Finite-size effects and error-free communication in Gaussian channels

The efficacy of a specially constructed Gallager-type error-correcting code to communication in a Gaussian channel is examined. The construction is based on the introduction of complex matrices, used in both encoding and decoding, which comprise sub-matrices of cascading connection values. The finite-size effects are estimated for comparing the results with the bounds set by Shannon. The critical noise level achieved for certain code rates and infinitely large systems nearly saturates the bounds set by Shannon even when the connectivity used is low.

Non-Gaussian statistics of an optical soliton in the presence of amplified spontaneous emission

A study was performed on non-Gaussian statistics of an optical soliton in the presence of amplified spontaneous emission. An approach based on the Fokker-Planck equation was applied to study the optical soliton parameters in the presence of additive noise. The rigorous method not only allowed to reproduce and justify the classical Gordon-Haus formula but also led to new exact results.

Low-complexity BCH codes with optimized interleavers for DQPSK systems with laser phase noise

The presence of high phase noise in addition to additive white Gaussian noise in coherent optical systems affects the performance of forward error correction (FEC) schemes. In this paper, we propose a simple scheme for such systems, using block interleavers and binary Bose–Chaudhuri–Hocquenghem (BCH) codes. The block interleavers are specifically optimized for differential quadrature phase shift keying modulation. We propose a method for selecting BCH codes that, together with the interleavers, achieve a target post-FEC bit error rate (BER). This combination of interleavers and BCH codes has very low implementation complexity. In addition, our approach is straightforward, requiring only short pre-FEC simulations to parameterize a model, based on which we select codes analytically. We aim to correct a pre-FEC BER of around (Formula presented.). We evaluate the accuracy of our approach using numerical simulations. For a target post-FEC BER of (Formula presented.), codes selected using our method result in BERs around 3(Formula presented.) target and achieve the target with around 0.2 dB extra signal-to-noise ratio.

The impact of bariatric surgery on estimated glomerular filtration rate in patients with type 2 diabetes:a retrospective cohort study

Background: Diabetes mellitus is the most common cause of end-stage renal disease, which is associated with increased morbidity and mortality. The impact of bariatric surgery on chronic kidney disease is unclear. Objectives: Our primary aim was to assess the impact of bariatric surgery on estimated glomerular filtration rate (eGFR) in type 2 diabetes (T2D) patients. Our secondary aim was to compare the impact of bariatric surgery versus routine care on eGFR in patients with T2D. Setting: University Hospital, United Kingdom. Methods: A retrospective cohort analysis of adults with T2D who underwent bariatric surgery at a single center between January 2005 and December 2012. Data regarding eGFR were obtained from electronic patients records. eGFR was calculated using the Modification of Diet in Renal Disease formula. Data regarding patients with T2D who did not undergo bariatric surgery ("routine care") were obtained from patients attending the diabetes clinic at the same center from 2009 to 2011. Results: One hundred sixty-three patients were included (mean age 48.5±8.8 yr; baseline body mass index 50.8±9.1 kg/m2) and were followed for 3.0±2.3 years. Bariatric surgery resulted in an improvement in eGFR (median [interquartile range] 86.0 [73.0-100.0] versus 92.0 [77.0-101.0] mL/min/1.73 m2 for baseline versus follow-up, respectively; P = .003), particularly in patients with baseline eGFR≤60 mL/min/1.73 m2 (48.0 [42.0-57.0] versus 61.0 [55.0-63.0] mL/min/1.73 m2; P = .004). After adjusting for baseline eGFR, glycated hemoglobin (HbA1C), body mass index, age, and gender, bariatric surgery was associated with higher study-end eGFR compared with routine care (B = 7.787; P< .001). Conclusion: Bariatric surgery results in significant improvements in eGFR in T2D patients, particularly those with an eGFR≤60 mL/min/1.73 m2, while routine care was associated with a decline in eGFR.