Chapter 3
Signals
and
Encoding/Modulating
BY
Mr.Sukchatri Prasomsuk
Contents :
•
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•
•
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3.1 Analog and Digital
3.2 Periodic and Aperiodic Signals
3.3 Analog Signals
3.4 Time and Frequency Domains
3.5 Composite Signals
3.6 Digital Signals
3.7 Digital-to-Digital Conversion
3.8 Analog-to-Digital Conversion
3.9 Digital-to-Analog Conversion
3.10 Analog-to-Analog Conversion
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Introduction :
• Information can be in the form of data, voice,
picture, image, numeric data, characters, or
code.
• You cannot roll up a photograph, insert it into
a wire and transmit it across network.
• must encoded description of the data.
• You can use an encoder to create a stream of
1 and 0 that tells the receiving device.
• To be transmitted, information must be
transformed into electromagnetic signals.
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3.1 Analog and Digital
• Analog refers to something that is continuous
: a set of specific points of data and all
possible points between.
• Ex : Analog data - voice, sound, light, wave,...
• Source: Sun, bulb, lamp, microphone, speaker, ….
Value
Time
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3.1 Analog and Digital
• Digital refers to something that is discrete :
a set of specific points of data with no other
points in between.
• Ex. Digital data - is data stored in the memory of a
computer in the form of 0s and 1s.
• Transfer from one position to another inside or outside
the computer. Such as : computer to Printer, CPU to RAM,
….
Value
Time
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3.1 Analog and Digital
•
•
•
•
Conclusion :
Signals can be analog or digital.
Analog signals can have any value in a range.
Digital signals can have only a limited number
of values.
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3.2 Periodic and APeriodic Signals
• Both analog and digital signals can be of two
forms: periodic and aperiodic (nonperiodic).
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3.2 Periodic and APeriodic Signals
• Periodic Signals : is a signal that it completes
a pattern within a measurable time frame,
called a period, and repeats that pattern over
identical subsequent periods.
• The completion of one full pattern is called a
cycle.
• A period is defined as amount of time(sec.)
required to complete one full cycle.
• The duration of a period represented by T.
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3.2 Periodic and APeriodic Signals
• Analog
Value
Time
T
• Digital
T
T
T
Value
Time
T
T
T
T
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3.2 Periodic and APeriodic Signals
• A Periodic or nonperiodic Signals, signal
changes constantly without exhibiting a
pattern or cycle that repeats over time.
• Analog
Value
Time
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3.2 Periodic and APeriodic Signals
• An aperiodic signals can be decomposed into
an infinite number of periodic signal.
• A sine wave is the simplest periodic signal.
• Digital
Value
Time
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3.3 Analog Signals
• Analog signal can be classified as simple or
composite.
• A simple analog signal, or a sine wave, cannot
be decomposed into simpler signals.
• A composite analog signal is composed of
multiple sine waves.
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3.3 Analog Signals
• Simple Analog signals : the sine wave is the
most fundamental form of a periodic analog
signal.
• Visualized as a simple oscillating curve, Its
change over the course of a cycle is smooth
and consistent, a continuous, rolling flow.
• Amplitude : refers to the height of the signal.
The unit for amplitude depends on the type of
the signal. For electrical signals, the unit is
normally volts, amperes, or watts.
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3.3 Analog Signals
• Amplitude :
Value
MAX.
amplitude
T1
Time
MIN.
amplitude
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3.3 Analog Signals
• Period and Frequency :
Value
Four period in one second ---> 4 Hz
1 Sec.
Time
T
Period = 1/4 second
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3.3 Analog Signal
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3.3 Analog Signals
• Unit of Period : Period is expressed in
seconds (s).
• The communications industry uses five unit
to measure period:
• Second
(s)
-3
• millisecond
(ms = 10 )
-6
• microsecond (us = 10 )
-9
• nanosecond (ns = 10 )
-12
• Picosecond
(ps = 10 )
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3.3 Analog Signals
• Unit of Frequency : Frequency is expressed in
hertz (Hz) .
• The communications industry uses five unit to
measure frequency:
• Hertz
(Hz)
3
• Kilohertz
(KHz = 10 Hz)
6
• Megahertz
(MHz = 10 Hz)
9
• Ginanosecond (GHz = 10 Hz)
12
• Terahertz
(THz = 10 Hz)
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3.3 Analog Signals
• Period is the amount of time it takes a signal
to complete one cycle;
• Frequency is the number of cycles per second.
• Frequency and period are inverse of each
other:
• Frequency (f ) = 1/T
• Or
• Period
(T) = 1/f
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3.3 Analog Signals
• Ex.: A sine wave has a frequency of 8 KHz.
What is its period?
• Solution :
• Period
(T) = 1/f
•
= 1/8000
•
= 0.000125 sec.
•
= 125 x 10-6 sec.
• Or
= 125 us #
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3.3 Analog Signals
High
Frequency
Change in a short span of time
T
Low
Frequency
Change in a long span of time
Note : If a signal does not change at all, its frequency is zero
Hz).
