2 - Transmission Media Copper Wire Glass Fibre Microwave...

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Unformatted text preview: Transmission Media Copper Wire Glass Fibre Microwave Infrared Laser Introduction Computer communication involves Computer encoding data into some form of energy and sending this across a transmission medium. sending This lecture introduces a few basic This transmission concepts as background transmission Specifically, it examines the properties of Specifically, different transmission media different Copper Wire The most common medium as its is The inexpensive and easy to install inexpensive Why copper? The biggest problem is interference which The results in noise noise At its worst when wires run parallel and At close together close Solution 1: twisted pair Shield the wires and then twist them Shield together (e.g., telephone wires) together Minimises both radiation and susceptibility Minimises to radiation to Solution 2: coaxial cable Single wire surrounded by cylindrical Single metal shield metal Shield provides a barrier in both directions Shielded twisted pair may be used if wires pass through strong electromagnetic fields pass Glass Fibre Also known as optical fibre - a thin glass tube that Also reflects light internally and is coated in plastic for flexibility flexibility Transmitter uses LED or laser and receiver uses a Transmitter light sensitive transistor light Advantages no electrical interference carry a signal much further than copper carry more information at a time only needs one fibre - unlike copper that only requires a pair to form a circuit requires Optical fibre continued Disadvantages installation requires more specialised installation equipment equipment breaks in the fibre are hard to detect and breaks repairs are difficult repairs Radio Broadcast of electromagnetic waves through the air at radio frequency (RF) through Each computer uses an antenna - no direct Each connection is required Properties vary according to frequency Size of antenna determines range - 2m pole Size across town vs. inside a laptop for a room across Microwave Higher frequency electromagnetic waves Advantages: They are directional (privacy implications) Can carry more information than RF Disadvantages: cannot penetrate metal structures so require tall cannot towers with direct line of sight towers Extending range with Satellites Microwave does not bend round the earth, so Microwave satellites are needed for long distances satellites Satellites are expensive - each will deal with many Satellites customers on different frequencies customers Typically 6-12 transpoders per satellite ( RF) Ground stations Satellite communication Geosynchronous 37 784 km Versus (arrays of) low earth orbit satellites 200-400 miles Problems of limited availability + Problems complex tracking complex Three satellites in Geosynchronous Orbit satellite north pole earth Supporting the Antarctic Scientist Johanna Laybourn-Parry investigating carbon cycling in freshwater and saline lakes in eastern Antarctica. They need to build a big picture of Antarctic lake systems which are responding to climate change very quickly Currently field scientists are poorly supported with limited links Currently Measurements taken then returned to base then annotated and models build Measurements then new project 2-3 years lifecycle 2-3 Davis Station Australian base provides support for Australian the scientists the A range of experiments run from range different stations different Measures are some distance from the Measures base base Linking to the remote site Remote device deployed to take readings Readings relayed to Davis (via IRIDIUM) Readings moved from Davis to “the Grid” The Grid Remote Measurement Wearable Device Easy Plug and Easy Play of Sensors Play Wireless Wireless connection to the grid grid Positioning Positioning information from GPS GPS Buss running Buss through wearable to allow new sensors sensors Sensor bus GPS arial Extending Mobility with Cellular Telephony cell office mobile phone switching office central office cell Infrared Initially used in remote controls Advantages: portable - no antennae required inexpensive Disadvantages: limited range sensitive to orientation of transmitter to sensitive receiver receiver Laser Use of light to carry information through Use the air (no fibre required) the A laser beam will stay focussed over a long laser distance distance Requires a straight line of sight and can Requires easily be blocked (e.g., by fog). easily Summary Various transmission media with different Various properties in terms of: properties range capacity to carry information cost directionality reliability (noise and blocking) ...
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This note was uploaded on 08/14/2011 for the course ELECTRONIC G52CCN taught by Professor Professorgail during the Spring '09 term at Uni. Nottingham.

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