Analog and Digital Communication: Introduction and Evaluation Scheme, Slides of Digital Communication Systems

Download Analog and Digital Communication: Introduction and Evaluation Scheme and more Slides Digital Communication Systems in PDF only on Docsity!

ANALOG & DIGITAL

COMMUNICATION

Introduction [Lecture 1 ]

Evaluation scheme

 Quiz 1 ------ 10 %

 Mid semester exam ------- 25 %

 Quiz 2 ------- 10%

 Project --------- 15 %

 End semester Exam ----- 40%

Signals and systems- Review

 What is a signal?

 Distinction between analog and digital signal

 Time domain description

 Convolution

 Impulse response

 Frequency domain description of signal

 Transfer function of a system

What does a communication system

do?

 Transmits information from a source to destination.

 What is the nature of information?

What is heard (Audio)

What is seen

Text , Image ,Video

Information transmitted as an electric

signal

 Why?

Transmission is easy

Mechanical transmission

Transducers

 These convert a given signal into an electrical signal

 Also convert an electrical signal into the desired

form

 Sound to Electrical

 Electrical to Sound

Other transducers

 Temperature to Electrical

Thermocouple

 Electrical to Temperature : Heater

Two important aspects in

communication systems

 Frequency response of the channel

 Noise

Frequency response of the line

Trans

mitter

Receiver

WIRED SYSTEM

1 2

2

R R

R

V

Vo

VoltageGain A

At f

1 2

1 2 : 2

R R

RR

R

R C

f

Cut off frequency

p p

c 

f fmax 

For no distortion

c 

Vo

Shorter the line , smaller

is R1 and C and fc is

larger

Problem 1

1 2

1 2

1 2

2

R R

RR

and R R C

where f

f

j f R R

R

A

Show that

p p

p

p

Suppose the transmission line resistance is 168 ohms/km.

Find the attenuation at zero frequency and also find the

cut-off frequency if the transmission line is 10 km long and is

terminated in 600 ohms resistance. C = 50nF

Answers to problem 1

 Attenuation at zero frequency : 11.6 dBs

 Cut-off frequency : 7200 Hz

Equalizer transfer function

1 2

1 2

1 1 1

1 2

2

R R

RR

R

R C

and f C R

where f

f

f R R j

f

f R j

A

Showthat

p

p

z p

p

z

Noise

 Noise in receiver

Thermal noise generated in resistors at receiver

Noise within active devices

 Remedies

Large transmitted power

Filtering

Coding