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Ask Slashdot: Overcoming Convention Hall Wi-Fi Interference?
bbowman writes "One of my job responsibilities is to set up the small network for our company's exhibit at the trade shows we attend. The mobile demo devices we use depend upon a reliable Wi-Fi connection to a router I have in the exhibit. In the days leading up to the opening of the trade show, W-iFi connections are reliable and work as expected. However, as soon as the show opens none of our devices can reliable maintain a Wi-Fi connection to the router. The devices we use at the trade shows are Windows-based laptops, iPods/iPads, Android tablets, and a variety of Wi-Fi enabled cell phones. I have tried using channels 1, 6, and 11 (as well as the others) and used different routers (Linksys, D-Link, Netgear) without success. I'm sure it is likely that there are poorly insulated electrical cabling, fluorescent lighting, and other issues that would contribute to Wi-Fi interference in the convention hall. A quick scan shows dozens and dozens of discoverable Wi-Fi networks nearby. If I take the router back to my hotel room, I have zero connection problems. How can I overcome this so that Wi-Fi works reliably in the convention hall?"
I'm sure everyone will understand.
Alternatively, install a giant metal Faraday cage. (Good luck with that.)
The World Wide Web is dying. Soon, we shall have only the Internet.
Try an RS232c null modem cable.
If your devices are 802.11n compatible, you could put your router in n only mode... The 5.4ghz band may be less crowded.
- Holy crap, I've got MOD points! Who thought that was a good idea.
If you want your equipment to work with the current standards, you need to mod it to use another radio frequency. In their current as-written form, the 802.11* standards just don't have a way for equipment negotiate graceful degradation in this situation, and that's what it would take.
For the devices that support it (decent laptops, iPad, and possibly other tablets), going to the 5 GHz band is a huge win. There are plenty of non-overlapping channels, and congestion is lower. The problem is that most WiFi enabled phones only support the 2.4 GHz band, so this will not cover all cases.
At least for the laptops. There's a lot more spectrum there, and it's much less saturated. Probably not an option for the phones, though. Also, wired ethernet when possible.
"'Tis great confidence in a friend to tell him your faults, greater to tell him his." --Poor Richard's Almanac
Get a enterprise class AP + controller. That will help you to do auto channeling, interference avoidance, etc. Saves lots of your time and effort.
The problem is intrinsically a hard one, 802.11* wasn't really designed for a zillion flacks in a large room, each toting personal cell routers and whatnot.
However, it is possible that the problem could be solved by money. Let's just say that "(Linksys, D-Link, Netgear)" isn't exactly an honorable lineup of the finest names in Serious Wifi. Cheap, yes, quite delightfully so. Built right down to price? Well, you could say that...
You might want to do some looking into the world of "industrial wifi" products. The environmental resistance of such will be total overkill for a tradeshow floor; but (successful) offerings in that sector are designed for people who need their network to work despite the fact that it is in the middle of a factory floor or next to the arc welder or what have you.
The trouble with going upmarket, though, is that it can be somewhat hard to tell what is genuinely better at wireless networking vs. what is just the same old shit on the wireless side; but in a POE, ruggedized, -40/+135 thermal resistant, with baked-in proprietary management protocols in the firmware, container. You really want the former, not the latter...
Same two options as always. Either overpower the interference or turn off interfering devices with a universal remote
Build your exhibit with a dungeon/prison them to hide the faraday cage that isolates you from the rest of the auditorium. Add lots of dry ice and flashing lights and not only will you have a working exhibit, it will look cool as well.
I am Slashdot. Are you Slashdot as well?
FYI Steve Jobs routinely uses out of spec channels. For WWDC, this used to be channel 13, which is not licensed for use in the US, but is in Japan.
This got to be a problem (leading to the famous "you've got a choice..." speech) when enough Japanese Mac developers attended without changing their locale, and all the Japanese machines ended up on channel 13 because it was "less crowded" (for obvious reasons).
-- Terry
In the days leading up to the opening of the trade show, W-iFi connections are reliable and work as expected. However, as soon as the show opens none of our devices can reliable maintain a Wi-Fi connection to the router.
