Activities over the past year

Apologies for little posting lately. Much activity included some with deadlines; this will be limited to the past twelve months. In 2017 my involvement in the annual GNSS+ Conference again included teaching the satnav/inertial integration tutorial sessions with OhioU Prof. Frank vanGraas. Part I and Part II are likewise being offered for Sept 2018. Also for that conference last September I wrote two manuscripts (with videos made to facilitate familiarization with the material), one for estimation and another providing opportunities for advanced warning.

For 2018 this will allow space for just one or two items from each event mentioned. The year began with attendance at Cognizant Autonomous Systems for Safety Critical Applications (CASSCA). For that highlight I’ll note an insightful presentation by a speaker from Wright-Patterson Air Force Base (WPAFB): pilot override prevented F-15 crashes through automatic pullup; “artificial” intelligence (AI) isn’t completely artificial. For my own work, April meant presenting “New Interface Requirements: Implications for Future” at Integrated Communications Navigation and Surveillance (ICNS). Highlight of that conference was a rare acknowledgement, at high levels within Mitre and FAA, that past methods are woefully inadequate for future air traffic needs.
The presentation just noted foreshadows a sequel scheduled for this year’s GNSS+ conference. The interface topic, also reviewed in a May SAE International meeting, was presented during that same month to the National Space-based Advisory Board. For the satnav/inertial integration topic, I recently completed my 25-page spread that will appear in a new edition of the satnav handbook co-edited by father-of-GPS Brad Parkinson; revised 25 years after its first appearance, it is expected to become available in 2019.

The Institute of Navigation’s GNSS+ 2018 Conference provides me the privilege of collaborating with two of the industry’s pillars of expertise. Ohio University Professor Frank van Graas and I are offering fundamental and advanced tutorials.  Then on the last day of the conference I’m coauthored with William Woodward, Chairman of SAE Int’l Aerospace Avionics Systems Division and hardware lead for next generation Resilient EGI (abstract on IoN’s website). The paper, our strong response to obstacles confronting position, navigation, and timing (PNT) from a large and growing array of challenges, describes
* a frank assessment of our industry’s glacial response to those challenges
* a fundamental step in the direction toward mitigating those obstacles
* how that step will enable several innovations discussed on the same website where a recent post cites a 3.5-day course expanding on the tutorials just announced. Both that course and the latter of those tutorials include, with registration, the book documenting the innovations and results with in-flight data.

At April’s ICNS meeting (Integrated Communications Navigation and Surveillance) as coauthor with Bill Woodward (Chairman, SAE International Aerospace Avionics Systems Division), I’ll present “NEW INTERFACE REQUIREMENTS: IMPLICATIONS for FUTURE“.  By “future” we indicate the initiation of a task to conclude with a SAE standard that will necessitate appearance of separate satellite measurements to be included among GPS receiver outputs.   Content of the presentation includes flight-validated dramatic improvements in multiple facets applicable to air traffic control (e.g., reduction in area of uncertainty at closest approach point by factors on the order of a million ;  major enhancement of achievable integrity, availability, etc.) — accessible from public domain with no requirements for scientific breakthroughs or new inventions. All benefits are derived from exploiting capabilities that have been available for decades, by discarding outdated practices devised largely to accommodate limitations in yesteryear’s provisions.

Although my writings for years expressed advocacy for these dormant advantages, concrete action was limited to embedded (often proprietary, inflexible) systems plus a modest number of scattered ventures, rather than widespread acceptance offering high accuracy at low cost. Dominance of simplified methods with huge performance penalty continues to this day, despite urgent need to cope with challenges to satellite navigation. For release from this “grip-of-inertia” a standard will mandate presence of individual satellite measurements at receiver output interfaces. The most obvious effect, ability to make use (finally !) of partial data, is only the beginning of a benefit list; advances in main pillars of performance criteria (accuracy, availability, integrity, and continuity) can be intense enough to reconsider some definitions.

Enhancements will materialize not only in aircraft — in air or on ground — but in maritime operation and land vehicles as well, whether manned or unmanned. Future extensions could involve other sensors. The purpose is empowerment of users through removal of constraints currently inhibiting robustness/resilience.  Immediately it is acknowledged — none of this will matter without victory in another area: security.  The battle of the spectrum and subsequent authentication must be won first.  As I noted in an earlier forum, everything I’ve advocated all this time is not a replacement for  but a recommended addition to  that important work.  As satnav cannot exist without authentic data, it cannot be resilient without raw data.

