8,272 research outputs found
Authentication enhancement in command and control networks: (a study in Vehicular Ad-Hoc Networks)
Intelligent transportation systems contribute to improved traffic safety by facilitating real time communication between vehicles. By using wireless channels for communication, vehicular networks are susceptible to a wide range of attacks, such as impersonation, modification, and replay. In this context, securing data exchange between intercommunicating terminals, e.g., vehicle-to-everything (V2X) communication, constitutes a technological challenge that needs to be addressed. Hence, message authentication is crucial to safeguard vehicular ad-hoc networks (VANETs) from malicious attacks. The current state-of-the-art for authentication in VANETs relies on conventional cryptographic primitives, introducing significant computation and communication overheads. In this challenging scenario, physical (PHY)-layer authentication has gained popularity, which involves leveraging the inherent characteristics of wireless channels and the hardware imperfections to discriminate between wireless devices. However, PHY-layerbased authentication cannot be an alternative to crypto-based methods as the initial legitimacy detection must be conducted using cryptographic methods to extract the communicating terminal secret features. Nevertheless, it can be a promising complementary solution for the reauthentication problem in VANETs, introducing what is known as “cross-layer authentication.” This thesis focuses on designing efficient cross-layer authentication schemes for VANETs, reducing the communication and computation overheads associated with transmitting and verifying a crypto-based signature for each transmission. The following provides an overview of the proposed methodologies employed in various contributions presented in this thesis.
1. The first cross-layer authentication scheme: A four-step process represents this approach: initial crypto-based authentication, shared key extraction, re-authentication via a PHY challenge-response algorithm, and adaptive adjustments based on channel conditions. Simulation results validate its efficacy, especially in low signal-to-noise ratio (SNR) scenarios while proving its resilience against active and passive attacks.
2. The second cross-layer authentication scheme: Leveraging the spatially and temporally correlated wireless channel features, this scheme extracts high entropy shared keys that can be used to create dynamic PHY-layer signatures for authentication. A 3-Dimensional (3D) scattering Doppler emulator is designed to investigate the scheme’s performance at different speeds of a moving vehicle and SNRs. Theoretical and hardware implementation analyses prove the scheme’s capability to support high detection probability for an acceptable false alarm value ≤ 0.1 at SNR ≥ 0 dB and speed ≤ 45 m/s.
3. The third proposal: Reconfigurable intelligent surfaces (RIS) integration for improved authentication: Focusing on enhancing PHY-layer re-authentication, this proposal explores integrating RIS technology to improve SNR directed at designated vehicles. Theoretical analysis and practical implementation of the proposed scheme are conducted using a 1-bit RIS, consisting of 64 × 64 reflective units. Experimental results show a significant improvement in the Pd, increasing from 0.82 to 0.96 at SNR = − 6 dB for multicarrier communications.
4. The fourth proposal: RIS-enhanced vehicular communication security: Tailored for challenging SNR in non-line-of-sight (NLoS) scenarios, this proposal optimises key extraction and defends against denial-of-service (DoS) attacks through selective signal strengthening. Hardware implementation studies prove its effectiveness, showcasing improved key extraction performance and resilience against potential threats.
5. The fifth cross-layer authentication scheme: Integrating PKI-based initial legitimacy detection and blockchain-based reconciliation techniques, this scheme ensures secure data exchange. Rigorous security analyses and performance evaluations using network simulators and computation metrics showcase its effectiveness, ensuring its resistance against common attacks and time efficiency in message verification.
6. The final proposal: Group key distribution: Employing smart contract-based blockchain technology alongside PKI-based authentication, this proposal distributes group session keys securely. Its lightweight symmetric key cryptography-based method maintains privacy in VANETs, validated via Ethereum’s main network (MainNet) and comprehensive computation and communication evaluations.
The analysis shows that the proposed methods yield a noteworthy reduction, approximately ranging from 70% to 99%, in both computation and communication overheads, as compared to the conventional approaches. This reduction pertains to the verification and transmission of 1000 messages in total
A review of differentiable digital signal processing for music and speech synthesis
The term “differentiable digital signal processing” describes a family of techniques in which loss function gradients are backpropagated through digital signal processors, facilitating their integration into neural networks. This article surveys the literature on differentiable audio signal processing, focusing on its use in music and speech synthesis. We catalogue applications to tasks including music performance rendering, sound matching, and voice transformation, discussing the motivations for and implications of the use of this methodology. This is accompanied by an overview of digital signal processing operations that have been implemented differentiably, which is further supported by a web book containing practical advice on differentiable synthesiser programming (https://intro2ddsp.github.io/). Finally, we highlight open challenges, including optimisation pathologies, robustness to real-world conditions, and design trade-offs, and discuss directions for future research
Gibbs–Wilbraham oscillation related to an Hermite interpolation problem on the unit circle
The aim of this piece of work is to study some topics related to an Hermite interpolation problem on the unit circle. We consider as nodal points the zeros of the para-orthogonal polynomials with respect to a measure in the Baxter class and such that the sequence of the first derivative of the reciprocal of the orthogonal polynomials is uniformly bounded on the unit circle. We study the convergence of the Hermite–Fejér interpolants related to piecewise continuous functions and we describe the sets in which the interpolants uniformly converge to the piecewise continuous function as well as the oscillatory behavior of the interpolants near the discontinuities, where a Gibbs–Wilbraham phenomenon appears. Finally we present some numerical experiments applying the main results and by considering nodal systems of interest in the theory of orthogonal polynomials.Ministerio de Economía y Competitividad | Ref. AGL 2014-60412-
