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Papers by Mohammed El-Absi

2015 Loughborough Antennas & Propagation Conference (LAPC), 2015

Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, 2015

2015 7th Computer Science and Electronic Engineering Conference (CEEC), 2015

IEEE Transactions on Vehicular Technology, 2015

Interference alignment (IA) is a promising transmission technology enabling essentially the maxim... more Interference alignment (IA) is a promising transmission technology enabling essentially the maximum achievable degrees of freedom (DoF) in K-user multiple-input multipleoutput (MIMO) interference channels. The ideal DoF of IA systems have been obtained using independent MIMO channels, which is usually hardly observed in reality, particularly in indoor environments. Therefore, the data sum-rate and symbol errorrate of IA are dramatically degraded in real-world scenarios since the correlation between MIMO channels decreases the signal-to-noise ratio (SNR) of the received signal after alignment. For this reason, an acceptable sum-rate of IA in real MIMO orthogonal frequency-division-multiplexing (MIMO-OFDM) interference channels was obtained in the literature by modifying the distance between network nodes and the separation between the antennas within each node in order to minimize the spatial correlation. In this paper, we propose to apply transmit antenna selection to MIMO-OFDM IA systems either through bulk or per-subcarrier selection aiming at improving the sum-rate and/or error-rate performance under real-world channel circumstances while keeping the minimum spatial antenna separation of 0.5 wavelengths within each node. Two selection criteria are considered: maximum sum-rate and minimum error-rate. In order to avoid subcarrier imbalance across the antennas of each user who is caused by per-subcarrier selection, a constrained per-subcarrier antenna selection is operated. Furthermore, a sub-optimal antenna selection algorithm is proposed to reduce the computational complexity of the optimal algorithm. An experimental validation of MIMO-OFDM IA with antenna selection in an indoor wireless network scenario is presented. The experimental results are compared with deterministic channels that are synthesized using hybrid EM ray-tracing models. Our performance evaluation shows that the practical feasibility of MIMO-OFDM IA systems is significantly increased by antenna selection in real-world scenarios.

2014 European Conference on Networks and Communications (EuCNC), 2014

ABSTRACT In this paper, we present a radio resource allocation algorithm based on interference al... more ABSTRACT In this paper, we present a radio resource allocation algorithm based on interference alignment (IA) for orthogonal frequency division multiplexing (OFDM) and filter bank multicarrier (FBMC) based MIMO cognitive radio (CR) systems. The algorithm provides the opportunity for all secondary users to share the available subcarriers simultaneously using IA technique. Besides, it allocates the power budget of each secondary user over the subcarriers in order to maximize the sum-rate of the system without inducing excessive interference to primary users. Simulations show that CR systems based on IA achieves a significant sum-rate increase compared to CR systems based on frequency division multiple access (FDMA). Moreover, IA based CR using FBMC physical layer achieves considerable throughput improvement compared to OFDM physical layer.

2010 6th International Conference on Wireless and Mobile Communications, 2010

Page 1. Using Pseudonoise Sequence Subcarrier Shuffling for Peak-to-Average Power Ratio Reduction... more Page 1. Using Pseudonoise Sequence Subcarrier Shuffling for Peak-to-Average Power Ratio Reduction in OFDM Systems Mohammed A. El-Absi Islamic University of Gaza Electrical Engineering Departement PO Box 108, Gaza ...

Ultra-Wideband Radio Technologies for Communications, Localization and Sensor Applications, 2013

2012 IEEE International Conference on Ultra-Wideband, 2012

ABSTRACT Main objective of this contribution is to apply Interference Alignment (IA) algorithms i... more ABSTRACT Main objective of this contribution is to apply Interference Alignment (IA) algorithms in real-world indoor environments for UWB MIMO MB-OFDM communication systems. In indoor environments, the required orthogonality between multi-users channels, which is necessary for proper IA, could be hardly reached. The spatial diversity among the users/nodes is mostly insufficient to obtain a robust performance for IA algorithms. In this work, a practical artificial channel diversity technique is applied through antenna selection to choose the best scenario providing the maximum orthogonality and consequentially the best overall system performance. Our analysis considers deterministic UWB MIMO channel model based on EM Ray-tracing in a real-world multi-user indoor environment. Simulation results present a significant enhancement in the overall system performance. Furthermore, the impact of the directional properties and the orientations of the antennas on the system are investigated.