I doubt it's this:
I'm sure it is likely that there are poorly insulated electrical cabling, fluorescent lighting, and other issues that would contribute to Wi-Fi interference in the convention hall.
...and more likely this:
A quick scan shows dozens and dozens of discoverable Wi-Fi networks nearby.
I would recommend trying a few things:
- Reduce your RTS threshold, if your AP supports it.
- Reduce the fragmentation threshold, if your AP supports it.
- Play with data rates, reducing them if your AP supports it.
If your AP does not support any of those options, go out and get a real AP.
Never start vast projects with half-vast ideas.
http://en.wikipedia.org/wiki/Faraday_cage
"Liechtenstein is the world's largest producer of sausage casings, potassium storage units, and false teeth."
Some Cisco and other high end access points have beamforming networks that can place antenna nulls in directions of interferes (other AP's, microwaves, etc) and point the peak of the beam directly at a user among all types of other fancy tricks.
They work wonderfully well in noisy, cluttered environments. Give them a shot.
http://www.cisco.com/en/US/prod/collateral/wireless/ps5678/ps10092/white_paper_c11-516389.html
http://en.wikipedia.org/wiki/Assault_rifle
Get a N class router with Linux firmware support (I recommend the RT-N16 + DD-WRT/Tomato). Set it up to run at 300Mbps on the dual-band and the transmit power upped to 100 or 125. It's practically a 2.4GHz G wireless jammer.
My consulting business specializes in providing show management services to associations putting on large meetings. I work with Facilities to provide wifi zones, as well as information kiosks, and internet access kiosks for attendees. I recently did a large meeting in Chicago (30,000+) attendees. This presented many challenges but the biggest issue was on the exhibit floor where a site survey revealed 160 rouge access points on 2.4ghz. Not only was the building Wifi having troubles it was like the wild west among the exhibitors, most had to be within a few feet of their access points while some others used amplifiers or enterprise class APs to get the extra signal strength, if all exhibitors upgraded their signal strength everyone would be back to square one. I tried to alleviate the problem by setting up a secondary SSID on the building infrastructure for exhibitors with decent bandwidth and tried to encourage some of the exhibitors to use this instead of their own. I got the rouge access points down to 90, but certain areas of the exhibit floor where still flooded. This is an inherent problem with wifi that the more APs competing over the same radio frequencies the more noise and less throughput you will manage. Without a doubt the best solution is to move to another frequency, as I found very few were operating on 5ghz (802.11a), The real challenge is to make exhibitors and attendees aware of the shortcomings of this technology in an environment with so many users and competing APs.
Channel 13 is allowed almost everywhere except the US. Channel 14 is the Japan-only one.
What is damned is alot of equipment is hard-wired to not allow channels over 11 worldwide, lest someone go use it in the US - lowest common denominator and all that.
Demo shutting down all the demos.
Wait till the last second to setup, leave your gear in hardened, conductive cases...EMP...clear networking.
I believe you are boned. Go out of spec. Your going to have to go further then japan out of spec. Too many people will be on 13 and 14. Getting the phones working will be joy.
Get a 3g enabled phone for all the networks on the off chance that the telco overbuilt the conference floor. Leave a demo server available on the net just on the chance that your phones will have 'good enough' 3g connections. It would suck to be boned on 802.11* and only running on cables for the laptops (you know it's your backup plan), and find one of your personal smartphones still had connection, but no server configured.
John McAfee 'It was like that time I hired that Bangkok prostitute; to do my taxes, while I fucked my accountant'
Why not simply use a narrow-field directional antenna for your demo? If you're just feet away from it, it seems unlikely that other nearby networks would be strong enough to drown out the signal.
"Tell me doctor, with all of your defenses, are there any provisions for an attack by killer bees?"
Sounds like either forcing 801.11n only or using 801.11a is the only inter-operable alternative unless you can modify the devices and play with other parameters.
What about getting the convention hall organizers (or you and your nearby booths) to try and build a mesh, so everybody is on the same network (and can somehow tweak parameters to reduce interference)? Maybe coordinate the channels between nearby booths so they don't overlap? Not that there are than many channels to distribute.
How do you know that he did this, out of curiosity?
