Orolia, a resilient positioning, navigation and timing (PNT) company, has entered into a definitive agreement to acquire Talen-X.
Talen-X is a U.S. technology innovator with the ability to characterize, enhance and implement advanced techniques and products to solve real-world GNSS vulnerability problems. It has expertise in GPS/GNSS performance, requirements, testing, integration and threat mitigation.
Orolia has completed 10 acquisitions since 2007, including Spectracom, Spectratime and McMurdo brands. The transaction is subject to customary closing conditions and approvals required by the U.S. Defense Security Service (DSS) and the Committee on Foreign Investment in the United States (CFIUS).
Through this acquisition, Orolia said it will significantly enhance Assured PNT capabilities across the global company’s portfolio to support mission-critical applications. The additional resources also strengthen Orolia’s commitment to serving the U.S. government, with further expansion of domestic capabilities and a greater U.S. footprint. Toward that end, the companies will reinforce their commercial cooperation to maximize market awareness and access.
“Military personnel know that accurate and trusted time and position information is a critical enabler for almost all warfighting functions and systems,” said Orolia CEO Jean-Yves Courtois. “Reliable PNT data are critical for communications, sensors, network synchronization, situational awareness, command and control or search and rescue missions. This acquisition reinforces Orolia’s position as a major supplier of Assured PNT technology and enhances our ability to offer unique end-to-end solutions.”
Talen-X has extensive technology integration and PNT engineering resources that will enable Orolia to rapidly develop and offer new, superior products and services to the U.S. market.
“Our culture of innovation, together with our demonstrated testing capabilities, will complement Orolia’s global technology expertise and significantly enhance the reliability, performance and safety of military operations,” said Tim Erbes, CTO of Talen-X.
The cellular 5G standard targets latencies under 1 millisecond, data rates of up to 10 gigabits per second, extremely high network reliability and better accuracy in positioning. With location awareness becoming an essential feature in many new markets, positioning is considered as an integral part of the system design of upcoming 5G mobile networks.
The cellular industry is currently implementing Long-Term Evolution (LTE)-Advanced, which might be called “4G” mobile broadband. Simultaneously, the industry is preparing the next step, a fifth-generation (5G) system. It will process communication 10 times faster than 4G, according to experts. 5G rollout will be complete in many international metropolitan areas by 2020.
Positioning Performance for 5G NR and other technologies in different environments. (Image: Fraunhofer IIS)
Adaptive array antennas
In addition to the precise positioning it will afford, 5G shares another characteristic with GPS/GNSS: adaptive array antennas for digital beamforming (DBF). Adaptive arrays have many advantages for PNT, primarily in mitigation for multipath, jamming and spoofing.
Emerging applications of DBF in 5G involve dense networks of picocells, small cellular base stations that typically cover a small indoor area. Picocells extend coverage where outdoor signals do not reach well, and add network capacity in areas with very dense phone usage. 5G architectures will use adaptive array technology to achieve high data rates, spectrum reuse and communications robustness.
The implications for PNT are that 5G will require improved (relative) PNT to operate effectively, and picocells will be a source of PNT information in constrained environments.
5G involves massive directional communications via multiple-input, multiple-output (MIMO), enabling high-bandwidth communications in fading (multipath) channels by using multiple antenna inputs to adapt to channels. It can do this without knowledge of user location, but it adds to the processing complexity. The directional capability can enable multiple users to be serviced in a picocell at different frequencies, while permitting spectrum re-use by nearby picocells through narrow beamwidth and the limited range of millimeter-wave (mmWave) frequencies.
The PNT implications of 5G architectures, according to Gary McGraw of Rockwell Collins, are that 5G picocells will be synergistic with PNT in challenged environments — naturally, indoor and dense urban. They will necessitate development of distributed, networked PNT processing and infrastructure.
Fraunhofer
The 5G positioning framework will integrate a multitude of sensors into a hybrid positioning scheme, according to the Fraunhofer Institute for Integrated Circuits (IIS) in Germany. Fraunhofer IIS is currently prototyping low-latency and high-precision positioning systems for legacy LTE and future 5G New Radio (5G NR).
5G NR enables positioning by providing high bandwidths for precise timing, new frequency bands at mmWave, massive MIMO for accurate angle-of-arrival estimation and new architectural options that support positioning. Improved accuracy, robustness and latency can be achieved, according to the institute.
