Transcript of "Radio communication and the mobile phone"
Radio Communication and the Mobile Phone<br />By Christian Sheehan<br />
Introduction<br />Mobile phones are a newer form of media compared to radios, though radios were the first means of communication.<br />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.<br />Now, about 40million enjoy the benefits of mobile phones all because of him.<br />
Key Words<br />Frequency - the number of times per second at which the wave oscillates, measured in Hz (hertz)<br />Electromagnetic waves – used to receive signals, also another names for radio waves<br />Carrier Wave – a radio frequency wave used for radio communication<br />Modulation – when information is added to the carrier wave in some way<br />
What is a Radio Wave?<br />Mobile phones and their base stations transmit and receive signals using electromagnetic waves (also referred to as electromagnetic fields, or radio waves). <br />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. <br />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<br />Waves of higher frequencies are known as microwaves and are used in things like telecommunication links and radar.<br />
How Radio Communication works, using amplitude modulation (AM)<br />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.<br />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.<br />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<br />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.<br />Then the size or amplitude of the RF carrier wave is made proportional to the size of the electrical modulating signal.<br />
Amplitude Modulation...<br />As you can see, if you modulate the carrier wave with the signal it becomes amplitude modulated.<br />
How a mobile phone network uses radio communication<br />Our mobile phones send and receive information by radio communication. <br />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. <br />Base stations link mobile phones to the rest of the mobile and fixed phone network.<br />This is done by either telephone cables or higher frequency radio links.<br />
‘Cellular’ Radio<br />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.<br />The size of a cell depends on 3 things: local terrain, frequency band in which the network operates and the capacity (number of calls).<br />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.<br />There is also a need for many as base stations can only take a certain number of calls. <br />
An ideal network?<br />The diagram below shows a possibly ideal network of overlapping hexagons. (They aren't this shape due to site availability)<br />
References<br />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].<br />Antenna And Radio Waves Clip Art [WWW] Clker. Available from: http://www.clker.com/clipart-23862.html [Accessed 26/01/11]<br />[WWW] Googling Magazine. Available from: http://googling.phpmagazine.net/upload/2006/01/google-radio.png[Accessed 26/01/11]<br />
A particular slide catching your eye?
Clipping is a handy way to collect important slides you want to go back to later.