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Performance assessment of XPM-limited direct-detection short-reach DSB OFDM optical systems

Alves , T. M. F. ; Cartaxo, A.

IEEE/OSA Journal of Optical Communications and Networking Vol. 7, Nº 8, pp. 736 - 747, August, 2015.

ISSN (print): 1943-0620
ISSN (online): 1943-0620

Journal Impact Factor: 1,128 (in 2010)

Digital Object Identifier: 10.1364/JOCN.7.000736

A closed-form expression for the normalized
variance of the fluctuations induced by cross-phase modulation
(XPM) in direct-detection (DD) double-sideband
(DSB) orthogonal frequency-division multiplexing (OFDM)
systems is proposed and validated. This expression is obtained
by adapting the analytical model for XPM-induced
intensity-modulated fluctuations derived in the past for
conventional on–off keying systems to DSB-OFDM systems
employing DD receivers. It is shown that the normalized
variance can be used as an error vector magnitude (EVM)
estimator in DD DSB-OFDM systems dominantly impaired
by XPM. This conclusion is drawn after validating the proposed
closed-form expression in two application scenarios:
1) distribution of DSB-OFDM ultra-wideband signals using
a radio-over-fiber infrastructure, and 2) transmission of
10 Gb/s DSB-OFDM signals in access networks. Excellent accuracy
between the EVM estimates provided by the normalized
variance expression and the actual EVM of the OFDM
system is demonstrated through numerical simulation for a
large set of system parameters. When the carrier-to-signal
power ratio (CSPR) is high, an EVM discrepancy not exceeding
0.3 dB is obtained in most of the analyzed cases.
When the CSPR decreases to 0 dB, the discrepancy between
the actual EVM and the normalized variance does not
exceed 0.5 dB. A maximum discrepancy between the actual
EVM and the normalized variance around 1 dB is also
shown when the spectral occupancy of the DSB-OFDM signal
leads to a dispersion-induced power fading in the most
affected subcarrier as high as 20 dB. These results suggest
that the proposed closed-form expression is a powerful tool
to provide fast and accurate estimates of the XPM-limited
capacity of wavelength division multiplexing DSB-OFDM
systems employing direct detection.