Abstract
The space-time whitened matched filter (ST-WMF) maximum likelihood sequence detection (MLSD) architecture has been recently proposed (Maggio et al., 2014). Its objective is reducing implementation complexity in transmissions over nonlinear dispersive channels. The ST-WMF-MLSD receiver (i) drastically reduces the number of states of the Viterbi decoder (VD) and (ii) offers a smooth trade-off between performance and complexity. In this work the ST-WMF-MLSD receiver is investigated in detail. We show that thespace compressionof the nonlinear channel is an instrumental property of the ST-WMF-MLSD which results in a major reduction of the implementation complexity in intensity modulation and direct detection (IM/DD) fiber optic systems. Moreover, we assess the performance of ST-WMF-MLSD in IM/DD optical systems with chromatic dispersion (CD) and polarization mode dispersion (PMD). Numerical results for a 10 Gb/s, 700 km, and IM/DD fiber-optic link with 50 ps differential group delay (DGD) show that the number of states of the VD in ST-WMF-MLSD can be reduced ~4 times compared to an oversampled MLSD. Finally, we analyze the impact of the imperfect channel estimation on the performance of the ST-WMF-MLSD. Our results show that the performance degradation caused by channel estimation inaccuracies is low and similar to that achieved by existing MLSD schemes (~0.2 dB).
Highlights
Maximum likelihood sequence detection (MLSD) receivers for nonlinear channels have been extensively investigated in the literature (e.g., [1, 2] and references therein)
Our results show that the performance degradation caused by an imperfect channel estimation is low and similar to that achieved by existing MLSD schemes (∼0.2 dB)
We focus on two key aspects of space-time whitened matched filter (ST-WMF)-MLSD: its performance, and its ability to reduce complexity
Summary
Maximum likelihood sequence detection (MLSD) receivers for nonlinear channels have been extensively investigated in the literature (e.g., [1, 2] and references therein). Since the complexity of both MFB and OS MLSD-based receivers grows exponentially with the channel memory, their practical application in transmissions over highly dispersive channels has been limited. Despite this fact, MLSD-based receivers are still preferred over decision feedback equalizers (DFE) in applications such as multigigabit intensity modulation/direct detection (IM/DD) fiber optic systems for the two following reasons. The major breakthrough of this proposal consists in a novel representation of the received signal obtained by a Gram-Schmidt-like orthogonalization of the kernels of a Volterra series expansion of the channel This procedure yields a special form of space-time whitened matched filter (ST-WMF) [19] whose baud-rate-sampled outputs are sufficient statistics with independent noise components in both space and time.
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