1-page summary

For reasons, consider a line from a song in Gilbert-&-Sullivan’s Gondoliers:
When everybody is somebody, then nobody is anybody” —
(too many cooks)

For consequences, consider this question:
Should an intolerable reality remain indefinitely intolerable?

While much of the advocacy expressed in my publications and website have focused on tracking and navigation, this tract concentrates instead on two major opportunities to apply a breakthrough solution that is virtually unknown.

60 Minutes alerted the public to an intolerable reality. Rather than repeating description of that problem I’ll jump immediately to the basis for my recommendation:
* Structures change shape before they fail.
* Changes in shape offer advanced warning.
* Reinforcement can be prescribed only for those exhibiting the warnings.
* Shape can be deduced from sets of measurements that are already in place.
* Those results can be acquired from computers processing all day every day.
* Neither computation nor data transmission to a central hub would be costly.
* Classical shape state analysis, limited to 2-D, has been extended to 3-D.
* That 3-D extension has already been validated by using GPS measurements.
* Hardly anyone knows that the 3-D extension happened.
* In fact, most techies are unfamiliar with shape states, even in 2-D.

Only the 7th and 8th items need any elaboration. The latter can be verified, in varying degrees of detail, through sources cited now. First, Figure 2 of a 3-page summary provides a quick glance. Those wanting more in-depth description can access a full manuscript with real data for verification . I also prepared a video with a preview that can be seen free of charge (just click inside the white circle). Finally, there’s also a blog

The one remaining item needing explanation will be covered here where the last video is entitled 3D Deformation Extraction for Morphometrics. Those who follow that video will see that the most widely known authoritative source is limited to two dimensions. Obviously the 3-D extension is essential for applications being described here (and in fact, even for accurate imaging — genesis from that field is incidental; subordinate to the present purpose). Further discussion of promise for anticipating structural failure appears in another blog.

Support for this work has been limited to (a)medical imaging verification and (b)a trip to present the quake data results. My voice can be heard in forums on navigation and tracking but, evidently, not by those responsible for safety in presence of structural dangers. I’m not claiming completion of everything required for operational readiness but, with no action at all, an intolerable reality will remain indefinitely intolerable. Seventy thousand bridges won’t be repaired any time soon but, with advanced knowledge where needed, the cost of essential action can be minimized. Continuous shape state computations fed by already in-place monitoring data could likewise give life-saving warnings.

Commercial value of this capability could be enormous, but a far better plan would be a low-cost pilot program with a lion’s share of eventual gain steered directly toward a worthy charity (one with a favorable rating from CharityWatch). I have no idea how to make that happen. Someone in a position of authority, with no ambition to become the next billionaire, could conceivably define a workable strategy.

Let me begin with a quote worth repeating — “Do we really need to wait for a catastrophe before taking action against GNSS vulnerabilities ?” — and follow with an extension of scope beyond.

It’s encouraging to see LinkedIn discussions recognizing ADSB limitations that preclude dependable collision avoidance capability – but that recognition needs to be far more widespread. The limitations are both severe and multifaceted including, in addition to vulnerability from inadequate security,
* accuracy goals based on present position instead of the monumentally more important relative velocity — ADSB allows 10 meter/sec velocity error (!), without characterization as vectorial or relative or probabilistic.
* the glaring but near-universal flaw of sharing coordinates, thereby failing to exploit what made differential operation spectacularly successful: work with individual measurements separately.
Note that these deficiencies existed long before the emergence of unmanned vehicles. The need to correct them is as fundamental as it is urgent. I’ve communicated these concerns over and over, most recently receiving a gratifying response from my June 11 presentation to the satnav National Advisory Board, with details available from URLs at the end.
In that presentation I cited a successful flight validation achieving accuracy on the order of cm/sec, for the crucially important relative velocity between vehicles that can be on or near a collision course. That is a thousand times less error than the 10 meter/sec allowed by ADSB. Furthermore, reduction by a thousand in each of three directions translates into a billion times less volume of uncertainty — or, in just two dimensions at fixed altitude, a million times less area. To realize this crucial safety improvement no new discoveries are needed and no new equipment needs to be invented; only the content of transmitted data needs to change: measurements rather than coordinates. Yet usage of the method is not being planned. After initially proposed before 2000, a limited support program started within the past few years is the only step taken toward this direction.