-- Nathan
Wifi channel space has obviously been used up. Use either:
http://michaelsmith.id.au
Perhaps the router could be connected to a dish above the booth pointed straight down like a street light. This could overpower other signals in your booth and reduce your interference to other users. Dishes at wifi frequencies aren't large.
I used to set up networks for training and conferences my group did. We picked up an Extricom http://www.extricom.com/. I never had problems in the dozen times I used it. Its an interesting system, it has a central Wifi unit, and you run cat-5 out to 4 remote transmitters. You can place them spread out over the area. Admittedly the model I used, the Extricom ESX400 and 4 radios no longer seems to be available but check it out. -Joe
http://en.wikipedia.org/wiki/Nicolas_cage
Obi-Wan: "I felt a great disturbance in the Force, as if millions of voices suddenly cried out in terror and were sudden
[edit : sorry, that's the repost under my account. My bad.]
On the first point I would recommend you stick with a simple ecosystem of same vendor / same model, or better then, with a spare one of another model of another vendor, just in case ;) (as far as monoculture is a concern, that would solve it). But the point is that routers of the same kind tend to have more reasons to interoperate better.
Another interesting choice : Make a map of the estimated coverage interlap of the routers in the field. Then colorize it with a color for each choosen channel, so that never two neighbors (closest overlapping person in that direction) share the same color.
With channel 1, 6 and 11, you would get 3 colors, but nstead of using 3 colors, use 4 colors by letting frequencies overlap better if 3 don't suffice. That would make channels 1, 5, 8, 11 (I prefer to give the extra space to the lowest frequency, on the logic that it spreads a bit better, so would be the least at ease).
Then, of course, if you could use some power control. Listen to neighbors, estimate their activity relatively to yours, and scale your power according to that difference. The less you're active, the less you merit to dispensate your imprint on the local spectrum.
My 2 cents, of course. But I admit I did a Ph.D in a related field.
glop
Tom's Hardware did an excellent and extensive test on WiFi networks not long ago. It is well worth the read, as is the first part of the series. http://www.tomshardware.com/reviews/wi-fi-performance,2985.html
Depends on the physical layout of what you are up to, but directional antennas on the mobile equipment and a 2.4ghz absorbing backdrop behind your stuff might work. Think old Pringles can style directional and a grounded copper mesh covered in cloth for the backdrop.
Comment removed based on user account deletion
Yea, and the FCC (and any other licensee who notices and/or cares) can come curb-stomp you for it.
For large sets, this will be our guide even unto death, for the LORD will work for each type of data it is applied to...
This doesn't meet the specs of the question, due to the particular devices you wish to support, and the fact that many of them are deliberately incompatible with it.... but there is a technology that I've used successfully many times in the past to overcome the problems inherent and unavoidable in any electromagnetic wireless communication system. This technology dramatically reduces signal attenuation due to distance, it reduces interference from external devices that use the same frequencies, it allows for dramatically higher data rates, and as a bonus it even adds a level of security/privacy: requiring extremely close physical proximity to sniff the signals. These features come standard with the tech itself, or can be enhanced with a special "shielded" version. There are even varieties capable of actually powering the devices. This technology is, of course: Wire.
One of these days I'm going to patent it, clean up on license fees for a few months before the patent gets invalidated, and retire to Mackinac Island.
http://alternatives.rzero.com/
And then read up on microwave amplifiers and horn antennas. You can then run a lot more power on the 2390 - 2450 MHz band. Your router becomes the exciter, feeding the amp, feeding a horn.
How do you know that he did this, out of curiosity?
-- Nathan
I am unsure if the channel 13 statement is true. I was in the room at WWDC when that happened, and I'd run up some tools on my laptop as the Wi-fi behaviour was awful.
There were over 1200 Mi-Fi type devices , a couple of hundred Android phones acting as wireless hotspots, and about 400 laptops sharing their interconnections.
I'd have thought the military term for nearly 2,000 Wi-fi networks in the same room was broad spectrum jamming ;)
But WLAN cables are hard to get.
