What is Cellular mobile communication technology

How is it that a friend thousands of kilometres away can talk to you as if you were face-to-face?

How is this possible?

--- Cellular mobile communication technology

As we know, the transmission distance of electromagnetic waves is limited, and the transmission distance, penetration and coverage effect of electromagnetic waves of different frequencies are all different.
In order to achieve global coverage of signals, cellular mobile communication technology was born

Communication carriers divide the geographical area into countless 6-sided sub-areas, like a bee's nest, there is a Signal Base Station Tower (BTS) in the middle of each area, which receives and transmits electromagnetic signals of 700MHZ-6GHZ (6G in the current development), and each BTS link to each city's mobile switching centre (MSC)  through the optical fiber, each city's MSC also link by fiber which sunk into the ground or submarine fibers connected to each other, thus realizing the long-distance signal transmission between cities, commonly known as the GSM (Global system for mobile communications)

Let's use a few diagrams to briefly describe this process

1. When you buy a mobile phone, you also need to buy a SIM card from the local operator, each card has a unique physical address, just like our ID card.

2. When we make a call, the RF signal is picked up by a nearby base station, converted into an optical signal by a micro-converter at the Tower bottom(that is, MU repearter in our fiber optic machines), and transmitted via optical fibre to the city's MSC.

3. MSC will find the MSC in the city where your friend's SIM is located and transmit the signal to the base station near your friend's location.

4. The base station of your friend's location will transmit the signal to his mobile phone, which will convert the electromagnetic wave signal into digital information such as voice and image to realise global instant communication.