Elmahdi Driouch

Université du Québec à Montréal, Montréal, Quebec, Canada

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Publications (12)4.13 Total impact

  • E. Driouch, W. Ajib
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    ABSTRACT: Cognitive radio is regarded as the ideal candidate for enhancing the efficiency of spectrum usage for next-generation wireless systems. In fact, this emerging technology allows unlicensed cognitive users to transmit over frequency bands that are initially owned by license holders through the use of dynamic spectrum sharing. In this paper, we propose a novel algorithm that efficiently solves the problem of spectrum sharing and user scheduling in a cognitive downlink multi-input-multi-output system (MIMO). We study the scenario where primary receivers do not allow any interference from a multiantenna cognitive base station, which serves cognitive users. Using graph theory, we model, formulate, and develop an algorithm that finds near-optimal spectrum sharing with the objective of approaching the maximum achievable secondary sum rate. Since the formulated graph-coloring problem is shown to be NP-hard, we design a low-complexity greedy algorithm. Following, we add the well-known proportional fairness to the proposed algorithm to ensure time-based fairness and to efficiently resolve the fairness/sum rate tradeoff. The problem is also formulated as a binary integer programming problem to find the optimal coloring solution. Computer simulations show that the proposed algorithm is able to achieve near-optimal performances with low computational complexity.
    IEEE Transactions on Vehicular Technology 01/2013; 62(8):3875-3885. · 2.06 Impact Factor
  • E. Driouch, W. Ajib
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    ABSTRACT: The cognitive radio technology allows the design of dynamic spectrum sharing techniques where unlicensed secondary users can use frequency bands owned by license primary holders. Thus, this emerging technology is regarded as the ideal candidate that can enhance the efficiency of spectrum usage for the next generation of wireless communication systems. In this paper, we consider the problem of spectrum sharing and user scheduling in a cognitive radio MIMO system. A secondary network made up of a multi-antenna base station and several secondary receivers share the same frequency bands owned by primary users.We study the scenario where the primary receivers do not allow any interference from the cognitive BS which serves its users in the broadcast channel.Using graph theory, we propose a novel algorithm that finds a near optimal spectrum sharing with the objective of approaching the maximum achievable sum rate of the secondary network. The spectrum sharing problem is formulated as a new vertex coloring problem. We show that this problem is NP-hard and then we design an efficient greedy algorithm using one out of four proposed selection criteria to solve the problem. We also formulate the coloring problem as a binary integer programming problem in order to find the optimal coloring solution. Through computer simulations, it is shown that the proposed algorithm is able to achieve near-optimal performances with very low computational complexity.
    Global Communications Conference (GLOBECOM), 2012 IEEE; 01/2012
  • E. Driouch, W. Ajib, T. Jalloul
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    ABSTRACT: We consider a point-to-multipoint cognitive network sharing the same frequency band with a primary network assuming a spectrum underlay model. We investigate the scenario where a cognitive base station equipped with multiple antennas attempts to serve secondary users through an antenna assignment scheme. We consider quality of service constraints for secondary users and an interference constraint for the primary receiver. Hence, the cognitive base station performs both antenna assignment and optimal power allocation for the selected secondary users. Due to the high computational complexity of this problem, we propose a heuristic algorithm that separates the two tasks and tries to maximize the number of served secondary users with respect to the system constraints. The antenna assignment phase is performed using an efficient selection criterion followed by an optimal power allocation as a second phase. We show that the proposed algorithm has a very low computational complexity compared to the brute force algorithm. Furthermore, simulation results show that the proposed heuristic algorithm is able to achieve performance very close to that of the optimal solution.
    Vehicular Technology Conference (VTC Fall), 2012 IEEE; 01/2012
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    Elmahdi Driouch, Wessam Ajib, Ahmed Ben Dhaou
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    ABSTRACT: In this paper, we propose a novel simple heuristic algorithm for scheduling the secondary link activation and provide a dynamic spectrum sharing in cognitive radio networks. This algorithm is presented for spectrum underlay where primary and secondary users transmit simultaneously on the same frequency bands in cognitive radio networks. The proposed algorithm is based on a graph-theoretical model. First, the cognitive radio network is modeled as a weighted graph. The spectrum sharing problem is then reduced to the one of finding a sensitive vertex coloring of the constructed graph. The spectrum sharing decisions are taken at the level of a spectrum server that coordinates the secondary transmissions in order to find the best transmission/spectrum pairs in terms of system sum rate. The spectrum server is also responsible for protecting the transmission of primary users from harmful interference via assigning appropriate transmitting power to the activated secondary transmissions. We show through simulations the gain that the proposed algorithm can extract in terms of system sum rate from the transmission selection diversity.
