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Use Multiple Channels for Faster Wireless Networking
icypyr0 writes "The Register reports: 'Current dual-mode 802.11 'a' and 'b' access points use only one of Wi-Fi's 11 RF channels at a time, with users taking turns. The Engim chipset can 'see' all 11 at once, and can use the three non-overlapping ones (1, 6 and 11) in parallel, increasing total throughput and enabling features to be incorporated in silicon that are usually implemented, at extra cost and performance degradation, in software.'"
Well, my polish is not that good (except my RPN/RPL) so i'll take your word for it....
....Excuse me, but
Err... My polish is crap, but unless I am mistaken they seem to have used a 500mW aplifier and a 27dbM antenna to boot.
What's next? Sticking it in the middle of Aresibo and claiming half a light year range?
Baker's Law: Misery no longer loves company. Nowadays it insists on it
http://www.sigsegv.cx/
or 66 miles for the math impaired (sigh). Still, that's rad! You could access that across the English channel!
stuff |
I for one find it ironic that someone can detect and possibly decode my WiFi signal from roughly 70 miles (per the new world WiFi record) but I can't get a useable signal on my laptop three rooms away from the WAP.
The article claims the experiment used off-the-shelf, commercially available, unmodified components (1.1m / 3.5ft parabolic antenna and a 500mW amplifier). Experiment was conducted in a mountainous region in southwestern Poland.
:)
So this isn't all that bad... considering the average laptop wireless card puts out, what, 20mW? 50mW? using a 500mW amp to achieve a much greater distance is pretty sweet. By comparison, the article quotes a Swedish experiment which used stratospheric baloons and a 6W amp, but they don't mention the distance achieved.
Mind you, rules about how much power certain appliances / transmitters can put out with or without a permit vary across the globe, and I'm not sure whether 500mW is legal for private unlicensed use in Poland or not. But if it is, more power to them.
Now, where can I get mine??
Have EVDO, will travel.
Good thing they did that in Poland. If they had tried this in the US, they'd have been sued by DirecTV for hacking a satellite TV system and the RIAA for trying to set up a P2P link. Of course, none of this would matter since they'd all be in a 3x2 federal pen cell awaiting for months to be charged with setting up a data link that could be used for terrorism ...
"A door is what a dog is perpetually on the wrong side of" - Ogden Nash
All of the channels basically overlap with the other channels. However, if you're on 1, 6, and 11, you manage to cover the entire chart without duplicating yourself.
Translation: They're covering the entire 2.4 GHz band, and making no appoligies to anybody else who hoped to use it near their systems. Any 2.4 GHz phones will have nowhere to hide.
I live right next to a university and I can see at least 15 different access points on any given day from my wireless link. I use it for internet access to the university and I can definatly tell when my neighbors are using their own LAN cause it causes a lot of packet drop outs. Not to mention about half of those APs have "linksys" as their SSID with no WEP enabled.
It gets better during the summer when a lot of the students around me leave and shut off their APs.
Are 1,6, and 11 the only channels that don't overlap?
You can get away with using four without much problem. I use 1, 4, 8, 11 for my wide-area 802.11b network.
You have to plan out in 3 dimensions when you have multiple access points like that. Often the strongest signal available to a roaming user is above or below them, rather than on their floor.
With only 3 channels available, it's too hard to map them out. With 4 you can at least guarantee that no two adjacent access points are on the same channel.
- Peter
INsigNIFICANT
Well, it's kinda handy when you don't want any, ah, wires.
Based on reading the article they are talking about a software defined radio (SDR) which is capable of operating discrete carriers and user communities on each of the 3 non-overlapping channels. They are not talking about bonding all 3 channels into a single data link.
Based on the article the chipset will be *capable* of using all 3 non-overlapping 2.4Ghz ISM channels. That will allow the associated users to be split across the 3 channels rather than all on a single channel and competing for access to the channel.
The same tradeoffs that drive WLAN design today will still exist. Its not a panacea, but it does add new possibilities to the engineer's set of available solutions.
