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Analog Transmission 01204325: Data Communication and Computer Networks Asst. Prof. Chaiporn Jaikaeo, Ph.D. chaiporn.j@ku.ac.th http://www.cpe.ku.ac.th/~cpj Computer Engineering Department Kasetsart University, Bangkok, Thailand Adapted from lecture slides by Behrouz A. Forouzan © The McGraw-Hill Companies, Inc. All rights reserved

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2 Outline Aspects of Digital-to-Analog Conversion Aspects of Digital-to-Analog Conversion Amplitude Shift Keying Amplitude Shift Keying Frequency Shift Keying Frequency Shift Keying Phase Shift Keying Phase Shift Keying Quadrature Amplitude Modulation Quadrature Amplitude Modulation

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3 Digital-to-Analog Conversion Required to send digital data over a band- pass channel Required to send digital data over a band- pass channel Also known as modulation Also known as modulation (band-pass channel)

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4 Carrier Signals Carrier signal is a high-frequency signal acting as a base for information signal Carrier signal is a high-frequency signal acting as a base for information signal Also known as "Carrier Frequency" Also known as "Carrier Frequency"

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5 General form: x(t) = A×sin(2 ft + ) General form: x(t) = A×sin(2 ft + ) period T = 1/f peak amplitude time signal strength Sine Waves Revisited phase / phase shift

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6 Conversion Techniques

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7 Bit Rate vs. Baud Rate Bit rate the number of bits per second Bit rate the number of bits per second Baud rate the number of signal elements per second. Baud rate the number of signal elements per second. In the analog transmission of digital data, the baud rate is less than or equal to the bit rate In the analog transmission of digital data, the baud rate is less than or equal to the bit rate

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8 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? Solution In 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 5.2

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9 Binary Amplitude Shift Keying Or Binary ASK Or Binary ASK Simplest form On-Off Keying (OOK) Simplest form On-Off Keying (OOK) f c – Carrier frequency 0 < d < 1

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10 Implementation of Binary ASK

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11 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? Solution The middle of the bandwidth is located at 250 kHz. This means that our carrier frequency can be at f c = 250 kHz. We can use the formula for bandwidth to find the bit rate (with d = 1 and r = 1). Example 5.3

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12 Full-Duplex ASK Bandwidth can be divided into two to support full-duplex communication Bandwidth can be divided into two to support full-duplex communication Two carrier frequencies are used Two carrier frequencies are used

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13 Binary Frequency Shift Keying Or Binary FSK Or Binary FSK

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14 Implementation of Binary FSK

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15 Multilevel FSK Use one frequency to send more than one bit at a time Use one frequency to send more than one bit at a time E.g., the whole bandwidth divided into 8 frequency ranges E.g., the whole bandwidth divided into 8 frequency ranges

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16 Binary Phase Shift Keying Or Binary PSK Or Binary PSK

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17 Implementation of Binary PSK

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18 Quadrature PSK Each signal element carries 2 bits Each signal element carries 2 bits

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19 Implementation of QPSK

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20 Find the bandwidth for a signal transmitting at 12 Mbps for QPSK. The value of d = 0. Solution For 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 5.7

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21 Constellation Diagrams A constellation diagram helps define the amplitude and phase of a signal element A constellation diagram helps define the amplitude and phase of a signal element

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22 Example 5.8 Show the constellation diagrams for OOK, BPSK, and QPSK modulations Show the constellation diagrams for OOK, BPSK, and QPSK modulations

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23 Constellation Diagram for 8-PSK

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24 Quadrature Amplitude Modulation Or QAM Or QAM A combination of ASK and PSK A combination of ASK and PSK

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25 Telephone Line Bandwidth

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26 V.32 and V.32bis Modem Standards

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27 Analog-to-Analog Conversion Process of transmitting analog information by an analog signal Process of transmitting analog information by an analog signal Although the signal is already analog, modulation is needed if a band-pass channel is available to us. Although the signal is already analog, modulation is needed if a band-pass channel is available to us.

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28 Types of Analog-to-Analog Modulations

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29 Amplitude Modulation (AM)

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30 AM Band Allocation

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31 Frequency Modulation (FM)

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32 FM Band Allocation

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

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