Amor Nafkha | University of Cambridge (original) (raw)

Papers by Amor Nafkha

Research paper thumbnail of Experimental Study on Cyclostationary Feature and Eigenvalue based Algorithms for Spectrum Sensing

Research paper thumbnail of Eigenvalue-Based Spectrum SensingWith Two Receive Antennas

Research paper thumbnail of Fixed Complexity Soft-Output Detection Algorithm Through Exploration and Exploitation Processes

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.

Research paper thumbnail of Users' Power Multiplexing Limitations in NOMA System over Gaussian Channel

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.

Research paper thumbnail of A new lower bound on the ergodic capacity of optical MIMO channels

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.

Research paper thumbnail of Cyclic Autocorrelation based Spectrum Sensing: Theoretical Derivation Framework

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

Research paper thumbnail of Convergence of the Newton Structure Transfer Function to the Ideal Fractional Delay Filter

IEEE Signal Processing Letters, 2019

Research paper thumbnail of Asymptotic Approximation of the Standard Condition Number Detector for Large Multi-Antenna Cognitive Radio Systems

EAI Endorsed Transactions on Cognitive Communications, 2017

Research paper thumbnail of Blind spectrum sensing using symmetry property of cyclic autocorrelation function: from theory to practice

EURASIP Journal on Wireless Communications and Networking, 2014

Research paper thumbnail of On the Performance Analysis and Evaluation of Scaled Largest Eigenvalue in Spectrum Sensing: A Simple Form Approach

EAI Endorsed Transactions on Cognitive Communications, 2017

Research paper thumbnail of Software Defined Radio Equipment: What's the Best Design Approach to Reduce Power Consumption and Increase Reconfigurability?

International Journal of Computer Applications, May 31, 2012

Research paper thumbnail of Noise Uncertainty Analysis Of Energy Detector: Bounded And Unbounded Approximation Relationship

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

Research paper thumbnail of Low Complexity Enhanced Hybrid Spectrum Sensing Architectures for Cognitive Radio Equipment

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.

Research paper thumbnail of 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.

Research paper thumbnail of Design Approach to Reduce Power Consumption and Increase Reconfigurability?

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 reconf...

Research paper thumbnail of Closed-Form Expressions of Ergodic Capacity and MMSE Achievable Sum Rate for MIMO Jacobi and Rayleigh Fading Channels

Research paper thumbnail of 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.

Research paper thumbnail of Network of Excellence NEWCOM # Network of Excellence in Wireless Communications # FP 7 Contract Number : 318306 WP 2 . 1 – Radio interfaces for next generation wireless systems

Research paper thumbnail of When Should We Use Geometrical-Based MIMO Detection Instead of Tree-Based Techniques? A Pareto Analysis

Research paper thumbnail of Blind free band detector based on the sparsity of the Cyclic Autocorrelation function

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].

Research paper thumbnail of Experimental Study on Cyclostationary Feature and Eigenvalue based Algorithms for Spectrum Sensing

Research paper thumbnail of Eigenvalue-Based Spectrum SensingWith Two Receive Antennas

Research paper thumbnail of Fixed Complexity Soft-Output Detection Algorithm Through Exploration and Exploitation Processes

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.

Research paper thumbnail of Users' Power Multiplexing Limitations in NOMA System over Gaussian Channel

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.

Research paper thumbnail of A new lower bound on the ergodic capacity of optical MIMO channels

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.

Research paper thumbnail of Cyclic Autocorrelation based Spectrum Sensing: Theoretical Derivation Framework

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

Research paper thumbnail of Convergence of the Newton Structure Transfer Function to the Ideal Fractional Delay Filter

IEEE Signal Processing Letters, 2019

Research paper thumbnail of Asymptotic Approximation of the Standard Condition Number Detector for Large Multi-Antenna Cognitive Radio Systems

EAI Endorsed Transactions on Cognitive Communications, 2017

Research paper thumbnail of Blind spectrum sensing using symmetry property of cyclic autocorrelation function: from theory to practice

EURASIP Journal on Wireless Communications and Networking, 2014

Research paper thumbnail of On the Performance Analysis and Evaluation of Scaled Largest Eigenvalue in Spectrum Sensing: A Simple Form Approach

EAI Endorsed Transactions on Cognitive Communications, 2017

Research paper thumbnail of Software Defined Radio Equipment: What's the Best Design Approach to Reduce Power Consumption and Increase Reconfigurability?

International Journal of Computer Applications, May 31, 2012

Research paper thumbnail of Noise Uncertainty Analysis Of Energy Detector: Bounded And Unbounded Approximation Relationship

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

Research paper thumbnail of Low Complexity Enhanced Hybrid Spectrum Sensing Architectures for Cognitive Radio Equipment

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.

Research paper thumbnail of 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.

Research paper thumbnail of Design Approach to Reduce Power Consumption and Increase Reconfigurability?

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 reconf...

Research paper thumbnail of Closed-Form Expressions of Ergodic Capacity and MMSE Achievable Sum Rate for MIMO Jacobi and Rayleigh Fading Channels

Research paper thumbnail of 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.

Research paper thumbnail of Network of Excellence NEWCOM # Network of Excellence in Wireless Communications # FP 7 Contract Number : 318306 WP 2 . 1 – Radio interfaces for next generation wireless systems

Research paper thumbnail of When Should We Use Geometrical-Based MIMO Detection Instead of Tree-Based Techniques? A Pareto Analysis

Research paper thumbnail of Blind free band detector based on the sparsity of the Cyclic Autocorrelation function

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].