Edge computing architectures have greatly benefited from high-performance end systems and new-generation cellular networks. Smart cities now have the potential to synthesize all the aspects of a heterogeneous communication and computing infrastructure, leveraging high-definition sensors to propose multiple applications to a variety of road users. However, with the advent of connected vehicles and due to the short lifetime of OBU-to-RSU links, the issue of mobility threatens the reliability of task and data offloading. We thus propose a multi-RAT data offloading scheme exploiting device-to-device communications. In particular, considering the large amounts of data generated by an on-board lidar, we establish a bilateral offloading scheme where the RSU hosts a management algorithm. Based on this algorithm, different packet sizes may be requested based on the networking performance of each vehicle. Through extensive field trials and simulations, performance evaluation shows clear performance discrepancies between C-V2X and DSRC, with C-V2X being more appropriate for dynamically-managed offloading. 4192-byte packets sent at a 10 ms interval achieve the highest throughput with 96 % delivery rates. The proposed algorithm then achieves 30-to-45% increases in throughput when compared to an OBUcentered scheme due to improved resource allocation.

The future of smart cities depends on the ability of devices to share contextual data in a quick and reliable manner. Deploying access points in close proximity to the side of the road greatly reduces the propagation distances of messages sent over the sidelink, achieving extremely low latencies. However, in challenging situations encountered in urban contexts, multiple obstacles hinder the availability of direct links between a device and its destination. While the usual fallback solution resides in cellular connectivity, the gap in performance is immense. We propose relaying packets sent using Cellular-V2X (C-V2X) sidelink, where the initial message is received by an intermediary with better connectivity to the targeted access point, then retransmitted from this new position. To explore the performance and reliability of such communications in urban V2X architectures, we present experimental campaigns exploiting C-V2X PC5, 5G, autonomous vehicles and state-of-the-art hardware. We study multiple scenarios, extending or shortening line-of-sight situations to analyze coverage and performance. Results analysis highlights high reliability of relayed C-V2X packets at up to 200-meter ranges from one peer to another, with observed latencies being, at worst, 42% more favorable than the cellular fallback.

Edge cloud technologies enable faster and more energy-efficient processing of user requests on servers located at the network’s edge. However, when compared to the cloud, edge resources are significantly more limited, prompting a critical question: as user requests arrive, how to determine which ones to allocate to the edge and which ones to the cloud. Additionally, to ensure a quality of service that considers task priorities, it is essential to reserve available resources for potential high-priority requests. This introduces a fundamental trade-off: reserving excessive computing resources at the edge, in anticipation of high-priority requests, is incompatible with reducing energy consumption. Conversely, allocating all edge resources may push higher-priority, potentially more delay-sensitive tasks into the cloud.To tackle this intricate problem, we present a multi-objective reinforcement learning approach utilizing a modified Q-learning process. This approach facilitates intelligent resource allocation, striking a careful balance between fulfilling high-priority requests and minimizing unused processing capacity. While the multi-objective agent ensures the satisfaction of high-priority services, it optimally utilizes the edge resources. Additionally, we introduce a framework for adapting the two cost components to specific requirements, favoring one objective over the other, and examining their impact on relevant metrics. Results demonstrate that this specialized strategy outperforms a conventional First Come First Served baseline, as well as a myopic strategy, which represents the unmodified Q-learning process, across these metrics.

Internet of Things (IoT) infrastructures can undoubtedly derive significant benefits from content-centric networking (CCN). Thus, a flurry of research focuses on their integration for better content retrieval. Despite the plethora of caching strategies available today, none stands out by efficiently taking into account the limitations of sensors and IoT systems such as low data-rate and energy, as well as limited memory and processing capability. In this work, we focus our attention on the effectiveness of caching on IoT edge gateways. To this end, we propose a novel Deep Reinforcement Learning (DRL) strategy that establishes an intelligent placement of contents and promotes the consideration of content popularity as well as the diversity of data in the network. Through extensive experiments and a real-world testbed on our campus, we perform an in-depth comparative analysis. We demonstrate that our approach decreases the data retrieval distance, assuredly leading to energy efficiency and reduced latency. Moreover, our DRL-based solution outperforms other strategies in terms of cache hit, content diversity, and content popularity support.

International audience

To enhance road safety and traffic fluidity, vehicles need to communicate amongst themselves and transfer large amounts of data to the infrastructure with extremely low latencies, through access points deployed closely to the road. However, in obstacle-heavy scenarios, latency increases when devices shift coverage areas. Though networks are heterogeneous by nature in the smart city era, very few mechanisms are provided in connected vehicles for multiple Radio Access Technology (multiRAT) selection. We thus present a networking approach to improve link stability, exploiting mobile and V2X technologies: LTE, 5G, Cellular-V2X, DSRC. Unlike opportunistic handover schemes taking advantage of Device-to-Device (D2D) communications when coverage is detected, we develop a proactive scheme leveraging the performance of received packets, to avoid link failure against pathloss and shadowing. An autonomous shuttle roams the playground, filling grids associating positions with QoS indicators. The grids then provide knowledge on RAT performance to incoming vehicles, facilitating selection according to position. Experimental studies show high performance of DSRC in short range, line-of-sight situations, while C-V2X offers up to 60% longer D2D ranges and more resilient coverage. Field trial analysis of our solution highlights a 27% reduction of high-latency packets, by extending V2I communications and limiting reliance on cellular connectivity.

Locating at-risk workers in hospitals using legacy private 5G networks is a daunting task that involves solving the problem of indoor localization using commercial off-the-shelf proprietary hardware. Currently, no full-stack schemes or realistic indoor positioning experiments have been conducted using 5G. In this study, we present the first comprehensive 5G framework that combines fingerprinting with the 3GPP Enhanced Cell ID (E-CID) approach. Our methodology consists of a machine-learning model to deduce the user's position by comparing the signal strength received from the User Equipment (UE) with a reference radio power map. This challenging method has four main contributions. First, the 3GPP protocols and functions are extended to provide open, secure, and universal core network-based localization functions. Second, to generate a reference map, the first paradigm of Optical Radio Power Estimation using Light Analysis (ORPELA) is introduced. Real-world experiments prove that it is reproducible and more accurate than state-of-the-art radio-planning software. Third, machine-learning models are designed, trained, and optimized for an ultra-challenging radio context. Finally, an extensive experimental campaign is conducted to demonstrate the expected indoor localization performance of realistic 5G private networks.

Today, LoRaWAN networks have reached a major milestone on the Internet of Things application domains thanks to their fascinating characteristics, especially in terms of large coverage and low energy consumption. Several studies have focused on the performance optimization of these networks. Indeed, gateway-centric allocation strategies look for the optimal configuration of the transmission parameters and send them to thousands of end-devices through MAC commands on the downlink. However, most of these allocation strategies are validated either by simulation or mathematical models. In this paper, we discuss the fundamentals and the requirements of the MAC commands transmission on the downlink. Our design allows IoT applications to transmit frames on the downlink hitherto reserved for MAC configuration commands, makes easier the implementation of new spreading factor assignment strategies, and provides an experimental framework for Downlink performance analysis. We validated our proposal through extensive experimental study, demonstrated the limitation of downlink over uplink due to the sensitivity of the end-device receiver, and finally we studied the impact of traffic load on the downlink performance.

The next step towards vehicular networks in smart cities would be the deployment of autonomous shuttles with multiple on-board applications. Their need to offload task towards Road Side Units (RSUs) is inevitable, especially with a certain proportion of urgent data needing to be processed in the shortest possible delay. Therefore, QoS-provisioning appears as imperative, along with the optimization of resource requesting at RSUs. To this end, we propose CAVTOMEC, a multi-RAT location-aware, context-aware task offloading solution with QoS provisioning for MEC vehicular networks. Our solution consists of three intertwined mechanisms: traffic classification, location-awareness exploiting the contents of CAM beacons and V2N-enhanced resource polling. Traffic classification identifies high, low, and indifferent task priorities, while location and resource awareness help to select the most appropriate RSU to offload tasks to depending on these priorities. Performance evaluations show that our proposal offers better load balancing at the RSUs than traditional offloading schemes, thus satisfying high priority task offloading at better rates and freeing up more resources in case an unexpected event occurs.

As part of its ongoing effort to standardize 5G and become a key enabler of the Internet of Things, 3GPP introduced NB-IoT – an LPWAN access technology for massive Machine Type Communications (mMTC) – in Release 13. Rooted in LTE, NB-IoT introduces several innovation aimed at meeting the 5G IoT requirements, especially in terms of capacity. Already a commercial success with 94 deployments in over 35 countries, the performance of NB-IoT remains, however, poorly understood.In this paper, we introduce a theoretical model based on M/D/1-PS queues for assessing the performance of NB-IoT as function of different network settings and protocol configurations. Our model is the first to accurately capture the random access procedure for connection establishment (the contention phase) and the entire communicate process, with signalling, connection release and uplink, downlink messages (the congestion phase).After using simulations to demonstrate its accuracy, we use our model to assess the performance of NB-IoT as function of its key parameters. Our analysis reveals a) the NPRACH/NPUSCH ratio has to be chosen carefully and take into account the traffic distribution, and b) for small packet sizes, the NB-IoT signalling becomes a significant bottleneck to the number of UEs that can be supported.

