Wireless Triangulation…


A cool project i am working on at the moment involves figuring out where you are based on 802.11 wireless signals.  We have developed a Pocket PC application that has a background thread that sample WiFi signal strengths from visible Access Points (APs) then sends them to a XML Web Service to do the number crunching and it sends back location information. 


This number crunching could be done on the PPC device but since we know we will have the WiFi network … and we want to be playing nice smooth Video on the device at the same time we opted for a server based approach.  It also simplifies the updating of the data required to do the crunching as we don’t need to re-deploy to each PPC. 


I cant get into all the details of exactly how it does the calculation but it involves signal strengths from the APs, MAC addresses and having gathered a bunch of signal strength information in a data logging exercise.


This really brings about an interesting application for these types of networks.  They can be used for delivering information to the device in the normal manner of usage. whilst at the same time being used as a positioning system.  Here in Wellington we have a WiFi network called CafeNet that you can sign up for and covers much of the CBD.  One interesting application i thought of would be to have a web site that showed you where you were in the CBD, information on shops and services & places you can go and sit if you want to work and get the best WiFi reception.  Another idea might be to offer CafeNet users one off ‘gifts’ like a free coffee or something when they enter a location.  Someone goes to the site to find a place to work or have a meeting, they see a Starbucks is close by and get more precise location information about it … then Starbucks might entice them in by offering them a free coffee if they choose to dine there. 


The opportunities are endless really… and it is something i think we will see a lot more of in the coming years… location aware applications built on existing and no added cost infrastructure.  Very cool.

Comments (18)

  1. Chris says:

    Hi, my comp-sci honours thesis seems very similar. Basically I am rendering a 3D environment on the PDA using openGL ES. I will then be attempting to use Wi-Fi triangulation to compute positional information about the PDA. This positional information can then be used to move the camera in the virtual environment. However, I am having trouble getting the tiangulation working and would appreciate any advice or information you could give me. There seems to be a lack of information on the web about this technique.

    Many thanks

    Chris Robson

    (rbschr001@mail.uct.ac.za)

  2. Brian Davis says:

    Hello, I was wondering if you’ve had any luck with this. I am considering using this technique in a project with our school (Portland State University) robotics society. If you have a second I’d like to hear what kind of results you got. How accurate are you able to get? How many access points are you sampling?

    Thanks,

    Brian Davis (briand@pdx.edu)

  3. You may be interested:

    http://www.skyhookwireless.com – company that invented WiFi positioning System (WPS)

    http://www.loki.com – toolbar for IE and FF that uses WPS to provide you with lots of great location aware services

  4. PATA_Broux says:

    Hello, I’m investigating wifi triangulation too. I have the same kind of questions as Sergey. One more: do you use WMI to retrieve signal strength and SSIDs or another low level API? Thanks in advance for any piece of information you’ll agree to share, as Chris said there’s not nuch data available on the subject on the net.

  5. chjohn says:

    Hi PATA_Broux,

    We used some Windows APIs to get the signal dtrengths … however i believe this can be done with WMI more easily.

    Be aware that different WiFi cards give different signal strength readings and the frequency of those readings can also vary quite a lot depending on the card.

    Chris.

  6. I’m interested in robotics application of this, too… which really is dependent on the precision of this technique. You seem to be doing "RF Fingerprinting", you simply call it data logging. How precise were you able to get?

  7. chjohn says:

    Hi Paul,

    within about 2-4 meters.  however walls etc… caused a few false readings once in a while.

    Thanks,

    Chris.

  8. chjohn says:

    Hi Paul,

    within about 2-4 meters.  however walls etc… caused a few false readings once in a while.

    Thanks,

    Chris.

  9. drogers says:

    Hello, I’m looking at WiFi triangualtion as a means of tracking players real-time during a paintball (ok airsoft – but same idea) game. I am currently in the research stage and have found very little available software wise on the topic, although much conjecture and talk. (and one big company that wants business clients and money). I have acces to software developers who are willing to humour me, but i’d like to try to make their job easier. Is this a project you’d consider collaboration on? I’m hoping for an end result of having 3 or more access points (routers) in the field, enter in their distances from one another (possibly by holding a GPS next to it and entering the lat/log) and then using (for now) laptops in backpacks to return triangulation data based on signal strength back to a server that then shows locations graphically between the three "beacons" placed around the field. There are other programs that will locate, but they rely on communication with an outside server and don’t allow new ones to be entered. I used to program myself until a job change forced me to forget alot…. Hope you still get notifes for this topic!

  10. mo says:

    hi guys, i’m using wi fi triangulation to find a position of a pda..

    i’m planning of using 3 access points, but one of the problems facing me is that i dont know where to place the access points..

    their location with respect to each other (angel and distance)

  11. Pete says:

    Hi, I am taking a look into the same thing, at the moment i have been able to perform some measurements but i am not able to map anything solidly and i feel like i have hit a wall,

    if possible can you send me your notes/some info so i can see how other people are going about this.

    Thanks,

    My email is bigredpeter@hotmail.com

    Peter

  12. Ian Hand says:

    Hi i need a solution to find buses parked in a bus depot if each bus had a wireless AP on it do you think you be able to find its location using this triangulation method. If so does any one her want to come up with a solution for me. Paid of course

  13. Sam says:

    Apple have included this in their most recent updates, meaning you can now find you location on an ipod touch as well as an iphone. this resulted in programs like GPS tracker (also uses the wifi trangulation technique, but thats handled by the itouch) their website is

    http://www.instamapper.com

    so they may be worth getting in touch with, if not apple is your next best.

    Sam

  14. DennisPerot says:

    I am looking at starting an LLC to develop a product along these lines, patent it, and market it to potential clients.  This triangulation method has some very beneficial applications for some of the ideas mentioned above among others.  If anyone is interested in discussing this business plan, get in touch with me @ daperreault@gmail.com

  15. teh_spartan says:

    what about turning this sofwhere around useing it to pinpoint a person within a network ie. a hacker and using it to arrest the suspect within a building. or using it to keep track of employees in an office building.

    if you know of a program that does this than please email me

    the_spartan@firestormpcs.net

Skip to main content