Amor Nafkha - Profile on Academia.edu (original) (raw)

Papers by Amor Nafkha

Purpose-Food supply chain (FSC) in Greece is dominated by small and medium-sized enterprises (SME... more Purpose-Food supply chain (FSC) in Greece is dominated by small and medium-sized enterprises (SMEs), who face several challenges in adopting green practices. The purpose of this paper is to identify the key drivers and barriers influencing the environmental performance of SMEs within the Greek dairy supply chain (SC). Design/methodology/approach-Descriptive research methodology attempts to prioritize the drivers and barriers for improving the environmental sustainability performance. Analytical hierarchy process and sensitivity analysis are used to understand the complex nature of the influencing factors. Findings-The analysis identifies five barriers and six drivers for the implementation of green practices within the dairy SC. While external drivers significantly influence the market structure and logistics network, government, competitors and customers are the driving factors for improving environmental performance. Research limitations/implications-The study contributes to filling the literature gap on key factors influencing the implementation of green practices within the FSC. The identified influential factors will contribute toward building a framework for improving sustainability performance within the Greek dairy SC. Practical implications-The study is expected to benefit the Greek and European SMEs by driving their environmental practices within the perishable SC network. Originality/value-The paper provides directions for researchers, practitioners and policy makers in understanding the challenges for implementing green practices in the dairy SC. The holistic approach followed in this paper is a building block for a conceptual framework on implementing environmental sustainability within the FSC. Apart from contributing to the current literature by extending the research horizon to SMEs' green adoption capability, this study also provides better understanding of the pivotal role of internal and external key factors in influencing sustainability performance.

-Le concept de la radio intelligente définit deux types d'utilisateurs: les utilisateurs primaire... more -Le concept de la radio intelligente définit deux types d'utilisateurs: les utilisateurs primaires (UP) qui ont accès aux ressources spectrales d'une façon prioritaire et les utilisateurs secondaires (US) qui exploitent les opportunités de communication laissées vacantes par les UPs. Dans ce papier on s'intéresse au problème de détection des ressources spectrales libres en utilisant les distributions du nombre de conditionnement (NDC) de la matrice de covariance des signaux reus par l'US. Une nouvelle formule mathématique est proposée pour la distribution du NDC dans le cas d'absence des UPs permettant ainsi de développer un nouveau algorithme de détection. Les résultats des simulations nous permettent de valider la formulation théorique et les hypothèses de bases.

In this paper, we propose a soft-output Multiple-Input and Multiple-Output (MIMO) detector algori... more In this paper, we propose a soft-output Multiple-Input and Multiple-Output (MIMO) detector algorithm, which is based on two complementary techniques: exploration and exploitation. The proposed detector, called List Exploration and Exploitation (L2E), achieves near-optimal performance with low and fixed computational complexity. It has a high parallelism degree, which makes it suitable for efficient practical implementation. The soft-output values are calculated by means of squared Euclidean distances in a max-Log Likelihood Ratio (LLR) approximation. The average Bit Error Rate (BER) performances of the L2E are compared to the well-known List Sphere Decoding (LSD) algorithm and it is shown that our method considerably reduces the computation complexity while maintaining near-optimal performance in comparison to LSD algorithm.

Non-Orthogonal Multiple Access (NOMA) is one of the promising techniques to ensure very high spec... more Non-Orthogonal Multiple Access (NOMA) is one of the promising techniques to ensure very high spectral efficiency in 5G mobile communications and beyond. In contrast to the orthogonal multiple access (OMA) technique, the NOMA shows outstanding performances in terms of throughput, user fairness, low latency and compatibility with the current and future communication systems. In this paper, we analyze the capacity region in NOMA system and the limited number of multiplexed users under a given power allocation vector (i.e. symmetric/asymmetric channel). In addition, we compare the downlink capacity of the OMA/NOMA systems. Moreover, we have investigated the effect of large constellation order on the power allocation and bit error rate (BER). Comparisons between the coded and uncoded schemes are also presented.