ABSTRACT Abstract—In this paper, interference alignment (IA) is utilized to obtain an efficient a... more ABSTRACT Abstract—In this paper, interference alignment (IA) is utilized to obtain an efficient and fair resource allocation algorithm in MIMO cognitive radio (CR) systems. In the proposed algorithm, IA enables all secondary users to share the available spectrum without affecting the quality-of-service of the primary system. The considered methodology increases the total degrees of freedom of the CR systems and achieves fairness among CR users. An optimal power allocation based on IA is formulated in order to maximize the total sum-rate while keeping the interference introduced to the primary system lower than the prescribed interference threshold. Furthermore, a sub-optimal power allocation scheme is proposed to overcome the high computational complexity of the optimal scheme. Simulations reveal that IA technique achieves significant sum-rate increase of CR systems compared to frequency division multiple access (FDMA) CR systems. Moreover, the sup-optimal algorithm approaches the optimal sum-rate performance.

2014 IEEE Global Communications Conference, 2014

2014 11th International Symposium on Wireless Communications Systems (ISWCS), 2014

2012 International Symposium on Communications and Information Technologies (ISCIT), 2012

ABSTRACT The main objective of this contribution is to develop a novel antenna selection algorith... more ABSTRACT The main objective of this contribution is to develop a novel antenna selection algorithm for Interference Alignment (IA) in multi-user communication systems. Successive IA requires high degree of independency among the channels, which could hardly exist in real-world environments. Therefore, the Bit Error Rate (BER) performance of the IA system suffers from a dramatic degradation, especially in indoor environments. Applying the developed antenna selection algorithm can effectively increase the channels diversity and improve the BER performance. This selection algorithm based on selecting the maximum Canonical Correlation (CC) between the desired signal subspace and the interference-free subspace in order to maximize the average received Signal-to-Noise Ratio (SNR) of the system. The influence of the CC on sum-rate would be presented mathematically. Simulation results show a significant improvement of the BER system performance based on the CC antenna selection algorithm compared with the maximum sum-rate selection algorithm.

Transactions on Emerging Telecommunications Technologies, 2014

Interference alignment is a joint-transmission strategy that significantly increases the sum rate... more Interference alignment is a joint-transmission strategy that significantly increases the sum rate of interference channels at high signal-to-noise ratios (SNRs). The recent iterative interference alignment approaches are incapable of guaranteeing the best sum-rate performance with the increase of the SNR amongst different K-user interference channels, especially at high SNR regime. In this paper, a new interference alignment algorithm is developed to improve the sum-rate performance of K-user multi-input multi-output (MIMO) and multi-carrier interference channels by minimising the interference leakage and maximising the desired power concurrently, which is called by min-maxing strategy. For a K-user MIMO interference channel, we design transmit precoding matrices and receive decoding matrices through an efficient iterative algorithm based on min-maxing strategy in a distributed way, in which each receiver maximises the desired signal power, whereas it preserves the minimum leakage interference as a constraint. This optimisation problem is reformulated and relaxed into a standard semidefinite programming form. The convergence of the proposed algorithm is proved as well. Furthermore, a simplified min-maxing algorithm is proposed for rank-deficient interference channels to achieve the targeted performance with less complexity. The numerical simulations show that the proposed algorithm proffers significant sum-rate improvement in K-user MIMO interference channels compared with the existing algorithms at high SNR regime. Moreover, the simplified algorithm matches the optimal performance in the systems of rank-deficient channels. Finally, the developed min-maxing algorithm has been extended to K-user multi-carrier interference channels, which outperform the previous approaches in terms of sum rate in several scenarios.

