Office Surveillance: Locating And Tracking 802.11b

securitas writes "The NY Times recently ran an article about locating and tracking users of 802.11b WiFi networks in three dimensions using triangulation (Google) with multiple base stations. The goal is to create context-aware networks that can allocate bandwidth and provide location-based services such as uploading relevant information to a PDA. The article can be seen in a new light when coupled with the growth in workplace surveillance of employees by corporate executives (Google / short version at IHT) and the associated practical, ethical and legal problems. Interlink Networks 802.11 wireless detection and tracking white paper (PDF)." (This seems as good a place as any to mention Kensington's handheld 802.11 detector; they claim it to be the only such device on the market today. This is the cheapest detector I've seen; have the others all disappeared?)

Comments

Cheapest tracking? Echelon!!

[jkrise]

I thought that was obvious??

-

Re:Cheapest tracking? Echelon!!

[SEWilco]

But getting the results is awkward. Their ventilation ducts are not large enough for the crowd in there.

Hmmm...

[Kai_MH]

I think Radio Detectors work fairly well, too, but they don't tell you whether it's 802.11x or not, so I guess that is pretty good.

Kensington WiFi detector

[Rosco P. Coltrane]

Features and Benefits

The only WiFi detector on the market today

Completely hassle free -- no more booting up your notebook to find a WiFi signal

Instantly detects WiFi networks with the press of a button

Three lights indicate signal strength


Messrs Kensington, could you make a version that

1) doesn't require me to push a button to detect WiFi networks (i.e. works continuously)
2) has a connector for an external antenna and an optional car lighter plug to power it
3) has a 4th led to indicate if the network uses encryption or not ?

I believe such a device would sell very much better. Thank you.

Re:Kensington WiFi detector

[pv2b]

And an LCD display showing ESSID's...

Re:Kensington WiFi detector

[pldms]

Does anyone know where I can get one of these in the UK?

Re:Kensington WiFi detector

[JamesP]

I have another couple of requirements too:

1) doesn't require a computer to access web pages
2) has lots of internal memory and automatically download all my MP3
3) Connects to slashdot and checks any new articles
4) if it's encrypted, automatically tries to infiltrate itselt
5) costs less than $10

thank you...

Re:Kensington WiFi detector

[Drakonian]

Don't forget that it has to play Ogg or I'm not buying!

Re:Kensington WiFi detector

[senducemhere]

Imagine a Beowulf cluster of these!

Re:Kensington WiFi detector

[kikta]

I just bought one at my local Best Buy yesterday. When you push the button, it actually works for 2 minutes, before powering itself off.

Heh

[bazik]

Do I see Google links in that article? ;)

hmmm

[Anonymous Coward]

Seems to me, it's the minor noblemen^W^H^WCorporate Executives who need greater scrutiny.

Demand Reciprocal Transparency!

How well does this work in indoor environments?

[pv2b]

The signal gets weaker as it passes through walls. Therefore, the signal strength can not be easilly be correlated to a distance from the base station for purposes of triangulation.

Triangulation traditionally relies on measuring distance through signal strengths and so is limited to an outdoor environment, where the signal loss per kilometer can be predicted with much greater accuracy than in an indoor environment.

The article is short on technical details -- did they somehow also enter a 3D-model of how the building weakens radio signals, and use that in order to create three 3D-shapes at the point of intersection the transmitter can be located? Just like traditional triangulation, but with weirder shapes than simple spheres...

Perhaps a better way would be to use "ping" to check the travel times, rather than the signal strength, compensating for any delays imposed by TCP/IP-stacks and hardware etc. Is this even possible, or is the Signal/Noise ratio just too low?

Re:How well does this work in indoor environments?

[Rosco P. Coltrane]

Triangulation traditionally relies on measuring distance through signal strengths and so is limited to an outdoor environment, where the signal loss per kilometer can be predicted with much greater accuracy than in an indoor environment.

Where did you get that ?

Triangulation works by being in 2 or 3 different locations, determining what direction the signal comes from with a directional antenna at each location, then drawing the lines on a map and see where they intersect. It'a called triangulation because it draws a triangle on the map. It has nothing to do with signal stength.

Re:How well does this work in indoor environments?

[pv2b]

Then the slashdot article is also wrong.

There is no way for the base station to know what direction the signal is coming from, since the antenna is omnidirectional, so I assumed it was using SNR's.

I was under impression that the word triangulation could be used for both techniques, both using directional antennas, and by determining the distance to the receiver from several points and checking where circles intersect.

Re:How well does this work in indoor environments?

[pv2b]

Parent post is a troll, getting moderators on crack to mod me down. (This claim is just as substantiated as the one in the parent post.)

Except, I invite any moderators to take a look at page 13 of the PDF file and note that they seem to be using the exact same method of positioning (signal strength) as I assumed in my grandparent post.

Granted, the word triangulation may be incorrect, but it's also the word the slashdot writeup used.

Re:How well does this work in indoor environments?

[Anonymous Coward]

Almost.

TRIangulation works exactly as you say (except the tri means 3 measurements only). Multiangulation uses >3 measurements in the same way.

