COMMUNICATION SYSTEM EECB353 Chapter 1 INTRODUCTION TO COMMUNICATION SYSTEMS

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COMMUNICATION SYSTEM EECB353Chapter
1INTRODUCTION TO COMMUNICATION SYSTEMS

• Dr. Anas bin Muhamad Bostamam
• Dept of Electronics Communication Engineering
• Universiti Tenaga Nasional
• http//metalab.uniten.edu.my/shafinaz

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INTRODUCTION TO COMMUNICATION SYSTEMS

• Chapter Outline
• 1.1 The Block Diagram of Communication System
• - Definition
• - Main Components
• - Mode of Communication
• 1.2 SNR, Bandwidth Rate of Communication
• 1.3 The Electromagnetic Frequency Spectrum
• 1.4 Modulation
• - Continuous-wave Modulation
• - Pulse Modulation
• Reference
• Frenzel, Chapter 1

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Significance of Human Communication

• Communication is the process of exchanging
  information.
• Main barriers are language and distance.
• Methods of communication
• Face to face
• Signals
• Written word (letters)
• Electrical innovations
• Telegraph
• Telephone
• Radio
• Television
• Internet (computer)

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1.1 The Block Diagram of Communication System

• Definition - Communication is the transmission of
  information from a source to a user via some
  communication link.

Figure 1 Com Sys Block Diagram
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POSSIBLE SCHEMES
COMMUNICATIONS SYSTEM ANALOG DATA OR DIGITAL DATA
SOURCE ANALOG DATA OR DIGITAL DATA
DESTINATION ANALOG DATA OR DIGITAL DATA
NUMBER OF POSSIBLE SCHEMES
A
D

• AAA
• AAD
• ADA
• ADD

• DAA
• DAD
• DDA
• DDD

A
D
A
D
A
D
A
D
A
D
A
D
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COMMUNICATIONS SYSTEMS EXAMPLES

DIGITAL
MODEM
MODEM
DIGITAL
ANALOG
WAN/LAN (DIGITAL)
IP GATEWAY
IP GATEWAY
ANALOG
ANALOG
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COMMUNICATIONS SYSTEMS EXAMPLES
AAAIR

FREE SPACE
RADIO STATION
ANALOG
ANALOG
ANALOG
DS1
ANALOG
ANALOG
CODEC
CODEC
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1.1 The Block Diagram of Communication System

• Main Components of Com Sys
• Input message can be
• Analog continuous signal i.e value varies
  continuously eg. human voice, music, temperature
  reading
• Digital discrete symbol i.e value limit to a
  finite set eg. data

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1.1 The Block Diagram of Communication System

• Analog Signals
• An analog signal is a smoothly and
  continuously varying voltage or current. Examples
  are
• Sine wave
• Voice
• Video (TV)

Figure Analog signals (a) Sine wave tone.
(b) Voice. (c) Video (TV) signal.
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1.1 The Block Diagram of Communication System

• Digital Signals
• Digital signals change in steps or in discrete
  increments.
• Most digital signals use binary or two-state
  codes. Examples are
• Telegraph (Morse code)
• Continuous wave (CW) code
• Serial binary code (used in computers)

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1.1 The Block Diagram of Communication System
Figure Digital signals (a) Telegraph (Morse
code). (b) Continuous-wave (CW) code. (c) Serial
binary code.
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1.1 The Block Diagram of Communication System

• (ii) Input Transducer
• A device that converts energy from one form to
  another.
• Convert an input signal into an electrical
  waveform.
• Example microphone converts human voice into
  electrical signal referred to as the baseband
  signal or message signal.

Baseband/message signal
Input message
input transducer
Eg. voice
microphone
Electrical signal
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1.1 The Block Diagram of Communication System

• (iii) Transmitter (Tx)
• Modifies or converts the baseband signal into
  format appropriate for efficient channel of
  transmission.
• Example If the channel is fiber optic cable, the
  transmitter converts the baseband signal into
  light frequency and the transmitted signal is
  light.
• Transmitter also use to reformat/reshape the
  signal so that the channel will not distort is as
  much.
• Modulation takes place in the transmitter. It
  involves static variation of amplitude, phase or
  frequency of the carrier in accordance to a
  message signal.

transmitted signal
Baseband/message signal
Tx
Optical signal
transmitter
Eg Electrical signal
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1.1 The Block Diagram of Communication System

