic aperture GNSS antenna allows us to form a certain antenna gain pattern and can thus be used to eliminate the effect of spoofing signals. Synthetic aperture antennas have so far received only limited attention from the GNSS community. Proof-of-concepts have been shown conducted by T. Lin et alia and the work by T. Pany et alia investigated several signal processing options for synthetic aperture antennas.

The work presented here uses a rotating GNSS antenna (similar to T. Pany et alia), but with an updated mechanical design rendering it water and ice proof (see Figure 4 (see inset photo, above right)). The antenna motion is measured precisely with a magnetic sensor allowing determination of the antenna position with sub-millimeter precision at every instant. The antenna rotates at a rate of one hertz and has a rotation radius of 50 centimeters. The rotation plane is horizontally aligned. A rotating antenna is mechanically relatively easy to realize and all mechanical components can be chosen for long-term operation without any maintenance. An RF slip ring is needed to connect the GNSS antenna.

Operation Principle of a Synthetic Aperture Antenna
The basic operating principle of the chosen synthetic aperture system is shown in Figure 5. It can be viewed as a variant of a vector tracking receiver. If the receiver has a PVT solution available, the receiver predicts this solution for the next beamforming interval (e.g., duration of one second) and uses this prediction to compute replica signals. The replica signals are then correlated against the received GNSS signal from the rotating antenna. The correlation time interval is short (e.g., four milliseconds) and in this case 250 correlation values are obtained for each received GNSS satellite signal over one rotation. The rotating antenna is therefore equivalent to a phased array antenna with 250 elements.

The correlation values are collected for satellites and all code phase offsets (e.g., early, prompt and late). Then the impact of the satellite motion and the receiver clock drift and jitter is removed. The receiver clock has a nontrivial impact on the correlation values and using more stable oscillators (e.g., atomic frequency standards) considerably simplifies the receiver clock estimation efforts.

Once those effects are removed, it can be shown that the correlation values can be treated as though they were received at the same instant. Consequently, the whole theory for phased array systems can be employed. Digital beamforming and null steering techniques can be employed, allowing an update of the synthetic array weight vector per the time-varying signals’ conditions, and thus adjusting the radiation pattern of the antenna array dynamically, at each instant. It can be a maximization process, such as the maximization of the signal-to-noise ratio, or of the signal-to-interference-and-noise ratio; or it can be a minimization process, such as the minimization of an error between a model and the actual signals (Minimum Mean Square Error (MMSE) algorithm), or of the variance of the beamformer output (Linearly Constrained Minimum Variance (LCMV) algorithm or Minimum Variance Distortion-less Response (MVDR) algorithm).

The beamforming algorithm produces combined correlation values eventually exploiting the spatial diversity. Those correlation values form the basis for the generated code and carrier pseudoranges. It is important to consider distortion-less response algorithms, as they ensure that the beamforming does not introduce any biases in the code or carrier pseudoranges.

For our tests, an adaptive beamforming algorithm was selected, as shown in Figure 6. The algorithm is tailored to handle spoofing signals. Being an engineering solution, it first eliminates the LOS signals from the compensated correlation values by applying suitable Null operators. This can be done to high precision, as the DoA of the LOS signals is known. In the next step, the received signal power is estimated as a function of the DoA. This is done on a grid of elevation and azimuth values with a grid resolution of one degree. It should be noted that the raw beam width of the synthetic aperture antenna is on the order of 10 degrees, due to the selected diameter of one meter and wavelength of 19.03 centimeters.

In the case where no spoofing signal is present (and no strong specular multipath reflection exists), the estimated received signal power (as a function of elevation and azimuth) is noise-like. In the case where a spoofing signal is present, it clearly shows up as a peak in this map (see later sections for real-world data) and its DoA can be retrieved.

The positions of the peaks are used to identify the DoA of the spoofing signals, which themselves are used to construct a Null operator to eliminate the spoofing signals from the compensated correlation values. After the spoofing signals have been eliminated, it is reasonable to assume that only the LOS is present and, by focusing the synthetic aperture antenna gain towards the LOS, optimal correlation values are obtained.

A characteristic of the chosen method is that spoofing signals are treated independently of their power. In other words, a weak spoofer is treated the same as a strong spoofer (provided the weak spoofer is detected). In contrast, an MVDR beamformer will react more adaptively on varying signal strengths. Furthermore, the implemented algorithms all require either pilot signals or known navigation data bits. Estimation of unknown navigation data symbols (or bits) for the LOS or for the spoofer signals is currently not considered.

