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Forget GPS, Hello WPS

Posted by timothy on Tue Jun 21, 2005 10:51 PM
from the ded-reckoning dept.
Wireless Networking Hardware Science Technology
No France writes "A company known as skyhook wireless has announced the commercial availability of its Wi-Fi Positioning System, or WPS. The company has compiled a database of every wireless access point it can find in a given city. When a mobile user running th Skyhook client is in a recorded area, their position is calculated by selecting the surrounding signals and comparing them to the reference database. Currently there are 25 US cities mapped, including New York City, Boston, Chicago, Los Angeles and San Francisco. Apparently this device is accurate to within 20-40 meters, though one has to wonder how well it deals with people moving their wireless access points."
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  • Too Simple (Score:5, Funny)

    by nxtr (813179) on Tuesday June 21 2005, @10:53PM (#12878442)
    They might as well give everybody a peice of paper with a huge X on it that says 'You are here'.

  • 20 - 40 meters? (Score:3, Insightful)

    by Anonymous Coward on Tuesday June 21 2005, @10:54PM (#12878452)
    20 - 40 meters? Who will be forgetting GPS with that kind of crappy accuracy?

  • Been there, done that! (Score:5, Informative)

    by wintahmoot (17043) on Tuesday June 21 2005, @10:55PM (#12878460) Homepage
    PlaceLab [placelab.org] has been doing this for a while, and it's free.

    • Re:Been there, done that! (Score:5, Interesting)

      by Myself (57572) on Tuesday June 21 2005, @11:38PM (#12878629) Journal
      Strange how the world turns, I just mentioned PlaceLab to a friend before loading Slashdot. Spooky!

      PlaceLab's big advantage is the ability to use multiple sources. Wardriving data is just one potential input. If you have a GPS receiver and a wi-fi card and a CDMA phone all connected, it'll use whichever is giving the most trustworthy results. So you can move smoothly between urban, rural, and indoor environments.

      What absolutely makes me giggle is this: "Morgan adds that GPS typically only locates things within a few hundred meters, whereas the Wi-Fi location system can get within 20 to 40 meters of an object."

      • Re:Been there, done that! (Score:5, Informative)

        by suineg (647189) on Wednesday June 22 2005, @12:15AM (#12878752)
        Well think about the fact that you pretty much need to be within 20 to 40 meters of an AP to even pick the signal up then it would make absolute sense.
        • But the original wardriving that put the APs into the PlaceLab database was using GPS as a reference.

          I see what you're saying though, that a moving GPS on a single wardrive will have some error based on atmospheric effects, but repeated resurveys of an area on different days would tend to average these out, similar to the long-term averaging of a stationary GPS receiver.

          My point was that the spokesdude in the article is either misquoted or misinformed about the accuracy of GPS, and that the neither Skyhoo

    • Ekahau did this as well, but better. (Score:4, Informative)

      by spiff42 (718678) <sd@@@symlink...dk> on Wednesday June 22 2005, @02:55AM (#12879158) Homepage
      I have been working with a commercial localization system called Ehahau Positioning Engine [ekahau.com] which we have acquired a license for at the Technical University of Denmark. This system uses the signal strengths of available access points to determine the position. The client is a piece of software running either on a laptop or PDA (they also have some nifty tags that can be used).

      The client software running on the tracked device measures the signal strength of the access points, forwards the data to the server which calculates the position. The big-brother scenario is avoided as long as you still have to install the client yourself.

      The major drawback of the system is that it needs extensive calibration, since they are using not only the available access points, but also the signal strength of these. Normally they suggest calibration in a 5x5m (15x15ft) grid. More calibration points yield a more accurate result.

      And now the piece of information you have all been waiting for: accuracy. With a good calibration this can yield accuracies of arround 1m. In my tests (indoor) the accuracies fluctuate a bit, but is at least better than 3m 95% of the time.

      Just as the system described in the original post, Ekahau requires no extra hardware (we already have 2-300 APs on campus).

      /Spiff

  • What a joke... (Score:5, Funny)

    by nemostultae (524156) on Tuesday June 21 2005, @10:57PM (#12878466) Homepage
    Apparently this device is accurate to within 20-40 meters

    Hell, I can guess where I am to that accuracy. I thought GPSs where accurate within 5-8 meters nowadays. And this sounds really useful out in the open ocean, you know, where all those rouge wireless access points hang out.

    • Re:What a joke... (Score:5, Informative)

      by Bogwood (855051) on Wednesday June 22 2005, @01:19AM (#12878932)
      But vanilla GPS just isn't accurate in urban canyons. In London's docklands area (high buildings) GPS gives accuracy in the 200 to 400m region due to multipath effects. As well as obscuring satellites, tall buildings cause reflections of GPS signals which can cause large errors in the pseudo-range calculations making accurate position reporting very difficult. Places like NYC or Chicago are useless for GPS.

