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  • Letters to the Editor: Another View of GPS Origins

    [Ed. Note: Mr. Beard’s letter has been significantly shortened — while trying to preserve its principal points and intent — to fit the space available in this print magazine. Here is a PDF of the full text of the letter and all accompanying footnotes. Scroll down for Brad Parkinson’s reply.]

     

    The articles in the May and June issues of GPS World on the origins of GPS by Drs. Bradford Parkinson and Stephen Powers presented a detailed view of the people involved in the development of the GPS Program. This view on the origin of GPS essentially begins with the so-called “Lonely Halls” meeting where Dr. Parkinson and a group of Air Force officers invented the GPS concept that was subsequently developed by the teams of people discussed in some detail.

    Missing from this view of the origin of the GPS concept are the developments and events leading up to the final decision on what was to have been the Defense Navigation Satellite System. The development, we are now expected to believe, originated from an Aerospace Corporation Study of 1964. The major events in the pre-history of the GPS program are not as well known as the events after the formation of the GPS program since, like the Aerospace study, they were classified and not generally available. Many of the documents of that pre-history have become declassified so that a more historical perspective can be made based on the actual documentation of events rather than subjective recollections of events.

    Having worked during that era, I began as a naval officer assigned as the TIMATION project officer, Navigation Satellite Branch, Astronautics Division, Naval Air Systems Command, from 1968 to 1971. After separation from active duty I began working at the Naval Research Laboratory (NRL) in June 1971 in the TIMATION program, through the origination of the GPS Program, the Navigation Technology segment of the GPS program and became the head of the NRL Space Applications Branch in 1984 onwards. I believe I have a unique perspective on the origins of GPS, having participated from the Navy side. In the following I have attempted to describe the evolution of the TIMATION project and events leading up to establishing the GPS Program from the official Navy record.

    It should be evident in this discussion that at the formation of the GPS Program, the TIMATION project ended, and the efforts following at NRL on NTS and space clock development were funded by the Navy as part of a Joint Program under the managerial direction of the GPS JPO. This relationship has been considerably de-emphasized and confused over the years, to the point where very few remember it.

    The TIMATION project originated in FY 1965 as the Rapid NAVSAT Readout project under tasking by the Bureau of Naval Weapons. This Exploratory Development project was to investigate the feasibility of advanced navigation satellite techniques, among which was the concept of using passive ranging. The project included a number of experimental investigations into the concept of utilizing passive ranging based on precise time synchronization between a satellite and user receiver to produce more accurate and rapid positioning. An experimental satellite was developed and launched into low earth orbit for experiments in determining accurate satellite ephemerides and demonstrating a simplified technique for position fixing based on celestial navigation concepts. These techniques were intended to demonstrate, but were not limited to, two-dimensional positioning. Position fixing utilizing the celestial navigation plotting technique also determined the time offset of the clock in the user receiver so that it could be corrected for positioning or applied to time transfer techniques. An atomic clock was not required. A number of navigation and time transfer experiments were performed with this first satellite and data was collected for analysis of the concept. Another satellite was designed to incorporate the lessons learned from the first satellite and to perform other analytical studies. It was ultimately launched in 1969.

    However, in 1968 the Joint Chiefs of Staff (JCS) formed a Navigation Requirements Panel to conduct a study, the results of which were approved on 24 September of that year. The new joint service navigation requirements established by this study included the ability of a user to precisely position themselves in three dimensions and precisely determine their velocity, continuously and worldwide. During the year following establishing of these new JCS requirements, the TIMATION project was expanded to address these new joint service navigation requirements.

    Consequently, from 1968 through 1970 the TIMATION concept grew from a category 6.2 exploratory development project into navigation satellite techniques to a 6.3 advanced development system concept employing a constellation of medium altitude satellites containing space qualified atomic clocks to a worldwide distribution of various, surface and airborne, passive ranging user equipment. Technical design studies conducted were designed to analyze or experimentally demonstrate the technical aspects proposed to be selected for the DNSS. The specific technical areas that were investigated were: specific frequencies to be used, single or dual frequencies, and the propagation errors associated with their use; arrangement of the constellation of satellites, total number required for worldwide coverage and quality of coverage; ground stations necessary to operate the satellites and their location (foreign soil or U.S. territory); ranging signals to be used, the accuracy provided, resistance to countermeasures and vulnerability to such things as multipath reflections into a simple user antenna; and capability of being denied to the enemy.

    The Navy and the Air Force 621B concepts were the two principal competing DNSS concepts for providing accurate three-dimensional navigational capabilities.

    In 1970 the Astronautics Division of NAVAIR, sponsor of the TIMATION project, requested preparation of a system development plan to include a demonstration phase which could directly transition into an operational system. Such a plan was required for the Advanced Development phase (category 6.3 funding) of the project, which began with the establishment of the Advanced Development Objective (ADO) 34-11X, the requirements document for the project. The plan described the project requirements, approach, and objectives in some detail. In their guidance letter to NRL, NAVAIR provided guidance on the content of the development plan. The primary technical requirement for the effort was the “Precision navigation requirements in Phase I of the JCS Navigation Study approved 24 September 1968. — The most stringent requirement (being) user three dimensional position within the stated accuracies continuously on a global basis.”

    [Ed: A detailed sequence of events, meetings, and memos excised here are fully viewable in this PDF.]

     

    At NRL a GPS program office (Code 7907) was set up in March 1974 to coordinate GPS activities with the GPS JPO and manage NRL program activities. [ . . . .]

    The development of space qualified atomic clocks at NRL, which had recommended and initially focused on cesium standards, began with the experimental rubidium standards on NTS-1. It was originally intended for experimentation with improved quartz crystal standards. The opportunity to include experimental rubidium clocks on NTS-1 presented itself some eight months before the satellite was completed. A new small rubidium frequency standard, model FRK, from Efratom of Munich became available and even though they were not specifically designed for space
    their small compact size and design was attractive as a candidate space clock. Several of the FRK models were purchased from Munich, evaluated and modified for a space experiment in NTS-1. Two units were integrated into NTS- 1 and operated alternately with the primary quartz crystal standard. This same Efratom Model FRK was selected and proposed by Rockwell International for use in their Block I satellites. [. . . . ]

    The clock development conducted and proposed by NRL was the subject of special program interest during these formative years. In February 1974 DDR&E in a memorandum to ASN (R&D) pointed out that “One of the most vital efforts in the recently approved NAVSTAR Global Positioning System (GPS) is clock development. Funds have been programmed under PE 63401N, NAVSTAR GPS, for programmatic developments defined in the DCP. However, there is a small, but important, effort which should be undertaken … I refer to the development of Space Qualified hydrogen maser clock and its correlative counterpart for the ground control station.” These funds mentioned and subsequent development efforts were Navy funds as part of the GPS joint development effort. The importance and emphasis on space qualified atomic clocks was highlighted in the DDR&E expansion of the GPS Phase I program to support the Submarine Launched Ballistic Missile Improved Accuracy Program. In that memo DDR&E called upon the Navy “to expand their NAVSTAR clock development effort. To reduce risk and provide timely NTS-2 support for the expanded satellite program the Navy should provide a second, parallel, cesium clock development, to be done by an aerospace contractor, for use on NTS-2. If either or both of the cesium clocks perform satisfactorily, cesium clocks should be used in any satellites subsequent to the initial six. The Navy NAVSTAR program should also provide in FY 1976 and beyond for (1) a hydrogen maser development for the NAVSTAR ground stations, and (2) efforts leading to a space qualified maser suitable for NTS-3 and future satellites.”

    Considerable documentation and other material describing the extent and contributions to the GPS program resulting from the TIMATION development beginning in early 1974 could be further detailed. But in the interest of keeping this letter relatively brief those aspects will be covered elsewhere.

    It should be evident in this discussion that the TIMATION project ended at the formation of the GPS Program. The subsequent NRL efforts on NTS and space clock development were funded by the Navy as part of a Joint Program under the managerial direction of the GPS JPO, however, many of the fundamental concepts and approaches began during the TIMATION program.

    It is worthy to note as well, that over the years in addition to the recognition afforded Dr. Parkinson as the first program director of the GPS program, the contributions by Roger Easton and NRL have also been recognized. This recognition includes NRL being included as a major contributor to GPS in the Collier Award of 1992.

    — Ronald L. Beard
    Head, Space Applications Branch,
    Space Systems Development Department,
    U.S. Naval Research Laboratory,
    Washington, D.C

    Brad Parkinson replies:

    I have great respect for Ron Beard and the many other fine engineers and spacecraft developers at NRL.

    That said, I respectfully submit that the letter completely misses the point. There was a substantial amount of Pentagon infighting up to the time I took over the Program in late 1972. Ron has done a great job in documenting this cumbersome history. It accurately shows the paper trail from the NRL point of view. Dr. Currie reset the direction when he designated me to lead the Joint Program in 1973. The past assignments were essentially overtaken by that decision. There is another set of paper, that could be dredged out of the USAF files, but to little point.

    The central issue is not paperwork. It is who conceived the concept, demonstrated the technique on the ground, and built the prototype system.

    With a wave of the hands, NRL declares their system was also three-dimensional, yet the Easton patent clearly was not and the patent was clearly burdened with a militarily-
vulnerable signal structure. Apparently they disown their own preferred design. Yet, the patent is the clearest public record of NRL thinking.

    The letter ignores:

    • 
The first clear explanation of the tradeoffs between the various space navigation alternatives was the 621B “Woodford and Nakamura” study of 1964/66. It included the three-dimensional technique we selected in the final GPS design.
    • The essential keys were: A. Single frequency transmission (CDMA) and B. Simultaneous ranging to four satellites. Both keys were conceived by 621B and demonstrated by the White Sands testing of real hardware (1970/1973). This became the basis for the GPS design in 1973. It is also the basis selected for all of the “copycat” systems by other countries (Russia has now announced a CDMA signal). NRL cannot point to any advocacy of such a system.
    • 
NRL was indeed (as Ron points out) charged with clock development (but their spacecraft CDMA transmitter was provided by the JPO, not by NRL). Note that the early 621B study advocated atomic clocks in space for the system. NRL was not able to provide a useful space-borne clock until the fifth GPS prototype satellite. This was after the Rockwell/Efratom clock had become the only operational satellite clock used in the first four prototype satellites and after the GPS system testing had gained approval to proceed to full-scale development in 1980. Problems with the NRL test satellite precluded its inclusion in the test constellation.

    It is correct that NRL advocated a MEO system, similar to the one we adopted for GPS. The Air Force’s 621B had wanted to demonstrate the four-dimensional technique using spacecraft, and launching the system a world-sector at a time. There are pros and cons both ways, but the controversy was both political and technical. The key to our selecting the GPS MEO constellation design was that it enabled the 4-6 satellite sub-constellation that was star (not solar) synchronized and that technique can be attributed to Major Gaylord Green of the Air Force. This allowed the extended testing on our well-instrumented range at Yuma Proving Ground.

    In 1973/74, my problem was to find a way to advocate the right system without re-igniting the NRL/621B warfare. At that time, I chose to ignore most of the true 621B heritage of the JPO proposal and, in public, talk up the NRL contribution. A number of my colleagues in Aerospace and the old 621B were very perplexed with my behavior. I felt it was the right path to allow us to proceed with actually building the system.

    I genuinely supported the NRL clock technology efforts, and was very disappointed when they were not able to meet our schedule. The space-qualified cesium clock, developed under NRL/Bob Kern, was a phenomenal accomplishment in spite of being late.

    — Bradford W. Parkinson,
    Edward C. Wells Professor of Aeronautics and Astronautics (Emeritus)
    and Hansen Experimental Physics Laboratory
    Stanford University, Stanford, California

  • Tablets Galore, But Apple May Still Ship 40 Million iPads Next Year

    Industry analysts estimate that Apple will sell as many as 43.7 million iPads in 2011. Apple reported it shipped 4.2 million iPads in the third quarter, ending September 25. This has certainly created chaos in the tablet computer business that has been relatively quiet for more than a decade. Predictably, with Apple shipping these kinds of numbers, it has stimulated other manufacturers and spawned a tremendous number of “iPad Killers” that have been introduced or are being introduced soon.

