Title: COMMUNICATION SYSTEM EECB353 Chapter 1 INTRODUCTION TO COMMUNICATION SYSTEMS
1COMMUNICATION 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
2INTRODUCTION 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
3Significance 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)
41.1 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
5POSSIBLE 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
A
D
A
D
A
D
A
D
A
D
A
D
6COMMUNICATIONS SYSTEMS EXAMPLES
DIGITAL
MODEM
MODEM
DIGITAL
ANALOG
WAN/LAN (DIGITAL)
IP GATEWAY
IP GATEWAY
ANALOG
ANALOG
7COMMUNICATIONS 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
91.1 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.
101.1 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)
111.1 The Block Diagram of Communication System
Figure Digital signals (a) Telegraph (Morse
code). (b) Continuous-wave (CW) code. (c) Serial
binary code.
121.1 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)
181.2 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
201.2 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.
211.2 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
221.2 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)
231.2 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.
24Important dates
- Proposal submission 24 Dec
- Mid term 23 Jan afternoon
- Project Demo 20 Feb
251.3 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).
281.3 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 (?).
?
291.3 Electromagnetic Frequency Spectrum
Figure Frequency and wavelength. (a) One cycle.
(b) One wavelength.
301.3 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)
311.3 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)
39Monopole Antenna
Typically used for lt2 MHz Large amount of energy
is launched as a ground wave
40Yagi-Uda Antenna
41Driven Collinear Array
421.4 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
43Continuous 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)
44AMPLITUDE MODULATION
45(No Transcript)
461.5 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)
48Amplitude Shift Keying (ASK) or On-Off Keying
(OOK)
Basic implementation of Binary ASK
49Frequency 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
50Phase 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
51Quadrature 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.
52Direct Sequence Spread Spectrum (spreading
factor 7)
531.5 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)
54Time 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
55FDM
- 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).
56Code Division Multiple Access (CDMA)
sender 1
sender 2
uses sender 1 code to receive sender 1 data
57Pulse Code Modulation
57
58Huffman Encoding - Example
(a)