Transcript Introduction to Analog And Digital Communications

Introduction to Analog And Digital
Communications
Second Edition
Simon Haykin, Michael Moher
Chapter 1 Introduction
1.1 Historical Background
1.2 Applications
1.3 Primary Resources and Operational Requirements
1.4 Underpinning Theories of Communication Systems
1.5 Concluding Remarks
“To understand a science it is necessary to know its history”
-Auguste Comte (1798-1857)
1.1 Historical Background

Telegraph
 1844, Samuel Morse,
 “What hath God wrought” transmitted by Morse’s electric telegraph
 Washington D.C ~ Baltimore, Maryland
 Morse code : variable-length code (a dot, a dash, a letter space, a word
space)

Radio
 1864, James Clerk Maxwell
 Formulated the electromagnetic theory of light
 Predicted the existence of radio waves
 1887, Heinrich Hertz
 The existence of radio waves was confirmed experimentally
 1894, Oliver Lodge
 Demo : wireless communication over a relatively short distance (150 yards)
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 1901, Guglielmo Marconi
 Demo : wireless communication over a long distance (1700 miles)
 1906, Reginald Fessenden
 Conducting the first radio broascast
 1918, Edwin H. Armstrong
 Invented the superheterodyne radio receiver
 1933, Edwin H. Armstrong
 Demonstrated another modulation scheme ( Frequency nodulation)

Telephone
 1875, Alexander Graham Bell
 Invented the telephone
 1897, A. B. Strowger
 Devised the autiomatic step-by-step switch
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
Electronics
 1904, John Abbrose Eleming
 Invented the vacuum-tube diode
 1906, Lee de Forest
 Invented the vacuum-tube triode
 1948, Walter H. Brattain, William Shockley (Bell Lab.)
 Invented the transistor
 1958, Robert Noyce
 The first silicon integrated circuit (IC) produce

Television
 1928, Philo T. Farnsworth
 First all-electronic television system
 1929, Vladimir K. Zworykin
 all-electronic television system
 1939, BBC
 Broadcasting television service on a commercial basis
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
Digital Communications
 1928, Harry Nyquist
 The theory of signal transmission in telegraphy
 1937, Alex Reeves
 Invent pulse-code modulation
 1958, (Bell Lab.)
 First call through a stored-program system
 1960, (Morris, Illinois)
 The first commercial telephone service with digital switching begin.
 1962, (Bell Lab.)
 The first T-1 carrier system transmission was installed
 1943, D. O. North
 Matched filter for the optimum detection of a unknown signal in a additive
white noise
 1948, Claude Shannon
 The theoretical foundation of digital communications were laid
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
Computer Networks
 1943~1946, (Moore School of Electrical Engineering of the Univ. of
Pennsylvania)

ENIAC : first electronic digital computer
 1950s
 Computers and terminals started communicating with each other
 1965, Robert Lucky
 Idea of adaptive equalization
 1982, G. Ungerboeck
 Efficient modulation techniques
 1950~1970
 Various studies were made on 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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
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
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
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
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1.2 Applications
 Broadcasting
 Which involves the use of a single powerful transmitter and numerous
receivers that are relatively inexpensive to build
 point-to-point communications
 In which the communication process takes place over a link between a
single transmitter and a single receiver.
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
Radio
 Broadcasting
 AM and FM radio
•

The voices are transmitted from broadcasting stations that operate in our
neighborhood
Television
•
Transmits visual images and voice
 Point-to-point communication
 Satellite communication
•
Built around a satellite in geostationary orbit, relies on line-of-sight radio
propagation for the operation of an uplink and a downlink
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
Communication Networks
 Consists of the interconnection of a number of routers that are made up
of intelligent processors
 Circuit switching

Is usually controlled by a centralized hierarchical control mechanism with
knowledge of the network’s entire organization
 Packet switching
 Store and forward
•
•

Any message longer than a specified size is subdivided prior to transmission into
segments
The original message is reassembled at the destination on a packet-by-packet
basis
Advantage
•
When a link has traffic to sent, the link tends to be more fully utilized.
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
Data Networks
 Layer
 A process or device inside a computer system that is designed to perform a
specific function
 Open systems interconnection (OSI) reference model
 The communications and related-connection functions are organized as a
series of layers with well-defined interfaces.
 Composed of seven layers
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
Internet
 The applications are carried out independently of the technology employed to
construct the network
 By the same token, the network technology is capable of evolving without
affecting the applications.
 Internal operation of a subnet is organized in two different ways


