Light Fidelity (LiFi) is a recent wireless technology that offers high data rates, low power consumption, and does not interfere with other radio technologies, such as Wi-Fi. However, its short range and need for a direct line of sight require integration with other wireless technologies for effective use in a wireless local area network (WLAN). In this paper, we study the feasibility and efficiency of Hybrid LiFi/Wi-Fi Networks (HLWNet). Our study aims to determine whether HLWNet is a viable solution for WLANs in terms of throughput and power consumption. We propose an approach to evaluate HLWNet deployments, specifying the optimal number and placement of access points (APs) for each technology to ensure throughput satisfaction for stations (STAs) while minimizing overall network power consumption. Our numerical results indicate that the use of LiFi is not advantageous in all scenarios.

Light Fidelity (LiFi) is a recent wireless technology that offers high data rates, low power consumption and do not interfere with radio frequency technologies. As a result, LiFi access points emerge as promising complements to Wi-Fi access points for hybrid LiFi/Wi-Fi networks (HLWNets). This combination can offer high data rates and energy efficiency. However, to fully benefit from hybrid networks, it is crucial to efficiently assign stations, whether with LiFi or Wi-Fi access points. In this paper, we formulate the AP assignment problem as an optimization problem. As a solution, we present an AP assignment strategy, in which we elaborate an algorithm with a low computational complexity. The algorithm allows to dynami-cally assign STAs to APs and benefits from the combination of the two technologies to enhance network performance (energy consumption and throughput satisfaction).

The IEEE 802.11 protocol has become the de facto communication technology for WLANs (Wireless Local Area Networks). While considered reliable and efficient for applications requiring high datarate, IEEE 802.11 is often disregarded for energy-sensitive applications such as IoT (Internet of Things). In fact, the IEEE 802.11 standard and its amendments have introduced several energy-saving mechanisms over the years that are rarely used in practice. In this paper, we consider seven possible energy-saving strategies for the MAC layer of IEEE 802.11. Using two case studies, we evaluate and compare these energy-saving strategies with regard to their network performance and energy saving. We conclude that most of the energy-saving strategies manage to support the levels of workloads considered in our case studies, and at the same time, they succeed to cut energy consumption by a factor ranging from two to eight. In particular, the "DL slot'' strategy leads STAs to consume only half (or even less) of what they would without running any strategy, without trading off the attained levels of throughput. The "DL prompt + UL slot'' strategy is the most efficient energy-wise, but this can come at the expense of a loss of throughput.

In this paper, we propose different strategies to efficiently deploy RSUs in a city with the ultimate goal of having an 802.11p-based infrastructure to deliver Internet services. Unlike most existing works, (i) our strategies' only prior information is the average density of vehicles in the studied area, and (ii) they rely on the forecast of a performance model of 802.11p to assist and guide their choices regarding the location of RSUs. With the help of two simulators, namely SUMO and ns-3, we investigate the behavior of each strategy in three scenarios inspired by the street map of real-life major cities. Our findings are twofold: (i) we demonstrate that any efficient RSUs deployment is tightly tied to the specifics of the considered city (namely, the arrangement of streets and the spatial density of vehicles); (ii) the best strategy is not to position RSUs where the traffic density is at its highest, nor at the street junctions where the traffic density is often at its highest but instead where they will be able to deliver the target QoS to a maximum number of vehicles.

The latest amendment 802.11ax to the IEEE 802.11 standard, better known by its commercial name Wi-Fi 6, includes a feature that aims at improving the spatial reuse of a channel: each device can adapt its Clear Channel Assessment sensitivity threshold and its transmission power. In this paper, we use the Multi-Armed Bandit (MAB) framework to propose a centralized solution to dynamically adapt these parameters. We propose a new approach based on a Gaussian mixture to sample new network configurations, a specific reward function that prevents starvations when maximized, as well as a method based on Thompson Sampling to select the best network configuration. We evaluate our solution using the network simulator ns-3 and different topologies. Simulation results confirm the large benefits that 802.11ax may bring to spatial reuse. They also demonstrate the efficiency of our solution in finding appropriate parameter configurations that significantly improve the quality of service of the networks.

