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Beware Of 2.4 GHz Interference
RobinX writes: "If you have any combination of cordless phones, wireless ethernet, wireless video, or Bluetooth you could be having problems. I've got two different 2.4 GHz phone brands that are interfering with each other and with my home 802.11b wireless ethernet network. It seems that the 2.4 GHz range isn't licensed so companies are free to do their own thing. Check out this article for more." I've been noticing problems recently as well, between phones from the same manufacturer and the WaveLan cards.
This article gives very little detail on whats going on here. They don't even say if the author even tried adjusting the frequency settings of the interfering components. 802.11 has 11 (in the US) -non Frequency hop mode frequency settings (most of which overlap) and selecting another one might have helped a bit!
:-(
Some background for the curious: 802.11 sends 'chirps' - the same bit is sent simultaniously on a range of frequencies, with some bits reversed. this is done to prevent interference, or blocking on one band from interfering with the transmition.
The channels look somthing like this (in ASCII anyway) (if this looks wrong, paste it into an xterm, or notepad, or somthing with a fixed-width font)
|
|............---7---
|..........---6---
|........---5---
|......---4---........---11---
|....---3---........---10---
|..--2---.........---9---
|---1---........---8---
+---------------------------------------------
frequency ----->
Note that the vertical axis doesn't represent anything, it's just used to stop everything going on top of everything else. The dots are there because slashdot slashes spaces, but leaves dots! Nor is this diagram accurate, or to scale or anything, it's just ment to give you the gist.....
Here each ---x--- is a range of frequencies over which the bits of the chirp are spread.
There only one set of 3 channels which don't overlap, so if you need more than 3 802.11 networks in the same place, you're our of luck.
If you run your network in frequency hopping mode, you only transmit one bit on one frequency at a time (chirps send about 12 bits), but change frequencies often, across the whole range (no channels) This means that interference on one range will only kill some of your data. You obviously than need to retransmit failed sends (by the time a retransmit happens you will have switched to a different frequency.
The quality of the hardware you use can also make a big difference. The better equipment uses two aerials, spaced apart, to prevent reflected signals and some other kinds of interference from silencing the signal. The idea is that if a signal and it's reflection interfere to create a minimum (no signal) at one point, there will be signal just a short distance sway.
Most devices just ship set to a channel, and it's nearly always the same one - surprise surprise - 1! I don't know about the phones, but they would probably be similar.
I guess no detail, or background research is about what we expect from ZDNet.....
1. If you are experiencing problems with your cordless phone, try adjusting the operating frequency of your access point. Any AP worth thier weight will allow you to choose different frequencys to operate on, all within the 2.4 GHz band. Most commonly: 2412, 2417, 2422, 2427, 2432, 2437, 2442, 2447, 2452, 2457, and 2462.
2. Access Point placement: Make sure to place your AP in a strategic location at your home/office. Central locations work best, and make sure your orientation is correct for the kind of radio you use. A bad place to set one of these things is next to your microwave (for obvious reasons)
3. Cordless Phone base placement. Minimize multipath transmissions by keeping your base station away from corners. Multipath transmissions from your cordless base station can and will take down your wireless network as it confuses your client radios on your other PCs due to all the 2.4 GHz traffic in the air.
4. The new Lucent 6.0 driver for their ORINICO WaveLAN cards has a new feature called "Microwave Oven Robustness." When this feature is enabled it prevents the radio from falling back to less than 2 MBit/sec when it thinks it is in poor coverage. This should only be enable in environments that will not experience fringe/poor coverage, however it should help your problems with interference if it is enabled in a good coverage area.
Numbers two and three are probably the most vital in getting multiple 2.4GHz devices to co-exist, so try many different placements! Try not to get discouraged, it does work!
-- Ian
I install 802.11 networks by Symbol, Lucent and Telxon (Aironet/Cisco) and this is something I come into contact with more and more.
Frequency Hopping (FH) devices tend to kill the reception by Direct Sequence (DS) devices, mainly due to the differences in signal strength. Multiple DS networks can happily coexist, and run at 1,2,5,11 or 25 MBit/s while keeping the actual signal at below ambient noise strength (nice - security-wise)
FH networks just tend to upset all other 802.11 networks, and they only go up to 2 Mbit/s at the moment. The reason people use them is that they are very stable and solid. They just work, without tweaking!