The Narrowband Internet Of Things, better known by the acronym NB-IoT, is spearheading 3GPP’s effort to address the massive Machine Type Communication (mMTC) segment of 5G. With 103 deployments in more than 40 countries, NB-IoT’s performance in terms of cell capacity and coverage is well established. However, the performance it can offer in terms of battery life, a foundational requirement of IoT, has received little attention. In this paper, we introduce the first theoretical model based on the M/D/H/K queues capable of evaluating the energy performance of NB-IoT in advanced cell scenarios defined by a coverage distribution, a payload uplink and downlink size, and an incoming communication rate. After using the values computed by 3GPP for single-terminal cells to demonstrate its accuracy, we use our model to evaluate the NB-IoT’s energy performance. Our analysis reveals that a) Early Data Transmission, originally designed for improving the latency and connection density, can also significantly improve the energy performance, and b) When the load in multi-terminal cell settings increases, the terminal battery lifetime collapses. Leveraging our model, we introduce a solution requiring no changes to the standard and show that it significantly improves the terminal battery life.

LoRaWAN is a promising enabling technology for connected things. Nowadays, it is largely used in many application areas thanks to its relevant features such as long-range, low-cost, and low power consumption. However, as with all wireless technologies, mobility remains a major concern bringing end-devices out of their home operator coverage. In this paper, we investigate the inter-operator roaming capability in mobile scenarios. We proposed a novel LoRaWAN roaming scheme to enable inter-operator roaming based on DNS resolution and end-device context migration between networks. Moreover, we extended the LoRaWAN architecture while maintaining the integrity of the existing mechanisms and with a minimum prior configuration requirements. In order to validate our solution, we designed and implemented a test-bed platform integrating our extensions to Chirpstack.

Although LoRa modulation is known for its robustness allowing devices to communicate kilometers away, it suffers from coverage issues especially where density of gateways is low or in dense urban areas. However, a simple 2-hop LoRaWAN communication can seamlessly extend the network coverage and even improve both data extraction rate (DER) and energy consumption. Experiments in this paper figure out cases under non line of sight (NLoS) conditions where relaying performs better. Regarding the exponential increase of airtime with the spreading factor (SF), as soon as a 2-hop SF7 link allows a better DER as a single hop SF8 link, it becomes more attractive to use a relay. Indeed, energy consumption is linked to the airtime - or the amount of time to send a frame - explaining the energy efficiency with the 2-hop relaying protocol. To verify this assert, LoRa network coverage with a testbed in urban environmens is first compared. Then, simulations help to study energy consumption according to the case study. Results prove that relaying effectively gives better results under NLoS conditions, particularly in dense areas, by improving the DER. It also highlights the limits of LoRa in urban areas where the DER can be under 0.5 using SF12 and with less than a kilometer range.

We present HandRate, the first smartphone-based system using a standard sensor (accelerometer) for opportunistically computing heart rate while a user holds their phone. Fundamentally, HandRate revisits ballistocardiography (BCG), a century-old technique for monitoring heart activity by measuring the body movement caused by the cardiac cycle. Traditionally performed using custom hardware, attached to a subject's body, revisiting BCG for the smartphone, held in hand, faces several challenges. The hand is an external organ furthest from the aorta and subject to motion artifacts, leading to a weak and noisy signal, while the position the phone is held in can impact which accelerometer axis best captures BCG. HandRate addresses these challenges by introducing a design involving two modules operating in tandem: the first aimed at transforming the accelerometer readings into a single-dimensional signal oblivious to how the phone is held, while the second module making heartbeat predictions based on this signal. Results from testing HandRate using data collected from 18 subjects show that it can estimate heart rate with accuracy similar to or better than systems requiring special sensors and/or active user participation.

In the race for Gigabit wireless links, IEEE introduced 802.11ad, an amendment aimed at delivering Gbps capacities in a WLAN setting by leveraging the 60 GHz band. The key innovation of the standard is its beamforming training protocol. Executed periodically at the beginning of every beacon interval, it enables the formation of directional links. To address contention during the uplink part of beamforming training, 802.11ad introduced A-BFT (Association BeamForming Training), an Aloha-inspired, two-level backoff race. While central to the functionality of 802.11ad networks, the performance of A-BFT, however, remains poorly understood. In this article, we propose an analytical finite-population model for evaluating the performance of IEEE 802.11ad A-BFT under two channel models: loss-free, and a channel introducing a constant bit error rate. After using an open-source simulator to demonstrate its accuracy, we use our model to assess the performance of A-BFT. We find that a counter-intuitive, quit-easily/be-lazy approach by the stations leads to the best overall beamforming training performance.

The recent standardization by IEEE of Fine Timing Measurement (FTM), a time-of-flight based approach for ranging has the potential to be a turning point in bridging the gap between the rich literature on indoor localization and the so-far tepid market adoption. However, experiments with the first WiFi cards supporting FTM show that while it offers meter-level ranging in clear line-of-sight settings (LOS), its accuracy can collapse in non-line-of-sight (NLOS) scenarios. We present FUSIC, the first approach that extends FTM's LOS accuracy to NLOS settings, without requiring any changes to the standard. To accomplish this, FUSIC leverages the results from FTM and MUSIC - both erroneous in NLOS - into solving the double challenge of 1) detecting when FTM returns an inaccurate value and 2) correcting the errors as necessary. Experiments in 4 different physical locations reveal that a) FUSIC extends FTM's LOS ranging accuracy to NLOS settings - hence, achieving its stated goal; b) it significantly improves FTM's capability to offer room-level indoor positioning.

LoRaWAN Enabled networks are expected to have a dizzying growth. Thus, an efficient allocation of wireless resources so as to support a large number of nodes is a major concern. In this paper we propose an SF assignment approach paying attention on the traffic load both per Spreading Factor and over the channels. Indeed, our strategy consists in finding a better distribution of the nodes on the SF by orchestrating an effective load balancing. Moreover, the performance of our solution is evaluated under diverse network configurations taking into account the capture effect and the non-orthogonality of SFs. In addition, we validated some assumptions by full-scale experiments like for the 3GPP path loss model which is used for the first time in LoRa simulations. Our results suggest that Load Shifting leads to better performance in terms of DER (Date Extraction Rate) while guaranteeing good scalability on the network size and density.

With the exponential increase in wireless data traffic risking to overwhelm the current networking infrastructures, mmWave networking is seen as on of the most promising paths out of the logjam. IEEE introduced a new standard recently, 802.11ad, that uses mmWave frequencies for delivering multi-Gigabit capacities in a WLAN setting. Such capacities, however, do not come for free: mmWave frequencies have poor propagation characteristics and suffer from blockage, whose consequences on the networking protocols are not fully understood.In this paper, we aim at in-depth understanding of two key primitives in 802.11ad networks in environments rich with blockage: user association and reliability. Using careful measurements on COTS hardware, we find that user association under blockage takes an unreasonably long time, and, after analyzing the causes, provide practical insights on how to reduce this time by an order of magnitude. Relying on a multi-layer tracing tool allowing unprecedented granularity in the analysis of 802.11ad networks, we find that the part of the new standard regarding reliability is underspecified leading to different interpretations in practice. Their potential impact on performance is then evaluated using trace-based simulations, which reveal an interesting throughput-reliability tradeoff. Finally, we find that TCP is poorly prepared for sudden changes in round-trip timeouts, as those induced by link blockage in mmWave networks, leading to an unnecessary increase in timeouts.

In this work, we present COLiDeR, the first practical system for two-path relaying using off-the-shelf half-duplex radios. While two-path relaying has been mostly studied from a theoretical perspective in the literature, our solution addresses the challenges of making it practical by introducing two key contributions. First, using a measurement-driven approach, we identify the best approach for a radio to handle two overlapping signals. Just as important, we carefully quantify its limits and introduce the concept of the decoding areas. Second, we introduce a cross-layer protocol that seamlessly navigates the decoding areas with the objective of maximizing throughput while minimizing decoding failures. Experiments on a 4-USRP testbed show that COLiDeR delivers between 80-95% of the relaying performance of an ideal full-duplex radio while incurring negligible decoding failures.