If a signal changes instantaneously, its frequency is infinity.
(0
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3.3 Analog Signals
• Phase : describes the position of the
waveform relative to time zero.
• Phase is measured in degrees or radians (360
degrees is 2 Pi radians).
o
• A complete period => a phase shift of 360
o
• half a period
=> a phase shift of 180
o
• A quarter period
=> a phase shift of 90
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3.3 Analog Signals
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3.3 Analog Signals
• Ex : A sine wave is offset 1/6 of a cycle with
respect to time zero. What is its phase?
Solution
we know that one complete cycle is 360 degrees.
Therefore, 1/6 of a cycle is
1/6 x 360 = 60 degree #
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3.3 Analog Signals
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3.3 Analog Signals
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3.4 Time and Frequency Domains
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3.4 Time and Frequency Domains
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3.4 Time and Frequency Domains
• A low-frequency signal in the frequency
domain corresponds to a signal with a long
period in the time domain and vice versa.
• A signal that changes rapidly in the time
domain corresponds to high frequencies in the
frequency domain.
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3.5 Composite Signals
• Composite Signals : a signal composed of more
than one sine wave.
• The frequency spectrum of a signal is the
combination of all sine wave signal that make
up that signal.
• Bandwidth : The difference between the
highest and the lowest frequencies of a
composite signal. It also measures the
information-carrying capacity of a line or a
network.
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3.5 Composite Signals
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3.5 Composite Signals
The frequency spectrum
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3.6 Digital Signals
• Digital signal : A discrete signal with a limited
number of values.
• O is zero voltage (0 V.)
• 1 is a positive voltage (5V.)
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3.6 Digital Signals
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3.6 Digital Signals
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3.6 Digital Signals
• Ex. A digital signal has a bit rate of 2000 bps.
What is the duration of each bit (bit
interval)?
• Solution
The bit interval is the inverse of the bit
rate.
Bit interval = 1/(bit rate)
= 1/2000 = 0.0005 sec.
-6
= 500x10 sec. = 500 us #
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Basics of Encoding Networking Signals
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Binary Encoding Schemes
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Binary Encoding Schemes
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Type of Modulation
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Encoding Signals as Voltages
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Encoding Singnals as Electromagnatics waves
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Encoding and Modulating
• We must transform data into signals to send
them one place to another.
• Different conversion schemes :
Conversion methods
Digital-Digital
Analog-Digital
Digital-Analog
Analog-Analog
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3.7 Digital-to-Digital Conversion
• Digital-to-Digital encoding : conversion is the
representation of digital information by a
digital signal.
101110011
Digital to Digital
Encoding
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3.7 Digital-to-Digital Conversion
• Type of digital-to-digital encoding
Digital-Digital encoding
Unipolar
Polar
Bipolar
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3.7 Digital-to-Digital Conversion
Polar
NRZ
NRZ-L
NRZ-I
RZ
Biphase
Manchester
Differential
Manchester
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3.7 Digital-to-Digital Conversion
• Unipolar encoding uses only one level of value.
• Polar encoding used two levels (positive and negative)
of amplitude.
• NRZ (Nonreturn to Zero) : NRZ-L, NRZ-I
• In NRZ-L the level of the signal is dependent upon
the state of the bit.
• In NRZ-I the is inverted if a 1 is encountered.
• RZ (Return to Zero) : anytime the original data
contain strings of consecutive 1s or 0s.
• A good encoded digital signal must contain a provision
for synchronization.
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3.7 Digital-to-Digital Conversion
• Biphase encoding is implemented in two different
ways : Manchester and differential Manchester.
• In Manchester encoding, the transition at the middle
of the bit is used for both synchronization and bit
representation.
• In differential Manchester encoding, the transition
at the middle of the bit is used only for
synchronization. Thebit representation is shown by
the inversion or noninversion at the beginning of the
bit.
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3.7 Digital-to-Digital Conversion
0
Amplitude
0
1
=
1
0
0
1
=
1
1
Time
Manchester
Differential
Manchester
Time
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3.7 Digital-to-Digital Conversion
• Bipolar encoding : we use three levels : positive, zero,
and negative.
Bipolar
AMI
B8ZS
HDB3
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3.7 Digital-to-Digital Conversion
Bipolar AMI encoding : is the simplest type of
bipolar encoding.
Amplitude
0
1
0
0
1
1
1
0
Time
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3.7 Digital-to-Digital Conversion
• B8ZS if eight 0s come one after another, we change
the pattern in one of two ways based on the polarity
of the previous 1.
B8ZS encoding
Polarity of
previous bit
Polarity of
previous bit
+
0
0
0
0
0
0
0
0
-
0
0
0
0
0
0
0
0
+
0
0
0
+
-
0
-
+
-
0
0
0
-
+
0
+
-
Violation
Violation
Violation
Violation
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3.7 Digital-to-Digital Conversion
• HDB3 (High-Density Bipolar 3 : If four 0s come one after
another, we change the pattern in one of four ways based on the
polarity of the previous 1 and the number of 1s since the last
substitution.