In this paper, we present an analytical lower bound on the ergodic capacity of optical multiple-i... more In this paper, we present an analytical lower bound on the ergodic capacity of optical multiple-input multiple-output (MIMO) channels. It turns out that the optical MIMO channel matrix which couples the mt inputs (modes/cores) into mr outputs (modes/cores) can be modeled as a sub-matrix of a m × m Haar-distributed unitary matrix where m > mt, mr. Using the fact that the probability density of the eigenvalues of a random matrix from unitary ensemble can be expressed in terms of the Christoffel-Darboux kernel. We provide a new analytical expression of the ergodic capacity as function of signal-to-noise ratio (SNR). Moreover, we derive a closed-form lower-bound expression to the ergodic capacity. In addition, we also derive an approximation to the ergodic capacity in low-SNR regimes. Finally, we present numerical results supporting the expressions derived.

2018 25th International Conference on Telecommunications (ICT), Jun 1, 2018

In this article, we propose a theoretical framework to derive the stochastic behavior of the cycl... more In this article, we propose a theoretical framework to derive the stochastic behavior of the cyclic autocorrelation power (CAP). This function is especially used in cyclostationaritybased spectrum sensing for its robustness to noise uncertainty and its low computational cost. We first express the theoretical probability density function (PDF) of the cyclic autocorrelation power-which proves to follow a central scaled (respectively noncentral) chi-square distribution if the received samples consist of additive Gaussian noise (respectively noise plus a cyclostationary signal). In order to verify the accuracy of the proposed theoretical derivation, simulation results are then provided in terms of detection and false alarm probabilities.

IEEE Signal Processing Letters, 2019

This letter presents a rigorous demonstration of the convergence of the Newton fractional delay f... more This letter presents a rigorous demonstration of the convergence of the Newton fractional delay filter to the ideal fractional delay filter. The Newton structure is a very efficient implementation of Lagrange interpolation using a variable fractional delay filter structure. Through the developed demonstration, a new approach is proposed to define the ideal fractional delay filter as the limit of any digital filter implementing on Lagrange interpolation. This letter also proves that the Z-transform expression of the ideal fractional delay has a fully defined frequency response on the unit circle.

EAI Endorsed Transactions on Cognitive Communications, 2017

Standard condition number (SCN) detector is a promising detector that can work efficiently in unc... more Standard condition number (SCN) detector is a promising detector that can work efficiently in uncertain environments. In this paper, we consider a Cognitive Radio (CR) system with large number of antennas (eg. Massive MIMO) and we provide an accurate and simple closed form approximation for the SCN distribution using the generalized extreme value (GEV) distribution. The approximation framework is based on the moment-matching method where the expressions of the moments are approximated using bi-variate Taylor expansion and results from random matrix theory. In addition, the performance probabilities and the decision threshold are considered. Since the number of antennas and/or the number of samples used in the sensing process may frequently change, this paper provides simple form decision threshold and performance probabilities offering dynamic and real-time computations. Simulation results show that the provided approximations are tightly matched to relative empirical ones.

EURASIP Journal on Wireless Communications and Networking, 2014

Spectrum sensing has been identified as the key step of the cognition cycle and the most importan... more Spectrum sensing has been identified as the key step of the cognition cycle and the most important function for the establishment of cognitive radio. In this paper, a blind cyclostationary feature detector, which is based on the symmetry property of cyclic autocorrelation function (SP-CAF), is implemented and tested using universal software radio peripheral platform and GNU Radio open-source software development toolkit. Performance of the SP-CAF is compared to the classical energy detector via various tests conducted in real scenarios where both detection algorithms are employed to blindly sense the spectrum for opportunistic access. This study shows that the blind cyclostationary feature detector outperforms the classical energy detector while guaranteeing acceptable complexity and low sensing time. Moreover, different experimental results indicate that the blind sensing detector can achieve high detection probability at a low false alarm probability under real channel conditions and low signal-to-noise ratio.

