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Transmission medias

Transmission medias. 2 nd semester 1440-1439. NET 205: Data Transmission and Digital Communication. 205NET LOC. 1-Introduction to Communication Systems and Networks architecture OSI Reference Model. 2- Data Transmission Principles 3- Transmission medias. Communication System. Outline.

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Transmission medias

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  1. Transmission medias 2nd semester 1440-1439 NET 205: Data Transmission and Digital Communication

  2. 205NET LOC • 1-Introduction to Communication Systems and Networks architecture OSI Reference Model. • 2- Data Transmission Principles • 3- Transmission medias

  3. Communication System

  4. Outline • Transmission Media • Guided Media • Unguided Media • Wireless Transmission and Antennas • Wireless Propagation • Channel Impairments • Channel Capacity

  5. Transmission Medias • A transmission media is the channel that provides the connection between the transmitter and the receiver. • physical or non-physical link • moves electromagnetic energy from one or more source to one or more receiver. • Which medium should be used?

  6. Types of Transmission Medias The Transmission media or channels can be classified as : • Analog Channels:These channels can carry analog signals.Examples: telephone system, commercial radio system • Digital Channels:These channels can carry digital signals.Example: computer communications

  7. Types of Transmission Medias Medias also can be classified as: • Bounded (guided) medias : signals are confined to the medium and do not leave it. • Unbounded (unguided) medias: signals travel freely and spread throughout the medium.

  8. Outline • Transmission Media • Guided Media • Unguided Media • Wireless Transmission and Antennas • Wireless Propagation • Channel Impairments • Channel Capacity

  9. Guided Media • It is also referred to as Wired or Bounded transmission media. • Signals being transmitted are directed and confined in a narrow pathway by using physical links. • Features: High Speed, Secure, Used for comparatively shorter distances

  10. Electrical Cables • Transmit electrical signals on a conductor, e.g. copper • To minimize interference: • Keep the cables away from other sources • Design the cables to minimize radiation and pick-up

  11. Twisted Pair Cable • A twisted pair consists of two insulated copper wires twisted together in a helical form.

  12. Twisted Pair Cable • Most commonly used and least expensive medium • Used in telephone networks and in-building communications • Telephone networks designed for analog signaling (but supporting digital data) • Also used for digital signaling • Two varieties of twisted pair: shielded (STP) and unshielded (UTP); also multiple categories (CAT5)

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

  14. 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

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

  16. 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. Electromagnetic isolation

  17. Comparison of Guided Media Optical Cables

  18. Outline • Transmission Media • Guided Media • Unguided Media • Wireless Transmission and Antennas • Wireless Propagation • Channel Impairments • Channel Capacity

  19. Unguided Media • It is also referred to as Wireless or Unbounded transmission media. • No physical medium is required for the transmission of electromagnetic signals. • There are 3 major types: Radiowaves, Microwaves, and Infrared • Features: • Signal is broadcasted through air , water • Less Secure • Used for larger distances

  20. Electromagnetic Spectrum • Electromagnetic spectrum is used by many applications • International and national authorities regulate usage of spectrum • Aim: minimize interference between applications/users, while allowing many applications/users

  21. Radio waves • These are easy to generate and can penetrate through buildings. • The sending and receiving antennas need not be aligned. • Frequency Range:3KHz – 1GHz. • AM and FM radios and cordless phones use Radiowaves for transmission. • Further Categorized as: (i) Terrestrial and (ii) Satellite.

  22. Microwave • It is a line of sight transmission • i.e. the sending and receiving antennas need to be properly aligned with each other. • Frequency Range:1GHz – 300GHz. • Higher frequency  carry large quantities of information. • The required antenna is smaller due to shorter wavelength (due to higher frequencies) • These are majorly used for mobile phone communication and television distribution.

  23. Infrared waves • Infrared waves are used for very short distance communication. • They cannot penetrate through obstacles. • This prevents interference between systems. • Frequency Range:300GHz – 400THz. • It is used in TV remotes, wireless mouse, keyboard, printer, etc.