2013 IEEE 14th Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2013

ABSTRACT The main objective of this contribution is to develop a new interference alignment (IA) ... more ABSTRACT The main objective of this contribution is to develop a new interference alignment (IA) algorithm, which improves the sum-rate performance of multiuser MIMO communication systems. The recent iterative IA approaches cannot guarantee robust sum-rate performance in different K-user MIMO interference channels, especially at high SNR regime. In our proposed distributed optimization algorithm, each receiver maximizes the desired signal power while preserving the minimum interference leakage as a constraint. A convex relaxation has been applied to this optimization problem after reformulating it into semidefinite programming form. This algorithm provides orthogonal precoders and decoders, which is fairly simple in practical implementation. Simulation results of the proposed algorithm proffer significant sum-rate improvement in various interference channels compared to existing algorithms.

Pediatrics in review / American Academy of Pediatrics, 2010

International Journal of Computer and Electrical Engineering, 2011

Page 1. International Journal of Computer and Electrical Engineering, Vol. 3, No. 2, April, 2011 ... more Page 1. International Journal of Computer and Electrical Engineering, Vol. 3, No. 2, April, 2011 1793-8163 176 Abstract—This paper proposes an efficient peak-to-average power ratio (PAPR) reduction method for multicarrier ...

Cardiology in the Young, 2008

This contribution presents an improved Interference Alignment (IA) method for arbitrary MIMOOFDM ... more This contribution presents an improved Interference Alignment (IA) method for arbitrary MIMOOFDM communication systems by exploiting spatial degrees of freedom of sophisticated multimode MIMO antennas. It is widely known that IA needs sufficient orthogonality between all the multi-user channels which is in typical indoor environments often not given due to insufficient spatial diversity. A significant improvement of the IA system performance has been achieved by using multimode MIMO antennas instead of classical and idealized omni-directional antennas. Such multimode MIMO antennas are capable to switch between different modes of the radiation patterns which significantly reduces the relevant channel coherence. Simulations of an indoor multi-user environment are carried out by a deterministic MIMO-OFDM channel model based on hybrid Electro Magnetic (EM) ray-tracing for being as close as possible to reality. Moreover, hardware implementation aspects are discussed as well demonstrating...

2015 Loughborough Antennas & Propagation Conference (LAPC), 2015

Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, 2015

2015 7th Computer Science and Electronic Engineering Conference (CEEC), 2015

IEEE Transactions on Vehicular Technology, 2015

Interference alignment (IA) is a promising transmission technology enabling essentially the maxim... more Interference alignment (IA) is a promising transmission technology enabling essentially the maximum achievable degrees of freedom (DoF) in K-user multiple-input multipleoutput (MIMO) interference channels. The ideal DoF of IA systems have been obtained using independent MIMO channels, which is usually hardly observed in reality, particularly in indoor environments. Therefore, the data sum-rate and symbol errorrate of IA are dramatically degraded in real-world scenarios since the correlation between MIMO channels decreases the signal-to-noise ratio (SNR) of the received signal after alignment. For this reason, an acceptable sum-rate of IA in real MIMO orthogonal frequency-division-multiplexing (MIMO-OFDM) interference channels was obtained in the literature by modifying the distance between network nodes and the separation between the antennas within each node in order to minimize the spatial correlation. In this paper, we propose to apply transmit antenna selection to MIMO-OFDM IA systems either through bulk or per-subcarrier selection aiming at improving the sum-rate and/or error-rate performance under real-world channel circumstances while keeping the minimum spatial antenna separation of 0.5 wavelengths within each node. Two selection criteria are considered: maximum sum-rate and minimum error-rate. In order to avoid subcarrier imbalance across the antennas of each user who is caused by per-subcarrier selection, a constrained per-subcarrier antenna selection is operated. Furthermore, a sub-optimal antenna selection algorithm is proposed to reduce the computational complexity of the optimal algorithm. An experimental validation of MIMO-OFDM IA with antenna selection in an indoor wireless network scenario is presented. The experimental results are compared with deterministic channels that are synthesized using hybrid EM ray-tracing models. Our performance evaluation shows that the practical feasibility of MIMO-OFDM IA systems is significantly increased by antenna selection in real-world scenarios.