    01/2012;
  • Elmahdi Driouch, Wessam Ajib
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    ABSTRACT: In multiple-input–multiple-output (MIMO) multiuser systems, simultaneously serving multiple users achieves high data rates. However, high-performance transmit beamforming requires an adequately designed user-selection scheme. Optimal scheduling can be only obtained through a high computationally complex exhaustive search, and hence, low-complexity heuristic algorithms are required. In addition, employing a multiple-access scheme such as code division (CDMA) largely increases the complexity of optimal scheduling, and it becomes unemployable even for a moderate number of users and antennas. In this context, this paper proposes three heuristic scheduling algorithms for MIMO CDMA systems using zero-forcing beamforming (ZFBF). We use a graph-theoretical approach to model the system as a weighted undirected graph. The problem of user selection is then formulated as a graph coloring problem, namely, the maximum weight $N$-colorable subgraph problem. Then, we design two heuristics to solve this graph problem. The first algorithm is a low-complexity greedy algorithm. The second algorithm is based on a tabu search approach to resolve efficiently the complexity/performance tradeoff. Numerical and simulation results show the sub-optimal performances and robustness of the proposed low-complexity algorithms.
    IEEE Transactions on Vehicular Technology 01/2012; 61(2):521-532. · 2.06 Impact Factor
  • E. Driouch, W. Ajib
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    ABSTRACT: Cognitive radio is regarded as an emerging technique developed to enhance the efficiency of spectrum usage. In this paper, we consider a point-to-multipoint secondary network sharing frequency bands with several primary transmitters and receivers. Assuming a cognitive base station equipped with multiple transmit antennas and single antenna receivers, we propose a greedy spectrum sharing algorithm in order to approach the maximum achievable sum rate of the secondary network. First, we model the overall studied system as a weighted graph, and then we formulate the spectrum sharing as a vertex coloring problem. Second, we show that the two problems are similar and we design a greedy algorithm to solve both problems using two selection criteria. We show through computer simulations that the proposed algorithm is able to achieve near-optimal performances with very low computational complexity.
    Communications and Information Technology (ICCIT), 2012 International Conference on; 01/2012
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    Elmahdi Driouch, Wessam Ajib
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    ABSTRACT: In today's wireless communication systems, the design of efficient packet scheduling algorithms at the MAC layer is proven to have significant impact on their overall performances. In the light of this fact, we propose and compare in this paper different scheduling techniques which aim at satisfying the users' requirements in terms of both rates and delays. The considered system is a downlink multi antenna code division multiple access (MIMO-CDMA) system which assumes both traffic arrival and users' mobility. First, the MIMO-CDMA system is modeled as a weighted graph. The weight of each vertex is then updated at each time slot according to a specified scheduling rule. Finally, we solve heuristically a graph coloring problem in order to find a near- optimal scheduling decision. We evaluate through simulations the performance of the proposed algorithms and show that a cross layer design taking the benefits of both MIMO and scheduling may be efficient to address the tradeoff between system capacity and users' quality of service requirements.
    Proceedings of the 73rd IEEE Vehicular Technology Conference, VTC Spring 2011, 15-18 May 2011, Budapest, Hungary; 01/2011
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    Elmahdi Driouch, Wessam Ajib, Mohamed Gaha
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    ABSTRACT: In multiuser multiple input multiple output (MIMO) systems, it is optimal to serve multiple users at the same time in order to achieve high data rates. However, the use of a transmit beamforming technique requires a well designed user selection scheme to obtain good performances. The optimal scheduling solution can only be obtained through a highly computationally complex exhaustive search. In addition, when employing a multiple access scheme, such as the code division (CDMA), the complexity of an optimal user selection becomes higher even for moderate number of users and antennas. In this context, this paper proposes a heuristic scheduling algorithm based on a tabu search approach for MIMO CDMA systems using ZFBF as a transmit technique. We use a graph theoretical approach to model the system as a weighted undirected graph. The problem of user selection is then formulated as a graph coloring problem. Numerical results show that the proposed algorithm outperforms the greedy scheduling scheme and achieves performances, in terms of system sum rate, very close to those of the highly complex optimal solution.
