Dual-Polarized Reconfigurable Intelligent Surface Assisted Broad Beamforming

A reconfigurable intelligent surface (RIS) consists of a large number of low-cost elements that can control the propagation environment seen from a transmitter by intelligently applying phase shifts to impinging signals before reflection. This paper studies an RIS-assisted communication system where a transmitter wants to transmit a common signal to many users residing in a wide angular area. To cover this sector uniformly, the RIS needs to radiate a broad beam with a spatially flat array factor, instead of a narrow beam as normally considered. To achieve this, we propose to use a dual-polarized RIS consisting of elements with orthogonal polarizations and show that the RIS can produce a broad beam if the phase shift configuration vectors in the two polarizations form a so-called Golay complementary sequence pair. By utilizing their properties, we also present a method for constructing configuration for large RISs from smaller ones, while preserving the broad radiation pattern of the smaller RIS. The numerical results corroborate the mathematical analyses and highlight the greatly improved coverage properties.Comment: This letter has been accepted for publication in IEEE Communications Letter

Asymptotic Analysis of SU-MIMO Channels With Transmitter Noise and Mismatched Joint Decoding

Hardware impairments in radio-frequency components of a wireless system cause unavoidable distortions to transmission that are not captured by the conventional linear channel model. In this paper, a 'binoisy' single-user multiple-input multiple-output (SU-MIMO) relation is considered where the additional distortions are modeled via an additive noise term at the transmit side. Through this extended SU-MIMO channel model, the effects of transceiver hardware impairments on the achievable rate of multi-antenna point-to-point systems are studied. Channel input distributions encompassing practical discrete modulation schemes, such as, QAM and PSK, as well as Gaussian signaling are covered. In addition, the impact of mismatched detection and decoding when the receiver has insufficient information about the non-idealities is investigated. The numerical results show that for realistic system parameters, the effects of transmit-side noise and mismatched decoding become significant only at high modulation orders.Comment: 16 pages, 7 figure

Time-and unit-cell splitting comparison for the autonomous operation of reconfigurable intelligent surfaces

In this work, we analytically compare the performance of the time-and unit cell-splitting protocols for satisfying the energy needs of reconfigurable intelligent surfaces (RISs) through wireless energy harvesting from information signals. We first compute the RIS energy consumption per frame for both protocols and subsequently formulate an optimization problem that maximizes the average rate under the constraint of meeting the RIS long-term energy consumption demands. Analytical solutions to the optimal allocation of resources that involve a single integral are provided for both protocols in the case of random transmitter-RIS links that are subject to Rician or Nakagami-m fading distributions. Moreover, closed-form solutions are provided for the case of deterministic transmitter-RIS links. In addition, increasing and decreasing monotonic trends are revealed, based on analysis, for the ratio of the achievable rates of the presented protocols with respect to the RIS energy consumption. Finally, numerical results validate the analytical findings and reveal that the unit cell-splitting protocol exhibits a notably higher average rate performance compared with its time-splitting counterpart throughout the feasible range of RIS energy consumption values. However, this comes at a cost of a notably reduced signal-to-noise ratio as the RIS energy demands increase.This work has been supported by the Luxembourg National Research Fund (FNR)-RISOTTI Project, ref. 14773976.Peer ReviewedPostprint (published version

Wireless energy harvesting for autonomous reconfigurable intelligent surfaces

In the current contribution, we examine the feasibility of fully-energy-autonomous operation of reconfigurable intelligent surfaces (RIS) through wireless energy harvesting (EH) from incident information signals. Towards this, we first identify the main RIS energy-consuming components and present a suitable and accurate energy-consumption model that is based on the recently proposed integrated controller architecture and includes the energy consumption needed for channel estimation. Building on this model, we introduce a novel RIS architecture that enables EH through RIS unit-cell (UC) splitting. Subsequently, we introduce an EH policy, where a subset of the UCs is used for beamsteering, while the remaining UCs absorb energy. In particular, we formulate a subset allocation optimization problem that aims at maximizing the signal-to-noise ratio (SNR) at the receiver without violating the RIS’s energy consumption demands. As a problem solution, we present low-complexity heuristic algorithms. The presented numerical results reveal the feasibility of the proposed architecture and the efficiency of the presented algorithms with respect to both the optimal and very high-complexity brute-force approach and the one corresponding to random subset selection. Furthermore, the results reveal how important the placement of the RIS as close to the transmitter as possible is, for increasing the harvesting effectiveness.This work was supported by the Luxembourg National Research Fund (FNR) under the CORE project RISOTTI (ref. 14773976), the European Commission’s Horizon 2020 research and innovation programme (ARIADNE) under grant agreement No. 871464, and the Digital Futures center.Peer ReviewedPostprint (published version