5G provides fast and reliable access to moving objects to achieve time-critical process control and optimization in industrial environments. Increased contextual awareness of goods, parts, machines and workers will enable new interaction and collaboration, the institute said.
The military is always looking at new techniques and technology for deriving position and, it seems, every few years signals of opportunity (SOOP) becomes fashionable again.
In broad terms, SOOP refers to the use of any signals for navigation, which are not normally intended for navigation. This might mean TV or radio broadcast signals, cellular network signals, or anything else you can receive.
Figure 1. Navigating using opportunistic signals, such as phone, TV and radio transmissions. (Image: Michael Jones)
The promise of SOOP
In the quest for resilient positioning and navigation, SOOP certainly sounds attractive. When GPS goes down, why not simply continue to navigate by receiving digital TV signals instead? Why not receive a whole pile of different signals, and make yourself virtually immune to jamming?
You can even turn jamming from a problem to a solution. If someone does decide to turn on a bunch of jammers, why not use the jammers themselves as signals of opportunity, and position yourself using those? With so many possibilities, it’s no wonder SOOP excites people. Certainly it’s of great interest to the military of many countries.
Let’s dip our toes into the world of opportunistic navigation.
What signals might we use?
The figure below shows what we get if you use a spectrum analyzer to quickly sample what’s on the airwaves in the UK, in this case looking fairly coarsely from 10 MHz to 3 GHz. A number of candidate signals immediately present themselves, which are labeled 1 to 11 and identified in the table.
Figure 2. Plenty of opportunistic signals are out there. (Image: Michael Jones)
There are, of course, many more signals-of-opportunity out there, but this illustrates a few of the more visible ones. How do we go about using these signals for positioning ourselves?
Bringing in defense techniques
For decades, one of the principle requirements in electronic warfare (EW) has been to geolocate enemy transmissions. This has given rise to a plethora of techniques for determining location, such as received signal strength (RSS), angle-of-arrival (AOA), time-of-arrival (TOA), time difference of arrival (TDOA), frequency difference of arrival (FDOA), and so on.
In a positioning application, we have the reciprocal problem: instead of trying to geolocate a transmitter relative to ourselves, we are trying to geolocate ourselves relative to a set of transmitters. But of course we use the same techniques: GPS is an excellent example of a TOA system.
Let’s look at the basics of TDOA. A signal s arriving at location 1 can be expressed as
where A1 is an amplitude scaling to account for attenuation over the path, n1 is additional noise, and d1 is the signal delay time. We can repeat the equation for further locations:
Usually we designate one location as the reference, in which case we can rewrite the above equations as:
The first problem is to determine D, the time difference of arrival. There are many ways to do this, but a popular method is to perform generalized cross-correlation:
Or, in a realizable digital form:
Finding the peak of this function gives us our estimate of the time difference D. It’s a little bit more involved in practice, as we would normally apply filtering functions to improve the TDOA resolution, but you get the idea. Each TDOA measurement gives a set of possible locations that form a hyperboloid. With three stations, we will have two hyperboloids, the intersection of which gives a set of possible locations along a hyperbola. The addition of a fourth signal allows us to plot three hyperboloids, from which we can then determine position.
Figure 3. Positioning using TDOA involves solving for the intersection of hyperboloids. (Image: Michael Jones)
There are various ways to solve for the hyperbolic intersections. With only four measurements it is possible to compute the solution analytically, but with many measurements an iterative approach or minimum mean squared error technique is often used.
TDOA, when used properly, can form the basis of a highly accurate positioning system. A number of navigation systems utilize TDOA technology, such as LORAN and its variants.
Now let’s consider angle-of-arrival. AOA techniques generally make use of an antenna array to provide spatial diversity, allowing the direction of a source transmission to be determined. Measured angles to multiple transmitters then allows triangulation to be performed and the position computed. There are some advantages to AOA techniques, when compared to TDOA: position can be computed with as few as three signals, there is no requirement for time synchronization in any form, and narrowband signals can be used without loss of accuracy. Disadvantages include larger physical size due to the use of an array of antennas, and potentially more susceptible to environmental effects such as multipath.
