Abstract
In this paper, an optimized detection based on log-maximum a posteriori estimation with the fixed number of surviving states (fixed-state Log-MAP) is proposed cooperating with equalizers to deal with spectral distortions for intensity-modulation and direct-detection (IM/DD) optical transmission systems. The equalizers compensate the spectral distortions caused by limited bandwidth and chromatic dispersion, and the optimized detection decodes the useful bits from equalized symbols with severe colored in-band noise. To more accurately extract the bits, the optimized detection with larger memory length is required. However, the classical optimized detection based on maximum likelihood-sequence estimation (MLSE) requires exponential-growing computational complexity and storage space with the increase of memory length. The fixed-state Log-MAP detection can decrease the computational complexity and storage space from the exponential order to linear order. Therefore, the fixed-state Log-MAP detection can support larger memory length to more accurately extract bits with less logic gate resources and storage resources compared to MLSE. We experimentally verified the fixed-state Log-MAP detection in a C-band 64Gbit/s IM/DD on-off keying optical system over a 100km dispersion-uncompensated link. The fixed-state Log-MAP detection not only improves the receiver sensitivity of 2dB, but also reduces the computational complexity and storage space by three orders of magnitude.
Highlights
Driven by the fast-emerging services such as video streaming, interactive games and cloud computing, the demand for high-speed data center interconnects is growing dramatically [1]–[3]
The classical optimized detection based on maximum likelihood-sequence estimation (MLSE) is used in the adaptive channel-matched detection (ACMD), which requires a large memory length to accurately extract the useful bits from equalized symbols with serious in-band noise
We proposed a fixed-state Log-MAP detection combined with equalizers to compensate the channel distortions for intensity-modulation and direct-detection (IM/DD) optical systems over dispersion-uncompensated links
Summary
Driven by the fast-emerging services such as video streaming, interactive games and cloud computing, the demand for high-speed data center interconnects is growing dramatically [1]–[3]. The bottleneck of MLSE lies in an exponential-growing computational complexity and storage space as the memory length increases. How to increase the memory length of detection algorithm with low computational complexity and less storage space is significant to improve the transmission performance for practical applications. The fixed-state Log-MAP detection is experimentally demonstrated in a C-band 64Gbit/s IM/DD OOK system over a 100km dispersion-uncompensated link. We propose a fixed-state Log-MAP detection with a low computational complexity and a less storage space. Experimental results show that the fixed-state Log-MAP detection availably overcomes the constraint of memory length. Under the condition of reducing the computational complexity and storage space by three orders of magnitude, the receiver sensitivity using fixed-state Log-MAP detection achieves a 2dB improvement than that using MLSE at 7% hard-decision forward error correction (HD-FEC) limit.
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