    From a geospatial point-of-view, the tablet war is not over. In fact, it’s barely begun. I’ve touched on this subject before, but it’s worth another look. The tablet hardware is only one facet of geospatial users adopting tablet computers in a big way. The other, of course, is application software. Having a tablet computer without application software is sort of like having a desktop computer without office software (e-mail, word processor, spreadshet, database, presentation) to use with it. Without application software, a tablet computer (or any computer for that matter) is just an expensive paperweight.

    With reportedly up to 13 million iPads projected to be shipped by the end of 2010, it seems like we should be seeing them cropping up everywhere in geospatial applications. Unless I’m missing something, that doesn’t seem to be the case. Of course, I know many people who own an iPad and swear they are the greatest things since doorknobs, but very few, if any that I know, are using them for serious geospatial applications. It begs the question “Why?”

    The answer is simple: lack of geospatial application software.

    Why is there a lack of geospatial application software?

    Developing and maintaining software for public consumption is an expensive endeavor. No matter your attitude is about Microsoft, Microsoft Windows made it a lot easier and less expensive to develop application software. There are literally tens of thousands of software tools that developers can buy for Windows to make it easier to develop application software. Furthermore, the market for computers running Windows is a lot bigger than for any other operating system (Linux, Unix, MacOS, etc.). Many software companies can’t financially justify developing and maintaining applications for more than one operating system. Of course, in that case developers will invariably choose the Windows platform because that’s the biggest market.

    The iPad (and iPhone and iPod) run an operating system called iOS. From a software developer standpoint, it’s not even close to Windows. Basically, it must be developed from scratch. Yuck.

    Let’s say you’re a company that’s developed software for mobile GIS. Most likely, you’ve developed it for Windows/Windows Mobile platform because that’s what the customers are using. Now, let’s say the iPad/iPhone/iPod devices become a hot commodity like they have. Certainly, as a software developer, you’re debating whether to start developing for the iOS operating system. That’s not an easy decision. In fact, for a smaller company, it can literally be a make-or-break gamble that could sink a small software company if the wrong decision is made.

    So, if you had a piece of software written for Windows, at what point would you consider spending tens of thousands of dollars (maybe more) to port the application to iOS? The cost is not only in developing the software application, but also in supporting and maintaining the software. Given the nature of the geospatial software industry (mostly comprised of small companies), it’s not hard to see why there is reluctance to take the plunge. Esri has made the argument for iOS a little more compelling with the introduction of its iOS API, which is a toolkit that makes it easier for software developers to write geospatial applications for the iOS platform.

    Imagine if the iPad was running Windows or Windows Mobile. There would be hundreds of geospatial apps running on it by now. But that’s dreaming, and of course, Windows would run like a turtle on the iPad hardware. The iPad wasn’t designed with a lot of CPU horsepower for general computing.

    What’s becoming more evident is that the success of the iPad has spawned a new generation of tablet computers in all different shapes and sizes. Some have been introduced, and some are yet to be introduced. Some are running Windows, but many are running other operating systems. Here are a few:

    1. Asus EP-90 (8.9″ display running Windows)

     

    2. Archos 9 (8.9″ display running Windows, also models running Android)

     

    3. Acer Tablet (10.1″ display running Windows, also a model running Android)

     

    4. Samsung Galaxy S (7″ display running Android)

     

    5. Blackberry Playbook (7″ display running Blackberry OS)

     

    6. Dell Streak (5″ and 7″ displays running Android)

    7. LG Tablet (10.1″ display running Windows or Android). Available only in Korea at this time.

    8. Viliv X70 (7″ display running Windows)

    9. Neofonie WePad (11″ display running Linux/Android)

    As you may have noticed, it’s not just a iOS vs. Windows debate. Google’s Android operating system is making a big splash, too. I read an article recently that surveyed application developers. Among other things, developers opined that whereas iOS had the most short-term upside, they saw the Android operating system having the most significant long-term upside. Secondly, when the developers were asked which is the most “open” platform, they voted for Android by far. However, this survey was slanted towards smartphone developers who are developing for the consumer market. Those apps have a much broader audience and market base than specialized geospatial apps.

    Since more and more iPad-like tablets running Windows are being introduced, I suspect that in the short term, most geospatial application developers will take the path of least resistance and support Windows-based platforms before making the jump to iOS or Android, if they do at all. Furthermore, with the Windows Phone 7 operating system introduced just last month, this strengthens the case for Windows on mobile devices for geospatial apps.

    Thanks, and see you next week.

    Follow me on Twitter at http://twitter.com/GPSGIS_Eric

  • GLONASS Launch Failed, Three Satellites Crash into Pacific Ocean

    Quoting industry sources, the Russian Federal Space Agency announced that the December 5 launch of three GLONASS-M satellites ended in failure when the Proton-M rocket’s Block DM upper stage and its three payloads crashed into the Pacific Ocean about 1,500 kilometers, or 932 miles, northwest of Honolulu. Although an investigation will look into the exact cause of the failure, early unconfirmed reports indicate a software error.

    Apparently, the Proton carrier’s third stage deviated from its planned trajectory.

    The three satellites were launched from the Baikonur cosmodrome in Kazakhstan. According to telemetry, the carrier rocket’s upper stage containing the satellites was launched into a “non-targeted orbit.” According to a BBC news report, the upper stage and GLONASS-M navigation satellite payload crashed into the Pacific Ocean near Hawaii. BBC news also reported that sources informed them that the launch rocket had deviated by eight degrees from its intended path after launch.

    The Russian Federal Space Agency reported that a “special board has been established to find out the cause of the contingency and to define the next steps.”

    According to the Russian News Agency RIA Novosti, incorrect calculations were loaded into the rocket’s onboard computer missiles. As a result, the rocket engine provided too much momentum, leading to the deviation of the vehicle from its planned trajectory.

    RIA Novosti also reported that because of the accident, the pace of satellite launches will have to be accelerated. For example, the launch scheduled for September 2011 is likely to take place earlier.

    The new generation GLONASS-K satellite is due to launch later this month from the northern Plesetsk cosmodrome.

    Video of the pre-launch rocket delivery can be viewed here:

     There are currently 20 operational GLONASS satellites, with another four undergoing maintenance and two reserved as spares.

     

  • Location Privacy Is Heating Up

    Last month, the Management Association for Private Photogrammetric Surveyors (MAPPS) issued a position letter to the Federal Communications Commission (FCC) urging the FCC to “use extreme caution and not implement any enforcement or broad regulation that would have a harmful affect on the broad private geospatial community.”

    The concern MAPPS has is valid and I support their position stated in their letter.

    MAPPS references an Associated Press article published November 10 that states that the FCC is investigating Google’s activities, including photographing neighborhoods for its Street View mapping feature.

    Google Street View

    The MAPPS announcement also references H.R. 5777, introduced in Congress earlier this year, according to MAPPS. If it is passed, MAPPS is concerned it would create “havoc in the geospatial marketplace and community.”

    The issue of location privacy is not a simple one. In fact, it’s a complex subject that has far-reaching implications. To compound the issue, it’s a highly technical subject that easily exceeds the capacity of the average state/federal legislator and administrator to understand. Therefore, they will rely on legislative assistants, industry folks, and lobbyists to guide them. That being the said, it’s important that the professional geospatial folks have a chair at the table.

    Notice I wrote “professional” geospatial folks. I did that intentionally. The reason is because surveying, GIS, engineering folks, and other people who create, manage and/or use geospatial data in the course of their daily professions will be affected by the fallout of legislative action taken in this area. In short, we will become collateral damage in a much larger battle.

    Whether you’re an engineer, surveyor, GIS professional, county planner, or CAD technician, the geolocation privacy battle being fought has nothing to do with what you do for a living. The privacy issue would be easy to address if it was only just one or two companies that need an attitude adjustment. However, that’s not the case. The big kahuna is LBS (location-based services).

    I’m super-excited about LBS applications. At least for me, I think it has a tremendous potential to make my life a lot more efficient and productive. Just think of what GPS and digital maps has done for you in the last five years. Getting lost is a thing of the past with your trusty Magellan/Garmin/TomTom on the dashboard. I don’t know how to calculate the number of hours it has saved me (and my wife) since I started using GPS navigation on a daily basis in 2004, but I know the number is big and I know hundreds of dollars I’ve spent on GPS navigation devices has paid for itself easily a hundred times over.

    Given that, I start salivating when I think of how a new breed of LBS apps will provide me new tools to help manage my life more efficiently. For me, the value is connecting my friends/family and my stuff. I’ve got a wife and four kids, with three of them playing school sports and one in college. Being able to text message them helps, but that requires an action on their part. If they’re in class, at practice, at home, out with friends, etc. and don’t see the text message (or there’s a delay in the wireless network), I don’t hear back. Being able to know where they are, without action on their part, is worth a lot to me. Ok, I realize you may think I’m a control-freak of sorts, but actually I’m far from it. I’m more of an efficiency-freak. I’m consistently over-committed and always looking for ways to save time, and I see LBS apps as huge time-savers.

    I wrote an article about the value of LBS to me (and privacy) earlier this year, and then a couple of months later I wrote an article after some idiot stole my car. If I’d had my car wire up with an LBS app, it would have saved me a lot of time and grief and would have provided a lot of satisfaction in seeing the thief in handcuffs. LBS goes way farther than connecting people and tracking my stuff. In fact, we don’t understand how far it’s going to go yet.

    One example is a technology called augmented reality. I’ve written about this in the past. From the safety aspect alone, it’s a tremendous technology. Look at this video from General Motors. Location is only part of the solution, but it’s a critical part and goes way beyond what the GM video discusses. Think about if a spatial database was accessible and you would be warned of accident-prone intersections or dangerous curves ahead of time via the Head-Up-Display (HUD). In a more efficiency-oriented application of augmented reality, check out this video from BMW.

     

     

    For those of you who enjoy shopping on Black Friday (the day after Thanksgiving), this year you could have used an app from Dealmap.com on your iPhone or Android phone to access a map of deals at more than 52,000 retail store locations.

    Dealmap.com Android app

    Ok, enough said about the up side of LBS apps.

    Of course, the core technology behind LBS apps is the L word: location. The apps generally make decisions based on where you are. If you’re driving down the street, a coupon may pop-up on the screen of your phone for a fast-food restaurant you are approaching, or a map might be displayed on your phone of all the bargain prices of LCD TV’s within three miles of your current location.

    This type of technology frightens people a lot. They assume that if their phone knows where they are, someone is watching. It really depends on what kind of app is running on your phone.

    Stealing from the article I wrote last February:

    Of course, a major concern by regulators and potential users is how personal location information will be used by the LBS application software. Will this be just another way that your personal information will be collected and sold to spammers? In addition to spammers, do you really want your family/friends knowing where you are 24/7? These are not unreasonable concerns.

    I don’t worry about privacy with LBS applications and I’ll tell you why.

    There is a lot of hyper-sensitivity about privacy with LBS applications (House congressional hearing
    this week on the subject) so I think LBS software vendors are well aware that a line has been drawn in the sand and a sort of zero-tolerance policy has been established. Secondly, leading LBS companies were involved with CTIA (The Wireless Association) in developing a document titled “Best Practices and Guidelines for Location-Based Services,” so they are intimately aware of the privacy issue.

    There are two guiding principles in the Best Practices guidelines mentioned above:

    1. LBS providers must inform users about how their location information will be used, disclosed, and protected so that a user can make an informed decision whether or not to use the LBS or authorize disclosure.
    2. Once a user has chosen to use an LBS, or authorized the disclosure of location information, he or she should have choices as to when or whether location information will be disclosed to third parties and should have the ability to revoke any such authorization. Read the entire CTIA Best Practices guideline here.

    The Final Analysis on LBS Apps

    One consideration I will give when subscribing to a LBS app in the future is to make sure I subscribe either through my wireless service provider (Sprint, AT&T, Verizon, etc.) or through an established, reputable LBS app provider. This kind of due diligence is no different from when you consider purchasing an application for your personal computer. Common sense tells you not to download an app from Nigeria. You’ll need to practice the same diligence when selecting an LBS application.

    I also wouldn’t consider an LBS application where I don’t have the opportunity to control my personal network of people who are granted access to my current whereabouts. In fact, I’d want the ability to shut off broadcasting my location altogether. Again, I think that any mainstream LBS application will have these features due to the high-profile sensitivity to privacy.