Over the past two decades, Wi-Fi technology (defined by the IEEE 802.11 standard) has become a prominent wireless network access technology. In many situations, a device may attach to several Wi-Fi access points within the radio range. The operating system makes its choice over metrics that do not take into account the actual available capacity. To fill this gap, several proposals have been made to infer capacity, for example by estimating the occupied proportion of the channel. However, these techniques are being thwarted by the mechanisms recently introduced in 802.11 to improve transmission speeds, in particular frame aggregation. In this article, we focus on busy time inference based on frame aggregation level. We propose an analytical model based on a Markov chain which estimates the theoretical aggregation level for different amounts of cross traffic. We validate its accuracy against simulations carried out on the ns-3 network simulator and an ad-hoc simulator. Results show that the theoretical model gives an accurate estimation of the frame aggregation level and that it can be used to infer the network load.

Mobile operators around the world have been caught off guard by the popularity of mobile data services and with the massive deployment of macro base stations, and mobile data traffic continues to increase at an exponential speed. This increases overall energy consumption, which translates into a much higher rejection of carbon dioxide into the atmosphere. By the integration of small cells, i.e., femtocells, in the new generation networks, important questions are raised about the energy consumption in heterogeneous networks. In this paper, a new proposed Dynamic transmit power (DTP) based scheme is proposed to decrease the network power consumption. A stochastic geometry model is used to describe the different femtocells position in the network with realistic constraints and to evaluate the performance of our solution. Performance has been studied in terms of energy consumption and energy gains. Simulation results are used to confirm the analytical results and show that the DTP based scheme can reach an energy gain up to 35% compared to the constant transmit power (CTP) based scheme.

We consider a VoD (Video on-Demand) platform designed for vehicles traveling on a highway or other major roadway. Typically, cars or buses would subscribe to this delivery service so that their passengers get access to a catalog of movies and series stored on a back-end server. Videos are delivered through IEEE 802.11p Road Side Units deployed along the highway. In this paper, we propose a simple analytical and yet accurate solution to estimate (at the speed of a click) two key performance parameters for a VoD platform: (i) the total amount of data downloaded by a vehicle over its journey and (ii) the total "interruption time'', which corresponds to the time a vehicle spends with the playback of its video interrupted because of an empty buffer. After validating its accuracy against a set of simulations run with ns-3, we show an example of application of our analytical solution for the sizing of an IEEE 802.11p-based VoD platform.

We propose a model based on stochastic geometry to assess downlink interference and signal over interference ratio (SIR) in LTE networks. The originality of this work lies in the proposition and combination of resource blocks assignment strategies, transmission power control, and realistic traffic patterns into a stochastic geometry model. For this model, we compute the first two moments of interference. They are used to parameterize its distribution from which we deduce the SIR distribution. Outage and transmission rates (modulation and coding rate) are then derived to evaluate the system performance. Simulations that cover a large set of scenarios show the accuracy of our proposal and allow us to compare these strategies with more complex ones that aim to minimize global interference. Numerical evaluations highlight the behavior of the LTE network for different traffic patterns/load, eNodeB density, and amount of resource blocks and offer insights about possible parameterization of LTE networks.

WLANs (Wireless Local Area Networks) have become ubiquitous in our everyday life, and are mostly based on IEEE 802.11 standards. In this paper, we consider the performance evaluation of an arbitrary-topology unsaturated network based on the IEEE 802.11 DCF. We present a conflict graph-based modeling approach to discover the attainable throughput of each node. Our model consists of a single Markov chain which aims at describing, at a high-level of abstraction, the current state of the entire wireless network. Owing to its low complexity, our approach is simple to implement, can cope with medium sized networks, and its execution speed is fast. We validate its accuracy against a discrete-event simulator. Results show that our approach is typically accurate, with associated relative errors generally less than 15%, and that it captures complex phenomena such as node starvation. We investigate two potential applications of our proposed approach in which, starting with a given network, we improve its performance in terms of overall throughput or fairness by throttling the throughput demand of a node, or by turning a node off altogether.

