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Physical Layer

Physical Layer. Nelson Fonseca. Principle in Action: Nyquist Theorem vs. Shannon Theorem. Nyquist Theorem: Nyquist sampling theorem f s ≧ 2 x f max Maximum data rate for noiseless channel 2 B log 2 L (B: bandwidth, L: # states to represent a symbol) 2 x 3k x log 2 2 = 6 kbps

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Physical Layer

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  1. Physical Layer Nelson Fonseca

  2. Principle in Action: Nyquist Theorem vs. Shannon Theorem • Nyquist Theorem: • Nyquist sampling theorem • fs≧ 2 x fmax • Maximum data rate for noiseless channel • 2 B log2 L (B: bandwidth, L: # states to represent a symbol) • 2 x 3k x log2 2 = 6 kbps • Shannon Theorem: • Maximum data rate for noisy channel • B log2 (2(1+S/N)) (B: bandwidth, S: signal, N: noise) • 3k x log2 (2 x (1+1000)) = 32.9 kbps Chapter 2: Physical Layer

  3. Twisted Pair • Long distances between repeaters • Bandwidth depends on the diameter and length of the cabe • Crosstalk and atenuation • telephony and data communicatiom • Introduces delay (skew) in vídeo atraso

  4. Twisted Pair • Category 3, 5 e 6 (UTP, Unshield Twisted Pair) • UTP 25 pairs

  5. Twisted Pair • Cat3 (16 MHz) 10BASE TX e 100BASET • Cat5 (100 MHz) 100BASE TX e 1000BASET • Cat 6 (250 MHz) 1000Base T (1 Gbps) • Cat 6e 10000Base T (10 gbps) • Cat7 and Cat7a (1Gbps and 10 Gbps) • Maximum distance – 100 meters

  6. Coaxical Cable • Base band Coaxical cabel Oliver Heaviside • 50 ohms • Digital transmission • Maximum 2 Gbits in 1 Km

  7. Coaxical cabel • Broad Band • 75 ohms • Analog transmission • Cable TV, channels 6 MHz - 3 Mbps • Unideractional repeaters: single and duo cable systems

  8. Coaxial cable

  9. Power Line • Uses

  10. Optical Fibers • Optical Refraction • Multimode and unimode • 100Gbps – no need of amplifier for 100 Km • Three componentes: light source, fiber and optical detector • Solitons: pulse inverse seno hyperpolic format pulsos – long distances without distortion

  11. Optical Fibers

  12. Optical Fibers • Diameter: multimode (50 micra), unimode (10 micra). • Conectors lose 10% to 20% of light , encaixadores (10% de perda), fusão. • Source of light: LEDs and semicondictor lasers, • Reception: photodiode 100 Gbps.

  13. Fiber Cables • (a) Side view of a single fiber. • (b) End view of a sheath with three fibers.

  14. Fiber Cables (2) • A comparison of semiconductor diodes and LEDs as light sources.

  15. Optical Fibers • Passive Interface: • Conectors, LEDs and photodiode connected with the fiber – no electronic conversion • Does not impair transmission in case of na elemento stops working • Loss of light in connections

  16. Optical fibers • Repeaters: • Converts optical to electronic signal and then to optical again to renerate the power • In case of a fualt of a device, transmission • Long distances

  17. Optical Fibers: connecting continents

  18. Optical fibers • Disadvantas: need of experts • Expensive interfaces • Unidirection

  19. Electromagnetic Spectrum • The electromagnetic spectrum and its uses for communication.

  20. Electromagnectic Spectrum • Electromagneticspectrum • Speedof light 3 x 108 m/s (2/3 in cables) • lf = c • spread spectrum – changeoffrequence HedyLamarr

  21. Radio • High frequencies signals tend to propagate in straight • AM uses MF band, 1000 Km raio. • HF, VHF –refracted at ionosphere • Omnidirectional: transmitter and receiver do not need to be aligned • Low frequence waves penetrate walls.

  22. Microwave • Above 100 MHz, the waves travel in nearly straight lines and can therefore be narrowly focused • Receiver and transmitter aligned. • Towers located higher than 100 m, need of repeaters every 80 Km. • Multipath fading, refracted in lower ionosphere • Widely used in telephony and TV distribution

  23. Microwaves • High frequencies (10 GHz) absorved by rain • Low costs • industrial,cientific and medical band – no need for permission -902 a 928 MHz 5.725 a 5.850 GHz – wireless phones, gates

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