Transcript
Introduction to Communications Part One: Physical Layer Transmission Media
Goals of This Lecture • A clear picture about guided and unguided media for telecommunications, students are enabled to choose a suitable medium for a specific transmission environment with some requirements.
Kuang Chiu Huang TCM NCKU Spring/2008 2
Outline of the Class
Warm Up
• Warm up • Chapter 7 Transmission Media •Q&A
• • • •
Any question for chapter 6? UTP cat 5 cables with 568 A 568 B EMI “Electromagnetic Interference” An unwanted disturbance that affects an electrical circuit due to either electromagnetic conduction or radiation emitted from an external source. • The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit 3
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Figure 7.1 Transmission medium and physical layer
7-1 GUIDED MEDIA Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable.
Topics discussed in this section: Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable
Figure 7.2 Classes of transmission media
Figure 7.3 Twisted-pair cable
Table 7.1 Categories of unshielded twisted-pair cables Figure 7.4 UTP and STP cables
Figure 7.5 UTP connector
Figure 7.6 UTP performance
Figure 7.7 Coaxial cable
Table 7.2 Categories of coaxial cables
Figure 7.9 Coaxial cable performance
Figure 7.10 Bending of light ray
Figure 7.11 Optical fiber
Figure 7.12 Propagation modes
Figure 7.13 Modes Table 7.3 Fiber types
Light source
Step index multimode LED or laser
Graded index multimode
Single mode
LED or laser
laser
bandwidth
200 MHz/KM
200 MHz ~ 3 GHz/KM
3 ~ 5 GHz/KM
connection
Easy
Easy
difficult
core
50 ~ 125 μm
50 ~ 125 μm
2 ~ 8 μm
cladding
125 ~ 400 μm
125 ~ 400 μm
15 ~ 60 μm
attenuation
10 ~ 50 dB/KM
7 ~ 15 dB/KM
0.2 ~ 2 dB/KM
cost
low
More expensive
Most expensive
Figure 7.14 Fiber construction
Figure 7.16 Optical fiber performance
Figure 7.15 Fiber-optic cable connectors
7-2 UNGUIDED MEDIA: WIRELESS Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication.
Topics discussed in this section: Radio Waves Microwaves Infrared
Figure 7.17 Electromagnetic spectrum for wireless communication
Figure 7.18 Propagation methods
Fresnel Zone: line of sight
Table 7.4 Bands
Figure 7.19 Wireless transmission waves
Figure 7.21 Unidirectional antennas Line of sight, antenna performance, and radiation pattern
Figure 7.20 Omnidirectional antenna
An example: cellular system
Note
Radio waves are used for multicast communications, such as radio and television, and paging systems.
Note
Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.
Homework 8 • Page 210 #11, #13, #14, #16 • Page 211 #19, #29, #21
Note
Infrared signals can be used for shortrange communication in a closed area using line-of-sight propagation.
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Thank you! Q&A 35
