Orthogonal Frequency Division Multiplexing (OFDM) - Telecommunications Blog

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Wednesday, January 12, 2011

Orthogonal Frequency Division Multiplexing (OFDM)

      Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation technique. OFDM provides high bandwidth efficiency because the carriers are orthogonal to each other and multiple carriers share the data among themselves. The main advantage of this transmission technique is their robustness to channel fading in wireless communication environment.

     OFDM is an attractive modulation scheme used in broadband wireless systems that encounter large delay spreads. OFDM avoids temporal equalization altogether, using a cyclic prefix technique with a small penalty in channel capacity.
Where Line-of-Sight (LoS) cannot be achieved, there is likely to be significant multipath dispersion, which could limit the maximum data rate. Technologies like OFDM are probably best placed to overcome these, allowing nearly arbitrary data rates on dispersive channels.

     OFDM signals have a large peak-to-average power ratio (PAPR) due to the superposition of all subcarrier signals. Therefore, in each Transmitter the power amplifier will limit the OFDM signal by its maximal output power. This also disturbs the orthogonality between subcarriers, leading to both intercarrier and out-of-band interferences, which is unacceptable.

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