Radio Communication and the Mobile Phone By Christian Sheehan
Introduction Mobile phones are a newer form of media compared to radios, though radios were the first means of communication. Marconi made the first transmission in 1895 and in over a hundred years the radio has been used by the likes of the police and military to communicate. Now, about 40million enjoy the benefits of mobile phones all because of him.
Key Words Frequency - the number of times per second at which the wave oscillates, measured in Hz (hertz) Electromagnetic waves – used to receive signals, also another names for radio waves Carrier Wave – a radio frequency wave used for radio communication Modulation – when information is added to the carrier wave in some way
What is a Radio Wave? Mobile phones and their base stations transmit and receive signals using electromagnetic waves (also referred to as electromagnetic fields, or radio waves). These waves are emitted by natural and mad-made sources. They are measured in frequencies, which are widely used for telecommunication, including broadcast radio and television, and comprise the radio frequency band. In the UK, AM radio uses frequencies between about 180 kHz and 1.6 MHz, and Cellular mobile services operate within the frequency ranges 872-960 MHz, 1710-1875 MHz and 1920 - 2170 MHz Waves of higher frequencies are known as microwaves and are used in things like telecommunication links and radar.
How Radio Communication works, using amplitude modulation (AM) A radio frequency wave used for radio communication is referred to as a carrier wave and is produced by a transmitter as a sine wave. This carries little information and simply repeats over and over and can be turned on and off, which is why it was used in Morse Code, an early radio communication. To carry more information, like speech, information has to be added, this is known as modulation.It involves some feature of the carrier wave being varied in accordance with the information transmitted For amplitude modulation (AM), the electrical signal from a microphone (e.g. speech or music) is used to vary the amplitude of the carrier wave. Then the size or amplitude of the RF carrier wave is made proportional to the size of the electrical modulating signal.
Amplitude Modulation... As you can see, if you modulate the carrier wave with the signal it becomes amplitude modulated.
How a mobile phone network uses radio communication Our mobile phones send and receive information by radio communication. Radio frequency signals are transmitted from the phone to the nearest base station and incoming signals (carrying the speech) are sent from the base station back to the phone at a slightly different frequency. Base stations link mobile phones to the rest of the mobile and fixed phone network. This is done by either telephone cables or higher frequency radio links.
‘Cellular’ Radio Each base station provides radio coverage to a geographical area known as a cell. A central switching centres connects them, and tracks calls and transfers them as the caller moves from one cell to the next. The size of a cell depends on 3 things: local terrain, frequency band in which the network operates and the capacity (number of calls). The need for so many base stations is due to the strength of the signals decreasing as the distance increases. GSM base stations usually cover about 35km. There is also a need for many as base stations can only take a certain number of calls.
An ideal network? The diagram below shows a possibly ideal network of overlapping hexagons. (They aren't this shape due to site availability)
References PUBLIC TELECOMMUNICATION NETWORKS UNIT (2001) How Mobile Phone Networks Work [WWW] Ofcom. Available from: http://www.sitefinder.ofcom.org.uk/mobilework.htm [Accessed 18/01/11]. Antenna And Radio Waves Clip Art [WWW] Clker. Available from: http://www.clker.com/clipart-23862.html [Accessed 26/01/11] [WWW] Googling Magazine. Available from: http://googling.phpmagazine.net/upload/2006/01/google-radio.png[Accessed 26/01/11]