2014 European Conference on Networks and Communications (EuCNC), 2014

ABSTRACT In this paper, we present a radio resource allocation algorithm based on interference al... more ABSTRACT In this paper, we present a radio resource allocation algorithm based on interference alignment (IA) for orthogonal frequency division multiplexing (OFDM) and filter bank multicarrier (FBMC) based MIMO cognitive radio (CR) systems. The algorithm provides the opportunity for all secondary users to share the available subcarriers simultaneously using IA technique. Besides, it allocates the power budget of each secondary user over the subcarriers in order to maximize the sum-rate of the system without inducing excessive interference to primary users. Simulations show that CR systems based on IA achieves a significant sum-rate increase compared to CR systems based on frequency division multiple access (FDMA). Moreover, IA based CR using FBMC physical layer achieves considerable throughput improvement compared to OFDM physical layer.

2010 6th International Conference on Wireless and Mobile Communications, 2010

Page 1. Using Pseudonoise Sequence Subcarrier Shuffling for Peak-to-Average Power Ratio Reduction... more Page 1. Using Pseudonoise Sequence Subcarrier Shuffling for Peak-to-Average Power Ratio Reduction in OFDM Systems Mohammed A. El-Absi Islamic University of Gaza Electrical Engineering Departement PO Box 108, Gaza ...

Ultra-Wideband Radio Technologies for Communications, Localization and Sensor Applications, 2013

2012 IEEE International Conference on Ultra-Wideband, 2012

ABSTRACT Main objective of this contribution is to apply Interference Alignment (IA) algorithms i... more ABSTRACT Main objective of this contribution is to apply Interference Alignment (IA) algorithms in real-world indoor environments for UWB MIMO MB-OFDM communication systems. In indoor environments, the required orthogonality between multi-users channels, which is necessary for proper IA, could be hardly reached. The spatial diversity among the users/nodes is mostly insufficient to obtain a robust performance for IA algorithms. In this work, a practical artificial channel diversity technique is applied through antenna selection to choose the best scenario providing the maximum orthogonality and consequentially the best overall system performance. Our analysis considers deterministic UWB MIMO channel model based on EM Ray-tracing in a real-world multi-user indoor environment. Simulation results present a significant enhancement in the overall system performance. Furthermore, the impact of the directional properties and the orientations of the antennas on the system are investigated.

ABSTRACT Abstract—In this paper, interference alignment (IA) is utilized to obtain an efficient a... more ABSTRACT Abstract—In this paper, interference alignment (IA) is utilized to obtain an efficient and fair resource allocation algorithm in MIMO cognitive radio (CR) systems. In the proposed algorithm, IA enables all secondary users to share the available spectrum without affecting the quality-of-service of the primary system. The considered methodology increases the total degrees of freedom of the CR systems and achieves fairness among CR users. An optimal power allocation based on IA is formulated in order to maximize the total sum-rate while keeping the interference introduced to the primary system lower than the prescribed interference threshold. Furthermore, a sub-optimal power allocation scheme is proposed to overcome the high computational complexity of the optimal scheme. Simulations reveal that IA technique achieves significant sum-rate increase of CR systems compared to frequency division multiple access (FDMA) CR systems. Moreover, the sup-optimal algorithm approaches the optimal sum-rate performance.

2014 IEEE Global Communications Conference, 2014

2014 11th International Symposium on Wireless Communications Systems (ISWCS), 2014

2012 International Symposium on Communications and Information Technologies (ISCIT), 2012

ABSTRACT The main objective of this contribution is to develop a novel antenna selection algorith... more ABSTRACT The main objective of this contribution is to develop a novel antenna selection algorithm for Interference Alignment (IA) in multi-user communication systems. Successive IA requires high degree of independency among the channels, which could hardly exist in real-world environments. Therefore, the Bit Error Rate (BER) performance of the IA system suffers from a dramatic degradation, especially in indoor environments. Applying the developed antenna selection algorithm can effectively increase the channels diversity and improve the BER performance. This selection algorithm based on selecting the maximum Canonical Correlation (CC) between the desired signal subspace and the interference-free subspace in order to maximize the average received Signal-to-Noise Ratio (SNR) of the system. The influence of the CC on sum-rate would be presented mathematically. Simulation results show a significant improvement of the BER system performance based on the CC antenna selection algorithm compared with the maximum sum-rate selection algorithm.