Physical-Layer Network Coding (PLNC) was first introduced as a solution to increase the throughput of a two-way relay channel communication. Unlike most wireless communication techniques which try to avoid collisions, PLNC allows two simultaneous transmissions to a common receiver. In basic topologies, this technique has been shown to significantly enhance the throughput performance compared to classical interference-free communications. However, quantifying the impact of PLNC in large multi-hop networks remains an open question. In this work, we introduce the first theoretical framework that, given a particular network topology and traffic matrix, can evaluate the optimal network throughput subject to a fairness constraint relative to the initial demand of each flow, when PLNC is adopted. Based on linear programming, our solution ensures to respect the particularities imposed by PLNC. We use this framework to evaluate three state-of-the-art PLNC schemes across a variety of topologies and traffic matrices. Our numerical analysis reveals that while in simple toy topologies PLNC can significantly increase the network throughput, in large topologies the verdict is mixed. For certain topologies and traffic patterns adopting PLNC can double the throughput while in others, depending on the scheme used for implementing PLNC, the gain can be as high as 60 percent or as low as 0 percent when compared to traditional interference-free transmissions.

As Internet usages expand quickly, access networks are modernized with new technologies like fiber-optic communications. However, upgrade costs are prohibitive in sparsely populated areas, the latter turning notably towards satellite connection. Indeed, this technology allows deploying a high-throughput Internet access quickly in these regions. Nevertheless, GEO satellites induce a long delay, not experienced on terrestrial infrastructures despite their low throughput. In this paper, we consider a heterogeneous network with both a satellite and a terrestrial path. This kind of architecture is known to be difficult to operate because of the important differences between used technologies. The emerging MP-TCP transport protocol, whose design enables to aggregate disparate paths properly, brought new hopes for heterogeneous networks. However, it does not take user Quality of Experience (QoE) into account as it focuses on maximizing the links occupancy. This paper propose an intelligent path selector using the content size to maximize users QoE in heterogeneous networks. Before detailing this method, we describe the architecture able to retrieve the size of delivered contents thanks to Content Delivery Network Interconnection (CDNI). Finally, we implement a testbed to evaluate the behavior of the proposed routing method. The results show a significant improvement of the delivery performance, outperforming MP-TCP.

The Internet Of Things (IoT) market is growing more and more every year. Today, the number of IoT devices is estimated around 8 billion but forecasts announce 20 billion devices for 2020. Terrestrial or satellite communications systems are already deployed to answer the connectivity need. These systems rely on a Random Access CHannel (RACH) used either to send resource allocation requests or directly the useful message. Because of the number of IoT devices, the overload on the RACH is an emerging issue since it may cause a service outage. This is especially the case for IoT satellite systems because of the wide area covered by a single satellite. The Access Class Barring (ACB) is the load control mechanism used within the Narrow Band IoT. Unfortunately, no method was specified to compute the load control parameters. In this paper, in the context of a satellite IoT system, we propose a method to compute dynamically ACB based load control parameters. Thanks to our method, the load control mechanism reach excellent results regarding transmission reliability and energy consumption for various traffic scenarios.

Today, we can use our smartphones to drive from Los Angeles to New York, yet we can not use them to find our way around Charles de Gaulle Airport. GPS simply does not work indoors and while outside areas are mapped very well, the indoors of most buildings remain a mystery to our favorite navigation apps. While the problem of indoor localization has attracted a lot of attention, with several solutions with meter-level accuracy emerging as research prototypes, the problem of building accurate and detailed indoor maps has been neglected. We present InPReSS, a solution for dynamic indoor map construction without explicit user input. It leverages the sensors available on off-the-shelf smartphones and their ubiquity to construct floor plans as users go about their daily business. The InPReSS approach consists of four steps: 1. Collecting readings from five sensors, tagged with their location from smartphones available in the target building, and divide the floor plan into cells using a Voronoi diagram. 2. Clustering the cells into rooms based on the sensor readings. 3. Identifying doors and ways between adjacent rooms using the Voronoi diagram and user movement traces. 4. Building a two-level graph of the floor plan for navigation.

We revisit Physical-Layer Network Coding (PLNC) and the reasons preventing it from becoming a staple in wireless networks. We identify its strong coupling to the Two-Way Relay Channel (TWRC) as key among them due to its requiring crossing traffic flows and two-hop node coordination. We introduce SE-PLNC, a Source-Encoded PLNC scheme that is traffic pattern independent and involves coordination only among one-hop neighbors, making it significantly more practical to adopt PLNC in multi-hop wireless networks. To accomplish this, SE-PLNC introduces three innovations: it combines bit-level with physical-level network coding, it shifts most of the coding burden from the relay to the source of the PLNC scheme, and it leverages multi-path relaying opportunities available to a particular traffic flow. We evaluate SE-PLNC using theoretical analysis, proof-of-concept implementation on a Universal Software Radio Peripherals (USRP) testbed, and simulations. The theoretical analysis shows the scalability of SE-PLNC and its efficiency in large ad-hoc networks while the testbed experiments its real-life feasibility. Large-scale simulations show that TWRC PLNC barely boosts network throughput while SE-PLNC improves it by over 30%.

The return link of broadband satellite systems has recently received more attention due to the spread of multi-beam antennas which enable spatial frequency reuse, and thus increase drastically the number of users that can potentially be served by one satellite. While interference isolation has so far been the way to go, with regular four-color frequency reuse scheme, there is a growing interest in densifying the frequency usage as is being done in cellular networks. In this paper, we address the return link radio resource allocation challenges, from spectral resource allocation to user scheduling, including modulation and coding scheme (MODCOD) selection. Our contributions highlight the potential gains of a two-color scheme and shed light on several levers to reap its benefits through interference management. We first consider the possibility to use a two-color scheme, while keeping the MODCOD selection and the scheduling local to each beam and we show that even though it yields a potential performance gain (+16%) with respect to the state of the art (SoA) (based on four colors), it is not viable due to a very high-block loss rate. Therefore, we propose a simple-yet fast and efficient-coordinated MODCOD selection process that alleviates the need of estimating interference and reduces drastically decoding failures. This coordination step offers significant gains (+58%) over the SoA, while leaving the per beam scheduler unchanged. Finally, we formulate a joint user scheduling and MODCOD selection problem across all beams and propose an offline heuristic to solve it efficiently. We obtain a 83% gain with respect to the SoA, but with higher computational complexity. Still, it confirms the great potential of coordinated scheduling.

We are facing a steady increase in Internet usages and bandwidth requirements. However, many terrestrial infrastructures remain unchanged due to exorbitant modernization costs, particularly in rural areas. In front of the aging of their infrastructures, concerned users are turning towards satellite internet access. Indeed, these solutions offer a high-throughput internet access at a moderate cost of deployment. Unfortunately, the long delay introduced by GEO satellite degrades significantly the user Quality of Experience (QoE) in many cases. In this paper, we consider a hybrid access, composed of a low data rate terrestrial path and a satellite path, within a Content Delivery Network (CDN) context. Thanks to the CDN, requested content size is known allowing to use this information in routing schemes to maximize the users' QoE. Then, we compare flow and packet based routing in this heterogeneous and size-aware context. We finally conclude on the limited interest in packet-based routing compared to flow-based routing, privileged by its simplicity and good performance from a QoE point of view.

High throughput satellites have proven to be an excellent solution to provide Internet services to white spots or to complement other existing infrastructures. With the use of multi-beam antennas, the same frequency may be reused dozens of times across a single satellite coverage area, increasing the system capacity and profitability. Legacy frequency reuse patterns such as uncoordinated 4-color scheme ensure interference isolation at the expense of important capacity reduction, using only one fourth of the operator's share in the scarce Ka band. Thus, to increase the per-beam available bandwidth, it is necessary to look for more aggressive and efficient Frequency Reuse schemes, generating higher Co-Channel Interference which has to be analyzed and handled. In this paper, we focus on the DVB-RCS2 return link of a multi-beam satellite and investigate the possibility of reaching the upper bound of a coordinated 2-color system capacity through the use of Interference-aware User Scheduling techniques. We first formalize the problem as an Integer Linear Program and study the impact of greedy simplifications on the optimality and processing times of our optimization models.

We investigate the potential gains of Physical-Layer Network Coding (PLNC) in multi-hop wireless networks. Physical-Layer Network Coding was first introduced as a solution to increase the throughput of a two-way relay channel communication. Unlike most wireless communications techniques which try to avoid collisions, PLNC allows two simultaneous transmissions to a common receiver. Such transmitted messages are summed at signal level and then decoded at packet level. In basic topologies, Physical-Layer Network Coding has been shown to significantly enhance the throughput performance compared to classical communications. However, the impact of PLNC in large multi-hop networks remains an open question. We therefore exploit Linear Programming to evaluate the impact of this paradigm in large realistic radio deployments. Our numerical results show that PLNC can increase the throughput in large multi-hop topologies by 30%. Such gains set theoretical benchmarks for designing new access methods and routing protocols to efficiently exploit the Physical-Layer Network Coding concept.

