Equalization-enhanced phase noise suppression advantage of CO-FBMC over RGI CO-OFDM

Summary form only given. Reduced-guard-interval (RGI) coherent optical orthogonal frequency division multiplexing (CO-OFDM) has been considered as a promising technique for high-speed optical fiber communication systems due to its simple equalization scheme and tolerance to residual chromatic dispersion (CD) [1]. However, one serious drawback of RGI OFDM is the high side lobes due to the `brick-wall' filtering, which leads to higher vulnerability to intercarrier interference (ICI) due to frequency offset, laser and nonlinear phase noise. As a result, RGI CO-OFDM transmission suffers seriously from equalization-enhanced phase noise (EEPN) which is a complicated interplay of laser phase noise, nonlinear phase noise and digital CD equalizer [2]. Here, we show, for the first time, that the impact of EEPN can be significantly mitigated by employing a specific version of OFDM called filter bank multicarrier (FBMC) in which the retangular pulse shape is replaced by a modified raised cosine function. Unlike OFDM signal, FBMC guarantees the orthogonality only in real fields where the receiverd signal is interfered by the so-called imaginary interference [3-4]. Therefore, the channel estimation and phase noise compensation in CO-FBMC are different from those of RGI CO-OFDM. In this work, we considered two equalization techniques (including both channel and phase noise estimations) for CO-FBMC, namely the auxiliary pilot (AP) and the coding pilot (CP). For RGI CO-OFDM transmission, the conventional pilot-aided equalization was applied.