The Tao of math: The numbers you can count are not the real numbers.
i work at a convention hall...are you sure they're not containing your AP? we don't allow outside managed gear although most people don't realize it until they can't connect to their router five feet away. we have our APs contain any rogue APs to avoid losing $$$ to folks showing up and trying to provide free wifi. most of the convention and exhibit centers we deal with do the same thing. the last thing we want is someone providing unsecure free wifi in the building and then we get blamed for 1) shitty bandwidth 2) mitm attacks 3) bad customer service because there's nothing wrong with our gear when you have an issue with dude in the next booth's cell phone tethered AP.
Yes, switching to 5 GHz should help, but not all your equipment may support it.
The other solution is to overpower them. Something like this can be cranked up to 19dBm assuming you only need internet-level speeds. You'll screw everyone else, but it should work.
I have been setting up wired and wifi networks in trade shows for 10+ years now. :)
Welcome to wifi Hell
I do not think achieving 100% reliability is a sane goal in that context, but I found that there are simple ways to greatly improve the odds.
> Consumer-grade routers / AP are no good. They often do a fine job, and they always give up quickly.
In my view, using small-business equipment is a better way to go : still affordable, and a lot more resilient.
For about 400 $ you should be able to find a basic gateway and access point (new - I'm thinking sonicwall / netgear prosafe / hp pro curve...)
And if it matters, you still have web-based interfaces available to configure them.
> Use fixed ip when possible. Avoid encryption if you can, avoid wep if you can't.
> Reserve the network for your demo gear. If you also have to provide internet access to people working on the booth, use a separate network/gateway (your current linksys/d-link/... router might do the trick if less critical).
> Also : wired.
Not an option for your whole setup as I understand, but maybe part of it.
I am no sysadmin/network admin/whatever so this is basic stuff, but works for me on a regular basis in your exact predicament.
Hope this helps, and good luck to you.
I was thinking that and I'm amazed that nobody had mentioned that earlier. Even relatively big parabolic antennas for WiFi (~1.5metre dish for 2.4GHz or 5GHz) are cheap and there are things like ubiquiti access points that even have much smaller directional antennas as part of the sealed unit.
There's a lot of different directional antennas out there.
CSMA (Carrier Sense Multiple Access) makes this a problem. The way this works is the AP and clients listen before transmitting. If they hear another signal above a certain threshold they will try to cooperate by not transmitting until the channel is clear. It's like trying to hold a conversation with a room full of people talking.
5 GHz will probably not work as your client equipment is most likely not equipped with 5GHz capable radios. If they have mini PCI cards you could upgrade them but otherwise your stuck with 2.4GHz.
Some high end WIFI APs have a signal threshold setting. This tells the AP to ignore signals below the set level. This could help as it could be set to ignore the radios further away, allowing the radio to transmit even when other weaker signals are present. This would severely limit your APs range but could help.
Terry works at Apple.
Congestion is what happens when there are too many clients busy on the channel that you are on. This is workable. Interference is what happens when there are clients/AP's on adjacent, overlapping channels (802.11b/g 2.4Ghz). This is unworkable. Just because you have your AP's on the proper channels, doesn't mean that those around you do. The best solution is to move to 802.11a (5Ghz) where there are a log more channels, and they don't overlap.
Get a network extender from sprint or verizon. connect it to the access point. connect everything via 3g to the extender. limit access to the phone numbers assigned to your devices. The extender ignores everyone else's device unless they're calling 911. Verizon - http://www.verizonwireless.com/verizon-network-extender.shtml Sprint - http://support.sprint.com/support/device/Sprint/AIRAVE_by_Sprint-dvc1230001prd
Look it up. These things will give you a more focused connection, but you will need setup the antenna correctly for the space you are using. I am assuming you have your wireless router/access point hardwired in your kiosk space. You need to setup 1 or 2 directional antenna and point them (preferably from above) at the area that you have your equipment/devices/demo space. The antenna you use will be dependent on the wireless connection frequency you use (802.11 a/b/g/n 2.4GHz, or 802.11n 5GHz). It will also depend on what kind of access point/router you have. Obviously this only works on routers which support different antenna, like the infamous Linksys WRT54GL.