+
0
0
0
0
-
0
0
0
0
+
0
0
0
+
-
0
0
0
-
a) If the number of 1s since the last substitution is odd.
+
0
0
0
0
-
0
0
0
0
+
-
0
0
-
-
+
0
0
+
b) If the number of 1s since the last substitution is even
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3.8 Analog-to-Digital Conversion
• Introduction :
MAX.
amplitude
T1
Analog to Digital
Conversion
(Codec)
MIN.
amplitude
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3.8 Analog-to-Digital Conversion
• PAM (Pulse Amplitude Modulation) :
M
AX.
am
plitude
Amplitude
T1
M
IN
.
am
plitude
PAM Signal
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3.8 Analog-to-Digital Conversion
• PCM (Pulse Code Modulation) : Pulse amplitude
modulation (PAM) has some applications, but it
is not used by it self in data communication.
However, it is the first step in another very
popular conversion method called pulse code
modulation (PCM)
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3.8 Analog-to-Digital Conversion
• Quantized PAM signal :
+ is 0 and - is 1
Ex. +26 = 00011010, +48 = 00110000, +127 = 011111111,
-80 = 11010000
Amplitude
+ 127
+ 48
+ 26
Time
- 80
PAM Signal
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3.8 Analog-to-Digital Conversion
• From analog signal to PCM digital code
Analog Signal
PAM
Quantization
Binary encoding
00110111011
Digital-Digital
encoding
+024
00011000
+038
0010110
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3.8 Analog-to-Digital Conversion
• Nyquist thorem : Highest frequency = x Hz
Sampling rate = 2x samples/second
Amplitude
+ 127
+ 48
+ 26
Time
Sampling interval = 1/2x
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3.8 Analog-to-Digital Conversion
•
Using analog signals to build digital signals
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3.8 Analog-to-Digital Conversion
• Ex. What sampling rate is needed for a signal with a
bandwidth of 10,000Hz (1,000 to 11,000 Hz)?
• Solution
The sampling rate must be twice the highest
frequency in the signal:
sampling rate = 2(11,000)
= 22,000 samples/second #
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3.8 Analog-to-Digital Conversion
• Bit Rate : After finding the number of bits per
sample, we can calculate the bit rate using the followig
formula:
• Bit rate = Sampling rate x Number of bits persample
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3.8 Analog-to-Digital Conversion
• Ex. We want to digitize the human voice. What is the
bit rate assuming eight bits per sample?
• Solution
The human voice normally contains frequencies from 0
to 4000 Hz. So the sampling rate is:
= 4000 x 2 = 8000 samples/second
The bit rate can be calculates as:
Bit rate = Sampling rate x Number of bits per sample
= 8000 x 8 = 64,000 bit/s = 64 Kbps #
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3.9 Digital-to-Analog Conversion
• Is the process of changing one of the characteristics
of an analog signal based on the information in a
digital signal (0 and 1).
MAX.
amplitude
Digital to Analog
Modulation
T1
MIN.
amplitude
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3.9 Digital-to-Analog Conversion
• Types of digital-to-analog modulation
Digital-to-Analog
Modulation
ASK
FSK
PSK
QAM
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3.9 Digital-to-Analog Conversion
•
•
•
•
•
•
•
ASK (Amplitude shift keying) : amplitude of carrier signal
FSK (Frequency shift keying) : frequency of carrier signal
PSK (Phase shift keying) : phase of the carrier signal
QAM (Quadrature amplitude modulation):phase+amplitude
Bit rate is the number of bits per second.
Baud rate is the number of signal units per second.
Baud rate is less than or equal to the bit rate.
So, Baud rate = number of signal elements
Bit rate = Baud rate X number of
bits/signal element
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3.10 Analog-to-Analog Conversion
• Is the representation of analog information by analog
signal.
MAX.
amplitude
MAX.
amplitude
T1
MIN.
amplitude
Analog to Analog
Conversion
T1
MIN.
amplitude
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3.10 Analog-to-Analog Conversion
• Type of analog-to-analog modulation
Analog-to-Analog
Conversion
AM
FM
PM
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3.10 Analog-to-Analog Conversion
• AM (Amplitude modulation) : The bandwidth of an
audio signal (Speech and music) is usually 5 KHz.
Therefore, an AM radio station needs a minimum
bandwidth of 10 KHz. (AM : 530-17 KHz)
• FM (Frequency modulation) : The bandwidth of an
audio signal (Speech and music) is usually 15 KHz.
Therefore, an AM radio station needs a minimum
bandwidth of 150-200 KHz. (FM : 88-108 MHz)
• PM (Phase modulation) is used in some system as as
alternative to frequency modulation.
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3.11 Network signal propagation
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3.12 Network attenuation
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3.13 Network reflection
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3.14 Noise
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3.14 Noise
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3.15 Dispersion, jitter, and latency
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3.16 Collision
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3.17 Messages in terms of bits
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Assignments & LAB
• Lab 10.6.6 & Lab 10.7.5 & Lab 10.7.7
• Due date : Next Friday
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