Communications II

9/2/2014

Communications II

Course information

Text book: J.G. Proakis and M. Salehi, Communication System Engineering (2nd Ed) • Syllabus – Introduction: [1.1, 1.2, 1.3, and 1.4] – Review of probability and random processes: [Chapter 4] – Digital transmission through the AWGN channel: [7.1, 7.2, 7.3, 7.4, 7.5, 7.6, and 7.7] – Digital transmission through bandlimited AWGN channels: [8.1, 8.3, 8.3, 8.4, and 8.7] – Information sources and source coding: [6.1, 6.2, and 6.3] – Channel capacity: [9.1 and 9.2] – Digital Transmission of analog signals: [6.5, 6.6, 6.7, 6.8, and 6.9] – Channel coding: [9.4, 9.5, and 9.6]

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Historical review

 Telegraph • 1799 Alessandro Volta invented electric battery, • 1837 Samuel Morse demonstrated telegraph and 1844 first telegraph line (Washington‐Baltimore) became operational. • 1858 first transatlantic cable between the US and Europe.

Historical review

 Telephone – 1875, Alexander Graham Bell – 1897, A. B. Strowger, Devised the automatic step‐ by‐step switch – 1915, transcontinental telephone company – 1960, digital switch, Illinois

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Historical review

 Wireless communications . 1831, Faraday demonstrates electromagnetic induction . 1864, J. Maxwell, theory of electromagnetic Fields, wave equations . 1877, H. Hertz, Maxwell’s theory verified experimentally. . 1895, Marconi, wireless telegraphy over a long distance . 1915, Wireless voice transmission New York ‐ San Francisco . 1920, Amplitude modulation

Historical review

 Wireless communications . 1933, Armstrong, Frequency modulation . 1929, TV, Vladimir K. Zworykin . 1939, BBC Broadcasting television service on a commercial basis

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Historical review

 Electronics . 1904, Eleming, vacuum‐tube diode . 1906, Lee de Forest, vacuum‐tube triode . 1948, Walter H. Brattain, William Shockley (Bell Lab.), Transistor. . 1958, Robert Noyce, The first silicon integrated circuit (IC) produce

Historical review

 Satellite Communications . 1945, C. Clark Studied the use of satellite for communications . 1955, John R. Pierce Proposed the use of satellite for communications . 1957, (Soviet Union)Launched Sputnik I . 1958, (United States)Launched Explorer I . 1962, (Bell Lab.)Launched Telstar I . Relay TV signals between Europe and the US.

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Historical review

 Optical Communications . 1966, K.C. Kao, G. A. Hockham Proposed the use of a clad glass fiber as a dielectric waveguide . 1959‐1960, The laser had been invented and developed. . Currently, most of wireline communications systems are being replaced by fiber optics.

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Historical review

• Digital communications – 1924, Nyquist, the maximum signaling rate over the telegraph channel (Nyquist rate) – 1942, Wiener, estimating a desired signal waveform in the presence of noise – 1943, North, matched filter for the optimum detection of a unknown signal in a additive white noise – 1948, Shannon, mathematical foundation for information theory, fundamental limits for digital communications – 1950, Hamming, error‐detecting and error‐correcting codes

Historical review

• Computer networks . 1971, Advanced Research Project Agency Network (APRANET) first put into service . 1985, APRANET was renamed the Internet . 1990, Tim Berners‐Lee, Proposed a hypermedia software interface to internet (World Wide Web)

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Elements of communication systems

 Transmitter – Convert Source (information) to signals – Send converted signals to the channel (by antenna if applicable)  Channel – Wireless: atmosphere (free space) – Wired: coaxial cables, twisted wires, optical fibre  Receiver – Reconvert received signals to original information – Output the original information

Elements of communication systems

• Frequencies of communications

twisted coax cable optical transmission pair

1 Mm 10 km 100 m 1 m 10 mm 100 m 1 m 300 Hz 30 kHz 3 MHz 300 MHz 30 GHz 3 THz 300 THz

VLF LF MF HF VHF UHF SHF EHF infraredvisible light UV

 VLF = Very Low Frequency UHF = Ultra High Frequency  LF = Low Frequency SHF = Super High Frequency  MF = Medium Frequency EHF = Extra High Frequency  HF = High Frequency UV = Ultraviolet Light  VHF = Very High Frequency

 Frequency and wave length:  = c/f wave length , speed of light c  3x108m/s, frequency f

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Channels • Wireline channels – Twisted pair (kHz) – Coaxial cable (MHz) – Fiber optic • Information is transmitted by varying the intensity of the light source. • Wireless electromagnetic channel – ground‐wave propagation (0.3‐3 MHz), AM – Sky‐wave propagation (<30 MHz) – Line of sight propagation (LOS), FM, TV, satellite,… • Underwater acoustic channel • Storage devices

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Digital communication

• Basic elements

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Digital communication

• Source encoder – Converting the output of either analog or digital source to a sequence of binary digits • Channel encoder – Introduce some redundancy in the binary information to overcome the effect of noise and interference • Modulator – Interface to the communication channel

• Atmospheric attenuation in signal propagation

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Digital communication

• Advantages – Better Signal fidelity than analog comm. – Regenerate the signal in long distance transmission – Remove redundancy in the message prior to modulation – Cheaper to implement

Mathematical models for communication channels

• Additive noise channel – n(t) from electronic components and amplifiers, Gaussian noise process • Linear filter channel

 r(t)  s(t)h(t)  n(t)  h( )s(t  )d  n(t) 

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Mathematical models for communication channels

• Linear time-variant (LTV) filter channel

r(t)  s(t)h(;t)  n(t)   h(;t)s(t  )d  n(t) 

– Multipath channel  It’s a special case of LTV  Widely used in wireless communications

LOS pulses

signal at sender signal at receiver