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L6 - Introduction to OFDMA 1 Motivation and Basic Structure...

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SYSC 5403 - 6 Copyright © 1995-2009 by R.H.M. Hafez 1 Introduction to OFDMA Introduction to OFDMA 1. Motivation and Basic Structure 2. Channel Estimation and Equalization 3. Transmission and Reception 4. SC-OFDM 5. OFDMA as a Multiplexing Scheme SYSC 5403 - 6 Copyright © 1995-2009 by R.H.M. Hafez 2 The OFDMA Concept z In order to transmit very high data rate over frequency selective channel. We breaks the single high data rate stream into many parallel low data rate stream and transmit them on parallel narrowband channels. z Each of the parallel channels exhibits “Flat Fading” condition OFDM Bc Bi Coherence BW Information BW
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SYSC 5403 - 6 Copyright © 1995-2009 by R.H.M. Hafez 3 Serial vs. Parallel Transmission Serial vs. Parallel Transmission Delay Strong Rays Delay Spread SC OFDM 1 2 3 N 1 2 3 N OFDM symbol = N TDM symbols Single Carrier Multi Carrier Frequency SYSC 5403 - 6 Copyright © 1995-2009 by R.H.M. Hafez 4 The OFDM Modulator The OFDM Modulator serial to Parallel High speed Data R N R 1 = R N /N Mod. 1 @ F 1 Mod. 2 @ F 2 Mod. 3 @ F 3 Mod. N @ F N Add Composite Signal
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SYSC 5403 - 6 Copyright © 1995-2009 by R.H.M. Hafez 5 The OFDM Composite Spectrum The OFDM Composite Spectrum R 1 /2 R 1 /2 F 1 F N R N F k F ) 1 k ( F F 1 k Δ + = 1 R F = Δ Freq. SYSC 5403 - 6 Copyright © 1995-2009 by R.H.M. Hafez 6 N- Parallel Modulators Parallel Modulators Cos ω κ t Sin ω κ t Signal Mapping Data @ rate R1 z k = x k + j y k x k y k Modulator # k x y z k QAM = Quadrature Amplitude Modulator ) t sin( y ) t cos( x k k k k ω + ω { } t j k k e z Re ω =
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SYSC 5403 - 6 Copyright © 1995-2009 by R.H.M. Hafez 7 The OFDM Symbol The OFDM Symbol z
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L6 - Introduction to OFDMA 1 Motivation and Basic Structure...

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