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André Gomes

Publications and source records attributed to André Gomes.

17 recordsLinked to original sources
arXiv2026

GeoRIS: Geofencing With Reconfigurable Intelligent Surfaces

Geofencing refers to controlling the availability of wireless services within a network perimeter. In this paper, we study how RIS can be used to achieve geofencing in outdoor-to-indoor network scenarios. Particularly, we propose GeoRIS, a RIS controller that achieves geofencing by exploiting beam management procedures to control beam alignment in networks with steerable directional transmission links. GeoRIS does not require control over the outdoor base station and can work with or without channel state information. Through simulations based on 3GPP network models, we validate GeoRIS and demonstrate that it can "shield" an indoor network area (for example, by weakening communication links to the point where indoor users cannot meet the minimum requirements of 5G eMBB services). We also highlight an interesting insight: the same RIS can play a dual role, extending or inhibiting outdoor-to-indoor communication. In our simulations, we show that GeoRIS can easily change an indoor space from a "strongly covered area" (e.g., supports eMBB services in approx. 90% of network area) to an "out-of-service area" (e.g., inhibits eMBB services in approx. 90% of network area), or vice-versa, an attractive characteristic in scenarios in which dynamic indoor coverage control is needed.

cs.NI↗
arXiv2026

HRRC on the Farm: Quantile Forecasting for Highly-Reliable Remote Control via LEO Networks

LEO satellite networks are an attractive solution to support farm automation in Agriculture 4.0 because of their ubiquitous coverage. However, LEO networks often suffer from high latency volatility, which can limit their utility in mission-critical farm operations such as remote control. This paper studies highly-reliable remote control over LEO networks by (i) casting highly-reliable remote control as a quantile forecasting problem and (ii) proposing a high-quantile estimator that can predict latency spikes at a given reliability level. Our results, drawn from a real-world OneWeb dataset collected in a major agricultural hub in the US, show that the proposed estimator can support highly-reliable remote control on the farm by meeting reliability requirements while allowing the remote-controlled vehicle to operate at speeds up to 138.6% higher than what would be possible otherwise.

cs.NI↗
arXiv2025

Deformation enduring conveyance of structured light through multimode waveguides and its exploitation for flexible hair-thin endoscopes

The remarkable advancements in our capacity to synthesise structured light have facilitated the generation of any desired optical landscapes and even controlling the spatial distribution of light propagating through optically complex media such as multimode fibres. The availability of precisely defined structured light at the extremity of an exceedingly narrow and flexible cable holds the potential to stimulate a diverse range of highly sought-after applications, encompassing rapid communication, quantum computing, and, notably, imaging. What we lack in reaching these aspirations is the resilience of such light transport to deformations of the waveguide. Although recent theoretical investigations have delineated the attributes of ideal multimode fibres capable of deformation-enduring conveyance of structured light, tangible fibres possessing this indispensable trait to a practical extent remain elusive. Our study takes a deep dive into the precision of commercially available multimode fibres with the highest probability of demonstrating the phenomenon. We identified minuscule imperfections in their refractive index distribution, examined how these affect light transport when the fibre is deformed, and studied their implications for imaging applications. Our investigation has confirmed that these imperfections are indeed responsible for the undesirable alterations introduced into the output structured light fields during bending. Finally, as an alternative to standard graded-index fibres, manufactured by drawing silica-based preforms, we present narrow multimode waveguides in which the refractive-index profile has been established by ion exchange. These waveguides indeed exhibit previously unseen resilience of structured light transport even under severe deformation conditions and aptly fulfil the requirements of imaging applications.

