Telecommunications: Past, Present and Future Branimir Vojcic ECE Dept, GWU.

Telecommunications: Past, Present and Future

Branimir VojcicECE Dept, GWU

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/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?

Communication Systems

An Overview

Communication Systems

CHANNELDISTORTION

NOISEINTERFERENCE

INPUT TRANSDUCER

TRANSMITTER

INPUTMESSAGE

INPUTSIGNAL

TRANSMITTEDSIGNAL

RECEIVEROUTPUT

TRANSDUCEROUTPUT

MESSAGEOUTPUTSIGNAL

RECEIVEDSIGNAL

Model of Communication Systems

COMMUNICATION USING ELECTRICAL AND OPTICAL SIGNALS IS:

Fast Far reaching Economical

• SPEECH

• MUSIC

• PICTURES

• COMPUTER DATA

INPUT MESSAGES ARE TRANSDUCED TO ELECTRICAL OR OPTICAL SIGNALS IF NECESSARY

• VIDEO

t

1 1 1 10 0

Carried InformationThe input messages can be:

Communication channels are physical media through which signals propogate.

Communication channels are physical media through which signals propogate.

EXAMPLES OF COMMUNICATION CHANNELS ARE:

WIRE

COAXIAL CABLE

WAVEGUIDE

OPTICAL FIBER

RADIO LINK

Physical Media

Communication channel introduces:

DISTORTION

NOISE

INTERFERENCE

0 100 200 300 400 500 600 700 800 900 1000-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500 600 700 800 900 1000-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500 600 700 800 900 1000-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500 600 700 800 900 1000-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500 600 700 800 900 1000-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500 600 700 800 900 1000-0.2

0

0.2

0.4

0.6

0.8

1

1.2

Communication Channel

0 50 100 150-1

0

1

CARRIER

0 10 20 30 40 50 60 70 80 90 100-1

-0.5

0

0.5

1

INPUT SIGNAL

0 50 100 150 200 250-1

0

1

AMPLITUDE MODULATED WAVE

1.182 1.184 1.186 1.188 1.19 1.192 1.194 1.196

x 104

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

FREQUENCY MODULATED WAVE

Modulation• Modulation is the process that modifies the input signal into a form appropriate

for transmission over a communication channel (transmitted signal)• Typically, the modulation involves varying some parameters of a carrier wave in

accordance with the input signal:

Receiver recovers the input signal from the received signal. Modulation can be:

ANALOG (Parameter changes of the transmitted signal directly follow changes of the input signal)

DIGIGAL (Parameter changes of the transmitted signal represent discrete-time finite-precision measurements of the input signal)

Primary communication system design considerations:Transmitted power, Channel bandwidth and Fidelity of output message

Digital communication systems are more efficient and reliable

ANALOG

MODULATION0 10 20 30 40 50 60 70 80 90 100

-1

-0.5

0

0.5

1

DIGITAL

MODULATION

+Δ

-Δ

Modulation Type

Optical Networks

Why Optical Transmission?• Immune to electrical interference• No radiation• Low attenuation, long transmission distance • Less bulky than cables• Tremendous capacity• High data rates• Less maintenance cost

coaxial transmission generally has a bandwidth limit of 500 MHz. Current fiber optic systems have not even begun to utilize the enormous potential bandwidth that is possible.

Attenuation vs. Frequency

Attenuation vs. Wavelength

Attenuation and Dispersion

Multiplexing

TDM vs. WDM

TDM

WDM

Relationship Between WDM & TDM

Optical Devices

Optical Networks Market ($Millions)

Wireless Networks

Wireless is Growing Rapidly

Source:The EconomistSept. 18-24, 1999

Traffic Increasingly Consists of Data

Source: http://www.qualcomm.com

Mobile/Cellular Communications

MobileStation

BaseStation

• Every cell corresponds to the service area of one Base Station

• Each frequency can be reused in a sufficiently distant cell

F1

F3

F4

F5

F6

F7

F2

F1

F3

F4

F5

F6

F7

F2

Cellular Concept

Network SwitchingSubsystem

PublicNetworksBase Station

Subsystem

Network Architecture

BSC

MSCHLR,VLRAUCOMC

ISDN

PSTN

PDN

MSBTS

BTS

BSC

Ad-Hoc Mobile Internet

ISP

LEOS

Mobile/Portable

Satellite Communications

Un-tethered, Global, Broadband, Mobile and Ubiquitous.

Satellite Regional Area

Wide Area Local Area

Wireless Mobility

Emerging Connectivity Solutions:Cellular, Satellite, Microwave, and Packet Radio

SOURCE: CISCO

Satellite Features

• New Wideband Frequency Allocations

• Global Access

• Rapid Deployment

• User Mobility

• Multicasting, Broadcasting

• Bypass and/or Serve Terrestrial Disaster

• High Startup Costs, Lower Incremental Cost

Existing Systems

• Global and Regional Trunking

• Direct TV Broadcast

• VSAT Networks

• Mobile Satellite Systems (MSS)

• Paging

• Aeronautical/ Maritime

• Global Positioning (GPS and GLONASS)

Iridium 66 Polar Orbits with spot beams

Local Area Networks

Local Area Networks (1)

• A local Area Network provides the interconnection of a heterogeneous population of mainframes, work stations,personal computers, servers, intelligent terminals and peripherals.

• Topologically, LAN’s connect the devices or stations in the form of a bus, a tree, a ring or a star configuration.

• Wireline (Token Ring, Ethernet)

• Wireless (802.11, Bluetooth, UWB,…)

Wireless Local Area Networks

Source: Proxim

Local Area Networks

Distribution System

Portal

802.x LAN

Access Point

802.11 LAN

BSS2

802.11 LAN

BSS1

Access Point

STA1

STA2 STA3

ESS

Bluetooth

LAN Applications• Client-Server communications

• Shared database access

• Word processing, Electronic mail

• Sharing of mass storage devices, printers and other peripherals, software and computational resources

• Data exchange between computers and mass storage devices

• CAD/CAM, Inventory control, Process control, Device control

A Lesson From the Past“Well Informed people know it is impossible to transmit the voice over wires and that, were it possible to do so, the thing would be of no practical value”

Excerpt from an 1865BOSTON POST editorial