When you have ranges (i.e. distances as derived from signal attenuation), it's called lateration. Trilateration == 3 ranges. Multilateration == >3 ranges.

However, triangulation is commonly used when lateration is meant, just because people are more familiar with the term.

Re:How well does this work in indoor environments?

[pv2b]

Thanks for clearing that up. (Mod parent up.)

Re:How well does this work in indoor environments?

[tim.kerby]

Not always. It can work on direction or signal strength or combination of the two (especially in terms of radio aerials). For instance, lets say we are in open land with omnidirectional aerials. Direction cannot be known so we plot strength (equating approximate distance) on a graph. Where the circles overlap gives us an approximate position. This can be done with other aerial shapes and in three dimensions by working out the signal in every aera on the map. Imagine it as three circles with a gradient pattern strongest in the centre. The starting strength at the receiver determines where on the gradient we start and it gets lighter the further out by the law dealing with signal strength (such as the inverse square law). The darkest points on the map indicate potential locations.

Given direction only, we draw three lines from our APs. Where they cross is the predicted location

Re:How well does this work in indoor environments?

[Anonymous Coward]

Granted, the word triangulation may be incorrect,

Translation : Just because I'm wrong, that doesn't make me wrong.

Ah Slashdot, where anyone with a logon gets to be an "expert".

Re:How well does this work in indoor environments?

[mlush]

There is no way for the base station to know what direction the signal is coming from, since the antenna is omnidirectional, so I assumed it was using SNR's.

It would be possible to create a directional antenna using a tetrahedron of omnidirectionals and measuring the signal delay between them, I don't know if thats what they did though

Re:How well does this work in indoor environments?

[Anonymous Coward]

I was under impression

If you're under an impression, say so.

Stating things as fact (Triangulation traditionally relies on measuring distance through signal strengths) where you're just plain wrong makes you look like an idiot.

Re:How well does this work in indoor environments?

[eyegor]

and let's not forget the effect of multi-path in the equation. In some cases, multipath will improve the SNR, in others, it will reduce SNR. Simply using signal strenth is inadaquate. Using a set of directional antennas will work better, but then you have to have helpers or some very expensive phase detection equipment that will work for azimuth and elevation.

Re:How well does this work in indoor environments?

[Anonymous Coward]

Then the slashdot article is also wrong

Translation: Since everything I know comes from Slashdot, I accept everything in Slashdot articles as gospel. Ergo, if a Slashdot article says it, it is fact. Ergo, if I'm completely talking out of my ass, it's not my fault.

Re:How well does this work in indoor environments?

[Anonymous Coward]

RF travels at the speed of light, so measuring raw "ping" times between 802.11 access points isn't feasible with the simple hardware available today.

Re:How well does this work in indoor environments?

[Anonymous Coward]

In order to get a 3-D position, you would need at least 4 directional measurements. However, because it's directional, signal strength and interference would not be as much an issue as possible signal reflection (echoes).

If you use 5 points of reference, you would significantly reduce the error. (Like GPS satellites.)

Re:How well does this work in indoor environments?

[Mr. No Skills]

The requirements for this are:

1) knowing the strength of the transmitter. While 802.11b transmitters are allowed to be up to 100 mW in power. Not all work at the highest levels, and they can be set less than this to limit propagation of the signal (and a very good way to limit exposure of warchalking).

2) knowing the propagation characteristics of the signal wavelength. Different wavelengths are absorbed or bounced by different materials. The short wavelengths used by 802.11 don't penetrate or bounce much (and don't really go through reinforced concrete at all...). Lower frequencies (10 Meter and lower) travel around the world by bouncing off the atmosphere.

I think because of this, using signal strength for location is extremely difficult unless the transmitters are well known, and directional triangulation is probably the only reliable way of getting an accurate reading for this application.

Re:How well does this work in indoor environments?

[forged]

It has nothing to do with signal stength.

Actually, it has everything to do with signal strength. I believe that the poster of the comment to which you responded to, meant that indoors you can't just assume that the signal strength will diminish on a more or less linear scale (or whatever) with distance.

Take into account the thickness and materials of the floors and walls, the office furniture, the people inside packed lecture rooms, and you will understand what he meant. You cannot just assume that because signal from base station A is twice as strong as signal from base station B, that user is closer to B. It may be that there is some obstacle on the path to A weakening the signal, making it look loke user is several meters apart the triangulated position assumed from the signal strength alone.

Ideally the calculations should be done based on knowlege of how well Wifi signals transmits through various indoors obstacles, and with a detailed map of the premices. But I can't think of anyone in their right mind who would want to do that unless they had considerable resources.

Re:How well does this work in indoor environments?

[Darnit]

All the triangulation schemes I've seen are based on time, not power. Of course they were all in college design labs. The premise was that each tower would send out a "packet" and the object would send a "packet" back with the time delay of the internal circuitry accounted for. The tower would recieve this signal and the time difference between the send/recieve minus the internal circuitry delay would be the travel time. Divide that by 2 to get the one way time delay. This coupled with the speed of propogation would give a distance from the tower. If 2 towers are used and a known distance from each is found you will get 2 points in a 2D space. If 3 towers are used they you will get 1 point in a 2D space. Using another tower that is not in the same plane as the first 3 towers will give you 1 point in a 3D space.

