What is the difference between cdma and gsm mobile phones related to their working
GSM (Global System for Mobile communications) is the most widely used cell phone system or standard in the world, with over 2 billion subscribers. There are many differences beween GSM and CDMA, but at the grossest level it is this: GSM uses TDMA (time division multiple access), that is, it allocates users on a freqency channel to different time slots. CDMA (code division multiple access) transmits to/receives from multiple phones at the same time in the same frequency channel and separates them by encoding the signal streams with mathematically orthogonal codes.
I suggest that you look CDMA, TDMA and GSM on Wikipedia for introductory material.
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