Abstract
Coherent optical orthogonal frequency division multiplexing (CO-OFDM)
systems have inferior nonlinear performance due to their high peak to average
power ratio (PAPR) characteristics. In order to mitigate fiber nonlinearities
for the CO-OFDM systems, we propose a novel discrete Fourier transform (DFT)-precoded
coherent optical OFDM combined with a Hermitian symmetry (DFT-precoded HS
CO-OFDM) system, which is a combination of the DFT-spread OFDM and the Hermitian
symmetry of the DFT. Furthermore, the proposed system can be easily implemented
by using a fast Fourier transform (FFT) algorithm. Because the proposed system
has a lower PAPR than the conventional CO-OFDM system, the DFT-precoded HS
CO-OFDM system provides superior nonlinear tolerance. Moreover, the proposed
system is superior to the conventional DFT-spread coherent optical OFDM (DFT-spread
CO-OFDM) system in terms of maintaining low PAPR in optical fiber transmission.
The low PAPR in the proposed scheme is suitable for long-haul optical transmission
systems, compared with the conventional DFT-spread CO-OFDM. For the DFT-precoded
HS OFDM system, we have developed a theoretical framework illustrating the
principles of the proposed system. The numerical results show that the DFT-precoded
HS CO-OFDM system outperforms the conventional CO-OFDM by 5.4% EVM performance
after 1200-km transmission and the conventional DFT-spread CO-OFDM by 4.5%
EVM performance after 2800-km transmission at a fiber launch power of -2 dBm.
© 2012 IEEE
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