Ahmed El Moussaoui

Genetic algorithms to optimize base station sitting in WCDMA networks

In UMTS network, radio planning cannot only be based on signal predictions, but it must also consider the traffic distribution, the power control mechanism as well as the power limits and the signal quality constraints. The present work aims to optimize the number of base stations used in the WCDMA radio network. In this paper, we propose a mathematical programming model for optimizing the base station locations considered for the uplink (mobile to BS) direction, and which considers the typical power control mechanism of WCDMA. The two contrasting objectives of the optimization process are the traffic coverage maximization and the installation costs minimization. A mimetic algorithm (AM) (genetic algorithm+ a local search) is proposed to find good approximate solutions of this NP hard problem. The Numerical results are obtained for reels instances, and generated by using classical propagation models.

The Effectiveness of Reputation-Based Voting for Collusion Tolerance in Large-Scale Grids

Large scale grids permit to share grid resources spread over different autonomous administrative sites in the internet. The rapid progress of grid systems opens the door for numerous companies to adopt this technology in their business development. This progress is characterized by the increasing openness and opportunity of resource-sharing across organizations in different domains. In the business context, these shared resources can be misused by some malicious users that can abuse the provided resources and make them behave maliciously to return wrong results and sabotage the jobs execution. The common technique used by most grid systems to deal with this problem is based on replication with voting. Nevertheless, these techniques rely on the assumption that the grid resources behave independently. They may be ineffective where a number of collusive resources collectively return the same wrong results of a job execution. In order to overcome this threat, we propose a reputation-based voting (RBV) approach, which investigates the trustworthiness of the grid resources through a reputation system, and then takes a decision about the results. In addition, the performance of our approach and other voting techniques, like m-first voting and credibility-based voting, are evaluated through simulation to perceive the effect of collusive grid resources on the correctness of the results. The obtained results show that our approach achieves a lower error-rate and better performance in terms of overhead.

SFL Algorithm for QoS-based Cloud Service Composition

With the advent of cloud service-based applications and Software as a Service (SaaS), new applications have recently known an increasing use of service-oriented architecture (SOA). This model has allowed computer science and associated industries to build new customized applications, by using the available and the existing cloud services bridged together dynamically to form a complex workflow process with more functionalities. However cloud services with similar and compatible functionalities may be offered by multiple providers but may also be offered at different QoS levels. Hence, to build a composite service with a high QoS, a decision should be made based on end-to-end QoS. This work proposes a new approach, for QoS-aware cloud service composition, which addresses a universal model, with end-toend QoS. It also proposes an effective evolutionary method based on Shuffled Frog Leaping Algorithm (SFLA), which is satisfying global and local constraints. Therefore, in order to evaluate the robustness of the proposed approach, we have evaluated the impact of several parameters that are highly significant in evolutionary methods, such as the impact of the population size, number of candidate services per task and number of criteria. The experimental results show that the chosen algorithm performs better than the ones based on Genetic Algorithm (GA).

Adaptive handover time scheme for dynamic load balancing in LTE systems

Future mobile communication systems will benefit from a significant degree of self-organization. Self-Organization (SON) methods have become one of the hot topics in wireless networks; these methods are a promising concept to automate the planning, deployment and optimization of radio access networks. In Self-Organizing Networks (SON), load balancing has been recognized as an effective means to increase network performance. In this paper, we present a framework for self-optimizing next generation mobile networks, such as 3G LTE. A load balancing algorithm based on automatic adjustment of handover thresholds in an LTE network is discussed.

Dual-band rectangular dielectric resonator antenna for ISM and 4 GHz bands applications

In this paper, we propose a dual-band rectangular DRA using the strip-fed method for 2.4 GHz ISM and 4 GHz bands applications. The proposed antenna is composed of small ceramic dielectric (21.65 mm × 15 mm × 26.1 mm, alumina). In order to achieve our goals, we made a cylindrical perforation through the DRA. The measured bandwidth and maximum radiation gain are 2.35 – 2.48 GHz (VSWR ≪ 1.05, 8.54 dBi at 2.4 GHz) and 3.5– 4.52 GHz (VSWR ≪ 1.02, 8.29 dBi at 4.25 GHz), respectively. From these results, it is demonstrated that our proposed antenna can be applicable to the ISM and 4 GHz bands applications.