EAI Endorsed Transactions on Cognitive Communications, 2017

Scaled Largest Eigenvalue (SLE) detector stands out as the optimal single-primary-user detector i... more Scaled Largest Eigenvalue (SLE) detector stands out as the optimal single-primary-user detector in uncertain noisy environments. In this paper, we consider a multi-antenna cognitive radio system in which we aim at detecting the presence/absence of a Primary User (PU) using the SLE detector. By the exploitation of the distributions of the largest eigenvalue and the trace of the receiver sample covariance matrix, we show that the SLE could be modeled using the standard Gaussian function. Moreover, we derive the distribution of the SLE and deduce a simple yet accurate form of the probability of false alarm and the probability of detection. Hence, this derivation yields a very simple form of the detection threshold. Correlation coefficient between the largest eigenvalue and the trace is also considered as we derive a simple analytical expression. These analytical derivations are validated through extensive Monte Carlo simulations

International Journal of Computer Applications, May 31, 2012

This article explores several hardware design methods used to implement a reconfigurable software... more This article explores several hardware design methods used to implement a reconfigurable software defined radio system. The promise of software defined radios for rapidly changing the operating characteristics of radios suggests further an exciting new method to create opportunities and means for interoperability among and between any number of different radio systems. The possibilities of run-time reconfiguration techniques are explained and quantified. In this article, we are going to limit our discussion to examine the reconfigurability and low power trade-offs between: (i) building dedicated functional modules providing high performance at a high cost (Velcro approach), versus (ii) parameterizable function blocks used in FPGA-based system development, versus (iii) dynamic partial reconfiguration which is the ability to reconfigured a portion of the FPGA while the remainder is still in operation. The main objective here is to explore and discuss the best method to design a reconfigurable, a high performance and a low power consumption software defined equipment.

Publication in the conference proceedings of EUSIPCO, Marrakech, Morocco, 2013

Abstract—Spectrum sensing enables detecting opportunities in licensed bands in order to access un... more Abstract—Spectrum sensing enables detecting opportunities in licensed bands in order to access unused portions of the licensed spectrum. In this paper we propose two low complexity detectors based on a combination of two well-known and complementary signal detection mechanisms: energy detection and mono-cycle detection, which exploits cyclostationarity property of the signals. In the first algorithm the mono-cycle detector iteratively corrects the thresholds of a double threshold energy detector, that will finally converge to the performance of the mono-cycle detector. The second algorithm uses the mono-cycle detector to directly estimate the noise level N0, which is used to fix the threshold of the radiometer. Simulation results conducted on different environments show promising performances of the proposed detectors especially in low SNR.

Implementation Scenario for Teaching Partial Reconfiguration of FPGA

— We present in this paper a lab on partial reconfiguration (PR) of FPGA for a video application.... more — We present in this paper a lab on partial reconfiguration (PR) of FPGA for a video application. This lab is dedicated to last year engineering students. The implementation target is a Xilinx Virtex5 of a ML506 design kit board. The structure of the proposed design, as well as the designing steps and the obtained results are detailled. This lab is based on the research done by the authors in the domain of software radio and cognitive radio during last decade. Index terms — partial reconfiguration of FPGA, Virtex, ICAP, education I.

IEEE Access, 2020

Multimode/multicore fibers are expected to provide an attractive solution to overcome the capacit... more Multimode/multicore fibers are expected to provide an attractive solution to overcome the capacity limit of the current optical communication system. In the presence of strong crosstalk between modes and/or cores, the squared singular values of the input/output transfer matrix follow the law of the Jacobi ensemble of random matrices. Assuming that the channel state information is only available at the receiver, we derive a new expression for the ergodic capacity of the MIMO Jacobi fading channel. The proposed expression involves double integrals which can be easily evaluated for a high-dimensional MIMO scenario. Moreover, the method used in deriving this expression does not appeal to the classical one-point correlation function of the random matrix model. Using a limiting transition between Jacobi and associated Laguerre polynomials, we derive a similar formula for the ergodic capacity of the MIMO Rayleigh fading channel. Moreover, we derive a new exact closed-form expressions for the achievable sum rate of MIMO Jacobi and Rayleigh fading channels employing linear minimum mean squared error (MMSE) receivers. The analytical results are compared to the results obtained by Monte Carlo simulations and the related results available in the literature, which shows perfect agreement. INDEX TERMS Additive white noise, channel capacity, detection algorithms, MIMO, optical fiber communication, optical crosstalk, probability density function, Rayleigh channels.

Generalization and Coefficients Optimization of the Newton Structure

2018 25th International Conference on Telecommunications (ICT), 2018

The Newton structure is a very efficient implementation of a variable fractional delay filter per... more The Newton structure is a very efficient implementation of a variable fractional delay filter performing Lagrange interpolation. In this paper, we study the generalization of this structure by developing the closed form expressions of the generalized structure. Through this, any Farrow structure can be replaced by the Newton structure that is more efficient in terms of complexity. Moreover, the closed form expression of the frequency response of the generalized Newton structure is developed. This expression enables the application of filter optimization methods to build customized Newton structures. We demonstrate how this makes possible the design of optimized Newton structures that offer a reduction in complexity by half compared to their Farrow counterparts, while keeping a similar filtering performance.