I've seen the 2D location used for radio waves and I've seen the 3D location used with sound waves.

Re:How well does this work in indoor environments?

[Anonymous Coward]

"Directional Antennas" are typically antennas that work better in one given direction. By rotating such an antenna, and monitoring received signal strength, you can identify a direction. Thus the relationship between clean signal strength and DF.

There is an alternative method, where the "antenna" is actually an array, and you can derive the incoming signal direction by the signal phase at each antenna at some precise instant. This is the technique used by modern military DF equipment.

WAPs have neither of these antenna types. Assuming the standard 3-5" whip and multiple WAPs you would be able to work out relative distances by signal strength. It wouldn't be very accurate, however.

Another issue is that you'd have to have three WAPS with overlapping coverage on the same channel, which would slow your network to a crawl.

Re:How well does this work in indoor environments?

[tim.kerby]

I'm wondering if custom hardware would provide some benefit here. An access point pings the client (the client will only be connected to one AP at a time anyway). A number of 2.4 Ghz receivers then look for the return signal from the client when it acknowledges. As you say calibrated receivers must be used and we would likely have to be outdoors

This brings an interesting point. It is far easier for a client to locate itself if it knows where access points are by connecting to each in turn and using directional finding. It would be much harder to locate a client unless you can force it to drop one connection and connect to another location

Re:How well does this work in indoor environments?

[Mr. No Skills]

I can't see the original article (requires subscription), so I can't comment on the details. However, this was my thought also -- that what is being worked on is a new type of access point that uses it's diversity antenna (2 or more) to get a direction on the signal. You would also need to tell the access points their location, at least in relation to each other, to be able to interpret the location on an actual floor plan.

While only one access point "works" the card at a time, I think multiple can "see" it. When you have multiple access points on the same LAN, I believe you set the specific channel of the points so that they don't interfere with each other. Advanced features than allow you to pass control of specific clients from access point to access point as they roam around the WLAN (at least this was how it worked with Cisco Aironet equipment) much like a cell phne network. As the client signal got weak on one point, another point might say it has a stronger signal and take control of the client, with the client switching broadcast frequencies to match the new card.

If I'm right about this, its probably a "6 of 1" issue as to whether the client does the calculation or the network (access points) does the calculation.

Re:How well does this work in indoor environments?

[Mark Programmer]

did they somehow also enter a 3D-model of how the building weakens radio signals, and use that in order to create three 3D-shapes at the point of intersection the transmitter can be located?

This is just off the top of my head, but if you're referring to the Carnegie Mellon project, CMU has been working for several years to get 100% wi-fi coverage across the entire campus. This work includes a complete analysis of each room of each buildings' wireless signal strengths to all visible routers, to assure that there are no dead-zones. So your hypothesis has merit; it is possible that the researchers used this information to construct an interpolated map of signal strengths and can calculate indoor positions in this manner.

If this is the case, then I worry about the project when someone playing soccer in a hallway accidentally bumps a router...

Re:How well does this work in indoor environments?

[Anonymous Coward]

too bad access points don't come with doppler shift antenna arrays. if they did, a few base stations could approximate your position by use of triangulation.

important...

[johnraphone]

I hope these companies that are building a network like this also deploy a security system that will prevent outsiders. Unfortunately "Most computers are pretty" so someone has to execute a good solution.

Simpler solution

[stefanvt]

In the article they mention the use of this in a hospital to push patient information to a handheld the doctor is carrying when doing rounds.

Instead of triangulating (requiring more power) wouldn't it be simpler and possibly quicker to outfit each bed with e.g. a rfid tag?

This seems an overly complex solution to a, relatively, simple problem.

The rfid would also be a plus when the patient is being transfered in his bed (from his room to the or)

Re:Simpler solution

[mashx]

Yup, agreed, then the doctor/surgeon/nurse just needs to read the patient code, and retrieve the info from the server. Wherever they are.

But rather than the bed, why not just put it in the wrist tag that most patients wear now? Then you wouldn't get any mix ups in the nursery, or any problems when patients go walkabout.

Re:Simpler solution

[stefanvt]

Actually, I think you could do both.

I think the added security (beds switched between chambers) in a hospital setting is absolutely necessary.

When in doubt the tag on the patients wrist has precedence.

Re:Simpler solution

[espo812]

Wouldn't it be simpler and possibly easier to outfit each patient with an RFID tag? I mean - that way there would be no confusion if a patient switched beds. The hospital could track all patient information in a database keyed on this tag. Then when nurses/doctors/security walk up they can easily scan and get all the relevant personal information.

Even better is that the hospital could then sell this information to preferred buisness partners (such as Wal Mart). This will allow the hopsital an alternative source of revenue, and thus your hospital stay would be cheaper (it's the economy stupid.) And the next time you walk into a Wal Mart or some other affiliate store with a pharmacy, they can start filling your perscription so by the time you get to the pharmacist he can greet you by name and hand you your pills. This would virtually eliminate botched perscriptions and be good for the environment (no need for the doc to sign dead tree for a script.)

