Mobile phones – communications on the goAustralia's analogue mobile phone system has been replaced by digital technology. But what does this mean, and how do mobile phones work anyway? Back to basics You will get more from this topic if you have mastered the basics of electromagnetic radiation – this link will take you to an annotated list of sites with helpful background information. Key textThe main difference between a standard telephone and a mobile phone is that a standard telephone converts the sound waves of your voice into electrical signals which are sent along telephone lines and a mobile phone converts the sound waves of your voice into radio waves which are transmitted through the air.Both types of phones require a transmission network. Standard phones use a network of wires; mobile phones use a network of antennas. Base stations connect mobile phones to the communication system Base stations consist of a number of antennas that both transmit and receive signals from mobile phones. These antennas are mounted on towers, or on the sides or roofs of tall buildings. After receiving the signal from a mobile phone, the base station then transmits the signals to a 'switching centre' - a telephone exchange for mobile phones. Here the call is connected - 'switched' – either to another mobile phone or to the telephone network. (Although this sounds like a lengthy process, it is virtually instantaneous.) Base stations are in 'cells' A mobile phone system requires a number of base stations. Each base station sits in the middle of a geographical area known as a 'cell'. (Mobile phones are also known as 'cellular' phones.) The number of calls (or 'traffic') that a base station can handle at any one time is limited by engineering design constraints. In order to operate the mobile phone network as efficiently as possible, base stations are located so as to maximise the number of calls that can be connected during peak use periods. Therefore, the geographic size of a cell depends on the traffic during these periods. Cells in populated areas, with many mobile phone users, will be smaller than cells in less populated areas. As you cross the boundary of one cell, the cell next to it will automatically take over. This is called a 'hand-over' or 'hand-on', and it is controlled (usually without you noticing) by a computer in the switching centre. The switching centre knows which cell your mobile is in, and switches it to the next cell if you move across a boundary. Your call will continue to get 'handed on' to each cell in turn until you reach the edge of the last boundary. Then you will be out of range of any cells and your call won't be transmitted. Mobile phones 'check in' regularly to base stations An important thing to remember is that mobile phones cannot talk directly to each other without going through a base station first.
Mobile phones in Australia used to operate on two systems, analogue and digital. The analogue Advanced Mobile Phone System (AMPS), was first established in 1987 and it formed the basis for the early expansion of mobile phone use across the nation. It used frequencies in the range 825-890 megahertz. Within this range of frequencies, there were 666 channels for receiving and 666 for transmitting. The digital Global System for Mobile Telecommunications (GSM), which has been in use in Australia since 1993, uses the frequencies 890-960 megahertz. Within this range of frequencies, there are 124 channels for receiving and 124 for transmitting. (The digital system has the advantage that each channel can handle up to eight calls simultaneously.) Dialling the future In the early 1990s, the Australian government passed legislation ruling that GSM would take over from AMPS in the year 2000. However, because GSM has a much smaller range than AMPS, it is difficult for this system to provide adequate mobile phone coverage in country areas. Telstra upgraded its AMPS network to a new digital technology, Code Division Multiple Access (CDMA). CDMA uses the same frequencies as AMPS and can provide the same coverage to country areas but it offers the benefits of digital technology. There is some debate whether CDMA is an adequate replacement for the analogue system in regional Australia. Another change on the horizon that could be important for those in remote areas is the launch of more telecommunications satellites. We may see some base stations replaced by 'low Earth orbit' satellites (LEOs), which will circle the Earth low enough to pick up your call. The LEO will then re-transmit your message just like a base station. This technology is not fully developed yet, but expect to see some more major advances in mobile phones before too long. Mobile phones and health Mobile phones are very useful and are growing in