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Is it possible? How would it work?

Consider IEEE 802.11 (aka.Wi-Fi); for instance.
There's such an incredible amount of devices out there, measuring and reporting WLAN AP signal strength (RSSI, RCPI, mW, dBm); but I've never actually seen one that was capable of demonstrating any real sense of direction or spatial awareness.

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  • \$\begingroup\$ The fact that you have not seen something doesn't mean no product uses it. Beamforming and spatial multiplexing is used in some products. Also see en.wikipedia.org/wiki/Spatial_multiplexing and en.wikipedia.org/wiki/Beamforming \$\endgroup\$ – Bimpelrekkie Dec 8 '15 at 13:37
  • \$\begingroup\$ @FakeMoustache "The fact that you have not seen something doesn't mean..." This, I know.. Thanks for the links though. Pretty sure I'm just now hearing these terms for the first time.. \$\endgroup\$ – voices Dec 8 '15 at 17:10
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    \$\begingroup\$ 2-D direction finding for a narrowband signal is pretty straightforward conceptually. You put 3 or 4 antennas in a triangle or box arrangement. Measure the relative delay (somehow), do a little trig, and you get your heading. You can add radio-direction-finder (RDF) to your google search list. \$\endgroup\$ – mkeith Dec 8 '15 at 17:45
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WiFi antennas are naturally omni-directional and this means that they produce an even EM coverage to potential users in their localized area. An omni-directional field pattern means they cannot target "direction" like a radar does. On the other hand, if they used antenna diversity they could take a stab at it.

As regards distance (range), the amplitude of an RSSI signal does not inherently define the distance something is from the WiFi centre. For a start, a device's emitted RF power may not be precisely defined hence RSSI is just a received signal strength indicator.

RSSI does not permit the WiFi to tell the difference between something emitting 4 mW at a certain distance compared to something else emitting 1mW at a quarter of the distance. So how can the the WiFi measure range adequately?

Walls, windows, metal, water, people all modify the signal amplitude to a great extent. Signal attenuation, signal fading all make it really tricky to judge range.

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  • \$\begingroup\$ Very useful answer (+1). I just have a question for clarity, when you say "An omni-directional field pattern means they cannot target "direction like a radar does." Are you saying omni-directional antennas cannot be used for Angle of Arrival estimation ? \$\endgroup\$ – user127416 Oct 21 '16 at 14:10
  • \$\begingroup\$ @ElBazzi an omni-directional antenna has no idea what direction the transmission is coming from. In fact no antenna can know this - you can, with a single directional antenna make an estimate based on signal strength but that could be a weak signal in the "best direction" or a strong signal on a side-lobe - you'll get the same signal strength and therefore there is nothing inherent about any antenna that yields direction information. \$\endgroup\$ – Andy aka Oct 21 '16 at 14:21

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