Physical-Layer Network Coding (PLNC) was first introduced as a solution to increase the throughput in simple bidirectional communication schemes. Unlike most wireless communication techniques which try to avoid collisions, PLNC allows two simultaneous transmissions to a common receiver. In this work, we propose a MAC layer distributed and realistic scheduling policy targeting PLNC based networks. In order to easily operate in large ad-hoc networks, our solution is completely decentralized and runs in constant time. By basing the transmission priority of every node on the queue sizes of its local neighbors and PLNC opportunities, our solution ensures high throughput when compared to classical interference-free scheduling. Both our theoretical analysis corroborated by our simulation results highlight that the proposed algorithm outperforms existing scheduling policies with throughput gains of around 35%.

Wireless sensor network applications are becoming the main concern of several studies. Not only they allow to maintain more varied measures in several fields notably that of real time hydraulic systems control and surveillance. But their dense deployment decreases granularity which can lead to the comprehension of some unexplainable phenomena. However, the effectiveness of a sensor network not only depends on the quality of the sensors individually, but also on their collaboration. The latter is only possible with reliable routing protocols which have to adjust to fit the constraints imposed by the application. With this aim in mind, we suggest in the current work a new extension of SCTP (Stream Control Transmission Protocol) that we call SCTP-WSN (wireless sensor network). This extension will have as a main function to improve the communicative performances of sparse wireless sensor networks with dynamic topologies. In order to do this, this extension will have to improve the availability of the links in sparse sensor networks by a better integration of the Multihoming concept, representing therefore a more reliable data collection subsystem for a real time detection of possible disorders affecting drinking water supply systems.

We present Acrux, the first indoor localization system to achieve meter level accuracy while relying exclusively on a single fix and the sensors commonly found in off-the-shelf smartphones. Acrux uses dead-reckoning, the approach that gives probably the best chance at a completely autonomous indoor localization system. Unfortunately, it has not been mastered on smartphones beyond a few dozen meters due to its inherent integration drift. As a result, all dead-reckoning based solutions in literature require periodic recalibration using input from outside -- attaching strings preventing indoor localization from becoming mainstream. While it is virtually impossible to completely eliminate integration drift, Acrux is the first solution to succeed in dead-reckoning with meter level accuracy for several hundred meters, enough to relax the requirement for periodic recalibration in most indoor scenarios. To accomplish this, Acrux replaces step-counting, the standard approach for measuring distance using sensors, with an approach that measures the speed of locomotion. Although a straightforward accurate estimation of motion speed using the erroneous sensors found on smartphones is infeasible, Acrux combines a novel approach with measurement based analysis to achieve that. Leveraging its excellent dead-reckoning capability, Acrux is shown to provide indoor localization with median error between SI0.7 meter and SI1.2 meter and 98% percentile error of SI3 meter in a dozen of scenarios in 4 different buildings -- without any recalibration.

The integration of social networks with mobile communication has led to the rise of a new paradigm, the mobile social network (MSN). Recently, MSN has emerged as a new hot spot of research attracting much interest from both academia and industrial sectors. For instance, MSN opens new horizon for information diffusion-based applications such as viral marketing. Thus, it is a fundamental issue to select an efficient subset of seed-nodes (i.e. initial sources) in a MSN such that targeting them initially will maximize the information diffusion to interested nodes. This paper studies the problem of identifying the best seeds through whom the information can be diffused in the network in order to maximize the content utility (i.e. a quantitative metric that determines how satisfied are the users). A multi- layer model that combines the social relationships and the mobile network in order to design an efficient information diffusion is proposed. Based on this multi-layer model, different seed selection approaches are proposed for information diffusion environment (e.g. mobile advertising) where users have heterogeneous interests for the different information generated in the network. Simulation results show the effectiveness of multi-layer based seed selection approaches comparing to a classical approach.

Satellite networks are easy-to-deploy solutions to connect rural un-served and underserved areas. But satellite latency has a significant negative impact on performance. Hybrid networks, combining high-throughput long-delay links (e.g. GEO satellites) and short-delay low-throughput links (e.g. poor ADSL), can improve user experience by the use of intelligent routing. Emerging solutions, such as MultiPath TCP (MPTCP), already optimize the throughput in these hybrid networks. However, this kind of solutions does not take into account QoE requirements by the lack of relevant flows information, leading to sub-optimal path selection. This paper proposes an architecture able to retrieve the content size through interconnection with Content Delivery Networks (CDNs). Then, we conduct an analytical study of a probabilistic and a size threshold based routing schemes with the Mean Value Analysis (MVA) method. This shows the great benefit brought by size information in terms of QoE. To solve the limitations due to the threshold configuration, we propose a third algorithm that takes into account the path delay and capacity. Finally, we develop a testbed in order to validate our model and to compare this third scheme to the previous ones. We obtain results equivalent to the size threshold scheme, without its disadvantages.

Studies have shown that in places like New York City drivers often spend over 20 min looking for parking, contributing to as much as 30% of the total traffic. In response, cities like San Francisco have deployed systems capable of pointing drivers to the closest available parking spot. Unfortunately, such systems have gained little traction as they rely on specialized infrastructure that is expensive to build and maintain. We present SmartPark, a smartphone based system that relaxes the requirement for specialized infrastructure by relying on the smartphone's sensors and ubiquitous Wi-Fi and cellular infrastructure. To accomplish this, SmartPark addresses two major challenges, under the constraint of minimum impact on battery life: automatic transportation mode detection and location matching. Solved together, they enable SmartPark to automatically detect when a user pulls out of a parking spot, making it available again. It addresses each challenge using a combination of thorough statistical analysis of the sensor readings and a novel Random Forest based classification algorithm. Experimental results from 12 volunteers, using 7 different smartphones, in 3 different cities show that SmartPark can distinguish 9 different transportation modes with accuracy between 95.57-100%, enabling it to correctly detect unparking events virtually 100% of the time. This is accomplished with a minimum impact on battery life-running SmartPark on a fully charged LG Google Nexus 5 for 5 h straight caused the battery level to drop only about 4%.

The rapid increase of portable devices providing a multitude of mobile applications have led to excessive cellular traffic demands and consequently to the overload of cellular networks. Recently, migrating this traffic by opportunistic vehicular networks has attracted a great interest and appeared as a promising solution. Indeed, only a limited set of vehicles (seeds) is selected to download objects from an Internet-content server through the cellular network and then propagate the content gradually by opportunistic communications (i.e. vehicle-to-vehicle V2V). This paper proposes SIEVE, an innovative seed selection scheme, that exploits two key criteria: users' interests and near-future contacts prediction. Based on these criteria, SIEVE allows to select the seeds in order to maximally satisfy the users' interests and, hence, achieve a maximum content utility (i.e. quantitative metric that determines how satisfied are the users). Simulations results show that SIEVE can improve the content utility when compared to other algorithms.

Depending on the congestion level and the network characteristics (e.g., buffer sizes, capacity of the bottleneck, deployment scenario, etc.) a fixed Initial Window (IW) would be either too conservative or too aggressive. This results in low usage of the network resource or damaging high congestion level. This paper presents a sender-side only modification to the slow-start of TCP, SmartIW, that bypasses the limitations and potential issues of a fixed IW. The Round Trip Time (RTT) is estimated during the establishment of the connection and further exploited by SmartIW to pace the transmission of an adequate number of packets during the first RTT. Our simulation results show that, since the IW has been set in adequacy with the available network information, larger IW can be transmitted without increasing the congestion level of the network. SmartIW eventually reduces the RTT dependence of the slow start stage to fairly provide significant performance improvements whatever the network characteristics (RTT and congestion level).

Sensor Networks can be envisaged to monitor mobile systems. Nevertheless, new challenges appear from mobility such as delay and connectivity disruptions. These challenges can be tackled by the Delay/Disruption Tolerant Networking architecture. However, implementing DTN mechanisms on sensors require to select the schemes which propose an efficient use of the memory. Our scheme, FREAK, aims at providing high performance with low-memory usage. This scheme relies on the mean frequency of past encounter with the base station. Transmissions are driven by this metric. The FREAK solution is keen because we assume that future can be predicted from the past events. The acknowledgements effects on performance is analysed. We run simulations using mobility quota-based mainstreammodels and real traces. FREAK is compared to several replication and quota-based mainstream DTN solutions and achieves quite better performance in realistic scenarios.

Ultra Narrow Band (UNB) transmission technique makes a powerful comeback in the frame of Machine-To-Machine (M2M) communications thanks to advances in signal processing. After explaining why, among others, it is one of the best candidate for Low Power Wide Area (LPWA) communications, we present its specificities and associated constraints. In particular UNB is inseparable from random access so we introduce Time/Frequency Aloha, a random access scheme adapted for UNB. Then, we propose an analytical model to evaluate its performance in terms of packet loss ratio and normalized throughput in both terrestrial and satellite context. Several axes of improvement based on advanced signal processing techniques are proposed to enhance the capacity of a system using UNB signals.

