Demodulation and Detection Schemes for a Memoryless Optical WDM Channel

TL;DR

This paper analyzes various demodulation and detection schemes for a nonlinear optical WDM channel, showing that while traditional methods are limited, a heuristic approach can achieve arbitrarily low error rates.

Contribution

It introduces a heuristic demodulator combined with minimum distance detection that outperforms traditional methods in nonlinear optical channels.

Findings

MFS-based receivers cannot achieve arbitrarily low SERs at high power.

The optimal receiver's SER approaches zero as power increases.

The proposed heuristic receiver achieves low SERs and is simpler than the optimal one.

Abstract

It is well known that matched filtering and sampling (MFS) demodulation together with minimum Euclidean distance (MD) detection constitute the optimal receiver for the additive white Gaussian noise channel. However, for a general nonlinear transmission medium, MFS does not provide sufficient statistics, and therefore is suboptimal. Nonetheless, this receiver is widely used in optical systems, where the Kerr nonlinearity is the dominant impairment at high powers. In this paper, we consider a suite of receivers for a two-user channel subject to a type of nonlinear interference that occurs in wavelength-division-multiplexed channels. The asymptotes of the symbol error rate (SER) of the considered receivers at high powers are derived or bounded analytically. Moreover, Monte-Carlo simulations are conducted to evaluate the SER for all the receivers. Our results show that receivers that are based on MFS cannot achieve arbitrary low SERs, whereas the SER goes to zero as the power grows for the optimal receiver. Furthermore, we devise a heuristic demodulator, which together with the MD detector yields a receiver that is simpler than the optimal one and can achieve arbitrary low SERs. The SER performance of the proposed receivers is also evaluated for some single-span fiber-optical channels via split-step Fourier simulations.