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Analog Angle Blog

Navigating Without GPS Requires Advanced Sensors, Intensive Analog

We're so accustomed to using the global positioning System (or its European and Russian counterparts, the Galileo GNSS and GLONASS systems) for location and navigation that it's easy to forget or ignore the obvious: GPS does not have a 100% assurance of availability.

What can impede GPS? Three classes of things can:

  1. Physical barriers such as underground tunnels, bodies of water, or even ordinary buildings, for starters
  2. Unpredictable solar events such as those huge “bursts” of high-energy particles that cause electronic storms and upsets in our atmosphere
  3. Unintentional local interference or intentional jamming

Given these weaknesses — and they are very real, not just “the sky is falling” crisis mongering to get more funding — the military and its Defense Advanced Research Project Agency (DARPA) are supporting projects that may lead to very precise navigation without GPS. A recent article in the always readable and enjoyable Physics Today provided a fascinating overview of these efforts, the progress thus far, and the problems ahead. Early in the article, there was a basic statement that's always worth keeping in mind: “Three pieces of information are needed to precisely navigate between two known points: orientation, acceleration, and time. Once an initial position is provided, inertial systems determine where to go.”

These next-generation inertial navigations systems would provide GPS-like accuracy on the order of a meter or better, but they would be completely independent of any outside signal reception. That's why they are called “inertial,” after all. The goal is provide position, navigation, and timing (PNT) information via inertial measurement units (IMUs) that are simultaneously orders of magnitude smaller, lighter, and lower-power than today's best IMUs.

IMUs, of course, are not new. Using extremely sophisticated mechanical gyroscopes, they have been used for missile guidance, and ring-laser gyros are now standard on commercial airliners. They are helping look for distortions in the space-time continuum caused by gravity. And MEMS-based IC gyros are now available at low cost, using little power and offering very good performance –- but not good enough for the DARPA project goals.

To get a sense of what inertial guidance and IMUs are all about, check out these two books: Inventing Accuracy: A Historical Sociology of Nuclear Missile Guidance by Donald MacKenzie (a somewhat unusual subtitle but a great read) and Modern Inertial Technology: Navigation, Guidance, and Control by Anthony Lawrence (more technical and quantitative).

Regardless of which IMU developments help DARPA reach the goals, there is no doubt that PNT instrumentation has advanced a long way in just a few decades, when precision analog circuits centered on low-drift op-amps were key building blocks. Regardless of how the next stage of IMU performance is implemented, it still starts with sensors (analog transducers) and analog signal-conditioning circuitry, which must somehow extract meaningful signals from an electrically challenging environment plagued by low signal level and low SNR (to cite just two issues) and do so with precision and stability.

The outputs of these analog stages are then enhanced and further enhanced in the digital world of processors and algorithms, including additional compensation and calibration, but these objectives can be reached only if the analog front end (sensor plus conditioner) has the required performance. The old maxim of “garbage in, garbage out” still carries a lot of truth in this situation, as it does in nearly all test and measurement scenarios.

How do you think non-GPS, next-generation IMUs will perform, compared to today's IMUs and GPS-based systems? Will there be a fundamental new-technology “breakthrough” (admittedly, a hard-to-assess benchmark, except in retrospect) that radically advances the state of the art? Or will it be the result of a series of modest but still significant incremental improvements that combine and leverage one another to yield substantial improvements along one or more dimensions of weight, performance, or power consumption?

39 comments on “Navigating Without GPS Requires Advanced Sensors, Intensive Analog

  1. bjcoppa
    November 11, 2014

    The overlap discussed in this article of analog chips with MEMS sensor applications is why many analog chip-makers like Maxim, Freescale and TI also produce MEMS sensors as well. Both require similar feature sizes and necessary process equipment which can be re-purposed for one manufacturing line or the other. There is no clear reason why this would change in the future either, especially to keep capex low as ASPs remain steady.

  2. Davidled
    November 12, 2014

    We might look the cost impact between no GPS with navigation and GPS with navigation. Navigation without GPS might require more external analog effort. In the short periods of time, performance and cost would be compared between vehicle with GPS and vehicle without GPS. Intensive analog might need more clarification.

  3. amrutah
    November 14, 2014

    @Bill:  Thanks for the post, cannot imagine a system different from GPS that could be helpful for navigation.

