Electromagnetic Interference in Cell Phones

[tyogav]

Consider two adjacent people speaking in cell phones. Why the signals don't interfere with one another? Does each phone communicate with a distinct frequency? If so, how?

 

[jedishrfu]

This is an example of spread spectrum technology in particular CDMA (Code Division Mulitiple Access)

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

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

From the above wikipedia articl is the analogy quoted below:

An analogy to the problem of multiple access is a room (channel) in which people wish to talk to each other simultaneously. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA is analogous to the last example where people speaking the same language can understand each other, but other languages are perceived as noise and rejected. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can communicate.