Transactions on Emerging Telecommunications Technologies, 2014

Interference alignment is a joint-transmission strategy that significantly increases the sum rate... more Interference alignment is a joint-transmission strategy that significantly increases the sum rate of interference channels at high signal-to-noise ratios (SNRs). The recent iterative interference alignment approaches are incapable of guaranteeing the best sum-rate performance with the increase of the SNR amongst different K-user interference channels, especially at high SNR regime. In this paper, a new interference alignment algorithm is developed to improve the sum-rate performance of K-user multi-input multi-output (MIMO) and multi-carrier interference channels by minimising the interference leakage and maximising the desired power concurrently, which is called by min-maxing strategy. For a K-user MIMO interference channel, we design transmit precoding matrices and receive decoding matrices through an efficient iterative algorithm based on min-maxing strategy in a distributed way, in which each receiver maximises the desired signal power, whereas it preserves the minimum leakage interference as a constraint. This optimisation problem is reformulated and relaxed into a standard semidefinite programming form. The convergence of the proposed algorithm is proved as well. Furthermore, a simplified min-maxing algorithm is proposed for rank-deficient interference channels to achieve the targeted performance with less complexity. The numerical simulations show that the proposed algorithm proffers significant sum-rate improvement in K-user MIMO interference channels compared with the existing algorithms at high SNR regime. Moreover, the simplified algorithm matches the optimal performance in the systems of rank-deficient channels. Finally, the developed min-maxing algorithm has been extended to K-user multi-carrier interference channels, which outperform the previous approaches in terms of sum rate in several scenarios.

2013 IEEE 14th Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2013

ABSTRACT The main objective of this contribution is to develop a new interference alignment (IA) ... more ABSTRACT The main objective of this contribution is to develop a new interference alignment (IA) algorithm, which improves the sum-rate performance of multiuser MIMO communication systems. The recent iterative IA approaches cannot guarantee robust sum-rate performance in different K-user MIMO interference channels, especially at high SNR regime. In our proposed distributed optimization algorithm, each receiver maximizes the desired signal power while preserving the minimum interference leakage as a constraint. A convex relaxation has been applied to this optimization problem after reformulating it into semidefinite programming form. This algorithm provides orthogonal precoders and decoders, which is fairly simple in practical implementation. Simulation results of the proposed algorithm proffer significant sum-rate improvement in various interference channels compared to existing algorithms.

Pediatrics in review / American Academy of Pediatrics, 2010

International Journal of Computer and Electrical Engineering, 2011

Page 1. International Journal of Computer and Electrical Engineering, Vol. 3, No. 2, April, 2011 ... more Page 1. International Journal of Computer and Electrical Engineering, Vol. 3, No. 2, April, 2011 1793-8163 176 Abstract—This paper proposes an efficient peak-to-average power ratio (PAPR) reduction method for multicarrier ...

Cardiology in the Young, 2008

This contribution presents an improved Interference Alignment (IA) method for arbitrary MIMOOFDM ... more This contribution presents an improved Interference Alignment (IA) method for arbitrary MIMOOFDM communication systems by exploiting spatial degrees of freedom of sophisticated multimode MIMO antennas. It is widely known that IA needs sufficient orthogonality between all the multi-user channels which is in typical indoor environments often not given due to insufficient spatial diversity. A significant improvement of the IA system performance has been achieved by using multimode MIMO antennas instead of classical and idealized omni-directional antennas. Such multimode MIMO antennas are capable to switch between different modes of the radiation patterns which significantly reduces the relevant channel coherence. Simulations of an indoor multi-user environment are carried out by a deterministic MIMO-OFDM channel model based on hybrid Electro Magnetic (EM) ray-tracing for being as close as possible to reality. Moreover, hardware implementation aspects are discussed as well demonstrating...