Alan Cameron Editor-in-Chief and Publisher, GPS World
“All the News that Fits” can sometimes be a hard motto to live up to, and it has turned out so this month. I want to get more material into our pages for your perusal, and it just could not be crammed into the System of System pages in this issue. Therefore, I cede my “Out in Front” editorial to the 27 gentlepeople, executives across the commercial, scientific and government agency spectrum, who wrote to U.S. Federal Communications Commission (FCC) chair Ajit Pai on July 18.
The core quotes from the letter appear here. However, there’s more meat on the bones and I want to present it here.
“The undersigned organizations, representing entities that provide and rely upon critical GPS, satellite communications (“SATCOM”) services, and essential weather and other environmental data, write to inform you that the threat of harmful interference from Ligado’s proposed ancillary terrestrial component (“ATC”) service continues to pose a significant risk of harmful interference despite Ligado’s May 31, 2018, amendments to its license modification applications in the above-referenced file numbers. The record, augmented by recent government reports, makes clear that the interference will be particularly impactful to the countless government and commercial entities that rely on GPS and SATCOM services for aviation safety and other critical services and the many groups that receive and depend upon real-time weather and related environmental information from National Oceanic and Atmospheric Administration (“NOAA”) satellites…
“We recognize the importance of ensuring that there is sufficient spectrum for mobile broadband, and the Commission has recently taken many steps to address that challenge. However, at a time in which the Administration has placed so much emphasis on the critical importance of space-based communications — through the revival of the National Space Council and other policy initiatives — the FCC should not undermine the nation’s critical space leadership.2 Granting Ligado’s request would harm the nation’s satellite industry and the broad sectors of the country that benefit from American space leadership every day in at least three ways. First, it would threaten the reliability of critical position, navigation and timing (“PNT”) services, including GPS and also an emerging satellite time and location (“STL”) capability augmenting GPS.
“Second, it would undermine the investment-backed expectations of those who operate commercial satellite systems by fundamentally altering the interference environment decades after licensing.
“And third, it would convert 40 MHz of increasingly rare satellite spectrum away from satellite use, rewarding a company for underutilizing its satellite spectrum rather than investing in new satellite technologies.”
In addition to several organizations, the letter is signed by the Aircraft Owners and Pilots Association, the American Geophysical Union, American Weather and Climate Industry Association and the National Emergency Number Association.
Ligado’s proposed broadband service continues to pose a significant risk of harmful interference to GPS, several key signatories wrote in a July 18 letter to U.S. Federal Communications Commission (FCC) Chairman Ajit Pai.
The interference would occur despite Ligado’s May 31 amendments to its license modification applications, the letter states. “The proposed Ligado operations, even after the recently proposed amendments, will harmfully impact a wide range of GPS receivers and thus should not be permitted.”
Key signatories include representatives of Iridium Communications, the International Air Transport Association, Lockheed Martin, Rockwell Collins and Satelles.
The letter urges the FCC to deny Ligado’s pending license modification application unless Ligado can show it has addressed the substantive GPS interference concerns. Also encompassed in the letter are concerns over interference with satellite communications (SATCOM) and weather data.
“The record, augmented by recent government reports, makes clear that the interference will be particularly impactful to the countless government and commercial entities that rely on GPS and SATCOM services for aviation safety and other critical services,” the signatories wrote.
“A number of data points underscore the flaws in the way in which Ligado has attempted to measure interference to GPS from its proposed terrestrial operations.”
Ligado recently acknowledged that its license modification request as originally filed is insufficient to protect certified aviation GPS receivers, but offered no changes to its proposal to address interference to uncertified GPS systems, SATCOM services (also important for aviation safety), or concerns of the weather data community.
“Evaluating Ligado’s recent amendment to ensure protection of uncertified GPS receivers and protection of GPS receivers from aggregate interference will be necessary,” the letter states.
1-dB Criterion. One issue is the 1-dB degradation interference protection criterion, which Ligado has suggested is “neither accurate nor reliable.” That criterion was used in the U.S. Department of Transportation’s Adjacent Band Compatibility assessment issued in April, which examined the maximum transmitted power levels of adjacent band systems that can be tolerated by GPS receivers. The study endorsed and strictly applied the 1-dB criterion, and termed it the “accepted, worldwide standard for PNT and many other radio communication applications.”
“Each of these government efforts supports one conclusion — the proposed Ligado operations, even after the recently proposed amendments, will harmfully impact a wide range of GPS receivers and thus should not be permitted…
“We urge the Commission to deny Ligado’s pending license modification application as proposed unless Ligado can show it has addressed the substantive GPS, aviation, SATCOM, and weather data interference concerns still outstanding in the record,” the letter concludes.
Eight years on, and the money generated by a hedge fund still seeks to destabilize the Global Positioning System and the billions of people who benefit from it, whether they create it, administer it, sell it or use it.
That accounts for just about everybody touched by telecommunications and the industrial network, including the brave individuals serving in the military.
For rewards to the few, the U.S. government is lobbied to levy hardship on the many. In the service of that lobbying, the truth is manipulated to suit the ends. Sound familiar?
See this article for facts and findings of years of detailed study of this matter, recounted in the recently released Department of Transportation’s Adjacent Band Compatibility (ABC) Assessment Final Report. That it appears almost a year after all the research and nearly all the analysis was completed suggests that powerful forces are at work, perhaps warring with each other, within the government. Let us hope that the guys and gals with the good hats on can prevail.
The matter now rests with the Federal Communications Commission, an appointed panel not subject to the electorate nor to Congress, whose decisions sometimes carry a scent of influence from hidden quarters. Note particularly the recent ruling against net neutrality, which most agree runs counter to public interest and correlative with private corporate interests.
As our news story states, the ability to use the mobile satellite services (MSS) band for terrestrial services is “limited.” The DOT ABC Assessment, using the 1-dB Interference Protection Criterion of a 1-dB drop in carrier-to-noise density ratio that’s accepted by everybody — specifically, every engineer — on Earth except Ligado Networks, demonstrates conclusively there is no chance the company could actually deploy a viable commercial terrestrial service in the MSS spectrum without disrupting or degrading vital GPS and GNSS services.
The U.S. government and the GPS industry have both expended far too much money and time trying to accommodate a force-fit of a non-compatible use into the bands adjacent to the radionavigation satellite service band, to the benefit of one commercial company’s bottom line.
It’s high time for this nonsense to stop. Nobody, least of all the government and the GNSS industry, owes Ligado anything.
The culmination of several years of test and analysis conducted by the U.S. Department of Transportation, the assessment will play a key role in the Federal Communications Commission’s upcoming decision on a proposal from Ligado Networks.
