The LightSquared/Ligado Networks saga, now in its second decade, continues. On Sept. 9, the Committee to Review FCC Order 20-48 Authorizing Operation of a Terrestrial Radio Network Near the GPS Frequency Bands of the National Academies of Sciences, Engineering and Medicine (NASEM) released its consensus study. Both sides claim the report supports their position.
According to Ligado, the report confirms the FCC’s finding that the company’s operations “can co-exist with GPS.” It cited the report’s conclusion that “the technology to enable compatibility has been in use for over a decade, and most consumer equipment, commercial general navigation, timing, cellular and aviation receivers will not experience harmful interference from Ligado’s operations.”
The NASEM report also confirmed, the company said, the FCC’s finding that “[a] small percentage of very old and poorly designed GPS devices may require upgrading.” Ligado reaffirmed its commitment to “upgrade or replace” federal equipment negatively impacted by its operations and expressed its hope that now the Department of Defense (DOD) and the National Telecommunications and Information Administration “will stop blocking Ligado’s license authority and focus instead on working with Ligado to resolve potential impacts relating to all DOD systems.”
By contrast, the GPS Innovation Alliance applauded the NASEM’s “reaffirmation that Ligado’s terrestrial operations would have a harmful, real-world impact on the millions of federal and commercial users that rely on GPS, satellite communications, and weather forecasting services every single day.” It further stated that the report “demonstrates that Ligado would pose an unacceptable risk to services critical to safety-of-life operations, our national security, and our economy” and urged “government action to address the imminent, but preventable, harm that would result from Ligado’s deployment.”
According to the DOD, the NASEM study “confirms that Ligado’s system will interfere with DOD GPS receivers, which include high-precision GPS receivers.” The study also concludes, DOD says, that the FCC’s proposed mitigation and replacement measures “are impractical, cost prohibitive, and possibly ineffective.”
The NASEM committee pointed out repeatedly in its report that matters are more nuanced than represented by either side and that test results and harmful interference depend on many factors — including the receiver’s signal processing architecture, the amount of SNR loss, the use case, and the relevant failure modes. “The determination of harmful interference is dependent on the particulars,” it said.
The committee also bemoaned “a lack of a quantifiable definition of harmful interference” and “the lack of common receiver assumptions” and called for “more definitive receiver standards.” It also pointed out that “many spectrum conflicts could be avoided if receivers were better designed and implemented.”
The GPS user base is in the billions. Therefore, even if “most” receivers will not be harmed by Ligado’s operations, as the committee reported, tens of millions of devices will be. I highly recommend reading the full report.
The five-member Federal Communications Commission (FCC) voted unanimously to approve an order to allow Ligado Networks to deploy a low-power nationwide 5G network.
The approval comes despite objections from the U.S. Defense Department (DOD), other federal agencies and major U.S. airlines, all of whom are concerned about near-band interference with GPS.
The FCC said the approval order included stringent conditions aimed at ensuring GPS would not experience harmful interference.
“After many years of consideration, it is time for the FCC to make a decision and bring this proceeding to a close,” said FCC Chairman Ajit Pai in an April 16 news release. “We have compiled an extensive record, which confirms that it is in the public interest to grant Ligado’s application while imposing stringent conditions to prevent harmful interference.”
Ligado is seeking to repurpose a swath of L-band spectrum for a 5G network focused mainly on connecting smart devices and other internet-of-things services. According to the FCC, the order will “promote more efficient and effective use of our nation’s spectrum resources and ensure that adjacent band operations, including the Global Positioning System (GPS), are protected from harmful interference.”
In response, members of both the Senate and House Armed Services Committees and other defense advocates are considering legislative action to overturn the order.
Two areas that rely heavily on the integrity of GPS signals include defense and transportation. The DOD issued a joint statement with the Department of Transportation (DOT) criticizing the FCC ruling.
“Americans rely on our Global Positioning System (GPS) each day for many things: to locate citizens in need of emergency assistance through our E-911 system, to secure our financial system, to order and receive shipments, to travel by car for work and leisure, to facilitate commercial trucking and construction work, and even to make a simple cellphone call. Our departments rely on GPS each day for all those reasons as well to coordinate tactical national security operations, launch spacecraft, track threats, and facilitate travel by air and sea. The proposed Ligado decision by the Federal Communications Commission will put all these uses of GPS at risk.”
House Armed Services Committee Chairman Adam Smith (D-Wash.) released a letter he sent to Defense Secretary Mark Esper and FCC Chairman Ajit Pai raising concerns about Ligado’s 5G network.
“While the United States must be a leader in the implementation of 5G networks, our creation of these networks must not hamper our military’s operational capacity in any way. China’s aggressive, global promotion of its 5G companies presents a considerable security challenge that must be addressed. However, Ligado’s proposal, which seeks a portion of spectrum adjacent to that used for Global Positioning Systems, poses an even larger security risk.
“The Department of Defense has been clear and direct: providing this license to Ligado would cause unacceptable operational impacts and adversely affect the military’s use of GPS. The military’s seamless use of GPS is vital to our national security. Our service members rely on GPS satellites for critical precision timing and navigation, and thousands of weapons systems are embedded with GPS signals.
“While I strongly support development of the world’s most robust, safe and secure network, using L-band spectrum in such close proximity to critical GPS, as Ligado’s proposal requires, carries an unacceptable risk that far outweighs the possibility of a 5G network.”
‘Risk of crippling’ GPS
Defense Secretary Mark Esper said via Twitter on Friday that the “Ligado proposal would needlessly imperil GPS-dependent national security capabilities. The Department continues to support domestic 5G options, but not at the risk of crippling our GPS networks. Nearly a dozen other federal agencies have joined us in opposing this proposal.”
“Although I appreciate the concerns that have been raised by certain Executive Branch agencies, it is the Commission’s duty to make an independent determination based on sound engineering. And based on the painstaking technical analysis done by our expert staff, I am convinced that the conditions outlined in this draft order would permit Ligado to move forward without causing harmful interference. For example, the draft order would authorize downlink operations at a power level that represents a greater than 99% reduction from what Ligado proposed in its 2015 application.”
Image: A-Digit/DigitalVision Vectors/Getty Images
The release also provided this background about the Ligado proposal, and the “conditions” under which the FCC decided to approve it.
In recent years, Ligado has amended its application to significantly reduce the power levels of its base stations from 32 dBW to 9.8 dBW (a reduction of 99.3%). Ligado has also committed to providing a significant (23 megahertz) guard-band using its own licensed spectrum to further separate its terrestrial base station transmissions from neighboring operations in the Radionavigation-Satellite Service allocation. As such, Ligado is now only seeking terrestrial use of the 1526-1536 MHz, 1627.5-1637.5 MHz, and 1646.5-1656.5 MHz bands. The Order is conditioned to reflect these technical requirements. It also requires Ligado to protect adjacent band incumbents by reporting its base station locations and technical operating parameters to potentially affected government and industry stakeholders prior to commencing operations, continuously monitoring the transmit power of its base station sites, and complying with procedures and actions for responding to credible reports of interference, including rapid shutdown of operations where warranted.
