Important Events in Development of Communication Systems

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University

KL University, Vaddeswaram, Dept. of ECE, II B. Tech ECE: Analog Communications 13-EC207 Lecture Notes-1

Fundamentals of Electronics Communications

System

1.0 Introduction.

1.1 Important events in development of communications systems

1.2 Electronic Communications Systems  Transmitter  Communication Channel  Receiver  Noise 1.3 Modulation and Demodulation  Need for Modulation  Analog electronic communications system  Types of Communications Systems 1.4 Propagation of electromagnetic waves

1.5 The Electromagnetic Frequency Spectrum

1.6 Objectives of Communications System Design

OBJECTIVES

 Define the fundamental purpose of an electronic communications system.

 Illustrate a basic electronic communication system and their elements.

 Explain the terms modulation and demodulation and why they are needed in

an electronic communications system.

 Describe the electromagnetic frequency spectrum and their propagation.

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University

1.0 Introduction: The fundamental purpose of an electronic communications system is to transfer information from one place to another. Thus, electronic communication can be summarized as the transmission, reception and processing of information between two or more locations using electronic circuits. The original source information can be in analog form, such as human voice or music, or in digital form, such as binary coded numbers or alphanumeric codes. Analog signals are time varying voltages or currents that are continuously changing, such as sine and cosine waves. An analog signal contains an infinite number of values. Digital signals are voltages or currents that change in discrete steps or levels. The most common form of digital signal is binary, which has two levels. All forms of information however must be converted to electromagnetic energy before being propagated through an electronic communication system.

There are numerous forms of communication. We have wired communication, wherein examples are telephone, broadband internet at home, local area networks at office, just to name a few. We also have wireless communication such as mobile, WiFi,

Bluetooth, radio broadcast, TV broadcast, and many others. It seems that our lives could not function properly without communication.

1.1: Important events in development of communication systems

1838: Telegraph (Cooke and Wheatstone)

1871: Telephone “Caveat” Some believe Antonio Meucci (not A.G. Bell) was the

inventor of the talking telegraph or telephone.

1900: Marconi sends wireless signal across Atlantic.

1920: Beginning of radio broadcasting.

1936: First public B/W TV broadcast.

1951: First public color TV broadcast.

1957: First earth satellite, Sputnik I.

1962: First communication satellite, Telstar I.

1966: Principles of fibre optic communications published (Kao and Hockham).

1973: Birth of Internet.

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University

1979: First-generation cellular phone service.

1985: Fax machines gain popularity.

1990’s: HDTV, second-generation cellular systems. 2000’s: Third-generation cellular systems, satellite radio, “anytime, anywhere, multimedia communications”.

2010’s: Online social networks, smart phones, LTE, wireless sensor networks (WSNs)

A Chronology of Electrical Communication Preliminary Developments: Volta discovers the battery; the mathematical treatises by Fourier, Cauchy, and 1800-1837 Laplace; experiments on electrical and magnetism by Oersted, Ampere, Faraday, and Henry; Ohm’s Law (1826); early telegraph systems by Gauss, Weber, and Wheatstone Telegraphy: Morse perfects his system; Steinhill finds that the earth can be used for a current path; commercial service initiated (1844); multiplexing techniques 1838-1866 devised; William Thomson (Lord Kelvin) calculates the pulse response of a telegraph line (1855); transatlantic cables installed by Cyrus Field and associates 1845 Kirchhoff’s circuit laws enunciated 1864 Maxwell’s equation predicts electromagnetic radiation Telephony Acoustic transducer perfected by Alexander Graham Bell, after earlier attempts by Reis; first telephone exchange, in New Haven, with eight lines (1878); 1876-1899 Edison’s carbon-button transducer; cable circuits introduced; Strowger devises automatic step-by-step switching (1887); the theory of cable loading by Heaviside, Pupin, and Campbell Wireless telegraphy Heinrich Hertz verifies Maxwell’s theory; demonstrations by Marconi and 1887-1907 Popov; Marconi patents a complete wireless telegraph system (1897); the theory of tuning circuits developed by Sir Oliver Lodge; commercial service begins, including ship-to-shore and transatlantic systems 1894 Marconi Radio broadcasting Oliver Heaviside’s publication on operational calculus, circuits, and 1892-1899 electromagnetics Communication electronics Lee De Forrest invents the Audion (triode) based on Fleming’s diode; basic filter types devised by G. A. Campbell and others; experiments with AM radio 1904-1920 broadcasting; transcontinental telephone line with electronic repeaters completed by the Bell System (1915); multiplexed carrier telephony introduced; E. H. Armstrong perfects the superheterodyne radio receiver (1918); first