• (iv) Channel
• Physical medium through which the transmitter
  output is sent.
• Divided into 2 basic groups
• Guided Electromagnetic Wave Channel eg. wire,
  coaxial cable, optical fiber
• Electromagnetic Wave Propagation Channel eg.
  Wireless broadcast channel, mobile radio channel,
  satellite etc.
• Introduces distortion, noise and interference
  in the channel, transmitted signal is attenuated
  and distorted. Signal attenuation increase along
  with the length of channel.
• This results in corrupted transmitted signal
  received by receiver, Rx

Transmitted signal
Received signal
channel
Distortion Noise
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1.1 The Block Diagram of Communication System

• (v) Receiver (Rx)
• Receiver decodes the received signal back to
  message signal i.e it attempts to translate the
  received signal back into the original message
  signal sent by the source.
• Reprocess the signal received from the channel by
  undoing the signal modification made by
  transmitter and the channel.
• Extract the desired signal from the received
  signal and convert it to a form that suitable for
  the output transducer.
• Demodulation takes place in the receiver.
• (vi) Output transducer
• Convert electrical signals to its original
  waveform.

Output signal
Received signal
Output message
Output transducer
Rx
Eg Electrical signal
voice
speaker
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1.1 The Block Diagram of Communication System

• Transceivers
• A transceiver is an electronic unit that
  incorporates circuits that both send and receive
  signals.
• Examples are
• Telephones
• Fax machines
• Handheld CB radios
• Cell phones
• Computer modems

Output transducer
Rx
input transducer
Tx
Received signal
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1.1 The Block Diagram of Communication System

• 3. Mode of Communication
• Broadcasting
• Involves the use of a single powerful transmitter
  transmit to many receivers. Demodulation takes
  place in the receiver.
• Information-bearing signals flow in one direction
• Eg. TV and radio (Simplex)
• ii. Point to point Communication
• Where a communication process takes place over a
  link between a single transmitter and a receiver.
• Information-bearing signals flow in
  bidirectional, which requires the use of a
  transmitter and receiver at each end of the link
• Eg. Telephone (Full Duplex) and walkie talkie
  (Half Duplex)

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1.2 SNR, Bandwidth Rate of Communication

• 1. Signal to Noise Ratio (SNR)
• SNR is defined as the ratio of signal power to
  noise power. Noise distorts the signal and
  accumulated along the path.
• The dB value is calculated by taking the log of
  the ratio of the measured or calculated power
  (PS) wrt a reference power (PN) level.
• Commonly referred to as the power ratio form for
  dB
• It is normally measured in Decibel (dB), defined
  as 10 times the algorithm (to base 10) of the
  power ratio.
• Eg. SNR of 10, 100 and 1000 correspond to 10,
  20, and 30dBs, respectively.
• dBm is a dB level using a 1mW reference.
• Example - Convert 1mW to dBm

SNRdB
SNR
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1.2 SNR, Bandwidth Rate of Communication
Example 1 A receiver produces a noise power of
200mW with no signal. The output level increases
to 5 W when a signal is applied. Calculate (S
N)/N as a power ratio and in decibels. Example 2
A measured value of 10mW will result in what
dBm power level? Example 3 - A laser diode
outputs 10dBm. Convert this value to (i)
watts (ii) dBW
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1.2 SNR, Bandwidth Rate of Communication

• Bandwidth
• Bandwidth is that portion of the electromagnetic
  spectrum occupied by a signal.
• Specifically, bandwidth is the difference between
  the upper and lower frequency limits of the
  signal or the equipment operation range.
• Figure 1, shows the bandwidth of the voice
  frequency range from 300 to 3000Hz. The upper
  frequency is f2 and the lower frequency is f1.
  The bandwidth, then is
• BW f2 f1

Bandwidth is the frequency range over which
equipment operates or that portion of the
spectrum occupied by the signal. This is the
voice frequency bandwidth.
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1.2 SNR, Bandwidth Rate of Communication

• Bandwidth
• Bandwidth of a channel is the range of
  frequencies that it can transmit with reasonable
  fidelity.
• Bandwidth of an information signal is the
  difference between the highest and lowest
  frequencies contained in the information.
• Bandwidth of a communication channel is the
  difference between the highest and lowest
  frequencies that the channel will allow to pass
  through it (ie its pass band).
• Data rate proportional to bandwidth

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1.2 SNR, Bandwidth Rate of Communication

• Rate of Communication
• Rate of information transmission is directly
  proportional with its bandwidth
• Shannon limit for information capacity, C
• C B log2 (1 SNR)
• 3.32B log10 (1 SNR)
• Where C information capacity (bps)
• B bandwidth (Hz)
• SNR signal to noise ratio (no unit)

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1.2 SNR, Bandwidth Rate of Communication
Example 4 - For a standard telephone circuit with
a SNR of 30dB and a bandwidth of 2.7 kHz,
determine the Shannon limit for information
capacity. Example 5 The telephone channel has
a bandwidth of about 3kHz. Calculate the capacity
of a telephone channel that has an SNR of 1023.
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Important dates

• Proposal submission 24 Dec
• Mid term 23 Jan afternoon
• Project Demo 20 Feb

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1.3 The Electromagnetic Spectrum

• Electromagnetic waves are signals that oscillate
  i.e the amplitudes of the electric and magnetic
  fields vary at a specific rate.
• These oscillation may occur at a very low
  frequency or at an extremely high frequency.
• The range of electromagnetic signals encompassing
  all frequencies is referred to as the
  electromagnetic spectrum.