Transmission count, the number of transmissions required for delivering a data packet over a link, is part of almost all state-of-the-art routing metrics for wireless networks. In traditional networks, peer-to-peer interference and channel errors are what define its value for the most part. In cognitive radio networks, however, there is a third culprit that can impact the transmission count: primary user interference. It may be tempting to think of primary user interference as no different than interference caused by other peers. However, unlike peers, primary users do not follow the same protocol and have strict channel access priority over the secondary users. Motivated by this observation, we carry out an empirical study on a USRP testbed for analyzing the impact of primary users. Our measurements show that a primary user has a distinct impact on the transmission count, which the de facto standard approach, ETX, designed for traditional networks, fails to capture. To resolve this, we present COExiST (for COgnitive radio EXpected transmISsion counT): a link metric that accurately captures the expected transmission count over a wireless link subject to primary user interference. Extensive experiments on a five-node USRP testbed demonstrate that COExiST accurately captures the actual transmission count in the presence of primary users -- the 80th percentile of the error is less than 20%.

The evolution of satellite communication towards packet-based communication and the adoption of modern physical layer techniques, such as Adaptive Coding and Modulation, raise new issues, brought by this variability, for scheduling algorithms. This paper addresses the problem of GSE packets scheduling over DVB-S2 with QoS support by adopting a utility-based scheduling strategy. Utility functions are considered as a mean to encompass parameters from several layers into a single scheduling process. By making use of a first-order approximation, a low complexity scheduling algorithm is derived from the utility functions optimization problem, adaptable to a wide range of functions. The algorithm determines the characteristics of the next BBFrame to be send, and which GSE packets it should contain. We focus particularly on delay as a joint metric to represent QoS requirements, and assess the performance of our algorithm and the relevance of our assumptions using comparative simulations.

The mobile context of Mobile Wireless Sensor Networks (MWSN) limits the existence of a direct route from source to destination. A Disruption Tolerant Networking (DTN) architecture fits the requirements for such a context where messages need to be stored, carried and forwarded. For this kind of DTN applications, the goal is to achieve a high delivery ratio at low transmission cost with the lowest latency. Some DTN routing protocols use this ACK information to decrease the number of useless transmissions. Nevertheless in memory-constrained environments, the proportion of memory allocated to ACKs is a problem to study. This paper focuses on the use of acknowledgements (ACKs). We model the network with a Markov chain, to study the effect of ACKs on buffer time occupancy. Finally, an extensive set of simulations is run to analyse the influence of the memory proportion allocated to ACKs, on the performance.

In this paper, we consider the problem of IP packet scheduling over a GSE/DVB-S2 satellite link. Scheduling flows with QoS requirements has been widely addressed in the mobile field, especially in LTE and WiMAX, with emphasis on fairness, efficiency and dynamic adaptation to transmission conditions. We focus on the well-known empirical scheduling rules known as PF, M-LWDF and EXP-PF for both QoS and MODCOD scheduling, and present how they were adapted to GSE/DVB-S2 encapsulation. Some of the challenging issues yielded by DVB-S2 are tackled, such as joint scheduling of both QoS and MODCODs, concatenation of numerous user packets into one BBFrame and fairness issues introduced by the scheduling algorithm, especially when dealing with various transmission scenarios. We show the potential of our scheduling algorithm using several simulations.

With a vast majority of Internet connections shorter than 10 segments, designing a new fast start-up TCP mechanism is a major concern. While enlarging the Initial Window (IW) up to 10 segments is the fastest solution to deal with a short-lived connection in uncongested networks, numerous researchers are concerned about the impact of the large initial burst on congested networks.

Recent work has shown that content dissemination protocols in vehicular networks can achieve throughput and fan-out delay optimization by either simple network flooding or destination-driven dissemination. While those content dissemination schemes work well, they require all nodes in the network to forward every data packet, which has inherent inefficiencies for non-flooding traffic patterns, where not all nodes need to receive the data. Hence, they support adequately safety applications, being not efficient for non-safety applications, whereby the flow of information is interest-driven rather than destination-driven, e.g. restaurant recommendation and sale advertisement. In this work, the concept of “useful” forwarder is formalized aiming at maximizing content utility for end users. Further, it presents I-SEND, a forwarder selection approach, which enables nodes to choose the most appropriate forwarders. Incorporating I-SEND on trace-driven and synthetic simulation scenarios can produce higher content utility than other concurrent schemes.

In this paper, a new cooperative MAC protocol with distributed relay selection and rate adaptation is proposed in the context of multi-rate ad hoc networks. When the wireless link between a source and a destination nodes experiences poor channel conditions, a relay station is selected in the vicinity of both nodes so that the low data rate direct link is replaced by a two-hop path with a higher data rate. The relay station is selected through a distributed contention process. The procedure requires no topology knowledge and no communication among potential relays. A data rate adaptation is also performed without any additional signaling. The best-relay selection and the rate adaptation are based on instantaneous channel measurements to adapt to dynamic channel conditions. Results show that cooperative transmissions significantly outperform conventional non-cooperative transmissions in terms of throughput, delay and energy consumption.

Satellite Digital Video Broadcasting is deeply changing : the next generation is dedicated to packet based communications and introduces (like many modern physical layers : WiMax, hsdpa, ...) fade mitigation techniques leading to variable throughput. Such tremendous changes need to be taken into account and the scheduling entity needs to be revisited. The purpose of this paper is to investigate utility function based algorithms. Such techniques have already been studied but never within this context. Dvb-s2 frames can encapsulate numerous ip packets, can offer variable payload length as well as variable transmission time, because of acm techniques. A more general approach is needed to encompass theses properties. As a consequence, the number of solutions among which a scheduler has to find the better is increased. We will then show that the algorithm implemented is an important issue.

In this paper, a new Medium Access Control (MAC) protocol combining Transmit Power Control (TPC), Rate Adaptation (RA) and Cooperative Transmission (CT) is proposed, in the context of multi-rate ad hoc networks. The protocol aims to achieve energy efficiency of data transmission while increasing the overall network throughput. The key idea of the protocol is to allow each wireless node to create a table with the optimal power-rate combinations based only on the network interface card specifications. In the presence of low data-rate nodes the network throughput is greatly degraded. To mitigate this well-known “rate anomaly” problem we use CT to replace the direct low-rate links by relayed high-rate links. By exchanging control frames and looking up the power-rate table, the wireless node chooses the most suitable transmission strategy (which consists of selecting the most optimal power-rate combination) for each data-frame as well as the transmission scheme (direct or relayed). Results reveal an important improvement in the overall network throughput as well as in the energy consumption with the new protocol compared to the scheme without TPC and without cooperation. Furthermore, simulation results show that our scheme deliver more data per unit of energy consumption than the IEEE 802.11 scheme.

With most internet connections being short-lived (i.e. 10 segments), it is very tempting to enlarge the TCP Initial Window (IW). This would save two of the three RTTs needed to transfer most of the web pages through a legacy slow start. However it has been demonstrated that the bursts created by a larger IW greatly impair global performance. An intuitive solution is the TCP Pacing. By spreading the transmission over the whole RTT, Pacing smoothes the bursts and delays the congestion. While postponing congestion provides good performance for short-lived connections, it could significantly deteriorate global network performance insofar as the reaction to congestion is also delayed. This paper analyzes the weaknesses of large IW and TCP Pacing and proposes a fast Start-Up mechanism to speed up short-lived connections while preserving long-term connections. Extensive simulations and analysis demonstrate that our solution is as efficient as a larger IW would be in an uncongested network and better than current mechanisms in congested environments.

Content distribution over ad-hoc networks has been widely studied and numerous solutions can be adapted to VANETs (vehicular networks). VANETs, however, can also benefit from an infrastructure in order to improve the efficiency of any content dissemination technique, while allowing more transmissions resources to be available for safety applications. Unfortunately, so far, no such solution has been proposed. In this paper, we introduce the use of an 802.11p infrastructure based on Road Side Units (RSU) for downloading data (eg a map) to vehicles on a highway. At the application level, the main challenge is then how to deliver data to a large number of moving receivers with limited connectivity. While broadcasting data through each RSU should efficiently provide the cars with most of the data, one could believe that some specific transmissions based on vehicles needs could help to reach full downloads. Using simulations, we observed however that the best performances are achieved by a pure broadcasting system.

Health care monitoring using wireless sensor networks is limited by energy, low bandwidth and small memory storage. In this kind of networks, Packet Delivery Ratio (PDR) is often too low, so it is a challenge to support transmission reliability. In heath care context, heterogeneous nodes are generally used. This paper presents a new approach to improve the transmission reliability with a new multicast routing protocol (HMR) which uses this heterogeneity. This approach exploits some powerful nodes instead of all nodes to forward packets avoiding the loss of packets and reducing the overhead. Simulation results show that this approach could be an interesting solution both in BAN (Body Area Network) and PAN (Personal Area Network).