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University

commercial broadcasting station, KDKA, Pittsburgh Transmission theory 1920-1928 Landmark papers on the theory of signal transmission and noise by J. R. Carson, H. Nyquist, J. B. Johnson, and R. V. L. Hartley Television Mechanical image-formation system demonstrated by Baird and Jenkins; 1923-1938 theoretical analysis of bandwidth requirements; Farnsworth and Zworykin propose electronic systems; vacuum cathode-ray tubes perfected by DuMont and others; field tests and experimental broadcast begin 1931 Teletypewriter service initiated 1934 H. S. Black develops the negative-feedback amplifier 1936 Armstrong’s paper states the case for FM radio 1936 First public B/W TV broadcast 1937 Alec Reeves conceives pulse code modulation World War II 1938-1945 Radar and microwave systems developed; FM used extensively for military communications; improved electronics, hardware, and theory in all areas Statistical communication theory 1944-1947 Rice develops a mathematical representation of noise; Weiner, Kolmogoroff, and Kotel’nikov apply statistical methods to signal detection Information theory and coding 1948-1951 C. E. Shannon publishes the founding papers of information theory; Hamming and Golay devise error-correcting codes 1948-1951 Transistor devices invented by Bardeen, Brattain, and Shockley 1950 Time-division multiplexing applied to telephony 1951 First public color TV broadcast 1953 Color TV standards established in the United States 1955 J. R. Pierce proposes satellite communication systems 1956 First transoceanic telephone cable (36 voice channels) 1957 First earth satellite, Sputnik I 1958 Long-distance data transmission system developed for military purposes 1960 Maiman demonstrates the first laser 1961 Integrated circuits go into commercial production 1962 Satellite communication begins with Telstar I High-speed digital communication Data transmission service offered commercially; wideband channels designed for digital signaling; pulse code modulation proves feasible for voice and TV 1962-1966 transmission; major breakthroughs in the theory and implementation of digital transmission, including error-control coding methods by Viterbi and others, and the development of adaptive equalization by Lucky and co-workers 1963 Solid-state microwave oscillators perfected by Gunn 1964 Fully electronic telephone switching system (No. 1 ESS) goes into service 1965 Mariner IV transmits pictures from Mars to earth

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University

Wideband communication systems Cable TV systems; commercial satellite relay service becomes available; 1966-1975 optical links using lasers and fiber optics; the forerunner of the Internet, ARPANET was created in 1969; 1973 Birth of Internet Integrated-circuit communication modules; high-frequency power MOS devices; digital signal processing with microprocessors; filter circuits using 1975-1985 switched capacitors and surface acoustic waves; rate distortion theory and predictive coding applied to data compression 1979 First-generation cellular phone service 1983 TCP/IP became the official protocol of ARPANET/Internet 1985 Fax machines gain popularity 1990 HDTV, second-generation cellular systems 1985 to Gigabit Networks, B-ISDN or ATM Networks, Digital TV present Third- and fourth-generation wireless systems (Advanced mobile beyond 2000 communications) International Mobile Telecommunications (IMT)-2000; Wireless ATM (WATM) 2010 Online social networks, smart phones, LTE, wireless sensor networks (WSNs)

1.2 Electronic Communication Systems:

Fig1.1 shows a simplified block diagram of an electronic communications system that includes a transmitter, a transmission medium, a receiver and system and other interference noise.

Fig1.1 Simplified block diagram of an electronic communications system

Transmitter: The transmitter is a collection of electronic components and circuits that converts the electrical signal into a signal suitable for transmission over a given

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University medium. Transmitters are made up of oscillators, amplifiers, tuned circuits and filters, modulators, frequency mixers, frequency synthesizers, and other circuits.