    Proceedings of the Global Communications Conference, 2010. GLOBECOM 2010, 6-10 December 2010, Miami, Florida, USA; 01/2010
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    E. Driouch, W. Ajib
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    ABSTRACT: In multiuser CDMA wireless systems where the base station is equipped with multiple antennas, the base station takes advantage from the spatial and code separability between the served users in order to enhance the performance of the system. However, this enhancement is constrained by the design of an appropriate scheduling scheme which is responsible of choosing the best users to serve. In this paper, we propose efficient scheduling algorithms for the downlink of multiantenna CDMA wireless systems using zero forcing beamforming. Our proposition maximizes the system sum rate and keeps the computational complexity low. We make use of a graph theoretical approach to represent the system as an undirected weighted graph. As a second step, we formulate the scheduling problem as the maximum weight k-colorable subgraph problem. We propose two heuristic solutions to find the users to serve in each time slot in an acceptable polynomial time. Finally we evaluate the efficiency of the proposed schemes by mean of simulations and the results show the near-optimal performance of the proposed schedulers with very low computational complexity compared to the optimal exhaustive search over all the possible users combinaisons.
    Wireless Telecommunications Symposium, 2009. WTS 2009; 05/2009
  • Abdelhalim Driouech, Wessam Ajib, Elmahdi Driouch
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    ABSTRACT: Multi hop wireless mesh networks presents a promising solution to extent the coverage and increase the number of clients sharing the same broadband connection. Introducing the MIMO technology at the physical layer of those networks allows to improve the performance and support a higher number of clients. However, in such systems the absence of an efficient and fair medium access strategy can lead to severe unfairness between the clients and to poor system performances. In this paper, we propose a fair scheduling algorithm that improves considerably the bandwidth utilization while the fairness is guaranteed. We evaluate our proposed algorithm by simulation in order to show the maximum throughput that can be obtained while the different nodes of the MIMO-based wireless mesh networks are served fairly.
    Proceedings of the 14th IEEE Symposium on Computers and Communications (ISCC 2009), July 5-8, Sousse, Tunisia; 01/2009
  • Elmahdi Driouch, Wessam Ajib
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    ABSTRACT: We design efficient scheduling algorithms for multiantenna CDMA downlink systems using zero forcing beamforming. Our proposition maximizes the system sum rate and keeps the computational complexity low. We make use of a graph theoretical approach to represent the system as an undirected weighted graph. As a second step, we formulate the scheduling problem as the maximum weight k-colorable subgraph problem. We propose two heuristic solutions to find the users to serve in each time slot in an acceptable polynomial time. Finally we evaluate the efficiency of the proposed schemes by mean of simulations and the results shows the near-optimal performance of the proposed schedulers with very low computational complexity compared to the optimal exhaustive search over all the possible users combinations. Assuming the use of non-orthogonal spreading codes, our proposed algorithms are shown to still have near-optimal performance even in the case of high values of the orthogonality factor.
    01/2009;
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    E. Driouch, Wessam Ajib
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    ABSTRACT: We propose efficient scheduling algorithms for down-link MIMO-CDMA systems using zero forcing beamforming to achieve high system throughput with low computational complexity. Based on a graph theoretical approach, we propose to represent the system as a graph and to formulate the scheduling problem as the maximum weight k-colorable subgraph problem. The proposed algorithms make use of two heuristic solutions to find the scheduled users in each time slot in an acceptable polynomial time. We evaluate the efficiency of the proposed schedulers and the results demonstrates that it can achieve near-optimal performance with very low complexity compared to the optimal exhaustive search.
    Computers and Communications, 2008. ISCC 2008. IEEE Symposium on; 08/2008