Performance of MLSE-based receivers in lightwave systems with nonlinear dispersion and amplified spontaneous emission noise

Abstract-Electronic signal processing is becoming very attractive to overcome various impairments that affect optical communications, and electronic dispersion compensation (EDC) represents a typical application in the currently designed systems. However, the inherent limits in performance achievable by electronically processing the signal at the output of a nonlinear photodetector have not received the attention they deserve. In this paper, we investigate the information-theoretic limits of electronic signal processing in transmission systems employing direct photodetection and two possible modulation formats: 1) on-off keying (OOK) with nonreturn-to-zero pulses; and 2) optical duobinary modulation (ODBM). The analysis is based on the computation of the information rate, i.e., the maximum achievable data transfer rate, and accounts for the modulation format as well as relevant parameters of the transmission scheme. In particular, we investigate the impact of sampling rate, uncompensated chromatic dispersion (CD), and quantization resolution of the electrical signal at the output of a direct photodetector. For OOK systems, the obtained results show that the optical signal-to-noise ratio penalty entailed by EDC can be limited to about 2 dB at most values of CD of interest in current applications. Moreover, ODBM systems at high values of CD can almost perform as OOK systems at zero CD. For all the considered modulation formats, the obtained results show that the received electrical signal can be sampled at a rate of two samples per bit interval and quantized with a precision of 3 bits per sample to practically achieve the ultimate performance limits.Index Terms-Direct photodetection, electronic dispersion compensation (EDC), information rate, maximum-likelihood sequence detection (MLSD), on-off keying (OOK), optical duobinary modulation (ODBM), quantization.

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“…The OSNR is 8 dB. is a very accurate alternative to the approximate closed-form formulas found in [11] and [34].…”

Section: Accurate Approximation Of the Pdf Of The Observablesmentioning

confidence: 91%

Fundamental Limits of Electronic Signal Processing in Direct-Detection Optical Communications

Franceschini

Bongiorni

Ferrari

et al. 2007

J. Lightwave Technol.

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“…In this case, the information symbols corresponding to the channel taps and are selected as described in Section IV-A, assuming and . 1 As one can intuitively understand, this brute-force state-complexity reduction should lead to a performance worse than that of RSSD, since the missing information bits are associated with the reduced state in a (temporally) fixed fashion. On the contrary, use of RSSD allows to dynamically associate the reduced states with the "best" (i.e., the most reasonable) missing information bits, i.e., those of the corresponding survivor.…”

Section: Rssd Versus Brute-force State-complexity Reductionmentioning

confidence: 99%

“…In the following, we briefly review MLSD schemes based on the VA and introduce the adopted branch metrics [1], [3]- [5], [8].…”

Section: Preliminaries On Mlsd Receiver Structuresmentioning

confidence: 99%

“…In the NRZ-OOK case, the modulator (MOD) comprises an NRZ pulse shaping filter, an electrical low-pass filter, and a Mach-Zehnder device in push-pull configuration. The input/output relation of the Mach-Zehnder device is as follows [14]: (1) where is the output electrical field, is the input electrical field from the laser source, is the modulation index, and is the input voltage normalized in the range ( 0.5,0.5). The modulated signal propagates through a linear optical fiber characterized by the following frequency response [15]: (2) where is the total amount of uncompensated CD (usually expressed in [ps/nm]), is the optical carrier wavelength (dimension: [nm]), and is the propagation speed ( m/s).…”

Section: Communication System Modelmentioning

confidence: 99%

“…Recently, several works have characterized various aspects of MLSD schemes for optical communications based on direct photodetection and operating in the electrical domain. In particular, in [1]- [5], MLSD schemes based on the use of the Viterbi algorithm [6] (VA) have been characterized in terms of tolerance against chromatic dispersion (CD) and polarization mode dispersion (PMD). In these papers, various models for the branch metrics of the VA have been considered.…”

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confidence: 99%

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State-Complexity Reduction in MLSD Receivers for Optical Communications With Direct Photodetection

Franceschini

Ferrari

Raheli

et al. 2008

J. Lightwave Technol.

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Abstract-We investigate the impact of state-complexity reduction on the performance of maximum likelihood sequence detection (MLSD) receivers for direct-photodetection long-haul optical communication systems affected by uncompensated chromatic dispersion (CD). We directly compare two possible approaches: (i) detection through a simple "brute-force" state-complexity reduction strategy and (ii) a more structured reduced-state sequence detection (RSSD) strategy. The performance of both state-complexity reduction techniques is evaluated considering two realistic optical transmission schemes, based on on-off keying (OOK) and optical duobinary modulation (ODBM), respectively. The detection algorithms are characterized considering the impact of the timing offset, the quantization scheme, and the amount of uncompensated CD. As one would expect, for a given number of states in MLSD receivers, the schemes based on RSSD exhibit better performance with respect to those based on simple brute-force state-complexity reduction. However, we show that MLSD schemes based on the use of brute-force state-complexity reduction are characterized by a better complexity/performance trade-off for low/medium CD values, whereas RSSD is the best choice for high CD values.Index Terms-Maximum likelihood sequence detection (MLSD), on-off keying (OOK), optical duobinary modulation (ODBM), optical fiber communications, reduced-state sequence detection (RSSD).

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Non-linear function for a Gaussian photo-reception in standard IM/DD systems

et al. 2010

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In this paper, a set of mathematical transformations is developed to obtain the nonlinear function that recovers the Gaussian statistics after the square law distortion produced by the photodetector in Intensity Modulated/ Direct Detected IM/DD systems. Linear impairments in the optical domain like the Amplified Spontaneous Emission (ASE) or the Rayleigh Backscattering (RB) noise are considered the predominant. Here for the first time, a mathematical non-linear function is obtained without assuming any predefined function form. The result is that the noise distribution can be considered more signal-independent Gaussian after this non-linear transformation, than by using any other previously published operation. Applying this function in post-detection enables to make the system more linear, and then would improve the performance of the conventional electronic equalizers (EE). When using Maximum Likelihood Sequence Estimators (MLSE), a simplified metric can be used. Since the channel transfer function can be easily reproduced, computational cost and complexity are reduced.

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Performance of MLSE-based receivers in lightwave systems with nonlinear dispersion and amplified spontaneous emission noise

Cited by 16 publications

References 12 publications

Fundamental Limits of Electronic Signal Processing in Direct-Detection Optical Communications

Fundamental Limits of Electronic Signal Processing in Direct-Detection Optical Communications

State-Complexity Reduction in MLSD Receivers for Optical Communications With Direct Photodetection

Non-linear function for a Gaussian photo-reception in standard IM/DD systems

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