Pushing Wi-Fi's Limits: Problems and Solutions

securitas writes "Forbes technology columnist Arik Hesseldahl discusses the problems with 802.11x Wi-Fi - speed and range - and how to push its limits in a pair of his Ten O'Clock Tech columns. He discusses the alphabet soup of Wi-Fi standards, so-called 'Super G' dual channel bonding that allows two of 11 channels to act as one (and the interference problems that ensue), and the multiple input/multiple output (MIMO) method 'using multiple antennas to break a single, high-rate signal into several lower-rate signals' that could be a solution. Pushing Wi-Fi's Limits, Part Two focuses on repeaters, Wi-Fi mesh networks, WiMax and a company called BelAir Networks that has deployed several Wi-Fi mesh networks."

Comments

Real issue

[kneecarrot]

While standards and spectrum sharing are definitely factors, hardware must move quite a bit forward if it is going to become more useful than small home networks and looking cool at a Starbucks. The real problem right now is the quality of the radio chips coming out of Taiwan. They are typically way under specified range and allow for alot of bleeding between channels. The average home user won't notice it, but when you are rigging up multi-antenna setups or relying on precise timing for a repeater, it matters to a HUGE extent.

Re:I wonder how healthy it is

[PurpleFloyd]

If you think that correlation implies causation, then I have an Eternal Life Braclet to sell to you.

The only way to determine the cause of an effect is via scientific experimentation - a double-blind study with experimental and control groups. We could, for example, take 100 mice, leave 50 in "normal" cages, and put the other 50 in cages near to a broadband EM source. Then, we examine the rate of cancer in each group - if it goes up, then and only then can we say that "electromagnetic radiation (at a certain level) causes cancer in mice, which are similar enough to humans that we can safely say to stay away from EM sources."

There could well be many other reasons for the higher cancer rates reported in the 20th century - in addition to all the reasons you have mentioned, people have started to live much longer; if you die from cholera or typhoid fever at 25, you won't live long enough to die from cancer at 65. Also, the broad penetration of medical care into the working class, as compared to the 19th century, means that deaths which previously had no known cause might now be easily diagnosed as cancer. There are many reasons why reported cancer rates might go up - an actual rise in the cancer rate is only one of them.

use more power

[max born]

Many of these problems can be easily solved with more power. The FCC has imposed severe power limitations on 802.11 of about 100-200mW per channel.

If the FCC would allow us amatuers to use, say, half the power that cell phone companies do, we'd be able to Wi-Fi the whole country.

Give us the tools and we'll finish job.

Re:use more power

[ofdm]

This is, unfortunately, a common misconception. Increasing the range of 11b means that the available bandwidth has to be shared more widely - meaning that each user gets less bandwidth, which is to say data throughput.

Imagine if you will, a world where you could hear everyone talking within a block of you. Sounds great - you can hear your stereo from a mile away (well, this already happens). Unfortunately you can also hear everyone elses stereo, and everyone else talking, and their refrigerators humming, and their dogs barking. The net result is that you can't hear anything clearly. It's very much the same as being in a very full pub towards the end of a horse race - everyone's making a tonne of noise, and you can't understand much of it at all.

The solution is to have smaller cells, in the limit pico-cells, where an individual user gets the full channel to herself, and 10m away another user gets their own full channel. An alternative is to have large cells, but with APs having different non-overlapping frequencies - so that the cells are isolated in the same manner as for the pico-cells. Sadly, the lack of spectrum for 11b at 2.4Ghz makes this second solution unrealistic.

Re:use more power

[max born]

Yes, but with 802.11g and 802.16 the specs allow for up to 50+Mbps, several T1s. For surfing the net and reading email this is enough to supprort more users than may be commonly found in the limited area covered by the current power restrictions.

The 802.X specs cleverly implement CSMA/CA, a collision avoidance system that seems to work pretty well. From my rooftop (downtown San Francisco), I can see 150+ networks yet never experience any symptoms of interference.

Also, in setting the 802.11 limits on power the FCC seems to have overlooked the "skin depth" wavelength/2*pi attenuation factor that limits microwave ranges by a factor exponetially greater than for the longer wavelengths of many cell phones.

I operate a couple of nodes as part of the sflan project and it would be nice if we could reduce the "line of sight" requirement just a tad by boosting the power, say from 200mW to 800mW.

It just ain't fair than big bucks phone comapanies can "buy" an FCC license and blast away at 1500W while us folks trying to provide a free community service have to operate with our hands tied.

Use directional antennas

[KC7YRN]

There's a problem, though, with using more power. You increase interference with everybody else while making a small improvement with your intended recipient. A directional antenna helps you when you receive as well as when you transmit. If you need to serve an area, you can still benefit from an antenna that concentrates radiation in a pancake shape so you don't waste power transmitting straight up. High power conflicts with sharing.