      I would imagine that supplementing GPS with other position determining mechanisms (like WiFi) could be beneficial in these circumstances.

        • GPS SA off since may 1, 2000 (Score:4, Informative)

          by slew (2918) on Tuesday June 21 2005, @11:23PM (#12878582)
          GPS selective availability has been turned off since May 1st 2000..Here's some more information [kwarc.org].

          Basically, the military figured out how to easily jam GPS in an area. But before then, there were GPS field units available that averaged out the error and got better than 2-3 meters so that it didn't really matter that much...

        • Re:What a joke... (Score:5, Informative)

          by Andy Dodd (701) <atd7 AT cornell DOT edu> on Wednesday June 22 2005, @12:11AM (#12878741) Homepage
          Sub-5-meter accuracy: As another poster pointed out, SA was turned off a while ago. Pretty much any GPS unit will be accurate to within 5 meters if it has a decent signal. With tricks like code smoothing, most errors are probably less than 3-4 meters even for a moving receiver.

          Sub-meter accuracy: A little bit of position averaging + basic DGPS makes this easy for a stationary receiver, even when SA was on DGPS could cure the intentionally added errors. Very difficult to use with a moving receiver unless combined with an inertial navigation system. (Rare except in modern airplane navigational systems)

          Millimeter accuracy: Also possible before SA was turned off, but required the receiver to be stationary for a long period of time, and required significant postprocessing of the data using a variant of DGPS. It still requires stationary receivers for nonmilitary systems.

          About the only thing that can't be done without a method for decrypting the P code is sub-centimeter positioning of a moving object. Even with the P code available it can't be done without combining a high-grade inertial navigation system with the GPS system.
  • 20 to 40 meters of accuracy? I work with various grades of GPS and even with low accuracy gps I can get within 10 feet no problem. I mapped wireless access points before and they really turn out to be VERY inaccurate overall.

    Oh well maybe some fun could be had, like PHYSICAL address spoofing.
    • 20 to 40 meters of accuracy? I work with various grades of GPS and even with low accuracy gps I can get within 10 feet no problem.

      My FAVORITE kind of slashdot post to respond to is this one. It's a combination of "I'm missing the point entirely" AND "I think I'm a lot smarter than I am." All rolled up into four little sentences.

      WHY IS WPS USEFUL: Because there are a lot of urban areas where you can't get GPS signals for shit. Try New York City, for one--you're lucky if you can get two or three satell

  • Dynamic data would be better (Score:3, Insightful)

    by photon317 (208409) on Tuesday June 21 2005, @10:59PM (#12878480)

    Rather than trying to maintain a static database of AP locations and signal strengths, they should just put some live wifi nodes out there with real GPS on them and track the AP map in realtime as it shifts. Or they could give free service to a select small percentage of customers in return for attaching a GPS device and helping recalibrate the map with some background software once a month or something.
  • Forget GPS

    Weeeeeee! This mean we can nuke the GPS stationary satellites now? ''Shut 'em down guys!''
    • It's probably not well known, but there have been effectively "GPS stationary satellites" in operation in major cities for quite a long time called WAAS. Basically WAAS (or Wide Area Augmentation System) has about 25 stationary ground system that correct for GPS signals with a signal that's compatible with GPS broadcasts. Originally designed by the FAA, it's really helpful for GPS car navigation systems...

      Read more at this site [garmin.com]...

      Sometimes reality is better than you know... ;^)

  • I honestly would expect it to be even worse.
    If this determines position by signal strength wouldn't it then be dependent on the type of antenna you were using with your WiFi card? Sometimes my signal moves around even in the same position or drops significantly lower in "dead spots". What if I'm using one of those crazy Pringles can antennas?

    "Hey! 100% signal here, I'm here, over there and...yep, that a ways too!"

    Anyhow, what an awesome idea, I mean, it's not like we have anything like this in exist

    • I'm thinking, worse than my wireless cards strength, what about that of the AP's around me? Wouldn't this have to work by triangulation, assuming all AP's broadcast with the same strength?
  • though one has to wonder how well it deals with people moving their wireless access points.

    And thats exactly what it will not catch on. No company in their right mind would make products that counted on devices that aren't guarenteed to not be moved. Although it might work if the WiFi APs received GPS data and then acted as base stations to enhance the resolution of your GPS device. What I'd really like to see if GPS that worked in buildings and underground.