Multipath Spoofing Attack
Spoofing detection and mitigation experiments were performed on the parking deck of the IFEN premises.

All spoofing experiments were performed on L1 GPS C/A and Galileo E1 OS pilot. As a first case, we analyze a multipath spoofing scenario, where the spoofer transmits an identical signal as the signal-in-space without any position or time deviation.

The effect of multipath spoofing is shown on

• a conventional receiver with typical frequency, phase, and delay lock loops; and on a
• receiver with the synthetic aperture antenna.

The goal of this scenario was to degrade the PVT solution of the receiver by the introduced multipath effects. Figure 7 shows a baseline processing between the rover receiver and the reference station receiver. The baseline processing made use of a dedicated analysis tool for static baseline processing. This tool calculates the position solution and the code and carrier residuals. The spoofing attack starts at around 12:43. The lower two plots of the conventional receiver (left column) immediately show increased phase and code residuals with the start of the multipath spoofing (Note: Phase residuals above 0.05 meters or code residuals above 10 meters were directly eliminated by the processing and are not shown here). Over the complete time period, the measurements show cycle slips for almost every epoch and signal. In effect, the data from the static receiver is completely useless during the multipath spoofing attack and the position solution also degrades. In contrast, the code and phase residuals of the receiver with synthetic aperture antenna (with and without Nulling) also slightly degrade after the start of the spoofing attack, but the phase residuals still are in a reasonable range and the observations show almost no cycle slips in the processing.

Code and carrier measurements have a degraded accuracy but can still be used for positioning. We also note a slightly higher accuracy if Nulling is applied (compared to synthetic aperture processing without Nulling) and conclude that focusing the antenna beam towards the satellite already eliminates the bulk of the spoofing signal energy.

Position Spoofing Attack
As a second case, we analyze a position spoofing scenario where the spoofer takes over the tracking loops of the receiver under attack and moves the position solution eastwards. The effect of position spoofing is shown on

• a conventional receiver with typical frequency, phase, and delay lock loops; and on a
• receiver with the synthetic aperture antenna.

The goal of this scenario was to capture the victim receiver’s tracking loops and shift the position solution eastwards. Figure 8 shows two position scatter plots, with the left plot referring to the conventional receiver and the right one to the synthetic aperture receiver. The left plot clearly demonstrates that it was possible to take over the control of the conventional receiver tracking loops and shift the position over 1.5 kilometers away from the receiver’s true position, with “a” referring to the true position when tracking the LOS without spoofing. The second circle labeled as “b” refers to the start of the spoofing attack and it shows increased position residuals indicated symbolically by a larger circle diameter. It is expected that this increased variance is caused by signal fading effects due to overlapping of the true GNSS signal and falsified direct and surface reflected spoofing signals during signal propagation. The introduced position drift was stopped after about 1.5 kilometers offset at label “c.” The synthetic aperture receiver shown on the right of Figure 8 detects and mitigates the spoofing attack and prevents the victim receiver from locking onto the falsified signal. The synthetic aperture receiver remains at the true PVT solution, as indicated in the right plot.

The initial PVT of the spoofing signal coincides with the attacked receiver’s PVT solution to take over the tracking loops smoothly, which means that the correlation function of the spoofer is exactly located in the LOS signal correlation function. Figure 9 shows the multicorrelator output of the conventional receiver in the middle of the spoofing attack. At that instant we have a constant position displacement of several hundred meters to the true PVT. Figure 9 further verifies that a spoofing signal is actually present, which results in clearly separated correlation functions in the code phase direction.

The above described beamforming method (spoofing detection and Nulling) allows us to estimate the signal power coming from a certain DoA by projecting the received signal onto the expected phase signature and integration over the beamforming interval. Based on this, signal power maps spanned over azimuth and elevation can be derived (see Figure 10). The upper plots show the received signal power with an adjustable greyscale in a typical satellite sky plot, while in this case +10 decibels to LOS relates to black and −25 decibels to LOS relates to white. The left plots in this figure correspond to spoofing detection where a spoofing signal is still present and the right plots show the same signal after elimination (Nulling) of the spoofer. The left lower plot clearly shows two peaks, with the right one corresponding to azimuth and elevation of the LOS signal, and the left one to the spoofer location (indicated in red in the corresponding sky plot). The LOS signal is eliminated via Nulling in the upper plots but retained in the lower plots.