However, The decision “appears to ignore the well-documented views of the expert agencies charged with preserving the integrity of GPS, specifically on the critical issue of what constitutes harmful interference to users of Global Navigation Satellite Systems (GNSS),” said J. David Grossman, executive director of the GPS Innovation Alliance (GPSIA). He continued,
J. David Grossman
“GPSIA has consistently advocated for adoption of the 1-dB Standard as the only reliable mechanism that provides the predictability and certainty to ensure the continuation of the GPS success story, with the support of the Department of Defense, the Department of Transportation and numerous other federal agencies. The 1-dB Standard for radiofrequency-based services is critical for GNSS. The FCC’s press release refers to conditions placed on Ligado’s application to prevent harmful interference, and GPSIA and its members intend to carefully review the details of today’s order while continuing to vigorously advocate for promoting, protecting and enhancing GPS.”
Ligado Networks President and CEO Doug Smith issued this statement in reaction to the approval.
“Ligado thanks the Commissioners for moving promptly to approve the order regarding our applications. We greatly appreciate their unanimous support as well as the expert engineering analysis determining that a terrestrial network can be deployed in the L-band to advance our country’s economic and security interests while fully protecting GPS. Our spectrum can be very instrumental in the transition to 5G, and we look forward to utilizing satellite and terrestrial services to deploy customized private networks and deliver innovative, next-generation IoT solutions for the industrial sector.”
Positive reactions to the decision
On April 20, the FCC released a compilation of responses to the decision, all of them in support.
Attorney General Bill Barr: “I applaud FCC Chairman Pai’s proposal to make available L-band spectrum, to be used together with C-band spectrum, for deployment of advanced wireless services, including 5G. As I said in my speech at the Center for Strategic and International Studies, swift FCC action on spectrum is imperative to allow for the deployment of 5G. This is essential if we are to keep our economic and technological leadership and avoid forfeiting it to Communist China.” (Statement, 4/16/2020)
Secretary of State Mike Pompeo: “I commend Federal Communications Commission (FCC) Chairman Pai’s draft order that would release the L-Band spectrum. Quick action on this order, in conjunction with the allocation of a portion of the C-Band for 5G, is vital to our national security and will help ensure that the United States is the global leader in advanced technologies such as AI, the Internet of Things, edge computing, and the next generation of telemedicine. Accelerating the deployment of 5G is essential to our country’s growth, and global economic security.” (Statement, 4/16/2020)
Sen. Ron Johnson (WI): “In a time when connectivity is and will continue to be more important than ever, it’s great to see @AjitPaiFCC move forward with freeing up critical spectrum resources for #5G.” (Tweet, 4/16/2020)
Sen. Mark Warner (VA): “As the U.S. works to lead the world in 5G innovation and promote wider high-speed internet coverage, it’s all the more important to put our valuable mid-band spectrum to use. I urge the @FCC to follow the Chairman’s lead and approve Virginia-based @LigadoInsights’s application.” (Tweet, 4/16/2020)
Rep. Billy Long (MO): “I applaud @AjitPaiFCC and the @FCC for taking action to unlock vital L-band spectrum that has been held hostage by bureaucratic slow-walking for far too long. Jobs and 5G is a win-win for the country.” (Tweet, 4/16/2020)
Rep. Doris Matsui (CA): “I called on the @FCC to move forward with new, innovative uses of L-band spectrum to advance 5G. Glad to see the Commission take action on this front today to encourage efficient use of our spectrum.” (Tweet, 4/16/2020)
Former Rep. Bob Barr (GA): “Federal Communications Commission Chairman Ajit Pai’s decision to circulate a draft FCC Order would at long last move forward the process of opening up a segment of mid-band satellite spectrum for commercial use in 5G technology deserves praise. … If adopted by the five-member Commission headed by Pai, the draft Order would tangibly signal to the country and the world that the United States is committed to seize the leadership in deployment of 5G technology, a role China openly covets.” (Statement, 4/16/2020)
American Action Forum: “More good news from the FCC! 5G is incredibly important and this is yet another example of actions that will enable innovation in 5G and support the growing number of connected devices.” (Tweet, 4/16/2020)
American Enterprise Institute Visiting Scholar Mark Jamison: “@FCC approval of Ligado petition should accelerate 5G, bring diversity to marketplace, and increase efficient spectrum use. … Good leadership and bipartisan effort!” (Tweet, 4/20/20)
American Enterprise Institute Visiting Scholar Roslyn Layton: “Kudos @AjitPaiFCC for unlocking more vital mid-band spectrum for #5G. Record of 10 years shows @LigadoNetworks took many steps with agencies and firms to address potential issues with GPS. We must move quickly on 5G!” (Tweet, 4/16/2020)
Citizens Against Government Waste: “The FCC has the engineering expertise to determine the best use of this spectrum and whether alternative uses would cause undue interference. The adoption of the Chairman’s draft order will promote 5G and IoT development, while providing the necessary safeguards for services using adjacent bands, including GPS positioning. … The L-band would not be used at all for the foreseeable future unless the FCC takes action. Freeing up the spectrum requested by Ligado will not only expand the use of 5G, it will also help to prevent other countries, particularly China, from getting ahead of the U.S. in 5G deployment.” (Blog, 4/17/2020)
Competitive Carriers Association: “[We] commend Chairman Pai for circulating a draft order to approve Ligado’s applications, which will make much-needed mid-band spectrum, specifically L-band spectrum, available for terrestrial use. This long-awaited, positive progress comes at a critical time for all Americans, particularly those in rural areas, who are relying on mobile connections and services more than ever before. Mid-band spectrum provides real opportunities for deploying next-generation technologies, and competitive carriers are eager to access this valuable resource to expand and enhance their networks.” (Statement, 4/16/20)
Competitive Enterprise Institute: “Access to spectrum is crucial for our modern economy, connecting everything from radios, to cellphones, to satellites. But for too long, turf-wars between federal regulatory agencies have left spectrum bands largely unavailable for valuable commercial applications. Today’s FCC decision wrests spectrum away from bureaucratic waste and delivers it into the hands of people who will aide our economic recovery and resiliency in the aftermath of the COVID-19 pandemic.” (Statement, 4/16/2020)
CTIA—The Wireless Association: “We’re pleased to see that the FCC has managed to cut through the red tape to make a decision on Ligado. This multi-year process reveals the challenges at play in our nation’s spectrum policy and the need for stronger support for new commercial wireless services. We need to all learn lessons from this process and ensure that decisions on key spectrum bands like lower 3 GHz occur in a more expedited and collaborative manner.” (Statement, 4/16/2020)
FreedomWorks: “Freeing up broadband spectrum will make America a global technological leader and will lead to innovations and developments that will improve quality of life across the country. Chairman Pai and the FCC should be applauded for their work resolving these matters[.]” (Blog, 4/15/2020)
Free State Foundation: “Chairman @AjitPaiFCC has made a commendable decision to act on @LigadoNetworks’ proposal to put L-band spectrum into use for next-gen wireless services. This move takes seriously the @FCC’s responsibility and the urgent need for more commercial spectrum.” (Tweet, 4/16/2020)