The long-awaited Final Report for the U.S. Department of Transportation’s Adjacent Band Compatibility (ABC) Assessment was released on April 26.
The report is the culmination of several years of test and analysis conducted by the DOT, with input and assistance from the public and federal agency stakeholders. Though not explicitly motivated by it, the assessment appears to be responsive to the Positioning, Navigation, and Timing (PNT) Executive Committee’s (EXCOM’s) Jan. 13, 2012, memorandum to the National Telecommunications and Information Administration (NTIA) that sought to develop metrics to inform commercial non-space proposals for use of frequency bands adjacent to those used by GPS, so that existing and evolving space-based PNT services “vital to economic, public safety, scientific and national security needs” were not affected by implementing such proposals.
The assessment will likely play a key role in the Federal Communications Commission’s upcoming decision on a proposal from Ligado Networks to add an extensive complex of powerful ground transmitters to its system, broadcasting on frequencies allocated for satellites.
Open and Transparent. Two key attributes of the ABC assessment were that it was conducted openly and transparently, with numerous public workshops announced via the Federal Register, and it was agnostic to any particular proposal for use of bands adjacent to GPS/GNSS services. The approach chosen by DOT in performing its assessment was to develop maximum tolerable effective isotropic radiated power (EIRP) levels that could be transmitted at differing frequency offsets from the GPS L1 center frequency.
The term “adjacent” in this regard is a bit of a misnomer in that the assessment range extended to 100 MHz on either side of the GPS L1 center frequency of 1575.42 MHz. This approach was recently validated by the National PNT Systems Engineering Forum (NPEF), which found the ABC assessment was the only one of five test and analysis efforts conducted since 2011 on adjacent-band terrestrial operations that met all six of the test criteria recommended by the experts serving on the National PNT Advisory Board. The NPEF analysis is available here.
Measurements on 80 civil GNSS and GPS receivers were performed at White Sands Missile Range (WSMR) in New Mexico. The Air Force conducted a prior week of testing on military GPS receivers at WSMR, and while the results of that testing are classified, an Air Force briefing at the November 2017 PNT Advisory Board meeting indicated the military receiver test results supported the conclusions drawn by the DOT ABC assessment. Certified aviation GPS/GNSS receivers were analyzed by RTCA Inc. and are being analyzed by the FAA in terms of determining power levels in adjacent bands that don’t exceed FAA Technical Standard Orders. However, the overall ABC assessment indicates that certified aviation receivers are not the limiting case for tolerable interference from adjacent-band services to GPS and GNSS receivers.
Test Procedures
Compatibility assessment for the civil receivers consisted of conducting the initial measurements at WSMR for six categories of receivers: aviation (non-certified), cellular, general location/navigation, high-precision, timing, and space-based receivers. These were evaluated to determine what DOT called Interference Tolerance Masks (ITMs) for each category of receiver and each receiver tested. The ITMs define the maximum aggregate interfering power that can be tolerated by a given GPS or GNSS receiver. The ITMs are based on the internationally accepted Interference Protection Criterion (IPC) of a 1-dB drop-in carrier-to-noise density ratio (C/NO) for the receiver, or, equivalently, an interference density-to-noise ratio (IO/NO) of –6 dB. This 1 dB IPC standard, which NTIA directed to be used in the NPEF evaluation of the original LightSquared (now Ligado) adjacent-band proposal in late 2011, is explained in great detail in a white paper the Air Force made publicly available in 2017.
The assessment then developed, with input from the public at several workshops convened by the DOT, use cases to determine how close a receiver for a particular GPS or GNSS application might be to a base station or handset of a commercial terrestrial service in an adjacent band. Proximity distances of 10 and 100 meters were selected from these use cases, and maximum tolerable transmit EIRP levels for a given frequency offset were determined; see Figure 1. The high-precision receivers (HPRs) were the most susceptible to interference from terrestrial operations in the adjacent bands.
Figure 1. Maximum tolerable power level for GPS/GNSS receivers at 1530 MHz. (Table: DOT)
One thing that seems clear is that, with tolerable transmit power levels in the milliwatt and microwatt range, the potential to use the bands near GPS frequencies for commercial terrestrial wireless services may be limited. Illustrating that point further, the assessment shows that, based on the assumptions in the study, HPRs can be affected at distances beyond 14 kilometers (see Figure 2), and that loss of lock for low-elevation satellites can occur at distances of up to 3 kilometers from a base station providing terrestrial services using characteristics adopted internationally in the International Telecommunication Union (ITU) study groups.
Figure 2. Impact of a 29-dBW cellular base station transmitting at 1530 MHz on a high-precision GPS/GNSS receiver. (Chart: DOT)
Moreover, the assessment determined that the potential interference to other GNSS systems may be more problematic, noting that “the levels that protect all GNSS signals can be as much as 15 dB lower than those needed to protect L1 C/A signals from base station emissions with an average difference of 3.5 dB across all frequencies and five categories considered.”
Galileo’s Role. Since 2013, according to a Public Notice from the FCC, the European Commission has sought a waiver of FCC rules that require licensing of receivers operating with foreign satellites so that Galileo service can be provided in the United States. The FCC has yet to act on this waiver request, which was issued in a January 2017 Public Notice, despite overwhelming public support and a positive recommendation from the Executive Branch in 2015.
Figure 3. Bounding masks for each category corresponding to the 10 MHz LTE interference signal and L1 C/A GPS signal: general aviation, general location and navigation, high precision, timing, space-based, cellular. (Graph: DOT)
Conclusions
It is well known that all receivers take in some power from signals transmitted in nearby frequency bands. Considering this fact, the ABC assessment is relatively unique in that it examines the overall spectral environment in which GPS/GNSS operations can be affected rather than just the band allocated to the Radionavigation-Satellite Service (RNSS, the broad radiocommunication service defined in the ITU and in domestic rules under which GPS and other GNSS systems operate) between 1559–1610 MHz. That the overall environment should be considered is an important aspect of any discussion of protecting GPS and other GNSS services given the U.S. National Space Policy that was signed into effect June 28, 2010, that directs the U.S. government to “take necessary measures to sustain the radiofrequency environment in which critical U.S. space systems operate.” This policy is still in effect, and it would be difficult to argue that GPS is not a critical U.S. space system.
Recently, the reconstituted National Space Council adopted four recommendations, one of which related to spectrum used for satellite services and said that NTIA should coordinate with the FCC to ensure “the protection and stewardship of radio frequency spectrum necessary for commercial space activities.” Stewardship that is consistent with National Space Policy would include sustaining the RF environment for GPS.
