Communication Systems Chapter 1 Term 2 1433-1434

Communication systems by

Dr. Fahad Alraddady

Assistant professor of CIT

[email protected]

Taif University

Communication systems Course Objectives

To learn the basic concepts of communication systems

Text Book

Modern Digital And Analog Communication Systems

By B. P Lathi, 4rd Edition

Reference books

Communication Systems: Analog & Digital – Sanjay Sharma – Kataria & Son

Communication Systems by Bruce Carlson

Communication Systems 4th ed. By Simon Haykin

INTRODUCTION

Communication: is the process of establishing connection or link between two points for information exchange. Or it is simply the Process of conveying message at a distance or it is the basic process of exchanging information.

“A communication system is a process of conveying information from a source to a destination”

Information to be transmitted is called message.

INTRODUCTION

Communication system is a Components/subsystems act together to accomplish information

transfer/exchange. A digital communication system: transfers information

from a digital source to the intended receiver (also called the sink).

An analog communication system transfers information from an analog source to the sink.

INTRODUCTION

Information is data that has been processed in such a way as to be meaningful to the person who receives it. it is any thing that is communicated.

Data: is raw material for data processing.

Types of Data

Analog: it refers to some thing is continuous. It has

continuous value over time.

Examples: human voice, video, audio, acoustics or

physical parameter: temperature and pressure.

Some examples of Communication Systems

INTRODUCTION

Digital: it refers to some thing is discrete.

Examples: text, character strings and data stored in

memory.

To transmit data, it must be transferred to signal.

• Signal: it is electric, electronic or optical representation

of data, which can be sent over a communication media.

• Types of Signals

Analog signal: is a continuous wave form that changes

smoothly over time as shown in Figure:

Digital signal :is discrete , it can only a limited numbers

of defined usually 0 and 1.

Types of Data

Types of Signals

9

Requirements of Communication

Systems Rate of information transfer

◦ The rate of information transfer is defined as the amount of information that must be communicated from source to destination.

◦ It will determined the physical form and technique used to transmit and receive information and therefore determines the way system is designed and constructed

Purity of signal received

◦ The received signal must be the same as the transmitted signal

Requirements of Communication

Systems

Simplicity of the system

◦ Any communication system must be

convenient in order to be effective and

efficient and easy to use.

Reliability

◦ Users must be able to depend on a

communication system. It must work when

needed and transmit and receive information

without errors or with an acceptable error.

Elements of a communication

system:

Information source: the function of information

source is to produce required message which has to

be transmitted. Examples speech, television,

Facsimile and personal computers.

Input Transducer : A transducer is a device which

converts one form of energy into another form

(electrical, optical or electromagnetic).

◦ To convert the message to a form suitable for the

particular type of communication system.

◦ Eg: Speech waves are converted to voltage

variation by a microphone.


system: • The transmitter couples the input message signal to the

channel. It processes and modifies the input for efficient transmission over a channel.

• Signal processing operations performed by the transmitter include:

Amplification:

Filtering:

Modulation : it is a process designed to match the properties of the transmitted signal to the channel through a carrier wave.

The carrier wave form may be a continuous (analog signal)or a pulse waveform(digital signal).

In both cases, the carrier attribute (i.e., the amplitude, frequency or phase) can be changed in continuous or discrete fashion depend on the signal.


system:

The channel and noise : channel is the medium

between the transmitter and the receiver which the signal

travel through it. The function of the channel is to provide a

physical connection between the transmitter and the receiver.

There are two types of channel, point-to-point channels and

broadcasting channels. Examples of point-to-point channels

are wirelines, microwave links and optical fibers. Examples

of broadcasting channels like satellite which allow several

receiving stations to receive simultaneously from a single

transmitter. Or Guided media or unguided media.


system: The Signal undergoes degradation from noise,

interference and distortion.

There are three causes of impairment through the

channel, which are noise, attenuation and distortion.

Attenuation: is a loss of energy and measured in

decibel (dB).

Distortion: Means that the signal changes its form or

shape.

