Analog TransmissionAnalog Transmission

01204325: Data 01204325: Data Communication and Communication and Computer NetworksComputer Networks

Asst. Prof. Chaiporn Jaikaeo, Ph.D.Asst. Prof. Chaiporn Jaikaeo, Ph.D.chaiporn.j@ku.ac.thchaiporn.j@ku.ac.th

http://www.cpe.ku.ac.th/~cpjhttp://www.cpe.ku.ac.th/~cpjComputer Engineering DepartmentComputer Engineering Department

Kasetsart University, Bangkok, ThailandKasetsart University, Bangkok, ThailandAdapted from lecture slides by Behrouz A. Forouzan© The McGraw-Hill Companies, Inc. All rights reserved

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OutlineOutline Aspects of Digital-to-Analog Aspects of Digital-to-Analog

ConversionConversion Amplitude Shift KeyingAmplitude Shift Keying Frequency Shift KeyingFrequency Shift Keying Phase Shift KeyingPhase Shift Keying Quadrature Amplitude ModulationQuadrature Amplitude Modulation

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Digital-to-Analog ConversionDigital-to-Analog Conversion Required to send digital data over a Required to send digital data over a

band-pass channelband-pass channel Also known as Also known as modulationmodulation

(band-pass channel)

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Carrier SignalsCarrier Signals Carrier signalCarrier signal is a high-frequency is a high-frequency

signal acting as a base for signal acting as a base for information signalinformation signal

Also known as "Also known as "Carrier FrequencyCarrier Frequency""

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General form: General form: xx((tt) =) = AA××sin(2sin(2ftft + + ))

periodT = 1/f

peakamplitude

time

signal strength

Sine Waves RevisitedSine Waves Revisited

phase / phase shift

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Conversion TechniquesConversion Techniques

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Bit Rate vs. Baud RateBit Rate vs. Baud Rate Bit rateBit rate the number of the number of bitsbits per second per second Baud rateBaud rate the number of the number of signal signal

elementselements per second. per second.

In the analog transmission of digital data, In the analog transmission of digital data, the baud rate is less than or equal to the the baud rate is less than or equal to the bit ratebit rate

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An analog signal has a bit rate of 8000 bps and a baud rate of 1000 baud. How many data elements are carried by each signal element? How many different signal elements do we need?

SolutionIn this example, S = 1000, N = 8000, and r and L are unknown. We find first the value of r and then the value of L.

Example 5.2Example 5.2

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Binary Amplitude Shift Binary Amplitude Shift KeyingKeying

Or Binary ASKOr Binary ASK Simplest form Simplest form On-Off Keying (OOK) On-Off Keying (OOK)

fc – Carrier frequency0 < d < 1

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Implementation of Binary Implementation of Binary ASKASK

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We have an available bandwidth of 100 kHz which spans from 200 to 300 kHz. What are the carrier frequency and the bit rate if we modulated our data by using ASK with d = 1?

SolutionThe middle of the bandwidth is located at 250 kHz. This means that our carrier frequency can be at fc = 250 kHz. We can use the formula for bandwidth to find the bit rate (with d = 1 and r = 1).

Example 5.3Example 5.3

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Full-Duplex ASKFull-Duplex ASK Bandwidth can be divided into two to Bandwidth can be divided into two to

support full-duplex communicationsupport full-duplex communication Two carrier frequencies are usedTwo carrier frequencies are used

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Binary Frequency Shift Binary Frequency Shift KeyingKeying

Or Binary FSKOr Binary FSK

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Implementation of Binary Implementation of Binary FSKFSK

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Multilevel FSKMultilevel FSK Use one frequency to send more Use one frequency to send more

than one bit at a timethan one bit at a time E.g., the whole bandwidth divided E.g., the whole bandwidth divided

into 8 frequency rangesinto 8 frequency ranges

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Binary Phase Shift KeyingBinary Phase Shift Keying Or Binary PSKOr Binary PSK

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Implementation of Binary Implementation of Binary PSKPSK

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Quadrature PSKQuadrature PSK Each signal element carries 2 bitsEach signal element carries 2 bits

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Implementation of QPSKImplementation of QPSK

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Find the bandwidth for a signal transmitting at 12 Mbps for QPSK. The value of d = 0.

SolutionFor QPSK, 2 bits is carried by one signal element. This means that r = 2. So the signal rate (baud rate) is S = N × (1/r) = 6 Mbaud. With a value of d = 0, we have B = S = 6 MHz.

Example 5.7Example 5.7

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Constellation DiagramsConstellation Diagrams A constellation diagram helps define A constellation diagram helps define

the amplitude and phase of a signal the amplitude and phase of a signal elementelement

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Example 5.8Example 5.8

Show the constellation diagrams for Show the constellation diagrams for OOK, BPSK, and QPSK modulationsOOK, BPSK, and QPSK modulations

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Constellation Diagram for 8-Constellation Diagram for 8-PSKPSK

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Quadrature Amplitude Quadrature Amplitude ModulationModulation

Or QAMOr QAM A combination of ASK and PSKA combination of ASK and PSK

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Telephone Line BandwidthTelephone Line Bandwidth

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V.32 and V.32bis Modem V.32 and V.32bis Modem StandardsStandards

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Analog-to-Analog Analog-to-Analog ConversionConversion

Process of transmitting analog Process of transmitting analog information by an analog signalinformation by an analog signal

Although the signal is already Although the signal is already analog, modulation is needed if a analog, modulation is needed if a band-pass channel is available to us. band-pass channel is available to us.

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Types of Analog-to-Analog Types of Analog-to-Analog ModulationsModulations

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Amplitude Modulation (AM)Amplitude Modulation (AM)

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AM Band AllocationAM Band Allocation

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Frequency Modulation (FM)Frequency Modulation (FM)

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FM Band AllocationFM Band Allocation

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Phase Modulation (PM)Phase Modulation (PM) Considered a variation of FMConsidered a variation of FM