Georgetown Law Institute for Technology Law & Policy Distinguished Fellow Gigi Sohn: “This decision was a long time coming, but it’s the right one. … Kudos to @AjitPaiFCC for having the fortitude to move this forward.” (Tweet, 4/16/2020)
Information Technology & Innovation Foundation: “Great to see @FCC taking steps to finally approve @LigadoNetworks waiver for terrestrial use of their spectrum. This will be a boon to industrial IoT connectivity, bringing more productivity, safety, and resiliency for users of the network.” (Tweet, 4/16/2020)
International Center for Law & Economics: “Promoting deployment of 5G & next-gen IoT devices means finding new ways for incumbents to responsibly operate in ever-closer proximity. The @FCC’s Ligado order does that. Credit to @AjitPaiFCC for finding a way fwd that promotes innovation while limiting the risk of interference.” (Tweet, 4/16/2020)
Lincoln Network: “Access to spectrum is an essential feature in any working 5G plan. Frankly, one key barrier in opening up this vital resource is government’s stronghold on ‘beachfront’ spectrum whether they own it or not. … This proceeding has been in regulatory limbo for several years due in large part to government stakeholders’ speculative interference claims regarding GPS-applications. … The FCC’s draft order in this proceeding provides enough protection for incumbents in adjacent bands, adds more competition into the 5G-IoT space, and allows consumers to have more access to broadband. Everybody wins.” (Blog, 4/16/2020)
Mercatus Center Senior Fellow Brent Skorup: “Too often new tech is stalled by FCC regulation and incumbents. Chairman Pai pledged to breathe new life into Sec. 7. It’s great to see Chairman Pai and the FCC act on that pledge, liberalize spectrum, and expedite the deployment of new wireless services.” (Tweet, 4/16/2020)
National Security Institute: “Big move by @FCC Chairman @AjitPaiFCC today to support US 5G availability. This is a key nat sec issue w/ threat posed by China + econ benefits of broad 5G deployment in US.” (Tweet, 4/16/2020)
New America Foundation’s Open Technology Institute: “Kudos to @AjitPaiFCC @FCC for again standing up to Fed agencies trying to hoard spectrum they are not using – or, in this case, which is licensed to @LigadoNetworks! A big plus for #5G wireless ecosystem if it’s built out.” (Tweet, 4/16/2020)
R Street Institute: “If you can change your business model to be more productive and profitable, without hurting anyone else, then regulations shouldn’t stand in your way. Well done, @FCC!” (Tweet, 4/16/2020)
Progressive Policy Institute: “We applaud the FCC’s ongoing efforts to accelerate the deployment of 5G. Repurposing this commercial spectrum for a mobile broadband network is another step in the right direction.” (Tweet, 4/16/2020)
Public Knowledge: “The Chairman’s proposed Order reveals how the FCC has worked to both protect incumbent GPS users while allowing for pro-competitive commercial licensing of spectrum. … Congress has entrusted the FCC to strike the proper balance between the needs of incumbents and the potential benefits to new entrants or new users, and here, the FCC gets it right. In approving Ligado’s license, the FCC has taken an important step forward in its role as the sole arbiter of spectrum disputes and, in this instance, has correctly sided on behalf of the public interest to help deliver the potential of 5G to more Americans.” (Statement, 4/16/2020)
Technology Policy Institute: “Allowing the Ligado spectrum to lie fallow would represent a waste of valuable resources that could provide substantial benefits for consumers in the form of new Internet of Things and other uses. … Failure to approve the Ligado license modifications would have the opposite effect, transferring a large block of spectrum from the commercial sector back to the government. The Commission’s action today will avoid that outcome.” (Statement, 4/16/2020)
Wireless Infrastructure Association: “WIA applauds Chairman Pai for circulating a draft order to approve Ligado’s plans to deploy a nationwide network that would primarily support 5G and IoT services. After years of diligence, study, and discussion, today’s action is further evidence that the FCC bases its decisions on science and engineering. Freeing up more spectrum, especially mid-band spectrum, is vital to 5G deployment. Ligado’s proposal offers an enormous opportunity for infrastructure investment, deployment, and connectivity for Americans across the country right when we need it most.” (Statement, 4/16/2020)
Q: What is the biggest challenge facing designers of multi-constellation GNSS receivers today?
Javad Ashjaee, founder of Javad GNSS: The biggest challenge now is spoofing.
Some years ago the issue was jamming —the hot issue of LightSquared — that would hurt GNSS. To solve that problem we created the J-Shield and showed that J-Shield technology could protect against LightSquared and similar signals. We manufactured dozens of units that were successfully tested by several independent laboratories.
Now GNSS faces the spoofing issue. Reports of Black Sea spoofing and other examples show the urgency of paying attention to this problem. When a spoofer is successful, both position and time are spoofed.
A Nov. 3 CNN video report on this subject gives an example of how little people know about spoofing and about the work that has been done on this subject. The report claims that GNSS technology companies have not done much or spent money on this subject. Obviously the reporter doesn’t know what we have done, as I will report here.
I’ll review the spoofing methods and how we counter them.
Source: Javad GNSS
Spoofers use three methods: One simple way is to broadcast GNSS-like signals that provide the wrong ranging information which, when used, creates wrong position and time solutions. Most probably this is the method that Prof. Todd Humphreys used to spoof the GNSS receiver on the $80 million yacht [“GNSS Lies, GNSS Truth,” November 2014 GPS World.] This method fools the GNSS receiver into ignoring the correlation peak of the real satellite signal and using the correlation peak of the spoofer signal. To deal with this type of spoofer we take advantage of the 864 tracking channels and over 130,000 fast acquisition channels of our TRIUMPH chip. We assign more than one channel to each satellite signal and we track all their peaks: The real peak and the spoofer’s peaks. Then in Step 1, below, we exclude all signals with more than one correlation peak.
Method Two is broadcasting spoofed signals for satellites that are below the horizon in the spoofed area or for satellites that do not exist. In this case only one correlation peak exists. Our equipment and OEM boards can download valid and certified almanac data from our website to know the status of satellites and their visibility ahead of their mission. Almanac data can be used for several weeks.
Method Three is to cover the signal of a visible satellite with noise and on top of the noise add the spoofer signal with more power. We recognize such spoofers by their unreasonable signal power and the background noise.
In the first counter-spoofing step we ignore these signals:
Those with more than one peak;
Those that according to our almanac should not be visible;
Those with unreasonably high or inconsistent signal-to-noise ratio (SNR);
Systems whose satellites all have similar SNR.
Satellites that do not generate complete multi-frequency signals (spoofers usually generate only C/A code).
After removing all questionable signals, we use the remaining signals to compute our approximate position. We need at least 4 signals from the many available signals of GPS L1, L2P, L2C, L5, GLONASS L1, L2, L3, and the many signals of BeiDou, QZSS and IRNSS.
In the second step we validate all questionable signals against the approximate position that we have calculated and keep only those that pass our validation. We then re-compute the more precise position using all good signals. We consistently throw away the spoofer correlation peak and use the real satellite signal.
If all signals of all satellites are spoofed, then we warn the user to ignore the GNSS signals and use some other sensors (like compass and gyro) to get out of the spoofed area. A spoofer that can spoof all signals of all satellites will be very expensive to build and deploy.