:D
Personally I have a 19dbi panel antenna which I use on emergency, which I carry in my laptop backpack along with the said WRT54GL. I have been able to pickup and connect to networks 2 miles away (with line of sight) in bridged mode to allow my laptop to get on the net in a pinch (this was before phones had data/internet access). Worked out great for a school project once where the class was held at a remote location and we then had to write a team report/paper on about it. The professor gave bonus points to the first team to complete the assignment and sent it to him via email. We were already working on laptops, and I simply broke out the router, aimed the antenna back at our campus, spoofed my laptop's wireless mac address for the router's (since my laptop was on the approved wireless access list), and we sent the report. We also let our professor connect his laptop so he could receive it
We were all warned a long time ago that MS products sucked, remember the Magic 8 Ball said, "Outlook not so good"
Easier than you might think. Assuming both devices have connectors... http://www.balticnetworks.com/ubiquiti-airmax-rp-sma-to-rp-sma-jumper.html
You're running into the big problem with wifi: Everything on the same channel has to take turns. If there's 40 APs all in the same vicinity, they're going to start a round-robin game of who-goes-first, and if there's enough other interference, they're all going to keep yielding, and nobody gets heard. See "myth" #1 here: http://www.cisco.com/en/US/prod/collateral/wireless/ps9391/ps9393/ps9394/prod_white_paper0900aecd807395a9_ns736_Networking_Solutions_White_Paper.html As it mentions, this is more accurately called co-channel cooperation, rather than interference. And it's a huge problem in a convention. You're really kinda screwed in that scenario... unless you can use another spectrum, but it sounds like that's not much of an option given that you're trying to demo on consumer client hardware that's almost invariably 802.11b/g/n, 2.4ghz. Use A band if you can. Another thing you can try, and this would take some serious cooperation with other convention-goers (read:social engineering, perhaps?) is to get everyone to turn down the broadcast power on their APs. That's what the real problem is. If everyone talks quieter in the library, more people can carry on their conversations in their corner of the woods. You can also try to work out a pattern with nearby AP users to switch their APs to channels that don't overlap with yours. Be careful with this one, cause if you've got two APs on channels 1 and 4, they overlap enough it might still cause co-channel cooperation. This is probably pie-in-the-sky thinking that your fellow convention goers (and possible competitors even) might cooperate to that level, but there's no hurt in trying, right?
"For WWDC, this used to be channel 13, which is not licensed for use in the US, but is in Japan."
Does he have special WiFi firmware to go with it?
Channel 13 stops working on my MacBook if any access points with the country code set to 'US' are nearby, even though I'm clearly in Australia (where 13 is allowed).
There are plenty of tools to try to find free channels:
https://market.android.com/details?id=com.farproc.wifi.analyzer&feature=search_result
While I personally use that program, at least on my EVO (Synergy GodMode ROM) once it starts seeing 20+ APs it tends to bog down so much it's about useless, even in simple "list" mode.
HEX
Horror & SciFi Erotic Nudes
Well sort of solved it. We were demo'ing a handheld wireless device that did not have a wired port. We opened the device, popped the nano sized connector from the wifi module to the PCB inverted "F" antenna and connected a very thin coax to the now vacant wifi module's antenna port. We connect all of the unit's coax leads to a RF mixer (think an analog version of a router) and also hooked up a generic wifi router via coax to the mixer so that the handheld units could talk to our on-site server (handheldmixerWiFi routerserver). Our demos worked perfectly. Nobody else had anything working and one of the main points of the show was to show off wifi capabilities. It took a bunch of cables and adapters/gender benders, etc as consumer routers have most of their pin's gender reversed so that you can't do this with retail parts and cables.
13 is allowed in Australia and Europe as well, but overlaps significantly with channel 11 and a few of the other higher channels.
There is a channel 14 that is only allowed in Japan and it is far enough above even channel 13 that there's virtually no overlap.
http://en.wikipedia.org/wiki/List_of_WLAN_channels
Specialist Mac support for creative pros, Melbourne
Wifi is inherently unregulated. It will have interference and lots of traffic from all the users and devices using the same ISM band. Everything from phones to toys to microwave ovens running in the green room of the booth next door which has a set dressing budget larger than your annual revenue.