Noise : is unwanted signal which tend to interface with

the required signal. interface is a Contamination by

extraneous signals from human sources.


system: The term SNR (signal to noise ratio) is used to measure

performance (noise) relative to an information analog

signal

The term BER (Bit Error Rate) is used in digital system to

measure the deterioration of the signal.

The receiver extract the input message from the signal and

performs this function through the process of

demodulation in addition to amplification and filtering.

Destination: it converts the electrical message signals to

its original form like loudspeakers and PC.

Output Transducer :Converts the electrical signal at its

input into a form desired by the system used.

Eg: Loudspeaker, PC and tape-recorders.


system:

Input

Transducer Transmitter

Channel

Receiver Output

Transducer

Information

source

Destination Transmission

medium

noise

Lecture 2 Outline

Review Lecture 1

Communication channels

Baseband and passband signals.

Channel effect, signal-to-noise ratio.

Representations of signals.

Power Measurments

The modulation process.

Fundamental limitation of communication Systems.


The channel is the physical path between the

transmitter and the receiver. which carries the

information. We can said basically there are four types

of channels, Telephone channels, Optical fibers, Mobile

radio channels and satellite channels.

A- Telephone channels: a telephone network use a

switching mechanism. The type of the signal is electrical

signal. It is linear. The bandwidth is limited band from

300-3100 Hz.

B-Optical fiber channel: is a dielectric waveguide

which transports light signals from one place to another.

It consists of core surrounding by a cladding layer and

jacket.


C-Mobile radio channel: the term “Mobile Radio”

means the terrestrial situation for the transmitter and the

receiver is capable of being moved. The receiver

received the signal from multipath. The type of the

channel is linear time varying channel.

D-Satellite channels : it covers a wide area. There are

geostationary satellite and orbit. It could be broadcast

and point to pint channel.

A channel may linear or non linear. A channel telephone

network is linear while satellite channel is non linear.

A channel may be time varying like mobile radio

channel or time invariant like optical fiber channel.


A channel may bandwidth limited or power

limited. A telephone channel is bandwidth

limited while optical fiber and satellite

channel power limited.

In summary, we can say the channel

properties determine the capacity of the

information and the quality of services

provided by the system.

Baseband and Passband signals

Baseband signal: is that describes signals whose range

of frequencies from close to 0 hertz to highest signal

frequency. If the signal is transmitted directly without

modulation, then it is known as Baseband

Transmission. The baseband transmission is used for

low frequency and short distance.

Passband signal: is a band of frequencies which passes

through some filter or set of filters. If the modulating

signal is impressed through the carrier signal, the

modulated signal is produced. The transmission is called

passband transmission and is used for long distance with

high frequency.

Baseband signals

Passband signals

CHANNEL EFFECT, Signal-To-Noise

Ratio Signal Bandwidth and Power

In communication System, the bandwidth and the signal

power are important factors to control the quality and

data rate.

The bandwidth can be defined in channel and signal.

Bandwidth of channels: is measured in Hertz and can

be defined as the range of frequencies that a channel can

pass. (In analog communication view)

Example: if the channel can transmit with reasonable

fidelity a signal whose frequency components from 0 Hz

to up to maximum 5kHz, the channel bandwidth B is

5kHz.

CHANNEL EFFECT, Signal-To-Noise Ratio

Signal Bandwidth and Power

Bandwidth of channel: is measured in bit per second,

and can be defined as the speed of bit transmission in a

channel or a link. (In Digital communication view)

Bandwidth of Signal : is the range of frequencies in a

composite signal. The faster a signal changes, the higher

its maximum frequency is, and the larger its bandwidth.

To have succeful transmit, the channel bandwidth must

be larger than the bandwidth of the signal.

The signal power: As the power increased, the signal

does not effect and the quality of the system is increased

as SNR is increased.

Power is the rate at which energy is delivered

Representation of Signals

To have a knowledge about the communication system,

we require some mathematical tools for representation

of signal and systems.

A- Periodic and nonperiodic signals

A periodic signal g(t) is a function of time which

satisfies the following condition:

Where denotes time and is the period and define

the duration of one complete cycle. Any signal does

not satisfy the previous condition is non periodic. In

other world does not exist.

tTtgtg allfor 0t

0T tg

0T


B- Deterministic and Random signals

Deterministic signal : it can be modeled as a

completely specified function of time or graphically

Random or Stochastic : it can not be modeled as a

completely specified function of time and must be

modeled probabilistically. It can be described as mean

value, mean square value, and so on.


