Lila Boukhatem

On the use of radio environment maps for interference management in heterogeneous networks

This article addresses the use of REMs to support interference management optimization in heterogeneous networks composed of cells of different sizes and including both cellular and non-cellular (e.g. WiFi) technologies. After presenting a general architecture for including REM databases in different network entities, the article analyzes the achievable benefits in relation to specific interference management techniques, including a discussion on practical considerations such as information exchange requirements, REM ownership, and security aspects. Finally, several research directions derived from the proposed framework are identified.

TCRA: a time-based channel reservation scheme for handover requests in LEO satellite systems

In this paper, we propose a time-based channel reservation algorithm (TCRA) suitable for handover and call admission control procedures in future mobile satellite systems. These systems are characterized by a high rate of handover attempts which can degrade significantly their performance. Therefore, we propose TCRA, a scheme which guarantees a null handover failure probability by using a channel reservation strategy in the cells to be crossed by the user. The performance of TCRA has been compared to the guaranteed handover (GH) scheme. The TCRA reservation method has the advantage of a better channel utilization by locking the resources only for their expected time of use. A mathematical model has been developed for both schemes, and its results have been validated through simulations.

Adaptive vehicular routing protocol based on ant colony optimization

Vehicular Ad hoc Networks (VANETs) pose many challenges to cope with, such as large network size, rapid topology changes and channel capacity limitations. To address these problems, we propose VACO (Vehicular routing protocol based on Ant Colony Optimization), a new adaptive multi-criteria VANET routing protocol. VACO combines both reactive and proactive components to respectively establish and maintain best routing paths. Reactive forward and backward ants are sent between source and target intersection (closest intersection to the destination vehicle) to explore and set up best routes consisting of a list of intersections. Routing decision is then realized at each intersection to opportunistically select best next intersection. The key feature of the route selection is to rely on a periodically estimated road segment relaying quality which is expressed in terms of three combined QoS parameters (latency, bandwidth and delivery ratio). The derived simulation results indicate that VACO shows better performance than a basic geographical routing protocol (GPSR) and a min-delay routing protocol (CAR).

A channel reservation algorithm for handover issues in LEO satellite systems based on a satellite-fixed cell coverage

In this paper, we propose a channel reservation mechanism referred to as time-based channel reservation algorithm (TCRA). The aim of TCRA is to handle the handover issue in low Earth orbit satellite networks. These systems face an important number of handover attempts due to the high satellite velocity when placed in low orbits. The TCRA scheme uses the deterministic satellite movement pattern to estimate the user residence time in each cell to be crossed. Two versions of the algorithm are proposed depending on whether the network disposes of a positioning system or not. These versions of TCRA allow to guarantee a null handover failure probability for the users. The performance of TCRA (with its two versions) is examined by simulations and compared to the guard channel scheme. The results show the behaviour of the schemes and their performance in terms of new call and handover blocking probabilities.

Adaptive Quality-of-Service-Based Routing for Vehicular Ad Hoc Networks With Ant Colony Optimization

Developing highly efficient routing protocols for vehicular ad hoc networks (VANETs) is a challenging task, mainly due to the special characters of such networks: large-scale sizes, frequent link disconnections, and rapid topology changes. In this paper, we propose an adaptive quality-of-service (QoS)-based routing for VANETs called AQRV. This new routing protocol adaptively chooses the intersections through which data packets pass to reach the destination, and the selected route should satisfy the QoS constraints and fulfil the best QoS in terms of three metrics, namely connectivity probability, packet delivery ratio (PDR), and delay. To achieve the given objectives, we mathematically formulate the routing selection issue as a constrained optimization problem and propose an ant colony optimization (ACO)-based algorithm to solve this problem. In addition, a terminal intersection (TI) concept is presented to decrease routing exploration time and alleviate network congestion. Moreover, to decrease network overhead, we propose local QoS models (LQMs) to estimate real time and complete QoS of urban road segments. Simulation results validate our derived LQM models and show the effectiveness of AQRV.

An Intersection-based QoS Routing in Vehicular Ad Hoc Networks

Vehicular Ad hoc Networks (VANET) face many challenging issues because of the rapid topology changes, frequent network partitions, and complicated urban environments. These special VANET characteristics seriously deteriorate the routing performance. In this paper, we propose a new vehicular routing protocol called Intersection based Routing with QoS support in VANET (IRQV). Based on Ant Colony Optimization (ACO), IRQV mainly consists of three processes, 1) terminal intersection selection process, 2) network exploration process, which is implemented using the QoS of local road segment and global end-to-end intersections, and 3) optimal routing path selection process. When initiating data packets forwarding session, IRQV dynamically chooses the optimal next intersection using latest routing information and adopts a simple greedy carry-and-forward mechanism to forward data between two adjacent intersections. In addition, we propose connectivity and transmission delay mathematical models for a 2-lane road segment scenario to estimate local QoS. Simulation results validate our derived road segment connectivity and transmission delay models, and show the effectiveness of IRQV compared with two geographical routing protocols in terms of delay, packet delivery ratio and overhead.