As the PNT EXCOM has made clear, GPS is “vital to economic, public safety, scientific, and national security needs” of the U.S. Moreover, economic analysis presented to the PNT Advisory Board in 2015 estimated the economic benefit to the nation of GPS services at over 68 billion dollars annually. With the release of the ABC assessment, definitive information is now available to inform decisions on use of frequencies near those used to provide space-based PNT services so these critical services are not disrupted or degraded.
On April 26, the U.S. Department of Transportation publicly released the long-awaited GPS Adjacent Band Compatibility Assessment. See the June issue of GPS World for an expert and measured analysis of this highly impactful document.
The article will be posted online when it becomes available in mid-to-late May.
Merger Mystery
Contrary to the “Out in Front” editorial published in the April issue of GPS World magazine, there was an Izvestia story published on March 28 touting a merger of the GLONASS and BeiDou systems, and there will be an International Conference on Advanced Technologies in Manufacturing and Materials Engineering in Harbin, China, at which such a possibility may hypothetically be discussed.
However, neither hard news nor any official statements have emerged to substantiate such a dubious claim, despite repeated queries to officials of both countries.
Javad Ashjaee (far left, above), CEO of JAVAD GNSS and based in Moscow, communicated that he spoke on a panel at an aerospace technology event organized by the American Chamber of Commerce in Russia, alongside representatives from NASA, Boeing, Honeywell and Roskosmos.
Ashjaee asked the Roskosmos official publicly about the prospect of a GLONASS merger with BeiDou, and “he knew nothing.”
Diverger Dilemma
As this magazine goes to press, stories emerge of a U.K. plan to launch a satellite-navigation system separate from the European Union’s Galileo project. This comes in response to an EU statement that the UK would be shut out of key elements of the European satnav program, particularly the Public Regulated Service, after Brexit.
Historically, in the late 1980s or early 90s the UK drew up plans for its own GNSS prior to the launch of Galileo. And UK-based Surrey Satellite Technology Ltd. built all operational Galileo payloads to date. So the country clearly has the capability. That SSTL is currently owned by Airbus (either German or Dutch division) may or may not constitute a wrinkle.
Finally, the UK spent 1.4 billion euros on Galileo, and may now file for a refund.
The Long Life of GPS III
By Robin Wrinn, Contributing Author
GPS III SV01 in electromagnetic interference, compatibility and passive intermodulation testing. (Photo: Lockheed Martin)
During interviews with Lockheed Martin and Harris Corporation at the 34th Space Symposium, time and space were a frequent focus of discussion, but not in the normal “continuum” kind of way.
Greater mission longevity is one of the key improvements GPS III delivers over those currently in service. Space Vehicles 1–10 have a planned mission life of about 15 years, 25 percent longer than their predecessors. Yet that begs the question “How long should a satellite live in space, with technology innovation occurring almost annually?”
Advanced payload technology provides a partial answer to that question. Both Lockheed Martin and Harris Corporation highlighted new payload capabilities with built-in flexibility to adapt satellites in orbit to technology advances, as well as changes in missions.
Lockheed Martin provided the media a tour of their Radio Frequency Payload Center of Excellence. Meanwhile, Harris recently announced completion of the fully digital Mission Data Unit (MDU), core to the navigation payload for GPS III 11 +. As a reminder, the current Harris payload for SVs 1–10 includes:
greater than three times reduction in range error,
up to eight times increase in anti-jamming power,
added signals, including L1C, compatible with other GNSS such as Galileo, and
greater signal integrity.
According to Harris, the fully digital navigation payload will provide the ability to change and upgrade the satellites incrementally over mission life.
Meanwhile, Lockheed announced a partnership with NEC to introduce artificial intelligence for computer learning in orbit. The company’s Payload Center experts touted significant advances in processers and a move toward next-generation antennas, arrays and transmitters to drive more satellite flexibility, capability and resilience.
Observation: The market pressures of ‘new space’ players is prompting delivery of products that can drive more value for less cost. In this case, delivery of a common payload architecture and electronically steered beams to make satellite antennas become any shape you want. Most likely, beams of a different size on demand is a much better business case than a static one built five years ago.
The day I interviewed Lockheed Martin’s Navigation Systems mission area Program Manager Johnathon Caldwell, the company had submitted its proposal for the U.S. Air Force’s GPS III Follow On (GPS IIIF) program. That same day, April 16, the media was given a tour of Lockheed Martin’s GPS III satellite assembly floor. It was clear from both Lockheed’s press materials and Caldwell that Lockheed Martin believes it is fully recovered from prior production hiccups and is
on track to deliver GPS Space Vehicles (SVs) 1 through 10, and
deserves to win the bid for GPS IIIF. Now that both Boeing and Northrop Grumman have dropped out of the running, Lockheed is virtually assured the contract. The government has said it will announce the award in March 2019.
What are the differences in the GPS III satellite payloads that were instituted to enable the new signals?
The main difference is the power. The Air Force’s requirements called for significantly more anti-jamming capability. All the transmitters are a higher power.
What was the most significant obstacle (or top obstacles, plural) in designing and manufacturing this new payload, to new Air Force specifications? How did you overcome it/them?
Same answer really, the higher power. Keeping in mind, we went from a 7-year mission life requirement to a 15 year. That higher power puts more strain on components and new cyber requirements in software. When you couple all that together we are not just upgrading payload technology. It is really engineering a new set of payload requirements. It’s new generation, advanced.
What are the advantages of a digital payload over the alternative?
The advantages and the 30 percent difference are the timekeeping system portion. We’re moving from a manual, analog timing to digital to deliver to the Air Force more flexibility. It’s a nice option to have to be able to reprogram in orbit and maybe enhance capabilities desired in the future.
with Johnathon Caldwell, Navigation Systems Mission Area Program Manager
Any changes in your production approach having completed SV01?
No, the performance on Vehicle 01 was as designed there were no technical or design changes necessitated throughout the rest of the fleet. So, it was a very successful from that perspective — from the standpoint of validating the design and wringing it out, Vehicle 01 served its purpose well.
It had a very good T-Vac. I would say overall when you look at the industry, Vehicles 01–02, our vacuum test campaigns are the most rigorous test. Both went through their tests quite well. Some of the best I’ve seen.
An independent technical review published earlier this month found sufficient data in three government-conducted tests to assess the risk of using frequencies near the GPS band for a ground-based communications network — specifically, the one proposed by Ligado Networks. The panel rejected two tests sponsored by Ligado Networks, saying they did not meet minimum criteria for inclusion or use.