Fourier-Gegenbauer Pseudospectral Method for Solving Time-Dependent One-Dimensional Fractional Partial Differential Equations with Variable Coefficients and Periodic Solutions
In this paper, we present a novel pseudospectral (PS) method for solving a
new class of initial-value problems (IVPs) of time-dependent one-dimensional
fractional partial differential equations (FPDEs) with variable coefficients
and periodic solutions. A main ingredient of our work is the use of the
recently developed periodic RL/Caputo fractional derivative (FD) operators with
sliding positive fixed memory length of Bourafa et al. [1] or their reduced
forms obtained by Elgindy [2] as the natural FD operators to accurately model
FPDEs with periodic solutions. The proposed method converts the IVP into a
well-conditioned linear system of equations using the PS method based on
Fourier collocations and Gegenbauer quadratures. The reduced linear system has
a simple special structure and can be solved accurately and rapidly by using
standard linear system solvers. A rigorous study of the error and convergence
of the proposed method is presented. The idea and results presented in this
paper are expected to be useful in the future to address more general problems
involving FPDEs with periodic solutions.Comment: 13 pages, 3 figures. arXiv admin note: text overlap with
arXiv:2304.0445
Direct Integral Pseudospectral and Integral Spectral Methods for Solving a Class of Infinite Horizon Optimal Output Feedback Control Problems Using Rational and Exponential Gegenbauer Polynomials
This study is concerned with the numerical solution of a class of
infinite-horizon linear regulation problems with state equality constraints and
output feedback control. We propose two numerical methods to convert the
optimal control problem into nonlinear programming problems (NLPs) using
collocations in a semi-infinite domain based on rational Gegenbauer (RG) and
exponential Gegenbauer (EG) basis functions. We introduce new properties of
these basis functions and derive their quadratures and associated truncation
errors. A rigorous stability analysis of the RG and EG interpolations is also
presented. The effects of various parameters on the accuracy and efficiency of
the proposed methods are investigated. The performance of the developed
integral spectral method is demonstrated using two benchmark test problems
related to a simple model of a divert control system and the lateral dynamics
of an F-16 aircraft. Comparisons of the results of the current study with
available numerical solutions show that the developed numerical scheme is
efficient and exhibits faster convergence rates and higher accuracy.Comment: 27 pages, 24 figure
Exact positive cubature formulas via generalized sampling on combinatorial graphs
We consider a disjoint cover (partition) of an undirected weighted finite
graph by connected subgraphs (clusters) and
select a function on each of the clusters. For a given signal
on the set of its weighted average values samples is defined via inner
products . The goal of the paper is
to establish exact quadrature formulas with positive weights which are
exploring these samples generated by bandlimited functions.Comment: 13 page
Proceedings of SIRM 2023 - The 15th European Conference on Rotordynamics
It was our great honor and pleasure to host the SIRM Conference after 2003 and 2011 for the third time in Darmstadt. Rotordynamics covers a huge variety of different applications and challenges which are all in the scope of this conference. The conference was opened with a keynote lecture given by Rainer Nordmann, one of the three founders of SIRM “Schwingungen in rotierenden Maschinen”. In total 53 papers passed our strict review process and were presented. This impressively shows that rotordynamics is relevant as ever. These contributions cover a very wide spectrum of session topics: fluid bearings and seals; air foil bearings; magnetic bearings; rotor blade interaction; rotor fluid interactions; unbalance and balancing; vibrations in turbomachines; vibration control; instability; electrical machines; monitoring, identification and diagnosis; advanced numerical tools and nonlinearities as well as general rotordynamics. The international character of the conference has been significantly enhanced by the Scientific Board since the 14th SIRM resulting on one hand in an expanded Scientific Committee which meanwhile consists of 31 members from 13 different European countries and on the other hand in the new name “European Conference on Rotordynamics”. This new international profile has also been
emphasized by participants of the 15th SIRM coming from 17 different countries out of three continents. We experienced a vital discussion and dialogue between industry and academia at the conference where roughly one third of the papers were presented by industry and two thirds by academia being an excellent basis to follow a bidirectional transfer what we call xchange at Technical University of Darmstadt. At this point we also want to give our special thanks to the eleven industry sponsors for their great support of the conference. On behalf of the Darmstadt Local Committee I welcome you to read the papers of the 15th SIRM giving you further insight into the topics and presentations
Weak Markovian Approximations of Rough Heston
The rough Heston model is a very popular recent model in mathematical
finance; however, the lack of Markov and semimartingale properties poses
significant challenges in both theory and practice. A way to resolve this
problem is to use Markovian approximations of the model. Several previous works
have shown that these approximations can be very accurate even when the number
of additional factors is very low. Existing error analysis is largely based on
the strong error, corresponding to the distance between the kernels.
Extending earlier results by [Abi Jaber and El Euch, SIAM Journal on Financial
Mathematics 10(2):309--349, 2019], we show that the weak error of the Markovian
approximations can be bounded using the -error in the kernel approximation
for general classes of payoff functions for European style options. Moreover,
we give specific Markovian approximations which converge super-polynomially in
the number of dimensions, and illustrate their numerical superiority in option
pricing compared to previously existing approximations. The new approximations
also work for the hyper-rough case
Convergence rate of numerical scheme for SDEs with a distributional drift in Besov space
This paper is concerned with numerical solutions of one-dimensional SDEs with
the drift being a generalised function, in particular belonging to the
Holder-Zygmund space of negative order in the spacial
variable. We design an Euler-Maruyama numerical scheme and prove its
convergence, obtaining an upper bound for the strong convergence rate. We
finally implement the scheme and discuss the results obtained.Comment: 20 pages, 3 figure
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