Communications II. Mohammad Fathi Text book: J.G. Proakis and M. Salehi, Communication System Engineering (2 nd Ed) Syllabus

Transcription

1 Communications II Mohammad Fathi Course information Text book: J.G. Proakis and M. Salehi, Communication System Engineering (2 nd 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] 1

2 Telegraph 1799 Alessandro Volta invented electric battery, 1837 Samuel Morse demonstrated telegraph and 1844 first telegraph line (Washington Baltimore) became operational first transatlantic cable between the US and Europe. Telephone 1875, Alexander Graham Bell 1897, A. B. Strowger, Devised the automatic stepby step switch 1915, transcontinental telephone company 1960, digital switch, Illinois 2

3 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 Wireless communications 1933, Armstrong, Frequency modulation 1929, TV, Vladimir K. Zworykin 1939, BBC Broadcasting television service on a commercial basis 3

4 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 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. 4

5 Optical Communications 1966, K.C. Kao, G. A. Hockham Proposed the use of a clad glass fiber as a dielectric waveguide , The laser had been invented and developed. Currently, most of wireline communications systems are being replaced by fiber optics. 5

6 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 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) 6

7 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 pair coax cable optical transmission 1 Mm 300 Hz 10 km 30 khz 100 m 3 MHz 1 m 300 MHz 10 mm 30 GHz 100 m 3 THz 1 m 300 THz VLF LF MF HF VHF UHF SHF EHF infrared visible 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 3x10 8 m/s, frequency f 7

8 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 8

9 Digital communication Basic elements 9

10 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 10

11 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( from electronic components and amplifiers, Gaussian noise process Linear filter channel r( s( h( n( h( ) s( t ) d n( 11

12 Mathematical models for communication channels Linear time-variant (LTV) filter channel r( s( h( ; n( h( ; s( t ) d n( Multipath channel It s a special case of LTV Widely used in wireless communications LOS pulses signal at sender signal at receiver 12