Though SDN (Software Defined Network) provides the executive building blocks for programming data-plane appliances, controller decisions must be grounded in an accurate outlook on the network topology and performance. In this context, we focus on the possibility of providing accurate measurements for the end-to-end (E2E) delay in SDN networks. In practice, like many variable quantities, a good description of the E2E delay requires characterizing its first two moments, i.e., expectation and variance. We propose to estimate the E2E delay by making use only of measurements collected locally on each node of the network. We extend a procedure that has been proposed to estimate the E2E delay in the case of one flow to handle the case of multiple competing flows. We compare its accuracy using several scenarios, with different types of traffic following real traces, different topologies and bandwidth. Also, an analysis of the computational and networking costs of our solution is proposed.

With Software-Defined Networking (SDN), computer networks will gain a better control and management on their physical resources and on flows requiring a specific type of QoS. To fulfil these objectives, networks must be able to characterize the end-to-end performance of flows, which are usually unknown and not directly measurable. Instead, networks have typically at their disposal only local measurements, collected at each node. In this paper, we propose a new method to evaluate the variance of the end-to-end delay based only on measurements collected on nodes. The core of our solution is to link samples of waiting times at different nodes in order to approximate the corresponding covariance terms, needed to refine the approximate value of the sought variance. We evaluate the accuracy of our solution using two different scenarios. The obtained results show that the method is generally good, with a relative error on the estimated standard deviation of the end-to-end delay usually close to 5%, though it may exceed 10% when the network is facing high levels of load and experiencing packet losses.

The diversity of applications' types in Vehicular Ad hoc NETworks (VANETs) has spawned a large variety of messages that need to be efficiently disseminated between connected vehicles. The most critical messages are those dedicated for safety applications such as road hazardous warning, signal violation warning, etc. The dissemination of this sort of messages is considered as a challenging task in mobile networks where the topology changes dynamically. Indeed, transmitted messages should achieve a high data reachability within a limited transmission delay and an acceptable overhead in a Vehicle to Vehicle (V2V) communication mode. In this work, we focus on a special type of data dissemination protocols based on the delay strategy. The purpose of this paper is to compare two basic distinguished techniques, namely the slotted technique and the continuous technique, and study in depth their impact on the data dissemination performance. A proper selection of the convenient technique according to the application's requirements is consequently deduced. For a faithful and rigorous study, simulations are performed by means of ns-3 simulator under a realistic VANET environment in terms of map layout, mobility pattern and radio model. Simulation results show that contrary to the theoretical reflection, slotted technique is approved as the most appropriate one for safety message dissemination. This technique achieves the same packet data ratio and redundancy ratio, compared to the continuous one, while reducing the data transmission delay.

Densification of Wi-Fi networks has led to the possibility for a station to choose between several access points (APs). On the other hand, the densification of APs generates interference, contention and decreases the global throughput as APs have to share a limited number of channels. Optimizing the association step between APs and stations can alleviate this problem and increase the overall throughput and fairness between stations. In this paper, we propose an original solution to this optimization problem based on two contributions. First, we present a mathematical model for the association optimization problem based on a realistic share of the medium between APs and stations and among APs when using the 802.11 DCF (Distributed Coordination Function) mode. Then, we introduce a local search algorithm to solve this problem through a suitable neighborhood structure. This approach has the benefit to be tuned according to the CPU and time constraints of the WLAN controller. Our evaluation, based on simulations, shows that the proposed solution improves the overall throughput and the fairness of the network.

In this paper, we propose an algorithm to estimate the second moment of the end-to-end delay experienced by the packets of a flow based only on delay measurements locally collected by the network nodes. Our solution estimates the standard deviation of the end-to-end delay in an easy and computationally efficient way. Based on thousands of simulations using a real-life trace, our solution is found to be accurate, typically differing by only a few percent from the actual value of the standard deviation of the end-to-end delay.

The diversity of applications' types in vehicular ad hoc networks (VANETs) has spawned a large variety of messages that need to be disseminated in a vehicle to vehicle (V2V) communication mode. The most critical messages are those dedicated for safety applications such as accident warning, road hazardous warning, signal violation warning, etc. The dissemination of this kind of messages is a challenging task in VANETs since they should be efficiently transmitted i.e. by achieving high packet delivery within a limited transmission delay and an acceptable overhead. In this work, we propose a robust and an original data dissemination protocol called ``Redundancy-based Protocol (RBP)''. Unlike most of density-based protocols, RBP is beaconless. It takes into account the surrounding vehicles' density during the broadcasting process through a specific metric, named ``Packet Redundancy Ratio'', calculated locally at each vehicular node. On the basis of this metric, each vehicle is able to dynamically define the probability of rebroadcast in order to mitigate the broadcast storm problem. The simulation results show that the proposed protocol outperforms the slotted 1-persistence scheme in terms of packet drop ratio, and network load while still maintaining a low End-to-End delay and high packet reachability. This scheme is suitable either for safety applications or for further kinds of applications by saving the network capacity consumption.