    I know the LBS applications are already available to accomplish the people-connecting that I want. But, like I wrote earlier, I don’t live on the bleeding edge of technology. I live a step back from the edge. I wasn’t the first to join Facebook (although I’m glad I eventually did) and I won’t be the first to run a people-connecting LBS application, but there’s no doubt in my find that it will eventually be an important tool for me and, most likely, you, too. The upside is just too big to ignore.

    What about the Geospatial Professional?

    I think it’s very important that the geospatial professional, whether a surveyor, an engineer, a GIS’r, or a CAD technician, not be loaded up with unreasonable liability by the FCC or other governing body as a result of the fall-out from LBS apps. It will be very easy for legislators (and voters), who are uneducated on this matter, for geospatial professionals to be tossed into the LBS barrel.

    This subject had me thinking about a measure that voters just passed in the State of Oregon. The title of the measure was “Requires Increased Minimum Sentences for Certain Repeat Sex Crimes, Incarceration for Repeated Driving Under Influence.” Of course, like privacy, this is a very emotional issue. Given the title of the measure, without further study, most people would vote in favor of such a measure. Who wouldn’t? With further study, you might find it wasn’t such a good measure to pass into law (it passed). This opinion piece ran in the Portland newspaper, The Oregonian, and spells out why it’s not such a good idea. Among other things, there’s collateral damage.

    Likewise, the public and the industry can’t afford for geospatial professionals to be swept into the privacy dustpan with LBS apps.
    Thanks, and see you next week.

    Follow me on Twitter at http://twitter.com/GPSGIS_Eric

  • Down and Deep

    More Satellites, More Sensors Take Urban Navigation Downtown and Deep Indoors

    By Frank van Diggelen

    As we all know, GPS is practically perfect in every way — as long as it’s outside and unobstructed. Even cell phones can now produce meter-level accuracy under open sky. There are still many deficiencies in state-of-the-art location, particularly in deep urban canyons and inside large buildings. Which technologies will lead personal navigation into the future?

    As we all know, GPS is practically perfect in every way . . . so long as it’s outside and unobstructed. Even cell phones can now produce meter-level accuracy under open sky. And, with Assisted GPS (A-GPS), those cell phones have mitigated the two great deficiencies of the original GPS: slow time to first fix (TTFF), and outdoor-only operation. A-GPS receivers can produce TTFF as fast as one second after a cold start, and (sometimes) work indoors.

    However, there are still many deficiencies in the state of the art of location, particularly in deep urban can yons and inside large buildings. In the latter you will soon notice that even if your A-GPS operates in your house, it does not operate everywhere. The term “indoor GPS” is rather like “off-road vehicle”: your four-wheel drive may let you cruise down the beach, but you certainly cannot use it to climb every mountain nor ford every stream. Similarly “indoor GPS” denotes the presence of a capability — not the absence of all limitations.

    And so what is the future of urban and indoor navigation, and which technologies will prevail? The short answer is: more satellites and more sensors. In this article we’ll look at the technologies that will move us from the era of GPS-only into the future of GPS-plus.

    Source: Frank van Diggelen
    This is Manhattan.
    Source: Frank van Diggelen
    This is Manhattan on Wi-Fi.

    Other GNSS

    The most likely addition to GPS will be the other global navigation satellite systems, and all GPS receivers will be replaced by true, multi-system, GNSS over the next two to three years. Not because this will ever fully solve indoor location, but because of the outdoor problem in deep urban canyons.

    When asked why he wanted to climb Everest, George Mallory famously said “because it is there.” Of the various GNSS systems, those with the most influence in the next few years will be GLONASS, because it is there, and QZSS because (as Mallory might have added) it is high. The first QZSS satellite recently began functional transmission. So let’s use QZSS as an example of why extra satellites are so important in the deep urban canyon.

    Figure 1 shows Shinjuku, Japan, a typical deep urban canyon and a terrible place for GPS. The blue dots show the positions of a GPS receiver. The white and orange lines show the actual line-of-sight vectors to the GPS satellites. The white lines are to GPS satellites in direct view. The orange lines are to satellites behind buildings. However, the high-sensitivity A-GPS receiver tracks all these satellites, by acquiring and tracking reflected signals. Thus the whole concept of GPS — of measuring distance by time-of-flight — breaks down. The reflected measurements are inaccurate because of the extra path length. And even if the receiver could somehow tell orange lines from white, the horizontal dilution of precision (HDOP) of the white-only lines is 58 in this real-life example. Now add two high-elevation satellites, shown by green lines, and things are much better. The green lines show the location of two QZSS satellites, and the HDOP of the five green + white satellites is 3.

    Figure 1 shows the problem of the deep urban canyon, and the value of extra satellites. The problem is that there are not enough satellites in direct view. This puts receiver designers in an insoluble dilemma: Track only strong satellites, and you will not have enough; or track weak satellites, and you will measure reflections with large measurement errors because of the extra path length of the reflection. Moreover, the reflected signals can be indistinguishable from direct signals in their characteristics, especially in mobile phones where the antennas are poor, and directional — so that signal strength is not a reliable indicator of whether a signal is direct or not.

    This example should put to rest the false notion that extra high satellites will not improve HDOP. In this case the HDOP improves by about 20 times, from 58 to 3. It is easy to find many similar examples using GPS + GLONASS or any other GNSS combination. More often than not, extra satellites improve the situation significantly.

    The QZSS system uses inclined geostationary orbits to provide high elevation coverage above Japan (and, as a by-product, neighboring regions.) In this respect it is unique amongst the major GNSS: it is exclusively designed to provide good urban coverage of its home region. Compass has a similar component, but ultimately it, like GPS, GLONASS, and Galileo, has global ambitions.

    Some other satellite systems, such as satellite radio, use inclined geostationary orbits like QZSS. With QZSS providing an alternative example of a new GNSS, European taxpayers might well ask why Galileo should provide medium-Earth orbit satellites that spend more time over America and Asia than over Europe. As a U.S. taxpayer, I’m all in favor of the current Galileo plan — after all, the United States has been sending GPS satellites over Europe for the last 30 years, so a little reciprocation seems only fair.

    Figures 2 and 3 show how the three satellites of QZSS provide better high-elevation coverage over Tokyo (and neighboring regions), than all of the 30 GPS satellites combined.

    QZSS-capable chips are already found in mobile phones and tablets available in the Asian market. As this article was being written, a Broadcom BCM4751 chip in Tokyo was computing the first-ever GPS+QZSS position.

    Source: Frank van Diggelen
    Figure 2. Elevation above horizon of the QZSS satellites, as seen from Tokyo. Note that the inclined-geostationary orbits of the QZSS system have been designed so that there is always one satellite above 70°.
    Source: Frank van Diggelen
    Figure 3. Elevation of GPS satellites as seen from Tokyo. About half the time none of the 30 GPS satellites is above 70° elevation, a quarter of the time one GPS satellite is above 70°, a quarter of the time two GPS satellites are, and for half an hour three GPS satellite are. The three satellites of the QZSS constellation provide better high-elevation coverage in Tokyo than the 30 GPS satellites.

    Wi-Fi

    After GNSS, the second-leading location technology is wireless local area networks, commonly known as Wi-Fi. Wi-Fi location works by using a database of media access control (MAC) addresses and locations. When a mobile device senses a Wi-Fi access point, the MAC address and database give the location of the access point (AP). A simple average of many APs gives position accurate to tens of meters.

    Wi-Fi location is already tightly integrated with GPS in many smartphones. Wi-Fi location accuracy is good enough that it is often mistaken for GPS, especially in cities where the density of APs is large. In Manhattan, for example, there are more than 25,000 APs per square kilometer (see opening figure.)

    Several major companies, including Apple, Broadcom, and Google, have worldwide databases of Wi-Fi AP

    locations that are used in mobile devices, especially smartphones and tablets.

    MEMS, Accelerometers, and Gyros

    The micro-electromechanical systems (MEMS) technique etches the silicon on a chip to exploit its mechanical and electrical properties. A MEMS chip, such as a chip-level accelerometer or rate gyro, thus has tiny moving parts that can sense acceleration or rate of turn, respectively. Both sensors are already common in smartphones, where they are used to set the correct screen orientation (portrait or landscape), and for gaming. Because they are already there, they are a natural addition to location technologies, and many companies are moving rapidly to integrate motion sensors with GPS for improved accuracy indoors and in urban canyons.

    As an example of the benefits of MEMS motion sensors, Figure 4 shows a test case where GPS was deliberately degraded by denying it the high direct-view satellites discussed earlier, and then adding nothing but low-cost MEMS sensors.

    Source: Frank van Diggelen
    Figure 4. GPS-only positions and GPS + MEMS. The red circles show where poor GPS-only performance was dramatically improved by the addition of low-cost MEMS accelerometers and rate-gyros such as those already found in certain smartphones and PNDs.

    Magnetic Compasses

    Like accelerometers and gyros, magnetic compasses are already found in many smartphones. The technology is rapidly evolving, and different techniques are used by different suppliers to determine magnetic north, including Hall effect sensors, fluxgate compasses, and MEMS. Performance is dramatically affected by nearby metal and severely affected by magnets. You may not think that you are surrounded by magnets, but you are — especially in your car where every speaker of your sound system is a magnet — and the better the speaker, the larger the magnet. Thus magnetic sensors alone are not a reliable location technology, but integrated with other sensors, such gyros or accelerometers, they can be and are very useful, especially for pedestrian applications.

    Altimeters

    Altimeters are another MEMS technology. Typically a hermetically sealed cavity on the chip is used to measure change in atmospheric pressure — the surface of the cavity is deformed as the outside pressure changes, and the deformation can be measured using piezoelectric strain gauges. The integration of altimeters with GPS is already well established for such applications as hiking receivers. Similar integration is likely in other consumer devices, especially smartphones.

    AFLT, MRL, and Cell-ID

    The three cellular-wireless technologies of AFLT, MRL, and Cell-ID are all components of A-GPS.

    AFLT (Advanced Forward Link Trilateration) is a technique used in CDMA phone systems, where the cell towers are precisely synced to GPS time. Because of this precise time synchronization, one can use the cellular signal to measure range from the cell tower, using time-delay just like GPS. CDMA phones with GPS are usually using AFLT when providing position indoors.

    MRL (Measured Results List), is the UMTS analogy of AFLT for non-synchronized systems. The MRL provides a list of neighboring cell towers and received power. Received power is used to estimate range, and from this, position. Accuracy is not nearly as good as AFLT, but can be decent, especially in cities where accuracy may be better than 100 meters, good enough for emergency location applications such as E-911.

    Cell-ID is simply the technique of looking up location in a cell ID database. This is analogous to Wi-Fi location, but not nearly as accurate since cell tower ranges are much greater than Wi-Fi. However, although perhaps the least exciting, this technique is the foundation of many important technologies. The AFLT and MRL techniques require Cell-ID as a necessary component. A-GPS usually uses Cell-ID for providing the assistance position, a necessary component of the high sensitivity that A-GPS provides. And Cell-ID alone is necessary for E-911 location, when A-GPS fails.

    Digital TV and Radio

    Location from digital TV works by measuring ranges from DTV towers, analogous to GPS and AFLT. However, DTV towers are not precisely synchronized to each other, and so DTV location requires the build out of fixed site infrastructure to deal with individual tower clock offsets.

    DTV location is in a way the opposite of Cell-ID. While Cell-ID is intellectually boring, the technique is practically very important and widely used. DTV, by contrast, is an exciting idea, because it can be accurate like GPS but with much more powerful signals. However, it has been a commercial failure.

    DTV location, or related technologies, may enjoy a resurgence in the future once mobile TV or digital radio (HD Radio and DAB — digital audio broadcasting) become more widely adopted.

    Pseudolites

    Well known to precison-location cognoscenti, pseudolites provide GPS-like signals from ground-based transmitters. They typically use a transmit frequency that is offset from GPS, but otherwise their signals are like GPS so that they can be used with a receiver with the same baseband as GPS.

    Pseudolites can be very accurate, as good as five centimeters when using carrier-phase measurements. They require local, fixed transmitters which are fairly sophisticated (since they must maintain time and phase coherency to work properly.) This makes them prohibitively expensive for widespread applications. However, pseudolites are highly valued and widely used in niche markets, and will probably remain so.