Impact of other-cell interferences on downlink capacity in WCDMA Network

Before the establishment of the UMTS network, operators are obliged to make the planning process to ensure a better quality of service (QOS) for mobile stations belonging to WCDMA cells. This process consists of estimating a set of parameters characterizing the radio cell in the downlink direction. Among them, we are interested in the Node B total required power PTot, and the maximum cell capacity, in the case of voice only and in the case of voice/video. To implement the effect of the other-cell interferences power, modeled as a fraction fDL of the own-cell received power, on various radio parameters described previously, we focused our study on two different scenarios: the first is based on an isolated cell and the second, on multiple cells. In addition, when the WCDMA cell reaches its maximum capacity, the introduction of admission control algorithms is essential to maintain the QOS of the ongoing mobile stations. For this purpose, we have proposed an admission control algorithm, based both on the Node B total required power and the cell loading factor. This algorithm gives rigorous results compared to the existing ones in the literature.

Compromised Resources Tolerance in Grid Computing Systems

In the past ten years, grid computing has been heavily researched and developed. At the present, grid technology has matured enough to enable the realization of workable and commercial infrastructures, platforms and tools, ready to be used in production environments ranging from scientific to commercial application domains. As grid resources are used outside of organizational boundaries, it becomes increasingly difficult to guarantee that a resource being used is not malicious in some way. However, the critical grid application domains require many protections against malicious entities or massive attacks. It is then necessary to detect and tolerate malicious behavior of grid resources (or resources provider) in order to enhance the efficiency of grid security architecture. In this paper, we will propose and discuss an attack-tolerance mechanism based on sabotage tolerance technique. The grid broker service will build the reputation of all resources provider, by observing their trustworthiness from their previous results. The reputation value can be used in the validation process of job result by using majority voting technique.

Capacity Enhancement by Using a Multi-User Detector on Uplink Synchronous Mode

The Uplink Synchronous Transmission Scheme [1], is a technique used by operators, that exploit the uplink orthogonality, to reduce multiple access interferences in uplink direction and consequently to increase uplink capacity. The USTS gives better performances when we have an ideal case presented by no channelization code restrictions per scrambling code. In reality, channelization codes are limited. To resolve this problem, several scrambling codes are used to admit more users in the cell. However, the use of different scrambling codes increases the multiple access interference and consequently decreases uplink capacity gain, since signals transmitted by users under different scrambling codes are non-orthogonal. To obtain more performances and therefore to increase the uplink capacity gain, we will study the introduction of a multiuser detector for interferences cancellation, in uplink synchronous mode. For that, two values of interference cancellation efficiency  of the multi-user detector are considered. In this study, only the multiple access interference is reduced. To show the effect of other-cell interferences on uplink synchronous mode capacity, two scenarios are considered: an isolated cell and a multiple cell network.

A new mechanism to ensure integrity for MapReduce in cloud computing

MapReduce has been widely used as a powerful parallel data processing model and is adopted by most cloud providers to built cloud computing framework. However, in open cloud systems, security of computation becomes a great challenge. Moreover, MapReduce data-processing services are long-running, which increase the opportunity that an adversary launches attack to the workers and make them behave maliciously and, then tamper with the computation integrity of user tasks where their executions are generally performed in different administration domains out of the user control. Thus, the results of the computation might be erroneous and dishonest. In this paper, we propose a new mechanism based on weighted t-first voting method for ensuring the integrity of MapReduce in open cloud computing environment. Our mechanism can defeat both collusive and non-collusive malicious entities and thus guarantee high computation accuracy.

A compact rectangular UWB Dielectric resonator antenna

A compact rectangular Dielectric resonator antenna (DRA) is presented for ultra wide band communication systems. Ansoft HFSS 3-D electromagnetic solver is used for the design optimization. The proposed antenna has a low profile (∼3), a small size and a low permittivity constant (10.2). An impedance bandwidth about 46% (from 6.9 to 11 GHz) was achieved making this antenna suitable for DS-UWB high band (i.e. 6 to 10.1 GHz) applications.