By opening up the front end of the radio they can look at the whole band and do some very interesting noise reduction techniques. This is alluded to in the article, but I think its the most promising part of the chipset. The ability to identify and reduce the affects of wideband noise will got a long way to improving reception of WLAN signals....
You can read this for a little more info.
What Engim is doing is actually a good bit more sophisticated than any of the Slashdot posts imply. When you transmit, you usually have two types of bandwidth: how much bandwidth you are using, and how much you are interfering with. For instance, a simple AM broadcast will require maybe 8KHz of the spectrum on which it actually transmits data. Since transmitters are imperfect, however, it may actually interfer with transmitters on, say, 20KHz of spectrum.
As a result, if you're in a big company, and set up 3 off-the-shelf 802.11b access points, on 3 different theoretically non-overlapping bands, you'll still get something on the order of, maybe, 1.6x the bandwidth you'd get with one.
What Engim does is it has an insanely fast ADC/DAC front-end, that grabs the entire 802.11b/g spectrum, including all the bands. Then, they have a fancy DSP that looks at the bands together, figures out how they interfere with each other, and sorts them out. As a result, in a theoretical world, where only notebooks were transmitting to the access point, they would have 3x the bandwidth. They do fancy transmitting techniques, so that notebooks on all 3 bands can hear at the same time. So if the wireless access point was transmitting, and all the notebooks receiving, they would, again, have 3x the bandwidth.
The problem is that notebooks don't have this sort of technology, so when they transmit, they cause interference for other notebooks. If the Engim WAP transmits on band 1 to notebook A, and notebook B transmits on band 2 at the same time, the transmission from notebook B may interfere with that from the WAP. As a result, in practice, it's a little less than 3x the bandwidth, but not a heck of a lot less. They try to juggle notebooks between bands, based on location, so this doesn't happen, but it doesn't really work too well.
The technology they have is wicked cool, actually. For those worrying about interference -- it's really not a problem. First of all, this isn't for personal WAPs, but for $1000 access points you'd see on an IBM or Microsoft campus. They won't be going in apartments any time soon. You need a minimum of 3 very expensive chips for a single WAP (RF front-end, ADC/DAC, and DSP). Those places don't tolorate employees setting up their own WAPs anyways.
Second, you still have the remaining bands. The way 802.11 works, with the interference issues described above, if I set up a WAP, and my neighbor sets up a WAP, we will be interfering. We'll both have wireless networks, but both with reduced bandwidth. You can still set up your own WAP on any of the remaining bands, and it'll work -- it's just that if you try to send a packet at the same moment as the Engim network, you'll get a collision and retransmit. This is what happens anyways. 802.11 was never designed to have many, non-interfering bands. It was designed to have many, interfering, overlapping networks, with packet collisions. By design, the total bandwidth of 5 overlapping networks, in the same area, is the same as if there was only one. Each network gets 1/5 of the bandwidth then. This is the exact issue Engim technology is meant to address.
In terms of cell phones, etc. my impression is that the Engim technology was actually smart enough to look for "interference sources" and try to pick bands around them. This last bit is from an Engim PowerPoint slide, so I'm not sure if it's actually implemented or vaporware.
Just log in to their default-passworded APs and set them to use channel 1. Then set yours to use channel 6. Let them deal with packet loss.
This is good info to have, Keep in mind if you are trying to impliment wireless in a corporate environment, crappy range is a good thing. I have common problems with Cisco and Symbol AP's having such good range that too many users will pick up the signal in the cube farms of todays corporate america.
I try to place my AP's so that 25 users will access them from there desks or conference room. Some conference rooms that are very large I will place 2 or 3 AP's on different channels with the power turned all of the way down so it will balance the user load between the them.
Since there are only 3 non overlaping channels it is often a chore to design wireless in a room where the same channels dont overlap with each other. Poor range solves this problem. Think of how to put 5 AP's in a room with 3 channels, it can be done, poor range is the key.
We urge our users to use their wired connection and use their wireless when in meetings or on the road at other corporate offices.