12,846 research outputs found
Soft Reverse Reconciliation for Discrete Modulations
No full textThe performance of the information reconciliation phase is crucial for quantum key distribution (QKD). Reverse reconciliation (RR) is typically preferred over direct reconciliation (DR) because it yields higher secure key rates. However, a significant challenge in continuous-variable (CV) QKD with discrete modulations (such as QAM) is that Alice lacks soft information about the symbol decisions made by Bob. This limitation restricts error correction to hard-decoding methods, with low reconciliation efficiency. This work introduces a reverse reconciliation softening (RRS) procedure designed for CV-QKD scenarios employing discrete modulations. This procedure generates a soft metric that Bob can share with Alice over a public channel, enabling her to perform soft-decoding error correction without disclosing any information to a potential eavesdropper. After detailing the RRS procedure, we investigate how the mutual information between Alice's and Bob's variables changes when the additional metric is shared. We show numerically that RRS improves the mutual information with respect to RR with hard decoding, practically achieving the same mutual information as DR with soft decoding. Finally, we test the proposed RRS for PAM-4 signalling with a rate 1/2 binary LDPC code and bit-wise decoding through numerical simulations, obtaining more than 1dB SNR improvement compared to hard-decoding RR
Information-Theoretic Tools for Optical Communications Engineers
No full textFundamental information-theoretic concepts are explained for nonspecialists, with emphasis on their practical usAge. The notions of a 'FEC threshold' and a 'nonlinear Shannon limit' are critically reviewed, highlighting their limitations and possible alternatives
On the error probability evaluation in lightwave systems with optical amplification
No full textWe review the time domain, frequency domain, and Fourier series Karhunen–Loéve series expansion (KLSE) methods for exact BER evaluation in intensity- and phase-modulated direct-detection optically amplified systems.We compare their complexity and computational efficiency, and discuss the most relevant implementation issues. We show that the method based on a Fourier series expansion has the simplest implementation and requires the minimum number of eigenvalues to converge to the exact BER value for various kind of optical filters. For this method, we also introduce an equivalent form of the moment generating function, that avoids the singularity for eigenvalues equal to zero, and derive an alternative expansion where signal and noise are expanded on the same orthonormal basis
A Comparative Analysis of Different Perturbation Models for the Nonlinear Fiber Channel
No full textDifferent models for the nonlinear optical fiber channel are compared in terms of accuracy. The regular perturbation, enhanced regular perturbation, and logarithmic perturbation models are considered, and a new model based on the Magnus series expansion is introduced
Nonlinear propagation in fiber-optic systems
No full textPresentazione su invito al X Convegno Biennale SIMAI 2010 svolto si a Cagliari dal 21 al 25 Giugno 2010.
http://openconference.simai.eu/index.php/sc/2010/schedConf/presentation
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