Chapter 3 SignalsandEncoding/Modulating BY Mr.Sukchatri Prasomsuk.

Chapter 3

Signals

and

Encoding/Modulating BY Mr.Sukchatri Prasomsuk

Contents :• 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, ….

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Value

Time


• 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, ….

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Value Time


• 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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• 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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• Analog

• Digital

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Value

Time

T T T T

T T T T

Value

Time


• A Periodic or nonperiodic Signals, signal changes constantly without exhibiting a pattern or cycle that repeats over time.

• Analog

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ValueTime


• An aperiodic signals can be decomposed into an infinite number of periodic signal.

• A sine wave is the simplest periodic signal.

• Digital

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ValueTime

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 :

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T 1

M AX.am plitude

M I N .am plitude

Value

Time

3.3 Analog Signals

• Period and Frequency :

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Value

Time

T

Four period in one second - - -> 4 H z1 Sec.

Period = 1/ 4 second

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)• millisecond (ms = 10-3)• microsecond (us = 10-6)• nanosecond (ns = 10-9)• Picosecond (ps = 10-12)

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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)• Kilohertz (KHz = 103 Hz)• Megahertz (MHz = 106 Hz)• Ginanosecond (GHz = 109 Hz)• Terahertz (THz = 1012 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

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T

High Frequency

Low Frequency

Change in a short span of time

Change in a long span of time

Note : If a signal does not change at all, its frequency is zero (0 Hz). If a signal changes instantaneously, its frequency is infinity.

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).

• A complete period => a phase shift of 360

o

• half a period => a phase shift of 180o

• A quarter period => a phase shift of 90

o

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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?

Solutionwe 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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• 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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The frequency spectrum

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.

= 500x10-6 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 :

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Conversion methods

Digital-Digital Analog-Digital Digital-Analog Analog-Analog

3.7 Digital-to-Digital Conversion

• Digital-to-Digital encoding : conversion is the representation of digital information by a digital signal.

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1 0 1 1 1 0 0 1 1Digital to D igital

Encoding


• Type of digital-to-digital encoding

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Digital-Digital encoding

Unipolar Polar Bipolar


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Polar

NRZ RZ Biphase

NRZ-L NRZ-I ManchesterDifferentialManchester


• 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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• 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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Am plitude

T im e

T im e

0 1 0 0 1 1 1

0 = 1 =

Manchester

D iff erentialManchester


• Bipolar encoding : we use three levels : positive, zero, and negative.

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Bipolar

AMI B8ZS HDB3


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Amplitude

Time

0 1 0 0 1 1 1 0

Bipolar AMI encoding : is the simplest type of bipolar encoding.


• 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.

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+ 0 0 0 0 0 0 0 0

+ 0 0 0 + - 0 - +

Polarity ofprevious bit

Violation Violation

- 0 0 0 0 0 0 0 0

- 0 0 0 - + 0 + -

Polarity o fprevious bit

V io lation V io lation

B8ZS encoding


• 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.

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+ 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

3.8 Analog-to-Digital Conversion

• Introduction :

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T 1

M AX.am plitude

M I N .am plitude

Analog to DigitalConversion

(Codec)


• PAM (Pulse Amplitude Modulation) :

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T 1

M AX.am plitude

M I N .am plitude

Amplitude

PAM Signal


• 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

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Amplitude

Time

PAM Signal

+ 127

- 80

+ 26

+ 48


• From analog signal to PCM digital code

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Analog Signal

PAM

Quantization

Binary encoding

00110111011

Digital-Digitalencoding

+024 +03800011000 0010110

3.8 Analog-to-Digital Conversion• Nyquist thorem : Highest frequency = x Hz

Sampling rate = 2x samples/second

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Am plitude

T im e

Sam pling interval = 1/ 2x

+ 127

+ 26

+ 48


• 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)?

• SolutionThe 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/secondThe 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).

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T 1

M AX.am plitude

M I N .am plitude

Digital to Analog Modulation


• Types of digital-to-analog modulation

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Digital-to-AnalogModulation

ASK FSK PSK

QAM


• 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

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3.10 Analog-to-Analog Conversion • Is the representation of analog information by

analog signal.

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T 1

M AX.am plitude

M I N .am plitude

Analog to Analog Conversion

T 1

M AX.am plitude

M I N .am plitude

3.10 Analog-to-Analog Conversion

• Type of analog-to-analog modulation

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Analog-to-AnalogConversion

AM FM PM

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 time

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Chapter 3 SignalsandEncoding/Modulating BY Mr.Sukchatri Prasomsuk.

Documents

analog signals analog

digital signals

periodic analog signal

analog conversion

composite signals

nonperiodic signals

digital data

composite analog signal