What is a cellular network?

Cellular network, as the picture shown above, is a wireless telecommunication network that divided its service area into cells. Each signal that covers these cells were transmitted by a transceiver station. These cells make sure that any user can roam mobile and have a continous communication with other user, as long as it still in coverage area of the network. These days, there are 2 common Radio Access Transmission (RAT) system that were known and used widely in the world, 2G and 3G. There also 4G, but it still only used in some countries