  24. Outline • Transmission Media • Guided Media • Unguided Media • Wireless Transmission and Antennas • Wireless Propagation • Channel Impairments • Channel Capacity

  25. Wireless Transmission Model • For unguided media, transmission and reception are achieved by means of an antenna

  26. 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 • Direction and propagation of a wave depends on antenna type: Isotropic, Omni-directional , and Directional.

  27. 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: radiates power in particular direction. Dish and Yagi are two common types.

  28. Antenna Patterns

  29. Outline • Transmission Media • Guided Media • Unguided Media • Wireless Transmission and Antennas • Wireless Propagation • Channel Impairments • Channel Capacity

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

  31. Wireless Propagation

  32. Microwave and Radio Signals Microwave and Radio wave • Microwave is quite suitable for point-to-point transmission and it is also used for satellite communications. • Radio frequency is lower frequency signalssuitable for omnidirectional applications. • It follow ground or sky wave propagation

  33. 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.

  34. Outline • Transmission Media • Guided Media • Unguided Media • Wireless Transmission and Antennas • Wireless Propagation • Channel Impairments • Channel Capacity

  35. Channel Impairments • Imperfect characteristics of the channel a signal is subjected to different types of impairments. • As a consequence, the received and the transmitted signals are not the same. • These impairments introduce • random modifications in analog signals leading to distortion. • error in the bit values in digital signals.

  36. Channel Impairments

  37. Attenuation • Irrespective of whether a medium is guided or unguided, the strength of a signal falls off with distance. • When a signal travels through a medium it loses energy overcoming the resistance of the medium • Attenuation means loss of energy  weaker signal. • The attenuation leads to several problems:

  38. Attenuation 1- Attenuated signal cannot be detected and interpreted properly  Amplifier 2. Attenuation Distortion

  39. Delay Distortion • Means that the signal changes its form or shape • How this happen

  40. Noise • As signal is transmitted through a channel, noise gets mixed up with the signal, along with the distortion introduced by the transmission media. • Noise is any unwanted energy tending to interfere with the signal to be transmitted. • The noise either be: • External Noise. This is noise originating from outside the communication system • Internal Noise: This is noise originating from within the communication system.

  41. Some Examples of Noise • Thermal Noise: This noise is due to the random and rapid movement of electrons in any resistive component. Electrons “bump” with each other. • Impulse noise is irregular pulses or noise spikes of short duration • Cross talk is a result of bunching several conductors together in a single cable. Signal carrying wires generate electromagnetic radiation, which is induced on other conductors because of close proximity of the conductors

  42. Signal-to-Noise Ratio • In the study of noise, it is not important to know the absolute value of noise. • Even if the power of the noise is very small, it may have a significant effect if the power of the signal is also small. • What is important is a comparison between noise and the signal. • The signal-to-noise ratio (SNR) is the ratio of signal power to noise power.

  43. Signal-to-Noise Ratio SNR = Ps / Pn

  44. Signal-to-Noise Ratio • Ideally, SNR = ∞ (when Pn= 0).In practice, SNR should be high as possible. • A high SNR ratio means a good-quality signal. • A low SNR ratio means a low-quality signal. • The SNR is normally expressed in decibels, that is: SNR = 10 log10 (Ps / Pn) dB

  45. Figure 3.30 Two cases of SNR: a high SNR and a low SNR

  46. Example • The power of a signal is 10 mW and the power of the noise is 1 μW; what are the values of SNR and SNRdB SNR = 10 × 10-3 / 10-6 = 10,000 SNRdB = 10 log10 (10 × 10-3 / 10-6) = 10 log10 (10,000) = 40 dB

  47. Example • If the SNRdB is 36 , find the value of SNR? SNRdB= 10 x log10(SNR) SNR = 10 (SNRdB/10) SNR = 10 (36/10) SNR = 103.6 = 3981

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