Introduction to Analog And Digital Communications

Second Edition

Simon Haykin, Michael Moher

Chapter 1 Introduction

1.1 Historical Background1.2 Applications1.3 Primary Resources and Operational Requirements1.4 Underpinning Theories of Communication Systems1.5 Concluding Remarks

“To understand a science it is necessary to know its history”-Auguste Comte (1798-1857)

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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 reasons1) The quality of a digitized audio/video signal, measured in terms of

frequency response, linearity, and noise, is determined by the digital-to-analog 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 well-developed 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.