        GPS uses a set of satellites to mark its position,  If the device uses IMU, then it is on its own, how does it relay its track.  I mean, if a device uses GPS then it has a ID and I can locate any device that is using it for navigation, but we use IMU how can we track a alien device.

       Am I missing any thing here?

  4. Bill_Jaffa
    November 14, 2014

    Not sure I understand the problem you are referring to. It is up to the “traveling” unit designer–whether it uses GPS or an IMU–to allow relaying of track information. Just because the unit has GPS doesnt mean outsiders will have to know where it is–GPS is a receiver. And if it is non-GPS, then the IMU could also have a link to relay position using some sort of ID number.

    But remember: the reason you need an IMU is because you are in an RF dead zone, so you have to learn to live on your own and not assume you can report your track. That may simply not be possible.

  5. amrutah
    November 14, 2014

    @Bill:  Thanks, you did answer my concern.  GPS system (transreceivers in satellite and receivers on ground) as a whole is used by military and civilian.

    What I meant was, GPS satellites have the information of each and every device like a central repository, unlike the IMU which is on its own then tracking such device becomes difficult.

  6. Bill_Jaffa
    November 14, 2014

    Yes, of course each GPS satellite has identifiers, but the GPS receivers do not. No one knows who is receiving and using the GPS signal, nor where the receiver is, unless that receiver is also designed to have some sort of transponder/reporting function added. Therefore, you cannot track GPS receivers, in general.

  7. Netcrawl
    November 16, 2014

    @Bill thanks for that great comment, the main GPS error source is due to inaccurate time-keeping by the receiver's clock, microwave signals travelling at the speed of light from at least three satellites are used by receiver's built-in computer system to calculate its position, altitude and velocity. There's a tiny discrepancies between the GPS receiver's onboard clock and GPS time, which synchronizes the whole GPS, mean distances calculated can drift but there's solution to this problem- the use of atomic click on each receiver. 

  8. Bill_Jaffa
    November 16, 2014

    Yes, the receiver clock is a major error source–but it isn't feasible to put an atomic clock in most receivers in use (size, cost, power etc).

    For a good discussion of the effect of clock error (where fractions of a nanosecond error lead to significant location error) and the many other sources of error (relativistic effects, gravitational effects, slightly elliptical orbits, and more), see:

    1. Relativistic Effects in the Global Positioning System, July 18, 2006. (http://www.aapt.org/doorway/tgru/articles/ashbyarticle.pdf)

    2. Relativity in the Global Positioning System, Living Reviews in Relativi ty , January 2003. (http://relativity.livingreviews.org/Articles/lrr-2003-1/download/lrr-2003-1Color.pdf)

    3. Relativity and the Global Positioning System, Physics Today , May 2002. (http://courses.washington.edu/ega/more_papers/GPS_relativity.pdf)

  9. Myled
    November 18, 2014

    Bill, what's the need for individual GPS system for each nation. Recently China and India also launched some set of satellites for navigation as an alternate source for navigation system. 

  10. Myled
    November 18, 2014

    “What I meant was, GPS satellites have the information of each and every device like a central repository, unlike the IMU which is on its own then tracking such device becomes difficult.”

    Amrutah, yes you are right. GPS has the details of all tracking devices but at the receiving end it may not. 

  11. PCR
    November 18, 2014

    Yes indeed DaeJ, cost is a critical factor if it going to be market, and also time factor will have an impact in this. 

  12. amrutah
    November 18, 2014

    Its a more of political issue.  There are many reasons, important being

    – self-reliance.

    – security (military purposes).

    – along with this, there are other innovations that helps people in various other fields.

  13. amrutah
    November 18, 2014

    @Bill:  Thanks for the information and papers you shared.

        Since the IMU are independent, does this mean we are getting rid of this big error source?

  14. nasimson
    November 18, 2014

    Its heartening to see that there are now emerging alternates to GPS that would by-pass the limitations of GPS. However its not the better system that would gain dominance, its the better eco-system. GPS has built round it an entire ecosystem of very strong components & players. So at least in short term, any better system would not replace GPS much.

  15. ue2014
    November 19, 2014

    >>>>>>>>>>>> but the GPS receivers do not. No one knows who is receiving and using the GPS signal, nor where the receiver is, unless that receiver is also designed to have some sort of transponder/reporting function added. Therefore, you cannot track GPS receivers, in general.>>>>>>>>>

    I think this is a very vital point when it comes to Forces etc. Forces does use GPS system a lot and depends much on the data in their operations. 