popularity. But some people are concerned that there is a possible health risk associated with mobile phone use. The mobile phone network uses radio waves (also called radiofrequency radiation), which is a part of the electromagnetic radiation spectrum. Some mobile phone users are concerned that having the phone's antenna close to their head exposes them to levels of radio waves that will increase the risk of brain cancer. With the research that has been done so far, scientists generally agree that radio waves cannot cause cancer, but there is some debate about whether they can make an already existing cancer grow faster. However, as far as digital or analogue mobile phones are concerned, there is no clear evidence in the existing scientific literature that the use of these devices poses a long-term health hazard. Research into these health issues continues around the world. The Australian government has provided about $4 million so that research on possible links between mobile phones and cancers may continue at a faster pace. At the international level, the World Health Organization has initiated an Electromagnetic Fields Project. The project, designed to standardise international research efforts and to increase our knowledge in this particular area, should be completed by 2001. Precautionary options Options to reduce exposure are available for mobile phone users who are concerned about the possible health risks. Minimising call times is obvious, but using an earphone/microphone cable attached to the mobile phone allows its use away from the user's head. Mobile phone covers that claim to shield the user's head are also available. Research to support this claim has not been published and phone manufacturers have stated that such covers inhibit the correct function of the phone. Related Nova topic:
Australasian Science April 2005, page 5 Study rejects evidence of sperm damage from mobile phones
New Scientist A collection of New Scientist articles on mobile phones is available.
10 March 2008, pages 24-25 Why every home should have a cellphone mast (by Duncan Graham-Rowe) Explores technology which allows for reliable cellphone signals.
5 September 2007, page 32 Cellphones could guide high-rise rescuers (by Paul Marks) Reports on development of a system used to locate mobile phone users in high-rise buildings.
30 August 2007, page 18 Cellphones affect human cells without heating them (by Caroline Williams) Reports on a possible mechanism in which radiation may affect cells.
4 August 2007, pages 24-25 Smartphones are the PCs of the developing world (by Jessica Marshall) Explores the use of smartphones in developing countries.
21 April 2007, page 23 Cellphones: A pollution risk Presents the environmental risks of mobile phones.
21 April 2007, page 17 If you're driving, stay off the phone Reports on the findings of a study examining the likelihood of an accident with drivers who use their cellphones.
9 December 2006 Cellphone networks could help with road tolls Looks at a method to charge motorists to use roads using mobile phone networks.
11 March 2006, pages 27-28 Welcome to the open source cellphone (by Mason Inman) Looks at alternative uses for mobile phones.
4 February 2006 Answering the radiation question (by Caroline Williams) Looks at the ongoing concern about the effect of mobile phones on health.
10 September 2005, pages 44-47 I'm on the plane (by David Cohen) Asks if using mobile phones on planes endangers passengers lives.
8 January 2005, page 26 Major cellphone safety studies to report A number of major studies are due to report their findings in 2005.
11 January 2005 Cellphones 'should not be given to children' (by Will Knight) Discusses recent studies suggesting cellphone radiation may pose a health hazard.
9 April 2004 Cellphones may boost forces on biological tissue (by Duncan Graham-Rowe) Mobile phone radiation may cause a massive increase in the forces that living cells exert on each other, suggests a new study from Sweden.
4 October 2003, pages 30-33 Enjoy it while you can (by Duncan Graham-Rowe) Discusses new 'smart' mobile phones and why they are susceptible to virus attacks.
13 September 2003 Will we ever know? (by Duncan Graham-Rowe) Discusses a forthcoming UK report on whether mobile phones pose a health risk.
Inside Science (No. 158), 15 February 2003 Do u wan2 tlk? ;-) (by Ian Sample) Explains the difference between analogue and digital mobile phones as well as the Global System for Mobile Communications (GSM).
RTD Info August 2005, pages 3-11 A collection of stories on mobile phone research including:
Scientific American May 2007, pages 15-16 Dialling in (by Sally Lehrman) Examines the challenges for mobile communications companies to develop a suitable mobile phone for developing countries.
