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.
  • 5G is designed to handle even more data and increased connectivity; its infrastructure will support the Internet of Things, which connects billions of connected objects. 5G technology will support tomorrow’s innovations in a wide variety of fields such as:
    – healthcare,
    – public safety,
    – transport,
    – smart cities.
    5G technology will be able to operate on both the lower frequencies of the spectrum (below 6 GHz) and higher frequencies, known as millimetre waves (greater than 6GHz).

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

  • DECT (Digital Enhanced Cordless Telecommunications), formerly Digital European Cordless Telephone, is a wireless digital telephone standard aimed at both private individuals and companies, which operates on a frequency range between 1,880 and 1,920 MHz. Even though this standard was designed for a wide variety of uses, it is now mainly used for voice calls.
  • Bluetooth is a communications standard which enables two-way exchanges of information over very short distances using UHF radio waves on the 2.4 GHz frequency band. Its aim is to simplify connections between electronic devices by bypassing cables. It can be used to replace cables between computers, tablets, speakers, mobile telephones between one another or with printers, scanners, keyboards, mice, game pads, portable phones, personal assistants, hands-free microphone or earphone systems, radios, digital cameras, bar code readers and interactive advertising booths.
  • 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 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.
  • Finally, Wi-fi may also be used to connect a mobile phone to an internet “box”.
  • LoRa is a long-range network technology which supports low bandwidth communication between connected objects. Like 3G/4G, the LoRa protocol can be used for both indoor and outdoor transmissions over longer distances. The great advantage of LoRa, compared with a conventional cellular network, is the autonomy of receivers as well as the cost of use. The LoRa network has been designed to minimize energy consumption. A connected object can thus remain autonomous for several years with a simple battery (water or electricity meters, etc.). Other advantages include gateway reach (~10km in rural areas and 1 km in cities), as well as low set-up costs.
  • LTE-M is used to send data, voice or text messages to and from objects that are moving, in buildings or underground. This technology is useful for logistical monitoring, remote medical monitoring and assistance, or managing fleets of vehicles.