Classical AOA methods include Capon’s method, but since the 1980s the preferred techniques have often been signal subspace methods such as Multiple Signal Classification (MUSIC), Estimation of Signal Parameters by Rotational Invariance Techniques (ESPRIT), and variants of these techniques. The most well known of the subspace methods, MUSIC, performs an eigendecomposition of the sample covariance matrix given by:
Once the signal and noise eigenvectors have been separated the array manifold is projected into the appropriate subspace to yield the MUSIC surface:
The peaks of the function P, give us the direction-of-arrival of any signals. From these multiple lines of bearing we can perform triangulation, and derive our position.
We’ve looked at TDOA and AOA methods, which are just two of many techniques that can be used to process signals-of-opportunity to derive position. But there are some perceived drawbacks to navigation by SOOP. By definition, SOOP makes use of transmitters that are uncooperative, and not generally designed with navigation in mind.
For TDOA you are dependent on signals that are transmitted synchronously (or else you need a separate source of reference), which may or may not be the case. You also need to know the locations of the various transmitters, for example the coordinates of any GSM base stations, digital TV transmitters, and so on. It may be difficult to obtain this information, especially in some parts of the world. But whilst it certainly helps to have this information, it isn’t entirely necessary. It is possible to both position yourself, and build up a map of the transmitter locations, without a-priori information.
SLAM
Simultaneous localization and mapping (SLAM) is a field popular in the autonomous vehicle and robotics communities. It’s often described as a machine-learning concept, which aims to solve the problem of positioning oneself within a map, whilst simultaneously constructing and updating that map. There are a pile of techniques and algorithms that have been applied to the problem, including the good old Kalman filter, and the particle filter.
In basic SLAM, you use a state vector to store an estimate of your position (and often orientation as well), just as you would in a typical GPS receiver. However, in SLAM, we also store estimates of the transmitter positions (called “features” in SLAM terminology). If we want to localize ourselves in a global coordinate frame it does mean we need an initial estimate of our position from some other means, like GPS. Otherwise we can only localize ourselves within the map we are generating.
From our initial position estimate, we then move in some way. We then estimate our position again, perhaps using some form of dead reckoning technique, like inertial or visual odometry. Together with our motion model, this forms the prediction phase of the Kalman filter. We perform the measurement phase by re-measuring any features (our transmitters of opportunity), along with any new ones.
Figure 4. Basic SLAM concept: simultaneously estimate the locations of both the vehicle and the transmitters of opportunity. (Image: Michael Jones)
If you know about Kalman filters, you might spot one of the problems with SLAM: As the number of features increases, the size of the state vector becomes larger, until you end up with huge matrices that are very time-consuming to solve. The solution time is a quadratic function of the number of state variables. For this reason, it is often necessary to constrain the problem in some way: perhaps by limiting the number of transmitters we keep track of.
But when done properly, SLAM is a powerful technique for signals-of-opportunity navigation.
Is SOOP worth it?
We’ve seen that, by using a variety of techniques, almost any radio signal can be used for opportunistic navigation purposes.
One disadvantage of SOOP is that it can require complex hardware to do it well. If you truly want to use all the opportunistic signals out there, then you need a receiver that can handle a very wide range of frequencies. You also need an antenna or set of antennas that can do the same.
When resilient PNT is a critical military requirement, you cannot afford to rely on signals that you don’t control. SOOP is also highly dependent on where you are. There aren’t many opportunistic signals at sea or in the desert, compared to in the urban environment (perhaps the odd satellite signal, or HF signal).
So SOOP is unlikely to become a primary technology for the military. But it does have the potential to be a powerful augmentation to GNSS, and it certainly deserves a place in the PNT kit bag.
Now the company has released from new tests using configurations with a differential source and with a more accurate OCXO clock, producing timing accuracy of 160 nanoseconds.
Gregory Gutt, president and chief technical officer of Satelles, made the presentation at the recent Institute of Navigation International Technical Meeting.
The 66-satellite Iridium LEO constellation transmits overlapping spot beams, which provide location-specific data that changes every few seconds. The featured image on this article (above) shows spot beam pattern for 2 of 66 satellites.
