communication systems chapter 1 term 2 1433-1434
TRANSCRIPT
Communication systems by
Dr. Fahad Alraddady
Assistant professor of CIT
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.
Elements of a communication
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.
Elements of a communication
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.
Elements of a communication
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.
Elements of a communication
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.
Elements of a communication
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.
Communication channels
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.
Communication channels
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.
Communication channels
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
Representation of Signals
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.
Representation of Signals
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
Representation of Signals
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
Power Measurement (dB, dBm)
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
Power Measurement (dB, dBm)
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