If the spoofing signal exhibits a certain threshold compared to the LOS signal, it is decided that a spoofing signal is present. In such a case the exceeding threshold is marked red in the sky plot as shown in the upper left plot of Figure 10 and azimuth and elevation angle are estimated to remove the spoofing signal by placing a Null into this spatial direction. The spoofing elimination result is shown in the right plot of the same figure, where only the LOS component remains. All spoofing detection information is written in real-time to a file and to the status window of the software receiver, as seen in Figure 11. The processing of different PRNs results in virtually identical DoAs as all originate from the same spoofing antenna.

Time Spoofing Attack
For the third case we analyze a time spoofing scenario, where the spoofer takes over the tracking loops of the receiver under attack and manipulates the receiver time by inducing a time drift in the spoofing signal.

The effect of this time spoofing is shown on

• a conventional receiver with typical frequency, phase, and delay lock loops; and on a
• receiver with the synthetic aperture antenna.

The goal of this scenario was to capture the victim receiver’s tracking loops and shift the receiver time more than 26.5 microseconds away. This threshold is given as an example by D.P. Shepherd et alia of success for a timing attack against phasor measurement units (PMU) in electric power control systems. Figure 12 shows the receiver clock error and drift plots for the time spoofing attack. The upper plot refers to the conventional receiver and the lower one to the synthetic aperture receiver. The upper plot clearly demonstrates that it was possible to take over the control of the conventional receiver tracking loops and shift the receiver clock up to 400 microseconds away from the receiver’s true clock error. For this scenario, the time spoofing started at 300 seconds with increasing time drift until the intended time drift of 1 nanosecond/second was reached and the time drift was kept constant for the whole spoofing period. The synthetic aperture receiver shown in the lower plot does not show any changes in the clock drift and remains at its true time solution.

Multiple Spoofers
A more sophisticated spoofing attack may involve multiple transmission antennas. To test the ability of the rotating antenna to detect and mitigate transmissions from multiple spoofers, the same spoofing signal was distributed to two antennas via an RF splitter. The transmission antennas were located at 49 degrees and 68 degrees azimuth and both at about five degrees elevation. The synthetic aperture antenna was able to process this scenario and output the estimated signal power as a function of elevation and azimuth. An example plot is shown in Figure 13. It is very important to note that it is quite difficult to visualize signal power from multiple sources if those sources have significantly different powers. For example, if the combined signal power is plotted (upper plot of Figure 13), only the LOS signal from the satellite is clearly visible. After elimination (via Nulling), the stronger spoofing signal at 49 degrees azimuth is visible (lower left plot) and after further Nulling of the 49 degree spoofer, the spoofing signal at 68 degrees becomes visible (lower right plot). This demonstrates very well the ability of the synthetic aperture antenna to discriminate, localize, and eliminate multiple spoofing signals.

To verify the ability of the antenna to separate two spoofing signals, Figure 14 shows the estimated azimuth for both spoofers during a stepwise reduction of the azimuth difference between the spoofers. Each blue dot in the plot corresponds to a detected spoofing signal. It can be seen that both spoofers can be separated and detected well within the first two sections. The spoofer with the lower signal power is at about 70 degrees and the spoofers with the higher signal powers at about 50 and 59 degrees. Post-processing analysis showed that the 70 degree spoofer seems to appear significantly weaker compared to the moving spoofer, which is assumed to be caused from destructive signal multipath effects. From Section 3 on, it seems that the azimuth difference is too low to separate them via the DoA estimation algorithm used. It might be that the weaker spoofer is partially suppressed when applying the nulling and thus becomes invisible because the signal power drops below the noise floor. Nevertheless the azimuth of the strong spoofing signal is still reliably detected.

An interesting effect is marked in yellow in Figure 14. During the regions when one spoofing antenna is actually moved, the algorithm tends to detect the static spoofer. It is assumed that this effect comes from an improperly adjusted spoofing antenna during the movement, which leads to a significantly lower signal power making the algorithms briefly able to detect the static antenna at the beginning of Sections 3, 4, and 5.

Table 4 lists the estimated and true azimuth angles for all sections. All reference azimuth angles have been calculated from surveyed signal reception and transmission points. We conclude that the azimuth of the spoofer can be determined with an accuracy of around two degrees. Improvements in the signal processing (super resolution methods) and better understanding of the signal propagation process may further increase the accuracy and are the subjects of ongoing research.