    IMES and Local Beacons

    IMES stands for indoor measurement system, and it, or something like it, could be the most interesting new location technology of all. IMES is a local-beacon system — it works by providing a very weak signal that is exactly like GPS, but is meant for data-transmission only, not ranging. Thus it is fundamentally different from pseudolites, which are designed for ranging. The power of each IMES transmitter is so low (0.1 to 0.4 nanowatts) that it can only be acquired within about 10 meters of the transmitter. The signal is modulated with a PRN code (PRN numbers 173 to 182) and data: the data contains the location of the transmitter. The system technology may be summarized as “if you can hear me, here you are.” And the accuracy is inherently about 10 meters.

    A fascinating detail of the IMES data message is that it contains (in message type 000): latitude, longitude and floor number.

    IMES is designed to work with any GPS receiver that can decode PRNs 173 through 182. And, because they are not intended for ranging, the transmitters do not have to be precisely synchronized with GPS or with each other. This makes them cheap to build and install. However, they do still need to be deployed in large numbers (at least one every 10 meters), and will require a government-sized effort to become reality. Interestingly, they might just get it: The IMES system is defined in an annex to the QZSS interface specification from JAXA, the Japan Aerospace Exploration Agency. But it is not clear how much funding is available for IMES, or if there is any mass deployment schedule.

    Even if IMES is never deployed, other, similar local-beacon systems may emerge. They will require a government-level (or similar) effort for the mass deployment required to make a system a reality for consumers.

    Thus IMES or similar local-beacon technology may amount to nothing, or it may be a complete game-changer, depending on how the game is played and how the cards fall.

    Summary

    We have seen that GPS is practically perfect, when outdoors. And because A-GPS has worked so well over the last decade, it has become the predominant location technology in consumer platforms such as smartphones and tablets. But, precisely because of this success, GPS is more challenged than ever as consumers expect it to work where it was never meant to: indoors, in deep urban canyons, and with very small, cheap, antennas.

    These challenges have led us to other technologies, in particular more satellites, sensors, and other wireless location techniques. The most prevalent and valuable additions to GPS in the next few years will be GLONASS and QZSS, as well as MEMS technologies, magnetic sensors, Wi-Fi, and cellular wireless technologies.

    Roughly speaking, the 1960s and ’70s were the decades of GPS conception, the 1980s the decade of development and delivery, and the 1990s the introduction to the world. Since 2000 we have had the decade of mass-market adoption, and the 2010s will be the decade of GPS-plus: other GNSS and other sensors.

    FRANK VAN DIGGELEN is senior technical director for GNSS, and chief navigation officer of Broadcom Corporation. He is the author of the bestselling textbook A-GPS: Assisted GPS, GNSS and SBAS, and holds more than 50 U.S. patents on A-GPS. He received his Ph.D. in electrical engineering from Cambridge University and is a consulting assistant professor at Stanford University.

     

  • Death of a Smartphone, Birth of an Ad Trend

    Kevin Dennehy
    Kevin Dennehy

    From a distance, the Garmin-Asus partnership to produce GPS-enabled smartphones looked pretty good — particularly during the market erosion for portable navigation devices. However, published reports indicate that the companies will not renew their partnership in January 2011.

    Switzerland-based Garmin and its Dutch competitor TomTom have seen steeply declining sales for personal navigation devices (PNDs) since the high point of the market two years ago, industry observers say.

    “[The Garmin-Asus divorce] was predictable. The product didn’t sell very well and no partnership can survive forever if there’s no revenue coming,” said Marc Prioleau, Technology Growth Advisors principal. “The smartphone market is incredibly competitive and navigation is a pretty standard feature. So you’ve got small revenues, limited differentiation…not much to build a long-term partnership around.”

    Since the Garmin-Asus strategic alliance in February 2009, the companies said they have developed and marketed six devices. These products are available through carrier and retail channels in several countries. One of the phones, the Garmin-Asus A10, a touchscreen smartphone running on the Android platform, is optimized for pedestrian navigation.

    Location-Based Advertising. TeleNav, which now has 17 million subscribers, recently launched a navigation-based mobile advertising platform that allows businesses to place a sponsored listing at the top of the search results located in its mobile navigation applications. The company says users can click on a sponsored listing to receive additional information such as coupons or menu information.

    The user can call, map, or receive turn-by-turn directions to the business — all of which are actions TeleNav measures and reports as metrics to advertisers. Sounds like an interesting concept — but are carriers committing to it?

    “We see location-based advertising (LBA) as a natural and important extension of our business. As an industry, I feel that we are only at the tip of the iceberg on advertising within the intersection of location and mobile,” said Ky Tang, TeleNav director of marketing. “This is new for us and for the industry as a whole. While it’s difficult to speak on behalf of a carrier, in general, I’d say that they too see a significant opportunity here.”

    TeleNav released data saying which brands are winning the battle for the attention of the mobile consumer. Through analyzing keyword searches of millions of its mobile users, the company is able to identify where consumers are looking to go while on the road.

    “We do not in any way, shape, or form provide user-specific information to our advertisers,” Tang said. “We only provide aggregate information of how our users are engaging with their ads within our application. So in addition to the traditional impressions and clicks, we let advertisers know how many people conducted a ‘drive to’ to a specific business.”

    Tang said that, in regard to the company’s data analysis, it does provide aggregate data on what users are searching for when using the application. “We believe that this type of information is insightful for brands to really understand how users who are on the go remember and prefer certain brands over others,” he said. “For those whose brand equity isn’t as strong — as measured by how often our users search for their specific name — we give them the ability to promote their brand to the top of the list. One of the implications behind this is that in the mobile, location-based arena, perhaps there’s an opportunity for more brand equality.”

    While it remains to be seen whether the LBA space is close to seeing rapid growth, some advertising agencies are taking notice. “Some leading, innovative ad agencies see it and get it right away. But by and large, there’s still a lot of education that is required in this space,” Tang said. “Location-based advertising is very powerful and we see it to represent the next major wave of digital advertising. But in the same way that it took online advertising some time to blossom and become more mainstream, we see the same thing here for location-based advertising.”

  • Expert Advice: The Strategic Significance of Compass

    Scott Pace.
    Scott Pace

    By Scott Pace

    On November 1, 2010, China’s state news agency reported that the sixth Compass satellite was launched from the Xichang Satellite Launch Center. This was the fourth Compass satellite put into orbit this year, following launches in January, June, and August. Joining the United States, Russia, and the European Union, China is deploying is own global navigation satellite system of five geosynchronous satellites, 27 in medium Earth orbit (MEO) and three in highly inclined geosynchronous orbits (IGSO).

    Sometimes referred to as Beidou-2, Compass is a global RNSS (radio-navigation satellite system) that broadcasts one-way precision time signals to enable receivers to calculate their position. An earlier Chinese satellite navigation system, Beidou-1, was an RDSS (radio-determination satellite system) that provided regional coverage and required two satellites to get a position fix using two-way communications with a centralized ground station.

    Like the U.S. GPS and the European Galileo system, signals from Compass use the CDMA (code-division multiple access) channel access method as distinct from the FDMA (frequency-division multiple access) method used by GLONASS. CDMA enables more precise positioning as compared to FDMA, and GLONASS is planning to shift to CDMA for its future satellites.

    Compass is designed to operate on three primary L-band frequencies:

    • 1559.052–1591.788 MHz,
    • 1166.22–1217.37 MHz,
    • 1250.618-1286.423 MHz

    while offering both an open service and an authorized service. The latter is expected to require cryptographic keys for access and will be reserved for military and public safety-related uses. Compass is intended to provide service to the Asia-Pacific region sometime in 2012 and to attain global-service levels around 2020.

    Reasons for Compass

    The Russian GLONASS was developed to support the Soviet Navy, and the U.S. GPS arose from the merger of previously separate Air Force and Navy satellite navigation efforts. China began researching satellite navigation and positioning technologies in the 1960s, but it was not until 1983 that a plan for satellite navigation and positioning system was developed. The “Double Star Rapid Positioning System” was the basis for the Beidou-1 two-satellite RDSS system that was formally approved for development in 1994. The impetus for the Compass systems is not fully known, but press reports attribute it to military requirements for more accurate missile targeting.

    The Chinese were close observers of the role of GPS in the first Gulf War. Chinese writings on military doctrine began to talk of “war under informationalized conditions” and how information from space-based systems such as GPS was changing the nature of modern warfare. Exploiting these new information sources required not just space capabilities but changes in how military forces were organized, trained, and equipped.

    Chinese security interests encompass not only China itself and nearby areas, but also the sea lanes that enable the import of raw materials and export of finished goods. In recent years, China has shown an increasing interest in “maritime domain awareness,” in which satellite navigation is used for monitoring the transit of ships in the Indian Ocean (for example, oil from the Middle East) and the South China Sea (minerals from Australia, fishing zones). Satellite navigation is a dual-use, commercial and military, interest for China, and this may have prompted support for the more advanced, independent GNSS that would become Beidou-2 or Compass.

    Regardless of the cause, People’s Liberation Army officials have said that China needs it own satellite positioning system to ensure its ability to conduct independent military actions. The later 1990s saw continued Beidou-1 satellite deployments while design of the newer Beidou-2/Compass satellites began. China joined the Galileo consortium in 2003 but abandoned it in 2006 in dissatisfaction over access to technology and work share arrangements. Efforts on Compass accelerated, and the first experimental satellite of the new system was launched in 2007.

    In a September 2010 interview with Chinese press, Duan Zhaoyu, vice president of BDStar Navigation, said that there are currently more than 20,000 civilian users of the Beidou-1 navigation system, 60 percent of whom use products from his company. More than 10,000 of these users are fishermen in the South China Sea. Not surprisingly, the Chinese government and military constituted the majority of users as it was also reported that as of August 2009, there were only 60,000 Beidou users in total. The number of registered terminal users amounted to only 1 percent of the system’s capacity, leaving the satellite resource seriously under-used.

    The underutilization of Beidou-1 is both a challenge and an opportunity for the Compass system in both domestic and international applications. The designer of the first Chinese satellites and current Beidou chief designer, Sun Jiadong has stressed the importance of actual utilization in arguing that “satellites in the sky should be coordinated with ground applications” and “pushing China’s Beidou satellite navigation system to bring as much economic and social benefit as early and as quickly as possible.” In order to do this, “…the state should promulgate corresponding policies, regulations, and systems as soon as possible to support development of the new satellite navigation application industry. It should guide, encourage, and attract even more Chinese enterprises and public institutions to actively participate in the construction of an industrial chain for ground applications.”

    Internationally, China has stressed cooperation with other GNSS systems. At the June 2010 meeting of the Asia-Pacific Economic Cooperation (APEC) organization, the Chinese presentation said that Beidou-2 (Compass) would “provide high-quality open services free of charge from direct users, and worldwide use of Beidou is encouraged,” and that Beidou-2 will “pursue solutions to realize compatibility and interoperability with other satellite navigation systems.”

    While satellite deployments have been accelerating, there continue to be delays in the public release of interface control documents (ICD) for incorporating Compass signals into GNSS receivers. The technical preparation of Beidou-2 Signal-in-Space ICD (version 1.0) has reportedly been finished but has not yet been posted on the Chinese government website for the program at www.beidou.gov.cn. In October 2009, Cao Chong, the director of the consulting center at the China Technical Application Association for Global Positioning System, gave a speech at Stanford University where he said that English and Chinese versions of the ICD have already been completed. But their release had been postponed due to pressure from domestic companies in China.

    The point of an open ICD, as done with GPS, is that as soon as it is released, anyone can use it on an equal basis. Reported opposition from Chinese companies seeking to gain a head start on foreign competitors would seem to indicate a domestic misperception of RNSS systems and an internal contradiction in Chinese policy toward Compass. Like other RNSS systems, Compass does not use a two-way signal for which direct users fees can be easily assessed; thus the idea of “head start” is illusionary. The necessary technologies for RNSS receivers are all found in consumer electronics and software — areas in which C
    hina is already capable.

    In addition, efforts to discourage or delay foreign adoption of Compass signals poses the risk of the system being of limited relevance to global markets, as is the situation of Beidou-1 today. This is contrary to the stated intent of the Chinese government that Compass be a world-class GNSS system.