physics.optics↗
arXiv2025

Funnelling super-resolution STED microscopy through multimode fibres

Holographic multimode fibre endoscopes have recently shown their ability to unveil and monitor deep brain structures with sub-micrometre resolution, establishing themselves as a minimally-invasive technology with promising applications in neurobiology. In this approach, holographic control of the input light field entering the multimode fibres is achieved by means of wavefront shaping, usually treating the fibre as a complex medium. In contrast to other unpredictable and highly scattering complex media, multimode fibres feature symmetries and strong correlations between their input and output fields. Both step-index and graded-index multimode fibres offer a specific set of such correlations which, when appropriately leveraged, enable generating high-quality focused pulses with minimal intermodal dispersion. With this, we funnelled pulsed super-resolution STED microscopy with time-gated detection through a custom multimode fibre probe, combining the correlations of both multimode fibre types. We demonstrate resolution improvements over 3-times beyond the diffraction limit and showcase its applicability in bioimaging. This work provides not only a solution for delivering short pulses through step-index multimode fibre segments but also marks a step towards bringing advanced super-resolution imaging techniques with virtually no depth limitations.

physics.optics↗
arXiv2025

Dimensioning and Optimization of Reliability Coverage in Local 6G Networks

Enabling vertical use cases for the sixth generation (6G) wireless networks, such as automated manufacturing, immersive extended reality (XR), and self-driving fleets, will require network designs that meet reliability and latency targets in well-defined service areas. In order to establish a quantifiable design objective, we introduce the novel concept of reliability coverage, defined as the percentage area covered by communication services operating under well-defined reliability and performance targets. Reliability coverage allows us to unify the different network design tasks occurring at different time scales, namely resource orchestration and allocation, resulting in a single framework for dimensioning and optimization in local 6G networks. The two time scales, when considered together, yield remarkably consistent results and allow us to observe how stringent reliability/latency requirements translate into the increased wireless network resource demands.

cs.NI↗
arXiv2024

Designing Reliable Virtualized Radio Access Networks

As virtualization of Radio Access Networks (RAN) gains momentum, understanding the impact of hardware and software disaggregation on resiliency becomes critical to meet the high availability requirements of mobile networks. Our paper presents an analytical model, using continuous time Markov chains, to study the impact of virtualization and disaggregation on RAN availability. Our evaluation, assuming typical parameter value ranges for failure and recovery rates, points to containerized platform reliability as a constraint on vRAN availability. We also find that with active-passive replication, increasing hardware replication factor beyond 2 may not bring any benefits unless failover times are reduced. We also compare the reliability of centralized and distributed virtualized central units.

cs.NI↗
arXiv2024

The Hele-Shaw free boundary limit of Buckley-Leverett System

This paper proposes a new approach to solving the Buckley-Leverett System, which is to consider a compressible approximation model characterized by a stiff pressure law. Passing to the incompressible limit, the compressible model gives rise to a Hele-Shaw type free boundary limit of Buckley-Leverett System, and it is shown the existence of a weak solution of it.

math.AP↗
arXiv2024

Path Cohomology of Locally Finite Digraphs,Hodge's Theorem and the $p$-Lazy Random Walk

The study of Markov chains on discrete spaces, such as digraphs, has captivated mathematicians in recent decades due to its interconnectedness with topology, geometry, dynamics, spectral theory, and differential equations. Furthermore, extensive exploration of these multifaceted relationships has been pursued for their practical utility in diverse fields, including machine learning and image segmentation. In recent times, these interrelations have been generalized to higher dimensions within the framework of finite-dimensional simplicial complexes. In this paper, we embark on a further extension of these concepts. Initially, we introduce a cohomology of infinite (though locally finite) digraphs in arbitrary dimensions. Subsequently, in the latter portion of this manuscript, we define a fresh family of Laplace operators and conduct an examination of their spectrum, culminating in the proof of the Hodge Decomposition Theorem within this framework. Finally, we conclude by presenting a Markov chain, the $p$-Lazy Random Walk, whose asymptotic behavior is intrinsically linked to these cohomologies, while its mixing time is related to the the spectrum of our Laplace operators. This development opens doors to numerous unexplored questions, particularly regarding potential generalizations of the Ollivier-Ricci curvature to this topology and these Laplacians.

