Dynamical depinning of chiral domain walls

The domain wall depinning field represents the minimum magnetic field needed to move a domain wall, typically pinned by samples' disorder or patterned constrictions. Conventionally, such field is considered independent on the Gilbert damping since it is assumed to be the field at which the Zeeman energy equals the pinning energy barrier (both damping independent). Here, we analyse numerically the domain wall depinning field as function of the Gilbert damping in a system with perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction. Contrary to expectations, we find that the depinning field depends on the Gilbert damping and that it strongly decreases for small damping parameters. We explain this dependence with a simple one-dimensional model and we show that the reduction of the depinning field is related to the internal domain wall dynamics, proportional to the Dzyaloshinskii-Moriya interaction, and the finite size of the pinning barriers

Low Complexity WMMSE Power Allocation In NOMA-FD Systems

In this paper we study the problem of power and channel allocation with the objective of maximizing the system sum-rate for multicarrier non-orthogonal multiple access (NOMA) full duplex (FD) systems. Such an allocation problem is non-convex and, thus, with the goal of designing a low complexity solution, we propose a scheme based on the minimization of the weighted mean square error, which achieves performance reasonably close to the optimum and allows to clearly outperforms a conventional orthogonal multiple access approach. Numerical results assess the effectiveness of our algorithm.Comment: 5 pages conference paper, 3 figures. Submitted on ICASSP 202

Generalized voter-like models on heterogeneous networks

We describe a generalization of the voter model on complex networks that encompasses different sources of degree-related heterogeneity and that is amenable to direct analytical solution by applying the standard methods of heterogeneous mean-field theory. Our formalism allows for a compact description of previously proposed heterogeneous voter-like models, and represents a basic framework within which we can rationalize the effects of heterogeneity in voter-like models, as well as implement novel sources of heterogeneity, not previously considered in the literature

A Robust Maximum Likelihood Scheme for PSS Detection and Integer Frequency Offset Recovery in LTE Systems

Before establishing a communication link in a cellular network, the user terminal must activate a synchronization procedure called initial cell search in order to acquire specific information about the serving base station. To accomplish this task, the primary synchronization signal (PSS) and secondary synchronization signal (SSS) are periodically transmitted in the downlink of a long term evolution (LTE) network. Since SSS detection can be performed only after successful identification of the primary signal, in this work, we present a novel algorithm for joint PSS detection, sector index identification, and integer frequency offset (IFO) recovery in an LTE system. The proposed scheme relies on the maximum likelihood (ML) estimation criterion and exploits a suitable reduced-rank representation of the channel frequency response, which proves robust against multipath distortions and residual timing errors. We show that a number of PSS detection methods that were originally introduced through heuristic reasoning can be derived from our ML framework by simply selecting an appropriate model for the channel gains over the PSS subcarriers. Numerical simulations indicate that the proposed scheme can be effectively applied in the presence of severe multipath propagation, where existing alternatives provide unsatisfactory performance

ML estimation of timing, integer frequency and primary sequence index in LTE systems

This paper addresses the problem of maximum likelihood (ML) estimation of slot timing, integer carrier frequency offset and primary sequence index for the downlink of Long Term Evolution (LTE) systems. The proposed algorithm is designed to exploit the knowledge of the pilot Zadoff-Chu sequence embedded in the primary synchronization signal (PSS). The estimation process is affected by the presence of a large set of nuisance parameters, which need to be estimated jointly with the parameters of interest. As a consequence, the exact ML solution is extremely complex and we have developed a suboptimal algorithm designed to provide a good balance between estimation accuracy and complexity. In particular, a key finding is a reduced-rank representation for the frequency response of the channel, which is required by the ML estimator but is not available at receiver prior to having acquired synchronization. Compared to existing alternatives, the resulting scheme exhibits improved accuracy in the estimation of all three parameters of interest

Periodic Preamble-Based Frequency Recovery in OFDM Receivers Plagued by I/Q Imbalance

