1 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 Shannon Theorem: Maximum data rate for noisy channel B log 2 (2(1+S/N)) (B: bandwidth, S: signal, N: noise) 3k x log 2 (2 x (1+1000)) = 32.9 kbps 14Chapter 2: Physical Layer

15 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

Twisted Pair Category 3, 5 e 6 (UTP, Unshield Twisted Pair) UTP 25 pairs 16

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 17

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

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

Coaxial cable 20

Power Line Uses 21

22 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

Optical Fibers 23

24 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.

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

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

27 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

28 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

Optical Fibers: connecting continents

30 Optical fibers Disadvantas: need of experts Expensive interfaces Unidirection

31 Electromagnetic Spectrum The electromagnetic spectrum and its uses for communication.

32 Electromagnectic Spectrum Electromagnetic spectrum Speed of light 3 x 10 8 m/s (2/3 in cables) f = c spread spectrum – change of frequence Hedy Lamarr

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

34 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

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