Abstract On the basis of coherent optical orthogonal frequency-division-multiplexing (CO-OFDM), CO-OFDM/ offset quadrature amplitude modulation (CO-OFDM/OQAM) improves the spectrum efficiency by utilizing specially designed filter banks to eliminate the cyclic prefix (CP) inserted between consecutive OFDM blocks and decreases the demanding of guard band between two channels, being a promising candidate for the next generation optical transmission link. Due to the relaxation of the orthogonal condition from the complex field to the real field, chromatic Dispersion (CD) and polarization mode dispersion (PMD) bring serious intrinsic imaginary interference (IMI) to an optical OFDM/OQAM system. Channel estimation schemes based on the interference approximation method (IAM) have been proved to be effective in suppressing the IMI with low complexity. For the IAMs, increasing the power of the pseudo pilot could decrease the effects of amplified spontaneous emission (ASE) noise and other frequency domain residual error on the channel estimation accuracy. In most of the previous reported IAM works, pilot blocks were designed according to the structure of the center pilot block loaded, while the two side pilots nulled for simplicity. However, the power of the pseudo pilot under this method did not reach the maximum, resulting in non-optimal channel estimation accuracy. In this paper, channel estimation method based on the combined phase offset (CMPO) is proposed and systematically discussed. For the proposed method, three consecutive full loaded blocks are treated as the pilot blocks and the optimal pilot structure have been obtained by utilizing the maximum likelihood algorithm. As validated by numerous Montel Carlo simulations results, system robustness against IMI, phase noised induced interference, and nonlinear effect have been improved significantly, thanks to CMPO.

中文翻译：

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光OFDM/OQAM组合相位偏移信道估计方法

摘要 在相干光正交频分复用（CO-OFDM）的基础上，CO-OFDM/偏置正交幅度调制（CO-OFDM/OQAM）通过利用专门设计的滤波器组消除循环前缀来提高频谱效率（ CP) 插入连续的 OFDM 块之间，降低了两个信道之间保护带的要求，是下一代光传输链路的有希望的候选者。由于从复场到实场的正交条件的弛豫，色散（CD）和偏振模色散（PMD）给光OFDM/OQAM系统带来了严重的固有虚部干扰（IMI）。基于干扰逼近法(IAM)的信道估计方案已被证明能有效抑制IMI，且复杂度低。对于 IAM，增加伪导频的功率可以降低放大自发辐射 (ASE) 噪声和其他频域残差对信道估计精度的影响。在之前报道的大多数 IAM 工作中，导频块是根据加载的中心导频块的结构设计的，而为了简单起见，两侧导频为零。但是这种方法下的伪导频功率没有达到最大值，导致信道估计精度不理想。本文提出并系统讨论了基于组合相位偏移(CMPO)的信道估计方法。该方法将三个连续的满载块作为导频块，利用最大似然算法得到最优导频结构。