When the operator receives a call, try to find the mobile phone to which it applies. Before roaming, the operator calls the phone via a massive signal to all cells in the region it operates, to find the phone and informs the mobile phone and base station cell frequency in which to operate.
When the mobile device is approaching the limit of the cell, the station perceives the signal is thinner, while the station discovers that the next cell signal is strengthening. Finally, the mobile phone receives the order to move from the first cell frequency to another frequency in the next cell. This operation is called the handoff.
Roaming
In modern systems, the mobile phone receives an operator ID system when turned on. If, at that time, the mobile phone detects that the ID system is not that of its operator, it is not roaming, or is using the services provided by another operator, a system that lets you use the same mobile phone different countries.
When switched on, the phone also transmits a registration request. Thereafter, the network will maintain contact and always present in that cell is the cell phone and will have no problem finding it in case of receiving a call. As the phone moves from one cell to another, the network will make a record. If the mobile finds that is not registered, then you are out of reach of the network and say "No network".
Digital mobile phones
The analog system has the tendency to congestion. Although dozens of people to use the same cell, there is always a limit to the number of people, once there is a limited number of frequencies.
Digital telephones, despite using the same radio technology as explained, makes the voice digital codes of 1s and 0s and compressed, so that each call takes 3 to 10 times less space than an analog call, in addition to allow greater manipulation of data to fit them into appropriate spaces, which dramatically increases the system capacity.
Impulse Transmission
In recent future, there will be phones with impulse transmission. While the 1st generation phones (analog) and 2nd Generation (Digital) transmitted through a continuous flow of radio waves, the future mobile transmit information into tiny rings. With this technology, the phones operate as it is transmitted in high-speed Morse code, where each cycle corresponds to a line or a point and that the speed is 40 million lines and points per second.
In this way, mobile phones get transmit huge amounts of information using very little energy to get better transmission quality. The mobile modular assume a constant flow of information, so that the signal has to overcome the noise, requiring more energy. With transmission of impulses, the system can ignore the existence of noise and then use less energy, and allows ease of handling signals becomes almost inexhaustible space transmission, the antennas do not interfere with each other, may ignore the signals from each other as noise.