Multipath Analysis
Signal reflections on a wall, for example, can be seen as weaker and delayed spoofing signals. The DoA estimation algorithm was tested by detecting the DoA of multipath signals. Therefore, the rotating antenna was placed beside a building wall in order to detect multipath signal reflections. GPS C/A signals were analyzed and Figure 15 shows the outcome of the verification experiment. The building wall is shown as a black line from (nearly) north to south within the sky plot. All tracked satellites which are visible in the sky plot are located in the west because the others are blocked by the wall. Within the signal power map, the LOS signal contribution was eliminated via Nulling. After Nulling, Figure 15 shows six clearly visible reflections. Due to the simple geometry, each reflection can be assigned to a GNSS satellite. The plot also shows the estimated signal strength in decibels with respect to the LOS signal and a yellow line outlines the corresponding satellite. No further analysis has been performed by the authors, but it is obvious that the synthetic aperture antenna provides a unique tool to analyze GNSS signal reflections.

Summary and Outlook
By performing theoretical investigations, simulations, and real-world experimentation, we demonstrated that a synthetic aperture antenna can reliably detect and mitigate even sophisticated spoofing attacks. The direction-of-arrival is a reliable metric to discriminate spoofing signals from LOS signals and also localize one or more spoofers with high angular resolution of two degrees.

Extensive real-world spoofing experiments have been conducted and the results obtained so far seem to confirm the theoretical expectations. Initial data processing shows that even sophisticated carrier phase based reference station data processing (e.g., for GNSS reference station networks) can be conducted during a (mitigated) spoofing attack. It can thus be expected that the synthetic aperture processing would represent an extremely robust solution for reference stations. In contrast, in all cases the conducted spoofing attacks caused the intended PVT degradation for a conventional GPS+Galileo receiver.

Further sophistication of the synthetic aperture processing should in our view include methods to constrain the receiver clock during a spoofing attack and methods to handle spoofing signals with a broadcast message being different from the true message. The synthetic aperture antenna can also be used to study GNSS signal reflections as it can reliably estimate the DoA of multipath signals.

Acknowledgments and Disclaimer
Acknowledgement should go to Eva Bauer and Daniel Koch for their support during the measurement campaigns and data analysis for this work. All work has been performed within the Galileo Evolution Programme EGEP funded project SETI (No. EGEP-ID 89-1.11) of the European Space Agency (ESA). The views expressed in this article are solely the opinions of the authors and do not reflect those of the ESA.

Additional Resources
[1] Humphreys, T. E., Ledvina, B. M., Psiaki, M. L., O’Hanlon, B. W., and Kintner, P. M., Jr., “Assessing the Spoofing Threat: Development of a Portable GPS Civilian Spoofer,” Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 2314-2325
[2] Ioannides, R. T., Pany, T., and Gibbons, G., “Known Vulnerabilities of Global Navigation Satellite Systems, Status, and Potential Mitigation Techniques,” Proceedings of the IEEE, Volume: 104, Issue: 6, June 2016, pp. 1174-1194
[3] Lin, T., Broumandan, A., Nielsen, J., O’Driscoll, C., and Lachapelle, G., “Robust Beamforming for GNSS Synthetic Antenna Arrays,” Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 387-401
[4] Pany, T., Falk, N., Riedl, B., Stöber, C., Winkel, J., and Ranner, H.-P., “GNSS Synthetic Aperture Processing with Artificial Antenna Motion,” Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 3163-3171
[5] Shepard, D. P., Humphreys, T. E., and Fansler, A. A., “Going Up Against Time – The Power Grid’s Vulnerability to GPS Spoofing Attacks,” GPS World, August 2012, pp. 34-38

The post Real World Spoofing Trials and Mitigation appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

Though the United States has been working on a backup for GPS for years, and was actually close to completing an equipment update to that end in 2009, Europe may be the first to put in place a fully independent alternative for positioning and timing data — an economic insurance policy against satellite navigation signals being jammed or disrupted.

Led by the United Kingdom, the Europeans are weighing how to deal with the vulnerabilities created by relying solely on signals from GNSS. As in the U.S. their options include recycling their old Loran C navigation sites to support an enhanced Loran (eLoran) service as a backup for GPS and Galileo. 

“There is a very increased focus on GNSS resiliency at the moment,” said an expert familiar with the issue. “A number of countries in Europe are working towards PNT (position, navigation and timing) strategies,” the source said, adding that “there’s a lot of discussion about PNT in the round — not just GNSS.”