Isn't technology great?

Re:Simpler solution

[RevMike]

But if we wanted to travel to Mars in order to start the reactor, wouldn't we need to stick a really nasty tool in our noses in order to remove the tag?

Re:Simpler solution

[Mr. No Skills]

There is a whole market niche in medicine for location tracking, which includes beds, patients, and equipment. If seen products based on RF, and the RFID things are just starting to influence these products.

I've also seen products based on IR, where there are sensors along the ceilings and the IR transmitters are on the tops of devices to be tracked.

FDA Guidlines

A Vendor group here

One vendor's explanation here

Re:Simpler solution

[Anonymous Coward]

I want mine on my forehead, or in my right hand...NOT!

Re:Simpler solution

[Elvisisdead]

Nice, except for the fact that it would violate HIPPA. Then, the hospital and Wal-Mart could pass the Civil Monetary Penalties on to you (it's the economy, stupid).

"On the Market Today"

[michaelp99]

Doesn't "on the market today" mean you can actually buy it?

I checked several places (though didn't put much effort into it) and everyplace has 0 in stock...

Insert "truth in advertising" rant here

Re:"On the Market Today"

[naner42]

I bought mine yesterday at the local Best Buy and they had at least a dozen. There's probably not a huge demand for this in Indiana though...
The thing doesn't work all that well. You press the button, then for two minutes it scans. I was 10 feet away from my WAP and it didn't show a signal. 8 feet: full signal, 12 feet: full signal - all within line-of-sight. It's a fun toy for $30, but It'd not a very practical/reliable tool.
Although it is fun to walk around downtown holding this little credit-card looking thing and acting like you're searching for radioactive emmisions... People get nervous when you point it at them and yell "Ah ha! It's YOU!" especially when it's right in front of a Borders book store and it's lit up like a Christmas tree.

Re:-1 MORON

[pv2b]

A troll? Or just someone thinking too fast? Either way I'll bite.

They provide any information you put in it. You could conceivably put an RFID tag on the hospital bed that said "I AM BED NUMBER 37" and the RFID receiver would get this information and know where it was.

More fun to....

[Anonymous Coward]

Just run it without and security and see how long before someone destroys everything.

Pretty stupid approach

[dg1kjd]

This is a pretty stupid approach from the communications theory point of view. 802.11b frames contain a pretty long preamble in front of the packet header and data payload. This preamble (basically 11-bit barker sequences convolved with a prn-sequence) have excellent autocorrelation characteristics since they must be used for time and frequency syncronization at the RX station.
By cross correlating the received signal with the (known) barker sequence at all three base stations precision would be increased drastically as it would be possible to measure the actual time lag (->way) the signal took to the receiver.

Re:Pretty stupid approach

[pv2b]

Moderate parent up.

At risk of being moderated as redundant here, I'll just attempt to clarify this.

Finding positions through time measurements is much more practical in a wireless solution than using directional antennas, mostly since you don't want to get the packet loss incurred by using a rotating directional antenna, although it might look cool. :-)

Signal/Noise ratio measurements, that the people mentioned in the article is doing, is problematic becuase the unpredictable nature of radio wave signal weakening (I don't know the technical term), although they seem to have tackled that problem to some degree of accuracy.

However, the speed of light is constant never mind how weakened the signal is, making it an excellent way to determine distance from the base station. This is in essence what GPS does, and also why it needs to carry along precise atomic clocks.

Re:Pretty stupid approach

[elsegundo]

However, the speed of light is constant

Well, the speed of light is constant in a uniform medium, but that doesn't mean that the speed of light is the same in all media. So a signal passing through air will have a different speed than one traveling through concrete.

Re:Pretty stupid approach

[EvilBudMan]

--However, the speed of light is constant never mind how weakened the signal is, making it an excellent way to determine distance from the base station. This is in essence what GPS does, and also why it needs to carry along precise atomic clocks.--

I guess with the price of atomic clocks spirialing downward, these 802.11_ detectors should be common place in a couple of years.

Re:Pretty stupid approach

[PureFiction]

"By cross correlating the received signal with the (known) barker sequence at all three base stations"

Try doing that within the tolerances required to measure distance based on the propagation of radio waves.

The only systems that can do triangulation worth a shit are phased array / smart antenna technology, which can determine direction without using a moving highly directional antenna.

Re:Pretty stupid approach

[Anonymous Coward]

BTDTGTT
You won't need an directional antenna when measuring time - in fact, a directional antenna is counter-productive in that case. The spatial resolution basically hangs on your modulation frequency, and you'll need at least n+1 distinguishable base stations (with n as the number of spatial dimensions you want, the '+1' gives you a time reference). Apart from that, the major problem is that in a scattering-rich environment the strongest signal path is not always the shortest signal path (and in this case, there probably is no LOS path).

Practical applications of that are EOTD for GSM mobile phone location (which is quite crude, since it uses time markers that were originally intended for other tasks) and location based services for UMTS phones (where the WCDMA demodulation, depending on your receiver, can give you quite a good position accuracy, at least for outdoor use).

