What is Communication Communication is the process of exchanging information.

Sending and receiving of messages from one place to another

is called communication.

The basic elements involved in communication—

1. Information Source

2. Transmitter

3. Communication Channel

4. Receiver

Types of Electronic CommunicationSimplex

This type of communication is one-way. Examples are: Radio TV broadcasting Beeper (personal receiver)

Half DuplexThe form of two-way communication in which only one party transmits at a time is known as half duplex. Examples are: Police, military, etc. radio transmissions Citizen band (CB) Family radio Amateur radio

Full Duplex • Most electronic communication is two-way and is referred to as Full-duplex. • When people can talk and listen simultaneously, it is called full duplex. The

telephone is an example of this type of communication.

Types of Communication Analog Communication

AM, FM, PM etc.

Digital Communication

ASK, FSK, PSK, QPSK etc.

Microwave Communication

Communication through radio/microwaves/frequencies

Optical Communication

Communication through Light

Basic Block Diagram of Communication System

Noise degrades or interferes with transmitted information

Figure: General Model of All Communication Systems

Basic Concepts of Communication

Analog Signals An analog signal is a smoothly and continuously

varying voltage or current. Examples are:

Sine wave Voice Video (TV)

Analog and Digital Signals

Basic Concepts of Communication

Digital Signals Digital signals change in steps or in discrete increments. Most digital

signals use binary or two-state codes. Examples are: Telegraph (Morse code) Continuous wave (CW) code Serial binary code (used in computers)

Analog and Digital Signals

Channel Multiplexing and Modulation

Modulation and multiplexing are electronic

techniques for transmitting information efficiently

from one place to another.

Modulation makes the information signal more

compatible with the medium.

Multiplexing allows more than one signal to be

transmitted concurrently over a single medium.

Channel Multiplexing and Modulation

Figure: Multiplexing and Modulation at The Transmitter

Channel Multiplexing and Modulation

Frequency Division MultiplexingEach signal is modulated to a different carrier frequencyCarrier frequencies separated so signals do not overlap

(guard bands)

Channel Multiplexing and ModulationTime Division MultiplexingMultiple digital signals interleaved in time domain.Time slots preassigned to sources and fixed.

Modulation FormatsNON-RETURN-TO-ZERO- In Communication, a non-return-to-zero (NRZ) line

code is a binary code in which ones are represented by one significant condition, usually a positive voltage, while zeros are represented by some other significant condition, usually a negative voltage, with no other neutral or rest condition.

RETURN-TO-ZERO- (RZ or RTZ) describes a line code used in communications signals in which the signal drops (returns) to zero between each pulse.

12

Need of Fiber Optic Communications

Fiber communication promised extremely high data rates,

which allow high capacity transmission quickly.

It also had the potential for transmission over long

distances without the need to amplify and retransmit along

the way.

Speed limit of electronic processing, limited bandwidth of

copper/coaxial cables.

Optical fiber has very high-bandwidth (~30 THz)

Optical fiber has very low loss (~0.25dB/km @1550nm)

suitable for long-distance transmission

Increase of the bit rate distance product BL for different communication Technologies over time.

Evaluation of Lightwave Communication Systems

A figure of merit of communication systems is the bit rate–distance product, BL, where B is the bit rate and L is the repeater spacing.

Frequency and Wavelength Graph

15

Optical Communicationamplitude

wavelength

position/distance

electromagnetic wave

carry energy from one point to another

travel in straight line

described in wavelength (usually in mm or nm)

speed of light in vacuum = 3108 m/s

Block Diagram of Optical Fiber Communication System

Figure: Basic Block Diagram of Optical Communication System

Block Diagram of Optical Fiber Communication System

Optical Transmitter

Optical Modulator

Optical Receiver

Advantages of optical fiber communication

Increased Bandwidth and Channel CapacityLow Signal AttenuationImmune to NoiseNo CrosstalkLower Bit Error RatesSignal SecurityElectrical IsolationReduced Size and Weight of CablesRadiation Resistant and Environment FriendlyResistant to Temperature Variations etc.

Disadvantages of optical fiber communication

Specialist skills neededCost of installationCost of transmission equipment from electrical to

optical signalsOptical fibers can not carry electrical power

Applications of optical fiber communication As fibers are very flexible, they are used in flexible digital cameras.

Fibers are used in mechanical imaging i.e. for inspection of mechanical welds in

pipes and engines of rockets, space shuttles, airplanes.

Fibers are used in medical imaging such as endoscopes and laparoscopes.

Fibers can be used under sea communication.

Fibers are used in military applications such as aircrafts, ships, tanks etc.

Nuclear testing applications use optical fiber phase sensors and transducers

Fibers are used in public utility organizations like railways, TV transmission etc.

Fibers are used in LAN systems of offices, industrial plants and colleges etc.

Fibers are used in telecommunication such as voice telephones, video phones,

telegraph services, message services and data networks.

Queries……..

?