The testing and various hearings before the Federal Communications Commission (FCC) come in response to increasing demand for commercial spectrum to support broadband wireless communications. The FCC and other branches of U.S. government are giving serious consideration to repurposing various radio frequencies, including the satellite communications bands next to GPS, to accommodate this.
Ligado Networks has petitioned the FCC to repurpose satellite frequencies near GPS to also support terrestrial telecom services, effectively transferring its license for space-based broadcasting to powerful terrestrially-based broadcast towers. Ligado’s custom networks would provide services for industrial operations such as power grids and connectivity for drones and driverless cars, in addition to consumer broadband services.
The National Executive Committee of the government’s National Coordination Office for Space-Based Positioning, Navigation, and Timing released the assessment by its National Space-Based PNT Systems Engineering Forum (NPEF) of testing methodologies used to analyze the impacts of adjacent band interference on GPS receivers. The assessment is also known as the “gap analysis.”
The NPEF evaluated five tests performed by the following organizations, the first three of them government organizations and the last two private tests sponsored by Ligado with little or no public or government input:
Federal Communication Commission (FCC)-mandated Technical Working Group (TWG) — done in 2011.
National Space-Based PNT Systems Engineering Forum (NPEF) — done in 2011.
Department of Transportation (DOT) Adjacent Band Compatibility (ABC) — done in 2017 but not previously released.
Roberson and Associates (RAA)
National Advanced Spectrum and Communications Test Network (NASCTN).
The gap analysis concluded that the results from the first three tests are sufficient and appropriate to inform spectrum policy makers on the major impacts of a proposed LTE network on GPS receivers. The DOT test results revealed the power levels that GPS and GNSS receivers can tolerate from interference sources in the adjacent band in an effort to inform the enforcement of a GPS interference protection criterion.
PNT Advisory Board’s set of minimum criteria. The two Ligado-sponsored tests are the RAA and the NASCTN. (Image: PNTAB)
The NPEF team found the scope and framework of the last two tests, sponsored by Ligado, to be insufficient when evaluated against the PNT Advisory Board’s set of minimum criteria. Key among these criteria is one that specifies use of the internationally accepted 1 dB degradation Interference Protection Criterion (IPC): a one-decibel (1 dB) degradation in C/N0, the carrier-to-noise power density ratio. Ligado has tried to redefine the standard measurement of interference to one more in its favor: a change in positioning and timing accuracy.
For further background on this and other aspects of the gap analysis, see the January 2018 GPS World article by Brad Parkinson, “A Grave Threat to GPS and GNSS.”
The NPEF strongly recommended that decisions impacting the GPS radio frequency environment be informed by data from tests that align with the PNTAB’s set of minimum criteria and with full consideration of the potential operational, scientific, and economic impacts.
The full gap analysis study can be downloaded here.
The NPEF is co-chaired by the Departments of Defense and Transportation and consists of representatives from at least 14 federal agencies.
While not as glamorous as mild-mannered Clark Kent holding down a day job while Superman comes to the rescue in time of crisis, there are professional surveyors who work day jobs to perform our duties as practitioners to make a living and participate in association activities in their off-hours to help promote and protect their profession as well as the public they serve.
Many of the hours spent to protect the profession are in the political arena, where the battle for budget dollars and service rights are fought on nearly a daily basis. Because of the reliance of the surveyor on technological advances, the profession has been thrust into the political arena at all legislative levels. The surveyor has been tasked with leading the discussion and help the public understand why significant dollars are needed for funding many different programs to continue with our high-tech trends and lifestyles.
Three of the four presidents on Mount Rushmore started as surveyors — George Washington, Thomas Jefferson and Abraham Lincoln. (Photo: National Park Service)
The role of the surveyor has not been considered political even though several significant U.S. presidents were surveyors in their early careers. Surveyors aren’t particularly known for their public personas, much less their political prowess. Other than states that still have county surveyors, rarely do practitioners stray beyond local municipal government. One is more likely to see a professional engineer or architect as an elected official than a surveyor, but that doesn’t mean the issues we face are any less important.
My current position is a professional land surveyor with a full-time job overseeing a department in a multi-discipline office in a major metropolitan area. Besides being a contributing editor to GPS World through these articles, I also voluntarily wear many hats within our state association and the national surveying society. Several of these hats are government affairs positions at both state and federal levels, as it has become a full-time operation to keep a watchful eye at all governmental levels. From changes in regulations, budgetary revisions and threats to our professionl by outside entities, government affairs take a small army of people to keep abreast of all situations.
This month’s submission is just a snapshot of the current National Society of Professional Surveyors (NSPS) Joint Government Affairs Committee action item list being addressed and monitored through its committee members and a governmental lobbyist. The importance of this list is to give the reader a sampling of the seemingly endless battles being waged on Capitol Hill by NSPS and its members nationwide.
All these issues have GNSS at their heart and will have dire consequences if any of these subjects fall short of their intended marks.
This is not just about the GNSS and how we collect data; it’s also about the necessity of large scale data collection to provide better and safer services to the citizens of the United States and its territories.
Our current datasets and standards for data collection, like our infrastructure, is aging and lacking in detail. Serious upgrades are overdue, so several actions have been put forth to try to rectify the shortcomings.
3DEP
Formally known as the 3D Elevation Program, this language was introduced as part of S. 1460 (“Energy and Natural Resources Act of 2017”) by Senator Lisa Murkowski of Alaska. This program is being created so that consistent elevation data, cultivated through many surveying and mapping sources including lidar, will be available for efficient design use throughout the American infrastructure.
While it currently does not have a single line item in any budget, the USGS Budget Summary lists its necessity in the Core Science Systems Program as part of the National Geospatial Program. This program is intended to provide high-quality topographic, geologic and hydrographic data nationwide to assist with further development of energy, transportation, drainage, emergency response and hazard mitigation.
As part of the 2019 President’s Budget, the USGS Green Book also lists having the entire nation covered by an ongoing lidar program by 2033, along with completing a significant amount of data collection by various means in Alaska by 2022, including high-resolution interferometric synthetic aperture radar (IfSAR) necessary for data collection in more difficult terrain.
The Green Book also lists high-resolution hydrographic data to support flood risk management studies, as the frequency of large scale flooding seems to be increasing substantially in more places than ever before. It also includes additional mapping data, programming and functionality for emergency personnel charged with oversight of public safety in times of crisis.
FAA reauthorization
The current FAA authorization bill expires on March 31. The biggest hang up holding up getting the bill reauthorized is privatization of the air traffic controllers, but there are rumors of tightening of UAV rules due to the rapidly growing use of the vehicles for business and personal use.