Bye
Markus

Slightly OT, but here's a nice OSS tool...

[pen]

AirTrafis a 100% passive packet sniffing tool for the wireless 802.11b networks. It captures and tracks all wireless activity in the coverage area, decodes packets, and maintains acquired information associated by access points, as well as detected individual wireless nodes. It dynamically detects any access points in the area, finds association between wireless clients and access points, and builds information table for each packet that is transmitted via the air. AirTraf is able to maintain packet count, byte information, related bandwidth, as well as signal strength of nodes.

Re:Slightly OT, but here's a nice OSS tool...

[Anonymous Coward]

Pretty much any e.m. receiver is not 100% passive at the hardware level - it WILL distort the electromagnetic field - has to, to div some energy out and thus pick up a signal. Remember also the radio engineer's rule: "every [resonant] receiver is also a transmitter".

While civilian-level tech generally doesn't give a crap, $SPOOK_AGENCY can and will detect your presence.

Re:-1 MORON

[c_g_hills]

Personally, I would give every tag a unique number, and store the pertinent information/references in a database somewhere. This is great for asset management! Especially in places where items have a tendancy to vanish, ie schools and libraries; just stick some detectors at all the entrances and you'll be able to track the tag's movement. Just make sure you dont put it in an obvious place, where its likely to be seen and removed :o)

Not that new...

[Anonymous Coward]

Positioning in office environments using WLAN really isn't that new. Microsoft did it in 2000 with the RADAR system (http://citeseer.nj.nec.com/bahl00radar.html), and loads of people have tried since.

There are two approaches to it:

1. Use signal strength to estimate range and then multilaterate. This usually does a poor job because you can't match distance reliably to signal strength because of wall attenuation etc. Also, most WLAN systems quantize the signal strength into a few bins. :-(

2. Pattern recognition. Have a calibration phase where you put the device in lots of positions around the office, measuring the signal strengths to various stations. Record all this. Then try to match what you're seeing to this database of strengths to localise yourself. Problem is, the radio environment changes VERY easily, so you need lots of points in calibration. Plus, if the environment changes, so do the signal strengths!

The best I've seen for a WLAN system achieved accuracy to about 2 metres. That used quite a few WLAN dase stations, too. And they had a fair error on that too - enough that you wouldn't be able to guarantee which office you're in...

Location indoors is a tricky business. It's an active research area. The best so far is based on ultrasonics (the Bat system at (www.uk.research.att.com/bat). UWB looks good too (www.ubisense.net).

This has been around for a while

[Jarit99]

The same discussion seems to be popping up every 6 months or so. Check out what companies such as Ekahau and BlueSoft are offering.

other wifi finder dissapeared...

[Anonymous Coward]

there used to be idetect, from www.idetect.co.sg.
based in singapore, i mailed them for prices, but they only had a product samples available, no real production was going on. now their site is down, have they dissapeared? their wifi finder was featured in wired magazine a few months back.

Real life example

[alanjstr]

This article on Computerworld talks about tracking down unauthorized access points.

The other detectors

[AndroidCat]

This is the cheapest detector I've seen; have the others all disappeared?

They were tracked and located.

well, duh! amateur radio ops do this all the time!

[Anonymous Coward]

= reinventing the wheel, move on

Erricsson does the same with GSM

[Peer]

Erricsson MPS allows for location aware services on GSM phones. I've seen a demo from a WAP (hehehe) site that showed your location on a map, but that was a few years ago. I haven't seen anything after that.

ERRICSSON'S MOBILE POSITIONING SYSTEM (MPS)

The Ericsson mobile positioning system (MPS) (to be delivered to the Taiwanese company) is a server based solution that allows positioning services to be introduced into any GSM network that has Ericsson switching systems. The system will work with any GSM standard radio network and all existing GSM phones. At the heart of the Ericsson MPS is the mobile location centre (MLC), a system that allows user applications to access position information for GSM phones. An application programming interface (API) will be available to allow the development of custom applications. The MLC also handles access security and protects subscriber privacy by allowing GSM users to choose whether or not their phones and other devices are tracked.

Re:Erricsson does the same with GSM

[gl4ss]

Yes this works fairly well, but i imagine it being rather heavy on the server side(at least in massive scale). And it's potential legal mess. Doesnt need anything from the gsm phone, iirc works by measuring round time from few gsmpoints,wouldnt work for 3d

Could this stop war-driving?

[KrunZ]

Could this be used to stop war-driving, by not letting anybody in that hadn't the right 2d/3d position (eg: inside the company)?
It would probably not stop sniffing, but possibly it could prevent a break-in?

Re:Could this stop war-driving?

[Anonymous Coward]

nothing will stop wardriving. wardriving has nothing to do with unauthorized network usage.

= a new security method?

[huntz0r]

It occurs to me that this system could seal a major hole in the concept of wireless security. As we all know, the biggest problem with trying to lock down a wireless network is that it's basically just a radio broadcast and anyone within range can easily tap into the signal (whether they can get anywhere from there is another matter, but theoretically it's always possible to crack through software guards). But if the triangulation worked well enough, then a system could be set up to, say, detect if a client is sitting on the ground in the alley next to the building, and if so shut off the connection to that client. Or it could be used to limit wireless access to only clients in certain offices or floors - no access for random people in the lobby, for instance.