  • Interesting. . . . (Score:5, Insightful)

    by Bagheera (71311) on Tuesday June 21 2005, @11:22PM (#12878575) Homepage Journal
    . . . but I suspect ultimately of little practical value. Having done quite a bit of RF scanning on the WiFi bands in one of their listed cities (San Francisco) I've seen first hand how signals behave in that dense urban environment.

    GPS and WAAS operate on time signals and highly accurate positioning. Cell towers would be inherently more accurate since thier positions are accurately known and don't change (except under very unusual circumstances.

    WiFi nodes come up and down constantly, and their position is rarely going to be accurately known by anyone but the person who installed it - and chances are they're not telling "you" exactly where the node is.

    Given "walk around surveying" to map the nodes, it's not really a surprise they have accuracy that's no better than an early 2 channel GPS receiver.

    And, as others have pointed out, if I'm in downtown San Francisco (or any other city) I don't need my GPS to tell me I'm at 5th and Townsend. For directions there's Mapquest, Google, Yahoo Maps, etc...

    Interesting technology. But it sounds more like something a hobbiest would come up with than business.

  • 20-40 meters? (Score:5, Interesting)

    by Jurisenpai (261790) on Tuesday June 21 2005, @11:25PM (#12878586) Homepage
    Don't these people realize how accurate GPS positioning has become?

    MGIS-grade equipment [trimble.com] can now give positions with sub-foot ( 30cm) postprocessed accuracy. Survey-grade equipment can get within 5-10 cm.

    As neat as WPS sounds, I don't think that anyone will be giving up GPS soon if WPS can't get any more accurate than 20-40 meters.
    • As neat as WPS sounds, I don't think that anyone will be giving up GPS soon if WPS can't get any more accurate than 20-40 meters.
      That was my first thought. 20-40 metres isn't even good enough for street navigation. What is it good for, telling you which wireless cafe you're sitting in?
    • Actually survey-grade equipment can give real-time positions within about 1cm via RTK GPS.
    • Yeah, but most GPS equipment of that grade falls into the "If you have to ask how much it costs, you can't afford it" price range.

      The system I work with can do sub-meter, sub centimeter with post-process. It retails for ~$40,000 plus a couple thou for a DGPS subscription and a few hundred to a couple thou for the DMI (odometer) equipment. And its precision falls off sharply (to as bad as 5 meters) in metropolitan areas where you get the GPS signal getting blocked by and bouncing off of tall buildings.

      My
      • I'm not sure what kind of system you're working with (or how old), but the system I linked to above is *very* roughly $3500. The software would add another $1500. So for about $5000, you have submeter accuracy. Multipath is still a problem, yes, but there have been great advances in solving that, too.

        GPS has come down in price incredibly in the last few years. You don't even need a subscription to a DGPS service anymore.
    • I wish there were an open source DGPS project out there.

      The premise seems simple enough: Have one GPS at a fixed position, and the other receives corrections via radio.

      But I haven't been able to find anything.

      My house sits on a large lot (over an acre) and I've wanted to survey it fairly accurately (within a foot at least) to recreate it digitally and be able to plan shops, gardens, landscaping, etc.

          • I hadn't looked into this for a while, and it looks like some work has been done on it.

            Several open source programs / projects are listed here [edu-observatory.org].

            I haven't tried whether they work the way I want them to, or whether they provide the accuracy I crave... :}

  • I'm currently surrounded by the SSIDs, "linksys" and "default". Can someone tell me where I am?
  • 20-40 meters? try to navigate on that.

    Not to mention the tons of other problems such as access points moving and disappearing and the inharently weak signal makes wps less reliable under minor amounts of interference.

    it's a neat trick for someone who has nothing better to do but with as advanced as gps is and the ability to track via cellphone I don't see this having any real market.

  • Not useful for typical GPS uses, but... (Score:4, Interesting)

    by SnprBoB86 (576143) on Wednesday June 22 2005, @12:07AM (#12878730) Homepage
    20-40 ft? This is totally useless for street navigation, surveying, etc.

    What this is useful for is grander scale positioning without the need for a GPS device built into a portable device.

    For example, timezones are far larger than 20-40ft. Laptops could be configured to automatically adjust the timezone setting to match the closest access points, no GPS device needed. A weather monitor utility could always automatically show the local weather. A star map could be configured to show the local sky. I'm sure many people can think of others.

  • What about RPS? (Score:4, Interesting)

    by scorp1us (235526) on Wednesday June 22 2005, @08:28AM (#12880207) Journal
    Can't you triangulate from FM radio station signal strength?

    It woud have the following advangates:
    Way smaller database
    Way more coverage

    It should be easy to do with the adevnt of software radio.