You are all unlicensed users and get to accept whatever QoS or lack thereof that you get. There's nobody to whine to, or whine about. It is what it is. On the other hand, there are scary licensed users on that band who have actual priority over the unlicensed users and can use tremendously bigger output power which could obliterate the signal for everybody else. They aren't supposed to do that but they can. And if they do, good luck to you. Your typical wifi router will be useless.
The real question you need to ask is why you are apparently running mission-critical or at least very important business stuff on an inherently congested and unregulated radio band that has no QoS and no promises? What the hell are you thinking? To do what you are doing is naive at best and stupid at worst and makes me wonder why I should trust whatever it is you sell to perform when such poor planning went into the tools you use to sell whatever it is to make.
It's the same when a company selling high-end items chooses to print their marketing collateral on the cheapest paper they can find and use morons to do the production thus ensuring that every book has an upside down cover, or the company name spelled wrong. Gee what a great impression.
You know what impresses? When the people working a tradeshow booth know their stuff, and the demos work, and they have their act together and do not whine about how everybody's iPhone or iPad is using up all the bandwidth.
Now, please excuse me as I use the microwave in my booth to reheat last night's pizza. It will only take a minute or so but your wifi will crumble during this time. Meh. No need to apologize. My dinner has as much right to the ISM band as your apps do.
Sig for hire.
I believe you can get licensed radio's from tranzeo. If not they have some other band solutions as well. They are not that expensive or hard to set up if this is all that important.
Oh Crap, I'm an optimist.....
RUN A CABLE
Great idea! Now where's the RJ45 jack on this here iPad again?
use a cable!
"The devices we use at the trade shows are... ...iPods/iPads, Android tablets, and a variety of Wi-Fi enabled cell phones."
Still looking for that RJ45 jack on my BlackBerry...
I just googled "you've got a choice speech" and the only result was this post.
Clearly not famous, but I'm interested in knowing more....
Channels 12 and 13 are technically allowed only with smaller output. A normal convention hall router would exceed these specs substantially, but for a limited-power small substation, channel 13 would be worth a try. While slightly overlapping with channel 11, you should have sufficient breathing room to convince a connection to stay enabled.
Right. Because running a cable will work perfectly well for "iPods/iPads, Android tablets, and a variety of Wi-Fi enabled cell phones".
Totally not happening...
Which dept? Ask JR what happens. I'm on the team
Show floor people need to know what you are doing. Ask them for a channel.
Nope. You'll just have the network provider at your booth in 3 min.
Is the problem. It works fine before the show starts and goes to shit after because the AP's are now keeping track of thousands of wandering WiFi enabled cell phones. Consumer grade AP's just can't handle it, some of them will even crash due to their MAC tables filling up (they still have to keep track of MAC addresses even before they authenticate)
In the future, invest $100 in a used Cisco Aironet off ebay. They cost $650 new while your Dlink costs $50 new for a reason.
The fact that this was modded "Insightful" adds a sublime ridiculosity to the Slashdot Friday Night.
You should try Airohive: it has nice APs and more importantly: an online wifi planning tool for optimally placing the APs for coverage and minimal channel overlap.
Horizontal polarization: try making all your antennas horizontal. Depending on the reflections around the room's interior it could work.
They can have my command prompt when they pry it from my cold dead fingers.
... and configure your devices to work in the 13cm "high speed data" segment.
I have run the networking at several 600-1200 attendee conferences, and have a few things you might want to try...
If any of your devices can use 5.2GHz, make sure you deploy APs for that. 5.2GHz has way more spectrum, and in my experience it tends to work where 2.4GHz is pretty spotty. Try deploying with fairly narrow beam antennas like 90 degrees, so you are just covering your booth, ideally mount it up high looking down. Run at the lowest power setting you can. Use 802.11n equipment, which often seems to have better antennas.
In the end though, 2.4GHz at conferences can be very tough... There just isn't enough spectrum there. My primary recommendation to attendees at the conference I run the wireless for is: Use 5.2GHz.
Since your hardware isn't as flexible as it could be, you can't get away with tricks like special channels and using inbetween spectrum.