Re:= a new security method?

[RevMike]

I was thinking the same thing, but with a public twist...

It is my opinion, which I know many share, that public hotspots are cheap enough that many businesses will soon provide free access as a loss leader. A potential problem is, however, that without a fee based subscription, there is substantial risk that free-loaders will use the internet access without using the services of the business.

As an example, I live withing 500 feet of a Starbucks. I have clear line-of-sight from my roof. With an appropriate antenna I can use the hotspot to tie my home network to the internet. The only thing stopping me now is that Starbucks charges $30 a month - and my cable modem is $50 a month - not enough savings for the trouble. But if Starbucks started offering it for free...

A system like this, implemented inexpensively, would allow the hotspot provider to insure that only people in their establishment could use the service.

Did anyone else read the subject and interpret ":=" as the PL/SQL assignment operator?

Re:= a new security method?

[Ummon]

If you get a tmobile phone then the hotspot is only $20 a month

Re:= a new security method?

[RiBread]

> Did anyone else read the subject and interpret ":=" as the PL/SQL assignment operator?

I read it as the Pascal assignment operator!

This is awesome!

[capt.Hij]

With this in place I just have to set up my laptop so that the network card turns on and off at the right times, and my boss can just sit in his office with that smug look thinking that I'm working my tail off while I'm sitting in the star bucks with my laptop working away.... Oh kr4p. Does Kensington sell an 802.11b emitter?

Re:This is awesome!

[SEWilco]

What is the meaning of this phrase "turn off"?
I know things can be turned on or turned around.

Re:This is awesome!

[Fesh]

It's kinda like a crash, except you choose to have it happen. Planned downtime, if you will.

Re:This is awesome!

[SEWilco]

Oh, so it's like when I "cardctl suspend" the WiFi card in my handheld when I get on a plane.

Great...

[deman1985]

Now my boss can track me down to the bathroom if I keep my PDA with me

Not that novel

[Anonymous Coward]

About 3 years ago, researchers at MSR created a system called RADAR, that tracks users based on RF signal strength. At around the same time, researchers at MIT created Cricket, which does the same thing, but with auxilliary hardware.

The novelty here is simply *tracking* users instead of letting users locate themselves, and then optionally telling everyone else where they are. That's what makes this story sexy (oooh, they can see where I am!) But, users are much more likely to adopt one of the above approaches to location.

Prices and usefulness

[v1]

Following the links, Kensington doesn't list an MSRP or sell it directly, but the other links indicated the "going rate" for the toy is $22.00, and I think that's well within budget for a computer toy.

It could really use an external antenna though. If it had this, (or if the unit itself exhibited some amount of directional reception?) then it would be much more useful to find the actual location (down to say, which building on the storefront) the hotspot was at. The closer bench gets the better connectivity!

Maybe someone will post a hack shortly that shows how to jurry-rig an antenna port on the little bugger. I'd also like to "me too" a previous post that suggested an external power connection. Just keep the puppy sitting on your dash whilst driving around town until the green lights start climbing up.

Was anyone able to spot where these could be bought at? (this really looks like something ThinkGeek would carry)

Re:Prices and usefulness

[naner42]

Best Buy carries them, but it seems like they may be selling quickly. They should be back in the computer department with all of the cheesy laptop accessories (ie. USB fans, lights, etc.). My local store had several but I've heard complaints that other stores sell out quickly.

Re:Prices and usefulness

[SEWilco]

Google for 33063 Kensington to find some retailers.

There also is a "where to buy" link on the Kensington site, but I don't know if that is for any product or a specific one.

i hope the concept of office surveillance...

[Anonymous Coward]

does not surprise anyone.

whereas before WiFi, a boss had to actually get up and ask around "have you seen Joe?" now he asks a computer by clicking on Joe's computer icon.

having worked in low-tech high surveillance offices before, I can tell you that this approach to managing people creates a really nasty environment. I can only imagine how much a high-tech high surveillance office would breed employee paranoia.

Re:i hope the concept of office surveillance...

[CharterTerminal]

Works both ways, of course. Think of a handheld detector from the Alien movies, displaying approaching coworkers instead of goo-spewing double-jawed monsters.

Ideally, you'd want to implant each coworker with their own RFID tag so that you could get identity as well as proximity information. How best to accomplish this is an exercise I leave to your own imagination.

Research Papers

[mrinal]

When searching for a suitable localization system for my robotics project, I found a few research papers which detail the methods used to determine the location of a wireless node to an accuracy of 1 meter. Here are the papers, and here is the site that contains both the papers.

Nope

[kikta]

Google only returns one site selling it, which list three retailers. All of them have 0 in stock. The link on the Kensington site is for all Kensington products & so far I haven't one that carries it.

Has anyone found a place that carries it? Someone mentioned Best Buy, but it's not on their website.

Re:Nope

[naner42]

I own one purchased from a retail location of Best Buy.