The European Commission (EC) is funding a study in support of a European radionavigation plan, said the source, and that study discusses the need for resilient PNT and looks at using terrestrial systems as well as space-based signals. The European Space Agency is also taking a broader perspective in its new navigation program, describing its new endeavor as a PNT effort, not a GNSS one, and putting a strong emphasis on hybrid systems, said the expert.

U.K. Initiatives
Feeding into those broad European efforts are two PNT-focused studies in the U.K., including a Blackett Review at the highest levels.

Sir Mark Walport, the U.K.’s Government Chief Scientific Adviser, is conducting the review, which should be completed by the end of this year, several sources, told Inside GNSS. All of those who described the work asked for anonymity to be able to discuss it freely. 

The Blackett team is looking at how dependent critical services are on GNSS and, therefore, how vulnerable they would be to GNSS disruption. The study springs from an earlier Blackett Review which recommended looking more closely at timing data, a course of work that was later expanded to include position and navigation. 

The review will incorporate the results of a separate but related study looking at the fiscal consequences of a GNSS disruption in the U.K.

“It just looks squarely at the economic impacts,” said one of the experts. 

Together, said one of the sources, the two studies will give a well-rounded view of the PNT-related economic and technical challenges faced by the U.K. including critical infrastructure dependencies. Perhaps more importantly, they will also look at possible solutions.

The Blackett Review will include recommendations, the source said, which could range from doing additional studies or developing a strategy to boosting funding in a particular area. The recommendations are quite high level, they said, but carry a lot of weight. 

“The recommendations are effectively from the government’s chief science adviser,” the source explained.

“That is a very powerful person to stand up and say we need to do this or we need to do that.”

The format of the Blackett Review may be especially useful. It is a type of study that follows a set process of analysis and presentation aimed at supporting government policymakers. 

“Awareness of the vulnerability of GPS, and of GNSS grows stronger,” said another source. “It’s almost complete amongst engineers but the difficulty is that it’s only patchy amongst politicians.” 

Depending on the findings the U.K. may move quickly to implement some of those solutions, an expert said. One of the options that could be suggested is the implementation of eLoran — though that is not a course of action Great Britain can undertake on its own. 

Dry and Warm
The eLoran system, which the British have been demonstrating at their Anthorn site, sends out powerful, low-frequency signals using terrestrial transmitters that do not have the same vulnerabilities as space-based systems to space weather or future on-orbit conflicts. The system is widely considered to be a promising backup for GPS, particularly for timing data.

“It’s delivering, certainly, a microsecond,” said David Last, a radionavigation expert following the Anthorn tests. “We are aiming for 100 nanoseconds service in due course and that will require a differential operation — but the substantial market is for a microsecond at the moment.”

“eLoran has a very stable frequency output, a frequency available because it’s based on three atomic clocks on the stations just like GPS has three atomic clocks in the satellite,” added Charles “Chuck” Schue, the co-founder, president and CEO of UrsaNav, which provides eLoran technology. UrsaNav has been working with the Harris Corp. and the U.S. government through a Cooperative Research And Development Agreement (CRADA) to test eLoran as a wide-area timing source in the United States. Schue is also a co-owner of Taviga with Charles Curry of Chronos Technology Ltd. Taviga supports low frequency PNT in Europe including eLoran. More information here.

Both the U.S. and Europe have a system of old Loran C stations that could be converted into eLoran stations. Unlike the U.S., which has removed the equipment and towers from the majority of its sites, the Europeans have been keeping their sites in working condition until a final decision on eLoran is made. 

There are five European nations with Loran sites. The U.K., Germany and Denmark each have one site, France has two (though one source expressed concern one had been shut down) and Norway has three. Norway did have four sites, but dropped its northernmost station. 

With the exception of that one Norwegian site, Schue said he believed the European Loran stations were being kept “dry and warm” — that is they are generally not operating but the power was still on. The Germans have repurposed their site for another kind of service but not one that would conflict with eLoran, said Schue, so a multi-purpose broadcast site remains possible. 

The U.K. has taken a collaborative approach in addressing eLoran’s potential, Schue told Inside GNSS. The U.K. hosted a meeting attended by the other Loran-equipped nations and potential eLoran users. The British are working with these countries to see if they can get back to where they were with the Northern European Loran system, Schue said, to provide “at least timing and frequency backup across their various coverage areas and possibly even positioning, depending on which nations and stations want to play.”