Surveyors are working with federal and state officials to help implement reasonable rules for use and coverage of the UAV as the field of surveying has been drastically affected by use of aerial vehicles. Many tasks that used to take days now take hours with increase accuracy, so the effects of the UAV will be seen for many years to come.
Digital Coast Act
One of the legislative acts that NSPS was a big part of in 2017 was Senate Bill 110, “The Digital Coast Act” which led to the introduction of the companion bill in the House as H.R. 4062. This Act will allow NOAA to perform the necessary actions to actively and effectively monitor all coasts (including the Great Lakes) by various means, including bathymetric and conventional survey methods. This will require services to be performed by public and private surveyors primarily with GNSS capability to provide NOAA with standardized information based upon established datum.
FLAIR Act
The Federal Land Asset Inventory Reform (FLAIR) Act of 2017 was introduced as House Resolution 2199 to help with creating a database of government property nationwide. The Government Accountability Office (GAO) has stated that the management of federal real property has become a “high-risk” item on its list of duties. Management of the number and value of properties has increased to a point that an overall dollar amount of federal buildings and land cannot be accurately determined.
How does the surveyor fit in with this issue? Simple. The U.S. government will need to upgrade its database of existing facilities through having them surveyed for asset management. Part of the requirements for providing these surveys will be completing the work in datums that will be following the geographical databases being designed to contain the parcel and building information. All this data will have geospatial information regarding parcel, address, utilities and functionality of the inventory, so providing the data with the sufficient attributes will become a key role for the surveyor. GNSS data collection will be at the heart of this monumental task.
Geospatial Data Act
As introduced in May 2017, the Geospatial Data Act (GDA) of 2017 is intended to jumpstart the nationwide initiative to develop and coordinate efforts to collect and maintain new datasets of elevation and infrastructure information. It is intended to improve and enhance federal geospatial activities to encourage state and local agencies to participate at the local level.
It is interesting to note, however, that the revised Geospatial Data Act was introduced by the same sponsors that did not include procurement procedures that follow the typical Brooks Act of quality-based selection, and instead relied on bid-based selection commonly found with suppliers. Both bills are being vetted by their sponsors and potential geospatial providers for clarity with ongoing debate going forward.
Hydrographic Services Improvement Act
H.R. 211 bring us the Hydrographic Services Improvement Act to provide NOAA with incentive and funding to standardize surveys desperately needed in waterway areas. Ongoing discussion continues this spring to determine sources of funding and priority of projects.
Infrastructure bill
February brought us the introduction of a significant infrastructure program aimed at improving roads, airports and bridges, with other major improvements across the country. This program is noteworthy in recognizing the need of current geospatial data and inventory of major infrastructure needs. The program sets forth the need for surveying, mapping and geospatial data for planning, design, construction, operations and maintenance for a multitude of projects nationwide. Much more will be discussed regarding the funding and priority of projects as the political year moves on.
LightSquared/Ligado
Readers may remember when the original confrontation with LightSquared began in 2011, and the subsequent battle over the frequency ranges adjacent to the GPS bandwidth. The FCC gave LightSquared initial but conditional approval to move forward with terrestrial-based transmission for 4G cellular transmission for up to 40,000 land-based stations. Testing by private and governmental agencies through 2011 and 2012 proved that LightSquared would greatly harm GPS activity for both public and private use. Once exposed, the conditional FCC approval was rescinded and LightSquared retreated into the shadows…until now.
Reformed as Ligado, it has fresh investors and is making a charge into 5G technology with a revised game plan. While it is also looking to use other spectrums for communication, it once again is dangerously close to other current uses. Couple the proximity of adjacent bandwidth with the intense land-based signal versus a very weak satellite signal, there will be significant overriding by the new user. All of this is still being worked out through the FCC and the Department of Defense, so final resolution is yet to be seen.
IMAGES Act
The National Flood Insurance Program (NFIP), as part of FEMA, is looking to move forward with legislation introduced as Improvement of Mapping, Addresses, Geography, Elevations and Structures (IMAGES) Act (H.R 4905). This act intends to reform the NFIP program by utilizing new elevation data collected through the 3DEP program, which will be combined with other parcel attributes including addresses and structure types. This data will then be combined with refined floodway information to identify parcels that are more susceptible to damage caused by storms and flooding.
New legislation can be a good thing, but only if funding can be provided. This bill could provide a major upgrade to the flood mapping and insurance program, but it will hit a big snag with lack of monetary support. The proposed funding for FY2019 is $100 million, yet the project costs for the FY2018 budget is $178 million. This significant difference will make a large impact on the effectiveness of the program and proposed revamp.
Railroad reauthorization
NSPS has spent several years working with various legislators trying to find the right bill to insert language to require railroads to monument their routes before removing tracks. But with the recent accidents of various rail lines, the spotlight has been put on various factors that cause the incidents and how to eliminate their occurrence.
Positive train control (PTC) systems incorporate geospatial data collected through GNSS, lidar and conventional surveying means to work with operational systems to assess dangerous situations. Surveyors will need to be at the forefront of the necessary data collection so our efforts to continue lobbying for railroad funding will continue.
Net Neutrality Act
A political hot topic the surveyor doesn’t typically think about is net neutrality. Most people think they will be affected by lack of neutrality slowing down their home internet or streaming service, but for surveyors it will be a much bigger deal.
A remarkable number of surveyors and mappers use cellular data streaming to provide a connection to a positional correction service. The throttling of this data will effectively slow down the performance and quality of the positional data, leading to less reliability and productivity. It will also slow down the data interaction of office and field staff exchanging data and image files critical to project productivity and success.
So, when the call goes out to contact your federal representative to protect net neutrality, remember how it will affect your surveying business model and make that call.
How professional land surveying associations get it done
Many thanks to the countless hours put in by the NSPS Joint Government Affairs team, consisting of Committee Chair Pat Smith, NSPS Government Consultant John Palatiello, NSPS Federal Lobbyist John “JB” Byrd and NSPS Executive Director Curt Sumner. This group is constantly monitoring legislative action across the country as well as in D.C. and is quick to respond when action is needed on legislative issues. They do a tremendous job, yet not many see them in action. Hopefully all surveyors will continue to see and feel the benefits of their results.
As simple as the process is, the political world has gotten much more complicated as time marches on. From local municipal offices to Washington, D.C., getting things done through legislation has become a long process that takes patience and plenty of money to get your voice heard. Surveyors are no different than any other profession in that we must stay out in front of issues that affect our physical and business world. The important part is to stay informed and have a voice.
