How did the first cell phones work?
First cell phones use a fixed frequency for a certain user. Such as, 900.1 MHz is for me, for you, 901.2 MHz like this, This is called AMPS or TACT, it is 1st generation.
Clearly, there cannot be lot of users in this way, because frequencies are limited.
Later, one fixed frequency, was divided into 8 parts ( fancy name: time slot). So, by using 900.1 , now 8 persons can use it. This is called GSM sytem or 2nd generation.
Then, in one fixed frequency, 256 codes ares introduced, Each user take one code and send his info to another. So, maximum 256 user can use 900.1 frequency now. This is called UMTS or 3rd generation .
Moving on, multiple antenna, receiver are added on every sides , so a user can have multiple signal receiving same time, if those r empty at moment. This is called LTE or 4th generation.
Going more, each side is given IP address , so every machine, human, appliance can now be connected to telecommunicaiton network - ( fancy name: ‘Internet of things' ) . This is called 5th generation ( no commercial name is still given).