Multi-Antenna Data-Driven Eavesdropping Attacks and Symbol-Level Precoding Countermeasures

In this work, we consider secure communications in wireless multi-user (MU) multiple-input single-output (MISO) systems with channel coding in the presence of a multi-antenna eavesdropper (Eve). In this setting, we exploit machine learning (ML) tools to design soft and hard decoding schemes by using precoded pilot symbols as training data. In this context, we propose ML frameworks for decoders that allow an Eve to determine the transmitted message with high accuracy. We thereby show that MU-MISO systems are vulnerable to such eavesdropping attacks even when relatively secure transmission techniques are employed, such as symbol-level precoding (SLP). To counteract this attack, we propose two novel SLP-based schemes that increase the bit-error rate at Eve by impeding the learning process. We design these two security-enhanced schemes to meet different requirements regarding complexity, security, and power consumption. Simulation results validate both the ML-based eavesdropping attacks as well as the countermeasures, and show that the gain in security is achieved without affecting the decoding performance at the intended users.Comment: Submitted to the IEEE Transactions on Information Forensics and Securit

Reconfigurable Intelligent Surfaces for Smart Cities: Research Challenges and Opportunities

The concept of Smart Cities has been introduced as a way to benefit from the digitization of various ecosystems at a city level. To support this concept, future communication networks need to be carefully designed with respect to the city infrastructure and utilization of resources. Recently, the idea of 'smart' environment, which takes advantage of the infrastructure for better performance of wireless networks, has been proposed. This idea is aligned with the recent advances in design of reconfigurable intelligent surfaces (RISs), which are planar structures with the capability to reflect impinging electromagnetic waves toward preferred directions. Thus, RISs are expected to provide the necessary flexibility for the design of the 'smart' communication environment, which can be optimally shaped to enable cost- and energy-efficient signal transmissions where needed. Upon deployment of RISs, the ecosystem of the Smart Cities would become even more controllable and adaptable, which would subsequently ease the implementation of future communication networks in urban areas and boost the interconnection among private households and public services. In this paper, we describe our vision of the application of RISs in future Smart Cities. In particular, the research challenges and opportunities are addressed. The contribution paves the road to a systematic design of RIS-assisted communication networks for Smart Cities in the years to come.Comment: Submitted for possible publication in IEEE Open Journal of the Communications Societ

Performance of Joint Symbol Level Precoding and RIS Phase Shift Design in the Finite Block Length Regime with Constellation Rotation

In this paper, we tackle the problem of joint symbol level precoding (SLP) and reconfigurable intelligent surface (RIS) phase shift design with constellation rotation in the finite block length regime. We aim to increase energy efficiency by minimizing the total transmit power while satisfying the quality of service constraints. The total power consumption can be significantly minimized through the exploitation of multiuser interference by symbol level precoding and by the intelligent manipulation of the propagation environment using reconfigurable intelligent surfaces. In addition, the constellation rotation per user contributes to energy efficiency by aligning the symbol phases of the users, thus improving the utilization of constructive interference. The formulated power minimization problem is non-convex and correspondingly difficult to solve directly. Hence, we employ an alternating optimization algorithm to tackle the joint optimization of SLP and RIS phase shift design. The optimal phase of each user's constellation rotation is obtained via an exhaustive search algorithm. Through Monte-Carlo simulation results, we demonstrate that the proposed solution yields substantial power minimization as compared to conventional SLP, zero forcing precoding with RIS as well as the benchmark schemes without RIS.Comment: 6 pages,4 figures. This paper has been accepted by IEEE International Symposium on Personal, Indoor and Mobile Radio Communication

Intersymbol and Intercarrier Interference in OFDM Systems: Unified Formulation and Analysis

A unified matrix formulation is presented for the analysis of intersymbol and intercarrier interference in orthogonal frequency-division multiplexing (OFDM) systems. The proposed formulation relies on six parameters and allows studying various schemes, including those with windowing in the transmitter and/or in the receiver (called windowed OFDM systems), which may add cyclic suffix and/or cyclic prefix (CP), besides the conventional CP-OFDM. The proposed framework encompasses seven different OFDM systems. It considers the overlap-and-add procedure performed in the transmitter of windowed OFDM systems, being jointly formulated with the channel convolution. The intersymbol and intercarrier interference, caused when the order of the channel impulse response is higher than the number of CP samples, is characterized. A new equivalent channel matrix that is useful for calculating both the received signal and the interference power is defined and characterized. Unlike previous works, this new channel matrix has no restrictions on the length of the channel impulse response, which means that the study is not constrained to the particular case of two or three data blocks interfering in the received signal. Theoretical expressions for the powers of three different kinds of interference are derived. These expressions allow calculating the signal-to-interference-plus-noise ratio, useful for computing the data rate of each OFDM system. The proposed formulation is applied to realistic examples, showing its effectiveness through comparisons based on numerical performance assessments of the considered OFDM systems

