what is the physical and legal difference between cellphone and wireles internet frequencies?

I have noticed that there doesn’t seem to be any laws governing setting up a wireless access point in a public place, e.g. libraries and Starbucks do it all the time. But, AFAIK, there are restrictions on setting up cellphone towers and starting a telecom.

Well, so what is the fundamental difference here? Is the cellphone spectrum somehow much more valuable and sparse than the wireless access spectrum? Or is it just a matter of how powerful your transmitting antenna is allowed to be without being regulated?

The wifi wireless access points operate at frequencies that the FCC (or equivalent agencies in other countries) have deemed that you don’t need a license to use. They also require that the equipment operates at pretty low power. Cell phones are on different frequencies.

Like gazpacho said, the particular frequencies that wifi wireless access points operate on are unlicensed, particularly the ISM bands.

http://en.wikipedia.org/wiki/ISM_band

Some cell phones, on the other hand, operate on the frequencies listed in the GSM article below.

http://en.wikipedia.org/wiki/GSM#GSM_frequencies

BJ

The main thing is the power level. At the power levels that wifi systems are allowed to use, you are talking ranges of maybe a couple hundred feet. Cell phone towers reach a couple of miles. It’s a significant difference. A cell phone tower will cover a significant chunk of a city or town. A wifi isn’t going to affect too much outside of the business or location where it is installed.

Wifi ended up on frequencies that are fairly crappy as far as long distance communication goes. The area around 1 to 10 GHz is absorbed fairly well by water, especially at about the 2.4 GHz part of it, which is what wifi uses (they also use 3.6 and 5 GHz which aren’t much better). This means that you really couldn’t pick much worse frequencies to transmit on as water vapor in the air tends to cut down your signal, especially in areas of high humidity. Not coincidentally, 2.4 GHz is also the frequency your microwave oven uses.

The folks who make wifi would have loved to have used a better frequency range, but the spectrum is pretty crowded, so they had to take what they could get. The fact that water vapor in the air tends to cut down the signal actually works to their advantage, as it further decreases the likelihood that one wifi spot will interfere with another nearby.

Wifi protocols are also fairly tolerant of errors, so if you do get two wifi systems interfering with each other, chances are everything will still work, but you may notice reduced data speeds due to data packets having to be re-sent because they got garbled or whatever.

Between the low power levels, poor signal propagation through the atmosphere, and fault tolerance inherent in the protocols used, the FCC doesn’t see any need to license wifi systems to prevent interference with nearby systems.

Cell phone towers, by contrast, easily interfere with their neighbors, and the FCC has to license them to make sure they don’t all cause each other problems.

To add to the above. The 2.4 GHz unlicensed region isn’t unrestricted in the manner it is used. To be allowed to use it, equipment must adhere to a basic set of protocol specifications. These specifications require that the system be spread spectrum. That is, the frequency used must continually move, and there are specifications as to the maximum time a unit may transmit on one frequency before moving. This leads to use of the spectrum in a way that inherently tends avoid interfereing with other services that share the frequency region. By interfere, we mean to block use of the region. In essense, spread spectrum techniques allow you to trade off a diffuse low grade interference that affects all users against the risk that one user wipes out another entirely. It isn’t just microwave ovens in the this space. Bluetooth and DECT portable phones are there also. As are many toys. Overall it is not a bad idea. Short range devices that can coexist with one another without much in the way of user configuration.

Mobile phone bands are different. Individual countries reserve the right to allocate regions of the radio frequency spectrum. And in the last decade odd have all started to realise that this is a very precious resource. Precious enough that they want serious money for access. Phone companies have paid litterally billions for the right to use spectrum. Of cousre they pass the costs onto the consumers, so in many ways it is a form of taxation. But access to any scare resource is going to cost. The conterpoint is that the goverment guarentees that no interloper will be allowed to set up a cell phone network in opposition on some other frequency.

The final thing is that licenses are only granted when the approrate agencies feel comfortable that there are suffienct safeguards that the useers of the specrum won’t interfere with services outside of the allocation. This may mean that devices must be approved, or that licencees have quite specific and onerous legal responsibilities placed upon them.

Timely discussion as the FCC wants to review the TV stations that aren’t using all their frequeny since the switch to digital. (You now can broadcast five or six standard def TV stations where you used to be able to do one analog station).

The FCC wants to use the space for broadband, and is thinking "Well if you’re not using all your frequency alloted for TV, then you should give it back