    ITU System Coordination

    A primary concern of all GNSS users and operators is compatibility, that is, the ability of multiple satellite navigation systems to co-exist in the same international spectrum allocations without causing harmful interference to any individual service or signal. The signals may or may not be interoperable but they should not harm each other. In the case of Compass, its signals do overlap some Galileo frequencies, particularly with respect to the Galileo Publicly Regulated Service (PRS) and to a lesser extent the edges of the GPS M-Code that is used exclusively for defense purposes. In general, however, Compass signals do not overlap the GPS or GLONASS frequencies. Informal Chinese comments suggest that they consider GPS and GLONASS to be well-established “legacy” systems that new arrivals should seek to avoid overlapping. On the other hand, Galileo and Compass are seen as having equal standing as new RNSS systems within the terms of the International Telecommunications Union (ITU).

    Chinese presentations have identified several Compass signals that would overlap those of other GNSS providers. These include the Compass B1 at 1575.42 MHz with the GPS L1 signal, B2a at 1176.45 MHz with the GPS L5 signal, and B2b at 1207.14 MHz with the Galileo E5b signal. The Chinese believe that “the frequency spectrum overlap of open signals is beneficial for the realization of interoperability for many applications” and makes it easier to develop and manufacture interoperable receivers. While these claims are true to a point, GNSS providers experiencing the overlap may not agree.

    Even if signals do not experience harmful interference from an overlap, the signal provider may suffer constraints on its ability to control the service it provides to specific users, as in public safety or military applications. The long negotiations between the United States and the European Union over Galileo proposals to overlay major portions of the GPS M-Code eventually resulted in the 2004 US-EU Agreement on GPS-Galileo Cooperation. More recently, the European Union has raised its concerns with China’s plans to overlay Compass signals on the Galileo signals used for the PRS service.

    Within the ITU, RNSS operators (which includes the GNSS system providers) engage in direct coordination under what is known as a Resolution 609 process. This process was adopted at the 2003 World Radiocommunication Conference in Geneva, Switzerland and calls for “Consultation Meetings between administrations operating or planning to operate systems in the aeronautical radionavigation service (ARNS) and systems in the radionavigation satellite service (RNSS) in the 1164–1215 MHz frequency band.” It should be noted that the resolution does not encompass all GNSS signals, but does focuses on those at the GPS L5, Galileo E5, and Compass B2. The most recent meeting was the 7th Consultation Meeting of Resolution 609, June 23–25, 2010 in Toulouse, France.

    EPFD Levels. As the Resolution 609 process has continued, calculations of aggregate, equivalent power flux density levels (epfd) show that levels from filed RNSS systems (some operational, some planned) are nearing the allowable maximum aggregate epfd level. This level is specified in Resolution 609 itself, as revised at the last World Radiocommunications Conference (WRC-07). The United States position is that it is important to discuss methods to ensure that this limit is not in fact exceeded.

    The Toulouse Consultation Meeting discussed three potential methods to achieve this important objective:

    • use of actual operational characteristics (for example, maximum operational power levels, instead of filed parameters);
    • use of the actual number of satellites in orbit, instead of the filed number; and
    • technical revisions to the epfd calculation methodology (per ITU-R Recommendation M.1642-2).

    The meeting also considered proposals in the case where calculations show the aggregate epfd level would be exceeded, to perform a second aggregate epfd calculation including only satellites that are in actual operation, or are planned to be in operation before the next Resolution 609 Consultation Meeting is scheduled to occur (that is, within the next 12 to 16 months). The point of the second calculation would determine that epfd actually being produced from RNSS satellites in the 1164–1215 MHz band will not in fact exceed the allowable epfd limit.

    In addition to the Resolution 609 multilateral meetings, the United States and China have also engaged in five operator-to-operator coordination meetings under ITU auspices from 2007–2010. The United States has also offered the possibility of direct bilateral talks with China on GNSS services and applications — as was done with Japan, Russia, and the European Union.

    Europe similarly has sought to have direct talks with China to coordinate their concerns over Compass-Galileo. There have been at least six meetings on frequency compatibility and interoperability during 2007–2010, alternating between Beijing and Brussels. While both sides continue to express support for compatibility and even interoperability, the European side continues to oppose Compass overlays of the Galileo PRS while China shows no indication of being willing to change its frequency plans.

    Finally, with respect to Russia, a Beidou-GLONASS frequency compatibility meeting was held in Moscow in January 2007, but there seems to have been little follow-up. Given the lack of overlap between the frequencies used by the two systems, this is not surprising.

    International GNSS Coordination

    Compass is represented in broader GNSS coordination activities, not just those involving the ITU. The most important of these is the International Committee on GNSS (ICG) that was established in 2005 as an outgrowth of the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS). The most recent, and fifth, meeting of the ICG was held in October 2010 in Turin, Italy.

    The purpose of the ICG is to “promote the use of GNSS infrastructure on a global basis and to facilitate exchange of information.” Through meetings of the ICG, GNSS providers have adopted various principles such as transparency for open services, that is, every provider should publish documentation that describes signal and system information, policies of provision, and minimum levels of performance for its open services.

    On a regional basis, China participates in the APEC GNSS Implementation Team. This team was established by the APEC Transportation Working Group in 2000 with a mission of promoting regional GNSS augmentation systems to enhance inter-modal transportation. The United States hosted the 14th APEC GIT meeting this past June in Seattle, Washinmgton; the next meeting is tentatively scheduled for Brisbane, Australia, in May 2011. The significance of the APEC meetings on GNSS is their recognition of the value of such systems to states at greatly varying levels of development, not just the providers of GNSS or major GNSS augmentations. Although the group has a transportation focus, the productivity, safety, and environmental benefits of GNSS uses provide an incentive for common efforts across the Asia-Pacific region.

    In addition, the group calls for cooperating with non-APEC organizations (such as the ITU) as necessary to provide for seamless implementation.

    Strategic Significance of Compass

    Unlike Galileo, Compass is not a multinational cooperative program nor did it ever consider being a public-private partnership. Like GPS and GLONASS, Compass was created as an independent strategic effort by
    a national government for military and economic benefits.

    Unlike the history of GPS and GLONASS, however, the Chinese government from the beginning recognized the dual-use nature of Compass signals. Like GPS today, Compass plans to deploy CDMA signals at multiple frequencies to support a full range of application, from transportation to precision positioning and timing.

    Like Galileo, Compass still has to demonstrate that its signals are stable, operationally reliable, and accurately represented by published interface control documents to attract manufacturers to build the capability into their products. Galileo, Compass, and GLONASS all have the challenge of meeting the expectation of the existing installed base of billions of GPS users — whether or not they know they are reliant on GPS.

    The technical management of Compass is clearer than its policy management. Compass and Beidou-1 are the responsibility of the China Aerospace Science and Technology Corporation (CASC), the administrative holding company for the China Academy of Spaceflight Technology (CAST), the primary state-owned contractor for the Chinese space program. The military plays a large role in all Chinese space activities, and in recent years there has been uncertainty as to who is the government policy leader for space. In particular, the role of the China National Space Agency (CNSA) appears to have diminished in recent years. CNSA leaders scheduled to speak at major international conferences, such as the International Astronautical Federation, have cancelled at the last minute, while PLA speakers have presented instead.

    When U.S. President Barack Obama and China’s President Hu Jintao met in Beijing in 2009, their joint summit statement included a call for the NASA administrator to meet with an unspecified Chinese counterpart. Some of this may be coincidence due to other time demands such as launch schedules, but the Chinese decision-making hierarchy for space remains as opaque as it does in so many other areas.

    The opaqueness of Chinese political decision-making prompts speculation as to what China’s long-term strategic intent is with respect to Compass. The advent of open Compass signals would be potentially positive for the current installed base of GPS users — providing interoperable signals that improved the availability of positioning solutions. Internationally, the Chinese presence helps secure the international use of the RNSS spectrum and could be a potential ally in suppressing commercial sales of GNSS jamming devices — some of which are manufactured in China today. The view from Russia with respect to GLONASS is likely to be similar to that of GPS; Compass is largely a complementary system.

    From a European perspective, however, Compass is more problematic, both technically and commercially. The signal overlay on the Galileo PRS is a potential complication for Europe being able to deny PRS access in times of emergency.

    Perhaps more importantly, the rapid pace of Compass satellite deployments means that Compass may reach an initially operational capability sooner than Galileo. This is highly probable for coverage in Asia and increasingly likely on a global basis as Galileo faces criticism over cost increases and schedule delays. While Galileo has published an open service ICD and China has not, it would be a simple matter for China to time the release of an official Compass ICD one product cycle (that is, 18 months) before the 2012 completion of Asia-Pacific coverage. This would make Compass potentially very attractive to manufacturers looking to decide what would be of most benefit to the existing installed base.

    In general, China pursues its space activities as part of broad approach to what might be termed “comprehensive national power” to include military power, economic power, diplomatic influence, scientific and technological capabilities, and even political and cultural unity. This need not necessarily mean that such power will be used for aggressive purposes.

    If China’s strategic intent is to ensure its own independence and a place at the global table, then it is possible that Compass will not be harmful to U.S. interests. This outcome will depend on whether China continues to work with the international community in forums such as the ITU, the ICG, APEC, and so on, maintains open markets, and does not use Compass in military efforts to force changes in the status quo regarding Taiwan, the South China Sea, or the Indian Ocean.

    Since China’s strategic intentions are unclear, it makes sense for the United States to seek bilateral discussions with China on Compass and to maintain a close strategic dialog with other countries in the region, notably Japan, Australia, Korea, Russia, and India. These countries are not only militarily and economically important, but also have their own GNSS-related systems and equities to consider.

    The choices for China are whether Compass will be part of its “peaceful rise” and will serve truly national interests. Those interests could be seen as harnessing the kinds of dramatic IT productivity benefits other economies have seen in GNSS applications — enhanced by open, market-driven innovation and competition.

    Alternatively, it is possible to imagine China closing off its domestic market, protecting domestic state-owned enterprises, and focusing on the space and military aspects of Compass rather than market-driven civil and commercial applications.

    The question for Chinese leaders is whether they should measure the success of Compass just by the success of Chinese firms at home or by the global acceptance of Compass as a reliable brand name for GNSS services and signals.

    Compass is like China itself, where there are both great promise and some concerns. The signs to date for Compass are positive and will hopefully continue on the path of engagement and cooperation. The United States and the global GPS community should continue to encourage those positive signs in working with China, commercially, diplomatically, scientifically, and (perhaps especially) with more direct military-to-military contacts. All of these efforts can increase the chances that China will join the United States as another good steward of GNSS.

    SCOTT PACE is the director of the Space Policy Institute and a professor at George Washington University’s Elliott School of International Affairs. His research interests include civil, commercial, and national security space policy. From 2005–2008, he served as the associate administrator for program analysis and evaluation at NASA. Previously, he was the assistant director for space and aeronautics in the White House Office of Science and Technology Policy.

  • The System: QZSS Puts L1C on the Air

    QZSS Puts L1C on the Air

    JAVAD Receivers Track the First Truly Interoperable Signal

    JAVAD GNSS engineers in Moscow have released plots of the C/A, L2C, L5, SAIF, and the new L1C signals broadcast by Japan’s QZSS Michibiki, the first satellite to transmit L1C.

    The company stated that all of its current GNSS receivers can track QZSS signals with a software update that is available as an option to purchase.

    A new civil signal, L1C is designed to be interoperable among GNSSs. Currently, agreements are in place between the U.S. GPS, Europe’s Galileo, and Japan’s QZSS systems regarding broadcast and use of L1C. The U.S. system is not destined to add the L1C signal until the GPS III block of satellites, still more than three years out.

    The SAIF (Submeter-class Augmentation with Integrity Function) signal is a GPS augmentation with information on positioning correction and system health. The QZSS L1-C/A, L2C, L5, and L1C signals are GPS augmentation signals that can be operated reciprocally with positioning signals provided by GPS. The figures supplied by JAVAD GNSS show SNR (top) and code-minus-phase (bottom) plots for L1C.

     

    Plot of QZSS L1C signal, SNR.

    Plot of QZSS L1C signal, code minus phase (above).


    EC’s Galileo Manager Discusses Progress, Interoperability

    Paul Verhoef, the European Commission’s program manager for European Union (EU) satellite navigation programs, discussed current issues at length with GPS World, in a conversation on November 10. He addressed aspects of interoperability with GPS and prospects for further development in that area, the need for an ongoing political commitment by the EU to Galileo, the challenges of financing, the prospects for an 18-satellite constellation (which he dismisses as unrealistic), military considerations for both Galileo and GPS, and the recent uncertainty around Galileo’s Public Regulated Service.