Overview of Satelles test configurations. (Chart: Satelles)
The testing employed three different configurations of equipment, services, and environment, as shown in the adjacent figure. Equipment employed in the tests included a Stanford Research Systems (SRS) rubidium vapor frequency reference, based on the PRS10 module, and a Satelles Evaluation Kit (EVK2) STL receiver, comprising a Maxim RF chip, Xylinx Spartan-3 FPGA , TI dual core DSP chip, and internal OCXO or external clock.
Parameters and equipment for the three test configurations:
Configuration #1 – Optimal. Outdoor antenna, Rubidium clock powered on for months prior to data collection, receiver configured in static mode with a known location, and high-quality antenna
Configuration #2 – Sub-optimal. Indoor antenna, Rubidium clock powered on 6 hours prior to data collection, receiver configured in static mode with an unknown location, and low quality antenna
Results from the first two tests are shown here:
Test results, configurations 1 and 2. (Chart: Satelles)
Configuration #3. Three independent receivers collecting data, receiver on-board OCXO, indoor antenna, receiver configured in static mode with an unknown location, low-quality antenna. Tests performed:
10 days with no local reference station running
10 days with local reference station, 20km away from test receivers, providing timing corrections to STL ground segment.
Results from these tests shown here:
Results from OCXO tests. (Table: Satelles)
With this individual test result:
OCXO timing result with base station. (Chart: Satelles)
Some of the commercially available products and evaluation kits that incorporate the STL service are shown here:
STL user equipment implementations. (Image: Satelles)
The U.S. Air Force is intermittently jamming its own GPS signals over southern Nevada and Utah this week and next as part of a massive air-to-air combat training exercise, Red Flag 18-1, based out of Nellis Air Force Base in Nevada. The jamming aims to challenge aircrews and their weaponry under realistic fighting conditions. The Air Force has warned that navigation systems including those found in commercial flights may be disrupted or jammed completely across the southwest U.S. during that time, ending February 16. So far no major commercial airline disruptions, flight delays or re-routings have been reported.
The U.S. military, heavily and perhaps overly reliant on GPS, is developing a range of position, navigation, and timing (PNT) technologies being to help overcome the loss of GPS during combat, an increasingly likely scenario now and in years to come. Some have speculated that this year’s exercise specifically has in mind a possible conflict on the Korean Penisula. GPS jamming has regularly emanated from North Korea over the past several years.
“We’re trying a few new and different things with Red Flag 18-1,” said Col Michael Mathes, 414th Combat Training Squadron commander. “This primarily is a strike package focused training venue that we integrate at a command and control level in support of joint task force operations. It’s a lot of words to say that we integrate every capability we can into strike operations that are flown out of Nellis Air Force Base.”
The exercise, which the Air Force conducts annually, typically involves a variety of attack, fighter and bomber aircraft with added participation from the U.S. Navy, U.S. Army, Marine Corps, Royal Australian Air Force and Royal Air Force. This year’s Red Flag is the largest in the exercise’s 42 year history.
Nellis Air Force Base in southern Nevada. (Image: USAF)
Affected Areas. “Arrivals and departures from airports within the Las Vegas area may be issued non-Rnav re-routes with the possibility of increased traffic disruption near LAS requiring airborne re-routes to the south and east of the affected area,” stated an Air Force bulletin. “Aircraft operating in Los Angeles (ZLA) center airspace may experience navigational disruption, including suspension of Descend-via and Climb-via procedures. Non-Rnav SIDs and STARs may be issued within ZLA airspace in the event of increased navigational disruption. Crews should expect the possibility of airborne mile-in-trail and departure mile-in-trail traffic management initiatives.”
Alternate Capabilities. Many Air Force planes have onboard inertial navigation systems, using accelerometers, gyroscopes, and magnetic sensors to continuously calculate position without GPS signal data, as well as at a higher hertz rate. When available, GPS signals can be used to correct inertial calculations, which tend to drift over time. Fighter planes can also use AESA-scanned array radars teamed with an inertial system for navigation over short ranges. Aircraft electro-optical and infrared sensors can also read terrain over short distances to provide additional navigation.
If strike aircraft have reliable communications or datalinks, other aircraft such as E-8 JSTARS, flying outside the GPS-disrupted zone, may be able to relay position and targeting information. Some missiles carried by strike aircraft have laser-guiding instead of or in addition to GPS-guiding.
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.