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1.3 Electromagnetic Frequency Spectrum

• Definition of the Electromagnetic Spectrum
• The total span of frequencies and corresponding
  wavelength used in communications systems.

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1.3 Electromagnetic Frequency Spectrum

• Frequency and Wavelength Frequency
• A signal is located on the frequency spectrum
  according to its frequency and wavelength.
• Frequency is the number of cycles of a repetitive
  wave that occur in a given period of time.
• A cycle consists of two voltage polarity
  reversals, current reversals, or electromagnetic
  field oscillations.
• Frequency is measured in cycles per second (cps).
• The unit of frequency is the hertz (Hz).

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1.3 Electromagnetic Frequency Spectrum

• Frequency and Wavelength Wavelength
• Wavelength is the distance occupied by one cycle
  of a wave and is usually expressed in meters.
• Wavelength is also the distance traveled by an
  electromagnetic wave during the time of one
  cycle.
• The wavelength of a signal is represented by the
  Greek letter lambda (?).

?
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1.3 Electromagnetic Frequency Spectrum
Figure Frequency and wavelength. (a) One cycle.
(b) One wavelength.
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1.3 Electromagnetic Frequency Spectrum

• Frequency and Wavelength Wavelength

Wavelength (?) speed of light frequency Speed
of light 3 108 meters/second Therefore ?
3 108 / f
Example What is the wavelength if the frequency
is 4MHz?
? 3 108 / 4 MHz 75 meters (m)
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1.3 Electromagnetic Frequency Spectrum
Example 6 A signal with a wavelength of 1.5m ,
what is its frequency? Example 7 A signal
travels a distance of 75ft in the time it takes
to complete 1 cycle. What is its frequency?
(Given 1m 3.28ft) Example 8 The maximum peaks
of an electromagentic wave are separated by a
distance of 0.203m. What is the frequency in MHz
ang GHz?
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1.3 Electromagnetic Frequency Spectrum

• The purpose of an electronic communications
  system is to communicate information between two
  or more locations/stations.
• This is accomplished by converting the original
  information into electromagnetic energy and then
  transmitting it to one or more received stations
  where it converted back to its original form.
• Electromagnetic energy can propagate as a voltage
  or current along a metallic wire, as emitted
  radio waves through free space or as light waves
  down an optical fiber.
• Electromagnetic energy is distributed throughout
  an almost infinite range of frequencies.

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1.3 Electromagnetic Frequency Spectrum

• Antenna Propagation
• Electromagnetic waves consists of electric field
  (E) magnetic field (H)
• Polarization is determined by the E-field, and
  thus same with antennas physical configuration

Polarization the field of the electric field of
an electromagnetic wave
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1.3 Electromagnetic Frequency Spectrum

• Types of radio wave propagation
• Ground Wave (Surface Wave)
• Radio wave that travels along the earths
  surface.
• The propagation is better over water, esp salt
  water.
• Not effective for freq above 2MHz
• Reception not affected by daily or seasonal
  changes.
• Application submarine application

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1.3 Electromagnetic Frequency Spectrum

• Space Wave
• Divided into 2 types? direct wave ground
  reflected wave
• Limited by line of sight (LOS)
• Antenna height and earth curvature become
  important factors

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1.3 Electromagnetic Frequency Spectrum

• Sky Wave
• Radiated from the transmitting antenna in
  direction toward the ionosphere.
• Skipping? the alternate refracting and reflecting
  of a sky wave signal between the ionosphere and
  earths surface.
• The ability of the ionosphere to return the radio
  wave depends on the ion density, frequency of
  radio wave and angle of transmission.

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1.3 Electromagnetic Frequency Spectrum

• Antennas
• Half Wave Antenna
• The physical length is 1/2 wavelength of the
  applied frequency.
• Typically used for gt2 MHz
• Dipole Antenna
• Straight radiator, typically ½ wavelength long,
  usually separated at center by insulator and fed
  by a balanced transmission line.