Let’s also remember those three fine individuals, memorialized on Mount Rushmore, who accomplished great things after their stints as surveyors, so anything is possible if we keep our voice in government.
Surveying has evolved into a highly technical professional with GNSS as a backbone method of data collection. With the U.S. government at the center of that technology, we need to make sure we, as the surveying practitioner, stays engaged.
It is the best of times, it is the worst of times. GPS modernization, once gasping for breath by the side of the track, is back in the race and pulling ahead. Relentless innovation in user equipment and newly opened software access mean that high-precision positioning may soon be available to owners of mere tablet computers. Spoofing counter-measures are growing in sophistication and availability. GPS continues to drive many sectors of the economy, with a benefit of as much as $65 billion per day to the U.S.
Yet there are a few flies in the modernization ointment. And GPS may soon collide, catastrophically, with that other U.S. military invention from the 1970s that also leaped the fence into the civic domain and life-changed billions of people around the world: the Internet.
Note: After this issue, we are temporarily suspending publication of the GNSS Design & Test e-newsletter. Subscribers who do not already receive the Navigate! Weekly e-newsletter will in 2018 find it in their inbox each Tuesday. Navigate! covers a broad range of GNSS and PNT industry news and all GNSS constellation and signal updates. You may freely unsubscribe if you wish. The final Navigate! newsletter of each month will carry my GNSS Design & Test column — so, I’m not going away!
— AC
Let’s open these boxes one by one.
Modernization. The first satellite GPS III satellite, declared available for launch in September, appears headed for a March 2018 lift-off. Both the GPS III digital navigation payload and the ground-control software programs are recovering momentum following earlier hiccups and delays. The first III satellite has successfully “talked” with the OCX system on the ground. Lockheed Marting is building 10 of the satellites for the Air Force. Harris Corporation delivered the fourth of 10 digital payloads to Lockheed, and said it would ship four more in 2018. Raytheon is the prime contractor for OCX.
The Government Accountability Office (GAO) projected that the current constellation of 31 GPS II satellites will remain operational until 2021, two years longer than previously estimated. This affords some breathing room for the seven GPS III satellites scheduled to be in orbit by then to start replacing the long-lived II generation. No longer need we fear the constellation gap, an alarm sounded by the same GAO back in 2009.
Problems Ahead. But this year’s GAO report also warns that GPS III’s increasing program complexity and upgrades required for new encrypted signals mean that it will take longer for ground infrastructure and user equipment to catch up in capability afforded by the new satellites.
Five programs are now encompassed under the rubric of GPS modernization: the satellites, next-generation ground control (OCX), military user equipment, contingency operations and military code (M-code) early use.
Just because the satellite schedule has regained its footing and is racing forward does not mean that M-code software and installing the receivers needed to acquire it aboard major U.S. weapon systems are keeping up pace with the pack. “Additional development is necessary to make M-code work with over 700 weapon systems that require it,” according to GAO analyst Christina Chaplain. Long message short: the new satellite constellation may be orbiting in the skies years before user equipment and software are in place. “War fighters will have to operate with a mix of older and newer receiver cards.”
Consumer Access to Precision. The January cover story in GPS World magazine will show the results of very promising new tests taking advantage of access to raw GNSS observables now possible thanks to Android. “For those who want high accuracy, but don’t need it full time, high-productivity dedicated professional solutions may not be cost-justified,” writes Stuart Riley along with his co-authors, all from Trimble. “In these cases, a positioning-as-a-service subscription could offer a viable use model. Achieving precision positioning with just a standard mobile device, a correction stream using the mobile device’s data connection and a high-accuracy positioning application produces a very low barrier to achieving high accuracy.”
One of the figures from “Positioning with Android.” Code RTX performance the dataset sampled Nov 20 and corresponding RTK and RTX phase solutions — cell-phone GNSS antenna.
“While we expect that dedicated system approaches employing a custom GNSS chipset and firmware and purpose-built precision applications will continue to be the right solution for industry professionals,” they continue, “it is clear that the ubiquity of consumer mobiles, with increasing compute power, ruggedness and an expanding feature set represents a fertile ground for new development of improved positioning systems that don’t have strict professional requirements.
“A range of new use models and applications will be enabled by consumer mobile phones with technology that improves positioning performance. The goal of the work presented here is to assess what level of performance can be achieved by using proprietary PVT (Position Velocity Time) engine(s) utilizing GNSS measurements from the Android GNSS measurement API.”
Look for the January issue in your mailbox by mid-next month.
Spoofing. This has been the hottest issue, by far, during the past year — maybe two — at technical conferences around the world. Its role has been speculated in some rather notorious seafaring accidents. Its potential to wreck many carefully wrought schemes of transport, finance, safety, security, defense, power supply and more has been resoundingly aired. But help is on the way. Javad Ashjaee in the January magazine’s Expert Opinion column lays out an anti-spoofing strategy that has been installed, as an option, in all OEM boards offered by JAVAD GNSS.
In its most basic form, it amounts to “it is vital that in areas that spoofing danger exists, users employ OEM boards that provide more satellite systems and more signals, rather than using a simple GPS C/A code, for example.”
Heartbreak Dead Ahead. Finally, the January issue contains a lengthy treatise by Brad Parkinson, variously the grandfather, godfather, or just plain father of GPS, on a burgeoning danger that threatens the whole system and the vast economic benefit it provides.
Widespread big data streaming, storage in the cloud, and the much-ballyhooed Internet-of-Things are accelerating the World Wide Web’s breakneck consumption of broadband. More, more, more is needed, and more again tomorrow. We are all complicit, to use a current term, in this.
Every single sliver of radio-frequency band is now worth billions. And this is neither an infinite nor a renewable resource. There’s only so much. No one’s talking about taking away the small radionav portion of the spectrum (yet), but serious, well-funded and well-friended efforts seek to park massive transmitters right next door to it and effectively obliterate the signal, not only of GPS but other GNSS as well.
LightSquared tried this once, in 2010-11, and failed. Now the company is back under a new name, and in the current political climate it has more than a fighting chance of knocking the RF legs out from under the PNT community and all who depend upon it. Which, again, is all of us.
Talk about conflicting priorities.
“I believe the concept of allowing the installation of transmitting towers that, by design, will interfere with normal GPS use at some distance away, opens the door to tacit approval of short-range (or not-so-short-range) GPS jammers,” writes Parkinson.
Well, let’s put all that trouble aside, just for a few more weeks. Enjoy, everyone out there, your winter holidays if you are lucky enough to have some, and we’ll return to business in January.
Ligado Networks will appear and present at the National Space-Based Positioning, Navigation and Timing Advisory Board’s (PNTAB) meeting on Nov. 15 in Southern California.
