Yet another round of invented controversy has started with the release of a new book by Devra Davis “Disconnect: The Truth About Cell Phone Radiation, What the Industry Has Done to Hide It, and How to Protect Your Family.” It’s gotten a lot more attention than it should, being that the claims are big on the sensationalism and lack solid scientific backing.
Davis recently made the following comment:
It’s not the amount of radiation, necessarily. It’s the pulsed nature of the signal. It’s like: You can snap a rubber band, and it’s fine; but if you keep snapping it over and over again, it will break. Smart phones are constantly looking for signals, and it’s that sudden stopping and starting that I’m concerned about, not the total amount.
This has come up time and time again. It’s a claim being made by a number of alarmists who want to make it seem as if newer 3G and 4G applications and technologies are more dangerous than the phones and devices that have been around since the 1980′s and earlier. The fact of the matter is that there is ZERO evidence that “Pulsed” emissions are any worse than continuous RF emissions. NONE. There’s also no theoretical reason why they would be. Your body can’t demodulate the signals – it only responds to the potential dialetric heating that microwave radiation can produce.
But there’s another point worth making. Even if pulsed RF emissions were more dangerous (which they’re not) this is not what 3G technologies and new high speed data applications do. They don’t pulse. No, not at all. Some older 2G systems based on a system called TDMA do, but those are the ones we’ve had for more than two decades.
Frequency Division Multiple Access:
Arguably not a “true multiple access” method, this is the simplest and the one used by nearly all analog systems and some early digital ones.áá Each transmitter is assigned a frequency.á Data or voice is carried on that frequency continuously.
No other transmitter in the area can use the same frequency until it becomes free.áá Other transmitters are assigned a different frequency.áá Usually a band of several designated channels exists.á Therefore, if you are talking to someone using 900.05 mhz, someone else may be talking on 900.10 mhz and someone else on 900.15 mhz etc.
Time Division Multiple Access:
Each transmitter is assigned a frequency, as in FDMA, however it is also assigned a “time slot” which is normally a period of a few milliseconds. á It broadcasts data only during this brief period of time.á Other transmitters can broadcast on the same frequency without interference because they are assigned a desperate time slot.
Since the rate of TDMA broadcast slots is very fast and because data is compressed into these transmission slots, there is no noticeableá interruption to voice.á The audio is buffered to create continuous speech.
TDMA is the standard for most second generation mobile systems such as GSM.á It has been in use since the 1970′s and has been employed in mobile phone networks since the 1980′s.
Code Division Multiple Access:
Compared to TDMA and FDMA, CDMA is much much more complex.á CDMA is considered a “spread spectrum” technology and uses RF channels that are generally larger than FDMA or TDMA systems. The transmitter broadcasts a continuous signal that distributes data across the channels bandwidth.
However, despite using a wide RF channel, CDMA can make efficient usage of spectrum by having multiple transmitters use this same spectrum simultaneously. Each signal is “encoded” differently in a manner that allows the receiver to receive the individual signal while ignoring the data from other signals
Without going into too much detail of how that actually works, each transmitted signal contains the data that is being transmitted riding on a carrier wave that is modulated using a pseudo-random code.ááá The receiver must also have the pseudo-random stream to demodulate the signal.á (This is done internally using a complex algorithm shared by transmitter and receiver.)
Despite being more complex, CDMA has numerous advantages.á It tends to be less prone to interference from RF noise, it’s extremely secure and it makes excellent use of spectrum.áá Most newer CDMA-based systems include additional features to allow for compensation of Doppler shifts and to improve error correction, dynamic spectrum allocation and to address what is known as the “Near-far problem.”
Systems that use FDMA:
- Nearly all analog transmission systems
- First generation mobile phones
- Many two-way radio systems
- Simple point to point transmissiters like baby monitors, cordless phones etc.
Systems that use TDMA:
- GSM, the most popular mobile standard in the world, in use since 1987
- Most other 2G mobile phone standards, some of which are now depreciated or used only regionally
- “2.5 G” data standards like GPRS and EDGE
- Industry standard multiplexed voice and data such as wireless frame relay
- Many digital 2-way radio systems like those used by police, fire, government, railroad and business radio
Systems that use variations ofá CDMA:
- IS-95, sometimes refered to simply as “CDMA,” a 2G phone and data standard used primarily in North America
- All “3G” systems including UMTS (W-CDMA), CDMA2000, HSDPA and others
- All “4G” systems including WiMax
- Other advanced wireless services such as satellite services and other high speed data systems
Many of the systems that use TDMA are still alive and in use.áá Even 3G phones may utilize the 2G TDMA systems for voice and rely on 3G systems for high speed data or in areas where 3G service is not yet available.áá However, the point is that the newer systems are not in any way “pulsed.”á Not that this matters anyway.
This entry was posted on Sunday, October 10th, 2010 at 8:53 pm and is filed under Bad Science, Good Science, inverse square, Not Even Wrong, Obfuscation. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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