van Uden Roy G H, Okonkwo Chigo M, Sleiffer Vincent A J M, de Waardt Hugo, Koonen Antonius M J
Opt Express. 2014 Jan 13;22(1):119-26. doi: 10.1364/OE.22.000119.
Optical multiple-input multiple-output (MIMO) transmission systems generally employ minimum mean squared error time or frequency domain equalizers. Using an experimental 3-mode dual polarization coherent transmission setup, we show that the convergence time of the MMSE time domain equalizer (TDE) and frequency domain equalizer (FDE) can be reduced by approximately 50% and 30%, respectively. The criterion used to estimate the system convergence time is the time it takes for the MIMO equalizer to reach an average output error which is within a margin of 5% of the average output error after 50,000 symbols. The convergence reduction difference between the TDE and FDE is attributed to the limited maximum step size for stable convergence of the frequency domain equalizer. The adaptive step size requires a small overhead in the form of a lookup table. It is highlighted that the convergence time reduction is achieved without sacrificing optical signal-to-noise ratio performance.
光学多输入多输出（MIMO）传输系统通常采用最小均方误差时域或频域均衡器。通过一个实验性的三模双偏振相干传输装置，我们表明，最小均方误差时域均衡器（TDE）和频域均衡器（FDE）的收敛时间可分别减少约50%和30%。用于估计系统收敛时间的标准是MIMO均衡器达到平均输出误差所需的时间，该平均输出误差在50000个符号后平均输出误差的5%范围内。TDE和FDE之间收敛减少的差异归因于频域均衡器稳定收敛的最大步长有限。自适应步长需要一个查找表形式的小开销。需要强调的是，在不牺牲光信噪比性能的情况下实现了收敛时间的减少。