With todays bandwidth demands, you have to go for the 25 Mbit/s gear (which gives you throughput roughly equivalent to a 40Mbit/s ethernet type protocol - due to use of CSMA/CA not CSMA/CD) so things should get better as more people use DS not FH:)
Frog51
Frog51
If you have any combination of cordless phones, wireless ethernet, wireless video, or Bluetooth you could be having problems. Not only will your bank balance will be suffering a from the debhilitating effects of continuous expenditure on unecessary geeky networking technologies, but your health will be in sever danger.
An article to be published in the Lancet later this month will show how people can suffer serious side effects from replacing all the cables in their house.
"It started happening after I went to one of those underground Linux install parties" reports a young man, who we'll call 'Alf'.
"At first, it was just phones. You know, people passing around some Nokia's and Ericssons, and it felt really good to be cordless. It was like I was with the in-crowd."
"After a few weeks though, people started getting out the infra-red enabled PDAs out. I didn't think anything of it at the time."
But, as the report shows, cordlessness is an unpleasant and addictive activity, and it's only a matter of time before the serious health implications start. 'Ben' has been in re-hab for three months now, getting used to staying in the same place when he talks on the phone, and being re-trained in Cat5 cabling.
"I can't remember much towards the end" says Ben, "I was really out of it. There was like about 4 of us in this house in Shoreditch, you know with serious 802.11b right through. It was like a permanent trip. We used to have these wild parties at weekends with loads of girls and booze, it was pretty wild, people doing it with like Psion5's and i-mode phones, really f**cked up stuff."
But although Ben is recovering, it's a growing problem thoughout London and the whole of the West. Dissatisfied with their parents' strict ideas of free love, home grown dope, and long skirts, the young generation are turning to hardcore wireless technologies, with street names such as Bluetooth, WAP and i-mode.
Next: The Goverment launches "War on Wireless" to stop this disturbing trend in our young people.
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- ETS 300 328
- ETS 300 826
The later standard is used for Bluetooth applications; from what I understand all equipment must abide to ETS 3090 328.The fact that the Siemens Gigaset and X10 are noisy could be that the ETSI standards actually allows them to do prett much what they want to; it could also be the case of bad design of the X10 or Gigaset equipment. I have seen plenty of cases where equipment from wellknown manufacturers claims to be approved according to CE emissions standards (EN55022/23), but when measured up proves to be way of.
Regarding Bluetooth, it is my understanding (after working with it for one year from a hardware designer perspective) that BT is designed to work in "noisy" environments. BTs frequency jumping scheme is designed to make the most of the frequency band, even if there are cordless phones and wireless LANs using the spectrum also.
Also, BT is a low power technique in contrast to IEE802.11 and possibly the cordless telephones.
I have followed some threads regarding possible interference between IEEE802.11 and BT, and the latest information is that they do not interfere and thus can coexist.
Standard disclaimer: I may be wrong
The author of the linked article is obviously inadept at grasping the reality of what he was witnessing.
The 802.11 cards and Siemens phone system are frequency-hopping. By switching frequencies often, they reduce overall interference at the expense of a little bandwidth (there's plenty of room at 2.4GHz for these things to co-exist). Some types of frequency-hopping "spread spectrum" devices will dynamically learn trouble-spots and avoid them, bringing bandwidth back up to a point approaching ideal (unless that entire block of spectrum is completely hosed).
So, the phone system and wirelss LAN should work fine together. There will be a slight (measurable, but imperceptable) decrease in bandwidth for the LAN while phones are in use. The phones, if they're poorly designed and/or the CODEC is intolerant of errors, may suffer an occasional (and very brief) dropouts; due to the real-time streamed nature of the device, retransmissions aren't possible as they are with 802.11. I don't suspect these dropouts would be overly bothersome, or even noticable in most instances.
Interestingly, the X10 video-sender box was the last thing he threw away. Oddly enough, that's the device which should have gone away *first*. It's cheap - too cheap to use any of the present-day bandwidth-reducing digital coolness of most other 2.4GHz devices. So, it spews forth broadband analog video - likely using *more* bandwidth than a TV station to avoid expensive modulation/demodulation parts - destroying the 2.4GHz for the rest of the household toys. Remember the remark above about the spectrum being completely hosed? This is probably a better example of an RF monster than anything else available to a consumer today.
Had he turned off the bargain-bin X10 stuff first, I strongly suspect he would have had no further difficulty (and would continue to enjoy the hideously-cool phone system).
That all said, I really don't see the need for moving to 2.4GHZ for *everything*. It offers more bandwidth for a given slice of spectrum, which is nice - and really not needed for things like telephones. I prefer to get my cancer from tobacco, standing too close to the microwave, and hanging out by 600,000 volt transmission lines - not talking on the phone.
Kid-proof tablet..