Fructose intervention for 12 weeks does not impair glycemic control or incretin hormone responses during oral glucose or mixed meal tests in obese men

Background and aims: Incretin hormones glucagon-like peptide (GLP)-1 and glucose-dependent insulinotropic polypeptide (GIP) are affected early on in the pathogenesis of metabolic syndrome and type 2 diabetes. Epidemiologic studies consistently link high fructose consumption to insulin resistance but whether fructose consumption impairs the incretin response remains unknown. Methods and results: As many as 66 obese (BMI 26-40 kg/m(2)) male subjects consumed fructose-sweetened beverages containing 75 g fructose/day for 12 weeks while continuing their usual lifestyle. Glucose, insulin, GLP-1 and GIP were measured during oral glucose tolerance test (OGTT) and triglycerides (TG), GLP-1, GIP and PYY during a mixed meal test before and after fructose intervention. Fructose intervention did not worsen glucose and insulin responses during OGTT, and GLP-1 and GIP responses during OGTT and fat-rich meal were unchanged. Postprandial TG response increased significantly, p = 0.004, and we observed small but significant increases in weight and liver fat content, but not in visceral or subcutaneous fat depots. However, even the subgroups who gained weight or liver fat during fructose intervention did not worsen their glucose, insulin, GLP-1 or PYY responses. A minor increase in GIP response during OGTT occurred in subjects who gained liver fat (p = 0.049). Conclusion: In obese males with features of metabolic syndrome, 12 weeks fructose intervention 75 g/day did not change glucose, insulin, GLP-1 or GIP responses during OGTT or GLP-1, GIP or PYY responses during a mixed meal. Therefore, fructose intake, even accompanied with mild weight gain, increases in liver fat and worsening of postprandial TG profile, does not impair glucose tolerance or gut incretin response to oral glucose or mixed meal challenge. (C) 2017 The Italian Society of Diabetology, the Italian Society for the Study of Atherosclerosis, the Italian Society of Human Nutrition, and the Department of Clinical Medicine and Surgery, Federico II University. Published by Elsevier B.V. All rights reserved.Peer reviewe

Role of Glomerular Proteoglycans in IgA Nephropathy

Mesangial matrix expansion is a prominent feature of the most common form of glomerulonephritis, IgA nephropathy (IgAN). To find molecular markers and improve the understanding of the disease, the gene and protein expression of proteoglycans were investigated in biopsies from IgAN patients and correlated to clinical and morphological data. We collected and microdissected renal biopsies from IgAN patients (n = 19) and from healthy kidney donors (n = 14). Patients were followed for an average time of 4 years and blood pressure was according to target guidelines. Distinct patterns of gene expression were seen in glomerular and tubulo-interstitial cells. Three of the proteoglycans investigated were found to be of special interest and upregulated in glomeruli: perlecan, decorin and biglycan. Perlecan gene expression negatively correlated to albumin excretion and progress of the disease. Abundant decorin protein expression was found in sclerotic glomeruli, but not in unaffected glomeruli from IgAN patients or in controls. Transforming growth factor beta (TGF-β), known to interact with perlecan, decorin and biglycan, were upregulated both on gene and protein level in the glomeruli. This study provides further insight into the molecular mechanisms involved in mesangial matrix expansion in IgAN. We conclude that perlecan is a possible prognostic marker for patients with IgAN. In addition, the up-regulation of biglycan and decorin, as well as TGF-β itself, indicate that regulation of TGF-β, and other profibrotic markers plays a role in IgAN pathology