© 2009 Pearson Education, Inc. Publishing as Prentice Hall More on Modulation Module B Updated January 2009 Raymond Panko’s Business Data Networks and Telecommunications, 7th edition May only be used by adopters of the book

© 2009 Pearson Education, Inc. Publishing as Prentice Hall B-2 Modulation Modulation converts an digital computer signal into a form that can travel down an ordinary analog telephone line PSTN Client A Server A Telephone 33.6 kbps Modem Binary Data Analog Modulated Signal Modem

© 2009 Pearson Education, Inc. Publishing as Prentice Hall Carrier Wave There is a carrier wave This carrier wave is modulated (changed) to carry information B-3

© 2009 Pearson Education, Inc. Publishing as Prentice Hall B-4 Modulation There are several forms of modulation –Amplitude modulation –Frequency modulation –Phase modulation –Quadrature amplitude modulation (QAM), which combines amplitude and phase modulation

© 2009 Pearson Education, Inc. Publishing as Prentice Hall B-5 Amplitude Modulation (AM) Amplitude is the intensity of the signal –Loud or soft Amplitude (power)

© 2009 Pearson Education, Inc. Publishing as Prentice Hall B-6 Amplitude Modulation (AM) Low Amplitude (0) High Amplitude (1) Amplitude Modulation (1011) Amplitude (low) Amplitude (high)

© 2009 Pearson Education, Inc. Publishing as Prentice Hall B-7 Waves Frequency of a wave –The number of complete cycles per second –Called Hertz –kHz, MHz, GHz, THz Frequency (Hz) Cycles in One Second

© 2009 Pearson Education, Inc. Publishing as Prentice Hall B-8 Figure B-1: Frequency Modulation (FM) Low Frequency (0) High Frequency (1) Frequency Modulation (1011) Wavelength

© 2009 Pearson Education, Inc. Publishing as Prentice Hall B-9 Phase Two signals can have the same frequency and amplitude but have different phases—be at different points in their cycles at a given moment Basic Signal 180 degrees out of phase

© 2009 Pearson Education, Inc. Publishing as Prentice Hall B-10 Figure B-2: Phase Modulation (PM) In Phase (0) 180 degrees out of phase (1) Frequency Modulation (1011)

© 2009 Pearson Education, Inc. Publishing as Prentice Hall B-11 Phase Modulation (PM) Human hearing is largely insensitive to phase –So harder to understand than AM or FM But equipment is very sensitive to phase changes –PM is used in all recent forms of modulation for telephone modems and all forms of radio transmission

© 2009 Pearson Education, Inc. Publishing as Prentice Hall B-12 Figure B-3: QAM Quadrature Amplitude Modulation (QAM) –Uses two carrier waves: sine and cosine (90 o out of phase), both amplitude-modulated

© 2009 Pearson Education, Inc. Publishing as Prentice Hall B-13 Figure B.3: QAM Suppose each carrier wave has four possible amplitude levels –In each clock cycle, there are 16 combined possibilities –In each clock cycle, can send 4 bits (2^4=16) Sine Wave Cosine (Quadrature) Wave High/High 1111

© 2009 Pearson Education, Inc. Publishing as Prentice HallB-14 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Printed in the United States of America. Copyright © 2009 Pearson Education, Inc. Copyright © 2009 Pearson Education, Inc. Publishing as Prentice Hall