Katia Jaffrès-Runser

Beyond traditional DTN routing: social networks for opportunistic communication

This article examines the evolution of routing protocols for intermittently connected ad hoc networks and discusses the trend toward socialbased routing protocols. A survey of current routing solutions is presented, where routing protocols for opportunistic networks are classified based on the network graph employed. The need to capture performance trade-offs from a multi-objective perspective is highlighted.

On predicting in-building WiFi coverage with a fast discrete approach

A new approach for predicting coverage of wireless LAN at 2.4 GHz is presented. Coverage prediction is one of the core parts of indoor wireless LAN planning tools. The main concern it has to deal with is providing a good trade-off between prediction accuracy and computational load. Usual approaches belong to either empirical or deterministic methods. A new perspective has recently been offered that exploits a discrete formalism based on the TLM formulation. It is referred to as Multi-Resolution Frequency Domain ParFlow (MR-FDPF). While ray-tracing handles computational load by restricting the number of considered paths, the proposed approach acts by adapting the spatial resolution. This paper presents the straight lines of MR-FDPF and details the conditions for efficient in-building coverage prediction at 2.4 GHz. In a second part this paper tackles the calibration problem and claims for an automatic calibration process to improve the fit between predictions and measurements. A couple of experiments are presented.

Spectral and Energy Efficiency Trade-offs in Cellular Networks

This paper presents a simple and effective method to study the spectral and energy efficiency (SE-EE) trade-off in cellular networks, an issue that has attracted significant recent interest in the wireless community. The proposed theoretical framework is based on an optimal radio resource allocation of transmit power and bandwidth for the downlink direction, applicable for an orthogonal cellular network. The analysis is initially focused on a single cell scenario, for which in addition to the solution of the main SE-EE optimization problem, it is proved that a traffic repartition scheme can also be adopted as a way to simplify this approach. By exploiting this interesting result along with properties of stochastic geometry, this work is extended to a more challenging multicell environment, where interference is shown to play an essential role and for this reason several interference reduction techniques are investigated. Special attention is also given to the case of low signal-to-noise ratio (SNR) and a way to evaluate the upper bound on EE in this regime is provided. This methodology leads to tractable analytical results under certain common channel properties, and thus allows the study of various models without the need for demanding system-level simulations.The design of next generation wireless networks is strongly motivated by the need to improve network energy efficiency (EE), while ensuring that the provided performance, often expressed in terms of spectral efficiency (SE), satisfies the vastly increasing user demands. In this context, this paper discusses about the SE-EE trade-off in Orthogonal Frequency-Division Multiple Access (OFDMA) wireless networks, achieved by an optimal joint resource allocation of transmit power and bandwidth on the system downlink direction. A novel theoretical framework is presented initially for the study of a single cell scenario, where a traffic repartition scheme is proposed that simplifies the inherent optimization problem and reveals useful insights. Special attention is also given to the case of the low signal to noise ratio (SNR) and a way to easily evaluate the upper bound of EE in this regime is provided. Finally, by exploiting useful properties of stochastic geometry, this work is extended to a more challenging multi-cell environment, where interference is shown to play an essential role. For this reason, several potential interference reduction techniques are investigated in order to enhance the performance of the SE-EE trade-off curves.

Mono- and multiobjective formulations for the indoor wireless LAN planning problem

Wireless LANs (WLANS) experienced great success in the past five years. This technology has been quickly adopted in private and public areas to provide a convenient networking access. The fast pace of development has often induced an uncoordinated deployment strategy where WLAN planning tools have been barely used. This article highlights the difficulty of planning such wireless networks for indoor environments. The first issue the WLAN planning problem has to face is to accurately describe the quality of a network, based on realistic propagation predictions. The second issue is to implement a search strategy that provides efficient deployment strategies. This article is introduced by a description of previously proposed planning strategies. Their study opens out onto a problem formulation that accounts for coverage, interference level and quality of service (in terms of data throughput per user). This formulation is then introduced as either a mono- or a multiobjective (MO) optimization problem. In the first case, we propose to solve the mono-objective problem with a Tabu search metaheuristic minimizing a weighted sum of the planning criteria. Then, we compare the outcome of this strategy to the results of our previously proposed MO Tabu search strategy. We highlight the fact that efficient solutions are obtained quickly with the mono-objective approach if an appropriate set of weighting coefficients of the evaluation function is chosen. The main issue of mono-objective search is to determine these coefficients. It is a delicate task that often needs several runs of the algorithm. MO search is an interesting alternative heuristic as it directly provides a set of planning solutions that represent several trade-offs between the objectives. Our MO heuristic looks for a set of non-dominated solutions expected to converge to the Pareto front of the problem and selects the most significant ones for the end user. Both QoS-oriented planning methods are illustrated on a realistic environment representing a building floor of about 12600m^2. Results show the assets of both approaches but mainly emphasize the benefit of the MO search strategy that offers several alternative solutions to the radio engineer.

