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Transmission Medias

Learn about types of transmission media, from electrical cables to wireless systems, their advantages, and how to minimize interference. Discover the impact of antennas, gain, and propagation on wireless signals.

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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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