Slashdot Mirror

More detail and a picture over here

Actually, it's worse at going through walls and barriers. It bounces around them.

Ahh multipath, the enemy of sub-cm accuracy GPS and now coming to a network connection near you.

From http://www.wi-fiplanet.com/tutorials/article.php/1 121691

Multipath propagation occurs when an RF signal takes different paths when propagating from a source (e.g., a radio NIC) to a destination node (e.g., access point). While the signal is en route, walls, chairs, desks, and other items get in the way and cause the signal to bounce in different directions. A portion of the signal may go directly to the destination, and another part may bounce from a chair to the ceiling, and then to the destination. As a result, some of the signal will encounter delay and travel longer paths to the receiver.

Multipath delay causes the information symbols represented in an 802.11 signal to overlap, which confuses the receiver. This is often referred to as intersymbol interference (ISI). Because the shape of the signal conveys the information being transmitted, the receiver will make mistakes when demodulating the signal's information. If the delays are great enough, bit errors in the packet will occur. The receiver won't be able to distinguish the symbols and interpret the corresponding bits correctly.

The electric carts are manufactured in Italy by the World Alternative Transportation Technologies Corpration (W.A.T.T. Corp). This particular model is called "Teener E". It is a small, enclosed two passenger electric vehicle powered by rechargable batteris and driven by an electric motor. It can climb up to 18% grade steep hills. It's speed does not exceed 35 mph and has a range of 50 miles. Full battery recharge is 4 hours. It complies with all Federal Motor Safety Standards (ie. seatbelt, roll cage, emergency brakes, etc.)

The WiFi transmit/receiver unit on the cart has range of 1 mile (1.6 km) compare to standard WiFi equipment of 300 - 500 ft. It runs on Linux operating system, able to auto-recognize and auto-configure into local WiFi mesh. Various businesses in downtown Tempe area have given permission to Nasco's group to install WiFi units on their properties.

Nasco is also in contact with city of Tempe to further WiFi coverage, hopefully in next few years the city will be complete wireless.

Now that is an example of folks working well together for a common good. I wish my town would do that. But, they will not even allow a single cell site so we barely have cellular phone service out here much less wifi. Oh, well, to some, the lack of cell phone service is seen as a benefit.

Here is another interesting article about Tropos: Mesh could be the solution to a proposed $1 billion wireless municipal network for New York City emergency workers.

The frequencies overlap. There is only 5MHz difference between wireless channels, yet each channel uses a 30MHz spread.

In the US (where channels 1-11 are available) The best you can do it use 1, 6, and 11. Adding any other channels will cause interference.

It is explained pretty well here

Finkployd

According to these guys, it costs 20 grand to put up a base station.
However, it seems to be an older article, so I'm not sure how correct it is.

very stupid question from a non-engineer : is it not possible to have non-directed optical signals ? Some sort of 'ambiet laser'

Um, yes. Just take a look at your closest lightbulb. There's your omnidirectional light source right there. One might actually consider variable stars as messages from outer space...

In the interests of mentioning something real that actually exists, take a look at 802.11 over IR

Lasers are used for point-to-point links because there is usually an intended recipient. All of the energy goes to that single, intended direction. However, there shouldn't be anything to stop creating ambient monocromatic light source..

WiFi (802.11b) and 2.4GHz Phones almost always will clash -- but there is a good article on wifi planet that gives some things that can be done to lessen interference.
http://www.wi-fiplanet.com/tutorials/article.php/2 191241/
Of course, the best solution is a 900MHz or 5.8GHz Cordless Phone.

NFC is very short range wireless (a few centimeters, so it's effectively a touch). More info here, and here. You can consider it an evolution in the user interface of existing wireless systems, like BT or WiFi.

Tom's Hardware and WiFi Planet... somewhat dishartening, i suppose..

Unfortunately, pissing off the right person can land you with a very large fine. In the US, the FCC has rules on this stuff, because WiFi devices fall under Part 15.

Omnidirectional antennae (if built to the letter of the law) can only have a limited amount of gain (dependant upon the power output of the radio itself, as it's measured using dBi), where directionals can have more gain because of the limited directional scope.

At any rate, doing the math when building an antenna is essential, because the government doesn't find ignorance of the law to be a sufficient excuse. Want more info? Here's a link.

No, you can't build a 50' collinear array legally.

I'm not saying that wireless is a bad technology, or that ethernet can do anything that 802.11 technologies can't. all that I am saying is that it can be affected interference with other devices on the 2.4GHz band, see Here. I could be wrong about the weather, but a lot of devices do run on the 2.4GHz band, and the potential for interference exists. The directional antennas would help with that. After reading that link, i guess I was wrong about the weather aspect. I had looked into getting a wireless lan some time ago, and had found that glass and fish tanks would cause significant signal loss.
I haven't had experience with setting up wireless networking equipment, but I don't know how easy it is for the average user to use (WPA? WEP? Firmware Update? Huh?), but ethernet has always been an attractive option for me, with no signal strength to worry about (my computers aren't that far away), and anyone else can plug it in and have it just work. I only need to setup dhcpd.conf once.
Even though I have never setup a wireless lan, I know how, and I have a tendency to lock everything down. Adding new mac addresses to the list isn't something I wan't to do when one of my friends brings a laptop around. There is also the issue of terrain to worry about, since to my knowledge directional antennas can't go around hills, but nothing stops Cat6. 802.11g would be a good idea for places where putting down cables would be hard. I just wouldn't run a whole town on it. Of course I could be completely wrong about all this.

IANART (Radio Technician), so if you are, don't take this over anything you think. It IS hard to change my mind quickly, and I still hold onto the past. I will learn to love wireless in time, but not yet.
For now, I have left only to say my brain hurts.

Go to: http://www.wi-fiplanet.com/tutorials/article.php/2 200071 Good info!

You've actually been able to do that for almost nine months now in the courtyard of the FCC's office on 12th St. SW, just south of the National Mall. Though, per their press release they seem to frown on the hacking part.

There are desk exercisers out there. One powers your monitor while you pedal.

Hell, someone even made a pedal powered Wi-Fi network for Laos.

Has anyone set up their wireless access point this way, and if so, is it straight-forward? I assume one can do it with OpenRadius?

You mean, something like this? (first link I could find. I'm sure you can use Google to find more/better.)

But you can't power printers and laptops off of it for very obvious reasons: LOOK AT THE GAUGE OF CAT5. It's a low power solution only: phones, access points, etc.

802.11i will use AES encryption. It looks like they're finally figuring it out.