RECAST: Telling apart social and random relationships in dynamic networks

Abstract When constructing a social network from interactions among people (e.g., phone calls, encounters), a crucial task is to define the threshold that separates social from random (or casual) relationships. The ability to accurately identify social relationships becomes essential to applications that rely on a precise description of human routines, such as recommendation systems, forwarding strategies and opportunistic dissemination protocols. We thus propose a strategy to analyze users’ interactions in dynamic networks where entities act according to their interests and activity dynamics. Our strategy, named Random rElationship ClASsifier sTrategy (RECAST) , allows classifying users interactions, separating random ties from social ones. To that end, RECAST observes how the real system differs from an equivalent one where entities’ decisions are completely random. We evaluate the effectiveness of the RECAST classification on five real-world user contact datasets collected in diverse networking contexts. Our analysis unveils significant differences among the dynamics of users’ wireless interactions in the datasets, which we leverage to unveil the impact of social ties on opportunistic routing. We show that, for such specific purpose, the relationships inferred by RECAST are more relevant than, e.g., self-declared friendships on Facebook.

U-GRAB: A utility-based gradient broadcasting algorithm for wireless sensor networks

This paper addresses the problem of reliable transmission of sensed data through a vast field of small and vulnerable sensors towards a sink node. We concentrate in this paper on networks deployed rapidly in harsh environments as needed for instance in disaster-relief scenarios. Hence, emphasis has to be put on the minimization of the global energy consumption of the network and on providing both fast data transmissions and a rapid network setup. Therefore, we introduce a new gradient broadcasting routing algorithm for wireless sensor networks, U-GRAB, where the broadcasting decision is taken according to a utility-based policy. This policy favors the broadcasting of packets for nodes that experience non-congested channels and have a satisfactory energy level. Our simulation results show that this new forwarding strategy greatly improves the robustness/energy/delay trade-off of GRAB, the current state-of the art solution in gradient broadcasting techniques.

Low Bound of Energy-Latency Trade-Off of Opportunistic Routing in Multi-Hop Networks

During the last decade, many works were devoted to improving the performance of relaying techniques in ad hoc networks. One promising approach consists in allowing the relay nodes to cooperate, thus using spatial diversity to increase the capacity of the system. However, this approach introduces an overhead in terms of information exchange, increasing the complexity of the receivers. A simpler way of exploiting spatial diversity is referred to as opportunistic routing. In this scheme, a cluster of nodes still serves as relay candidates but only a single node in the cluster forwards the packet. This paper proposes a thorough analysis of opportunistic routing efficiency under different realistic radio channel conditions. The study aims at finding the best trade-off between two objectives: energy and latency minimizations, under a hard reliability constraint. We derive an optimal bound, namely, the Pareto front of the related optimization problem, which offers a good insight into the benefits of opportunistic routing compared with classical multi-hop routing.

A QoS-based FAP criterion for Indoor 802.11 wireless LAN optimization

Several softwares have been developed for computer-aided design of radio networks. The first constitutive element of such a tool is the propagation modelling algorithm. The second is the planning process providing positions and setup of access points. The last one concerning the frequency channel allocation problem (FAP) is the focus of this paper. Many works devoted to this problem exploit a graph-based modelling that leads to an under-constrained problem as interference between mobile nodes are not taken into account. In this paper a new QoS-based FAP criterion is formulated. This QoS criterion measures the overall throughput taking downlink interference into account. We show on an example that our FAP model outperforms usual graph-based FAP approaches concerning the effective SINR obtained at mobile nodes. Results are based on realistic simulations exploiting a simulator called WILDE (Wireless Lan DEsign) and implementing the MR-FDPF propagation algorithm.

A thorough analysis of the performance of delay distribution models for IEEE 802.11 DCF

Deriving the complete distribution of the end-to-end delay in a wireless multi-hop network is of paramount interest when delay-sensitive flows have to be conveyed over such networks. First works have proposed models to derive the total delay distribution of networks assuming the well-known IEEE802.11 DCF medium access (MAC) protocol. Current derivations can be decomposed into two main steps: (i) the calculation of the total delay probability generating function (PGF) and (ii) its numerical inversion. We show in this paper that there is a need for a thorough performance evaluation of these models since both steps introduce errors, naming modeling and inversion errors. We argue that both types of errors have to be analyzed separately to characterize the accuracy of the analytical derivations of the literature. Therefore, this paper defines two performance evaluation metrics that measure the magnitude of both types of errors. Both metrics are illustrated to select and optimize the most accurate model to calculate the single-hop end-to-end delay distribution of nodes using the IEEE802.11 DCF MAC protocol. The most accurate model is extended to calculate the end-to-end delay distribution for a 2-hop wireless communication.

Combining LT codes and XOR network coding for reliable and energy efficient transmissions in wireless sensor networks

This paper tackles the problem of providing end to end reliable transmissions in a randomly deployed wireless sensor network. To this aim, we investigate the simultaneous use of gradient broadcast routing (for its inherent adaptability to any network topology and its changes), fountain codes (for their universal property) and intra-flow network coding (to introduce packet diversity in redundant copies). We present the impact of the proposed XLT-GRAB strategy on a realistic network. This work permits to highlight that, compared to basic gradient broadcast routing, the strategy not only improves the reliability and the delay in the network but also clearly increases its lifetime.