Do different cell phone carriers need different frequencies?

Question

I'm learning about cell phones, and I know that cell phone towers of different cells can use the same frequencies, but what if the cell phone towers belong to different carriers? Can they still operate on the same frequencies without interference?

Answer 1

"Cell phones" no longer exist. today people use "mobile phones". and, yes, there is a difference. the original purpose of cell phones is if everyone wanted a unique number they would need a unique frequency to be contacted on so the call would not interfere with other remote phones. when car phones got started (in Chicago) it was closer to having a dedicated CB radio, which is not practical for large scale use. one million users would require one million frequencies. so cells were invented. when you enter the there range of a tower (called the towers "cell") your phone would contact the tower and be assigned a frequency. towers had an A and B frequency. (although i think a tower might have been able to carry more than two calls, that info is so old it doesnt matter anymore). that was back whenever. now mobile phones use one of 3 protocols: GSM, CMDA or PCS. the first two are on the same frequency, and the later is on another. so, to answer your question, there are only two frequencies used. GSM is a world-wide standard adheard to everywhere, except the US. it is common here (every CMDA phone can also operate on GSM. the "S" means "standard") but CMDA is  the US standard. i know nothing more about GSM but CMDA (code division multiple access) sends a users phone an X and Y coordinate used to decoded the digitized info broadcasted across the available bandwidth. because digital is only 1 & 0, once the data vector is applied, everything is ignored except for the remainders (1&0) if the remainder is anything else, the bandwidth is ignored because it is for another phone with different vectors. because CMDA has a limited number of people that can talk across it, sprint invented PCS which operates at a different frequency (900mhz?, dont trust me on that), and they were able to move into areas where mobile carriers used up all of the available space for CMDA.

check out howstuffworks.com as i remember it, they had a great beginners level expatiation of cell and mobile phones. while you are there check out how automatic transitions work too. its good stuff.