1. 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 -L j  = Loss (dB) = 20 log 10 e  L = ’ L phase change =  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 f 1.5 and f 2

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 MediumFreq. rangeLoss (dB/Km)@ freq Open wire0-150 KHz0.03 0.2 1 KHz 200 KHz Twisted pair (Loaded) 0-1 MHz0.7 (0.2) 1 KHz (3.5 KHz) Cat 61-250 MHz21 60 1 MHz 10 MHz Coax0-500 MHz710 MHz

12. Optical Fiber Structure 1. Core (8 µm) 2. Cladding (125 µm) 3. Buffer (250 µm) 4. Jacket (400 µm) Optical cable

13. Fiber optics Optical propagation Refraction index n core > n cladding 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