Though the U.K. work seems to be moving smoothly there have been notable, nontechnical disruptions. It is unclear, for example, how the U.K.’s exit from the European Union (EU) will impact future cooperation and the rules of the June 8 U.K. election, which was still on the horizon at press time, required that British officials not make decisions, release study results or speak publicly. On top of that, should the U.K. government change hands there also likely will be transition-related delays.

In fact, there is at least one important personnel change already in the works. Sir Walport was recently tapped to lead the U.K. Research and Innovation (UKRI). Hopefully that shift will not delay the Blackett Review too much. Walport is to continue with the study, said one person familiar with the work, and his replacement will likely co-chair the research. 

Stuck
Meanwhile, across the pond in the United States, efforts to set up a GPS backup remain mired in studies. 

The U.S. is now roughly a year and a half into an effort to establish requirements for a GPS backup system. This followed an extensive research effort in 2014, which was itself a follow-up to a three-year study completed roughly seven years earlier. 

According to a Dec. 7, 2016 presentation by Jim Platt, the director of the Department of Homeland Security’s PNT Office, to the National Space-Based PNT Advisory Board, the validation of the timing requirements for critical infrastructure should be completed by September. 

Meeting the end-of-year deadline for the comprehensive and extensive report now being developed will be difficult, said Dana Goward, the president of the Resilient Navigation and Timing Foundation. “And then I imagine after that they’re going to have to do an analysis of alternatives, which I’m expecting is going to be nearly a repeat of what has been done before. They look at all the available technologies and compare them against each other and see which is the best compliment and backup system for GPS. My guess is …they will probably again find that eLoran is the best, if not the only, wide area compliment and backup system that is available. But that’s something that they have to grind through and all of that grinding through is going to take some time I’m sure.” 

Though the technology has not improved or changed significantly since earlier studies, Goward said the people in the administration feel this is the path they are compelled to pursue. 

“That said,” Goward told Inside GNSS, “we are hoping that some people at the political level will begin to understand this challenge better and perhaps take greater notice of the previous work that’s been done and shorten the process.”

In fact, a new bill was introduced in Congress May 18 with provisions mandating that the Secretary of Transportation work with the Commandant of the Coast Guard to establish eLoran as a backup for GPS in the United States. Among other things the new system would have to be wireless, terrestrial, synchronized with coordinated universal time, and able to penetrate underground and inside buildings — all characteristics of eLoran. 

Introduced by Duncan Hunter, R-Calif., an established supporter of eLoran, bill H.R. 2518 would require the Department of Transportation secretary to deliver a plan to lawmakers to establish such a system within three years — “subject to the availability of appropriations.”

That’s quite a proviso given that it’s been a lack of appropriations that has been holding up deployment of eLoran in the U.S. for years. 

A plan to deploy eLoran, the culmination of that three-year study, was first announced in 2008 by the Department of Homeland Security. With some $160 million in upgrades to the old sites nearly completed, DHS wanted to move the Coast Guard —which was and is responsible for Loran — to the National Protection and Programs Directorate or NPPD, which was in charge of infrastructure protection, according to Goward. The transfer was stalled, however, because DHS put the enacting language in its budget proposal and Congress failed to get it passed, resorting to a continuing resolution instead. The program was then cut on the recommendation of the Office of Management and Budget, which made a last minute change to President Obama’s first budget to showcase the White House’s ability to find savings. Despite loud protests the money for Loran C stayed cut, effectively killing eLoran in the process. Promises to restore the program were never fulfilled, according to Goward.

A more detailed summary of what happened can be found on the Foundation’s website.

Though Congress eventually ordered the sites preserved pending a final eLoran decision, the lawmakers were too slow to save the infrastructure. The Coast Guard was ordered to dismantle the sites and didn’t have the funding to do otherwise. They efficiently emptied the majority of the 25 sites, largely flushing the $160 million in upgrades in the process. 

It wasn’t their fault, said Schue. “They did the best they could.” 

Now, said Schue, “there’s only eight sites in the contiguous U.S. that still have antennas up and then at all the other sites the antennas are down both here in the U.S. and in Canada. Canada followed our lead and took their towers down. At most of the stations the technology has been taken out and disposed of including in some cases the generators, you know transformers, air conditioners — those kinds of things.”

New eLoran Standards
There is one bright spot amidst the tangle of delays and equipment loss — the launch of a new, formal development process for international eLoran standards. 

