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Overview of Communication Transmission Media in Modern Systems

This lecture provides a comprehensive overview of communication transmission media, covering both wired and wireless systems. We discuss key types of media such as telephony (voice, fax, modem, DSL), Ethernet/LAN, cable TV, and fiber optics. Detailed analysis includes transmission parameters, interference issues, and the advantages of twisted pair and coaxial cables. Additionally, we explore wireless communication principles, frequency allocation for different applications, and the workings of satellite systems like GPS. This resource is essential for understanding the dynamics of modern communication systems.

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Overview of Communication Transmission Media in Modern Systems

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  1. EE354 : Communications System I Lecture 13-15: Transmission media Aliazam Abbasfar

  2. Outline • Transmission media

  3. Communications systems • Wireline (wired) • Telephony (voice, fax, modem, DSL) • Ethernet/LAN • Cable TV • Backplane copper links • Wireless (Electromagnetic) • Over the air communication • Radio and TV broadcast • WLAN • Cellular • Radar • Fiber optics • High speed long haul data communication • High traffic data transfer

  4. Transmission media • Open wire • Twisted pair • Coaxial cable • Optical fiber • Air

  5. Open-wire • On utility poles • share power line routes • Interference limited (EMI) • Limits the BW too • Transposition to reduce interference • Early twisting scheme • 4 twists per Km • Environmental effects

  6. Twisted pair cable • Unshielded twisted pair (UTP) • Shielded twisted pair (STP)

  7. Transmission parameters • Lumped model • for a unit length • System response H(f) = e-gL g = a + j b = Loss (dB) = 20 log10e a L = a’ L phase change = b L • Loss increases with frequency

  8. Interference • Interference is the main limitation (BW) • Twisting reduces interference • Shielding further reduces interference • Cross talk (X-Talk) • Near end cross talk (NEXT) • Far end cross talk (FEXT) NEXT FEXT • Cable length  --  • Space between pairs   • NEXT and FEXT decreases with frequency • f1.5 and f2

  9. Applications • Communication networks • Subscriber lines • Analog (Voice) • Digital (ADSL, HDSL, VDSL) • Links (E1,T1) • Computer networks • LAN • Cat 3 < 10 Mbps • Cat 4 < 100 Mbps • Cat 5 < 150 Mbps • Cat 6 < 350 Mbps

  10. Coaxial cable • Low cross talk • Increases with frequency • High speed/Long links • Long distance communication links • Cable TV • WAN/MAN

  11. Wireline media comparison

  12. Optical Fiber • Structure • Core (8 µm) • Cladding (125 µm) • Buffer (250 µm) • Jacket (400 µm) • Optical cable

  13. Fiber optics • Optical propagation • Refraction index • ncore > ncladding • Fiber types • Step index • Graded index • Single mode • Multi mode

  14. Optical fiber • Loss • Absorption • Scattering • Connectors • Low loss : 0.2 dB/Km • Color dependent • Dispersion • Multi modes = different paths • Refraction index is frequency (color) dependent • High bandwidth ( > 1 GHz) • Wavelength division multiplexing (WDM) • DWDM • Data rate > TB/s in a single fiber !

  15. Wireless communication • Frequency allocation needed in shared environment • To avoid interference • Spectrum is a very valuable resource • Band allocation to applications • Government regulations and policies • ITU coordinates between nations • Freq band: • 3-30KHz Very low freq. (VLF) • 30-300KHz Low freq. (LF) • 300K-3MHz Medium freq. (MF) • 3-30MHz High freq (HF) • 30-300MHz Very high freq (VHF) • 300M-3G Ultra high freq (UHF) • 3-3GHz Super high freq. (SHF)

  16. Electromagnetic waves propagations • Ground waves travels along the surface of the earth • ( freq < 2 MHz) • Sky waves reflected by ionosphere • Very variable – seasonal • Angle and loss of reflection • Freq < 30 MHz • Line of sight (LOS) • No reflection or refraction • Non Line of sight • Local reflections/refractions

  17. Wireless issues • Path loss • Fading • Mobility • Interference

  18. Satellite systems • LEOs • Lower power • Smaller delay • Need many satellites • Shift towards LEOs in 1990 • Global domination • Compete with cellular systems • Failed miserably (Iridium ) • Big, power hungry mobile terminals • Global Positioning System (GPS) • Satellite signals used to pinpoint location • Popular in cars, cell phones, and navigation devices • Natural area for satellite systems is broadcasting • Now operate in 12GHz band • 100s of TV and radio channels • All over the world

  19. Reading • Carlson Ch. 1 • Proakis Ch. 1

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