Types of Communication System

Types of Communication System Simplex -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

-two way communication system which

system,signals can only be transmitted

can transmit and receive signal

and receiver alternally

simultaneously

Basic Components of  Communication System Transmitter -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 Media Two 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.

Information Analogue 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 6

5

4

3

Column3 Column1

2

1

0

Example data from computer

Column2

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. v

3 2.5 2 1.5 1 0.5 v

0 -0.5 0

0.5

1

-1 -1.5 -2 -2.5

Example carrier signal

1.5

2

2.5

3

(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 

-Frequency modulation is the process of 

varying the carrier amplitude by the

varying the frequency of the carrier

modulating signal without changing the

signal in synchronize with the carrier

carrier frequency frequency and phase.

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

 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.

Quantization

 Encoding involves the process of conding voltage level with predetermined binary bits.

Encoding

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.

ANALOGUE SIGNAL

ADVANTAGE

DISANVANTAGE

1.Narrow bandwidth.

1.Easily affected by noise

2.Simple and low cost circuit

2.A carrier is needed during transmission. 3.Difficult to improve the signal quantity.

DIGITAL SIGNAL ADVANTAGES

DISANVANTAGE

1.Imunity to noise

1.Wider bandwidth

2.High speed

2.Need precise synchronization