In a very difficult situation, the user can enter their approximate position to quickly understand if spoofers exist, and then identify them.
All the counter-spoofing methods that I have discussed here are the subject of patents for which we have applied.
Since currently most of spoofers spoof the L1 C/A code, we can simply initially ignore the C/A signals to compute the initial approximate position and use it to identify the spoofed signals.
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.
Finally I would like to challenge Prof. Todd Humphreys [professor and director, Radionavigation Laboratory, University of Texas-Austin] to spoof any of our receivers that have this anti-spoofing option. We offer this as an option on all of our OEM boards.
By Bradford Parkinson Vice-chair, U.S. PNT Advisory Board
In the coming months, the U.S. Federal Communications Commission (FCC) may allow high-powered, ground-based, communication transmitters to broadcast at a frequency near GPS L1. U.S. Department of Transportation (DOT) tests have shown that such transmitters effectively become jammers for many existing GPS receivers.
I believe that this possibility is the greatest current threat to the position, navigation and timing (PNT) community.
L1 is the primary band for GPS as well as for similar GNSS. For example, the international signal called L1C is to be centered at L1, albeit with wider spreading than the current L1 civil signal, C/A.
Why is this of critical importance? An economics study that only considered a small subset of benefits concluded that the U.S. alone realized $65 billion per year in direct economic value. A more complete recent study for the UK, extrapolated to the U.S., estimated the total impact of the loss of GPS to be over $3 billion per day for a five-day outage — a far greater rate. Virtually all GPS applications rely on the signals at L1. Thus, any threat to GPS is not simply an inconvenience, it would have great potential to do economic harm.
The PNT Advisory Board (PNTAB)has been trying to protect PNT, particularly GPS, and at the same time accommodate Ligado, a company that has requested repurposing of nearby spectrum. At our November meeting, we reviewed the Ligado proposal and framed a response that will be made public in due time. Meanwhile, these observations and conclusions are my own.
History
In 2011, LightSquared proposed that existing restrictions on its existing frequency authorization in the Mobile Satellite Service (MSS) band (a faint signal, satellite-to-ground) be waived so that the band is effectively repurposed to allow for high-power terrestrial transmissions.
The company has two space-to-ground authorizations in the 1525–1559 MHz band (1526–1536 MHz and 1545–1555 MHz) very close to the GPS primary frequency (L1 at 1575MHz). Initially it requested repurposing to ground transmission of 42 dBW (15.8 kW).
Faced with tests and analysis that showed this would be very destructive to GPS, it proposed to abandon the closer band and reduce power in the further band to 32 dBW, or 1580 Watts.
Ligado filings suggest a spacing of approximately ¼ mile between transmitters. A GPS receiver would find even these weaker signals 5 billion times the power of GPS at the maximum range of ¼ mile.
Most PNT users would be much closer.
International criterion
To ensure ranging accuracy, the international standard for interference to GPS is a 1-dB increase in noise levels. In conventional terms, this max allowable 1 dB is a 25.8% increase in background noise. The power of the weak GPS signal is only about 1% of the background radio noise. Sophisticated signal processing algorithms allow the signal to be reconstructed.
The result: the international 1-dB standard is equivalent to a 25% reduction in GPS radiated power.
Two additional points
The 1 dB is not simply to protect signal lock, it is to protect ranging accuracy. Most GPS receivers will stay locked for higher levels of interference but lose high precision. This is particularly a problem for high-precision receivers, which need relative timing to sub-nanosecond accuracies.
These measurements are equivalent to the time it takes light to travel ¼ inch. Protecting such accuracies is of paramount importance to PNT users and applications.
Allowing such maximum degradation from a single source is not the whole picture. There are many other potential sources of interference and attenuations of the GPS signal. For example, foliage may reduce the GPS signal.
A receiver must cope with all of these difficulties. Allowing a single cause, such as the Ligado repurposing, the 25.8% equivalent reduction might be considered quite generous, but it is the accepted International Standard.
Ligado has specifically rejected this criterion, largely because testing has shown that the Ligado repurposing would then be unacceptable for many PNT user classes.
To support its rejection of the International Standard, Ligado has repeatedly alleged that five of the major manufacturers are in complete agreement regarding its repurposing. This is a substantial distortion. The record was set straight by Brian Ramsay of MITRE at the November PNTAB meeting: “Four of the five parties that reached agreements with Ligado (except for Topcon Positioning) support the 1-dB Interference Protection Criterion (IPC) in comments filed in response to this Public Notice.”
Further support was highlighted by Captain Robyn Anderson: “In June 2017, the Air Force produced a white paper on the 1-dB IPC that explained the relationship between harmful interference (levels that affect GPS receiver performance) and the 1-dB IPC (keeps interference below a level that would cause harmful interference).”
Lightsquared’s motivation in 2011 was clear: a $10 billion windfall profit (estimated increased value of the spectrum on open-market auction). The FCC did not confirm Lightsquared’s modified request, and in 2012 the company went into bankruptcy.
Reorganizing as Ligado and emerging in December 2015, it continued to pursue repurposing of its spectrum, sponsoring tests by Roberson and Associates, and tests at National Institute of Standards and Technology (NIST)/National Advanced Spectrum and Communications Test Network (NASCTN) to establish test procedures.
Both groups of tests were carefully reviewed by our PNTAB who found serious flaws. In general, Ligado rejected the 1-dB criterion and did not accept the need to protect all classes of users, particularly high-precision receivers. In addition, it did not consider the new GPS L1 signals (L1C and L1M), nor did it check the impacts on the international GNSS. The PNTAB assembled a 14-point summary of deficiencies and requested updates and corrections for the flaws.
NASCTN’S response did not really address the points, or claimed that there were no funds to correct the problems. The PNTAB then developed a Six-Point Criteria for acceptable interference testing,summarized as:
Accept and strictly apply the 1-dB criterion.
Verify interference for all classes of receivers.
Test and verify for all operating modes.
Focus analysis on worst cases.
Include the new GNSS signals.
Include GNSS expertise and openly publish results.
Image: PNTAB
We believe it is a very reasonable set that aims to protect PNT users and our economic benefits. In its sponsored tests, and in representations to the FCC, Ligado has consistently overlooked a basic facet of radio ranging: it is ranging accuracy, not simply locking onto a signal, that is the fundamental objective for PNT.
Both Ligado test sets clearly failed on all six points.
DOT ABC tests
While the Ligado-sponsored tests were neither independent nor adequate, the Department of Transportation, led by Karen VanDyke, sponsored a very complete set of independent tests; these are the most credible estimates of harmful interference. The ABC results have been made public. The PNTAB’s six points were published after DOT testing had begun, but DOT expanded and modified their effort to satisfy the criteria. The DOT conclusions, based on modeling real-world antennas and propagation patterns, are shown in Table 1.