No claim is made that the last word has been spoken or that introduction of the needed modifications — nor accompanying regulation — would be trivial.  The intent here is not criticism and complaints for the sake of criticism and complaints.  Emphasizing unwelcome reality always caries risk of drawing wrath.  Nevertheless, especially now with growing usage of unmanned vehicles, sounding an alarm is better than passively waiting for a calamity. So here’s an alarm: Inadequate preparation for collision avoidance is a microcosm of a much wider overall flaw in today’s decision-making process. For years substantial numbers of qualified people have spent extensive effort trying to prevent cataclysmic failures in one area or another involving PNT (position/navigation/timing).  They definitely deserve attention and action.

Anything approaching a thorough compilation of worthy advocacy would require considerable length; just a few recent examples are cited here.  Explanations tracing inaction to current shortcomings can logically include a diagnosis of dissatisfaction expressed at a pinnacle of authority within DoD. An even more current offering is only the latest expression of regret over insufficient support for satnav, describing a highly relevant chain of inaction over a multiyear period. Near the beginning of that period, a cover story for Coordinates magazine repeated a quote from the previous month’s cover story   The quote worth repeating, cited at the start of this, is a perfect expression of the frustration prevalent over a decade following the universally acclaimed 2001 Volpe report. Now, almost a decade-and-a-half after that report, partial progress toward a solution coexists with minimal progress toward collision avoidance — while unmanned vehicles are already threatening passenger flight safety. Now to extend the quote: “Do we really need to wait for a catastrophe before making better use of measurements — GNSS or otherwise — to prevent collisions in the presence of increased manned and unmanned traffic?”


After wide distribution of my recent InsideGNSS letter I’ve received very
encouraging responses from a number of heavy hitters. There have always been
knowledgeable individuals agreeing with the points raised therein, but current
conditions offer an increased sense of urgency. With uncertainty of support
for vital resources, a real-world precedent (five years without LORAN), and a
Defense Secretary who hates GPS, my impulse toward advocacy has grown more
determined; in fact, crystallized. Not everyone will welcome this, but it
will go down much easier if viewed as a vital opportunity, Here goes.

Among the methods awaiting basic modification for navigation and tracking, one
is especially glaring: the ubiquitous practice of sharing coordinates. Those
familiar with my work know me as a relentless advocate (in print, since 1977)
of sharing raw measurements instead of coordinates. The seemingly unremarkable
character of that step is deceptive; despite its operational simplicity, the
resulting improvements would be profound. For quick verification of that claim
recall how major errors cancel (from each satellite separately of course) in
differential GPS — and that’s only the beginning.

As important as accuracy is, additional performance traits of equal importance
are also dramatically affected. Without separate measurements, integrity
testing can’t be done. Furthermore, with partial data usage, two more main
performance criteria (availability & continuity) would be vastly improved —
in fact, calling for their redefinition to account for the immense benefit.

The list of reasons (rigorous accounting for correlations as well as different
statistics of errors in different directions, at different times, from sensors
with different tolerances; immunity of scalar measurements to an occasionally
misconstrued reference datum etc.) continues on and on. Among those not yet
mentioned here, I now choose an especially important feature for illustration:
ability to achieve precise dynamics. Flight tests by Ohio University produced
cm/sec velocity residuals for navigation (GNSS Aided Navigation & Tracking,
with results in Chapter 8 and public domain algorithms in earlier chapters),
then later for trackinga THOUSAND times better than ADSB’s 10 meter/sec.

It’s not as if we didn’t know how to accomplish these objectives. We’ve known
how to combine myriad data sources, sequentially and optimally, for well over
a half-century. Yet even now, given information from two different subsystems
(e.g., GNSS and DME), how are they processed now? Either internally (and
invisibly in costly inflexible embedded systems) or externally by averaging
coordinates. A most elementary example highlights futility of the latter:
imagine data from one sensor offering precise latitude and extremely degraded
longitude — mixed with another offering the opposite.

The fundamental nature of these reasons is matched by an equally fundamental
course of action needed to achieve the requisite goals: simply replace data
bits in standard messages. No scientific breakthroughs nor hardware redesigns
— just change what’s transmitted by UAT or Mode-S extended squitter messages.
Most of the content (preamble, error correction, etc.) can remain unchanged;
just replace information bits (latitude, longitude, etc.) by measurements.