Energy-Efficient On-Board Radio Resource Management for Satellite Communications via Neuromorphic Computing

The latest satellite communication (SatCom) missions are characterized by a fully reconfigurable on-board software-defined payload, capable of adapting radio resources to the temporal and spatial variations of the system traffic. As pure optimization-based solutions have shown to be computationally tedious and to lack flexibility, machine learning (ML)-based methods have emerged as promising alternatives. We investigate the application of energy-efficient brain-inspired ML models for on-board radio resource management. Apart from software simulation, we report extensive experimental results leveraging the recently released Intel Loihi 2 chip. To benchmark the performance of the proposed model, we implement conventional convolutional neural networks (CNN) on a Xilinx Versal VCK5000, and provide a detailed comparison of accuracy, precision, recall, and energy efficiency for different traffic demands. Most notably, for relevant workloads, spiking neural networks (SNNs) implemented on Loihi 2 yield higher accuracy, while reducing power consumption by more than 100$\times$ as compared to the CNN-based reference platform. Our findings point to the significant potential of neuromorphic computing and SNNs in supporting on-board SatCom operations, paving the way for enhanced efficiency and sustainability in future SatCom systems.Comment: currently under review at IEEE Transactions on Machine Learning in Communications and Networkin

Discovery of a young and massive stellar cluster: Spectrophotometric near-infrared study of Masgomas-1

Context: Recent near-infrared data have contributed to the discovery of new (obscured) massive stellar clusters and massive stellar populations in previously known clusters in our Galaxy. These discoveries lead us to view the Milky Way as an active star-forming machine. Aims: The main purpose of this work is to determine physically the main parameters (distance, size, total mass and age) of Masgomas-1, the first massive cluster discovered by our systematic search programme. Methods: Using near-infrared (J, H, and Ks) photometry we selected 23 OB-type and five red supergiant candidates for multi-object H- and K-spectroscopy and spectral classification. Results: Of the 28 spectroscopically observed stars, 17 were classified as OB-type, four as supergiants, one as an A-type dwarf star, and six as late-type giant stars. The presence of a supergiant population implies a massive nature of Masgomas-1, supported by our estimate of the cluster initial total mass of (1.94\pm0.28)\cdot10^4 M_{sun}, obtained after integrating of the cluster mass function. The distance estimate of 3.53 kpc locates the cluster closer than the Scutum--Centaurus base but still within that Galactic arm. The presence of an O9V star and red supergiants in the same population indicates that the cluster age is in the range of 8 to 10 Myr.Comment: 11 pages, 6 figures, 2 tables, A&A accepte

The stellar population of the star forming region G61.48+0.09

- Context: We present the results of a near-infrared photometric and spectroscopic study of the star forming region G61.48+0.09. - Aims: The purpose of this study is to characterize the stellar content of the cluster and to determine its distance, extinction, age and mass. - Methods: The stellar population was studied by using color-magnitude diagrams to select twenty promising cluster members, for which follow up spectroscopy was done. The observed spectra allowed a spectral classification of the stars. - Results: Two stars have emission lines, twelve are G-type stars, and six are late-O or early-B stars. - Conclusions: The cluster's extinction varies from A_{K_S} = 0.9 to A_{K_S} = 2.6, (or A_{V}~8 to A_{V}~23). G61.48+0.09 is a star forming region located at 2.5+/-0.4 Kpc. The cluster is younger than 10 Myr and has a minimum stellar mass of 1500+/-500 Solar masses. However, the actual total mass of the cluster remains undetermined, as we cannot see its whole stellar content.Comment: 20 pages, 10 figures. Accepted for publication in A&

In utero exposure to cigarette smoke dysregulates human fetal ovarian developmental signalling