    The full conversation is available here. Here are a few extracted quotes:

    Interoperability. “We have seen in the process with the U.S. that first of all there has been a quite clear political commitment on both sides, at the highest levels, that interoperability was wanted. Secondly, in the implementation we’ve had a very good working relation with our U.S. colleagues in order to establish that. The advantage that I see is that we have been able at a very early stage to deliver on such an interoperability agreement, that this is clear to industry, it provides for predictability. It allows industry to monitor clearly how the two systems are evolving, and when this interoperability is actually going to be available in the marketplace, and it allows them to time their investments, their R&D, their production, and all the rest.” [ . . . . ]

    Challenges. “It is time that Galileo delivers something concrete. We’ve had many years of discussion behind us on whether the system will come, and if it will come, and how it will come, and what it will look like, and all the rest. For my part, I’m very happy to see that in 2011, we plan to launch.

    The first four satellites are on the way; they are almost ready. About half the ground infrastructure is currently under implementation, we have every couple of months the opening of another ground station around the world. With this, the system becomes a reality, and I think once the satellite launches will go across television screens in the whole world, people will see that the system is becoming a reality. And I think that is desperately needed in order to give it a sense that things are moving forward. I’m really looking forward to that. That is a piece of good progress we have achieved over the last couple of years.

    Constellation. “There is a bit of a discussion for some reason in Europe, for some reason some people seem to think that we could do away with 18 satellites. Well, from me you will hear a solid ‘No.’

    “The availability figures for an 18-satellite constellation are around 90 percent on average, which means that for an aggregate total of some six weeks a year you would not receive sufficient views, not have sufficient satellites in sight to actually determine a position. There are going to be sectors like aviation where this is completely unacceptable, and they would never invest in anything if that is what we’re going to do. So my sense is that we will always have a lot of upward pressure in terms of constellation size. Of course it needs to be offset against costs and other considerations, but I think the pressure is always going to be there. It is very premature for people to be trying to take a shortcut, to think, well, maybe we could do with less. Because in the end you would have a constellation with a technical performance which the marketplace is not interested in, and then you would have a real problem.”

    Click here for the full discussion, spanning many topics.

    GPS Control Upgrade

    The U.S. Air Force 2nd Space Operations Squadron is scheduled to release the next software upgrade for the GPS ground system in early December, as part of an ongoing effort to improve and maintain the GPS Operational Control Segment before the next-generation GPS Control Segment is deployed in 2015. The upgrade is expected to be completed in early January 2011. The upgrade does not change the navigation message and should be transparent to GPS users. Tests have shown that the navigation message produced by the new software is identical to that produced by the current ground software. While no anomalies are expected, civilians experiencing any anomalies should contact the Coast Guard Navigation Center at (703) 313-5900.

    GLONASS Launch Fails

    The Russian Federal Space Agency announced that the December 5 launch of three GLONASS-M satellites ended in failure when the Proton-M rocket’s Block DM upper stage and its three payloads crashed into the Pacific Ocean about 1,500 kilometers (932 miles) northwest of Honolulu. Although an investigation will look into the exact cause of the failure, early unconfirmed reports indicate a software error. According to the Russian News Agency RIA Novosti, incorrect calculations were loaded into the rocket’s onboard computers.

    Compass Settles, Moves

    The Beidou/Compass G4 satellite launched on October 31 achieved geostationary orbit by November 6. The satellite is positioned at about 160 degrees east longitude. G4 is the furthest east of the operational Beidou geostationary satellites. Meanwhile, the orbital location of the Beidou 1A satellite has been changed.

    On or about October 27, as indicated by NORAD tracking data, the satellite underwent a significant delta-V, raising its orbit by about 200 kilometers. Its orbit had been slightly drifting for a few weeks before the maneuver, and there was speculation that the satellite had been placed in a disposal or graveyard orbit. However, on November 24 a second delta-V was observed that returned the satellite to the geostationary belt.

    The two maneuvers placed the satellite at a new location at about 60 degrees east longitude — the furthest west of any of the Beidou satellites. The satellite may eventually end up at 58.75 degrees east, one of the Beidou orbital slots registered with the International Telecommunication Union.

    The geostationary satellite, the first for the demonstration regional Beidou system or Beidou-1, was launched on October 30, 2000, and positioned at 140 degrees east longitude. Following several years of use, there were unofficial reports that the satellite was no longer functional. However, station-keeping was maintained, implying some usefulness of the satellite. It remains unclear how functional the satellite is and whether it is still useful for the Beidou-1 demonstration system.

  • Out in Front: One and One

    Two figures for your holiday mulling here. I keep putting one and one together, and coming up with three.

    The first one points to a value of $1,000 billion. Or, as we like to say, one trillion dollars. That has a nice ring to it.

    The second one hovers at a lower level, around $230 billion, not nearly as melodic as the first. But if the second one creates the first one, how much magic is there in that — do you see what I’m saying?

    Let me elucidate the second one first. It emerged at the European Navigation Conference, when a spokesperson for Galileo Services put forth the assertion that, currently, European industry holds a market share of around 20 percent of global GNSS hardware, software, and services, a market size he estimated at 180 billion euros, or $230 billion. Thus the first figure.

    The speaker’s point was that in other high-tech sectors, European industry held a market share of 33 percent, so really, they could be doing better. But that’s beside my point, which takes, as a rough estimate — and much subject to debate, granted — that the current global market of GNSS hardware, software, and services lies in the neighborhood of $230 billion.

    Returning to the first figure, it comes from a conversation with Paul Verhoef of the European Commission; a lengthy interview treats other issues, but I don’t want to let this snippet get away. He stated, based on some market research the EC has done but not yet released (you bet I’m trying), that “at the moment, 6 to 7 percent of the European Union gross domestic product (GDP) is directly dependent on the availability of GPS. This is a GDP value of around 800 billion euros; this is more than $1,000 billion.”

    A cool trillion dollars of European economy directly dependent on GPS availability.

    Wouldn’t it be nice if we knew the similar figure for the U.S. economy?

    Let’s just assume, for the sake of argument, that it roughly equals the European number. So United States and Europe combined, two trillion dollars of GDP directly dependent on GPS availability. Throw in the rest of the world and I’ll bet you’re at three trillion dollars.

    Boy, I wish I had an investment portfolio that I could throw $230 billion at, and wind up with $3 trillion at the end of the day.

    What, what, what are world governments doing, pinching pennies and cutting back programs and replenishing on need and sliding to the right — when they could be feeding a roaring economic engine, a behemoth that would support and stimulate so many other industries, and their GDPs as a whole?

    Come to think of it, Russia and China are pushing forward with this capitalist plan. It’s Western countries that appear ignorant of, and thus unable to learn from, their own economic history.

  • GNSS RF Compatibility Assessment: Interference among GPS, Galileo, and Compass

    By Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    A comprehensive methodology combines spectral-separation and code-tracking spectral-sensitivity coefficients to analyze interference among GPS, Galileo, and Compass. The authors propose determining the minimum acceptable degradation of effective carrier-to-noise-density ratio, considering all receiver processing phases, and conclude that each GNSS can provide a sound basis for compatibility with other GNSSs with respect to the special receiver configuration.
    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu
    Power spectral densities of GPS, Galileo, and Compass signals in the L1 band.

    As GNSSs and user communities rapidly expand, there is increasing interest in new signals for military and civilian uses. Meanwhile, multiple constellations broadcasting more signals in the same frequency bands will cause interference effects among the GNSSs. Since the moment Galileo was planned, interoperability and compatibility have been hot topics. More recently, China has launched six satellites for Compass, which the nation plans to turn into a full-fledged GNSS within a few years. Since Compass uses similar signal structures and shares frequencies close to other GNSSs, the radio frequency (RF) compatibility among GPS, Galileo, and Compass has become a matter of great concern for both system providers and user communities.

    Some methodologies for GNSS RF compatibility analyses have been developed to assess intrasystem (from the same system) and intersystem (from other systems) interference. These methodologies present an extension of the effective carrier power to noise density theory introduced by John Betz to assess the effects of interfering signals in a GNSS receiver. These methodologies are appropriate for assessing the impact of interfering signals on the processing phases of the receiver prompt correlator channel (signal acquisition, carrier-tracking loop, and data demodulation), but they are not appropriate for the effects on code-tracking loop (DLL) phase. They do not take into account signal processing losses in the digital receiver due to bandlimiting, sampling, and quantizing. Therefore, the interference calculations would be underestimated compared to the real scenarios if these factors are not taken into account properly. Based on the traditional methodologies of RF compatibility assessment, we present here a comprehensive methodology combining the spectral separation coefficient (SSC) and code tracking spectral sensitivity coefficient (CT_SSC), including detailed derivations and equations.

    RF compatibility is defined to mean the “assurance that one system will not cause interference that unacceptably degrades the stand-alone service that the other system provides.” The thresholds of acceptability must be set up during the RF compatibility assessment. There is no common standard for the required acceptability threshold in RF compatibility assessment. For determination of the required acceptability thresholds for RF compatibility assessment, the important characteristics of various GNSS signals are first analyzed, including the navigation-frame error rate, probability of bit error, and the mean time to cycle slip. Performance requirements of these characteristics are related to the minimum acceptable carrier power to effective noise power spectral density at the GNSS receiver input. Based on the performance requirements of these characteristics, the methods for assessing the required acceptability thresholds that a GNSS receiver needs to correctly process a given GNSS signal are presented.

    Finally, as signal spectrum overlaps at L1 band among the GPS, Galileo, and Compass systems have received a lot of attention, interference will be computed mainly on the L1 band where GPS, Galileo, and Compass signals share the same band. All satellite signals, including GPS C/A, L1C, P(Y), and M-code; Galileo E1, PRS, and E1OS; and Compass B1C and B1A, will be taken into account in the simulation and analysis.

    Methodology

    To provide a general quantity to reflect the effect of interference on characteristics at the input of a generic receiver, a traditional quantity called effective carrier-power-to-noise-density (C/N0), is noted as (C/N0)eff_SSC. This can be interpreted as the carrier-power-to-noise-density ratio caused by an equivalent white noise that would yield the same correlation output variance obtained in presence of an interference signal. When intrasystem and intersystem interference coexist, (C/N0)eff_SSC can be expressed as

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    Ĝs(f) is the normalized power spectral density of the desired signal defined over a two-sided transmit bandwith ßT, C is the received power of the useful signal. N0 is the power spectral density of the thermal noise. In this article, we assume N0 to be –204 dBW/Hz for a high-end user receiver. Ĝi,j(f) is the normalized spectral density of the j-th interfering signal on the i-th satellite defined over a two-sided transmit bandwith ßT, Ci,j the received power of the j-th interfering signal on the i-th satellite, ßr the receiver front-end bandwidth, M the visible number of satellites, and Ki the number of signals transmitted by satellite i. Iext is the sum of the maximum effective white noise power spectral density of the pulsed and continuous external interference.

    It is clear that the impact of the interference on (C/N0)eff_SSC is directly related to the SSC of an interfering signal from the j-th interfering signal on the i-th satellite to a desired signal s, the SSC is defined as

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    From the above equations it is clear that the SSC parameter is appropriate for assessing the impact of interfering signals on the receiver prompt correlator channel processing phases (acquisition, carrier phase tracking, and data demodulation), but not appropriate to evaluate the effects on the DLL phase. Therefore, a similar parameter to assess the impact of interfering signals on the code tracking loop phase, called code tracking spectral sensitivity coefficient (CT_SSC) can be obtained. The CT_SSC is defined as

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    where Δ is the two-sided early-to-late spacing of the receiver correlator.

    To provide a metric of similarity to reflect the effect of interfering signals on the code tracking loop phase, a quantity called CT_SSC effective carrier power to noise density (C/N0), denoted (C/N0)eff_CT_SSC, can be derived. When intrasystem and intersystem interference coexist, this quantity can be expressed as

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    where IGNSS_CT_SSC is the aggregate equivalent noise power density of the combination of intrasystem and intersystem interference.

