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July 27, 2007 4:00 AM PDT
FAQ: The 411 on radio frequency interference
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The cell phone interference issue seems to be a bigger problem for people using certain carrier networks. Why?
It's true, customers on AT&T/Cingular, T-Mobile and the old Nextel networks experience this problem more frequently than those on Verizon Wireless and Sprint networks. The reason is that AT&T/Cingular, T-Mobile and Nextel use cell phone technologies that use a radio channel access method known as TDMA (time division multiple access).
Networks for AT&T/Cingular and T-Mobile are built on GSM (Global System for Mobile Communications), while Nextel uses iDEN (Integrated Digital Enhanced Network). These TDMA-based technologies allow several users to share the same frequency channel by dividing the signal into different timeslots. The users transmit in rapid succession, one after the other, each using his own timeslot. This allows multiple stations to share the same transmission medium or radio frequency channel while using only the part of its bandwidth they require.
Because these networks operate in a "time division" fashion their radio frequency transmitters are turned on and off at fast rates. And this can often be picked up by nearby devices.
Verizon and Sprint's network use a technology called CDMA (code division multiple access). It does not use TDMA for sharing channels. CDMA transmitters are transmitting signals almost constantly, so they don't cause the interference buzz.
GSM and iDEN are 2G technologies. Will this problem still occur as mobile operators migrate to 3G technology?
It shouldn't be as prevalent. AT&T/Cingular has built its 3G network using WCDMA, which is based on CDMA technology. So new 3G phones on AT&T's network should not have as many interference issues.
Is there anything consumers can do to reduce this problem?
Unfortunately, the answer is no. The best solution is to turn off cell phones when you're near a speaker or some other device that is amplifying the cell phone signal. Or you can try to stay far enough away from speakers and other electrical equipment if they're turned on. For example, if you're on a conference call using a speakerphone don't put your phone on the table next to the speaker.
Hospitals for years have banned cell phones, but can cell phones really interfere with medical equipment?
Hospitals use sensitive equipment such as ventilators and ECG (electrocardiography) monitors for patient care. And just like TVs or speakers, some of this equipment is susceptible to electromagnetic interference.
But some hospitals are starting to lift the ban on cell phones as newer digital cell phone technologies and better shielding on hospital equipment have decreased the potential for interference. Plus the ban is nearly impossible to enforce.
Still, some hospitals have kept the policy in place, mainly to keep noise levels down so that patients aren't disturbed by people gabbing on their cell phones.
Do cell phones interfere with communications on airplanes?
Experts have debated for years whether it is safe to use cell phones on airplanes. Most of the evidence suggesting that it interferes with aviation equipment is anecdotal. But last year, researchers at Carnegie Mellon University concluded that cell phones can disrupt normal operation of key cockpit instruments, especially Global Positioning System receivers, which are increasingly vital for safe landings, according to Bill Strauss, an expert in aircraft electromagnetic compatibility at the Naval Air Warfare Center in Patuxent River, Md., and one of the researchers who conducted the study. Strauss said risks are caused by radio emissions from cellular calls that are higher than previously believed.
Is that the only reason why the FCC and Federal Aviation Administration have banned cell phone use on planes?
There is another reason why the FCC isn't keen on allowing people to chat on cell phones while flying. The problem is that when cell phones are used in flight they are traveling rapidly over hundreds if not thousands of cell phone towers. As the plane flies over these towers, the cell phones inside the plane are connecting and disconnecting from various cell towers much faster than was intended. The rapid signal hand-off from tower to tower of hundreds or thousands of cell phones flying overhead could disrupt service on the ground, affecting millions of cellular customers.
What about other consumer electronic devices such as iPods and laptops? Why do those need to be turned off too?
Actually, the Carnegie Mellon study also found that other electronic devices such as laptops and handheld games can send out potentially harmful signals that interfere with aviation equipment.
The bottom line is that RF interference is a fact of life, says Craig Mathias, a principal analyst for Farpoint Group.
"Most people have just learned to deal with it," he said. "The alternative is to live without wireless, and who would be willing to give up their cell phone?"
See more CNET content tagged:
radio frequency, consumer electronics, cell phone company, interference, radio
28 comments
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Want to get rid of it? Get a CDMA carrier.
This does not occur with CDMA (Code Division Multiple Access). In CDMA, each user gets a different code applied to his signal, so the base station can separate the users apart that way. This allows all users to transmit at the same time, so the radio isn't switching on and off at 217Hz (or any other rate in the audio spectrum).
I used to have Cingular, and I amazed everybody when I would pick up my phone to answer the call before it started ringing :-). Can't do that anymore with Verizon, but I'm glad the interference is gone.
cell phone rung, it got frozen. Freezing (e.g. BSOD) wasn't even
known on Amiga unless you get somehow infected by one of
rare viruses.
Of course Amiga 1200 was a computer from 1993. The
electronics engineer forgot to tell ONLY the electronic devices
having special workarounds in GSM age isn't effected from cell
phones. They are designed in a way not to fail or get real actual
effect from that huge interference.
For example, if you got a car with ABS made before cell
phones, e.g. a very good quality Mercedes you can't give up
from 1991, you better ask your car manufacturer whether to
use ordinary cell phone while driving or buy a car kit (real one
with ex. antenna).
They start to 'oscillate' a few seconds before the Motorola
actually rings. So I can pick up the phone before it rings---
freaks out people around me. ESP.
On the other hand, I can't believe they devoted an article to RF
interference. There will always be cross-talk. I would have
thought readers who frequent CNET have at least a very basic
scientific or technical background and understand exactly what
the sticker from the FCC, which adorns all of our electronics,
actually means.
other similar devices (two way radios) are designed to emit RF;
that's how they work. And since we are all looking for better
performance out of these devices, the manufacturers will
continue to ramp up their output power and cause even more
interference. The real fault here is crappy shielding and
grounding schemes that are so prevalent in 'consumer' & 'pro-
sumer' level audio devices. The RFI is only heard if the
interference has a path into the amplification circuit - block the
path and the interference disappears.
There are audio mixing consoles out there that a five watt radio
can be right beside without a problem, and other (less well
designed) ones that the radio can't be within ten feet without
causing RFI problems.
Not the radios fault -- its the audio manufacturer's.
The problem should have been more obvious years ago with the first generation GSM phones should it had been GSM's fault because back then there were not strict regulations with regard to the RF emission of those phones, and I believe they did emit much more RF than modern models do. I suppose back then we had more quality comsumer products. The cheaper the computer parts were getting over the years the more I was noticing this interference problem. In fact, the first time I personally noticed this issue was when I changed an old but quality Sony monitor for a newer but cheaper Samsung model.
I believe we'll see more and more of this issue in the years to come because the world only is going to see more and more of RF emiting devices, such as phones.
It tends to be really loud and it actually cranks up the volume on its own. Happened on a few night where I would get freaked out when all of a sudden I would hear this screaming sound right next to my head almost. Learned my lesson to turn the speaker off at night...then it won't pick up anything.
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Glad to see that industry appears to be moving towards eliminating this annoying issue.
Just wanted to dispell anyone believing it was ONLY GSM phones. iDEN is older than any current US technology by the major carriers ( It just took awhile for a carrier in the states to pick up teh technology, ie Nextel.
amount of interference as a text message was being delivered. I
had to step away three feet before it would stop, lol.