The nature of this Deliverable of WP2.1 ("Radio interfaces for nextgeneration wireless systems") ... more The nature of this Deliverable of WP2.1 ("Radio interfaces for nextgeneration wireless systems") is mainly descriptive and its purpose is to provide a report on the status of the different Joint Research Activities (JRAs) currently ongoing, some of them being performed on the facilities that are available at EuWIn. Keywords: The main topics addressed are the need for more (efficient use of the) spectrum, channel modelling and performance evaluation of wireless systems, high data rates, and indoor location. Authors IMPORTANT: The information in the following two tables will be directly used for the MPA (Monitoring Partner Activity) procedure. Upon finalisation of the deliverable, please, ensure it is accurate. Use multiple pages if needed. Besides, please, adhere to the following rules:  Beneficiary/Organisation: For multi-party beneficiaries (CNIT) and beneficiaries with Third Parties (CNRS and CTTC), please, indicate beneficiary and organisation (e.g.,

IEEE Access, 2020

The soft-output multiple-input multiple-output (MIMO) detection problem has been extensively stud... more The soft-output multiple-input multiple-output (MIMO) detection problem has been extensively studied, and a large number of heuristics and metaheuristics have been proposed to solve it. Unlike classical tree-search based detectors, geometrical heuristic algorithms involved two consecutive steps: (i) an exploration step based on the geometry of the channel matrix singular vectors; (ii) a local exploitation step is performed in order to obtain better final solution. In this paper, new enhancements for geometrical heuristics are introduced to significantly reduce the complexity in quadrature phase-shift keying (QPSK) and allow 16 quadrature amplitude modulation (QAM) capability through new exploration techniques. The performance-complexity trade-off between the new detector and two tree-based algorithms is investigated through Pareto efficiency. The Pareto framework also allows us to select the most efficient tuning parameters based on an exhaustive search. The proposed detector can be customized on the fly using only one or two parameters to balance the trade-off between computational complexity and bit error rate performances. Moreover, the Pareto fronts demonstrate that the new geometrical heuristic is especially efficient with QPSK since it provides a significant reduction in regards to the computational complexity while preserving good bit error rate (BER) performance and ensuring high flexibility.

21st European Signal Processing Conference (EUSIPCO 2013), 2013

In this paper, we will firstly show that the Cyclic Autocorrelation function (CAF) is a sparse fu... more In this paper, we will firstly show that the Cyclic Autocorrelation function (CAF) is a sparse function in the cyclic frequency domain. Then using this property we propose a new CAF estimator, using Compressed Sensing (CS) technique with OMP algorithm [1]. This estimator outperforms the classic estimator used in [2]. Furthermore, since our estimator does not need any information, we claim that it is a blind estimator whereas the estimator used in [2] is clearly not blind because it needs the knowledge of the cyclic frequency. Using this new CAF estimator we proposed in the second part of this paper a new blind free bands detector. It assumes that two estimated CAF of two successive packets of samples, should have close cyclic frequencies, if a telecommunication signal is present. This new detector is a soft version of the detector already presented in [3]. This methods outperforms the cyclostationnarity detector of Dantawate Giannakis of [2].

2018 25th International Conference on Telecommunications (ICT), Jun 1, 2018

IEEE Signal Processing Letters, 2019

EAI Endorsed Transactions on Cognitive Communications, 2017

EURASIP Journal on Wireless Communications and Networking, 2014

EAI Endorsed Transactions on Cognitive Communications, 2017

International Journal of Computer Applications, May 31, 2012

Publication in the conference proceedings of EUSIPCO, Marrakech, Morocco, 2013

Implementation Scenario for Teaching Partial Reconfiguration of FPGA

IEEE Access, 2020

Generalization and Coefficients Optimization of the Newton Structure

2018 25th International Conference on Telecommunications (ICT), 2018

IEEE Access, 2020

21st European Signal Processing Conference (EUSIPCO 2013), 2013