Both WSNs (Wireless Sensor Networks) and observation satellites are able to get measurements from a geographic area. To interconnect these technologies, we propose to use a store-carry-and-forward architecture relying on the DTN (Disruption and Delay Tolerant Networking) Bundle Protocol. This architecture aims at being generic, so it is application-agnostic and suits a wide range of scenarios. WSN may collect sporadically large data volume while terrestrial stations communicating with Low Earth Orbit (LEO) satellites have to endure long link disruptions when the satellite is not in the line of sight. These sporadic growths within the WSN coupled with the large latency on satellite links require to schedule data to provide quality of service to several flows. We propose a scheduling policy based on deadline of Bundles and compare it with classical DTN solutions.

In this paper a two level resource allocation scheme is proposed to enhance the Quality of Service (QoS) for multimedia services in LTE downlink system. It corresponds to a solution that combines cooperative game theory, a virtual token mechanism, and the EXP-RULE algorithm. By using cooperative game theory such as bankruptcy game and Shapley value, the proposed mechanism works by forming coalitions between flow classes to distribute bandwidth fairly. EXP-RULE algorithm has been modified to use a virtual token mechanism to improve its performance. By taking into account constraints such as Shapley value fairness and the virtual token robustness, the proposed mechanism can increase remarkably the performance for real time flows such as video and VoIP in downlink system. The performance evaluation is conducted in terms of system throughput, packet loss ratio (PLR), cell spectral efficiency and fairness index.

Efficient radio resource management and Quality of Service (QoS) guarantee are very important aspects in order to provide a good service in LTE Networks. Although the base station performs a smart scheduling scheme for resource allocation, the expected result could be affected due to interference, specially in femtocell scenarios. This article investigates the problem of interference in femtocell networks in LTE. The proposed method achieves inter-cell interference mitigation though a dynamic power self-control performed at each femtocell. In this paper we use the modulation and coding scheme (MCS) to obtain the optimum power value which assures a trade-off between Signal-to-Interference-plus-Noise-Ratio (SINR) and bit-rate efficiency. The main objective of our work is to optimize the sub-bands in order to decrease the interference and maintain the throughput at the same time. The performance evaluation is conducted in terms of throughput, Packet Loss Ratio (PLR) and SINR.

Initially deployed for TV broadcasting, geostationary satellite networks and DVB standards have become mature technologies for IP communications. Also used to interconnect wide IP networks, dynamic IP routing is required in geostationary mesh satellite networks. Nevertheless, terrestrial IP routing protocols are not optimized for satellite networks. Especially, as far as BGP operates over TCP at transport layer, it does not provide any multicast support and is not optimized for natural broadcast properties of satellite systems (e.g. DVB-S2), involving a significant amount of overhead and important complexity at the satellite terminal side. To integrate and interconnect satellite systems to the IP world, the use of BGP (as EGP) is required. Therefore, this paper analyzes the different ways to deploy BGP in DVB-S2/RCS networks and the opportunity to take advantage of a reliable multicast transport layer. A light, multicast and reliable mechanism to transport BGP4 is proposed and compared to the existing solutions.

In wireless sensor networks several constraints decrease communications performances. In fact, channel randomness and energy restrictions make classical routing protocols inefficient. Therefore, the design of new routing protocols that cope with these constraints become mandatory. The main objective of this paper is to present a multi-objective routing algorithm RBCR that computes routing path based on the energy consumption and channel qualities. Additionally, the channel qualities are evaluated based on the presence of relay nodes. Compared to AODV and AODV associated to a cooperative MAC protocol, RBCR provides better performances in term of delivery ratio, power consumption and traffic load.

In order to enhance the Quality of Service in LTE, femtocell architecture has been proposed as a promising solution. However, interference is the main weak point in femtocell scenarios which causes a serious impact on multimedia services performance. Femtocell interference mitigation in LTE networks is the principle objective of this paper. We propose an enhancement of the well known four-coloring method for interference mitigation by combining it with cooperative game theory. Our proposed scheme aims to provide a solution to effectively achieve femtocell interference mitigation while guaranteeing the bitrate application for real-time services. The basic metrics of quality of service (QoS) such as throughput, Packet Loss Ratio (PLR), delay and Signal-to-Interference-plus-Noise-Ratio (SINR) are investigated. Our simulation environment is derived from realistic scenarios in order to study the performance of real-time service like Video and VoIP applications. Throughout our numerical results, we demonstrate the improvement of QoS constraints along with balancing between interference reduction requirement and resource allocation efficiency for real-time applications.

Inter-vehicular communications are considered to be an efficient proactive approach for reducing the number and the consequences of road accidents. After a series of remarkable standardisation efforts, one of the last points needing to be addressed in order for safety vehicular networks to become a reality is the scalability problem of the CSMA-based medium access control layer. With node densities that can range from very sparse to several hundred contending stations, the MAC protocol needs the capacity to adapt to the state of the vehicular network without compromising the performance of the safety applications. While previous studies focused on individual mechanisms for data rate selection or transmission power control from a global point of view, this paper proposes a complete congestion control framework aiming to increase the message reception probability in the immediate neighbourhood under heavy congestion conditions. We propose a new concept for physical carrier sensing, which takes into account the location of the transmitter, and we combine it with transmission power control and a recently proposed backoff mechanism to obtain an important improvement over the original protocol. Several implementation problems are discussed, showing the feasibility of the solution using existing hardware, and a simulation study confirms the performance of this enhanced channel access method.

Contention-based protocols for Medium Access Control (MAC) in Vehicular Ad-Hoc Networks (VANET) are currently under development in several standardization organizations. The availability and maturity of the IEEE 802.11 technology makes it the first choice for the future vehicle-to-vehicle communications. At the same time, safety applications in a vehicular environment are expected to intensively use broadcast messages. However, the IEEE 802.11 standard has not been designed for broadcast communication and a number of problems arise from this. In this paper, we analyze the impact of the minimum Contention Window (CW) on the MAC layer performance in a realistic vehicular environment and we propose a simple solution for adapting CW to the network density in order to improve the reception probability of broadcast messages.

Over the last decade cooperative communication in wireless sensor networks (WSN) received much attention. A lot of works have been done to propose a MAC layer that supports cooperative communication. However the impact of the association of a cooperative communication technique with a low power listening scheme was not studied in the literature. In this paper we propose CL-MAC, a Cooperative Low power mac protocol for WSNs. CL-MAC implements jointly Low Power Listening and cooperative communication. More precisely, we propose two variants of this protocol: a proactive version CL-MAC(P) and a reactive version CL-MAC(R). In order to evaluate the performances of the two proposed CL-MAC variants, we compare its to those of X-MAC. Simulation results proved that our protocol is able to enhance the use of the channel and to reach promising energy preservation especially in dense networks.

Adding communication capabilities to vehicles and road infrastructure has become a major goal in the intelligent transportation systems industry. The IEEE 802.11p amendment has specially been conceived for the Wireless Access in Vehicular Environments (WAVE) architecture. In this paper we study the performance of this standard by the means of extensive simulations and we argue that the current version of the protocol can not cope with high vehicular densities. We propose a simple but efficient modification of the back off mechanism which has an important impact on the quality of communications on the control channel.

Enhancing road safety using vehicle-to-vehicle communication has become an important goal for the automotive industry. A lot of effort has been put in the design of an efficient medium access control protocol, capable to function correctly even under heavy congestion. The solutions proposed so far focus on data rate or transmission power control. In this paper, we argue that the most important parameter for congestion control in vehicular ad hoc networks is the carrier sense threshold. We support this theory with analytical and simulation results and we demonstrate that the optimal threshold depends on the vehicular density. Furthermore, we propose an adaptive mechanism for physical carrier sense control and analyse its performance, showing an important increase in message reception probability.

The LTE specification provides QoS of multimedia services with fast connectivity, high mobility and security. However, 3GPP specifications have not defined scheduling algorithms to support real time and non-real time application services. In this paper we propose a two level scheduling scheme composed by cooperative game concept and EXP-RULE scheduling algorithm. By using cooperative game theory such as bankruptcy game and Shapley value, the proposed mechanism works by forming coalition between flow classes to distribute the bandwidth fairly. To make a performance judgment, the proposed downlink scheduling scheme has been compared to other well known schedulers such as M-LWDF and PF. Simulation results show that the proposed scheme can improve the performance on the used metrics among services. The performance evaluation is conducted in terms of system throughput, packet loss ratio (PLR), cell spectral efficiency and fairness Index.

The proliferation of low power networks like Wireless Sensor Networks (WSN) rose up new challenges. Power conservation and channel quality become the most important parameters. Obviously, hop count based routing protocols are no more adapted to such networks having power limitations and channel problems. Several alternatives were suggested to cope with these constraints. In MAC layer for example, cooperative protocols were designed to enhance the channel use: the neighbor nodes help the source to retransmit its packets. However, if the path proposed by the routing protocol contains poor channels, the cooperative communications will not save all the packets. Therefore, the design of new routing protocol becomes compulsory. In this paper we propose ECAR, a routing protocol that optimizes two objectives at the same time: energy and Channel State Information (CSI). Compared to AODV, ECAR provides considerable enhancements in delivery ratio, end-to-end delay and power consumption.