    Equivalent Noise Power Density. When more than two systems operate together, the aggregate equivalent noise power density IGNSS ( IGNSS_SSC or IGNSS_CT_SSC ) is the sum of two components

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    IIntra is the equivalent noise power density of interfering signals from satellites belonging to the same system as the desired signal, and IInter is the aggregate equivalent noise power density of interfering signals from satellites belonging to the other systems.

    In fact, recalling the SSC and CT_SSC definitions, hereafter, denoted Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niuor Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu as Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu, the equivalent noise power density (IIntra or IInter) can be simplified as

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    where Ci,j is the user received power of the j-th signal belonging to the i-th satellite, as determined by the link budget.

    For the aggregate equivalent noise power density calculation, the constellation configuration, satellite and user receiver antenna gain patterns, and the space loss are included in the link budget. User receiver location must be taken into account when measuring the interference effects.

    Degradation of Effective C/N0. A general way to calculate (C/N0)eff, (C/N0)eff_SSC , or (C/N0)eff_CT_SSC introduced by interfering signals from satellites belonging to the same system or other systems is based on equation (1) or (4). In addition to the calculation of (C/N0)eff , calculating degradation of effective C/N0 is more interesting when more than two systems are operating together. The degradation of effective C/N0 in the case of the intrasystem interference in dB can be derived as

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    Similarly, the degradation of effective C/N0 in the case of the intersystem interference is

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    Bandlimiting, Sampling, and Quantization. Traditionally, the effect of sampling and quantization on the assessment of GNSS RF compatibility has been ignored. Previous research shows that GNSS digital receivers suffer signal-to-noise-plus interference ration (SNIR) losses due to bandlimiting, sampling, and quantization (BSQ). Earlier studies also indicate a 1.96 dB receiver SNR loss for a 1-bit uniform quantizer. Therefore, the specific model for assessing the combination of intrasystem and intersystem interference and BSQ on correlator output SNIR needs to be employed in GNSS RF compatibility assessment.

    Influences of Spreading Code and Navigation Data. In many cases, the line spectrum of a short-code signal is often approximated by a continuous power spectral density (PSD) without fine structure. This approximation is valid for signals corresponding to long spreading codes, but is not appropriate for short-code signals, for example, C/A-code interfering with other C/A-code signals. As one can imagine, when we compute the SSC, the real PSDs for all satellite signals must be generated. It will take a significant amount of computer time and disk storage. This fact may constitute a real obstacle in the frame of RF compatibility studies. Here, the criterion for the influences of spreading code and navigation data is presented and an application example is demonstrated. For the GPS C/A code signal, a binary phase shift keying (BPSK) pulse shape is used with a chip rate fc = 1.023 megachips per seconds (Mcps). The spreading codes are Gold codes with code length N = 1023. A data rate fd = 50 Hz is applied. As shown in Figure 1, the PSD of the navigation data (Gd(f) = 1/fd sin c2 (f/fd) ) replace each of the periodic code spectral lines. The period of code spectral lines is T = 1/LTC. The mainlobe width of the navigation data is Bd =2fd.

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu
    Figure 1. Fine structure of the PSD of GPS C/A code signal (fd = 50 Hz ,without
    logarithm operation).

    For enough larger data rates or long spreading codes, the different navigation data PSDs will overlap with each other. The criterion can be written as:

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    Finally,

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    When criterion L ≥ fc/fd is satisfied, navigation signals within the bandwidth are close to each other and overlap in frequency domain. The spreading code can be treated as a long spreading code, or the line spectrum can be approximated by a continuous PSD.

    C/N0 Acceptability Thresholds

    Receiver Processing Phase. The determination of the required acceptability thresholds consider all the receiver processing phases, including the acquisition, carrier tracking and data demodulation phases.The signal detection problem is set up as a hypothesis test, testing the hypothesis H1 that the signal is present verus the hypothesis H0 that the signal is not present. In our calculation, the detection probability pd and the false alarm probability pf are chosen to be 0.95 and 10–4, respectively. The total dwell time of 100 ms is selected in the calculation.

    A cycle slip is a sudden jump in the carrier phase observable by an integer number of cycles. It results in data-bit inversions and degrades performance of carrier-aided navigation solutions and carrier-aided code tracking loops. To calculate the minimum acceptable signal C/N0 for a cycle-slip-free tracking, the PLL and Costas loop for different signals will be considered. A PLL of third order with a loop filter bandwidth of 10 Hz and the probability of a cycle slip of 10–5 are considered. We can find the minimum acceptable signal C/N0 related to the carrier tracking process. For the scope of this article, the vibration induced oscillator phase noise, the Allan deviation oscillator phase noise, and the dynamic stress error are neglected.

    In terms of the decoding of the navigation message, the most important user parameters are the probability of bit error and the probability of the frame error. The probability of frame error depends upon the organization of the message frame and various additional codes. The probability of the frame error is chosen to be 10–3. For the GPS L1C signal using low-density parity check codes, there is no analytical method for the bit error rate or its upper bound. Due to Subframe 3 data is worst case, the results are obtained via simulation. In this article, the energy per bit to noise power density ratio of 2.2 dB and 6 dB reduction due to the pilot signal are taken into account, and the loss factor of the reference carrier phase error is also neglected.

    Minimum Acceptable Degradation C/N0. The methods for accessing the minimum acceptable required signal C/N0 that a GNSS receiver needs to correct
    ly process a desired signal are provided above. Therefore, the global minimum acceptable required signal carrier to noise density ratio (C/N0)global_min for each signal and receiver configuration can be obtained by taking the maximum of minima. In addition to the minimum acceptable required signal C/N0, obtaining the minimum acceptable degradation of effective C/N0 is more interesting in the GNSS RF compatibility coordination. For intrasystem interference, when only noise exists, the minimum acceptable degradation of effective C/N0 in the case of the intrasystem interference can be defined as

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    Similarly, the minimum acceptable degradation of effective C/N0 in the case of the intersystem interference can be expressed as

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    Table 1 summarizes the calculation methods for the minimum acceptable required of degradation of effective C/N0.

    Simulation and Analysis

    Table 2 summarizes the space constellation parameters of GPS, Galileo, and Compass.

    For GPS, a 27-satellite constellation is taken in the interference simulation. Galileo will consist of 30 satellites in three orbit planes, with 27 operational spacecraft and three in-orbit spares (1 per plane). Here we take the 27 satellites for the Galileo constellation. Compass will consist of 27 MEO satellites, 5 GEO, and 3 IGSO satellites. As Galileo and Compass are under construction, ideal constellation parameters are taken from Table 2.

    Signals Parameters. The PSDs of the GPS, Galileo and Compass signals in the L1 band are shown in the opening graphic. As can be seen, a lot of attention must be paid to signal spectrum overlaps among these systems. Thus, we will concentrate only on the interference in the L1 band in this article. All the L1 signals including GPS C/A, L1C, P(Y), and M-code; Galileo E1 PRS and E1OS; and Compass B1C and B1A will be taken into account in the simulation and analysis.

    Table 3 summarizes GPS, Galileo and Compass signal characteristics to be transmitted in the L1 band.

    Simulation Parameters. In this article, all interference simulation results refer to the worst scenarios. The worst scenarios are assumed to be those with minimum emission power for desired signal, maximum emission power for all interfering signals, and maximum (C/N0)eff degradation of interference over all time steps. Table 4 summarizes the simulation parameters considered here.

    SSC and CT_SSC. As shown in expression (1) or (4), (C/N0)eff is directly related to SSC or CT_SSC of the desired and interfering signals. Figure 2 and Figure 3 show both SSC and CT_SSC for the different interfering signals and for a GPS L1 C/A-code and GPS L1C signal as the desired signal, respectively. The figures obviously show that CT_SSC is significantly different from the SSC. The results also show that CT_SSC depends on the early-late spacing and its maximal values appear at different early-late spacing.

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu
    FIGURE 2. SSC and CT_SSC for GPS C/A-code as desired signal.
    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu
    FIGURE 3. SSC and CT_SSC for GPS L1C as desired signal.

    The CT_SSC for different civil signals in the L1 band is calculated using expression (3). The power spectral densities are normalized to the transmitter filter bandwidth and integrated in the bandwidth of the user receiver. As we saw in expression (3), when calculating the CT_SSC, it is necessary to consider all possible values of early-late spacing. In order to determine the maximum equivalent noise power density (IIntra or IInter), the maximum CT_SSC will be calculated within the typical early-late spacing ranges (0.1–1 chip space).

    Results and Analysis

    In this article we only show the results of the worse scenarios where GPS, Galileo, and Compass share the same band. The four worst scenarios include:

    ◾ Scenario 1: GPS L1 C/A-code ← Galileo and Compass (GPS C/A-code signal is interfered with by Galileo and Compass)

    ◾ Scenario 2: GPS L1C ← Galileo and Compass (GPS L1C signal is interfered with by Galileo and Compass)

    ◾ Scenario 3: Galileo E1 OS ← GPS and Compass (Galileo E1 OS signal is interfered with by GPS and Compass)

    ◾ Scenario 4: Compass B1C ← GPS and Galileo (Compass B1C signal is interfered with by GPS and Galileo)

    Scenario 1. The maximum C/N0 degradation of GPS C/A-code signal due to Galileo and Compass intersystem interference is depicted in Figure 4 and Figure 5.

    Scenario 2. Figure 6 and Figure 7 also show the maximum C/N0 degradation of GPS L1C signal due to Galileo and Compass intersystem interference.

    Scenario 3. The maximum C/N0 degradation of Galileo E1OS signal due to GPS and Compass intersystem interference is depicted in Figure 8 and Figure 9.

    Scenario 4. For scenario 4, Figure 10 and Figure 11 show the maximum C/N0 degradation of Compass B1C signal due to GPS and Galileo intersystem interference.

    From the results from these simulations, it is clear that the effects of interfering signals on code tracking performance may be underestimated in previous RF compatibility methodologies. The effective carrier power to noise density degradations based on SSC and CT_SSC are summarized in Table 5. All the results are expressed in dB-Hz.

    C/N0 Acceptability Thresholds. All the minimum acceptable signal C/N0 for each GPS, Galileo, and Compass civil signal are simulated and the results are listed in Table 6. The global minimum acceptable signal C/N0 is summarized in Table 7. All the results are expressed in dB-Hz.

    Effective C/N0 Degradation Thresholds. All the minimum effective C/N0 for each GPS, Galileo and Compass civil signal due to intrasystem interference are simulated, and the results are listed in Table 8. Note that the high-end receiver configuration and external interference are considered in the simulations. According to the method summarized in Table 1, the effective C/N0 degradation acceptability thresholds can be obtained. The results are listed in Table 9.

    As can be seen from these results, each individual system can provide a sound basis for compatibility with other GNSSs with respect to the special receiver configuration used in the simulations. However, a common standard for a given pair of signal and receiver must be selected for all GNSS providers and com
    munities.

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    Source: Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

    Conclusions

    At a minimum, all GNSS signals and services must be compatible. The increasing number of new GNSS signals produces the need to assess RF compatibility carefully. In this article, a comprehensive methodology combing the spectral separation coefficient (SSC) and code tracking spectral sensitivity coefficient (CT_SSC) for GNSS RF compatibility assessment were presented. This methodology can provide more realistic and exact interference calculation than the calculation using the traditional methodologies. The method for the determination of the required acceptability thresholds considering all receiver processing phases was proposed. Moreover, the criterion for the influences of spreading code and navigation data was also introduced.

    Real simulations accounting for the interference effects were carried out at every time and place on the earth for L1 band where GPS, Galileo, and Compass share the same band. It was shown that the introduction of the new systems leads to intersystem interference on the already existing systems. Simulation results also show that the effects of intersystem interference are significantly different by using the different methodologies. Each system can provide a sound basis for compatibility with other GNSSs with respect to the special receiver configuration in the simulations.

    At the end, we must point out that the intersystem interference results shown in this article mainly refer to worst scenario simulations. Though the values are higher than so-called normal values, it is feasible for GNSS interference assessment. Moreover, the common standard for a given signal and receiver pair must be selected for and coordinated among all GNSS providers and communities.

    This article is based on the ION-GNSS 2010 paper, “Comprehensive Methodology for GNSS Radio Frequency Compatibility Assessment.”