TABLE 1. DOT ABC test results. Maximum tolerable effective radiated power (EIRP) for classes of the most susceptible GPS receivers for modified Ligado proposal (P2) of 1.58 kilowatts. In red are the factors that Ligado P2 exceeds the maximum tolerable radiated power. (Chart: GPS World)
At 100 meters, all classes of receivers tested had results that would exceed the 1-dB threshold, even for the reduced power level (P2, 1580 Watts) that has been the most recent filing. The shaded square is particularly troublesome. It shows that, for the most susceptible high-precision receivers, the Ligado proposed power exceeds the 1-dB threshold by over 200,000. This result is particularly damning for the proposed repurposing, because it is this class that produced the highest payoff in the recent Department of Commerce Study — over $30 billion per year.
PNT operations at risk
These are examples of unintended and potentially hazardous consequences of repurposing.
UAVs. Unmanned aerial vehicles (drones) will fly very close to the dense array of transmitters that Ligado would deploy. They usually require GPS for flight control. Even more important, if we are to monitor them and keep them from collisions, GPS offers the only viable techniques with 3D accuracy and almost 100% availability.
Precision survey. This is routinely used in urban areas for building construction and is a major source of productivity gains. These survey receivers are all high precision and routinely make measurements to better than ¼ inch.
Helicopters. These are found in urban area at all altitudes. They are used for law enforcement, rescue and passenger transportation. GPS is mainly used for general navigation.
Public safety vehicles. Fire, police and ambulances use GPS for both navigation and dispatch tracking. In a city, they would drive in and out of susceptible high-interference zones.
The PNTAB believes the DOT results are representative, accurate and credible. The National Coordinating Office for PNT also sponsored an evaluation of all testing to date. A summary report is now in coordination, as a combined Department of Defense (DOD) and DOT effort.
The DoD, which uses GPS in the national airspace for routine flight, testing, training, guiding rocket launches, and for humanitarian rescue missions, has opposed repurposing. The Air Force reported, “Results from the DOD ABC Assessment support the conclusions drawn from Department of Transportation’s ABC Assessment.”
November PNTAB meeting
At our November meeting, the board invited Ligado to make a presentation on its repurposing proposal. The invitation said: “Specifically describe your implementation plan, with a corresponding test plan addressing 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 signals.”
Valerie Green, executive vice president and chief legal officer of Ligado Networks, represented Ligado. In the run-up to the meeting, the Six-Point Criteria had been sent to Ligado. Green did not address the six points at all.
She did offer to reduce initial power to “the safe power level in the 1526–1536 MHz channel ranges from 9 to 13 dBW EIRP nationwide,not just near airports.”
FIGURE 1. Potential impacts on high-performance receivers. Red: loss of lock of all satellites. Yellow: loss of lock of low-elevation satellites. Green: 1-dB degradation. (Chart: PNTAB)
The 13 dBW corresponds to initial power levels of 19.95 W. However, Ligado has made clear in its FCC filings that it ultimately still wants a full 32 dBW base-station transmit power level, consistent with typical 4G/LTE networks.
The initial reduced power sounds like a major move in the right direction, but further questioning revealed two major issues:
Tower Spacing. Green was very evasive on the spacing of transmitter towers. Clearly, at the reduced power level, greater density would be needed to carry the original data bandwidth. At about 1/100th the power, density would have to increase by a factor of 100, and the spacing would have to decrease to 1/10th for the same data output rate.
Green referred us to an earlier filing which specified 0.25 mile, but did not clearly state that this was the plan; she claimed the details were proprietary. If this fundamental parameter, spacing, is not specified, it is hard to see the basis for the FCC evaluation of any new proposal. If the transmitter spacing is reduced to less than 1/10th of a mile, the sources of potential harm would be multiplied in a very worrisome way.
Future power constraint.A public presentation does not ensure that Ligado will actually file and agree to abide by those power constraints indefinitely. Board members pressed Green on the permanence of the power constraint.
She suggested it would be tied to the RTCA Minimum Operational Performance Standard. Revising the MOPS takes many years, if not decades, both to formulate and to implement. Retrofitting the commercial aircraft fleet is very expensive and time-consuming.
Further, her statement focuses only on commercial aircraft, ignoring the high-precision classes as well as future signals.
A modified summary chart (Table 2) for the lower power, based on the DOT ABC test results, shows that even at the lower power, the threshold for high-precision receivers is exceeded by a factor of over 3,000 at 100 meters. In fact, only cell phones, which are relatively inaccurate, could operate at 100 meters without exceeding the threshold.
TABLE 2. Results of DOT ABC test with Ligado transmitters constrained to 19.95 Watts (13 dBW). This illustrates that the International Interference Limit is exceeded many times over at 100 meters for certain high-precision receivers, highlighted in red. (Table: GPS World)
With these expectations and uncertainties, the PNTAB did not find the new revision acceptable to the PNT community.
Three fundamental issues
Ligado has steadfastly not accepted the realities of non-interference.
1 dB. Acceptance of the 1-dB (25.8% noise increase) International Interference standard is fundamental to protecting GPS applications throughout the country.
All current and future uses. Users of great concern are emergency services, helicopter and general aviation, UAVs, and precision survey and machine control. For example, many of the underground utilities in the U.S. have been mapped with precision, GPS-based, geographic information receivers. This application requires sub-meter accuracy and operates in both rural and urban environments.
Ligado has tended to simply focus on certified aviation, claiming that protecting that class of user is enough. The PNT community rejects that view. All current and future PNT users must be protected.
Worst–case interference. The recent round of testing was largely in a laboratory. Extrapolating to the real world must examine the situations with greatest interference. For example:
Number of simultaneous interfering transmitters. A single transmitter situation is not typical; three or more are apt to be in range. The additive power must be considered.
Propagation models. Propagation models for communications differ from those for evaluating potential interference to a navigation signal. For assured communication, a typical model assumes transmitted signal fall-off a little faster than 1/(distance squared). Ligado would naturally prefer to use this model, which is far from worst-case for interference. The early round of tests in Las Vegas verified the communications model would vastly underestimate interference levels, by factors of 10 or more. A more realistic model must be used.
Degradation Radius. This is the size of the circle within which the International Standard is violated for receivers in a specified class. If the spacing of transmitters is 400 meters, and the degradation radius is 200 meters, virtually all receivers are in the degradation zone. Ligado suggested an appropriate degradation radius is 250 feet for aviation (approximately 100 meters). Thus, they claim the PNT community should tolerate violation of the standard when closer than 100 meters to their transmitters. At 400 meters spacing, 25% of the area would be in violation.
But the ABC test results reveal a much graver situation. They show that, for the current Ligado proposal (1580 watts), the degradation radius is over 14 kilometers for high-precision receivers. See Figure 2.
The 1-dB criterion is the correct, accepted and somewhat generous allocation of interference that can be accepted by the PNT community. We would hope that the FCC would continue to insist on this standard.
PNT users must, yet again, defend the spectrum vigorously. Most of us are scientific and technical people. We are not used to discussions that deliberately avoid the technical issue or deny scientific evidence. We reject arguments that violate the fundamental laws of physics.
The currently filed proposal, 1580 Watts at spacing of ¼ mile, is unacceptable. It will do grave harm to many important PNT applications
We must be very leery of the new proposal by Ligado of 9–13 dBW. It still would violate the 1-dB criterion at 100 meters for many PNT users.