math.PR↗
arXiv2024

Malicious RIS versus Massive MIMO: Securing Multiple Access against RIS-based Jamming Attacks

In this letter, we study an attack that leverages a reconfigurable intelligent surface (RIS) to induce harmful interference toward multiple users in massive multiple-input multiple-output (mMIMO) systems during the data transmission phase. We propose an efficient and flexible weighted-sum projected gradient-based algorithm for the attacker to optimize the RIS reflection coefficients without knowing legitimate user channels. To counter such a threat, we propose two reception strategies. Simulation results demonstrate that our malicious algorithm outperforms baseline strategies while offering adaptability for targeting specific users. At the same time, our results show that our mitigation strategies are effective even if only an imperfect estimate of the cascade RIS channel is available.

eess.SP↗
arXiv2023

Dimensioning spectrum to support ultra-reliable low-latency communication

Industry-led initiatives such as the Next G Alliance (NGA) are currently considering how to dimension the spectrum required to support new classes of services envisioned beyond 5G. In particular, support for URLLC brings the challenge of how to dimension stochastic wireless networks to meet stringent reliability and latency requirements. Our analysis indicates that the bandwidth needed to meet URLLC goals can be in the order of gigahertz, beyond what is available in today's mobile networks. Network densification can ease those bandwidth needs but requires new deployment strategies involving substantially larger numbers of sites. As an alternative, we consider multi-connectivity and multi-operator network sharing as efficient ways to reduce the demand for bandwidth without outright deployment of additional base stations.

cs.NI↗
arXiv2022

Reconfigurable Intelligent Surfaces: The New Frontier of Next G Security

RIS is one of the significant technological advancements that will mark next-generation wireless. RIS technology also opens up the possibility of new security threats, since the reflection of impinging signals can be used for malicious purposes. This article introduces the basic concept for a RIS-assisted attack that re-uses the legitimate signal towards a malicious objective. Specific attacks are identified from this base scenario, and the RIS-assisted signal cancellation attack is selected for evaluation as an attack that inherently exploits RIS capabilities. The key takeaway from the evaluation is that an effective attack requires accurate channel information, a RIS deployed in a favorable location (from the point of view of the attacker), and it disproportionately affects legitimate links that already suffer from reduced path loss. These observations motivate specific security solutions and recommendations for future work.

cs.CR↗
arXiv2021

Rough paths and regularization

Calculus via regularizations and rough paths are two methods to approach stochastic integration and calculus close to pathwise calculus. The origin of rough paths theory is purely deterministic, calculus via regularization is based on deterministic techniques but there is still a probability in the background. The goal of this paper is to establish a connection between stochastically controlled-type processes, a concept reminiscent from rough paths theory, and the so-called weak Dirichlet processes. As a by-product, we present the connection between rough and Stratonovich integrals for c{à}dl{à}g weak Dirichlet processes integrands and continuous semimartingales integrators.

math.PR↗
arXiv2014

A theorem about vector fields with the "proportional volume property"

In this paper, we define a certain "proportional volume property" for an unit vector field on a spherical domain in S3. We prove that the volume of these vector fields has an absolute minimum and this value is equal to the volume of the Hopf vector field. Some examples of such vector fields are given. We also study the minimum energy of solenoidal vector fields which coincides with a Hopf flow along the boundary of a spherical domain of an odd-dimensional euclidean sphere.

math.DG↗
arXiv2011

Foliations on double-twisted products

In this paper we present a certain class of geodesic vector fields of the double-twisted product R X R. Some examples of totally geodesic foliations are given.

math.DG↗
arXiv2011

A note on subordination

In this paper we present a result about analytic functions f defined on the open unit disc and with a finite number of exceptional values containedin the real interval (0, 1). We find an upper bound for the modulus of f' in 0. This bound is sharp in the case of one exceptional value. We also analyzed the case of two exceptional values.

math.CV↗