Telecommunications-I

Spring 2015

Section 1.0 Outline

• Why is telecommunications important?• History of telecommunications• What is the state-of-the art?• What can we expect in the future?

Telecommunications versus Society/EconomyComment “Why engineering is nothing without economy”?

Ancient Communications Systems

• Pigeons• Messengers• Optical signals using mirrors and light sources• Smoke signals• …

History of Modern Communications (1)

• 1837: The telegraph was invented by Samuel Morse (telegraph = distance writing) which marks the beginning of electrical communications; Morse code consists of a dot, a dash, a letter space and a word space

• 1864: James Clerk Maxwel formulated the electromagnetic theory of light and predicted the existence of radio waves

History of Modern Communications (2)

• 1875: Emile Baudot invented telegraphic code for teletypewritters; each code word consists of 5 mark/space symbols (1/0 in today’s terminology)

• 1875: Alexander Graham Bell invented the telephone for real-time speech transmission (the first step-by-step switch was invented in 1897 by Strowger)

History of Modern Communications (3)

• 1887: Heinrich Hertz demonstated the existence of radio waves

• 1894: Oliver Lodge demonstrated radio communication over short distance (150 yards)

• 1901: Guglielmo Marconi received in Newfoundland a radio signal that originated in England (1700 miles)

History of Modern Communications (4)

• 1904: John Ambrose Fleming invented the vacuum-tube diode

• 1906; Lee de Forest invented the vacuum-tube triode• 1918: Edwin Armstrong invented the superheterodyne

radio receiver• 1928: First all-electronic television demonstrated by Philo

Farnsworth (and then in 1929 by Vladimir Zworykin) and by 1939 BBC had commercial TV broadcasting

History of Modern Communications (5)

• 1937: Alec Reeves invented pulse-code modulation (PCM) for digital encoding of speech signals

• 1943: D.O. North invented the matched filter for optimum detection of signals in additive white noise

• 1946: The idea of Automatic Repeat-Request (ARQ) was published by van Duuren

History of Modern Communications (6)

• 1947: Kotel’nikov developed the geometric representation of signals

• 1948: Claude Shannon published “A Mathematical Theory of Communication”

• 1948: The transistor was invented in Bell Labs by Walter Brattain, John Bardeen and William Shockley

• 1950: Golay and Hamming proposed first non-trivial error correcting codes

History of Modern Communications (7)

• 1957: Soviet Union launched Sputnik I for transmission of telemetry signals (satellite communications originally proposed by Arthur Clark in 1945 and John Pierce in 1955)

• 1958: The first silicon IC was made by Robert Noyce

• 1959: The Laser (Light Amplification by Stimulated Emission of Radiation) was invented

History of Modern Communications (8)

• 1960: The first commercial telephone system with digital switching

• 1965: Robert Lucky invented adaptive equalization

• 1966: Kao and Hockham of Stanford Telephone Laboratories (UK) proposed fiber-optic communications

• 1967: Viterbi Algorithm for max. likelihood decoding of convolutional codes

History of Modern Communications (9)

• 1971: ARPANET was put into service

• 1982: Ungerboeck invented trellis coded modulation

• 1993: Turbo codes introduced by Berrou, Glavieux and Thitimajshima

• What’s next?

Wireless History1901: First radio reception across the Atlantic Ocean

1924: First Mobile Radio Telephone

Signal• How will u define term “Signal”?• How many domains of signal by appearance there?• How signal graphically represented?• How signal mathematically represented?

Parameters of Signal

Analog Signal

• Amplitude• Wavelength• Frequency• Time Period

• Phase Angle

Digital Signal

• Amplitude• Bit rate

Section 2.0Communication Systems

An Overview

Communication Systems

Bandwidth and spectrum of communication system

• Bandwidth refers to what?• Spectrum defines?• Human voice frequency band?• Human ear can detect sound range?• Bandwidth for a wired communication channel? (like

in landline system)

Communication Systems

CHANNELDISTORTION

NOISEINTERFERENCE

INPUT TRANSDUCER TRANSMITTER

INPUTMESSAGE

INPUTSIGNAL

TRANSMITTEDSIGNAL

RECEIVEROUTPUT TRANSDUCER

OUTPUTMESSAGE

OUTPUTSIGNAL

RECEIVEDSIGNAL

Model of Communication Systems

Basically Communication model is comprised of 3 main entities

• Transmitter (Source)• Medium / channel (Wired/wireless)• Receiver (Destination)

Difference Between Transducer & Transcoder?

Difference between Amplifier and regenerator