Communication Channel: The communication channel is the medium by which the electronic signal is sent from one place to another.

Types of media include

 Electrical conductors

 Optical media

 Free space

 System-specific media (e.g., water is the medium for sonar).

Receivers: A receiver is a collection of electronic components and circuits that accepts the transmitted message from the channel and converts it back into a form understandable by humans. Receivers contain amplifiers, oscillators, mixers, tuned circuits and filters, and a demodulator or detector that recovers the original intelligence signal from the modulated carrier.

Noise: Noise is random, undesirable electronic energy that enters the communication system via the communicating medium and interferes with the transmitted message.

Transceivers: A transceiver is an electronic unit that incorporates circuits that both send and receive signals.

Examples are:  Telephones  Fax machines  Handheld CB radios  Cell phones  Computer modems

1.3 Modulation and Demodulation: To transmit a message signal to a long distance over a communication channel, we need to modify the message signal into a suitable form for efficient transmission over the channel as shown in Fig 1.2. Modification of the message signal is achieved by means of a process is known as modulation.

The transmission channel is best suited for high frequency signal transmission. The high frequency signals are called carriers. Modulation is a scheme which alters some

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University characteristics of the high frequency carrier in accordance with the low frequency message signal called the modulating signal. Modulation is performed in a transmitter by a circuit is called a modulator. A carrier that has been acted on by an information system is called modulated signal. Demodulation is a reverse process of modulation and converts the modulated carrier back to the original signal. Demodulation is performed in a receiver by a circuit called demodulator.

Fig 1.2. Illustration of Modulation process

Need for Modulation: There are various reasons why modulation is necessary in electronic communication systems.

(a) Ease of Radiation / Transmission: It is extremely difficult to radiate low frequency signals from an antenna in the form of electromagnetic energy. For efficient radiation of electromagnetic energy, the radiating antenna should be in the order of a fraction or more of the wavelength of the driving signals. For many baseband signals, the wavelengths are too large for reasonable antenna dimensions. For example the speech signal is concentrated at frequencies in the range of 100 Hz to 3000 Hz. The corresponding wavelengths are calculated as below:

We know that the frequency of a signal and its wavelength is related by

Cf X 

Where f is the frequency of the signal,  is the wavelength of the signal and

C = 3 X 108 m/s is the velocity of light. 8 For 100 Hz,  C 3X 10  3000 Km , f 100

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University

8 For 3000 Hz,  C 3X 10 100 Km f 3000

Hence the speech signals in the range of 100 Hz to 3000 Hz required the wavelengths is 100 to 3000 Km, which is practically impossible. Instead by modulating a high frequency carrier, we effectively translate the signal spectrum into the neighborhood of the carrier frequency, the corresponding wavelength is much smaller and practicable. For example a 10 MHz carrier frequency has a wavelength of 30 meters, and its transmission can be achieved with an antenna size on the order of 3 meters (  /10 ), which is practically possible.

(b) Multiplexing: Simultaneous Transmission of Multiple Signals: Modulation allows multiple signals to be transmitted simultaneously between two points. Modulation schemes enable one to multiplex a number of signals at the same time in a single channel without any interference themselves. This multiplexing scheme is utilized in long distance telephony, data telemetry etc.

(c) Reduction of Noise: The noise and other interference are two major limitations of any communication system. These effects cannot be eliminated completely. However, certain modulation schemes can suppress the noise and interference to some extent.

Ex: Spread spectrum.

(d) Narrow banding: The process of modulation (frequency translation) may be used to change a ‘wideband’ signal into a ‘narrowband’ signal which may be more conveniently processed.

For example an audio range extends from say 50 Hz to 104 Hz. The ratio of the highest audio frequency to lowest is 200. Therefore the antenna size is either too short or too long. Suppose that by modulation, the audio spectrum is translated into the range from (105+50) to (105+104). Then the ratio of the highest frequency to lowest is 1.01. Hence the modulation is useful to process the wide range of signals.

(e) Channel Matching: Modulation is used to make sure that the message signal conforms to the limitations of its channel.

(f) Modulation is used to place the signals at desired frequency band (translation) for signal processing purposes such as filtering, amplification, multiplications etc.