  16. bjcoppa
    November 19, 2014

    Interconnection of more and more sensors is critical for effective IoT. GPS has a role in fitness monitoring which is expected to be big selling point for Apple iWatch. People wearing one will go jogging and want to track GPS metrics such as speed and distance and location traveled. Heart rate monitoring and weather sensors including temp and humidity will also be charted and integrated into common cloud data folder accessible from iPad and iPhone as well in ideal IoT world.

  17. Myled
    November 20, 2014

    “Its a more of political issue. There are many reasons, important being – self-reliance- security (military purposes) – along with this, there are other innovations that helps people in various other fields.”

    Amrutah, I hadn't found any military reason. Am a defence R&D person, working closely with Radar & Satellite designs/developments. 

  18. Myled
    November 20, 2014

    ” but the GPS receivers do not. No one knows who is receiving and using the GPS signal, nor where the receiver is, unless that receiver is also designed to have some sort of transponder/reporting function added. Therefore, you cannot track GPS receivers, in general”

    Ue2014, exactly and no requirement for that too.  Users can use it for tracking the path; they travelled with their GPS devices and no where its storing other than user devices.

  19. amrutah
    November 20, 2014

    @Myanalog

    No one will tell the exact military use, every country having a GPS of their own, have restricted disclosure about the military usage.

    However you can get the feelers while reading other sources.  You may want to read from other sources like

    http://www.claws.in/1274/strategic-significance-of-irnss-1c-launch-radhakrishna-rao.html

    en.wikipedia.org/wiki/Indian_Regional_Navigation_Satellite_System (Look at the references section for details, especially #3and #13)

     

  20. Myled
    November 24, 2014

    “No one will tell the exact military use, every country having a GPS of their own, have restricted disclosure about the military usage.”

    Amrutah, military uses are different and for sake of national security none of the countries are going to disclosure such fine details.

  21. Myled
    November 24, 2014

    “However you can get the feelers while reading other sources.  You may want to read from other sources like www.claws.in/1274/strategic-significance-of-irnss-1c-launch-radhakrishna-rao.html”

    Amruthah, thanks for this link. I think this article is specific to Indian context.

  22. amrutah
    November 24, 2014

    @Myanalog: Yes, this is just a specific example I took.  But the important point is countries with their own GPS systems prowess will have greater influence globally and thus the race.

        The interesting thing is, the 7 satellite constellation SPS (Standard Positioning System) has a rubidium based atomic clock.  I would really like to know how would this fare against the IMU based system.

  23. Myled
    November 25, 2014

    ” The interesting thing is, the 7 satellite constellation SPS (Standard Positioning System) has a rubidium based atomic clock.  I would really like to know how would this fare against the IMU based system.”

    Amrutah, recently I read that both India and China launched 7 sets of satellites for global position purpose. My question is, if all countries started launching 7 set of satellites, then it's going to be another war is space!!!!!!!! 

  24. amrutah
    November 25, 2014

    @Myanalog: I agree, that's the race that is happening, a dominance at global platform (but currently not war).

    US has a GPS which is 31 satellite constellation, GLONASS of Russia is a 24 satellite constellation, while China's is a 35 satellite constellation and India's is a 7 satellite constellation.  The more the number of satellites, the better coverage (positional coverage) of the globe. 

  25. Myled
    December 1, 2014

    ” I agree, that's the race that is happening, a dominance at global platform (but currently not war).”

    Amrutah, war means not weapon war; war with satellites and space objects. As a space engineer, I can say if countries are launching more satellites; then within a couple of years, we may face colloidal issues in space.

  26. Myled
    December 1, 2014

    “US has a GPS which is 31 satellite constellation, GLONASS of Russia is a 24 satellite constellation, while China's is a 35 satellite constellation and India's is a 7 satellite constellation.  The more the number of satellites, the better coverage (positional coverage) of the globe. “

    Amrutah, but recent statement from Indian space organization, if they are able to success in launching atleast 4 satellites; it can cover India fully.

  27. goafrit2
    December 2, 2014

    >> Both require similar feature sizes and necessary process equipment which can be re-purposed for one manufacturing line or the other. 