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1.3 Electromagnetic Frequency Spectrum

• Antennas
• Radiation Pattern? diagram indicating the
  intensity of radiation as a function of direction
• Omnidirectional? a spherical radiation pattern
• Directional? concentrating antenna energy in
  certain directions at the expense lower energy in
  other directions
• Beamwidth? Angular separation between the half
  power points on an antennas radiation pattern
• Antenna gain? How much more power in dB an
  antenna will radiate in a certain direction with
  respect to the reference antenna (isotropic point
  source or dipole)

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Monopole Antenna
Typically used for lt2 MHz Large amount of energy
is launched as a ground wave
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Yagi-Uda Antenna
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Driven Collinear Array
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1.4 Modulation

• Modulation is the process of putting information
  onto a high frequency carrier in a transmitter.
• Modulation is important because
• Ease of radiation - related to antenna design
  smaller size. Low loss and low dispersion.
• Simultaneous transmission of several signals
  enables the multiplexing i.e combining multiple
  signals for tx at the same time over the same
  carrier.
• Classification of modulation process
• Analog modulation- consists of Continuous Wave
  (CW) modulation and pulse modulation
• Digital Modulation- ASK, PSK, FSK

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Continuous Wave (CW) Modulation

• CW modulation means that some characteristic of a
  sinusoidal carrier is varied in accordance with
  the message (modulating) signal.
• In CW modulation, the modulated carrier is
  normally sinusoidal signal of the form

Where V, fc and ? are the instantaneous
amplitude, frequency and angle respectively, of
the carrier. Varied characteristics Amplitude
Amplitude Modulation (AM) Frequency Frequency
Modulation (FM) Phase Phase Modulation (PM)
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AMPLITUDE MODULATION
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1.5 Multiplexing Demultiplexing

• Multiplexing is a process of combining several
  signals for simultaneous transmission over same
  channel.
• Demultiplexing is a process of extracting
  individual signal from a combined signal.
• There are 4 types of multiplexing
• Frequency Division Multiplexing (FDM)
• Time Division Multiplexing (TDM)
• Code Division Multiplexing (CDM)
• Wavelength Division Multiplexing (WDM)

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Amplitude Shift Keying (ASK) or On-Off Keying
(OOK)
Basic implementation of Binary ASK
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Frequency Shift Keying (FSK)

• Use logic levels in the data to control the
  frequency of the carrier wave.
• Data 1 for high frequency
• Data 0 for low frequency

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Phase Shift Keying (PSK)

• Example binary 1 is represent with a phase 0,
  while binary 0 is represented with a phase of
  180.
• PSK is equivalent to multiplying the carrier by
  1 when the info is 1, and by -1 when the info is
  0.

Bipolar NRZ
binary 1
binary 0
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Quadrature PSK (QPSK)

• The term quadrature implies that there are four
  possible phases (4-PSK) which the carrier can
  have at a given time.
• The pair of bits represented by each phase is
  called dibit.
• The rate of change (baud) in this signal
  determines the signal bandwidth.
• BUT the throughput or bit rate for QPSK is twice
  the baud rate.

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Direct Sequence Spread Spectrum (spreading
factor 7)
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1.5 Multiplexing Demultiplexing

• Multiplexing is a process of combining several
  signals for simultaneous transmission over same
  channel.
• Demultiplexing is a process of extracting
  individual signal from a combined signal.
• There are 4 types of multiplexing
• Frequency Division Multiplexing (FDM)
• Time Division Multiplexing (TDM)
• Code Division Multiplexing (CDM)
• Wavelength Division Multiplexing (WDM)

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Time Division Multiplexing

• Definition TDM is the time interleaving of
  samples from several sources so that the info
  from these sources can be transmitted serially
  over a single communication channel.
• In brief, TDM is a digital multiplexing technique
  for combining several low-rate channels into one
  high-rate one.
• Can be used for analog digital information
  signal.

Figure gives a conceptual view of TDM. Note that
the same link is used as in FDM here the link
is sectioned by time rather than frequency
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FDM

• In communication systems, Frequency Division
  Multiplexing (FDM) is a method in which each
  signal (channel) is allocated a frequency slot
  within the overall line/transmission bandwidth.
• In other words the total available frequency
  bandwidth on the transmission line is divided
  into frequency channels and each information
  signal occupies one of these channels
• The signal will have exclusive use of this
  frequency slot all the time (i.e. each subscriber
  occupies his/her own slot).

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Code Division Multiple Access (CDMA)
sender 1
sender 2
uses sender 1 code to receive sender 1 data
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Pulse Code Modulation
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Huffman Encoding - Example
(a)