A mobile phone network is a telephone network that allows the simultaneous use of millions of wireless, motionless and mobile phones, including high-speed and long-distance travel.
To achieve this goal, all radio access technologies must solve the same problem: distribute as efficiently as possible, a single radio spectrum between many users. For this, various multiplexing techniques are used for the cohabitation and separation of users and radio cells: time division multiplexing, frequency multiplexing and code multiplexing, or most often a combination of these techniques [1].
A mobile phone network has a "cellular" structure that makes it possible to reuse the same frequencies many times; it also allows its mobile users to switch cells (handover) without interrupting communications in progress. In the same country, at busy times, several hundred thousand or even millions of devices are in use with (in the case of GSM) only 500 channels available.