The direct conversion receiver (DCR) architecture has received much attention in the last few years as an effective means to obtain user terminals with reduced cost, size, and power consumption. A major drawback of a DCR device is the possible insertion of I/Q imbalances in the demodulated signal, which can seriously degrade the performance of conventional synchronization algorithms. In this paper, we investigate the problem of carrier frequency offset (CFO) recovery in an OFDM receiver equipped with a DCR front-end. Our approach is based on maximum likelihood (ML) arguments and aims at jointly estimating the CFO, the useful signal component, and its mirror image. In doing so, we exploit knowledge of the pilot symbols transmitted within a conventional repeated training preamble appended in front of each data packet. Since the exact ML solution turns out to be too complex for practical purposes, we propose two alternative schemes which can provide nearly optimal performance with substantial computational saving. One of them provides the CFO in closed-form, thereby avoiding any grid-search procedure. The accuracy of the proposed methods is assessed in a scenario compliant with the 802.11a WLAN standard. Compared with existing solutions, the novel schemes achieve improved performance at the price of a tolerable increase of the processing load

A Lexicographic Public Good Ranking

In this paper, we consider the consistency of the desirability relation with the ranking of the players in a simple game provided by some well-known solutions, in particular the Public Good Index [12] and the criticality-based ranking [1]. We define a new ranking solution, the lexicographic Public Good ranking (LPGR), strongly related to the Public Good Index being rooted in the minimal winning coalitions of the simple game, proving that it is monotonic with respect to the desirability relation [15], when it holds. A suitable characterization of the LPGR solution is provided. Finally, we investigate the relation among the LPGR solution and the criticality-based ranking, referring to the dual game

A Practical Scheme for Frequency Offset Estimation in MIMO-OFDM Systems

This paper deals with training-assisted carrier frequency offset (CFO) estimation in multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. The exact maximum likelihood (ML) solution to this problem is computationally demanding as it involves a line search over the CFO uncertainty range. To reduce the system complexity, we divide the CFO into an integer part plus a fractional part and select the pilot subcarriers such that the training sequences have a repetitive structure in the time domain. In this way, the fractional CFO is efficiently computed through a correlation-based approach, while ML methods are employed to estimate the integer CFO. Simulations indicate that the proposed scheme is superior to the existing alternatives in terms of both estimation accuracy and processing load

Sviluppo di modelli ed algoritmi per la simulazione della dinamica delle pale nel rotore di un elicottero

La presente tesi ha come oggetto il miglioramento delle potenzialità del codice Hedyson, sviluppato in collaborazione tra il Dipartimento di Ingegneria Aerospaziale dell’Università di Pisa e la Sistemi Dinamici S.p.A. per valutare le grandezze caratteristiche di un velivolo ad ala rotante in diverse condizioni di volo. La base di tutto il lavoro è la traduzione del codice dalla versione Matlab, precedentemente generata [3], ad una versione in Fortran, adatta in particolare alla simulazione della dinamica dell’elicottero in real time, che presenta delle novità di rilievo come l’estensione del modello di rotore da pala singola ad N pale e l’introduzione di un modello di velocità indotta più raffinato del precedente. A conclusione di questa attività è stato sviluppato poi un modello Simulink del rotore principale mediante l’utilizzo delle S-function, uno strumento molto efficace per l’integrazione temporale di sistemi dinamici del secondo ordine. Tale modello permette di tracciare la risposta dinamica dell’elicottero rispetto all’ingresso di comandi pilota (passo collettivo e ciclico), ma allo stadio attuale risulta ancora incompleto

GIS and 3D Models as Support to Documentation and Planning of the Baku Historical Centre (Republic of Azerbaijan)

The walled city of Baku, Icherisheher has been described as one of the best examples of a city that has retained its historical stratigraphy in over a thousand years, where the different influences and its evolution in time may be appreciated. In realising the Master Plan of the historical city, many problems were solved with different information technologies (GIS, DEM, DTM, etc.) for the survey and data mapping management during all the phases of the project. Initially the analysis was addressed to systematic reading of the documents collected during the iconographic study, verifying the process of deterioration that the historic city had suffered during various periods from the Khans to the Tsarist domain, and from the Republic of Azerbaijan to the Soviet period through to its independence. The entire central part of the historic city was analyzed, including not only on its special architectural and urban monuments, but even minor buildings, which are in part still intact, used as a basis for a digital map created in order to focus on Baku's historical evolution. A three-dimensional model of the historic centre of Baku was then produced as a basis not only for virtual navigation in real time, but as additional support for planning studies and to better understand the principles of various design choices. The request to produce a model in VRML format addressed the choice of better modelling methods. The combination of these different technologies and their application in the analysis of historical cities led to further considerations on data acquisition systems, standardization of formats, the use of survey instruments and the use of different software, etc., all fundamental elements to the define their correct use.DiSBEF, University of Urbino, Campus Scientifico "E. Mattei", 60129 Urbino, Italy, GESP s. r. l., Italy