    The only down side, is that you wouldn't need this company anymore!
    • A human being may not need GPS to figure out where he is in a city(*), but it's definitely useful for automated navigation systems. It's nice to be able to press a button and have a friendly voice guide you back to the freeway.

      (* though that's debatable - what if you're in an unfamiliar area, and it's the middle of the night so you can't find anyone to ask?)
      • It's nice to be able to press a button and have a friendly voice guide you back to the freeway.

        Until somebody unplugs their AP and the friendly voice tells you the freeway has gone missing.

        Really though, it's not like a GPS receiver is going to cost any more than an "WPS" receiver. Even dirt cheap GPS receivers are accurate withing about 10-15 feet, all day, every day.

    • Re:but there's really no point! (Score:5, Interesting)

      by JanneM (7445) on Tuesday June 21 2005, @11:03PM (#12878504) Homepage
      Cities are the one place a positioning system is useless, so why develop it there?

      You haven't tried to find a specific place in Tokyo or Osaka, have you?

      Having a Gps is a life saver. You look up the place you want to go to on an online map, get the coordinates, and you're set. Without it, it's just too easy to miss the right building, mistake streets for each other or get lost in many other creative ways.

      You could argue the other way round (and just as stupidly) - since there's one single highway or road in the entire area, why would you need a Gps to know which one you're on?
        • Road naming is non-existant outside major thouroughfares; it works more by an irregular grid numbering system of blocks, not the roads in between them. House numbering is similarly vague, with no guarantee that house number 2 will be beside number 3 or 4. Block nameplates are usually pretty small and not in easy-to-predict places very often; GPS, even for pedestrians, is very useful in Japan. Even the taxi drivers haven't a clue where most places are!
        • u do have a road map in teh car dont u?

          I'll get a road map in my car the moment I get a car. I'll put it right next to my dictionary.

    • GPS is useful in the city... if you want your computer to know where you are. Imagine being able to broadcast "I am [here]" to your friends (and have them reciprocate) so that your computer tells you when you happen to be in the same place and you can meet.

      Imagine being able to enter meetings in your PIM software by saying to someone "Let's meet here tomorrow at five" and having the computer know where "here" is (it would also know who you're talking to, using facial recognition, but that's a different to
      • Actually, this is right along the lines of what I was going to suggest. For me, I'm horrible at remembering appointments and other such tasks. Sure, I can set up reminders and what not to remind me at 5:00 that I'm meeting a friend after work, but what about stopping at the bank on my way to the groccery store. Can't tell you how many times I've forgotten to make that stop. So a *PS-enabled system to remind me to turn left at the light and go to the bank instead of right to the groccery store would be ve

    • Re:Oh man. (Score:5, Insightful)

      by nmb3000 (741169) <nmb3000@that-google-mail-site.com> on Tuesday June 21 2005, @11:40PM (#12878636) Homepage Journal
      To be honest, I don't care how novel their ideas are. Using a system where position is located based on such arbitrary measurements is not only silly, but a waste of time. Not only can anyone move the access points around, but as they get shut off or more get added it will only make things worse. Also considering it can be influenced by minute things like weather and the position of the microwave in the apartment across the street make it a waste of time. You'd need to rescan it at least monthly to maintain even 20-40 feet (screw that) accuracy.

      Let's see, a near-absolute positioning system based on immobile and unchanging (or extremely slowly) data, or something based on what could probably be described as a chaotic system? Not to be a jerk about it, but "Forget GPS"? More like "Ignore WPS".

      • Re:Oh man. (Score:4, Insightful)

        by andy jenkins (874421) on Wednesday June 22 2005, @12:26AM (#12878787)

        Yes, but my iPaq has Wi-Fi not GPS. And the screen can show a good map.

        I could ensure I'm always carrying a GPS reciever or just a city map but you know what, I own both these and only carry them when I know I need them. Which in the case of GPS, is never.

      • Now the real question is, how often do access points get moved or shutdown?

    • Assuming people don't get swap-happy and trade access points all over the place, the reliability should be very high, too.

      Well, that would be an issue, wouldn't it? And, unlike, say, a system you own, other folks own and control these datapoints that your system depends on.

      I have to say that I regularly reconfigure my WAP becasuse, well, it's mine, and I chose to use it like a toy. I notice that a great many of my neighbors have WAPs of their own, but, not so surprisingly, I find that everytime I look

    • Re:Karma whore (Score:5, Funny)

      by nametaken (610866) on Tuesday June 21 2005, @11:54PM (#12878677)

      I'm worried less about privacy, and more about how I'm going to tape my wireless access point to my roomba just to mess with them.

      But then, with such poor accuracy, it's not like anyone will be worried about 40 or 50 feet here and there.

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