Comments on: OpenBeacon: Active RFID Platform

By: wim

wim — Wed, 03 Oct 2007 20:32:15 +0000

bob clarke: who needs Intel’s support? OSHW works whether or not some dinosaur is interested in it or not.

By: Henryk PlÃ¶tz

Henryk PlÃ¶tz — Wed, 03 Oct 2007 13:58:53 +0000

CaptainQueeg: Generally, no. Especially not in the OpenBeacon project which is an active transmitter, with a microprocessor and all, and therefore has widely varying response times. (Though there are plans to build an OpenBeacon based radio frequency access control system with some protection against forwarding attacks by introducing some time boundaries into the challenge response protocol. 1ms should be possible. While this still is a long way with regards to the speed of light, it should foil forwarding attacks, because it generally would be hard to forward messages between the door and the tag with a bandwidth of 2 MBit/s and less than 1ms of forwarding delay.)

Even outside of OpenBeacon nobody really uses response time measurements. Which is of course due to the fact that most RFID solutions are passive and usually only have a range of 1cm, 10cm or 1m. (I think there were reports about experiments in a Czech airport which included RFID boarding passes based on an UHF backscatter system with ranges on the order of 50m.)

There are papers about RFID distance bounding protocols, which by acurately measuring the response time with very high precision can physically guarantee that the tag is within some preset distance (e.g. 30m) of the reader. See for example Gerhard Hancke, Markus Kuhn, "An RFID Distance Bounding Protocol", 2005. I'm not aware of any actual implementations of that though. (Needs specialized tag hardware.)

--
Henryk PlÃ¶tz
GrÃ¼Ãe aus Berlin

By: bob clarke

bob clarke — Tue, 02 Oct 2007 17:56:37 +0000

Will Intel support open hardware project? It is a big time oss fun, but oshw? Let wait an see.

By: Bruno

Bruno — Tue, 02 Oct 2007 07:07:33 +0000

This is just another way for “them” to find you… *puts on tinfoil hat*

By: alex mccown

alex mccown — Tue, 02 Oct 2007 03:38:25 +0000

i got an rfid tag about 4 weeks ago i got a parallax reader and use it to log in to my comp

By: CaliRaisin

CaliRaisin — Tue, 02 Oct 2007 00:18:18 +0000

apparently what was done is the device (tag) transmits at four different power levels, and the packet loss per power level at each base station is used to approximate the distance. with enough base stations placed at strategic points, the position of the person can be estimated. (got this from the presentation papers under the downloads section).

very nifty :)

By: Phelps

Phelps — Mon, 01 Oct 2007 22:30:01 +0000

This is likely based on RSSI readings, a measurement of signal strength. It would be possible to determine an approximate relative distance with multiple stationary base stations in a known geometry.

By: captainqueeg

captainqueeg — Mon, 01 Oct 2007 22:06:27 +0000

Well, if light goes at 3×10**8m/s, and if you can sample at 2×10**9/sec, it works out to .15 meters/cycle, or about 5″.

The reason I asked is that I don’t know how consistent ping reply times are, or how small a time slice a receiver can realistically measure. What I’m wondering how accurate position triangulation from multiple rfid transponders could be.

By: davr

davr — Mon, 01 Oct 2007 20:33:42 +0000

Use RFID ping times to measure distance? doesn’t the R in rfid stand for Radio? as in, radio waves, transmitted at the speed of light? thus, 1 ms difference in ping times would be equivalent to 186 miles difference in distance…

By: CaptainQueeg

CaptainQueeg — Mon, 01 Oct 2007 18:53:16 +0000

A question for you RFID’ers out there….

Are RFID ping response times consistent enough to use the total round trip time of a ping and reply as a measure of distance, good to an inch or so?