Types of Communication

SystemSimplex

-One party can only send information and the other party can only receive the

information.

Duplex

-In a duplex communication system,two-system communication is possible

between the transmitter and receiver.A duplex system can be categorized in two

types.Half duplex (HD) and full duplex (FD)

HD FD

-two way communication

system,signals can only be transmitted

and receiver alternally

-two way communication system which

can transmit and receive signal

simultaneously

Basic Components of

Communication SystemTransmitter

-The transmitter receives the and must either be analogue and digital

information.The original information to be transmitted must either be compatible

with the medium of transmission or it must be first converted the appropriate

form.

Medium

-The transmission medium links the transmitter and receiver.The function of the

transmission medium is to propagate the signals.Howeve, during propagation,

there are possibilities og disturbance attenuation distortion and noise

Receiver

-The receiver will demodulate the receiver signals.In order to do this,the receiver

station must first be tuned to the transmitted frequency.The signals received are

then channeled to the demolutor which outputs the original information.

Transmission MediaTwo Wire Line

-The two wire line commonly used in the telephone lines. It consists of two

parallel insulated wires that are twisted together and insulated with different

coloured plastics insulator.The reason for twisting the wires together is to

decrease the cross line interference

Coaxial Cable

-In communication specially the ratio communication system is the coaxial

cable.The advantage of using this cable are its bandwitch and rabutness

Compared to twisted pair cable.

Fibre Optic Cable

-Fibre optics cable is another medium that is highly in demand in the field of

communication.Yhe cost of this cable is lower and fibre optic offer wider

bandwidth of about 5GHZ.Fibre optics is durable, immune to noise and has

extremely small attenuations

Microwave

-Microwave are transmission frequencies that are usually transmitted through

air.The signal is form an antenna which acts as a transmitted media.Microwave

propagation is base on line-of-sight communication or straight line

communication.The transmitting antenna and the referring antenna must be

located base on point to point communication.In reference ,the transmitting

antena and the recerving antenna are connected by using the repeaters. To avoid

signal attention,due to the distance between P and R repeater Q is

necessary.Repeater R is neede because the signal need to cross the mountain.

Satellite Communication

-Satellite communication is similar to microwave propagation .The earth

transmitter station will transmit modulated signals using the uplink frequencies

that have been allocated .The received frequencies are then converted to

downlink frequencies and are sent to the earth receiver station.

InformationAnalogue Information

-Analog information may have any value within the amplitudes,frequency and

prase range .The physicals quantity being measured may be of any value and

values depending on what is measured

Digital Information

-At any instant in time, digital signals are allowed to have one predefined value

from a set of value such as +1 +2 +3 +4 and in binary from 0V and 5V

0

1

2

3

4

5

6

Column3Column1Column2

Example data from computer

Propagation

-Propagation distance is the maximum distance travelled by the signals.

Multiplexing

-Multiplexing is a sharing technique that allows one or more signal to be

transmitted by serve stations through a signal channel.

(a)Modulating Signal

-Modulating signal is the original information signal that transmitted by a

communication system.

(b)Carrier Signal

-Carrier signal is the signal that carries the modulating signal over long distances.

0 0.5 1 1.5 2 2.5 3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5v

v

Example carrier signal

(c)Modulation

-Modulation is the process of varying the carries signal according to the

modulating signal. A modulator needs two kinds of input signals-the carries and

the modulating signal.

(d)Modulate signal

-The out put of a modulation process is the modulate signal which is then

transmitted to the receiver.

(e)Demodulation

-Demodulation is the process of repreducing the original from the modulated

signal.

(f)Sidebands

-Sidebands are frequencies produced as a result of the modulation process.

(g)Bandwidth (BW)

-Bandwidth is range of modulated frequencies that consist of the carrier signal

and sidebands.

(h)Repeater

-A repeater receiver weak signal, amplifies and retransmits these signals.

ANALOGUE MODULATION

-Analogue modulation is a process of changing one of the characteristic of the

electromotive signals that is either amplitude ,frequency are phase so that it

synchronizes with the modulating signal.

Amplitude Modulation (AM) Frequency Modulation (FM)

-Amplitude modulation is a process of

varying the carrier amplitude by the

modulating signal without changing the

carrier frequency frequency and phase.

-Frequency modulation is the process of

varying the frequency of the carrier

signal in synchronize with the carrier

signal in synchronize with the variations

of the modulating signal.

Digital Modulation

-Digital modulation involves the conversion of analogue to digital signals.

Technique Characteristic

PAM The pulse amplitudes varies with

analogue signals amplitude.

PCM The analogue signal is

sampled ,quantized and encoded to

produced a train of outputs bits.

Pulse Amplitude Modulation (PAM)

-Pulse Amplitude modulation involves the conversion of analogue signal to digital

signals in the form of pulse.

Pulls Code Modulation (PCM)

-Pulls code modulation is a technique of converting analoque signals.The pan

process consists of sampling , quantization and encoding.Sampling is similar to the process in pulse amplitude moddulation.The sampling signal is fed as input to the quantization.Quantization involves the process of approximating each sampled signal to the nearest standard voltage.Encoding involves the process of conding voltage level with predetermined binary bits.

The performance of the digital signal is much better compared to the

performance is the analogue signal.This is due to immunity of the digital signal to

noise. Noise affects the amplitude of the analogue signal in the transmission line.

ADVANTAGE DISANVANTAGE

1.Narrow bandwidth.

2.Simple and low cost circuit

1.Easily affected by noise

2.A carrier is needed during

transmission.

3.Difficult to improve the signal

quantity.

ANALOGUE SIGNAL

DIGITAL SIGNAL

ADVANTAGES DISANVANTAGE

1.Imunity to noise

2.High speed

1.Wider bandwidth

2.Need precise synchronization