Supplementary Channel - Supplementary Material Channels 1...

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1 Supplementary Material Channels
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2 General Block Diagram of a Communication System SOURCE Source Info. Transmitter Transmitted signal User Received signal Receiver Received info. Noise Channel A channel is an integral part of a communication system. In the following, we will briefly discuss the physical channels commonly encountered in practice. Specifically, we briefly discuss the following four type of channels. Metallic Cable Optical Fiber Communication Satellite •M o b i l e
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3 Metallic Cables: Coaxial Cable A pair of straight wires is the simplest connection technique. It is sensitive to noise, interference, loss, and signal reflection. It is only suitable for short distance and low data rate application. A twisted pair is produced by twisting or wrapping the two wires around each other to reduce induction of outside interference. Typically, 1 to 5 twists per inch. It is for cheap and moderate bit rate applications, such as a few kms distance and bit rates up to 10Mb/s. With improved technology, 100Mb/s can be achievable for short distance applications like 100m.
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4 Metallic Cables: Coaxial Cable A coaxial cable consists of a center conductor surrounded by a concentric outer conductor. A coaxial cable can support higher frequency operations than a twisted pair. It is used for, e.g., antenna to TV, RF connections between broads and equipments. It can provide excellent shielding against external interference at high frequency with very small radiation power/loss. The main disadvantages are high cost and unbalanced mode.
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5 Optical Fiber An optical cable can support very high capacity (over 10Gb/s) due to the inherently large bandwidth available with optical frequency. It has immunity to external interference or crosstalk, e.g. lighting, magnetic induction, … etc. It is also smaller and lighter than metallic cables and has lower attenuation (implying long repeater spacing of over 100km).
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6 Major Characteristics of Optical Fibers Made of different layers of glass, in cylindrical form. The core has a higher refractive index than the cladding. Light beam travels in the core by means of totally internal reflection. The whole fiber will be further wrapped by some plastic materials for protection. The size of a fiber is denoted by writing its core diameter and then its cladding diameter (both in mm) with a slash between them. For example, a 50/125 fiber means one with a 50 mm core and a 125 mm cladding cladding core light beam
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7 Single-Mode Transmission A single-mode optical fiber has a small core diameter so that there is essentially only one path that light can travel. The dispersion effect is minimum because all rays propagating down the fiber with the same delay time. This results in wider bandwidth (i.e. high bit rate). Because of the small central core, it is difficult to couple light into and out of the this type of fibers.
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This note was uploaded on 01/11/2011 for the course EE 3008 taught by Professor Pingli during the Fall '08 term at City University of Hong Kong.

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Supplementary Channel - Supplementary Material Channels 1...

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