The medium access control protocol of a future vehicular ad-hoc network is expected to cope with highly heterogeneous conditions. An essential parameter for protocols issued from the IEEE 802.11 family is the minimum contention window used by the backoff mechanism. While its impact has been thoroughly studied in the case of wireless local area networks, the importance of the contention window has been somehow neglected in the studies focusing on vehicle-to-vehicle communication. In this paper we show that the adjustment of the minimum contention window depending on the local node density can notably improve the performance of the IEEE 802.11 protocol. Moreover, we compare through simulation in a realistic framework five different methods for estimating the local density in a vehicular environment, presenting the advantages and the shortcomings of each of them.

Long Term Evolution (LTE) prevails as the next 4thgeneration of mobile communications. Hybrid satellite and terrestrial LTE network takes advantages from the large satellite coverage for several emergency applications, such as providing civil security communications. In this paper we propose a LTE architecture partly composed of an integrated component with satellite backhaul on the LTE-S1 interface. Since ensuring seamless communications is essential in LTE, we describe an optimization of the handover mechanism adapted to this specific architecture. This paper focuses on the handover between an eNB with a satellite S1 interface and an eNB with a standard terrestrial S1 interface.

The LTE specification provides QoS of multimedia services with fast connectivity, high mobility and security. However, 3GPP specifications have not defined scheduling algorithms to support real time and non-real time application services. In this paper we propose a modified version of M-LWDF and EXP/PF scheduling algorithms based on token mechanism, which provide better performance to real time flows such as video and VoIP in downlink system. By taking the arrival rates of packets to queues into account, the proposed mechanism included in previous scheduling algorithms, can increase remarkably the bit-rate for multimedia services. Simulation results show that the proposed modified algorithms can achieve a throughput gain for real time services specially for video traffic. Performance evaluation is conducted in terms of system throughput and packet loss ratio (PLR).

The use of inter-vehicle communication is considered the next step to be taken in order to reduce the number of traffic accidents. The design of a versatile and efficient protocol that would manage the access to the control channel reserved for safety applications would represent a significant progress towards a generally accepted technology. However, the solutions proposed hitherto rarely took into account the broadcast nature of the messages produced by the safety applications. Furthermore, the specific properties of periodic vehicular beaconing are yet to be considered by any technical committee or research study. We present the specificities of this type of messages and discuss their impact on the performance of the medium access control layer, using both analytical and simulation tools.

The lifetime of Wireless Sensor Networks (WSN) is crucial. The goal of all WSN application scenarios is to have sensor nodes deployed, unattended, for months or years. In this work, we investigate the problem of energy consumption and lifetime maximizing in a many-to-one sensor network. In such network pattern, all sensor nodes generate and send data to a single sink via multihop transmissions. In our previous experimental studies, we noticed that, since all the sensor data has to be forwarded to a base station via multihop routing, the traffic pattern is highly nonuniform, putting a high burden on the sensor nodes close to the base station. In this paper, we analyze and propose some strategies that balance the energy consumption of these nodes and ensure maximum network lifetime by balancing the load as equally as possible.

Vehicular Ad-Hoc Networks (VANET) aim to increase security in the current transportation system by the means of wireless communication between vehicles and between vehicles and road infrastructure. In order to realize this goal, the Medium Access Control (MAC) protocol has to be highly reliable and has to assure a certain fairness between the nodes. In this paper, we make an in-depth analysis of the properties required from a MAC protocol in a VANET context. We then use these properties to compare the performance of two MAC protocols, one based on Carrier-Sense Multiple Access and the other using Time Division Multiple Access techniques in the case of a "heartbeat" application.

The Return Channel for Satellite (DVB-RCS) standard has become a mature technology for Internet communications via satellite access networks. Because of the propagation delay, as well as the expensive and scarce resources, the QoS support has to be optimized and harmonized. Indeed, it is provided at different independent layers (mainly layer 2,3 and application level) which are potentially either redundant or inconsistent. This paper suggests optimizations (between layer 2 and 3) for the resource sharing based on traffic contracts and using cross layer mechanisms. The traffic contracts are mainly used to perform a prediction of the incoming traffic evolution in order to reduce the effects of the transmission delay. In addition, a way to coordinate layer 2 and 3 schedulers is introduced. A first performance assessment of the proposed mechanisms in a DVB-RCS context shows that the layer 3 delays (introduced by queuing) are significantly reduced.

Initially designed for TV broadcasting, DVB standard families have become mature technologies for Internet communications via satellite access networks. A generic encapsulation protocol is therefore required for the forward link, the return link, and for mesh satellite systems. Moreover, because of the cost and the scarcity of resources, this should be as efficient and light as possible. The GSE (Generic Stream Encapsulation) protocol enables efficient transport of any protocol, originally designed for DVB-S2, that is to say on Quasi Error Free (QEF) forward links of satellite systems. This paper addresses limitations in GSE for the return link context and examines the requirements for an encapsulation mechanism for satellite systems using multiple access. This includes the return link but also mesh satellite systems and any satellite systems that uses multiple access. This paper also analyses approaches to derive requirements and provides a first analysis of these requirements.

Route computation relies on the definition of performance indicators called routing metrics. Popular metrics are the number of hops, throughput, end-to-end delay and jitter. However, in a store and forward network displaying link disruptions, these metrics are questionable. This contribution defines seven metrics for characterising routes in a store and forward network. These metrics are: number of hops, route lifetime, end-to-end delay, capacity, synchronicity, simultaneousness and discontinuity. Some of these metrics are borrowed or adapted from classical networks, others are specifically conceived for store and forward networks. Simulations for routing in a satellite constellation show that these metrics help to capture the specifics of store and forward networks and therefore improve routing decisions.

Temperature control is a major concern in cold chain monitoring and traceability services for the largest cause of food poisoning. Considerable work has examined the use of wireless solutions in warehouses. However, the maintaining of the chain during the transportation phase remains very crucial. In this paper, we present new wireless sensor network (WSN) solution for cold chain monitoring. This solution is based on self-organizing protocols and aims at saving energy in order to increase the sensor lifetime and as a result the global network longevity within the given context. Furthermore, this solution does not need any base station or central equipment. To save energy, periodical active/sleep schedule is adopted in the design of our protocols which were dimensioned and validated by an analytical model described in this paper.

Until now, the interaction and the handover between the satellite and wireless radio networks of next generation has not yet taken into account because of the wide difference of operation between the two networks; and the difference of their protocol stacks structures. In this context, we propose an interaction model between a network based on wireless radio technology: the mobile WiMAX, and a spatial network based on satellite broadcasting and return of data: DVB-S/RCS. We suggest also to use the multi-homing protocol: MSCTP to provide the vertical handover for Mobile Terminals that are moving between the two networks. And we propose finally a new DVB-S/RCS protocol stack amended and based on MSCTP and IP protocols to be more interactive with the mobile WiMAX and the end users exchanging IP traffic. In this model we try to ensure good QoS for video streaming traffic; and we will show some experimental results of our vertical handover model using Network Simulator (ns2).

In order to offer a better QoS during L2 handover of a mobile station, we propose in this paper to compare the performance of the two L2 HO techniques: Soft and Hard handover for different types of traffic with same architecture IEEE 802.16e in an urban area (City).

The main challenge in the development of future wireless communication systems is to provide users with a wide range of services across different radio access technologies through a single mobile terminal, while maintaining the quality of service requirements. Thus, the need for seamless inter-working between heterogeneous wireless communication systems consisting of multiple radio access technologies and overlapping networks emerges. In this article, we address the main issues that arise while implementing the interworking mechanisms between different radio access networks. An interworking mechanism based on IEEE 802.21 framework is proposed and described in detail. We combine concepts of autonomic computing in the design of the framework in order to use intelligence to provide flexibility, accessibility and transparency to the mobile users.

Satellite digital video broadcasting is deeply changing: the next generation is dedicated to packet based communications and introduces (like many modern physical layers: WiMax, HSDPA, ...) fade mitigation techniques leading to variable throughput. Such tremendous changes need to be taken into account and introduce the need for a scheduling entity. This paper investigates the opportunity to implement classical scheduler techniques tailored to suit fade mitigation techniques. With the help of a dedicated encapsulation scheme allowing fragmentation and concatenation, we show that stability can be achieved even at high load with basic algorithms. We then show that reclassification (an opportunity that can be described as a side effect of fade mitigation techniques) induces a significant improvement on the system performance.