Ligado and its predecessors have sought to install high-powered ground transmitters that have been shown to harm and overwhelm GPS signals and receivers in their general vicinity. The controversy has simmered for at least eight years without resolution.
That final resolution will ultimately be taken by the Federal Communications Commission (FCC), although congressional participation is also conceivable, since national infrastructure security is involved.
Meeting Locale. The PNTAB meeting will take place Wednesday, November 15, 2017, 9:00 a.m. to 5:00 p.m.; and Thursday, Nov. 16, 9 a.m. to 1 p.m., at the Crowne Plaza Redondo Beach & Marina Hotel, 300 North Harbor Drive, Redondo Beach, California, approximately a half hour’s drive south of Los Angeles International Airport. The meeting will be open to the public up to the seating capacity of the room. Visitors will be requested to sign a visitor’s register.
From June 28, 2017, PNTAB presentation by Brad Parkinson.
The central issue in this long-running fight is the as-yet unknown — though uniformly predicted by the various rounds of testing over the last eight years — effects of Ligado signals on a huge installed industrial and governmental base of GPS receivers, some of which are essential to the nation’s critical infrastructure.
Ligado Networks, the current-day incarnation of once-bankrupt LightSquared, seeks FCC permission to apply the satellite-based frequency licenses it owns to be broadcast from a ground-based network. This would put a powerful nearby signal immediately adjacent to the much weaker, more distantly emanating GPS signals, and by the way, those from other GNSS as well. Tests in 2011 and further testing in 2016 demonstrated these powerful signals interfering with GPS receivers.
Brad Parkinson
The Ligado appearance comes in response to an open letter, posted on Oct. 10 by PNTAB First Vice-Chair Brad Parkinson, inviting Ligado CEO Doug Smith to speak to the Advisory Board. That invitation itself emerged after a season of what have been termed “attack” statements issued in various forums by Ligado, which were in turn stimulated by two early-summer letters:
1. A June 27 letter from the American Geophysical Union, Aerospace Industries Association, American Meteorological Society, Aircraft Owners and Pilot s Association, Airlines for America, General Aviation Manufacturers Association, International Air Transport Association, Iridium Communications, Thales USA and other organizations (totaling 22) to the FCC opposing Ligado’s request.
“The undersigned organizations . . . write to reiterate that the threat of harmful interference from Ligado’s proposed ancillary terrestrial component (“ATC”) service remain real and persistent. Contra ry to the assertions in Ligado’s FCC advocacy and recent media blitz, its proposed terrestrial operations continue to pose a significant interference risk to numerous parties . . . . The risks to these critical services are very real and, consistent with the public interest, cannot be brushed aside.
That letter further notes that “Ligado seeks the ability to sell its spectrum to the highest bidder, underscoring the uncertainty of any prospective value of the services it has on previous occasions suggested it may provide. There is a clear effort by Ligado to downplay the significance of the technical concerns it continues to receive from numerous directions.”
2. A July 5 letter from the PNT Advisory Board to Deputy Secretary of Defense Robert O. Work and Deputy Secretary of Transportation Jeffrey A. Rosen, the co-chairs of the National Executive Committee for Space‐based Positioning, strongly opposing the Ligado proposal.
From June 28, 2017, PNTAB presentation by Brad Parkinson.
“The revised [Ligado] proposal to the FCC is fundamentally unchanged from a previous proposal reviewed in 2011. Extensive government testing in 2011 and in 2016, clearly shows that both proposals cause definitive harmful interference to many classes of GPS receivers.”
“All GPS stakeholders should be wary of any incremental approaches to deploying mobile broadband services in the mobile satellite systems (MSS) band. For example, initial services could operate at reduced power levels on a temporary basis to protect only a subset of GPS users, before moving to full — power levels that will cause widespread interference to many other classes of GPS users. Regulatory decisions must be based on the ultimate end-state of any systems proposed for operation in the bands adjacent to GPS, and must protect all classes of GPS users. Unfortunately, the latest industry proposal does not acknowledge the legitimacy of, and the need to protect, dozens of precise applications of great national importance.”
From June 28, 2017, PNTAB presentation by Brad Parkinson.
Round Two. The struggle has been a prolonged one, with many twists and turns, however coalescing into two main periods of activity:
2011-12, when the first round of tests showed then-LightSquared’s proposed network would overload the vast majority of GPS receivers. The Federal Communications Commission (FCC) tabled the proposal, and the company, holding spectrum licenses whose value could range far into the billions of dollars, filed for bankruptcy.
2016–18. LightSquared emerged from Chapter 11 in 2015 as Ligado Networks, positing a modified network plan, but one whose organizing concept remains unchanged, causing deep and continued alarm over GPS interference. 2017 tests, conducted by a firm and a government organization hired by Ligado, essentially reconfirmed the 2011 results. The tests found that the proposed ground towers would significantly interfere with GPS receivers as far away as 4 to 5 kilometers, “killing them dead” in the words of one expert who reviewed the test data.
Parkinson’s October 10 letter invites Ligado CEO Doug Scott “to provide the committee with clear up-to-date design information. . . . How might the system as now envisioned be deployed? How many ground terminals are needed, for example, and where would they be?”
Previous LightSquared and Ligado presentations have been long on promise but short on details. In fact, sound technical underpinning has not been communicated.
From June 28, 2017, PNTAB presentation by Brad Parkinson.
Parkinson writes “we would therefore encourage you to specifically describe your implementation plan , with a corresponding test plan address ing the issues we have openly raised . We request you specifically focus on those regarding the potential for interfering with any GPS /GNSS services that operate in the protected Space – to – Earth L band (1559 – 1610 MHz) . Included should be all modes of operation and the use of all current and future GNSS sign als. Without these specific technical details and corresponding evaluations, we can only conjecture as to what you are really proposing .”
Later, he affirms “our focus is to provide advice based on deep engineering and related expertise . As you know, interference to GPS/GNSS can adversely affect numerous safety – of – life systems , other vital national assets, and applications comprising over $60 billion of annual U.S. productivity benefits .”
Parkinson and the PNTAB have had better luck securing a Ligado appearance than did GPS World magazine. In August of this year, Ligado’s senior vice president and chief engineer for radio access technologies thrice declined an invitation to give a brief Expert Opinion for the September issue on the question: How can the safety, security, and full utility of GNSS applications be ensured while evolving best, most efficient use of limited, very valuable electromagnetic spectrum?