C- Energy and Power signals

The electrical signal may be represented by voltage or

current and for resistance is equal to on ohm

The total energy and the average power are :

is an energy signal if and only if the total energy of

the signal is finite and nonzero (i.e 0<E <)

dttgdttgE Tg )(|)(|lim 2

T

T

T

T

T

T dttgT

dttgT

P 22 )(2

1lim|)(|

2

1lim

)(tg


is power signal if and only if the normalized

average power of the signal is finite and nonzero (i.e

0<P <)

Note : an energy signal has zero average power,

whereas a power signal has infinite energy.

Signals that are both deterministic and non-periodic are

classified as energy signals

Power signal has finite average power but infinite energy.

As a general rule, periodic signals and random signals

are classified as power signals

)(tg

Power Measurement (dB, dBm)

The decibel (dB) is a transmission-measuring unit used to express gain and losses an electronic devices and circuits

for describing relationship between signal and noise ◦ dB 1W

◦ dBm 1mW

◦ example: 100W = 10 log10 100 = 20dB

= 10 log10 100 = 50 dBm

1mW


If two powers are expressed in the same unit (eg: watts

or microwatts), their ratio is a dimensionless quantity

that can be expressed in decibel form as follows:

)(log10 dB 2

110

P

P

Where P1 = power level 1 (watts)

P2 = power level 2 (watts)

The dB value is the difference in dB between P1 and P2


When used in electronic circuits to measure a power gain or loss,

that equation can rewritten as

)(log01Gain 10(dB)

in

out

P

P

Where Gain (dB) = power gain (dB)

Pout = output power level (watts)

Pin = input power level (watts)

in

out

P

P

absolute power • (+) dB - power gain

•output power is greater than input power

• (-) dB power loss

•output power is less than input power

Examples

Solution:

Power gain, Ap (dB) = 10 log10 [200]

= 10(2.3)

= 23 dB

Solution

Power gain, Ap (dB) = 10 log10 [Pout/Pin]

2.3 = log10 [Pout/Pin]

[Pout/Pin] = antilog 2.3

= 200

1. Convert the absolute power ratio of 200 to a power gain in

dB

2. Convert the power gain Ap = 23 dB to an absolute power ratio

Examples

3. Convert a power level of 200mW to dBm

Solutuion:

dBm = 10 log10 [200mW/1mW]

= 10 log10(200)

= 23 dBm

The modulation process

• When the information does not match with the channel, the transmitter make some process such as a modulation, which involves varying some parameter of a carrier wave in according with message signal.

The process of shifting the baseband signal to passband range is called Modulation.

Modulation : is a process designed to match the properties of the transmitted signal to the channel through a carrier wave.

• The carrier wave form may be a continuous (analog

signal)or a pulse waveform(digital signal).

The modulation process

• In both cases, the carrier attribute (i.e., the amplitude,

frequency or phase) can be changed in continuous or

discrete fashion depend on the signal.

The process of shifting the passband signal to baseband frequency range is called Demodulation.

The signal resulting from the process of the modulation is called Modulated signal. The transmitted signal is called Modulating signal.

• Benefit of Modulation

A-Design practice of an antenna

B- remove interference

C- reduction of noise

Fundamental limitation of

communication Systems • Noise limitation: it is unwanted signal which tend to

interface with the transmission and reception of the

desired signals in a communication system. Type of

noise

• A- external noise

• B- internal noise

• Bandwidth limitation

• Equipment limitation

◦ Equipment ability

◦ Economy and cost factor

◦ National and international law and agreement as well as standardization

(such as ITU etc)

◦ Interaction with existing system

Homework 1

1- Solve Problem 2.1-1a,b and c page 54

2- Solve Problem 2.15 a and b page 54

3- Solve Problem 2.2-1 page 55

Communication Systems Chapter 1 Term 2 1433-1434

Documents

mobile radio channel

optical fiber channel

passband signals

communication systems

communication channels

optical fibers

telephone channels

communication system