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.

2.4 Ghz Interference

Another often overlooked culprit around this frequency band is the microwave oven. These run in the neighborhood of 2.45 GHz (give or take). Even a small leakage from the RF shielding can produce a detectable signal on or about this frequency.

Also, the the band from 2.3 GHz to 2.45 GHz [arrl.org] is (and had been for quite sometime) used by amatuer radio operators. A higher powered ham tramsmitter could also be a source of interfere with this equipment. Technically, low-power consumer equipment should have been located on another band.

Poorly designed equipment can "mix" signals on different bands and hear interference on their operating frequency, also.

Precious little detail

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..... :-(

2.4 Interference

First off guys, there are some things you can do to help trim down problems you may have with interference from other 2.4 devices.

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

X10 Video Sender is a PIG!

I can definitely confirm the problems referenced in the article. I had almost the same set-up, with a Sony 2.4 gHz phone, a BreezeCom wireless LAN, and the X10 Video Sender.

The short answer is that the X10 Video Sender is a piece of ca-ca and was the source of all of the problems. The other 2 devices do frequency hopping and spread spectrum transmissions to avoid (and compensate for) interference. The cheesy X10 device just blasts away on a fixed frequency with a very low quality transmitter that spills all over adjacent frequencies.

The best answer I found was to stick to 900 mHz phones and run a wire for video. I boxed up the Video Sender and gave it to my Dad. It was just a bad idea all around.

This is only the beginning

And I'm not just talking about one device influencing the other here. I'm also very concerned where human health is concerned. There are so many different frequencies being used and we hardly know anything about the real effect it has. And to be honost; this article is only the top of the iceberg.

I'm from Holland and like in every country we also got out television and radio stations, next to a line up of GSM networks. All of these have transmitters. The GSM's have small antenna's which are spreak among the country but the television and radio have one big antenna which allmost covers the entire country. And here the fun part begins.... People living there are having extremely difficult times in buying electrical equipment. Why? Because it hardly works and or acts extremely funny. And I'm not talking about weirdness like we all know from Windows. No; this is serious stuff. Like electronic stoves going crazy (hot / cold), microwaves which act crazy or not at all for no reason what so ever, electric trains which run out of their own; a copper wire is more then efficient. Things are so bad that most people just can't use any electrical devices such as computers; they don't work as it should. Things are so extreme that local re-sellers are refusing to sell these people electrical equipment since they keep claiming due to problems.

So basicly this article doesn't come as a surprise to me. There is more going on then people know, and all the radio waves out there are doing something. IMHO even more then most people realize.

This is a known problem

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

Re:Phones

Well, the phones have a whole stack of problems in their own right. First, any idiot can tune in to them (no encryption). Second, they interfere with each other a lot.

Not true, at least for DECT phones like the Siemens phone mentioned in the article. First of all, DECT is a frequency-agile standard (the handset continuously monitors the signal from the base station, and can initiate a handoff to another frequency/time slot or basestation if the quality drops too low). Second, the DECT standard defines authentication and encryption algorithms which are supposed to be supported by all DECT-compatible equipment.

Unfortunately, like all other ETSI encryption standards these are not publicly available, and as far as I know there has been no effort put into cryptanalysing them. If they are anything like other ETSI-sourced algorithms (for example those in use in the GSM system) they are probably full of holes.

Interestingly, Siemens claim to have implemented their own encryption algorithm in their GigaSet range of products, but since they don't publish the details they have exactly the same problem...

* Warning *

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.

Regulations in the 2.4GHz band

This is interesting: although the 2.4GHz band is "unlicensed" it doesn't mean there is no regulation. For example, in Europe all 2.4 GHz equipment has to fulfill certain regulations derived by ETSI (European Telecomunications Standards Institute):

• 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 :-)

FUD alert

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.

Re:Commercial radio vs. my cellphone

The radio signals induce currents in the wires inside your TV/radio/whatever. The currents are rectified by any active semiconductor (transistor, ic, whatever) and the resulting signal has frequencies all over the spectrum. So your nice 900MHz GSM signal gets transferred to audio spectrum. This "artifact" is used in primitve AM receivers to convert the filtered (just the channel you're listening to) high frequency signal to an audio frequency signal.

The reason older analog cellular phones don't do this is that they send a continuous but relatively low power signal. Digital phones send bursts of high power signal so audio electronics picks it up a lot easier. The average power over time is about same for analog and digital phones tho.