More and more people are using mobile phones nowadays than the world could have ever imagined in the past. It is predicted that by 2005 there will be 1.6 billion mobile phone users worldwide.

Mobile phones are two-way radios that use radio frequency waves - a type of electromagnetic field (EMF) - to communicate information. The radio signal from the handset is transmitted through the air to the antenna (or aerial) of the nearest base station, which then passes the signal on to the network and through to its destination.

The building blocks of a mobile phone network are radio base stations that transmit and receive calls. The term 'base station' refers to the antenna fixed to the mast and connected to the radio transmission equipment stored in a secure cabinet. Each station covers a small area called a cell, hence the term 'cellular'. As radio waves reach only limited distances, mobile communication over a large geographical area requires a network of many base stations, with each station providing radio coverage over a particular area.

The geographic distribution of these antennas is predominantly related to two factors: (refer to diagram adjacent)

• Coverage is needed in order to communicate in most locations;
• Capacity is required to allow access to the network, given that each station has a finite capacity. If communication demand increases then other stations have to be installed. As a consequence, the transmission power of a set of stations reduces, as they become more numerous in order to avoid interference. This is why the base stations are closer to one another in an urban environment.