Moreover, the company history has been to bait and switch; it has an authorization for MSS Ancillary Terrestrial Component (MSS ATC) stations to fill the gaps in satellite coverage with ground transmitters. These must operate in conjunction with the space-to-ground link that made them effectively self-limiting. However, in 2011, it almost succeeded in switching this to a ground-only system, which would have achieved a huge financial windfall.
Open-air verification
If the FCC continues to consider this proposal, there is one step that it should take before granting it. It should require Ligado to deploy an array of transmitters in its advocated configuration, and run real-world, open-sky testing to assess the harm that may result, particularly to high-precision accuracy.
Such testing was done when the issue was first raised in 2011 and conclusively demonstrated unacceptable interference. Nothing has really changed from the baseline that was tested and found unacceptable then.
The company should carry the full financial burden of such a verification, under PNT supervision. The government, having already spent millions of dollars to defend the spectrum, should not bear the cost of such retesting.
Without this confirmation, it is hard to conceive of putting GPS and PNT at significant risk to satisfy investors who want to flip a company, after gaining “rezoning” permission for their spectrum.
From 20,000 feet altitude
If we examine the situation without the technical details, we have this: Fundamentally Ligado wants to provide service using its allocated frequency band for an unlimited number of Internet-of-Things installations.
It is not proposing a small, fixed number of transmitting towers located in isolated regions, but rather an accelerating deployment of private networks, many of which will be close to commercial and essential infrastructure where GPS use is critical.
It seems unrealistic that Ligado can or will reliably guarantee that these widespread installations will be continually adjusted and monitored to avoid GPS interference.
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.
While I can commend the entrepreneurial spirit, the Ligado proposal seems very reckless indeed. The incremental value of an additional broadband transmitting system when there are at least five already in existence seems trivial compared to the potential damage done to the modern utility named GPS.
I sincerely hope the FCC can find a spectrum swap or deny outright the current Ligado application.
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.
In life, few things are certain. In family, love and friendship, fewer. Add more people — workplace, groups, associations, government, society, nations, war — and the complications multiply, the certainties become more scarce.
Some things, however, remain fixed, and true. We call them facts. They are not subject to denial or claims of fakery. They can sometimes be distorted, or their interpretation disputed, but at the end of the day they remain what they were at the beginning. Facts. True.
They do not require a majority to believe in them, nor even a powerful minority. They exist outside belief, heedless of the powers of persuasion, cajolery, hucksterism.
The facts do not always, to their detriment, speak for themselves. Reason does not always prevail. But the facts continue to exist, ruling the operations of the universe.
It has been said that journalism’s duty is to print the facts and raise hell (Chicago Times, 1861). I submit to you that it is a scientist’s duty — and an engineer is a scientist — to live and practice by the facts, to preserve the facts if necessary. To raise hell? That may be a matter of taste or personal style. But to see that the facts are known, shared, publicly available — that can be undertaken without uncomfortable or unpleasant hell-raising.
Guerrilla archiving and data rescues have mushroomed across the U.S., in response to fear that the U.S. government will remove facts it dislikes from its own websites. All-day hackathons are organized by volunteers; the events focus on downloading federal science data sets, particularly those related to climate change, from government websites and uploading them to a new site, datarefuge.org, an alternative source for data. They’re also feeding tens of thousands of government web pages into the Internet Archive, a nonprofit digital library with the mission of “universal access to all knowledge.” And of course someone has devised a custom-built app specifically for this purpose.
Climate-change data has a geospatial aspect, and much of it was collected with GPS equipment. Positioning coordinates lie at the heart of so much key information. So an attack on carefully assembled, scientifically overseen data can be interpreted as an attack on the validity of global positioning technology. Whether or not we take it personally, we should be wary of any attempt to deny or abolish any facts, anywhere.
We’ve seen this before, in other forms. The LightSquared episode in 2011–12 produced blatant denials of the physics of radio-frequency waveforms, for personal and institutional profit. We don’t yet know if this is happening again, whether government data has been erased or simply moved elsewhere.
Whether or wherever they appear or disappear, the facts continue to exist, and perhaps they deserve more respect than they’ve been getting.
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.).”
The next-generation GPS ground-control system, known as OCX.
The White House budget request for the Next Generation Operational Control System (OCX) comes to $393.3 million for fiscal year (FY) 2017.
The updated OCX budget appears as the Air Force officially acknowledges a two-year delay in the program, which could slide as late as 2023 for implementation.
The total cost for OCX now amounts to $4.81 billion.
In a cautionary move meant to span a suddenly yawning gap in ground control capabilities, the GPS Directorate awarded a $96 million contract modification to Lockheed Martin Space Systems to provide GPS III Contingency Operations services (COps).
By the end of 2019, Lockheed will “modify the current GPS control segment to operate all GPS III satellites that are launched prior to the transition” to OCX, as well as GPS III satellite vehicle simulation modules, a GPS simulator and updates to the GPS Positional Training Emulator.
Late delivery of OCX Block 1 “puts GPS constellation sustainment at risk since the current control segment cannot operate GPS III satellites,” according to a Pentagon statement.
The Air Force will “re-phase the GPS III space vehicle procurement profile,” delaying procurement of the 11th and all following GPS IIIs to FY18.
User Equipment. In contrast, the Pentagon substantially increased its request for developing user equipment to $278.2 million for FY17.
The added funds for Military GPS User Equipment (MGUE) seek to speed platform integration of M-code capability for munitions, warfighters, armored vehicles, planes and all military platforms: a stronger signal and data authentication capability.
OCX must navigate latest acquisition reforms
Acquisition reform mandated by Congress for the U.S. military, and known as Better Buying Power 3.0 guidance and initiatives, poses a tough new challenge for the Pentagon, not least for the Air Force and GPS.
This comes in the face of an impending (some say already underway) cyberwar targeting core infrastructure, much of it controlled or metered to some extent by GPS.
Under-Secretary of Defense for Acquisition, Technology and Logistics Frank Kendall stated in 2014 that the United States is “under attack in the cyber world” and “we’ve got to do a better job protecting our things.”
The cyber realm changes and innovates much faster than the material weaponry realm to which the acquisition cycle is obsolescently tied. Currently, funding, developing and fielding a new capability is a multi-year cycle.
At the heart of this storm is OCX, a new ground control system for GPS that is meant to be cyber-hardened.
“The dynamic nature of the cyber threat, the catastrophic implications to attacks on our GPS-related infrastructure, and the relatively slow acquisition cycle demands the Air Force follow through with added funding to OCX,” wrote Robert Newton, a retired Air Force acquisition officer, in Defense News.
“Consideration of scrapping such an important program may sound politically correct, but would be disastrous and place us years behind an already escalating threat,” Newton said.
In the longer term, Newton wrote, both the Pentagon and Congress must develop new methods and closer cooperation to quickly anticipate and counter threats before they fully materialize.
GPS OCX will be a key test of the government’s and the military’s joint sability to function.
LightSquared testing: The sequel
The U.S. Department of Transportation (DoT) announced in March that testing for the Adjacent Band Compatibility (ABC) Assessment will start in April. Conducted at the U.S. Army Research Laboratory, White Sands Missile Range, the tests seek to determine power limits for spectrum bands near the GPS L1 signal.
