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Comment by DavidSJ | Hacker News Reader

This may be an incredibly naive question, but is there any reason wireless communication isn't directional, to mitigate some of these interference and square of distance problems? You'd obviously need some lower-bandwidth isotropic mechanism to locate other devices, and then a number of heuristics to track and predict motion.

Perhaps this is already how these things work?

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the military has perfected phase array multi-target tracking technologies quite a long time ago :) There were similar movements in the consumer WiFi arena - that can be equated to hub-to-switch movement that happened in the wired Ethernet years ago - yet somehow it didn't pick up:

http://boingboing.net/2003/02/17/vivato-releases-pric.html

note especially nice thing about beam forming "which allows it to emit at very high, focused power, extending range without running afoul of FCC regs."

People have managed to achieve much greater ranges (like more than a kilometre) with 802.11 technology using "cantennas" -- directional antennas like what you're talking about.

While it's theoretically possible, I'm not sure whether this is practical for general use on a LAN. You'd probably have to have a wireless antenna poking out of your laptop, which you'd point at the access point. Seems a little bit inconvenient.

Pointing a big antenna is not how it would work.

You don't need to point the antenna at anything; you can use multiple antennas that steer the beam ("beamforming") in a desired direction. Link:

http://en.wikipedia.org/wiki/Smart_antenna

Basically you can have a "phased array" of N antennas (2 counts as an array, but you can think of a line of say N=8 antennas) that delay their broadcasts relative to each other in such a way that the N signals interfere constructively along some directions and destructively along other directions. This is because, from far away,

  cos(angle_from_line_of_antenna_array) = const*propagation_delay_between_antennas

Ah, clever! Thanks for the link.

While I'm not an expert in the field, the reason it's not used for standard WiFi networks is probably both that connections would drop out really frequently and that it doesn't scale well (or at all) to large numbers of clients. Directional (line of sight) wireless communication is used in situations where you don't want to or aren't able to lay cables, and have a one-to-one relationship (or one-to-many, as with satellite tv), though.

AFAIK beamforming is already used in 802.11n.

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