Loran C never had a classic set of standards to govern the development of receivers and other equipment; it operated under an instruction from the Commandant of the Coast Guard. SAE International, a professional association and standards development organization with over 127,000 members worldwide, has elected to change that.

The SAE Aerospace Council is taking on standards development for eLoran equipment as part of the work of a new committee devoted to position, navigation and timing standards. Committee AS-5, which is under the Aerospace Avionic Systems Group chaired by Bill Woodward, met for the first time in May. 

The group did two things at its inaugural meeting, said Woodward, who works for the Virginia firm Geodesicx. It took the commandant’s instruction and converted it into a Word document for publication as an SAE standard. “That’s not going to change,” he said, “It’s just going to say that now there is a standard for what we used to call Loran C.” 

They also launched work on an Interface Control Document for eLoran. This contains the kind information necessary to build transmitters and receivers and Woodward said he hoped to have it published in 90 days — that is by roughly the end of August. In addition, the committee is writing an AIR or Aerospace Information Report on eLoran, which aims to address any misperceptions by publishing accurate information and thereby creating a common foundation for discussion. 

According to AS-5’s Work In Progress list there are another three other documents under development — so it’s no surprise that Woodward is looking for technical experts to join the committee.

“We have different types of members within a committee,” he said including mailing list recipients and liaisons. “The liaisons can actually access documents and download them.” 

Voting members, who should be able to contribute technical expertise to the committee’s work, attend three meetings in a row, making it an 18-month process to become a voting member. Continued good attendance is necessary to maintain a voting membership. 

Woodward may be hoping that the establishment of AS-5 and formal standards can ease the development of eLoran systems as well as new eLoran equipment. 

“The feedback I was getting from folks is that every time they talk to Congress, people always say: ‘Where’s the standard?’ ” Woodward told Inside GNSS. “You really can’t build anything unless you have a standard.”

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Though civilian GNSS activities fared reasonably well in the just-signed 2017 federal budget, the White House has already forecast cuts across non-defense agencies next year leaving the funding outlook for civil GNSS programs uncertain at best.

President Trump signed the fiscal year 2017 (FY17) spending bill on May 5, preventing another government shutdown and ensuring funding for agencies including the Department of Transportation (DoT), which is responsible for supporting civil GPS needs.

Though civilian GNSS activities fared reasonably well in the just-signed 2017 federal budget, the White House has already forecast cuts across non-defense agencies next year leaving the funding outlook for civil GNSS programs uncertain at best.

President Trump signed the fiscal year 2017 (FY17) spending bill on May 5, preventing another government shutdown and ensuring funding for agencies including the Department of Transportation (DoT), which is responsible for supporting civil GPS needs.

Among the DoT programs covered by the spending bill was the Wide Area Augmentation System (WAAS), which got its full request of $111.6 million. In fact, WAAS has enjoyed solid financial support over the last few years. The FY17 allocation was up slightly from the $107.2 million the program got in FY16 and significantly better than the trimmed-back allocations of $98 million in FY15 and $84 million in FY14.

Lawmakers were less generous with funding for DoT’s Office of the Assistant Secretary for Research and Technology (OST-R), which supports position, navigation and timing (PNT) activities including the Adjacent Band Compatibility Assessment. The two-phase ABC Assessment is a research effort aimed at protecting GNSS receivers from interference by determining a set of interference masks — that is testing satellite navigation receivers to map, by frequency, how much interference they safely can handle before their function is impacted. 

Congress cut nearly $5 million from the total request of just over $18 million for OST-R, leaving an allocation of $13.04 million for FY17. That budget supports salaries and expenses, which the Senate suggested trimming by nearly 10 percent, as well as five different activities. The PNT work appears to be headed for full funding at $1.61 million, though lawmakers left the ultimate allocation of the budget to the Secretary of Transportation to decide.

A source familiar with the final numbers told Inside GNSS that $5.6 million of OST-R’s budget is set to go to the Air Force to support civil signal monitoring. This is, once again, an amount far less than what was requested. In FY14 the administration asked for $20 million and got $6 million. In FY15 the request was for $27 million, of which DoT got only $10 million. DoT did slightly better in FY16, getting $15 million of the $27 million requested. For FY17 the original request was for $10 million.

The prospects for FY18 don’t look any brighter. The White House is expected to release its spending request for fiscal year 2018 the week of May 22, 2017. Though President Trump promised to pump money into American infrastructure, the budget summary released by the administration in March cuts $2.4 billion, that is 13 percent, from DoT’s then-anticipated FY17 budget — and that was before the effort to kill Obamacare foundered, threatening promised tax cuts.