The case is quite compelling for application of known methods, to not only
satnav but all sources of data to be used in navigation and tracking. All
benefits will become reality if we adopt, VERY belatedly, the basic step
recommended in the title of a 1999 publication

Vulnerability of everyday life in America, through vulnerability of GPS, is not widely recognized. That gap in awareness would be filled instantly if GPS ceased to operate. Functions we take for granted, not only for transportation but also communication, affect multiple processes in ways vitally dependent on satellite navigation. Its steady improvement over recent decades has spawned increasing usage of its capabilities — and growing reliance on continuation of its spectacular success.
Far-reaching ramifications of that theme were analyzed in depth at a June 11 gathering of the National Space-Based Positioning, Navigation, and Timing Advisory Board. After kickoff by the Space Agency Headquarters Executive Director, followed by an opening presentation from the father-of-GPS, several speakers addressed a broad range of topics. Many of those involved the crucial importance of protecting and augmenting GPS, plus specific present and future steps planned to accomplish that.
Much of the discussion covered items under military or government control, i.e., the satellites or ground stations used to track and communicate with them. A minority aimed at protective measures devised for user equipment — receivers on ships, airborne, or on the ground. Toward the end of the day my own presentation expressed recommendations, some obvious and some more subtle, demonstrably capable of producing dramatic improvements in both accuracy and robustness. While those considerations revisited advocacy I’ve offered in the past, I was able to say-it-with-data. Immediately following my title slide, in-flight results showed precise velocity — in both navigation and tracking — by using the methods proposed.
An example will illustrate the effectiveness of those methods: the tracking demonstration obtained velocity accuracy a thousand times better than official ratings quoted for the latest-and-greatest Next Generation Air Transportation System — Automatic Dependent Surveillance Broadcast (ADSB). Although that test was just a first step (no all-encompassing claims are being attempted), the huge advantage in velocity — which directly affects collision avoidance capability — clearly warrants further investigation. There’s much more (my last page listed several URLs); sufficient for this summary is a reminder that monumental improvements are achievable, just through simple adjustments to receiver interfaces. A few suppliers already make measurement data available; another post will cover relevant opportunities within the industry.

Low pass filter

Decisions are made, understandably, on the basis of a decision-maker’s beliefs.  In general, the better the knowledge base, the better the anticipated outcome.  Inevitably there are times when choices must be made from incomplete information.  Even that can still produce success, but the likelihood of a favorable outcome depends on recognition of those uncertainties.  Likelihood of an unfavorable outcome, then, increases when those information gaps go unrecognized.  That is, when we are unaware of the fact that we don’t know (“don’t-know-squared”).  To make that case for this site I’ll use an example from an area outside of navigation and tracking:

One field that has received thorough investigation is the study of a low-pass filter.  Users of those commonly believe that they know all that is needed to make the wisest design selection.  Quite often they know much – but not everything that would be useful to them.  It is not unusual for a maximally-flat (Butterworth) attenuation characteristic to be chosen while assuming that nothing much can be done about the accompanying nonlinear phase; latency often precludes usage of phase equalizers.  It is known – but not widely known – that a trade-off has been available for decades.  A near-linear phase characteristic over the passband can be realized if some of the attenuation requirements can be relaxed.  Full details can be found in

Handbook of Filter Synthesis by Anatol I. Zverev
ISBN 10: 0471986801 / 0-471-98680-1     ISBN 13: 9780471986805                                                           and
Filtering in the Time and Frequency Domains
by Herman J. Blinchikoff and Anatol I. Zverev
ISBN-10: 1884932177     ISBN-13: 978-1884932175

Already I’ve said as much as I intend to say here about low-pass filters.  To go this far without misinterpreting some points I found it necessary to consult a coauthor (Blinchikoff) of the second reference just cited.  The rest of the blogs on this site involve navigation and tracking – where avoidance of don’t-know-squared is still very much an issue.  Examples from those areas won’t all be obvious (e.g., a pilot believing his broken altimeter), but there is much to be gained from “looking under the hood” and uncovering missed opportunities.  If we’re willing to pursue that, let me assure you that vast improvements in performance are available.