The upcoming annual conference sponsored by the IGNSS Society will take a close look at autonomy and provide GNSS constellation updates.
IGNSS is the southeast Asian region’s premier conference on GNSS and related position, navigation and timing (PNT) technologies.
This year’s conference theme is “Trusted Positioning: From Here to Autonomy.” The event, sponsored by Lockheed Martin, takes place Feb. 7-9 on the campus of the University of New South Wales in Sydney, Australia.
At the conference, leaders in GNSS and PNT will gather to examine the latest technology, present cutting-edge research and discuss in open forums the implications for policy, market development and positioning infrastructure deployment.
IGNSS 2018 will showcase a number of contemporary topics, including
the role of PNT in automated land, aerial and marine vehicles;
the growing range of commercial precise positioning services;
hard infrastructure issues such as space based augmentation systems; and
soft infrastructure issues such as datum modernization and mitigation of system vulnerabilities.
These topics will be discussed in the context of the latest system developments fueling the multi-GNSS era.
Running over two days immediately prior to IGNSS2018 is a meeting of the RTCM SC-104; all attendees are invited to attend.
Also running one day before IGNSS2018 is the Japan-Australia Quasi-Zenith Satellite System Industry Utilisation Workshop. IGNSS delegates are also welcome to attend this free workshop.
The IGNSS conference takes place on the UNSW campus in Sydney. (Photo: University of New South Wales)
IGNSS2018 Highlight Sessions
Global GNSS service provider updates
SBAS Testbed overview and project updates
Panel: positioning autonomous systems
Keynote Speakers
Air Vice-Marshall Kym Osley, Department of Defence
Kent Rosser, Discipline Leader Aerial Autonomous Systems, DST Group
Dorota Grejner-Brzezinska, The Ohio State University
Joe Burns, Sensurion
Rod Bryant, u-blox
Kendall Ferguson, RTCM Board of Directors & SC-104 Chair
Representative from the Expert Reference Group conducting the Review of Australia’s Space Industry Capability
Representative from the iMove CRC
The IGNSS Association runs the SE Asian region’s premier conference on Global Navigation Satellite Systems and related Position, Navigation & Timing technologies. This year’s IGNSS is hosted in conjuction with the Australian Centre for Space Engineering Research at UNSW Sydney.
The U.S. Army is soliciting proposals for research, development, design and testing that directly supports battlefield technologies in the area of positioning, navigation and timing (PNT).
Broad Agency Announcement (BAA W56KGU-18-R-PN22) was issued by the U.S. Army’s Communications-Electronics Research, Development and Engineering Center (CERDEC) on Nov. 24 through FedBizOpps.gov.
CERDEC — based at the Aberdeen Proving Ground in Maryland — aims to discover technical approaches to improve and enhance current and future land warrior capabilities, flexibility and responsiveness in line with its strategic vision for enhancing warfighter capabilities to operate in both symmetric and unsymmetrical environments.
GPS-denied environments. “The goal is to support CERDECs Strategic Thrust for PNT by providing technical and operational capabilities that enables the soldier to continue their operations in hostile RF and GPS-denied environments,” reads the BAA. “Proposed technical approaches may apply to operations both before and after the cessation of hostilities.
“This announcement emphasizes approaches that address the very different challenges presented by urban fighting and dramatically enhance warfighter capabilities, for example, the ability to interact, maneuver and operate under a time constrained environment. These changes should generally result in lower casualties, lower collateral damage, and the effective use of combat power.
“The specific topics of interest revolve around the research and development of technologies may provide revolutionary improvements to the entire spectrum of PNT.”
Soldiers with 18th Military Police Brigade, assault opposing enemy threats during an Urban Operations training at the 7th Army Training Command’s Grafenwoehr Training Area, Germany, Oct. 20, 2017. (U.S. Army photo by Spc. Javon Spence)
CERDEC’s plan is to support multiple and potentially multiphase efforts that pursue the design, development, integration and demonstration of critical and enabling technology and system attributes pertaining to PNT. Proposed efforts will primarily be of service and material with aims at resolving technical barriers.
Proposals. Proposals submitted should range in scope from study and analysis type work with limited data and deliverables, to larger efforts for component developments, techniques and demonstrations with breadboard or prototype-style deliverables.
The contracts are expected to be cost-plus-fixed-fee, but can be negotiated.