Connected manner : where the connections are called virtual circuits, in analogy with
physical circuits set up in a telephone system.
Connectionless manner : where the independent packets are called datagrams, in
analogy with telegrams.
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
Integration of Telephone and Internet
 VOIP’s Quality of service
 Packet loss ratio :
•

the number of packets lost in transport across the network to the total number of
packets pumped into the network
Connection delay :
•
The time taken for a packet of a particular host-to-host connection to transmit
across the network
 IN future
 VOIP will replace private branch exchanges (PBXs)
 If the loading is always low and response time is fast, VOIP telephony may
become mainstream and widespread
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
Data Storage
 The digital domain is preferred over the analog domain for the storage
of audio and video signals for the the following compelling reasons
1) The quality of a digitized audio/video signal, measured in terms of
frequency response, linearity, and noise, is determined by the digital-toanalog conversion (DAC) process, the parameterization of which is under
the designer’s control.
2) Once the audio/video signal is digitized, we can make use of welldeveloped and powerful encoding techniques for data compression to
reduce bandwidth, and error-control coding to provide protection against
the possibility of making errors in the course of storage.
3) For most practical applications, the digital storage of audio and video
signals does not degrade with time.
4) Continued improvements in the fabrication of integrated circuits used to
build CDs and DVDs ensure the ever-increasing cost-effectiveness of these
digital storage devices.
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1.3 Primary Resources and Operational Requirements

The systems are designed to provide for the efficient utilization of
the two primary communication resources
 Transmitted power
 The average power of the transmitted signal
 Channel bandwidth
 The width of the passband of the channel
 Classify communication channel
 Power-limited channel
•
•
•

Wireless channels
Satellite channels
Deep-space links
Band-limited channel
•
•
Telephone channels
Television channels
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 The design of a communication system boils down to a tradeoff
between signal-to-noise ratio and channel bandwidth
 Improve system performance method


Signal-to-noise ratio is increased to accommodate a limitation imposed on
channel bandwidth
Channel bandwidth is increased to accommodate a limitation imposed on
signal-to-noise ratio.
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1.4 Understanding Theories of Communication Systems

Modulation Theory
 Sinusoidal carrier wave
 Whose amplitude, phase, or frequency is the parameter chosen for
modification by the information-bearing signal
 Periodic sequence of pulses
 Whose amplitude, width, or position is the parameter chosen for
modification by the information-bearing signal
 The issues in modulation theory
 Time-domain description of the modulation signal.
 Frequency-domain description of the modulated signal
 Detection of the original information-bearing signal and evaluation of the
effect of noise on the receiver.
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
Fourier Analysis
 Fourier analysis provides the mathematical basis for evaluating the
following issues




Frequency-domain description of a modulated signal, including its
transmission bandwidth
Transmission of a signal through a linear system exemplified by a
communication channel or filter
Correlation between a pair of signals
Detection Theory
 Signal-detection problem
 The presence of noise
 Factors such as the unknown phase-shift introduced into the carrier wave
due to transmission of the sinusoidally modulated signal over the channel
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 In digital communications, we look at
 The average probability of symbol error at the receiver output
 The issue of dealing with uncontrollable factors
 Comparison of one digital modulation scheme against another.

Probability Theory and Random Processes
 Probability theory for describing the behavior of randomly occurring
events in mathematical terms
 Statistical characterization of random signals and noise.
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1.5 Concluding Remarks

Communication systems encompass many and highly diverse applications
 Radios, television, wireless communications, satellite communications, deep-
space communications, telephony, data networks, Internet, and quite a few
others

Digital communication has established itself as the dominant form of
communication. Much of the progress that we have witnessed in the
advancement of digital communication systems can be traced to certain
enabling theories and technologies.

The study of communication systems is a dynamic discipline, continually
evolving by exploiting new technological innovations in other disciplines
and responding to new societal needs.

Last but by no means least, communication systems touch out daily lives
both at home and in the workplace, and our lives would be much poorer
without the wide availability of communication devices that we take for
granted.
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