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Communications II

Mohammad Fathi

mfathi@uok.ac.ir

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

1 Mm300 Hz

10 km30 kHz

100 m3 MHz

1 m300 MHz

10 mm30 GHz

100 m3 THz

1 m300 THz

visible lightVLF LF MF HF VHF UHF SHF EHF infrared UV

optical transmissioncoax cabletwisted pair

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

)()()()()()()( tndtshtnthtstr

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Mathematical models for communication channels

• Linear time-variant (LTV) filter channel

– Multipath channel

It’s a special case of LTV

Widely used in wireless communications

)();()()( tnthtstr

)()();( tndtsth

signal at sender signal at receiver

LOS pulses