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iainw: You can triangulate 802.11 devices in a similar manner to GPS. You need at least 3 access points to do it though. Signal attenuation due to distance is indestinguishable from signal attenuation due to physical barriers. To do it, you need fairly complicated software algorithms, and need to give them an awareness of the physical location - what sort of walls are where etc.
If you are looking to locate a device, another alternative is to use directional antenna and an appropriate search pattern to determine where the device is.
This generally falls in the too hard and not worth it basket for home use.
Ianw, don't think this would work for an 802.11 device. Whilst you could triangulate WIFI using a directive antenna, GPS does not use that method, it uses a time source. I don't think that a WIFI router generates the accurate time signal that would be needed to use a method similar to GPS.
Cheers Mike
AeroScout is the only vendor that calculates both RSSI and TDOA-based location, coming from the same tag signals. Unlike vendors who promote just one of these algorithms, AeroScout recognizes that each fills a specific need, and offers tags that can smoothly transition between the two. This means that AeroScout tags can roam seamlessly between environments and continue to be located, without switching frequencies or suffering a loss of accuracy.
Received Signal Strength Indication (RSSI): The RSSI algorithm compares the strength of Wi-Fi RFID signals to an expectation of that strength, in order to determine accurate positioning. RSSI is ideal for indoor asset tracking, where receivers (access points) are often already installed for data and/or voice services. RSSI is typically used in RTLS systems that utilize 2.4 GHz or 915 MHz.
Time Difference of Arrival (TDOA): The TDOA algorithm measures the time of arrival of a signal from multiple points, and compares those times of arrival to determine the accurate source of the signal. Because time of arrival is related in a linear manner with distance, the TDOA algorithm is ideal for asset tracking in wide open spaces such as outdoors or open indoor areas (hangars, manufacturing facilities, etc.) TDOA is typically used in RTLS systems that utilize 2.4 GHz or UWB.
rossmnz: just tidy up a bit.
Im sure you will find your cellphone eventually!!!
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