how does a mobile phone work?


To communicate with a mobile phone, it is necessary to be within range of the base station of one’s operator and receive a radio signal of sufficient quality: this is indicated by the bars on the display screen of the phone. Today, they are often accompanied by a sign (“4G”, “3G” or “E” for “Edge”, for example) specifying the type of technology available in the area.

When making a call on a mobile, the first thing the phone does is search for the nearest signal form the base station antenna of its operator and establish a radio link with it. To receive a call, the principle is the same, except that it is the base station antenna that needs to establish the connection. And in this case, to route the call, the operator needs to know the network cell of the recipient. This is why, when they are switched on and even sometimes when not being used for calls, mobiles ‘report’ to the network – or update their applications (for smartphones) – at regular intervals.

Calling on the move: “handover”
The major advantage of this type of communication is that of being able to make calls on the move. This is no problem when you move a few metres inside the cell to which one is currently connected. But if one moves away from the antenna, the signal weakens and communication may be interrupted. To avoid this, the mobile continuously measures the quality of nearby signals. And during a call, below a certain threshold, it is able to automatically switch the connection to another closer or less-congested antenna of the operator. This jump from cell to cell is called “handover”.

Different technologies used by mobiles
Nowadays, mobile phones primarily use three technologies based on antenna cell networks.

  • GSM (or 2nd generation mobile telephony – 2G) runs on the 900 MHz and 1800 MHz frequency bands. 2G offers a limited output at 88 Kb/s for data transmission (SMS, photos, internet, etc.) or 200 Kb/s for EDGE which is the most advanced version. A GSM phone can provide up to a maximum power of 2W during a call, and in the best reception conditions, the power can be a thousand times lower (about 0.001 W).
  • UMTS (or 3G) passes through the 900 MHz and 2 GHz frequency bands. More advanced than 2G, 3G has popularised internet usage and mobile media as a result of output greater than 384 Kb/s (and up 40 Mb/s for 3G+, H+ evolutions).This technology is also far more effective in signal processing, because in optimal conditions for receiving, a 3G mobile can operate at power levels several million times less than its maximum power (its maximum power is 0.25 W).
  • LTE (or 4G) runs on the 800 MHz, 1800 MHz and 2600 MHz frequency bands previously used by other applications: the 800MHz frequency, for example, was used for analogue TV before the arrival of DTT. Using new encoding technologies, 4G can already triple the output obtained in 3G to reach 100 Mb/s, and thus makes uses like “video” calls or live TV possible while on the move.

In recent years, other technologies have emerged and enriched mobile uses:

  • NFC (“Near Field Communication”) is a communication technology for contactless exchange of information at very short distances (up to a few centimetres) between a mobile terminal (after validation by the user) and a receiver. With some mobile phone models, it is already being used for paying and validation of transport tickets, and could eventually replace credit cards (see here (opens in a new window) an example of NFC application).
  • RFID (“Radio Frequency Identification”) is also a contactless technology for radio frequencies. It allows automatic detection with reading distances greater than for NFC.
  • With a range of ten metres, Bluetooth can be used to interconnect devices, such as a mobile phone with a headset or a hands-free kit.
  • Finally, Wi-fi may also be used to connect a mobile phone to an internet “box”.