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Transmission Medias

Transmission Medias. 2 nd semester 1438-1439. Outline. Transmission Media Guided Media Wireless Transmission Antennas and Antenna Gain Wireless Propagation Electromagnetic Spectrum. Transmission Medias. A transmission media is the channel that

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Transmission Medias

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  1. Transmission Medias 2nd semester 1438-1439

  2. Outline • Transmission Media • Guided Media • Wireless Transmission • Antennas and Antenna Gain • Wireless Propagation • Electromagnetic Spectrum

  3. Transmission Medias • A transmission media is the channel that • provides the connection between the transmitter and the receiver. • moves electromagnetic energy from one or more source to one or more receiver.

  4. Types of Transmission Medias The Transmission media or channels can be classified as : • Analog Channels:These channels can carry analog signals. • Digital Channels:These channels can carry digital signals. • Bounded (guided) medias : signals are confined to the medium and do not leave it • Unbounded (unguided) medias : the signals originated by the source travel freely into the medium and spread throughout the medium. (Antenna)

  5. Outline • Transmission Media • Guided Media • Wireless Transmission • Antennas and Antenna Gain • Wireless Propagation • Electromagnetic Spectrum

  6. Electrical Cables • Transmit electrical signals on a conductor, e.g. copper • Cable carrying electrical current radiates energy, and can pick-up energy from other sources • Can cause interference on other cables • Other sources can cause interference on the cable • Interference results in poor quality signals being received. • To minimize interference: • Keep the cables away from other sources • Design the cables to minimize radiation and pick-up

  7. Twisted Pair Cable • A twisted pair consists of two insulated copper wires twisted together in a helical form. • Two varieties of twisted pair: shielded (STP) and unshielded (UTP); also multiple categories (CAT5) • Most commonly used and least expensive medium • Used in telephone networks and in-building communications

  8. Coaxial Cable • Coaxial cable consists of two conductors. The inner conductor is held inside an insulator with the other conductor woven around it providing a shield. An insulating protective coating called a jacket covers the outer conductor.

  9. Coaxial Cable • Provide much more shielding from interference than twisted pair: Higher data rates; more devices on a shared line; Longer distances. • Widely used for cable TV, as well as other audio/video cabling. • Used in long-distance telecommunications, although optical fiber is more relevant now

  10. Fiber Optic Cables • These cables carry the transmitted information in the form of a fluctuating beam of light in a glass fiber.

  11. Fiber Optic Cables • Used in long-distance telecommunications, as well as telephone systems, LANs, and city-wide networks • Advantages of optical fiber over electrical cables: 1. Lower loss: can transfer larger distances 2. Higher bandwidth: a single fiber is equivalent to 10's or 100's of electrical cables 3. Small size, light weight: lowers cost of installation 4. Electromagnetic isolation

  12. Comparison of Guided Media • Electrical Cables • Moderate data rates: 1Gb/s • Maximum distance: 2km (twisted pair); 10km (coaxial) • Cheapest for low data rates • UTP: easy to install, susceptible to interference • STP, Coaxial Cable: rigid, protection against interference • Optical Cables • Very high data rates: 100Gb/s+ • Maximum distance: 40km • Expensive equipment, but cost effective for high data rates • Difficult to install

  13. Outline • Transmission Media • Guided Media • Wireless Transmission • Antennas and Antenna Gain • Wireless Propagation • Electromagnetic Spectrum

  14. Wireless Transmission Model • Common wireless systems for communications include: • Terrestrial microwave, e.g. television transmission • Satellite microwave, e.g. IP star • Broadcast radio, e.g. IEEE 802.11 WiFi (wireless LAN) • Infrared, e.g. in-home communications

  15. Wireless Transmission Model • Transmit electrical signal with power Pt • Tx antenna converts to electromagnetic wave; introduces a gain Gt • Signal loses strength as it propagates; loss L • Rx antenna converts back to electrical signal, gain Gr • Receive signal with power Pr

  16. Wireless Transmission Issues • What is the role of an antenna? • What is antenna gain? • How does the signal propagate in different environments? • How much power is lost when it propagates?

  17. Outline • Transmission Media • Guided Media • Wireless Transmission • Antennas and Antenna Gain • Wireless Propagation • Electromagnetic Spectrum

  18. Antenna • An antenna can be defined as an electrical conductor or system of conductors used either for radiating electromagnetic energy or for collecting electromagnetic energy. • For transmission of a signal, electrical energy  electromagnetic energy • For reception of a signal, electromagnetic energy  electrical energy

  19. Antenna Types • Isotropic antenna radiates power in all directions equally. The actual radiation pattern for the isotropic antenna is a sphere with the antenna at the center.(ideal) • Omni-directional antenna radiates power in all directions on one plane (circle , donut). • Directional antenna: radiatespower in particular direction. Dish and Yagi are two common types.

  20. Antenna Patterns

  21. Antenna Gain • In a transmitting antenna, the gain describes how well the antenna converts electrical power into electromagnetic waves headed in a specified direction. • In a receiving antenna, the gain describes how well the antenna converts electromagnetic waves arriving from a specified direction into electrical power. • The gain of an antenna (in any given direction) is defined as the ratio of the antenna power in a given direction to the power of a isotropic antenna in the same direction.

  22. Isotropic Antenna (2D) Directional Antenna (2D) • Transmit with same power Pt • Blue shape: at each point, received power is Pr • Measure received power 1m away to be Px • Gain of antenna (compared to isotropic) is Px/Pr Transmit with power Pt Measure received power 1m away to be Pr Received power is same at any point equidistant from transmitter (black circle)

  23. Outline • Transmission Media • Guided Media • Wireless Transmission • Antennas and Antenna Gain • Wireless Propagation • Electromagnetic Spectrum

  24. Wireless Propagation • A signal radiated from an antenna travels along one of three routes: ground wave, sky wave, or line of sight (LOS).

  25. Wireless Propagation • Ground Propagation: The signal travel through the lowest portion of the atmosphere, hugging the earth. , e.g. AM radio. • Sky Propagation: The signal bounces back and forth between the earth’s surface and the earth’s ionosphere (for the higher HF frequencies), e.g. amateur radio, international radio stations. • Because it depends on the Earth's ionosphere, it changes with the weather and time of day.

  26. Wireless Propagation • Line of sight propagation transmits exactly in the line of sight. The receive station must be in the view of the transmit station. • It is limited by the curvature of the Earth for ground-based stations (100 km, from horizon to horizon). • To facilitate beyond-the-horizon propagation, satellite or terrestrial repeaters are used

  27. Multipath Propagation • In unguided channels, signals are not only transmitted directly from source to destination but also a lot of paths from source to destination by reflection, diffraction , …etc. • So the receiver receive multiple copies (components) of transmitted signal. • Line of sight (LOS) is the fastest component reaching to destination.

  28. Outline • Transmission Media • Guided Media • Wireless Transmission • Antennas and Antenna Gain • Wireless Propagation • Electromagnetic Spectrum

  29. Electromagnetic Spectrum • It is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths • Electromagnetic spectrum is used by many applications • International and national authorities regulate usage of spectrum

  30. Microwave and Radio Wave • Microwave signals are higher frequency signals used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. • Higher frequency  carry large quantities of information. • The required antenna is smaller due to shorter wavelength (due to higher frequencies) ( the size of the antenna required to transmit a signal is proportional to the wavelength (λ) of the signal).

  31. Microwave and Radio Waves • Radio wave is lower frequency signalssuitable for omnidirectional applications, such as radio and television. • Infrared waves can be used for short-range communication in a closed area using line-of-sight propagation

  32. Any Questions ?

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