Presentations from the 20th meeting of the National Space-Based Positioning, Navigation, and Timing Advisory Board (PNTAB), held Nov. 15-16, are now available online at GPS.gov.
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.
PNTAB provides independent advice to the U.S. government on GPS-related policy, planning, program management, and funding profiles in relation to the current state of national and international satellite navigation services.
Q: What is the GNSS/PNT industry “Issue of the Year”?
Jose Angel Avila Rodriguez, signal and security implementation engineer, European Space Agency
A: The growth of PNT applications has been impressive and will continue. Assurance of PNT will thus gain an ever-increasing role, in both the security and the civil domains.
For GNSS, the key PNT contributor, there is in addition another challenge: its piece in the PNT cake will be contested by newcomers, such as telecom networks. Whether we will continue talking about A-GNSS or instead talk about Assisted 5G, with GNSS in that case taking on the role of signal of opportunity — that will depend on today’s decisions about future GNSS upgrades, the modernized versions of Galileo second generation, GPS III, and Beidou/Compass III, that will be flying around 2040.
Gyles Panther, president and CTO, Tallysman Wireless, Inc.
A: The key issues for PNT going forward, and into the indefinite future, are simply stated: availability and accuracy. Re-deployment of the eLoran infrastructure is a no-brainer. A potentially highly negative step would be the introduction of communication services within the mobile satellite L-band downlink frequency band (1525 MHz to 1559 MHz). Multi-constellational receivers track a much larger number of satellites and better disposed SVs (space vehicles) provide a lower horizontal DOP and hence greater accuracy.
Finally, GNSS needs to be defended against interference both intentional and accidental. Why on earth would we want to damage something that is providing so much utility to mankind?
Orolia, through its Spectracom brand, has launched VersaPNT. VersaPNT provides virtually failsafe battlefield navigation, even in GPS-denied environments, to protect critical networks with Assured PNT technology, the company said.
The new, ground, air or sea vehicle-mounted solution is designed for military environments, with a ruggedized, compact, low-power and lightweight form factor.
Today, military vehicles are portable networks, providing seamless connections with U.S. headquarters, regional command posts and individual soldiers. Remote areas are challenging environments for military networks, and enemy forces are jamming, spoofing and disrupting operations.
“VersaPNT provides continuous mission assurance and C4ISR support, even in hostile environments,” said Rohit Braggs, Orolia vice president, PNT networks and sources. “This innovative technology solution protects critical networks for complex military and homeland security land, air and sea operations.”
Every minute counts on the battlefield, and VersaPNT provides critical decision support with real-time situational awareness to facilitate a rapid response, according to the company. This lifesaving technology can also help keep soldiers and civilians out of harm’s way, while ensuring continuous tracking of friendly and enemy forces.
VersaPNT provides essential command and control, navigation, communication and electronic intelligence support for U.S. and allied military, homeland security, first responder, civilian agency, special operations and intelligence missions.
Demonstrations are available at the AUSA Annual Meeting, Orolia Booth #2944.
DOT serves as the civil lead for the GPS and chairs the CGSIC in this capacity. NAVCEN is assigned duties as deputy chair and executive secretariat for the CGSIC.
Subcommittees of the CGSIC for Timing, State and Local Government, International Information, and Survey, Mapping and Geosciences will hold meetings Sept. 25, and a summary of these meetings will be presented to the CGSIC plenary session Sept. 26.
The keynote speaker for this year’s plenary session will be Keith Conner, Ph.D., Senior Engineer, Science and Technology First Responders Group, U.S. Department of Homeland Security.
Presentations include:
Operational status and modernization of the GPS constellation of satellites
U.S. Space-Based Position, Navigation and Timing policy
GPS augmentation systems
Briefings from the National Aeronautics and Space Administration (NASA) and the National Parks Service
Information related to U.S. engagement with other international Global Navigation Satellite Systems as well as a variety of applications of the use of GPS
The full agenda is available. CGSIC presentations will be posted online shortly after the meeting ends.
Orolia has completed 10 acquisitions since 2007, including Spectracom, Spectratime and McMurdo brands. The transaction is subject to customary closing conditions and approvals required by the U.S. Defense Security Service (DSS) and the Committee on Foreign Investment in the United States (CFIUS).