Re:Nope

[kikta]

Yeah, I guess I'll drive down there & have a look. Calling them is pointless. Our Best Buy seems hopelessly inept over the phone. :-)

Re:Nope

[arkane1234]

Not to cut on Best Buy employees.. well, I guess I am lol, but most employees that work at Best Buy can't really tell the difference between an Athlon and an Intel processor, much less an 802.11(alphabet soup) detector.

Re:Nope

[Anonymous Coward]

Just curious as to why you added me to your foes list. This is Trolling4Dollars posting incognito to avoid a mod bombing.

Re:Nope

[Anonymous Coward]

Because I'm an idiot who can't seem to pay attention to what he's clicking on. Check now. Better?

RF detectors

[stapedium]

What I need is a cellphone detector and short range directional jammer so I can keep people from getting calls during movies, lectures and exams.

Re:RF detectors

[Nukenbar2]

I believe that this has been thought of before. The problem is that there is too much liability in doing this because of the possibility of emergency calls. (i.e. the doctor doesn't know to get back to the hospital)

Re:RF detectors

[Anonymous Coward]

I remember reading several months ago that ritzy restaurants and other high-culture gathering places (typically in Asia and Europe) are installing/experimenting with "tactical interference" devices that make cell phones and pagers useless within the confines of the event. The problems they're running into are people like doctors not getting pages to save someone's life or Johnny's mom not showing up to the hospital after he got hit by a buick in the street.
And even if you did manage to find such a device portable enough for you to use on the street without looking like a Ghost Buster, the FCC would be all over your ass the second anyone found out about it. I forget the specifics, but there is legislation that prohibits the "jamming" of public/liscenced frequencies.

Re:RF detectors

[Anonymous Coward]

Then all you'll need is a cork. For when the FCC sends you to prison. You know, for your ass.

Cisco Wireless LAN Solution Engine

[Anonymous Coward]

I don't believe this is covered by an NDA, because it was presented to the "general public" at Cisco Networkers 2003 and certain questions could not be answered in this general session because the speaker said he didn't know who had an NDA or not (implying anything he presented was not covered). So...

The 2.5 version of the Cisco WLSE due out in the Fall timeframe is supposed to have rouge AP detection. You would import the floor plans of your building into the system and place the APs where they are installed. The APs would use a new protocol to report information up to the WLSE (using a WDM [Wireless Domain Manager I think]) to store all the info (the WLSE would pull the info from this device, which right now is a designated AP but is supposed to be moved up into switch and router code so that they could host the information). You can then display maps with "hot" spots indicating the true triangulated location of rouge APs.

Other features include the ability to do a FA (Facilities Analysis) by using a special mode that temporariy puts all APs on the same channel and at max power. You would then walk the premesis with a laptop and it would take readings. The WLSE then would automatically program all the APs with appropriate channel information, and power ratings, for the best coverage.

Another big feature is that if an AP were to die the WLSE would automagically program the surrounding APs to boost their power to cover the "hole" in coverage temporarily until the AP could be replaced.

Technology is also supposed to be integrated into the CCX equipment, which almost all other vendors have signed up for, so that you can get true RF bandwidth utilization. So, not only APs but wireless cards in laptops, handhelds, etc, will all participate in taking bandwidth readings (how much of the time is someone transmitting) to create a true reading. It may also be possible (this is just a guess on my part) to create "hot spot" projections on your imported maps, so that you are told where a lot of wireless users are congregated, prompting you to install additional APs and lower the power on them so that you create more "cells" that are smaller to handle the larger load.

All in all, some pretty neat technology.

Re:Cisco Wireless LAN Solution Engine

[Anonymous Coward]

The 2.5 version of the Cisco WLSE due out in the Fall timeframe is supposed to have rouge AP detection.

I don't get it -- why does it matter what color the access points are? And who would apply red makeup to electronic equipment anyway? (Are we trying to figure out if they're in promiscuous mode?)

I haven't seen this referenced...

[Bagheera]

One pertinant thing I noted in the article was the following:

As part of that work, Dr. Junglas modified a Wi-Fi network that operated in the business school's two buildings so that each of its many base stations had a radius of about 15 feet.

Emphasis mine. This is an insanely dense network of AP's! At over $100 a pop for a cheap one, it seems wildly impractical to simply use stock access points with software corelation to figure out where people are - assuming such density is required.

In a commercial deployment, AP's are going to be deployed in such a way as to give good coverage without costing too damn much. ie: as few AP's as will give adequate coverage for the site.

There are other solutions, of course. Using a phased array antenna (sorry, no cool rotating dish) to get a direction and using signal strength to approximate range (random attenuation in the site will have a large affect on accuracy) or using multiple antennas in fixed locations to triangulate a source location (the more vectors you can get, the more accurate your fix will be) Using signal timing between different AP's (time difference between arriving signals) is plausible, but would add considerably to the cost (current AP's aren't equipped with ultra accurate clocks and transmission times over the network aren't accurate enough for the purpose.)

Phased arrays for direction finding use precise measurements between antenna elements to get their accuracy. They effectively use a harmonic tone to determing the shift angle between antennas, and thus the relative direction to the source. Accurately placing and orienting the AP's would be vital.

