16-OFDM - OFDM Advantages Orthogonal Frequency Division...

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1 Orthogonal Frequency Division Multiplexing (OFDM) Mary Ann Ingram ECE 4823 OFDM Advantages ± OFDM is a spectrally efficient modulation technique ± It is conveniently implemented using IFFT and FFT operations ± It handles frequency selective channels well when combined with error correction coding OFDM Disadvantages ± More complex than single-carrier modulation ± Requires a more linear power amplifier OFDM Concept ± Suppose the symbol length is T u ± Sinusoidal signals differing in frequency by 1/ T u will be orthogonal over the period T u [] 0 1 2 2 = + + dt e e u s s u o o T t t t T f j t f j π Conceptual Transmitter Block Diagram t f j o e 2 X X X () t T f j u o e / 1 2 + t T N f j u o e / 1 2 + ) ( 0 t b Σ ) ( 1 t b M ) ( 1 t b N OFDM “Useful Part” T u sec long “1” “1” “0” 0 u T 0 u T 0 u T ) ( 0 t b ) ( 1 t b ) ( 1 t b N Subcarriers ± Each branch corresponds to a subcarrier ± Subcarriers are separated by 1/ T u Hz ± Each subcarrier modulates a different symbol ± b k can be QAM t f j o e 2 X X X t T f j u o e / 1 2 + [ ] t T N f j u o e 1 2 + ) ( 0 t b Σ ) ( 1 t b M ) ( 1 t b N
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2 One OFDM Symbol < < = =
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16-OFDM - OFDM Advantages Orthogonal Frequency Division...

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