Combining Optical Phase Conjugation and Volterra Equalisation: a Novel Nonlinearity Compensation Scheme

A novel nonlinearity compensation scheme combining optical phase conjugation and Volterra equalisation is proposed and assessed. This hybrid approach outperforms both Volterra and optical phase conjugation schemes, individually applied, by over 4 dB in EDFA-amplified fibre links

Digital techniques for ultra-high data rate optical fibre transmission

The exponential growth of the demand for higher data rates is pushing scientists to find ways to improve the internet infrastructure, which crucially relies on optical fibres. The main obstacle to increasing transmission rates of optical fibre systems is presented by the fibre Kerr nonlinear effect, which impairs signal transmission as the transmitted power is increased. Fortunately, optical coherent detection, in combination with digital signal processing techniques, have enabled more sophisticated digital receivers, tailored to the optical fibre channel. This thesis describes a comprehensive study on the performance of two digital receiver-side techniques: digital back-propagation (DBP) and maximum likelihood sequence detection (MLSD). DBP is the most widespread digital technique to mitigate fibre nonlinearity at the receiver. The performance of DBP, is assessed for long-haul, wide-bandwidth systems, highlighting theoretical gains and practical limitations. Analytical models to predict DBP performance are discussed and compared to numerical results. The impact of polarisation-mode dispersion on the capability of DBP to remove nonlinear impairments is investigated. The principles of detection theory are discussed in the context of the optical fibre nonlinear channel. Following such principles, MLSD strategies are studied and their performance analysed for unrepeatered systems. A close to optimum receiver scheme, using the Viterbi algorithm, is proposed and investigated for the first time in a singlespan fibre system. Finally, information-theoretic tools are used to predict achievable information rates of both receiver schemes, when employed in combination with forward error correction codes. In particular, pragmatic coded modulation schemes were examined to assess the potential of off-the-shelf channel codes. Both receiving strategies analysed were demonstrated to significantly outperform conventional receivers optimised for the additive white Gaussian noise channel. The results of this thesis provide a useful insight on the properties of the optical fibre channel and on the design of receivers aiming to maximise information rates through it

Geometric Shaping of 2-D Constellations in the Presence of Laser Phase Noise

In this article, we propose a geometric shaping (GS) strategy to design 8, 16, 32, and 64 -ary modulation formats for the optical fibre channel impaired by both additive white Gaussian (AWGN) and phase noise. The constellations were optimised to maximise generalised mutual information (GMI) using a mismatched channel model. The presented formats demonstrate an enhanced signal-to-noise ratio (SNR) tolerance in high phase noise regimes when compared with their quadrature amplitude modulation (QAM) or AWGN-optimised counterparts. By putting the optimisation results in the context of the 400ZR implementation agreement, we show that GS alone can either relax the laser linewidth (LW) or carrier phase estimation (CPE) requirements of 400 Gbit/s transmission links and beyond. Following the GMI validation, the performance of the presented formats was examined in terms of post forward error correction (FEC) bit-error-rate (BER) for a soft decision (SD) extended Hamming code (128, 120), implemented as per the 400ZR implementation agreement. We demonstrate gains of up to 1.2 dB when compared to the 64 -ary AWGN shaped formats

Revision of the Student Adaptation to College Questionnaire (SACQ) for Use with Italian Students

Background: This multistudy report was aimed at examining the psychometric properties in the Italian context of the Student Adaptation College Questionnaire (SACQ) that represents the most important self-report measure for assessing how students adjust to university. Methods: Three studies were conducted in order to revise and improve the instrument for being more efficient in measuring adjustment to university. Results: The final result was the SACQ-SF consisting in 12 item assessing three dimensions: a) student’s perception of one’s study skills (Studying); b) student’s sense of satisfaction with courses and programs (Satisfaction with curriculum); c) student’s evaluation of the degree to which he has social skills and is making new friends (Social adjustment). Conclusions: Convergent and construct validity may be considered also adequate. In sum, the SACQSF can be considered a promising valuable and efficient instrument in measuring adjustment to university in the Italian context, and probably in the European one too. Further, as a brief instrument, it can be easily administered and used as a quick screening tool

Seroprevalence of Toxoplasma gondii in swine slaughtered in Sicily

Several studies showed that the consumption of raw or undercooked meat contaming Toxoplasma gondii tissue cysts from infected animals is one of the most important sources of human toxoplasmosis. Foods of animal origin most frequently contaminated are pork and small ruminants\u27 meat. In order to investigate the seroprevalence of Toxoplasmosis in Sicilian pig farms, 1063 swine sera were collected dunng the slaughtering from locally born and bred ammals and 1312 from imported ones (from France and Spain). The local animals came from 154 farms distributed along Sicily, representing pigs of all ages: the others came from lairages

Volterra-Assisted Optical Phase Conjugation: A Hybrid Optical-Digital Scheme for Fiber Nonlinearity Compensation

Digital nonlinearity compensation (NLC) schemes such as digital backpropagation and Volterra equalization are well known to be effective techniques in mitigating optical fiber nonlinearity, thus offering improved transmission performance. Alternatively, optical NLC, and specifically optical phase conjugation (OPC), has been proposed to relax the digital signal processing complexity. In this paper, a novel hybrid optical-digital NLC scheme combining OPC and a Volterra equalizer is proposed, termed Volterra-Assisted OPC (VAO). It has a twofold advantage: it overcomes the OPC limitation in asymmetric links and substantially enhances the performance of Volterra equalizers. When NLC is operated over the entire transmitted optical bandwidth, the proposed scheme is shown to outperform both OPC and Volterra equalization alone by up to 4.2 dB in a five-channel, 32 GBaud PM-16QAM transmission over a 1000 km EDFA-amplified fiber link. Moreover, VAO is also demonstrated to be very robust when applied to long-transmission distances, with a 2.5-dB gain over OPC-only systems at 3000 km. VAO combines the advantages of both optical and digital NLC offering a promising tradeoff between performance and complexity for future high-speed optical communication systems

