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TRANSMISSION MEDIA – 2

TRANSMISSION MEDIA – 2. SYSC 4700 Telecommunications Engineering Halim Yanikomeroglu and David Falconer Carleton University. March 1, 2018. Radio. Microwave Line of Sight (LOS) Cellular, WLAN, WiMax, sensor, ad hoc, PAN Dispatch, paging Pro

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TRANSMISSION MEDIA – 2

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  1. TRANSMISSION MEDIA – 2 SYSC 4700 Telecommunications Engineering Halim Yanikomeroglu and David Falconer Carleton University March 1, 2018

  2. Radio • Microwave Line of Sight (LOS) • Cellular, WLAN, WiMax, sensor, ad hoc, PAN • Dispatch, paging • Pro • Low real estate and installation cost (don’t need to install wires or fibers to every possible customer), good coverage • Mobility • Con • Subject to interference and propagation disturbances • Security, privacy a concern

  3. Line of Sight (LOS) Radio Propagation Free space path loss in linear scale: (4πd/λ)^2 Free space path loss (FSPL) in dB =10 log10 (input power/output power) = -147.6 + 20 log10 f + 20 log10 d where frequency f is in Hertz and distance d is in metres. Path loss in LOS conditions is similar to FSPL.

  4. Sample Link Budget for a Radio Link Transmitter Receiver Distance d Noise Given: Signal centre frequency f = 4 GHz Distance d = 20 km. Total antenna gains and cable losses = Gt + Gr= 24 dB Bandwidth = B = 10 MHz Noise figure = 10 dB; Temp = 17°C Required SNR = 20 dB

  5. Sample Link Budget for a Radio Link Transmitter Receiver Distance d Noise Given: Signal centre frequency f = 4 GHz Distance d = 20 km. Total antenna gains and cable losses = Gt + Gr= 24 dB Bandwidth = B = 10 MHz Noise figure = 10 dB; Temp = 17°C Required SNR = 20 dB Free space path loss (FSPL) in dB = -147.6 + 20 log10 f + 20 log10 d = 130.4 dB [f is in Hz and d is in m.] Noise power in dBW = - 228.6 + 10log10(273 + C°) + 10log10(B) +F = -124 dBWRequired received power in dBW = SNR + Noise Power = 20 – 124 = -104 dBW Required transmit power = Required received power + Path Loss - Gains = -104 + 130.4 - 24 = 2.4 dBW = 1.74 watts

  6. Non-Line of Sight Radio Propagation Diffraction Reflection Impulse response: Frequency response: Obstruction (shadowing) Scattering, diffraction “Multipath”

  7. Shadowing • Path loss variation due to obstructions, combined with distance • Path loss (dB) = avg. path loss + random path loss Avg. path loss Path Loss (dB) Measured path loss Free space path loss Distance (log scale)

  8. Non Line of Sight (NLOS) Radio Propagation Free space path loss in linear scale: (4πd/λ)^2 Free space path loss (FSPL) in dB =10 log10 (input power/output power) = -147.6 + 20 log10 f + 20 log10 d where frequency f is in Hertz and distance d is in metres. Average PL in NLOS terrestrial radio links: PL = A + 20 log10 f + 10n log10 d where n (>2) is the propagation exponent.

  9. Fiber Optic Cable • Most long-haul trunks in Canada and U.S. are now carried on optical fiber. • Huge capacity. • High installation cost (but low cost per circuit in large capacity systems). • Immune to electromagnetic interference. • Low attenuation. • Long life. • Small size - makes better use of cable ducts. • Excellent for digital signals.

  10. Satellites • Microwave frequency repeaters in geostationary orbits (~40,000 km.) • Large coverage; e.g., all of Canada. • Large capacity, high quality. • Extensively used by TV networks. • Capacity shared by multiple access. • Excellent for providing fixed or mobile coverage in remote areas, across oceans (although fiber is taking over).

  11. Low Earth Orbit (LEO) • 500km-1500km from earth  low delay • Non-stationary, satellites rise and fall (orbit time ~ 90 minutes) • Smaller satellites with less transponders (~100 kg to 500 kg) • Closer  lower launch costs and requirements • Closer  smaller antennas, lower power requirements (ground terminals, satellite) • Need many, many satellites to provide global, uninterrupted coverage (example: original Teledesic needed 800! Skybridge requires 80) • Hand-off required, complex signal routing needed • Geo-stationary Earth Orbit (GEO) • 30,000 km - 40,000 km from earth larger delay • Appear stationary to earth observer (Clarke’s orbit!) • Larger satellites with many transponders (~ 1 to 20 tons!) • Further  higher launch costs and requirements • Further  larger antennas, Kwatts of power requirements • Theoretically, can cover earth with 3 satellites • No-hand-off needed, simpler signal routing • Medium Earth Orbit (MEO) • 4,000-12,000 km from earth Orbits (LEO, GEO, MEO)

  12. Satellite Types • Bent Pipe Satellites • Simple Repeaters in the sky • Receive a signal on frequency F1, amplify it, transmit it on frequency F2 • Almost all of today’s commercial satellites are bent pipe • Regenerative Satellites • Deploy on-board processing (OBP) • Receive signals, demodulate them, make intelligent decision on where to send them, modulate them and transmit them • Restricted to a few military satellites, they are becoming the preferred type of the next generation communication satellites • Iridium is a Regenerative satellite

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