Later tests will focus on potential interference with the L5 signal and frequencies of other satellite navigation constellations.
In 2012, after tests at that time demonstrated that the proposed LightSquared network of ground-based transmitters would interfere with GPS, the Federal Communications Commission (FCC) denied LightSquared’s petition while authorizing further tests — never conducted until now.
Testing will take place across a 200-megahertz band spanning 1575.42 MHz, GPS L1. An interference tolerance mask is defined as the point at which the interference test signal power level causes a one-decibel degradation in the signal-to-noise ratio.
GPS and GNSS receivers designed for aviation (noncertified), cellular, general location/navigation, precision, timing, network-, and space-based application will be run through the high-powered gauntlet.
“The Department requests voluntary participation in this study by any interested GPS/GNSS device manufacturers or other parties whose products incorporate GPS/GNSS devices.” the DOT said.
Ligado, the renamed LightSquared company from 2012, came to separate legal settlements with GPS companies Garmin, Trimble and John Deere in 2015; the terms have not been disclosed.
“Use of a defined change in the noise floor (1 dB),” wrote a Deere attorney to the FCC, “provides a readily identifiable and predictable metric that all interested parties can take into account now and in the future.”
Lift-off of IRNSS-1F.(Photo: ISRO)
IRNSS nears completion
The sixth satellite in the Indian Regional Navigation Satellite System (IRNSS) launched on March 10, and all subsequent orbital steps proceeded according to plan. IRNSS-1F was injected to an elliptical orbit very close to its intended final orbit.
The Indian Space Research Organization’s (ISRO’s) Master Control Facility (MCF) at Hassan, Karnataka, took over the control of the satellite. Maneuvers will position the satellite in geostationary orbit at 32.5 degrees East longitude.
IRNSS-1F is the sixth of the seven satellites constituting the space segment of the Indian regional system. All five previosly launched satellites are functioning satisfactorily from their designated orbital positions.
A complete constellation of seven is planned for the second half of this year.
The first IRNSS position fix announced by ISRO, providing longitude, latitude and altitude, took place in April 2015. Since then, position fixes using stand-alone IRNSS receivers have obtained accuracies of better than 15 meters for a minimum of 18 hours in a day over India.
The regional SBAS broadcasts navigation signals in the L5 and S-band frequencies, and computes user position solutions for a restricted service and a standard positioning service.
GLONASS special K
A new-generation Russian GLONASS-K satellite began regular broadcasts on Feb. 15.
The K model line transmits five navigation signals in the GLONASS L1, L2, and L3 bands and carries a COSPAS-SARSAT payload for international search and rescue.
K satellites will gradually replace the GLONASS-M generation, bringing with them new CDMA civil signals compatible with GPS and Galileo.
Eleven new K satellites will take to space starting in 2018, using European and Chinese components as well as those being developed under an accelerated Russian import substitution program.
UPDATE (9/10/15): A public workshop will be held in Washington, D.C., on Oct. 2 to provide an opportunity to discuss the draft test plan and address questions before the close of the public comment period. The workshop will be held in the RTCA NBAA/Colson Room, 1150 18th St. NW, Suite 910, Washington, D.C., 20036. Click here to register for the workshop.
The U.S. Department of Transportation today published a Federal Register Notice seeking public comment on a draft test plan for the GPS Adjacent Band Compatibility Assessment effort. The plan aims to obtain interference tolerance masks for GNSS receivers in the L1 radiofrequency band (1559-1610 MHz).
The objective of the test is to collect data to determine Interference Tolerance Masks (ITM) for categories of 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 to receive differential corrections.
Demand for commercial spectrum to support broadband wireless communications — in particular, LightSquared — has led the government to consider repurposing various radio frequencies, including the satellite communications bands next to GPS. The ITMs will be used to assess the adjacent band interference power levels that can be tolerated by GNSS receivers processing desired signals in the RNSS band.
The document outlines the requirements, the overall test plan, and the associated output data needed to successfully perform this component of the GPS Adjacent Band Compatibility assessment.
The plan can be downloaded here. Deadline for comments is Oct. 9.
In December 2012, the DOT developed its GPS Adjacent Band Compatibility Assessment Plan that identifies the processes to:
Derive adjacent-band transmitter power limit criteria for assumed new applications necessary to ensure continued operation of GPS services, and
determine similar levels for future GPS receivers utilizing modernized GPS and interoperable GNSS signals.
The DOT has previously held three public workshops to discuss the Adjacent Band Compatibility Assessment.
In a late June filing with the Federal Communications Commission (FCC), Lightsquared asked the agency to reassign its spectrum licenses — which were at the root of a prolonged dispute in 2010 and 2011, and have never been fully utilized — to a new licensee that would be wholly owned by a new company, New LightSquared. This is part of LightSquared’s efforts to re-emerge from bankruptcy.
LightSquared wants to resume its own interference testing scheme, floated in 2011 after an independent, collaborative effort found ample LightSquared interference with GPS. The company has contracted with Roberson and Associates, a technology consulting firm, to develop its interference study.
LightSquared is being represented before the FCC by Reed Hundt, a former FCC chairman who served from 1993 to 1997.
LightSquared listed 28 different GPS receivers and related devices that it wants to test for interference with its terrestrial mobile broadband service. The devices include certified and non-certified aviation receivers and avionics equipment, general location, cell phones and 13 different high-precision clocks and receivers.
Hundt specificaly identifed three companies — Trimble, Garmin, and John Deere — that he wants to come forward and provide proprietary technical and business information “in confidence” to tester Roberson. In statements to the FCC, Hundt twice used the phrase “speak now or forever hold your peace.”
In March of this year, LightSquared obtained U.S. court permission to exit bankruptcy protection, which it entered in 2012. At that time, the FCC had concluded, after lengthy testing, hearings, charges and countercharges, that the wireless broadband service proposed by LightSquared would interfere with GPS signals and associated positioning, navigation, and timing.
New LightSquared reportedly has $1.25 billion in operating funds to help “make full use of its spectrum to provide existing and innovative services.”
In a recent trial involving the assets of the bankrupt company, the value of its spectrum bands was estimated at possibly $4.5 billion or higher.
GPS Industry Response. The GPS Innovation Alliance responded in early July to media reports on LightSquared’s position regarding the testing of the compatibility of terrestrial broadband and GPS.
Following is the GPS Innovation Alliance’s response:
“The GPS Innovation Alliance (GPSIA) supports a consensus-driven process, including all government and non-government stakeholders, to clearly identify and address remaining technical issues raised by LightSquared proposals to repurpose mobile satellite spectrum for terrestrial broadband use.
“The technical challenges posed by these proposals are formidable, as evidenced by the conclusions of multiple U.S. government entities. Specifically, the U.S. Departments of Defense and Transportation and the NTIA have all found in the last several years that LightSquared’s proposals have significant potential to interfere with GPS.
“Contrary to LightSquared’s recent suggestions, this is not simply a private matter between three GPS companies and LightSquared, but is important to all GPS users who rely on this critical technology every day. The Department of Transportation has sponsored an ongoing effort to assess adjacent band issues, and the GPS industry is actively engaged with the Federal Communications Commission (FCC), Department of Transportation (DOT) and other government stakeholders to drive consensus around next steps.
