L09_digital_modulation_01

L09_digital_modulation_01 - Digital Modulation (Part I)...

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1 6.02 Spring 2008 Lecture 9 Digital Modulation (Part I), Slide 1 Digital Modulation (Part I) Communication using symbols and bits Constellation diagrams and decision boundaries Transmit bandwidth vs.intersymbol interference Eye Diagrams and sample time sensitivity All rights reserved. 6.02 Spring 2008 Lecture 9 Digital Modulation (Part I), Slide 2 Advantages of going Digital Increased robustness Allows error correction to be achieved Less sensitivity to radio channel imperfections Enables compression of information More efficient use of channel Allows information to be “packetized” Can compress information in time and efficiently send as packets through network In contrast, analog modulation requires “circuit-switched” connections that are continuously available Inefficient use of radio channel if there is “dead time” in information flow Supports a wide variety of information content Voice, text and email messages, video can all be represented as digital bit streams
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6.02 Spring 2008 Lecture 9 Digital Modulation (Part I), Slide 3 Review of Analog I/Q Modulation Consider modulating with both a cosine and sine wave and then adding the results This is known as I/Q modulation The I/Q signals occupy the same frequency band, but one is real and one is imaginary We can recover both of these signals I stands for in-phase component Q stands for quadrature component 6.02 Spring 2008 Lecture 9 Digital Modulation (Part I), Slide 4 Review of Analog I/Q Demodulation Demodulate with a cosine and sine wave Both I and Q channels are recovered! bandwidth
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This note was uploaded on 08/23/2009 for the course EECS 6.02 taught by Professor Terman during the Spring '08 term at MIT.

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L09_digital_modulation_01 - Digital Modulation (Part I)...

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