The mobile phone network is made of groups of cells, hexagonal in shape.
Each cell site covers
a specific geographic area of several kilometres in diameter.
That is why is a mobile phone is sometimes called cellular phone.
Each cell has its own
base station linked to a Mobile Telephone Switching Centre which
connects the call to the public switched telephone network.
A base station can be recognised by its transmission-reception
tower which usually has three sets of antennas, each set covering
120 degrees.
Each cell uses a radio
channel which is different from the radio channel of its six adjacent
neighbours to avoid interference.
Cellular phones are able to switch from channel to channel in
a fraction of a second and as the user travels from one cell area
to another, the call is passed to the next cell site .
Cellular technology involves the re-use of radio channels over and over again.
This can be done by using very low transmitter power: the radio waves can only travel a few kilometres and then those frequencies are re-used by another call.
One of the limitations of the mobile phone is that you cannot make a call if the transmitter signals from the phone and carrier are not strong enough.
More and more communication systems are based on the use of computers: they play an important role in relaying signals quickly, efficiently and with reliability.
Mobile phones or cellular phones are telephones which use a "radio" called a transceiver (transmitter-receiver) to send and receive signals to and from the mobile telephone network.
Mobile phones operate in the 800 / 900 / 1800 MHz ranges of the electromagnetic spectrum.