Stan Collender, a federal budget expert and an executive vice president with the Qorvis MSLGROUP, expects the administration to make few changes to the numbers released in March.

"I don’t think anything has changed," Collender told Inside GNSS. "I think they stick with what they included in their earlier document."

The FY18 budget document will include revenue numbers, he said, plus economic forecasts and projections of the deficit and debt. But as far as spending levels are concerned, Collender does not anticipate seeing anything new. "I think they’ve already made their decisions for 2018 on the discretionary side, and they’re going to keep them."

At least they are going to try.

When asked if Congress would follow the White House’s lead on next year’s budget numbers, Collender said "almost certainly not."

"They already rejected it once — for 2017," he said, noting that lawmakers had nixed almost all the proposed spending cuts and virtually all the spending increases, or at least the magnitude of the increases. "I think they’ve basically said to the president with the 2017 funding bill ‘Butt out. We can do this ourselves.’ "

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When Inside GNSS first reported on the formal announcement to the start of Galileo Initial Services last December, there was plenty of excitement about the program’s potential, and with good reason.

The European Commission (EC), owner of Europe’s GNSS system, Galileo, made the formal announcement at that time about the start of Galileo Initial Services, the first step towards full operational capability. With further launches continuing to build the satellite constellation, gradual improvements to the system performance and availability worldwide are expected.

With that initial announcement, came word that Galileo was now providing three service types, the availability of which will continue to be improved — Open Service (OS), Search and Rescue (SAR), and Galileo’s Public Regulated Service (PRS).

Recently, the Galileo SAR was officially launched, signaling yet another milestone brought about by the Galileo satellite constellation. According to the European Global Navigation Satellite Systems Agency (GSA), among the many benefits SAR brings is a faster response time when every minute matters.

Launched as part of the Galileo Initial Services, Galileo is the first GNSS constellation offering global SAR capability. Available at sea, in the mountains, across the desert and in the air inside the Galileo/SAR Service Coverage area, this essential Galileo service helps operators respond to a distress signal faster and more efficiently, the GSA states.

The Galileo SAR service is comprised of two components:
• An automatic forward link distress alert
• A unique return link alert that informs the sender that their message has been received (planned to be available at the end of 2018)

Once fully integrated into the COSPAS-SARSAT system, the Search And Rescue Transponder on Galileo satellites will pick up signals emitted from distress beacons in the 406 to 406.1 MHz band and broadcast this information to dedicated ground stations (MEOLUTs) in the L6 band. Once these signals are detected and the beacons located by the MEOLUTs, COSPAS-SARSAT Mission Control Centres (MCC) will receive the beacon location information and distribute the data to the relevant rescue centers worldwide.

More on COSPAS-SARSAT
The Galileo SAR service is Europe’s contribution to the upgrade of COSPAS-SARSAT, an international satellite-based SAR distress alert detection and information distribution system. Established in 1979 by Canada, France, the United States and the former Soviet Union, it is used to detect and locate emergency beacons activated by aircraft, ships and individuals. It is designed to provide accurate, reliable and timely alert and location data to help SAR operators find and help people in distress.

COSPAS-SARSAT operates through a satellite system maintained and coordinated by its participants. This system detects distress alert transmissions from radio beacons that comply with COSPAS-SARSAT specifications and standards, determines their location, and provides the information to SAR teams.

Currently, 43 countries and organizations participate in the operation and management of the COSPAS-SARSAT system. COSPAS-SARSAT also cooperates with various international organizations including the International Civil Aviation Organization (ICAO), the International Maritime Organization (IMO) and the International Telecommunication Union (ITU).

With Galileo and the increased positioning accuracy it provides integrated into COSPAS-SARSAT, users will benefit from:
• a reduction in the time it takes to detect a person at sea or in the mountains from one hour to just 10 minutes after the distress beacon is activated
• improved localization of the distress beacon from 10 kilometers to less than 5 kilometers
• increased availability
• better detection of signals in difficult terrain and weather conditions
• a return link that ensures users that their distress signal has been received and help is on the way (planned to be available end of 2018)

With these types of services in place, the Galileo SAR service is saving more lives, the ESA reports.

For more on Galileo services, you check out the Inside GNSS webinar “GALILEO: Dawn of a New Age of GNSS Service”, or read Galileo’s Commercial Service Implementing Decision Adoption to Bring Added Value to Users.  

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