So with standard equipment and standard frequencies:
1) Use 802.11n, 5 GHz if possible (less crowded)
2) Try the wider modes (HT40) to see if they can hop around your interference better (just force it and see what happens)
3) Put metal bug screen around the back of your posters and such, (with your AP not behind them). This will decrease sensitivity to whatever is behind your bords but it will not help with anything infront of them.
4) Turn your beacon interval way down, so that if a device does loose signal it will find it relatively quickly.
5) More power for your AP will help, directional antennas are good *if* you know you're only going to be in a specific area (usually, at least a hemispherical panel works)
6) follow good RF practices (don't put antennas against other objects, for example)
7) operate multiple APs at once with the same SSID -- may help, might not too, depends on how bad your interference is. And how intelligent your wifi clients are. Some won't jump AP until the signal is almost uselessly low.
Hope that helps.
Reroute the phase coils through the plasma regenerator, then boost the particle stream with a subspace flux inducer. If that doesn't work, try routing your signal through an anti-neutrino pulse, you should be able to generate one by modifying the main deflector.
It's amazing what you can learn about this stuff from a combination of Star Trek reruns and a complete lack of practical experience!
The world you experience is only a close approximation of reality.
I thought all of Apple's employees where in that huge sweat shop in china where they routinely commit suicide.
google for this: Either turn off your Wi-Fi (devices) or I give up
How many more years will slashdot have an off-by-one error on your Score in your profile?
Sorry, no useful advice for your particular situation, but it does remind me that exhibition hall interference is a problem that goes way back.
In the late 80s I worked for an exhibition company and we built a huge pond made up like Portsmouth Docks which ran a couple of remote controlled boats that punters could play with, and were meant to take part in a timed race. (Left unsupervised of course, they much preferred the sport of ramming each other until one sank). The first version used standard 27MHz radio control gear and was utterly hopeless - monitoring the channel using a CB proved that there was a positive noise-to-signal ratio. Version 2 ran the same basic gear but used infra-red transmissions from four strategically placed towers at the corners of the pond and an omni-directional pickup on the boats. Worked totally reliably. We never successfully solved the ram-and-sink problem though.
I wrote code for the 802.11b stack, and have gotten a lot of feedback from the test team as well, and here is my 2c:
1. Stacks should handle at least 127 radios on one channel, but most implementations crash with as few as 8 radios alive. Make sure you use a stack that handles many radios. Test your router and your gear (netgear and D-link passed, but check with your current router anyway)
2. Nearby channels appear as noise. If you have many TX on nearby channels, you may not have enough signal/noise ratio. Make sure all gear is MI-MO, and maybe add directed antennas to your router that keep your signal strong in your area.
3. Use channel 14 (you may want to check legality of this in your area) Standard US HW is limited in FW to use ch1-11. Ch 12,13 and 14 is all in virgin territory, and you would be alone at those frequencies, unless of course, you traveled to Spain or Japan or other where you this would look different.
don't cut it off www.mgmbill.org
Quite a few routers will use "other" channels with after market firmware such as DD-WRT.
Like -5 or something? You could try sqrt -2, I'd bet not many APs do that one.
Just bought a new quantum computer, but I'm uncertain how it works.
Set up the public network on 2.4 Ghz and your own network on 5Ghz. Done and done????
I've the same app on my CM7's Color Nook. Works great, and I've not noticed an issue with lots of APs... although I've only seen up to 25 or so at once, no bogginess, etc.
Don't blame me, I voted for Kodos
HE'S APPLE!
They use PROTOTYPE equipment all the time... He owns the peeps that can set the channel to whatever Steve wants.
It actually makes sense that Steve would set the network up that way.. It would also keep "nuisance" hackers out of his demo. It does make it extra funny to know Steve was using a channel people in the room should not have been able to access... Not a slightly geeky crowd much?
But on topic, short of having firmware access to unlicensed bands, there's not much you can do. Perhaps convention halls should get infrastructure level equipment put in and force everybody to use their channels? That would fix the problem of battling networks kicking each other out. Then YOU, the presenter, would still have to use VPN fir your products to prevent snooping.