Six topics on telecommunications are available:
How Stuff Works (USA)
Billions and billions of dollars in orbit: Global links for mobile phones (Australian Parliamentary Library)
Explains the difference between high geostationary Earth orbit satellites (GEOs) and low Earth orbit satellites (LEOs). Lists many of the proposed systems.
The impact of the mobile telephone in Australia (Academy of Social Sciences in Australia)
A 2004 report on the impact of the mobile phone in Australia.
Australian Broadcasting Corporation
Mobile phones: Frequently asked questions (WorkSafe Western Australia)
Briefly outlines possible health risks from mobile phone use and suggests ways to reduce exposure to the radio waves of mobile phones.
Australian Radiation and Nuclear Protection Agency
International EMF project (World Health Organization)
A number of news releases and fact sheets relating to health effects of electromagnetic fields. Of particular interest is Electromagnetic fields and public health: Mobile telephones and their base stations.
channel. A band of radio frequencies assigned for a particular purpose. Code Division Multiple Access (CDMA). This technology converts analogue signals into digital which are then transmitted over a network. CDMA enables multiple phone calls to be carried on the same frequency by using a voice-coding system. For more information see How cell phones work – cellular access technologies (How Stuff Works, USA). electromagnetic radiation. Electromagnetic radiation is simply energy which travels through space at about 300,000 kilometres per second – the speed of light. We imagine radiation moving like a wave. The distance between two adjacent wave crests is called a wavelength. The shorter the wavelength, the more energetic the radiation is said to be. Also, the shorter the wavelength, the greater the frequency of the radiation. Other than wavelength, frequency and energy there is no difference between a radio wave, an X-ray and the colour green. They all possess the same physical nature. For more information see Back to Basics: Electromagnetic radiation (Australian Academy of Science) and Electromagnetic Spectrum (NASA Goddard Space Flight Center, USA). frequency. A measure of how frequently an electromagnetic wave goes up and down (oscillates) or the number of waves passing by in a second. A hertz is a unit of frequency – 1 oscillation per second; a kilohertz (kHz) is 1000 hertz – 1000 oscillations per second; a megahertz is 1 million hertz – 1 million oscillations per second. For more information see Sound properties and their perception – pitch and frequency (The Physics Classroom, USA). Global System for Mobile Telecommunications (GSM). Digital systems of mobile phones convert voices into a series of on-or-off electrical pulses which are then relayed in short bursts as packages of data. GSM is efficient because in the intervals between bursts, other phones can also send packets of data: in this way, this digital technology enables up to eight conversations to be held on the same channel virtually simultaneously. More information on analogue and digital systems can be found at Sound into pulses: The benefits of digital transmission (Telstra Learning Centre, Australia) and What is the difference between analog and digital cell phones? (How Stuff Works, USA). radio waves. Low frequency electromagnetic radiation. Radio waves have wavelengths ranging from less than a centimetre to as long as 100 kilometres. The hertz (Hz) is the unit of frequency and means one complete oscillation per second. Many frequencies are much higher than this so other units are used (eg, 1 megahertz (1MHz) = 1,000,000Hz). We divide the radio wave part of the electromagnetic spectrum into bands that are allocated to different uses. These include AM radio (amplitude modulation), FM radio (frequency modulation) and CB radio (citizens' band), television, aircraft communications, satellites, mobile phones and pagers. Within each band, no two transmissions can use the same part of the spectrum – or frequency – at the same time. For this reason, each band within the radio wave spectrum, itself a part of the broader electromagnetic spectrum, must be managed carefully to ensure the best use of this limited resource. The frequency of radio waves used in magnetic resonance imaging range from 1-100 megahertz, depending on the strength of the magnetic field in the scanner. This is close to the range of frequencies used for FM radio (88-108 megahertz). For more information see How the radio spectrum works (How Stuff Works, USA).
External sites are not endorsed by the Australian Academy of Science. Posted August 1998. The Australian Foundation for Science is also a supporter of Nova. This topic is sponsored by the Australian Government's National Innovation Awareness Strategy.
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