Just a Refresher. The PNTAB meeting will be held Wednesday, November 15, 2017, 9:00 a.m. to 5:00 p.m.; and Thursday, November 16, 2017, 9:00 a.m. to 1:00 p.m., at the Crowne Plaza Redondo Beach & Marina Hotel, 300 North Harbor Drive, Redondo Beach, CA, approximately a half hour’s drive south of Los Angeles International Airport. The meeting will be open to the public up to the seating capacity of the room. Visitors will be requested to sign a visitor’s register.
Ligado is by no means the only item on the Committee’s docket, but is very likely to be the pièce de résistance. The full agenda for the meeting includes:
Update on U.S. Space-Based Positioning, Navigation and Timing (PNT) Policy and Global Positioning System (GPS) modernization.
Prioritize current and planned GPS capabilities and services while assessing future PNT architecture alternatives with a focus on affordability.
Examine methods in which to Protect, Toughen, and Augment (PTA) access to GPS/Global Navigation Satellite Systems (GNSS) services in key domains for multiple user sectors.
Assess economic impacts of GPS/GNSS on the United States and in select international regions, with a consideration towards effects of potential PNT service disruptions if radio spectrum interference is introduced.
Review the potential benefits, perceived vulnerabilities, and any proposed regulatory constraints to accessing foreign Radio Navigation Satellite Service (RNSS) signals in the United States and subsequent impacts on multi-GNSS receiver markets.
Explore opportunities for enhancing the interoperability of GPS with other emerging international GNSS.
Examine emerging trends and requirements for PNT services in U.S. and international fora through PNT Board technical assessments, including back-up services for terrestrial, maritime, aviation, and space users.
Two workshops convened in recent weeks in the U.S. and Canadian capitals, respectively, sought to bring into focus looming threats to the nations’ positioning, navigation and timing capabilities and critical infrastructures. Some of the threats are pervasive — jamming and spoofing — and formed the general topic of the Canadian workshop. Some threats are specific — powerful terrestrial transmitters overwhelming GPS/GNSS receivers — and occasioned the U.S. gathering.
Canada. In a first for Canada, the October 21 GNSS Vulnerabilities Innovation Policy (VIP) Workshop brought together 19 federal government departments as well as provincial and municipal agencies and private sector companies. U.S. State Dept. and Homeland Security gave presentations, as did the European Space Agency, Bell Canada, NovAtel and Spirent Communications.
Integrity challenge for automotive positioning, presented by NovAtel
The workshop was sponsored by the the Federal Global Navigation Satellite Systems Coordination Board (FGCB), a government board with representations from various government departments and agencies. The GNSS Coordination Office (which organized the workshop) is hosted at Canada’s Ministry of Innovation, Science and Economic Development and sponsored by the FGCB members.
Presentations covered such topics as Demonstration of the Geolocation of GPS Jammers, GNSS & the Telecom Sector, Detecting and Protecting Against GPS Cyberthreats, and Safety Critical, High Precision, GNSS Positioning for Autonomous Vehicles.
United States. The U.S. Department of Transportation (DOT) hosted its fifth workshop on the GPS Adjacent-Band Compatibility Assessment effort on October 14. This lengthy, thorny and occasionally acrimonious process started out benignly enough in 2010 with the statement, “Demand for commercial spectrum to support broadband wireless communications has led the government to consider repurposing various radio frequencies, including the satellite communications bands next to GPS.”
The workshop discussed the results from testing of various categories of GPS/GNSS receivers including aviation (non-certified), cellular, general location/navigation, high precision and networks, timing, and space-based receivers. The workshop also included a discussion on the development of use-case scenarios for these categories — which is where the going got heavy and differences of opinion truly emerged.
The furor stems from a renewed effort by Ligado, formerly known as LightSquared and now re-emergent from a 2-year bankruptcy process, to convert relatively inexpensive satellite-to-earth spectrum into very valuable terrestrial spectrum. The company stands to gain billions of dollars and secured rights from the process.
Members of the DoT team presented the first results from the GPS Adjacent-Band Compatibility (ABC) Assessment, an effort to determine the power limits by frequency, or interference tolerance masks (ITM), needed to protect both existing and future GPS receivers. Test results indicated a need to limit interfering signals at different levels depending on the type of receiver being used. 80 receivers in six categories were tested: cellular, general location/navigation, general aviation, timing, high precision and space receivers. Certified and military receivers are undergoing separate tests.
The tests of current receivers took place April 25–29 at White Sands Missile Range, New Mexico, using a 100 x 70 x 40 anechoic chamber. The signals used in the test included GPS L1 C/A-code, GPS L1 P-code, GPS L1C, GPS L1 M-code, GPS L2 P-code, SBAS L1, GLONASS L1 C, GLONASS L1 P, BeiDou B1I and Galileo E1 B/C. Tests were conducted within 100 megahertz on either side of the GPS L1 center frequency of 1575.42 using a 10-megahertz LTE signal and a narrow bandwidth 1-megahertz bandpass white noise signal.
The tests were conducted for GPS and GNSS receivers processing signals in the 1559–1610 MHz Radionavigation Satellite Service (RNSS) frequency band, as well as receivers that process Mobile Satellite Service (MSS) signals in the 1525–1559 MHz band to receive differential GNSS corrections.
The tests determined the power levels at which each device experienced a one-decibel degradation in the carrier-to-noise density ratio (CNR) at a particular frequency. The DoT team graphed results for each device. The recommended power limits were the lowest in frequencies closest to the GPS bands.
The receivers most affected by the test transmissions were identified as high-precision receivers. They experienced interference at power levels as low as –90 to –95dBm at around 1550 MHz and –90 dBm at roughly 1610 MHz.
The strictest limit for both the general aviation, general navigation/location, and timing receivers was a little below –80 dBm at about 1550 MHz, while space-based receivers were equally sensitive on both sides of the RNSS band with the toughest limit being about –85 dBm.
FAA. The Federal Aviation Administration (FAA) has authority to set power and out-of-band emissions limits to meet aviation safety standards, and it had been thought that these limits might address interference with other types of receivers as well. But the test results showed that “protecting the FAA-certified mask does not necessarily protect the rest of the receiver categories,” according to Hadi Wassaf, technical lead for GPS interference analysis at DoT’s Volpe Center.
Use Cases. Ligado has proposed that position error as experienced by the user is a better guide to interference levels than degradation in the carrier-to-noise density ratio. The GPS community generally opposes this approach. The next step is the development of use cases. According to the test plan, use cases define the regions of operations for a receiver, and they identify applications that “that are vital to economic, public safety, scientific, and/or national security needs and any other factors supporting why this particular receiver model is important to be tested (e.g., quantity in use, economic impact, etc.).”