Locating wireless source points isn't exceptionally hard, and could be rather useful. But accuracy costs. Existing AP's would give limited accuracy, so this study used lots of them. More acurate location capability on an AP would cost more.

Take your pick.

Re:I haven't seen this referenced...

[otee]

I built a real-time mapping system that dynamically displays user-locations (if they are connected to the wireless lan). Unfortunately, the resolution is fairly low (b/w 30 and 100+ feet depending). It essentially takes various parameters such as signal strength and AP name into account to discern location. Check out the map at: http://www.cmusky.org/map_usercentric.html

Re:I haven't seen this referenced...

[Bagheera]

Interesting site you have there. Especially interesting since one of my former cohorts was a CMU grad and one of our interns is about to head there for his Masters.

This seems veryt similar to the system described in the original thread. What are you using to get relative directions to the hosts?

Wrong Department

[OECD]

from the oh-really-mister-anderton dept.

I think that should be Mr. Anderson.

I'm sorry, it just bugged me.

Related Work

[Anonymous Coward]

There is work at UCSD being done to track students who have wireless devices to figure out if freinds are nearby etc. etc. using 802.11 signal as the signal source for triangulation:
http://activecampus.ucsd.edu/

Works on a pda, laptops, etc. etc.

Sorry...

[sean.peters]

You're wrong - or maybe missing the point.

The original poster answered his own question... there wouldn't in general be any way of knowing how the signal would attenuate in various directions, so measuring the signal strength wouldn't be a viable way of determining the DISTANCE to the transmitter. It's not just a matter of permanent structures affecting the signal... atmospherics, movable office furniture, etc, would all change the signal attenuation in unpredictable ways.

However, as someone else in the thread pointed out, you could rather easily determine the DIRECTION of the incoming signal, and using three (or more) directional receivers, draw three (or more) lines on a map to localize the transmitter.

Sean

Why buy a device when a laptop works great?

[SassyDave]

Just pick up a prism-based pcmcia card and download airfart.

Surveillance in the workplace?

[el_cabong]

I'm just as whiney as the next guy about Big Brother, but businesses monitoring their facilities for 802.11 traffic is not about Big Brother, it is about network security. What use is hardening your wired network if someone can put a $99.00 wireless access point on your network and open a gaping hole in your security. For this reason it seems prudent network security to monitor for these "rogue" wireless access points. We use a product called AirMagnet, which is an iPaq based, packet sniffer developed by the guy who developed NetXray (now known as Sniffer) to periodically survey the facilities for these rogue access points. We've have added a 4db gain directional antenna to really hone in on these access points. Another advantage of this product is that we can use it to ensure that our legitimate wireless access points are configured securely. It would be nice to have a distributed system to perform these surveys automagically, but the solutions I have seen (including AirMagnet's) are a bit cost prohibitive. Most people wouldn't consider packet sniffing, intrusion detection, and other wired network monitoring as "workplace surveillance", so why rail against 802.11 sniffing as another example of Big Brother's "workplace surveillance"? What you call surveillance in this example, I call basic network security.

Pattern recognition can work well

[reedsturtevant]

I've seen demos and installations of a commercial product that does decent indoor 802.11 location tracking. It uses a clever implementation of a pattern matching algorithm and gets _better_ results in a complicated environment.

It's called WiFi Watchdog from Newbury Networks in Boston and they've installed it at the Smithsonian Institution, at Dartmouth College, and some other places.

Travel times is much better, but...

[Ungrounded Lightning]

The signal gets weaker as it passes through walls. Therefore, the signal strength can not be easilly be correlated to a distance [...]

Perhaps a better way would be to use "ping" to check the travel times, rather than the signal strength, compensating for any delays imposed by TCP/IP-stacks and hardware etc. Is this even possible?

It's possible. But IMHO indoors the variability of the response time of the processor to the message will probably introduce far too much jitter for the result to be useful. Finding the right neighborhood, or even the right house, yes. Finding the right desk, no.

But I understand that some of the underlying net-discovery and scheduling protocols (where the cards are talking directly to each other and picking times to transmit) give you a much better measurement of transit time, which may be good enough for the purpose.

Perhaps someone with more intimate knowlege can fill us in.

= = = = =

Given a good measure of transit time, two base stations can construct a hyperboloid on which the mobile is located. (With uncertainty it's actually the space between two hyperboloids.) Add a third and you intersect two hyperboloids, giving you a curved line. Add a fourth and you've got it located to a single point (or two points if all four bases are in the same plane).

It's basically GPS or LORAN run backward (with an extra base station relative to LORAN to give you altitude, since you don't know you're "on the ocean's surface").

Next model

[DigiShaman]

Your getting ahead of yourself there buddy. Those features are for the NEXT years model. If your the only one on the market with a unique product, why out-inovate yourself out of potential profit?

Kensington lies!

[mazor]

Fluke Networks, makers of industrial test instruments, has two extremely powerful handheld wireless network analysis tools that make the Kensington ping detector look like a Fisher-Price telephone.

-mazor