Amplitude modulation - For amplitude modulation

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Communications 1 ELCN 306 Hebat-Allah M. Mourad Professor Cairo University Faculty of Engineering Electronics & Communications Department
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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
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Course Contents - Introduction to modulation - Different analog modulation techniques: Amplitude, Frequency and Phase -Transformation from analog to digital: Sampling, Quatization, PCM, DM, ADM -Random process
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Grading system Mid term 20 Quiz 20 Lab + section participation + attendance 20 Final 40 Total 100
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Intended Learning Outcomes (ILO’s ( 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
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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 λ =
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Baseband Power Spectrum
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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(
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Basic Modulation Types s (t( = A (t( cos [ Ө (t( ] Ө (t( = ω t + φ (t( ‘ A c cos ω c t ‘ is called un-modulated carrier Analog Modulation Digital Modulation
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Modulator m(t) Acos(2 f π c t + ) φ modulated signal: s(t) Un-modulated carrier
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Modulation Types (Analog Modulation (
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Modulation Types (Digital Modulation (
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Analog Modulation - Different analog modulation techniques - For each type:- - Mathematical presentation * Bandwidth * transmitted power - Modulators - Demodulators - Applications
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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 π f c t = A c cos ω 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, linearly with the base band signal
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1 - Amplitude Modulation s(t( = A c cos 2 π f c t + m(t( cos 2 π f c t = [A c + m(t( ] cos 2 π f c t = modulated signal S(ω( = π A c [ δ(ω + ω c ( + δ(ω - ω c ( ] + (1/2( [ M(ω + ω c ( + M(ω - ω c ( ]
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1 - Amplitude Modulation s(t(= un-modulated carrier + upper side band (U.S.B( + lower sideband (L.S.B.( Bandwidth (B.W.( = 2W | M(ω( | | S( ω ( | 0 0 W - W - ω c + ω c
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Condition : A c + m(t( > 0 for all t A c ≥ m(t( min (absolute –ve peak amp.( Define: μ = modulation index = m(t( min / A c 0 ≤ μ 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 : μ > 1 μ x 100 = percentage modulation
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