Mobile phone networks are often referred to as "cellular" networks. This is because the radio signal area covered by a base station is known as a cell.
Each cell is usually split into three sectors, which overlap with the sectors of neighbouring cells to create an uninterrupted network. When people travel, the signal is passed from one base station to the next, and typically never has to travel further than the nearest base station.
The size and shape of each cell is determined by the features of the surrounding area, such as buildings, trees and hills, which can block signals. Cells are largest in flat open landscapes, where they can cover up to a 30 kilometre radius. Cells in urban areas in Australia cover between 2 and 5 kilometre radius. The smallest cells are in built up areas, where micro-cell base stations are used to provide extra coverage and capacity.
Radio signal coverage in the valley township above cannot be achieved by simply raising the existing base station.
Each base station can only handle a limited number of calls at a time. In areas of high demand, additional antennas are often added to a base station to send and receive more calls and other mobile services, or an extra base station is installed. All this means is that a large number of base stations are needed to allow more people to use mobile phones for more services, from more locations, and for coverage to be continuous when moving around.
Base stations use radio signals to connect mobile phones to the network, enabling people to send and receive calls, texts, emails, pictures, web, TV and downloads. Without base stations, mobile phones will not work. They are made up of three main elements:
Base stations are connected to each other by cables or wireless technology such as radio transmission dishes, to create a network. A base station can only handle a specific number of calls at the same time. Therefore, as the number of users in an area increases so does the number of base stations required to cover demand.
High usage city area has small diameter (1-2km or less) cells so that base stations do not interfere with each other. This is achieved by lowering the base station operating power.
Low population (rural) area has large diameter cells that may even exceed 35 km.
Radio transmission dishes are used to provide line of sight communications with other antenna installations such as in satellite television, wireless LAN (local area network) services and mobile phone networks. They operate with a power of between one milliwatt and up to one watt maximum depending on the size of the dish and distance of the link.
They are used to link individual radio base stations to each other, and, through a series of links, into the wider mobile phone and fixed line networks. Transmission dishes send a narrow conical RF wave around one or two degrees wide overhead, directly linking with a neighbouring dish at a nearby telecommunications facility. This radio wave does not disperse onto the ground below and simply replaces the cables used in underground systems.
Mobile phone systems operate by transferring voice (conversations), text (messages) and data (photographs, music, videos, etc.) via radiofrequency (RF) waves.
When a mobile handset is switched on, it periodically communicates with the antenna which provides coverage in the specific area where they are located. In this way, the mobile phone sends its position to the mobile network so that the user can make or receive a call from any point in the country. If the person is on the move then the signal transmitted by the mobile phone is identified by the respective antennas in the area in which he or she is moving.
Each time we make or receive a call using our mobile phone, radiofrequency (RF) waves are transmitted from our handset to the closest antenna able to provide the strongest signal coverage. Following that the antenna dispatches those waves to a digital switching centre and from there to another antenna and then another mobile phone or fixed phone. If during the call the caller or called person moves, the mobile network transfers the call from one antenna to another, so that the conversation is not interrupted.
The base station receives radio signal from the mobile phone, transfers it to a digital exchange which then connects to the number called (either on a fixed network or on another mobile base station, depending on whether the call is intended for a fixed or mobile phone.
Developments in technology allow mobile phones to be able to automatically control their power levels, in other words to increase or reduce the quantity of electromagnetic energy emitted during a call. The maximum operating power of a mobile phone is around 0.25 watts, however, the operating power during a call depends on the signal level received. Factors affecting the signal strength include:
When a mobile phone receives a "strong" signal (in other words when it is near an antenna) it emits the minimum possible energy, that is to say much less than the maximum value of 0.25 watts. On the contrary, when there is "weak" signal in an area (i.e. when there is no antenna close enough) the mobile handset emits more energy to communicate with the antenna.
A mobile handset operates using the least possible power levels, when it receives a “strong signal”, in other words when it is near a mobile antenna.
The mobile handset has strong signal when it is close to a base station, hence it operates at a power level much below the maximum power of around 0.25 watts. On the contrary, when the mobile handset is far away from a base station, its signal is low, the coverage is poor or there is no coverage at all and consequently, the mobile handset operates at its maximum power level.