Robust Hybrid Precoding for Interference Exploitation in Massive Mimo Systems

In this paper, we consider a multiuser massive MIMO system with hybrid analog-digital precoding architecture. The phase shifters in the hybrid precoding architecture are assumed to be imperfect, where the true values of both phase and magnitude of the phase shifters are different from their nominal values. For a given analog precoding matrix, we develop an iterative algorithm to compute robust digital precoders based on the interference exploitation approach to eliminate any potential symbol errors due to the phase shifter impairments. Numerical experiments demonstrate the performance of the proposed algorithm and show its advantage over a conventional robust precoding technique

Interference Exploitation-Based Hybrid Precoding With Robustness Against Channel Errors

The extremely high cost associated with massive multiple-input multiple-output (MIMO) systems when it is employed with fully digital precoding can be reduced by applying hybrid precoding at an expense of increased transmit power. In such a hybrid precoding system, the transmit power required to achieve a certain quality-of-service (QoS) can be significantly reduced by employing the constructive interference (CI) precoding technique. However, as illustrated in the paper, the symbol error rate (SER) performance of CI-based precoding is very sensitive to channel errors. To address this challenge we propose a hybrid precoding approach with robustness against channel quantization error and channel estimation error. Simulation results demonstrate the superior energy efficiency of the proposed robust hybrid precoding when compared to that of a conventional non-robust precoding scheme in achieving a required QoS target

Bifurcations in the wake of a thick circular disk

Using DNS, we investigate the dynamics in the wake of a circular disk of aspect ratio χ = d/w = 3(where d is the diameter and w the thickness) embedded in a uniform flow of magnitude U0 perpendicular to its symmetry axis. As the Reynolds number Re = U0d/ν is increased, the flow is shown to experience an original series of bifurcations leading to chaos. The range Re ∈ [150, 218] is analysed in detail. In this range, five different non-axisymmetric regimes are successively encountered, including states similar to those previously identified in the flow past a sphere or an infinitely thin disk, as well as a new regime characterised by the presence of two distinct frequencies. A theoretical model based on the theory of mode interaction with symmetries, previously introduced to explain the bifurcations in the flow past a sphere or an infinitely thin disk (Fabre et al. in Phys Fluids 20:051702, 2008), is shown to explain correctly all these results. Higher values of the Reynolds number, up to 270, are also considered. Results indicate that the flow encounters at least four additional bifurcations before reaching a chaotic state

Patient survival after renal transplantation: IV. Impact of post-transplant diabetes

Patient survival after renal transplantation: IV. Impact of post-transplant diabetes.BackgroundThe development of de novo diabetes mellitus is a serious complication of kidney transplantation. This study examined the cardiovascular risk profile of patients with post-transplant diabetes (PTDM) and assessed the impact of PTDM on patient survival.MethodsThis analysis included 1811 adult, renal allograft recipients, transplanted in a single institution between 1983 and 1998. Patient survival was analyzed by univariable and multivariable Cox regression considering PTDM as a time dependent variable.ResultsAfter a follow-up period of 8.3 ± 4.5 years, 293 patients (20%) developed PTDM, 14% lost their graft, and 20% died. Compared to patients without DM (NoDM, N = 1186) patients with PTDM were significantly older (40 ± 14 vs. 48 ± 12 years, P < 0.001), heavier (76 ± 23 vs. 86 ± 25 kg, P < 0.001), and included more African Americans (18 vs. 28%, P = 0.001). In addition, the incidence of PTDM was significantly higher in patients who were transplanted after 1995 than prior to that year. In contrast, there were no significant differences between PTDM and patients who had DM before the transplant (DM; N = 332). Compared to NoDM, patients with PTDM had significantly higher total serum cholesterol and triglycerides (TG), higher systolic blood pressure and higher pulse pressure throughout the post-transplant period. Of interest, all of these abnormalities preceded the development of PTDM. Hypertriglyceridemia was particularly pronounced in PTDM and elevated TG levels correlated with the subsequent development of PTDM, independent of other risk factors (P = 0.001 by multivariate Cox). Compared to NoDM (16% mortality) a significantly higher percent of DM (31%, P < 0.001) and PTDM (22%, P = 0.005) patients died. By Cox regression, PTDM correlated with reduced patient survival (hazard ratio = 1.80, CI 1.35 to 2.41, P = 0.001), and that relationship was independent of other correlates of reduced survival that included: increasing age; transplant year; reduced serum albumin; and male sex.Conclusions: PTDM is associated with an unfavorable cardiovascular risk profile that precedes the development of hyperglycemia. PTDM is an independent predictor of reduced survival in renal allograft recipients

Novel Optical Chemical Sensor Based on Molecularly Imprinted Polymer Inside a Trench Micro-machined in Double Plastic Optical Fiber☆

Abstract For the detection of chemical agents in different environments, the combination of plastic optical fibers (POFs) and molecularly imprinted polymer (MIP) layers has been tested as a way to obtain a low cost, highly selective and sensitive surface plasmon resonance (SPR) chemical sensor. A novel type of optical chemical sensor based on POF-MIP has been designed and fabricated, and in this work it has been applied for the selective detection of dibenzyl disulfide (DBDS) in transformer oil. This analyte is important in the control of transformer oil, since it is responsible for the corrosive properties of the oil. The new optical sensor platform is based on two plastic optical fibers coupled through a polymer molecularly imprinted for DBDS. The new sensor has been found to be useful for the determination of DBDS in transformer oil

Diagnosis and treatment of pulmonary embolism: a multidisciplinary approach

The diagnosis of pulmonary embolism (PE) is frequently considered in patients presenting to the emergency department or when hospitalized. Although early treatment is highly effective, PE is underdiagnosed and, therefore, the disease remains a major health problem. Since symptoms and signs are non specific and the consequences of anticoagulant treatment are considerable, objective tests to either establish or refute the diagnosis have become a standard of care. Diagnostic strategy should be based on clinical evaluation of the probability of PE. The accuracy of diagnostic tests for PE are high when the results are concordant with the clinical assessment. Additional testing is necessary when the test results are inconsistent with clinical probability. The present review article represents the consensus-based recommendations of the Interdisciplinary Association for Research in Lung Disease (AIMAR) multidisciplinary Task Force for diagnosis and treatment of PE. The aim of this review is to provide clinicians a practical diagnostic and therapeutic management approach using evidence from the literature. © 2013 Lavorini et al