Power adjustment mechanism using context information for interference mitigation in two-tier heterogeneous networks

This paper deals with the interference issue in a two-tier heterogeneous network. Although the co-channel spectrum allocation provides larger bandwidth for both macrocells and femtocells, the resulting cross-tier interference may prevent macrocell users to achieve the minimum required SINR. Therefore, in this work, we propose a centralized control strategy of downlink interference generated by femtocells to increase the performance requirement of macrocell users. Our mechanism presents two possible power control strategies for interference management which take benefit from some context information on femto and macrocell users positioning. System-level simulations show a better performance in terms of throughput for macrocell users while maintaining a targeted QoS for femtocell users.

Energy-Efficient Resource Allocation for Device-to-Device Communications Overlaying LTE Networks

In this paper, we investigate the energy-efficient resource allocation problem for the device-to- device (D2D) communications overlaying LTE networks, where the D2D user equipment (UE) shares the spectrum with the cellular UE in an orthogonal way such that the interference between them is completely eliminated. We consider both the non- orthogonal and orthogonal resource allocation strategies for D2D communications, where the resources allocated to different D2D pairs are non-orthogonal and orthogonal respectively. In the non-orthogonal strategy, the interference exists among different D2D pairs, and the resource allocation only concerns the transmit power control for each D2D pair; whereas in the orthogonal strategy, there is no interference, and the resource allocation concerns both the resource block (RB) allocation and the transmit power control. In the two strategies, the related resource allocation problems are firstly formulated as a fractional programming (FP) problem and a mixed-integer nonlinear fractional programming (MINLFP) problem respectively, both of which are then transformed into equivalent optimization problems in parametric subtractive form by exploiting the property of FP. As the transformed equivalent problems are non-concave, we develop the sub-optimal energy-efficient resource allocation schemes by solving them based on Dinkelbach and Powell-Hestenes-Rockafellar augmented Lagrangian methods. Simulation results demonstrate the effectiveness of the proposed schemes and show that the non-orthogonal strategy outperforms the orthogonal one in terms of the energy efficiency.

Mobility-aware dynamic inter-cell interference coordination in HetNets with cell range expansion

To encourage traffic offloading from the Macrocell to its overlaid Picocells in a Heterogeneous Network (HetNet), Cell Range Expansion (CRE) has been widely envisioned, enabling more Macro users to be offloaded to the less saturated Picocells, and enhancing the throughput performance of the entire system. By doing so, users in the Picocell expanded area may experience high interference from the Macrocell Base Station (MBS). This effect is mitigated by enhanced Inter-Cell Interference Coordination (e-ICIC) schemes that reserve part of the MBS bandwidth to those Pico users exclusively. Here, we propose a mobility-aware e-ICIC scheme which turns-off some of the Resource Blocks (RBs) in the Macrocell in function of the mobility behaviour of the range-expanded Pico users, thereby providing an efficient trade-off between Macrocell and Picocell achievable throughputs. Our numerical results confirm that point, and show that our proposed method outperforms reference e-ICIC methods.

An Intersection-based Delay sensitive routing for VANETs using ACO algorithm

Vehicular Ad hoc Networks (VANETs) have gained considerable attention in recent years because of the extensive applications. However, VANETs are confronted with numerous difficulties and challenges, which lead to communication performance degradation and even data delivery failure. In this paper, we propose a new routing protocol called Intersection-based Delay sensitive Routing using Ant colony optimization (IDRA). Firstly, we derive a mathematical delay model for a two-lane road segment. Then based on proposed terminal intersection concept, IDRA makes use of Ant colony optimization (ACO) to find robust and optimal route with min-delay. The forward ants are in charge of exploring routes consisting of a succession of intersections, which are selected considering local road segment delay and global delay from current intersection to the terminal intersection of the destination. The backward ants take charge of collecting global delay and updating ant pheromone along the explored routes. Data packets are forwarded by dynamically choosing the next intersection utilizing updated ant pheromone. Greedy carry-and-forward mechanism is adopted by IDRA to forward data packets between two adjacent intersections, reducing the effects of individual vehicle movement on routing paths. Simulation results validate our derived road segment delay model and also indicate that IDRA shows better communication performance compared with an intersection-based geographical routing protocol (GSR) and a min-delay routing protocol (CAR).