“While we welcome the participation of LightSquared consultants, any further analysis of the technical issues should be informed by input from all of the relevant stakeholders, rather than the one-off efforts of an interested party.”
Tenth GPS Block II Follow-On Satellite Rises Above
This one’s in orbit now. Photo shows the nose cone containing GPS IIF-10 being lowered into position atop the launch vehicle, inside the rocket gantry at Cape Canaveral.
The tenth GPS IIF satellite lifted off from the Space Launch Complex (SLC)-41 at Cape Canaveral, Fla., on schedule at 11:36 local time (15:36 UTC) — at the start of a nineteen-minute window.
Later that same day, United Launch Alliance (ULA) officials declared the launch mission a success. The Centaur upper stage completed its second burn and released the GPS IIF-10 satellite into the navigation network to complete the launch of the Atlas 5 rocket.
This is the second of three GPS constellation replenishment flights planned in 2015. The first launch, of GPS IIF-9 using a Delta IV rocket, occurred on March 25. A third launch, of GPS IIF-11 using an Atlas rocket, is scheduled for Sept. 22. The launch of GPS IIF-12 is scheduled for Jan. 26, 2016.
The Boeing-built GPS IIF-10 is one of the next-generation GPS satellites, incorporating various improvements to provide greater accuracy, increased signals, and enhanced performance for users. GPS IIF-10 was the 70th spacecraft to be launched as part of the GPS constellation and the tenth in the Block IIF series that began launching in May 2010.
GPS IIF-10 marks the 55th Atlas V launch since the vehicle’s inaugural launch in 2002 and the 27th flight of the 401 configuration. Every operational GPS mission has launched on a United Launch Alliance or heritage rocket. While the government has certified ULA competitor SpaceX for GPS III launches, a SpaceX Falcon 9 rocket exploded June 29, two minutes after launch of an International Space Station resupply mission.
The Boeing-built GPS IIF satellites provide improved signals to support both the warfighter and the growing civilian needs of the global economy, the U.S. Air Force said in a statement. The GPS IIF satellites will provide improved accuracy through advanced atomic clocks, a longer design life than previous GPS satellites, and a new operational third civil signal (L5) that benefits commercial aviation and safety-of-life applications. It will also continue to deploy the modernized capabilities that began with the GPS IIR satellites, including a more robust military signal.
In a late June filing with the Federal Communications Commission (FCC), Lightsquared asked the agency to reassign its spectrum licenses — which were at the root of a prolonged dispute in 2010 and 2011, and have never been fully utilized — to a new licensee that would be wholly owned by a new company, New LightSquared. This is part of LightSquared’s efforts to re-emerge from bankruptcy.
LightSquared wants to resume its own interference testing scheme, floated in 2011 after an independent, collaborative effort found ample LightSquared interference with GPS. The company has contracted with Roberson and Associates, a technology consulting firm, to develop its interference study.
LightSquared is being represented before the FCC by Reed Hundt, a former FCC chairman who served from 1993 to 1997.
LightSquared listed 28 different GPS receivers and related devices that it wants to test for interference with its terrestrial mobile broadband service. The devices include certified and non-certified aviation receivers and avionics equipment, general location, cell phones and 13 different high-precision clocks and receivers.
Hundt specificaly identifed three companies — Trimble, Garmin, and John Deere — that he wants to come forward and provide proprietary technical and business information “in confidence” to tester Roberson. In statements to the FCC, Hundt twice used the phrase “speak now or forever hold your peace.”
In March of this year, LightSquared obtained U.S. court permission to exit bankruptcy protection, which it entered in 2012. At that time, the FCC had concluded, after lengthy testing, hearings, charges and countercharges, that the wireless broadband service proposed by LightSquared would interfere with GPS signals and associated positioning, navigation, and timing.
New LightSquared reportedly has $1.25 billion in operating funds to help “make full use of its spectrum to provide existing and innovative services.”
In a recent trial involving the assets of the bankrupt company, the value of its spectrum bands was estimated at possibly $4.5 billion or higher.
GPS Industry Response. The GPS Innovation Alliance responded in early July to media reports on LightSquared’s position regarding the testing of the compatibility of terrestrial broadband and GPS.
Following is the GPS Innovation Alliance’s response:
“The GPS Innovation Alliance (GPSIA) supports a consensus-driven process, including all government and non-government stakeholders, to clearly identify and address remaining technical issues raised by LightSquared proposals to repurpose mobile satellite spectrum for terrestrial broadband use.
“The technical challenges posed by these proposals are formidable, as evidenced by the conclusions of multiple U.S. government entities. Specifically, the U.S. Departments of Defense and Transportation and the NTIA have all found in the last several years that LightSquared’s proposals have significant potential to interfere with GPS.
“Contrary to LightSquared’s recent suggestions, this is not simply a private matter between three GPS companies and LightSquared, but is important to all GPS users who rely on this critical technology every day. The Department of Transportation has sponsored an ongoing effort to assess adjacent band issues, and the GPS industry is actively engaged with the Federal Communications Commission (FCC), Department of Transportation (DOT) and other government stakeholders to drive consensus around next steps.
“While we welcome the participation of LightSquared consultants, any further analysis of the technical issues should be informed by input from all of the relevant stakeholders, rather than the one-off efforts of an interested party.”
Figure 1. LightSquared propagation models can underestimate interference by more than a factor of 100 (>20 dB). Two-ray models accounting for ground reflections show LightSquared signals at levels 6 dB above free space predictions several miles out. (Figure from August 2011 GPS World.)
The GPS Innovation Alliance has responded to recent media reports on LightSquared’s position regarding the testing of the compatibility of terrestrial broadband and GPS.
LightSquared is asking the GPS industry to participate in new tests on interference between LightSquared’s spectrum and GPS receivers or waive its right to complain, according to a lawyer representing LightSquared.
Following is the GPS Innovation Alliance’s response:
“The GPS Innovation Alliance (GPSIA) supports a consensus-driven process, including all government and non-government stakeholders, to clearly identify and address remaining technical issues raised by LightSquared proposals to repurpose mobile satellite spectrum for terrestrial broadband use.
“The technical challenges posed by these proposals are formidable, as evidenced by the conclusions of multiple U.S. government entities. Specifically, the U.S. Departments of Defense and Transportation and the NTIA have all found in the last several years that LightSquared’s proposals have significant potential to interfere with GPS.
“Contrary to LightSquared’s recent suggestions, this is not simply a private matter between three GPS companies and LightSquared, but is important to all GPS users who rely on this critical technology every day. The Department of Transportation has sponsored an ongoing effort to assess adjacent band issues, and the GPS industry is actively engaged with the FCC, DOT and other government stakeholders to drive consensus around next steps.
“While we welcome the participation of LightSquared consultants, any further analysis of the technical issues should be informed by input from all of the relevant stakeholders, rather than the one-off efforts of an interested party.”
In a filing last week with the FCC, LightSquared listed 28 different GPS receivers and related devices that it wants to test for interference with its terrestrial mobile broadband service. The devices include certified and non-certified aviation receivers and avionics equipment, general location, cell phones and 13 different high-precision clocks and receivers.
