Simple Feedforward Carrier Phase Estimation for Optical FBMC/OQAM Systems

Filter-bank multi-carrier based on offset quadrature amplitude modulation (OQAM) has recently been proposed to improve the spectral efficiency of optical fiber communication systems. Unfortunately, it is prone to the laser phase noise (PN) that results in significant inter-subcarrier interference due to the loss of OQAM orthogonality. Based on the analysis of the OQAM constellation obtained at the output of the analysis filter bank, we propose a modified blind phase search algorithm working based on the observation of all subcarriers simultaneously. It efficiently compensates for the PN and incurs a low number of multiplications. The proposed method is analytically derived and numerically validated with 4-, 16-, and 64-OQAM modulations. The impact of the number of subcarriers used per optical channel is also investigated. The results show that up to 256 subcarriers can be utilized with negligible performance degradation. Moreover, the method provides a tolerated linewidth and symbol duration product of 1.4×10
^-4
, 2.5×10
^-5
, and 6.2×10
^-6
for respective 4-, 16-, and 64-OQAM modulations to limit the SNR penalty to 1 dB at a BER of 10
^-3
.