Mobile phones are sophisticated two-way radios that use radiofrequency (RF) signals to transmit and receive voice and data. When you make or receive a call, your mobile phone communicates with a network of low powered radio transceivers called base stations.
Each base station covers a small geographic area, referred to as a "cell", and cells are interlinked to create the cellular network. A typical base station is made up of antennas and transmission dishes that are connected to an equipment cabin by electrical cable. The base station is responsible for collecting phone signals and passing them on again.
A mobile phone may communicate with several different base stations during a single call which makes it possible for you to continue your call while on the move. When a call is established, both the mobile phone and the base station adjust to the minimum power level required to maintain a quality call. This "adaptive power control" makes the mobile phone system one of the most efficient communications systems available today.
Often, transmission dishes can be observed on base station facilities. These dishes are used to link one cell to the next. Transmission dishes send a narrow microwave beam overhead, directly linking with a neighbouring dish at a nearby telecommunications facility. This beam does not disperse onto the ground below and simply replaces the cables used in ground telephone systems. Mobile phone base station antennas are designed to cater for a limited capacity of simultaneous calls. A typical Vodafone base station can accommodate approximately 40-60 simultaneous voice and data signals.
When the call demand exceeds base station capacity, the mobile phone signal is transferred to the nearest available base station. If the distance to the next base station is too far, or this station is also fully loaded, a temporary connection error would occur. If you've ever had problems connecting to the network, it is possible the base stations in your area were fully loaded at the time. With increased demand for mobile communications, additional base stations are required.
How Is The Mobile Phone Network Developed?
Vodafone monitors base station activity and plans the development of the network to meet customer demand. Regular high usage at one base station requires an additional base station to be installed at another location.
Within each cell, the base station transmits low power radio signals from the base station to a mobile phone handset operating within its distance range. There is no benefit in the base station transmitting at high power as it is the mobile phone handset power which is limiting usage. Further, when closer to the base station, the phone and the base station reduce their signal strength through "adaptive power control".
When a base station is designed, radio-engineers calculate the predicted RF exposure levels for that site using the standardised Australian Radiation Protection & Nuclear Safety Agency (ARPANSA) method. The RF exposure levels from a base station in all public areas are generally hundreds of times lower than that permitted by the ACMA's mandatory limits (i.e. ARPANSA Standard). The design of a cellular network is a complicated process, balancing the needs of customers with the constraints of the local terrain. Because radio signals generally travel in straight lines, the topography of the surrounding environment and buildings impact heavily on base station placement.
Base stations must be positioned so that they can send and receive calls from mobile phones anywhere within the cell, limiting call 'drop out' from insufficient signal strength at a particular location. It is also important to restrict coverage of a base station, limiting interference between calls in adjoining cells.
In reviewing network coverage, radio-engineers can predict where additional base stations are required, and how they are to be linked to adjacent base stations. Engineers can also predict the required base station height to ensure radio and network coverage. After identifying base station requirements, detailed investigations are undertaken to locate preferred environmentally-sound sites. Consultation with relevant authorities and a detailed environmental assessment is undertaken, as is the feasibility review of co-location with other carriers.
For mobile networks to work, low powered base stations are required to be located in proximity to where people use their phones. Industrial and commercial locations are sought in preference to residential areas. Locating facilities on existing structures such as buildings and water tanks is also given preference to constructing new towers. In order to provide quality coverage, it is not always possible to locate base stations in areas far away from residences.
Vodafone seeks options that will provide the very least community impact while offering mobile phone customers optimum coverage and service.
For further information, please contact
Vodafone's EME Manager.
Phone: (02) 9415-7002 or (02) 9415-7008
Email: ememanagement.au@vodafone.com
