Slashdot Mirror
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.'"
or 66 miles for the math impaired (sigh). Still, that's rad! You could access that across the English channel!
stuff |
So this is a relatively cheap method to get Internet access in distant locations, specifically in mountains, where it is difficult to get a wire.
Regards
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.
Here
is the story from July of an outfit getting 310km using WiFi from ground to a balloon. This was done by Alvarion and the Swedish Space Corporation and acknowledged by Guinness (as in world records not as in beer).
I did a 21.7 mile shot using Cisco Aironet BR342, Andrew 19dB solid dishes, and YDI
500 mw amps.
I'm a bit embarrased to admit using a wireless LAN product for backhaul work, but some morons overtightened
the patch cable on an Andrew P2F 5.2-5.8 GHz 2' dish hooked to a WiLan AWE-120 5.8 GHz radio and put their link out
of service.
Despite extensive tweaking the link never managed more than analog modem speeds. It helped in recomissioning the UNI band stuff, but was otherwise
useless for hauling traffic.
802.11[bag] is NOT an access product. Take a look at Alvarion's Breeze Access II, or better yet just wait for an
802.16 product meant to do access work.
802.11[bag] is NOT a mobile access product. That market belongs to licensed band products with ISDN like performance offered by cellular companies.
Anecdotal evidence of mobile access to one police department in a town of 12,000 does not equal proof of concept for operation in urban areas; its plain
dumb luck coupled with no competing ISM band ISP(yet).
802.11[bag] is NOT a backhaul product. Backhaul radios are made by WiLan, Redline, Aperto, Proxim, and others. The minimum cost is $2,500 an end just for
the radio, most of them are in the UNI band, the full duplex products are generally split band 5.2/5.7 GHz, and they provide typically eight to ten
mbits for entry level products, unlike 802.11b which NEVER, EVER gets 11 mbits in long shots, with 1 or 2 mbits being the typical rate.
802.11[bag] SHOULD NOT BE DEPLOYED BY MONKEYS. Are you a MoNkEy? If you haven't read Matthew S. Gast's 802.11 book published by OReilly and you
don't fully grok the implications of the shared MAC layer, you are just throwing nuts and filth from the treetops into the already busy ISM band.
Slashdot's coverage of other topics is relatively even. The coverage of radio is focused on 802.11[bag] and this is quite laughable most of the time
to those of us who have actually owned and operated a wireless ISP. Personally I think the editors ought to be giving us a whole lot more information
on ICOM's D-STAR, a 23cm (1.2 GHz) amateur band voice/data system.
I am very easy to get along with, but I don't have time to waste being nice to people who are being stupid. -Theo
Actually you can't use a 24db antenna with a 100mw card. The maximum EIRP allowed under the FCC for point to point is 8 watts (39db) and 4 watts for point to multipoint. If you use 100mw (20db) input into a 24db gain antenna, your total EIRP will be 44db or 25 watts. Not legal at all. Also not healthy to stand in front of the antenna for more than a few minutes.
Any connection uses actually, the three channels around it for the connection anyways,
if you've ever tried actually haveing 11 acess points on different channels you'll notice massive interfearence
come comment on the madness at http://slashdot.org/~phreak03/journal/
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.
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.