That will block out all the crazies. In this case it needs to be a little bigger than the traditional one. More seriously, I'm guessing that putting your router in an aluminum foil dunce cap above your booth would be sufficient to allow the clients below to connect. Put another router underneath for decoration. You'll have to experiment with how to make it look good but I'm thinking that you could take a cone or hemisphere made with standard lightweight tradeshow construction and cover it with aluminum foil from the grocery store and save yourself the cost of the copper.
Put the router in a grounded metal box with the side facing the stage open. Ensure the people on stage have line of sight while the audience doesn't. This will block the RF from the audience and give you exclusive use.
Even in a crowded environment you might to well to remove the antenna from a router and place it very close to the mobile device (inches). This would reduce the gain at the receiver and allow the nearby mobile device a significant SNR advantage over the rest of the access points in the room.
Linksys, Netgear and D-Link are generally consumer grade equipment (crap)
Try a higher end product like an Engenius ECB-3500 if you desire omnidirectional coverage, or the EOC-2611P for coverage from the sidelines or in a particular direction.
Both models have excellent receivers, and they have up to 600mW of output power. That will punch through a noisy environment. 600mW is 10 times the power that most "consumer" stuff offers, and their receivers are far better.
The ECB-3500 is an indoor model which has two 5dBi antennas with diversity, and the EOC-2611P is an indoor/outdoor model and has a 10dBi panel antenna that is configurable for horizontal or vertical polarization, or diversity between the two.
Either one can be had for under $100.00. I've been using Engenius/Senao gear for a long time and I will say that it is worth three times the money.
Out of order? Fuck! Even in the future nothing works! - Dark Helmet (Rick Moranis) "Spaceballs"
Free tin foil hats for everybody!!!
What are the chances Uncle Charlie's sniffers are going to pick up his slightly-out-of-band 100mW unlicensed RF emissions at a trade show booth during the three days of the show? In the extremely unlikely event that he got busted, he could probably even convince the investigator that it was ignorance: "It wasn't working so I just clicked every box I could find on my WiFi settings until it worked." "OK, well don't do that again, it's illegal."
And he'd have to know his venue. At DEFCON, of course, he's very likely to encounter federales of every stripe, including the FCC. But at Joe's Semi-Annual Southeastern Minnebraska's Trade Show and Tractor Swap, he probably won't be tweaking anyone's noses.
John
While the N specification does indeed enable the use of 5GHz, the vast majority of equipment I've seen can only operate in the 2.4GHz range.
Thus, spend the money, get equipment capable of operating at 5Ghz, and you're probably gold even past the point when the rest of convention goers start doing it, due to the vastly larger signal space.
I don't read AC A human right
It will if you can place the antenna on the end of the cable next to said device. Of course, it might also kill the impression you're trying to make.
Channel 14 isn't that helpful though as it is only allowed for 802.11b which tops out at 11Mbps. Some devices will connect at 54Mbps on channel 14 but most g and n equipment doesn't even list it in the driver.
const int one = 65536; (Silvermoon, Texture.cs)
SJW, n: "Someone I don't like, and by the way I'm a fuckwit" - AC
If I'm trying to demo a WiFi connected cell phone, for example, how is ethernet going to help?
Sometimes switching to Google's DNS servers at 8.8.8.8 or 8.8.4.4 and/or using a local DNS caching server rather than using whatever DNS server is provided to you via DHCP can solve the problem (because sometimes the heavy traffic is causing greater problems with local DNS server overload than with wireless packet collisions etc.).
I have been wondering lately if switching to using a tiny IP packet size would fix the problem, by minimizing the number of aborted packets due to random wireless collisions. My theory is that if my packets are much smaller than anybody else's, they will have a higher chance of getting through. Has anybody tried this?
I have been wondering if switching to using a tiny IP packet size would fix the problem, by minimizing the number of wireless collisions. My theory is that if my packets are much smaller than anybody else's, they will have a higher chance of getting through. Has anybody tried this?
Copper as a reflector will create multipath problems. It is best to use something designed to absorb the radiation to attenuate it. Visit the microwave cookware booth nearby and offer to display all their browning dishes on your backdrop. This will convert the signal to heat and attenuate it. This works for signals entering your area as well as your spill out to your neighbors. You will want a lot of dishes to fully tile your wall.
The truth shall set you free!