STUDY QUESTION How does maternal cigarette smoking disturb development of the human fetal ovary?<p></p> SUMMARY ANSWER Maternal smoking increases fetal estrogen titres and dysregulates several developmental processes in the fetal ovary.<p></p> WHAT IS KNOWN ALREADY Exposure to maternal cigarette smoking during gestation reduces human fetal ovarian cell numbers, germ cell proliferation and subsequent adult fecundity.<p></p> STUDY DESIGN, SIZE, DURATION The effects of maternal cigarette smoking on the second trimester human fetal ovary, fetal endocrine signalling and fetal chemical burden were studied. A total of 105 fetuses were studied, 56 from mothers who smoked during pregnancy and 49 from those who did not.<p></p> PARTICIPANTS/MATERIALS, SETTING METHODS Ovary, liver and plasma samples were collected from electively terminated, normally progressing, second trimester human fetuses. Circulating fetal hormones, levels of 73 fetal ovarian transcripts, protein localization, density of oocytes/primordial follicles and levels of 16 polycyclic aromatic hydrocarbons (PAHs) in the fetal liver were determined.<p></p> MAIN RESULTS AND THE ROLE OF CHANCE Circulating fetal estrogen levels were very high and were increased by maternal smoking (ANOVA, P = 0.055–0.004 versus control). Smoke exposure also dysregulated (two-way ANOVA, smoking versus gestation weeks interaction, P = 0.046–0.023) four fetal ovarian genes (cytochrome P450 scc [CYP11A1], NOBOX oogenesis homeobox [NOBOX], activator of apoptosis harakiri [HRK], nuclear receptor subfamily 2, group E, member 1 [NR2E1]), shifted the ovarian Inhibin βA/inhibin α ratio (NHBA/INHA) transcript ratio in favour of activin (ANOVA, P = 0.049 versus control) and reduced the proportion of dominant-negative estrogen receptor 2 (ERβ: ESR2) isoforms in half the exposed fetuses. PAHs, ligands for the aryl hydrocarbon receptor (AHR), were increased nearly 6-fold by maternal smoking (ANOVA, P = 0.011 versus control). A fifth transcript, COUP transcription factor 1 (nuclear receptor subfamily 2, group F, member 1: NR2F1, which contains multiple AHR-binding sites), was both significantly increased (ANOVA, P = 0.026 versus control) and dysregulated by (two-way ANOVA, smoking versus gestation weeks interaction, P = 0.021) maternal smoking. NR2F1 is associated with repression of FSHR expression and smoke-exposed ovaries failed to show the normal increase in FSHR expression during the second trimester. There was a significantly higher number of DEAD (Asp-Glu-Ala-Asp) box polypeptide 4 (DDX4) VASA-positive (ANOVA, P = 0.016 versus control), but not POU domain, class 1, transcription factor 1 (POU5F1) OCT3/4-positive, oocytes in smoke-exposed fetuses and this matched with a significantly higher number of primordial follicles (ANOVA, P = 0.024 versus control).<p></p> LIMITATIONS, REASONS FOR CAUTION The effects of maternal smoking on establishment of the maximum fetal primordial follicle pool cannot be reliably studied in our population since the process is not completed until 28 weeks of gestation and normal fetuses older than 21 weeks of gestation are not available for study. Our data suggest that some fetal ovaries are affected by smoke exposure while others are not, indicating that additional studies, with larger numbers, may show more significant effects.<p></p> WIDER IMPLICATIONS OF THE FINDINGS Fetal exposure to chemicals in cigarette smoke is known to lead to reduced fecundity in women. Our study suggests, for the first time, that this occurs via mechanisms involving activation of AHR, disruption of inhibin/activin and estrogen signalling, increased exposure to estrogen and dysregulation of multiple molecular pathways in the exposed human fetal ovary. Our data also suggest that alterations in the ESR2 positive and dominant negative isoforms may be associated with reduced sensitivity of some fetuses to increased estrogens and maternal smoking

The Quintuplet Cluster I. A K-band spectral catalog of stellar sources

Three very massive clusters are known to reside in the Galactic Center region, the Arches cluster, the Quintuplet cluster and the Central parsec cluster. We obtained spectroscopic observations of the Quintuplet cluster with the Integral Field Spectrograph SINFONI-SPIFFI at the ESO-VLT. The spectral range comprises the near-IR K-band from 1.94 to 2.45 micrometer. The 3D data cubes of the individual fields were flux-calibrated and combined to one contiguous cube, from which the spectra of all detectable point sources were extracted. We present a catalog of 160 stellar sources in the inner part of the Quintuplet cluster.Comment: 14 pages, 9 figures, 3 tables, accepted by A&