Abstract
The impact of the fiber Kerr effect on error statistics in the nonlinear (high power) transmission of the OFDM 16-QAM signal over a 2000 km EDFA-based link is examined. We observed and quantified the difference in the error statistics for constellation points located at three power-defined rings. Theoretical analysis of a trade-off between redundancy and error rate reduction using probabilistic coding of three constellation power rings decreasing the symbol-error rate of OFDM 16-QAM signal is presented. Based on this analysis, we propose to mitigate the nonlinear impairments using the adaptive modulation technique applied to the OFDM 16-QAM signal. We demonstrate through numerical modelling the system performance improvement by the adaptive modulation for the large number of OFDM subcarriers (more than 100). We also show that a similar technique can be applied to single carrier transmission.
Highlights
In modern optical fiber links the nonlinear transmission effects are one of the major factors limiting system performance
We propose and apply here the adaptive modulation technique that aims to reduce the impact of the nonlinear transmission effects at high signal powers, when statistics of errors are affected by nonlinear interactions
We apply the adaptive modulation in order to reduce the nonlinear transmission impairments in the OFDM-system employing the 16-QAM modulation format
Summary
In modern optical fiber links the nonlinear transmission effects are one of the major factors limiting system performance. The operation of optical communication systems in such nonlinear regimes is rather different from the conventional lower power mode This calls for the development of new approaches and techniques to better understand the peculiarities of high signal power transmission regimes and the root cause of errors. Improvement can be achieved by modifying the shape of the transmitted signal by changing the constellations or by using non-uniform distribution for the occurrence probability of the symbols in a pre-selected constellation. These two kinds of signal shaping are often distinguished as geometric and probabilistic shaping [10,11,12,13,14,15,16]. Forward error correction and modulation methods can be jointly employed to improve practically achievable rates
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