    WEI LIU is a Ph.D. candidate in navigation guidance and control at Shanghai Jiao Tong University, Shanghai, China. XINGQUN ZHAN is a professor of navigation guidance and control at the same university. LI LIU and MANCANG NIU are Ph.D. candidates in navigation guidance and control at the university.

     

  • What Do Your Colleagues Think? Part 2

    In my last column, I presented the poll results from my November 16 webinar “A Buyer’s Guide to GPS/GIS Mapping Equipment.” I’ve conducted many webinars over the years, and the audiences have been comprised of hundreds (if not thousands) of participants who have the ability to ask questions and also participate on various polls I conduct during the webinars. This column continues the look back at previous polls conducted during the various webinars in 2010 to give you an understanding of what your colleagues are thinking.

     

    August 31, 2010 Webinar: “Solar Activity, SBAS, and 24+3 GPS Constellation Updates”

    Poll #1 (Aug. 31, 2010 webinar): How concerned are you about solar activity affecting your GNSS operations?


    Gakstatter comment: These numbers don’t surprise me. Personally, I probably fall in the “Somewhat” category, but my GPS/GNSS field work is pretty flexible so I can easily adjust without much inconvenience. However, if I had several crews using GPS/GNSS on a daily or near-daily basis or I had equipment relying on GPS/GNSS, I think I’d be in the “Very” category because the $$ impact would be much higher.

    Poll #2 (Aug. 31, 2010 webinar): If it was available, would you be interested in receiving alerts/warnings of solar activity that may affect GNSS operations?


    Gakstatter comment: I’m not surprised at these results either. When I initially considered this poll, I was thinking about asking which type of platform you would prefer to receive alerts/warnings with the choices being Droid app, iPhone app, Blackberry app, text message, e-mail, etc. If you have a preference on that, fire off a quick e-mail to me. Secondly, a few of you pointed out that NASA has an app for this, but keep in mind that the system I’m considering is focused specifically on high-performance/precision GPS/GNSS users, which would eliminate a lot of the baggage of the alert/warning systems available today.

    Poll #3 (Aug. 31, 2010 webinar): Do any of your GPS receivers use SBAS (WAAS/EGNOS/MSAS) as a primary source of corrections?


    Gakstatter comment: Not much to say here except that a substantial number of commercial GPS users are relying on SBAS. This has definitely been the trend over the past five years.

    Poll #4 (Aug. 31, 2010 webinar): Do you expect that the GPS 24+3 configuration will improve your GPS productivity?

    Total votes: 172

    Gakstatter comment: Like most of you, I have great expectations for the 24+3 configuration. While launching more satellites with L5 would be nice, that’s a long-term effort, whereas the 24+3 configuration is something we will benefit from in a few months and are seeing some marginal benefit now. In January 2011, once all the satellites have arrived at their destination slots, I’ll plot new visibility charts and see where we stand.

    June 24, 2010 Webinar: “GIS Mapping for Forestry, Agriculture, and Other Natural Resource Professionals”

    Poll #1 (June 24, 2010 webinar): What kind of mapping data do you primarily collect?


    Gakstatter Comment: These results don’t surprise me. The only note I’d like to make is that some people collect point data in the field and then connect the points in the office to generate line and polygon data.

    Poll #2 (June 24, 2010 webinar): Is having an aerial photo or satellite imagery in the background important?


    Gakstatter Comment: Again, these results don’t surprise me. My feeling is that if imagery was easier to locate and integrate, nearly 100% of users would prefer them. The challenge is finding accessible, affordable imagery that is easy to integrate.

    Poll #3 (June 24, 2010 webinar): How much are you willing to spend on a GPS receiver? I’m going to list the possible answers here because they don’t fit in the bar graph.

    1. $0 – No thanks.
    2. $200-500. I’m satisfied with 3-5 meter accuracy, limited use under forest canopy and limited data collection functionality.
    3. $500-1,500. I’m satisfied with 3-5 meter accuracy and limited use under forest canopy, but want more mapping data collection functionality.
    4. $1,500-$3,000.  I want a sub-meter accurate GPS receiver that will perform well under forest canopy and I’m willing do a little work to put together my own mapping system.
    5. $3,000-6,000. I want an out-of-the-box, sub-meter accurate GPS receiver that’s ready to go and works well under forest canopy.
    6. $6,000-10,000. I want a high-performance GPS receiver that will give me centimeter-level horizontal and vertical accuracy, but also work well under forest canopy (not centimeter-level).

    height=”261″ alt=”” src=”/files/gpsworld/nodes/2010/10757/0624Poll3.jpg” />


    Gakstatter Comment: I was surprised at the number of respondents who selected the “high-end” system.

    Poll #4 (June 24, 2010 webinar): Select the three most important features you need in mapping software. I’m going to list the possible answers here because they don’t fit in the bar graph.

    1. Ability to draw points, lines and polygons on your computer using a mouse.
    2. Ability to manage digital photos associated with features on the map.
    3. Ability to plot a professional-looking map.
    4. Ability to import aerial/satellite imagery.
    5. Ability to measure distances between points and calculate areas of features.
    6. Ability to import a wide variety of vector data (including GPS).


    Gakstatter Comment: This is about what I expected. Of course, the ability to draw using a mouse is highly related to the ability to import imagery.

    April 22, 2010 Webinar: “GPS, GLONASS, and SBAS Constellation Updates”

     

    Poll #1 (April 22, 2010 webinar): Have you or your work crews had to stop or alter your work pattern due to the lack of GPS satellites?


    Gakstatter comment: This is consistent with other polls I’ve conducted regarding GPS satellite availability. The great majority of you (73%) expressed that you have to adjust your work pattern due to lack of satellites. The new GPS 24+3 configuration will help mitigate this problem (and the new configuration is largely complete). Read more about the new GPS 24+3 configuration in a three-part series I wrote earlier this year.

     

    Poll #2 

    (April 22, 2010 webinar): How often do you upgrade your GPS equipment?

     


    Gakstatter comment: There’s no clear pattern here except to say that 46% of the users wait until at least 3 years before they consider upgrading their GPS equipment. That makes sense to me.

     

    Poll #3 

    (April 22, 2010 webinar): Does any of your GNSS equipment utilize GLONASS?

     


    Gakstatter comment: When considering the result of this poll, keep in mind that there are very few “mapping-grade” receivers that are designed to utilize GLONASS (but that is changing). For example, there are very few, if any, sub-meter receivers that utilize GLONASS, primarily due to the lack of correction sources. SBAS doesn’t support GLONASS, DGPS (radiobeacon) doesn’t support GLONASS, and most CORS do not support GLONASS. Only recently did OmniSTAR begin supporting GLONASS. I think this trend in mapping-grade receivers supporting GLONASS will continue, although I doubt that SBAS or DGPS (radiobeacon) will support GLONASS in the foreseeable future.

    However, manufacturers have developed methods to utilize GLONASS measurements to augment GPS positioning without the need of an SBAS or DGPS correction.

     

    Poll #4 (April 22, 2010 webinar): Does any of your GNSS equipment utilize SBAS (WAAS/EGNOS/MSAS) as a primary source of corrections?

     


    Gakstatter comment: This poll result doesn’t surprise me. Given that SBAS corrections are widely available, free of charge, reasonably accurate, and require no action by the user, it makes a lot of sense they are being used.

    February 18, 2010 Webinar: “GPS for GIS Data Collection — 101”

     

    Poll #1 (February 18, 2010 webinar): Do you currently use GPS for collecting GIS data?

     

     

    Gakstatter: No comment of significance. Sort of a dumb question now that I look at it again. Sorry :-)

     

    Poll #2 (February 18, 2010 webinar): What accuracy do you require in a GPS mapping system?

     

    Gakstatter: I’ve asked this same question in more than one webinar. The
    response from this particular audience, which was substantially GIS-oriented, was that sub-meter (33.1%) and cm-level (28.4%) were the most preferred levels of accuracy, with 1-3 meters accuracy at 22.3%.

     

    Poll #3 (February 18, 2010 webinar): Select the three most important items to you in a GPS mapping system. 

    Gakstatter: This was a multi-answer question with the top three answers clearly being; collecting attribute data (selected by 88.1%), accuracy (selected by 87.1%), and cost (selected by 71%).

    Thanks, and see you next time.

    Follow me on Twitter at http://twitter.com/GPSGIS_Eric

  • What Do Your Colleagues Think?

    Over the past several years, I’ve conducted many webinars on different GPS/GNSS and other geospatial technologies. The audiences have been comprised of hundreds (if not thousands) of participants who have the ability to ask questions and also participate on various polls I conduct during the webinars.The poll results are a powerful tool that illustrates what your colleagues think about GPS/GNSS, their field practices and general attitude about geospatial technology.

    In this column, I’ll published the poll results from last week’s webinar as well as some select polls from previous webinars in an effort to paint a picture of what your colleagues are thinking.

     

    Poll #1 (Nov. 16 webinar): What’s your budget, per unit, for GPS/GIS data collection systems this year?

     

    Gakstatter comment: “It is what it is” in this economy. 32.2% of you have no budget for this., 22%, 11.9%, 16.9% and 16.9% respectively. The good news is that if you scrape and scrap and are able to use some existing hardware/software you might have, you may be able to put together a good quality GPS mapping system a lot less than buying a new system off-the-shelf.

     

     

    Poll #2 (Nov. 16 webinar): Which ergonomic form factor do you prefer?

     

    Gakstatter comment: This is the first time I’ve asked this question in a poll. The reason I asked is because traditionally, the manufacturers have been focused on all-in-one handheld systems, but in the past several years with the emergence of PDA’s, smartphones and tablet computers, there’s a definitely trend towards separating the GPS receiver and the data collector to increase flexibility. For example, with a separate GPS receiver, you can choose to use a PDA or a tablet depending on the project task. With an All-in-One handheld, you don’t have that flexibility. However, an All-in-one handheld certainly has the advantage of being simpler and more ergonomical. The poll result shows almost an even split with Modular at 52.9% and All-in-one handheld at 47.1%

     

    Poll #3 (Nov. 16 webinar): Which category of data collection software do you prefer?

     

    Gakstatter comment: Like Poll #, this is really about flexibility vs. simplicity. In this case, maximum flexibility means that you are selecting software that is not tied to the hardware (hardware-independent). These types of software, like ArcPad, SurvCE, Field CE GIS, etc. work on several hardware platforms and with several different manufacturers of GPS receivers. The risk is that when there’s a problem, there might be finger pointing between hardware and software vendors. The advantage of a single vendor, of course, is that you have a single point of contact for technical support. In the poll, 58.2% of you chose hardware-independent software (Max flexibility) and 41.8% of you chose hardware-dependent software (Single vendor).

     

     

    Poll #4 (Nov. 16 webinar): What accuracy do you require from a GPS/GIS data collection system?

     

    Gakstatter comment: This is sort of a loaded question because the webinar was marketed more towards surveyors/engineers rather than general GIS. I think it skewed the results a bit on this poll, but nonetheless, there is a definite trend towards high-accuracy GIS. The poll results show that 34.5% require 1-2cm accuracy, followed by 23% requiring sub-meter, 20.7% requiring sub-foot, 17.2% requiring 1-3 meters, 3.4% requiring 3-5 meters and only 1.1% are happy with 5-10 meters.

     

     

    Poll #5 (Nov. 16 webinar): How much of your data collection work is under tree canopy?

     

     

    Gakstatter comment: This is another question I asked for the first time. I didn’t know what to expect. Nearly 70% of you work under tree canopy 25% of the time or less.

     

     

    Poll #6 (Nov. 16 webinar): For a data collection device, I prefer a:

     

     

    Gakstatter comment: This is also the first time I’ve asked this question in a poll. The result surprises me a bit due to the emergence of tablet computers and smartphones. However, after thinking about, it’s going to take some time for people to become comfortable with tablets and smartphones for GIS data collection. It’s also going to take time for the industry software vendors to settle down and choose a platform (or develop for all) such as Apple, Windows, Droid, etc. The poll results show that users still prefer handhelds (57.7%) with tablet computers following at 26.9%, then notebook computers a 9%, then smartphones at 6.4%. There is a definite trend, though, towards smartphones. I think we’ll see a substantial increase in popularity over the next couple of years.

     

    Thanks, and see you next time.

    Follow me on Twitter at http://twitter.com/GPSGIS_Eric

     

    Read PART 2 here.