The femtocell — Wi-Fi integration is a promising approach to solve the problem of inter-tier or intra-tier interference in heterogeneous networks. In this paper, multimode femtocell base stations are deployed which form a Wi-Fi mesh network to communicate between themselves while deploying cellular technology (e.g., LTE) for communications with mobile users, thus ensuring ultimately connectivity between mobile users and their macro base stations to improve the network coverage. We propose a tractable model for coverage/outage to evaluate the benefits of such integration in terms of SINR and received signal strength. Our work is based on point processes in two-dimensional plane that models locations of femtocell — Wi-Fi (also referred to as multimode) nodes. The proposed model is more realistic than the classical Poisson point process, as the distribution of points is more homogeneous and it ensures that the nodes are not too close to each other. The derivation of coverage/outage formula allows us to determine operational parameter ranges for the Wi-Fi network to form a mesh network. In addition, it helps in the design of the femtocell network to ensure a suitable coverage for users in terms of SINR and received signal strength.

In IEEE 802.11p VANET networks the transmission scheduling is distributed and asynchronous. The number of simultaneous transmitters is thus closely related to the CSMA/CA mechanism which limits the spatial reuse of the channel. The capacity is bounded by a determined constant whatever the number of nodes and the type of routing schemes. This paper aims to evaluate the spatial reuse of a VANET (using CSMA/CA) and to deduce its maximum capacity. The proposed model is an extension of a classical packing problem. We prove formally that the intensity of the maximum number of simultaneous transmitters (the maximal spatial reuse) converges to a constant and propose a simple estimate of this constant. Realistic simulations show that the theoretical capacity offers a very tight bound on the real capacity of the network.

The multi-user medium access mechanism OFDMA has to provide each node with a given amount of radio resources. In this paper we present a new distributed algorithm for the allocation of resource blocks in an OFDMA ad hoc network. We are principally interested in allocating resources fairly because the ad hoc networks which we work on are dedicated to be deployed in the areas of natural or man-made disasters and where the guarantee of connectivity is an important issue. Contrary to the commonly applied approach, we consider a resource allocation on the links under a two hop interference distance. The proposed allocation procedure is coupled with our other algorithm which detects and corrects two hop interferences and which has been revised and improved. The performance of our algorithm is evaluated by simulation for different topologies. We observed that simultaneous allocations in large networks allow a constant convergence time to be kept despite the networks size.

In this paper, we present and analyse a link management technique for pro-active routing protocols for ad-hoc networks. This mechanism is based on signal strength hence cross layer approach is used. The hysteresis mechanism provided by OLSR is improved upon by using signal strength in combination with the hello loss based hysteresis. Thus it now takes into account temporal as well as signal strength stability of a link. This not only makes the link management more robust but also helps in anticipating link breakages thereby greatly improving performance.

We propose a short overview of models and results based on spatial models used to evaluate the performance of ad hoc networks. Locations of nodes are distributed in a two dimensional area according to a stochastic point process, which allows us to obtain the averages and distributions of different performance quantities. It is particularly suited in the context of ad hoc networks as the topology has an important impact on performance. The different models presented are related to the radio properties, connectivity and capacity of ad hoc networks.

In this paper, we are interested in the properties of vehicular ad hoc networks (VANET). We study the mean connection lifetimes to evaluate the feasibility to support non-safety applications. Because connection lifetimes are in the order of a few minutes, an infrastructure network is highly recommended to maintain connectivity between car clusters. Using an hybrid network, we perform comparisons of routing protocols used in the VANET. We show that reactive and geographic routing protocols are very close in terms of performance. However the reactive protocol are more accurate since it does not require neither geolocalization systems nor location services. We propose the use of hybrid networks and we give dimensioning rules to ensure connectivity of the network