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arXiv 1804.08545eess.SP
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定点硬件对光纤非线性补偿算法的影响

On the Impact of Fixed Point Hardware for Optical Fiber Nonlinearity Compensation Algorithms

Tom Sherborne, Benjamin Banks, Daniel Semrau, Robert I. Killey, Polina Bayvel, Domaniç Lavery

摘要:

使用数字信号处理的非线性缓解已被证明可增加光纤传输链路的可实现数据速率。一种特别有效的技术是数字反向传播(DBP),一种能够同时补偿线性和非线性信道失真的算法。然而,实现这种技术的最大障碍是其高计算复杂性。近年来,已经提出了几种具有降低的计算复杂度的DBP的替代方案,尽管这样的技术没有表现出与实现的复杂度相称的性能益处。为了充分表征DBP的计算要求,当约束于数字相干接收机中使用的逻辑时,需要对算法行为进行建模。这样的模型允许根据真正的硬件复杂度来分析任何信号恢复算法,其中,关键地,包括乘法运算的位深度。在有限比特深度的情况下,存在由每个算术运算引入的量化噪声,并且不能再假设常规DBP算法将优于其低复杂度替代方案。在这项工作中,DBP和一个单一的非线性步骤DBP的实现,\textit{Enhanced Split Step Fourier}方法(ESSFM),线性均衡使用一个通用的软件模型的定点硬件进行了比较。讨论了位深和快速傅里叶变换(FFT)尺寸的要求,以检验这两种数字非线性补偿方案的最佳工作状态。对于1000 km的传输系统,发现(假设优化的FFT大小),在SNR方面,对于高达13位的所有硬件分辨率,ESSFM算法优于传统DBP。

英文摘要:

Nonlinearity mitigation using digital signal processing has been shown to increase the achievable data rates of optical fiber transmission links. One especially effective technique is digital back propagation (DBP), an algorithm capable of simultaneously compensating for linear and nonlinear channel distortions. The most significant barrier to implementing this technique, however, is its high computational complexity. In recent years, there have been several proposed alternatives to DBP with reduced computational complexity, although such techniques have not demonstrated performance benefits commensurate with the complexity of implementation. In order to fully characterize the computational requirements of DBP, there is a need to model the algorithm behavior when constrained to the logic used in a digital coherent receiver. Such a model allows for the analysis of any signal recovery algorithm in terms of true hardware complexity which, crucially, includes the bit-depth of the multiplication operation. With a limited bit depth, there is quantization noise, introduced with each arithmetic operation, and it can no longer be assumed that the conventional DBP algorithm will outperform its low complexity alternatives. In this work, DBP and a single nonlinear step DBP implementation, the \textit{Enhanced Split Step Fourier} method (ESSFM), were compared with linear equalization using a generic software model of fixed point hardware. The requirements of bit depth and fast Fourier transform (FFT) size are discussed to examine the optimal operating regimes for these two schemes of digital nonlinearity compensation. For a 1000 km transmission system, it was found that (assuming an optimized FFT size), in terms of SNR, the ESSFM algorithm outperformed the conventional DBP for all hardware resolutions up to 13 bits.

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