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Unformatted text preview: Communications 1 ELCN 306 HebatAllah M. Mourad Professor Cairo University Faculty of Engineering Electronics & Communications Department Text Book Modern Digital and Analog Communication Systems Third edition B.P.Lathi Chapters: 4 5 6 11 Communication systems, S. Haykin, John Wiley and Sons inc., 4 th edition Course Contents Introduction to modulation Different analog modulation techniques: Amplitude, Frequency and PhaseTransformation from analog to digital: Sampling, Quatization, PCM, DM, ADMRandom process Grading system Mid term 20 Quiz 20 Lab + section participation + attendance 20 Final 40 Total 100 Intended Learning Outcomes (ILOs To know the function of different components of a communication system , to understand the different types of modulation (AM, FM, PM, PAM, PCM, DM, DPCM and demodulation techniques . Calculate two main communication system parameters: power and bandwidth. Design FDM and TDM systems. Solve problems. Choose the best modulation/ demodulation technique for a practical engineering system and analyze the system . How to represent mathematically a random process Why Modulation ? Mainly for two reasons 1  Practical antenna dimensions light velocity Wavelength frequency Dimension is in the order of a quarter wavelength f c = Baseband Power Spectrum Why Modulation ? 2 Multiplexing Better utilization of the available frequency band Spectrum Frequency M 1 (f M 2 (f M 3 (f M N (f Basic Modulation Types s (t = A (t cos [ (t ] (t = t + (t A c cos c t is called unmodulated carrier Analog Modulation Digital Modulation Modulator m(t) Acos(2 f c t + ) modulated signal: s(t) Unmodulated carrier Modulation Types (Analog Modulation Modulation Types (Digital Modulation Analog Modulation Different analog modulation techniques For each type: Mathematical presentation * Bandwidth * transmitted power Modulators Demodulators Applications 1 Amplitude Modulation (A.M Conventional Amplitude Modulation Consider a sinusoidal Carrier wave c(t the un modulated carrier. c(t = A c cos 2 f c t = A c cos c t A c = carrier amplitude f c = carrier frequency A.M is the process in which the amplitude of the carrier wave c(t is varied about a mean value, 1 Amplitude Modulation s(t = A c cos 2 f c t + m(t cos 2 f c t = [A c + m(t ] cos 2 f c t = modulated signal S( = A c [ ( + c + (  c ] + (1/2 [ M( + c + M(  c ] 1 Amplitude Modulation s(t= unmodulated carrier + upper side band (U.S.B + lower sideband (L.S.B. Bandwidth (B.W. = 2W  M(   S(  W W c + c Condition : A c + m(t > 0 for all t A c m(t min (absolute ve peak amp. Define: = modulation index = m(t min / A c 0 1 since there is no upper bound on A c and A c m(t min The envelope has the same shape of m(t Over modulation : > 1 x 100 = percentage modulation 1...
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This note was uploaded on 03/19/2012 for the course ELCN 306 taught by Professor Hebatmourad during the Spring '10 term at Cairo University.
 Spring '10
 HebatMourad

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