Phased Array using 802.11b

A phased array is a system for focusing and triangulating the signals of any kind of propigating wave. This mainly applies to wireless technology and communications. It uses a minimum of 4 antennas and overlaps their broadcasts in specific ways so as to strengthen the signal in one direction and lets the rest dissapate into the surrounding environment. This is also applied to incoming signals. The incoming signals are timed and the relative times that each antenna recived the signals is used to mathematically calculate the direction of the incoming signal. It is essentialy a super precisce method of triangulation.

802.11b is a IEEE protocol pertaining to wireless communications in the 2.4 ghz bandrange. It is being adopted by community networking efforts because it is cheap, effective and public domain. It is capable of transfering data at 11mbps, and has ranges of up to 12 miles. A basic directional setup can be purchased for about $300. An 'access point' with omni-directional antenna will run around $500-$1000 (or more).

802.11b has recently been enabled with bridging, so that any device connected to the network should be able to talk to any other device connected to the network regardles of direct line of sight to the final recipient. The reason phased arrays are usefull is their inherent directionality. They can track the location of any transmission made to them and transmit information in fairly specific directions. I propose that an 802.11b phased array could be built by anyone using 4 ordinary omnidirectional antennas in a specialized mounting frame, and either 4 wireless card connections to a PC running intelegently designed software, or a dedicated 'smart box' that provided the same functionality.

Pricision. Omnidirectional Antennas are made cheaply and cover a large area, so there is little concern for the level of pricision in the device. Also the cards may introduce random delays for various processes. It is critical for the application that the data be maintained relevant to the current time.

I envision it as being possible to require at a minimum, 4 omnidirectional antennas, 4 coaxial cables, 4 wireless network cards and a computer smart enough to be able to see all 4 and use them appropriately. Worst case is requiring a proprietary setup with 4 custom omnidirectional antennas, 4 precision coaxial cables and a custom built smartbox to run the whole shebang.

Wireless networking inside and out. Some strong physics and math. Any other wireless techology expirience may be beneficial. 802.11b protocol, and probably device implementaion of that protocol. Its hard to make something work for you if you dont understand it quite well. Knowing about coaxial cable will be quite useful. Hardware, firmware, and software programing will be esential to effective implementaion. And a little marketing never hurt anyone.

Well my initial idea was to bounce signals between the local antennas and, using only that information, determine your arrays topology, so it didnt matter if you had them alligned perfectly, the system would adjust around them. But if the topology has to include a random, non linier secion of coaxial cable, this process is a lot more difficult. I hope that there is some way to bounce a signal off the antenna from 'inside' so that the coaxial cables induced delay can be subtracted/added and thereby factored out of the equations. The other option I see is to force the user to use very precise coaxial cables of all the same length and factor out their known propigation delay.

The array keeps track of client locations, and adresses. Whenever it recieves a signal it does the router thing and list the adress in some sort of table. Whever it gets a signal bound for a device in range, it sends it only to the appropriate recipient and avoids cluttering up the airwaves quite as much. A cool side benefit of having the arrays is that you can use triangulation and any baseline to meause and/or plot your network. Spiffy eh?

Brain Dump by ColinDabritz Here were a few useful links. First, a great visual example of phased arrays (shockwave) http://www.explorescience.com/activities/Activity_page.cfm?ActivityID=49 and the always useful google searh: http://www.google.com/search?query=phased%20array&num=10