The Partially-Coherent AWGN Channel: Transceiver Strategies for Low-Complexity Fibre Links

Carrier phase estimation (CPE) is one of the key requirements to perform intradyne coherent detection in optical communication systems. Residual errors in the phase estimation at the receiver, also known as residual phase noise (RPN), follow the so-called Tikhonov distribution. In the digital domain, a channel where the phase has already been estimated by the CPE is generally known as a partially-coherent additive white Gaussian noise (PCAWGN) channel. Herein, we present a joint strategy to modulate and demodulate a 2-dimensional (2D) signal in a PCAWGN channel. Using a low-complexity demapper, we geometrically shape (GS) 8- to 64- ary modulation formats for a PCAWGN channel. Through numerical simulations, we then assess the bit-wise achievable information rates (AIRs) and post forward error correction (FEC) bit error rates (BER) of the presented constellations with the: theoretical optimum model, Euclidean model and the low-complexity PCAWGN model. The resulting constellations are shown to be tolerant to a significant amount of RPN and are therefore applicable to coherent optical communication systems using high linewidth lasers (e.g., >500 kHz) and/or lower symbol rates. Moreover, we demonstrate that shaped PCAWGN constellations combined with a low-complexity demapper can either significantly relax laser linewidth (LW) or carrier phase estimation (CPE) requirements. Assuming a rate-9/10 LDPC scheme, we demonstrate post-FEC BER shaping gains of up to 2.59 dB and 2.19 dB versus uniform 64QAM and 64-ary constellations shaped for the purely AWGN channel, respectively

On the bandwidth dependent performance of split transmitter-receiver optical fiber nonlinearity compensation

The Gaussian noise model is used to estimate the performance of three digital nonlinearity compensation (NLC) algorithms in C-band, long-haul, optical fiber transmission, when the span length and NLC bandwidth are independently varied. The algorithms are receiver-side digital backpropagation (DBP), transmitter-side DBP (digital precompensation), and Split NLC (an equal division of DBP between transmitter and receiver). For transmission over 100×100 km spans, the model predicts a 0.2 dB increase in SNR when applying Split NLC (versus DBP) to a single 32 GBd channel (from 0.4 dB to 0.6 dB), monotonically increasing with NLC bandwidth up to 1.6 dB for full-field NLC. The underlying assumptions of this model and the practical considerations for implementation of Split NLC are discussed. This work demonstrates, theoretically, that, regardless of the transmission scenario, it is always beneficial to divide NLC between transmitter and receiver, and identifies the transmission regimes where Split NLC is particularly advantageous

The benefit of split nonlinearity compensation for single-channel optical fiber communications

In this Letter we analyze the benefit of digital compensation of fiber nonlinearity, where the digital signal processing is divided between the transmitter and receiver. The application of the Gaussian noise model indicates that, where there are two or more spans, it is always beneficial to split the nonlinearity compensation. The theory is verified via numerical simulations, investigating transmission of single channel 50 GBd polarization division multiplexed 256-ary quadrature amplitude modulation over 100 km standard single mode fiber spans, using lumped amplification. For this case, the additional increase in mutual information achieved over transmitter- or receiver-side nonlinearity compensation is approximately 1 bit for distances greater than 2000 km. Further, it is shown, theoretically, that the SNR gain for long distances and high bandwidth transmission is 1.5 dB versus transmitter- or receiver-based nonlinearity compensation

T-786→C polymorphism of the endothelial nitric oxide synthase gene is associated with insulin resistance in patients with ischemic or non ischemic cardiomyopathy

Background: Insulin resistance (IR) and endothelial dysfunction are frequently associated in cardiac disease. The T-786→C variant in the promoter region of the endothelial nitric oxide synthase (eNOS) gene has been associated with IR in both non-diabetic and diabetic subjects. Aim of the study was to assess the reciprocal relationships between T-786→C eNOS polymorphism and IR in ischemic and non-ischemic cardiomyopathy.Method: A group of 132 patients (108 males, median age 65 years) with global left ventricular (LV) dysfunction secondary to ischemic or non-ischemic heart disease was enrolled. Genotyping of T-786→C eNOS gene promoter, fasting glucose, insulin, and insulin resistance (defined as HOMA-IR index > 2.5) were determined in all patients.Results: Genotyping analysis yielded 37 patients homozygous for the T allele (TT), 70 heterozygotes (TC) and 25 homozygous for C (CC). Patients with CC genotype had significantly higher systemic arterial pressure, blood glucose, plasma insulin and HOMA index levels than TT. At multivariate logistic analysis, the history of hypertension and the genotype were the only predictors of IR. In particular, CC genotype increased the risk of IR (CI% 1.4-15.0, p < 0.01) 4.5-fold. The only parameter independently associated with the extent of LV dysfunction and the presence of heart failure (HF) was the HOMA index (2.4 CI% 1.1-5.6, p < 0.04).Conclusions: T-786→C eNOS polymorphism was the major independent determinant of IR in a population of patients with ischemic and non-ischemic cardiomyopathy. The results suggest that a condition of primitive eNOS lower expression can predispose to an impairment of glucose homeostasis, which in turn is able to affect the severity of heart disease. © 2012 Vecoli et al.; licensee BioMed Central Ltd