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University

(g) In digital communication, Modulation is used to map digital information sequence into waveforms.

Analog electronic communication system: Fig 1.3 is a simplified block diagram for an analog electronic communication system showing the relationship among the modulating signal, the high frequency carrier and modulated wave. The information signal (intelligence signal) combines with the carrier in the modulator to produce the modulated wave. The information signal is up-converted from low frequencies to high frequencies in the transmitter and down-converted from high frequencies to low frequencies in the receiver. The process of converting a frequency or band of frequencies to another location in the total frequency spectrum is called frequency translation. Frequency translation is an intricate part of electronic communications because information signals may be up- and down-converted many times as they are transported through the system is called a channel. The modulated signal is transported to the receiver over a transmission system. In the receiver, the modulated signal is amplified, down-converted in frequency, and then demodulated to demodulated the original source information.

Fig 1.3 is a simplified block diagram for an analog electronic communication system

Types of Communications Systems: Basically the electronic communication systems are classified as analog communication and pulse (digital) communication as shown in Fig1.4. An analog communication system is a system in which energy is transmitted and received in analog form. With analog communications systems, both the information and the carrier are analog signals. Pulse communication is a technique, some parameter of each pulse (carrier) is modulated by a particular

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University sample value of the message signal. On the other hand the digital communication covers broad range communication techniques, including digital transmission and digital radio. Digital transmission is a true digital system where digital pulses are transferred between two or more points in a communication system.

Fig1.4 Types of Modulation techniques

1.4 Propagation of electromagnetic waves:

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University

Fig1.4 Propagation of electromagnetic waves

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University

1.5 The Electromagnetic Frequency Spectrum: The purpose of an electronic communication system is to communicate information between two or locations commonly called stations. This is accomplished by converting the original information into electromagnetic energy and then transmitting it to one or more receiving stations where it is converted back to its original form. Electromagnetic energy can propagate as a voltage or current along a metallic wire, as emitted radio waves through free space, or as light waves down an optical fiber. Electromagnetic energy is distributed throughout almost infinite range frequencies. The following table illustrates the

International Telecommunications Union (ITU) band designations.

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University

Spectrum of Communication Systems Transmission Propagation Frequency Designation Applications Media Modes Infrared Wideband Data, Optical fibers Laser beam 1 THz – 430 THz Multimedia and ATM Super High Frequency Line-of-Sight (LOS) Satellite, Microwave Waveguides (SHF)3 GHz – 30 GHz Radio Radar and Navigational Ultra High F’cy (UHF) Waveguides/ LOS Radio UHF TV, Mobile 300 MHz – 3000 MHz Co-axial cable Very High F’cy (VHF) Mobile Co-axial cable LOS Radio 30 MHz – 300 MHz VHF TV, FM High F’cy (HF) CB Amateur Radio Co-axial cable Skywave Radio 3 MHz – 30 MHz Civil Defense Medium F’cy (MF) Co-axial cable Groundwave Radio AM 300 kHz – 3000 kHz Low F’cy (LF) Aeronautical Wire pairs Groundwave Radio 30 kHz – 300 kHz Transoceanic Radio Very Low F’cy (VLF) Wire pairs Groundwave Radio Telephone and Telegraph 3 kHz – 30 kHz Audio F’cy (AF) Wire pairs 20 Hz – 20 kHz

1.6 Objectives of Communications System Design:  Two primary resources in communications

 Transmitted power

 Channel bandwidth (very expensive in the commercial market)

 In certain scenarios, one resource may be more important than the other

 Power limited (e.g. deep-space communication)

 Bandwidth limited (e.g. telephone circuit)

Objectives of a communication system design

 The message is delivered both efficiently and reliably, subject to certain

design constraints: power, bandwidth, and cost.

 Efficiency is usually measured by the amount of messages sent in unit power,

unit time and unit bandwidth.

 Reliability is expressed in terms of SNR or probability of error.

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University

Questions Chapter-1

1. Draw the block diagram of electronic communications system explain the each element in brief. 5 M

2. Determine the wavelength of a signal having the frequency of 100 KHz. 1M

3. Explain the terms modulation and demodulation and why they are needed in an electronic communications system. 5 M