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Title: COMMUNICATION SYSTEM EECB353 Chapter 1 INTRODUCTION TO COMMUNICATION SYSTEMS


1
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

2
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

3
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)

4
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
5
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
6
COMMUNICATIONS SYSTEMS EXAMPLES

DIGITAL
MODEM
MODEM
DIGITAL
ANALOG
WAN/LAN (DIGITAL)
IP GATEWAY
IP GATEWAY
ANALOG
ANALOG
7
COMMUNICATIONS SYSTEMS EXAMPLES
AAAIR

FREE SPACE
RADIO STATION
ANALOG
ANALOG
ANALOG
DS1
ANALOG
ANALOG
CODEC
CODEC
8

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

9
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.
10
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)

11
1.1 The Block Diagram of Communication System
Figure Digital signals (a) Telegraph (Morse
code). (b) Continuous-wave (CW) code. (c) Serial
binary code.
12
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
13

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
14

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
15

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
16

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
16
17

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)

18
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
19

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
20
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.
21
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

22
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)

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

25
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.

26

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

27

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).

28
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 (?).

?
29
1.3 Electromagnetic Frequency Spectrum
Figure Frequency and wavelength. (a) One cycle.
(b) One wavelength.
30
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)
31
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?
32

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.

33

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
34

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

35

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

36

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.

37

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.

38

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)

39
Monopole Antenna
Typically used for lt2 MHz Large amount of energy
is launched as a ground wave
40
Yagi-Uda Antenna
41
Driven Collinear Array
42
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

43
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)
44
AMPLITUDE MODULATION
45
(No Transcript)
46
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)

47
(No Transcript)
48
Amplitude Shift Keying (ASK) or On-Off Keying
(OOK)
Basic implementation of Binary ASK
49
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

50
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
51
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.

52
Direct Sequence Spread Spectrum (spreading
factor 7)
53
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)

54
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
55
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).

56
Code Division Multiple Access (CDMA)
sender 1
sender 2
uses sender 1 code to receive sender 1 data
57
Pulse Code Modulation
57
58
Huffman Encoding - Example
(a)
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