    It goes even beyond that. You can get one product and name them different things depending on the results fro qualifications. The good ones get sold for high dollars while the bad ones are sold cheaper. When you open them, there is no difference except that the error margin is higher.

  28. goafrit2
    December 2, 2014

    >> Navigation without GPS might require more external analog effort. In the short periods of time, performance and cost would be compared between vehicle with GPS and vehicle without GPS.

    The key part of this is that economic modelling will provide that the person will GPS will do better. There is no reason why that will not be the case. I do not even understand why that is debatable. Go to some developing world with no marks and see how difficult and frustrating it could be to travel

  29. goafrit2
    December 2, 2014

    >> Bill, what's the need for individual GPS system for each nation. Recently China and India also launched some set of satellites for navigation as an alternate source for navigation system

    Satellites are all part of the nexus of GPS. That India and China sent satellites to the space will not change the fact that. I guess they have satellites that can offer some services which will involve navigation.

  30. Myled
    December 3, 2014

    “Satellites are all part of the nexus of GPS. That India and China sent satellites to the space will not change the fact that. I guess they have satellites that can offer some services which will involve navigation.”

    Goafrit2, I referred to satellites meant in lue of GPS system. In other aspects like satellites for surveillance, communication, weather forecasting etc are very much needed.

  31. Davidled
    December 3, 2014

    A few country has its own Satellities. The autonomous military ground vehicle could be tracked and controlled by control room, while keeping human personnel out of harm's way. Frequency range and antenna configuration related to pattern shape of ground vehicle geometry, changes the performance of GPS making sure that data is received during an abnormal circumstances related to location. 

  32. fasmicro
    December 4, 2014

     I referred to satellites meant in lue of GPS system. In other aspects like satellites for surveillance, communication, weather forecasting etc are very much needed.

    That is noted – but I think very soon these satellites will be composites with them having more functionalities. With the roadmap in design Planet Labs is pioneering, this will be a commodity business soon.

  33. fasmicro
    December 4, 2014

    >> The autonomous military ground vehicle could be tracked and controlled by control room, while keeping human personnel out of harm's way.

    That is the expected result but it is looking like some warfares will require having men on harm's way. Think of the ISIS fight in Iraq where bombing from air seems not to have done much to stop the impacts.

  34. amrutah
    December 8, 2014

    Myanalog:  You may have read it correctly, for GPS to locate properly we need a min of 3 satellites.  Having additional satellites helps improve coverage.

  35. amrutah
    December 8, 2014

    “war means not weapon war; war with satellites and space objects”

    @My analog:  In future, that may be the case.  Already spying, hacking of data is already going on.  Very recently there were cases where a asian country's spacecraft was said to be on a spying mission and arrived near to some US or european satellite.  There were also rumors that the recent US-Boeing space plane that completed 2 years in space orbiting earth was on suspicious activity.

    io9.com/usafs-top-secret-x-37b-space-plane-lands-after-almost-2-1647851013.

      You never know what is in-store in future.

  36. Myled
    December 8, 2014

    “You may have read it correctly, for GPS to locate properly we need a min of 3 satellites.  Having additional satellites helps improve coverage.”

    Amrutah, thanks for the clarification. 

  37. Myled
    December 8, 2014

    “That is noted – but I think very soon these satellites will be composites with them having more functionalities. With the roadmap in design Planet Labs is pioneering, this will be a commodity business soon.”

    Fasmicro, may be difficult because of the number of transponders in each satellite. That's really a limitation.

  38. Myled
    December 8, 2014

    “A few country has its own Satellities. The autonomous military ground vehicle could be tracked and controlled by control room, while keeping human personnel out of harm's way. Frequency range and antenna configuration related to pattern shape of ground vehicle geometry, changes the performance of GPS making sure that data is received during an abnormal circumstances related to location. “

    Daej, thanks for this info. Since the tracking is happening with a bird-eye view, terrestrial blockings can be easily avoided.

  39. Myled
    December 21, 2014

    “In future, that may be the case.  Already spying, hacking of data is already going on.  Very recently there were cases where a asian country's spacecraft was said to be on a spying mission and arrived near to some US or european satellite.  There were also rumors that the recent US-Boeing space plane that completed 2 years in space orbiting earth was on suspicious activity.”

    Amrutah, I meant the same. Thanks for this interesting info.

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