Supporting future large-scale vehicular networks is expected to require a combination of fixed roadside infrastructure and mobile in-vehicle technologies. The need for an infrastructure, however, considerably decreases the deployment area of VANET applications. In this paper, we propose a self-organizing mechanism to emulate a geo-localized virtual infrastructure (GVI). This latter is emulated by a bounded-size subset of vehicles currently populating the geographic region where the virtual infrastructure is to be deployed. An analytical model is proposed to study this mechanism. More precisely, this model is proposed to study the GVI in the frame of its main use: data dissemination in VANETs. Despite being simple, the proposed model can accurately predict the system performance such as the probability that a vehicle is informed, and the average number of duplicate messages received by a vehicle, and allows a careful investigation of the impact of vehicular traffic properties and system parameters on performance criteria. Analytical and simulation results show that the proposed GVI mechanism can periodically disseminate the data within an intersection area, efficiently utilize the limited bandwidth and ensure high delivery ratio.

Wireless sensor networks (WSN) have received much attention during the last few years especially with regard to energy consumption and scalability. In this paper, we will focus on mechanisms which may be implemented for small WSNs. So, in the present work, we design energy-aware self-organization algorithms for WSNs in such a context. These algorithms can be used to design effective and adaptive protocols. The first protocol concerns the initialization or the setting up of the network topology under a chain form. The second one (steady-state protocol) implements the communication part or the information exchange between the different nodes of the chain. Our algorithms were dimensioned and validated by an analytical model. We also perform a detailed study of these algorithms by using TOSSIM, a simulation environment for TinyOS, the operating system for the Berkeley sensor nodes. Finally, we achieve an experimental test using Tmote Sky nodes, a popular commercial hardware platform for wireless sensor systems. The results emphasize the interest of the proposed algorithms.

In this paper, we investigate the use of a size-based scheduling policy, LASTOTAL, inWLANs. A size-based scheduling policy is a priority policy where the priority of a flow is based on its size. LASTOTAL replaces the legacy IP level FIFO scheduler at the access point. The lower protocol layers, and especially the MAC 802.11 layer are left unchanged. We demonstrate using realistic synthetic workloads, that LAS-TOTAL solves the unfairness issue due to DCF in 802.11 WLANs and ensures small response times to the majority of the flows under any load conditions. The latter property is desirable as short flows correspond to interactive applications and maintaining low response times for those flows despite load variations, significantly improves user experience. We also introduce and validate Markovian queuing models to assess the response time of the access point for both FIFO and LASTOTAL.

We consider a channel aware scheduling for the downlink multi-service flows in orthogonal frequency division multiple access (OFDMA) based mobile WiMAX (Worldwide Interoperability for Microwave Access)system. We propose an intelligent medium access control (MAC) that adapts with the physical layer in response to the different QoS requirements of the diverse service flows in the system. This adaptation is represented by a joint packet scheduling and slot allocation scheme interaction in both MAC and PHY layers. Based on this interaction, a fair and efficient QoS guaranteed resource allocation for a mixed real-time and non real-time service flows is achieved. We provide extensive simulation results showing the performance aspects of the proposed cross-layer scheme.

Next generation networks will be characterized by variable and high data rates, QoS, and seamless mobility, within a network and between heterogeneous networks with different technologies and service providers. In this paper, we consider a model of mobility for WiMAX network users introducing horizontal handover mechanism with channel reservation. We take into account several approaches in order to carry out the reservation. We evaluate the performance of the proposed model. The results show, by means of simulation, that channel reservation mechanism improves horizontal handover without reducing the performance of the system.

Mobility issue and service continuity represent important challenges for next generation networks. The integration of a satellite segment within a terrestrial network (especially WiMAX) has several advantages in a 4G context. In this paper, we focus on channel reservation mechanisms to ensure quality of service. Primary results show, by means of simulation, the gains and limitations of each mechanism. It is shown that the best results are obtained when the mechanisms are performed by the base stations when the density of users is low. Otherwise, cooperative solutions for which reservations are done by neighboring nodes may improve the performance of the system.

We consider a cross-layer scheme for the downlink multiuser Orthogonal Frequency Division Multiple Access (OFDMA) for mobile WiMAX (Worldwide Interoperability for Microwave Access) based on IEEE802.16e. We propose an intelligent Medium Access Control (MAC) that adapts with physical layer in response to the different QoS requirements of the service flows in the system. Our scheme satisfies the maximum delay requirement for real-time service flows as well as minimum reserved data rate for non real-time service flows sessions while maintaining a high capacity of the whole system. We provide extensive simulation results showing the performance aspects of the proposed cross-layer scheme.

IEEE802.16e is expected to support mobility for broadband wireless access with the capability of delivering high data rates over long ranges. We consider IEEE 802.216e scheme for scheduling and mapping higher layer data into the basic resource allocation units (slots) of OFDMA frames. Then, we introduce two simple allocation schemes that consider fair allocation among users with adaptive modulation. Both scheduling and mapping approaches are based on the quality of service (QoS) requirements of each service flow in terms of data rate and bit error rate (BER). The performance of both algorithms is studied by simulation. The results show that the proposed algorithms yield fairness among real-time and non real-time service flows as well as guaranteeing their constraint in term of QoS and outage probability.

Satellite constellations like Orbcomm provide store and forward message communication services. Inter-satellite links (ISL) are not considered in order to keep the system simple and the costs moderate ([1], [2]). Rather, gateways may act as relays between satellites. In this context, routing is important because it helps to control the end-to-end delay and resources utilization (e.g. on-board memory). However, routing must face frequent changes and partitioning of the network because of the satellite motion. Similar routing problems have been studied in the transportation field (e.g. subway and railways). In this contribution, the shortest path problem with time windows (SPPTW) is applied to satellite constellations and a pre-computed routing algorithm is derived. Simulation results show how this algorithm reduces the end-to-end delay of the routes.

Packet-based optical access ring is becoming a promising solution in metropolitan networks. Its performance depends mainly on how optical resource sharing takes place among the different competing access nodes. This network architecture has mostly been explored with regard to synchronous transmission, i.e., slotted wavelength-division multiplexing (WDM) ring. However, in this paper, we focus on the performance of asynchronous transmission-based networks with variable packet sizes. Analytical models are presented in an attempt to provide explicit formulas that express the mean access delay of each node of the bus-based optical access network. We prove that in such a network, fairness problems are likely to arise between upstream and downstream nodes sharing a common data channel. Furthermore, we show that sharing the channel's available bandwidth fairly but arbitrarily between access nodes, as in slotted WDM rings, does not resolve the fairness problem in asynchronous system. In this regard, we exhibit the inherent limitations of the token bucket access rate-based algorithm once applied to asynchronous transmission bus-based networks. To alleviate the aforementioned problem, we device a new strategy called traffic control architecture using remote descriptors. The proposed solution is based on a preventive mechanism to grant access to the shared resource. As illustrated in this paper, the proposed solution alleviates the performance degradation and the resource underutilization, while achieving fairness among bus nodes.

We propose an efficient solution to optimize buffer dumping allowing to reduce significantly the losses caused by buffer overflow. To highlight the proposed architecture we have analyzed its performance compared with different configurations of polling scheme.

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 that 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 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.

The satellite component of the future Universal Mobile Telecommunications System (UMTS) is anticipated to be partly composed of non-geostationary satellites such as Low-Earth Orbit (LEO) satellites. Those networks are designed to support multimedia traffic with different quality of service (QoS) requirements. This paper deals with the performance evaluation of a new channel resource management technique in Low-Earth Orbit (LEO) satellite systems based on a satellite-fixed cell concept. In cellular and satellite networks the resource capacity is shared among handovers and new calls. Forced termination has a significant impact on the quality of service perceived by the users. This is especially the case for those which have delay constraints (such as video or voice traffic). The guard channel scheme is an access priority that has been proposed in order to reduce the handover failure probability. Its effectiveness has been emphasized in terrestrial cellular networks. In this paper, we propose a dynamic reservation scheme for satellite networks which adapts the number of reserved channels, according to the current number of ongoing calls (voice or video traffic) and on the localization of users. A performance evaluation of the proposed mechanism has been carried out by simulations as regards with the blocking probabilities of each type of users.

Satellite systems will be employed to extend the terrestrial cellular networks and to provide a global coverage, for both mobile and fixed users. In these networks, the resource capacity is shared among handoffs and new calls. Forced termination has a significant impact on the user's quality of service. Several mechanisms such us guard channels or handoff queuing have been proposed in order to reduce handoff failure probability. The guard channel scheme consists in giving a prioritized access to the handoff calls. The penalty is the reduction of the total carried traffic. This paper proposes a dynamic reservation scheme for LEO satellite system, which adapts the number of reserved channel according to the current number of ongoing calls and on the localisation of users in the considered area.

This paper deals with the performance evaluation of different channel resource management techniques in low Earth orbit (LEO) satellite systems based on an Earth-fixed cell concept. Both fixed and mobile users have been considered resulting in several classes of users. Each class requires a given quality of service (QoS) and thus a fixed part of the shared resource. Two channel allocation techniques have been investigated: fixed channel allocation (FCA) and dynamic channel allocation (DCA). An analytical model has been derived to analyse the performance of the FCA scheme supporting different kinds of users. A performance comparison of FCA and DCA strategies has also been carried out by simulations as regards the blocking probabilities of each type of users.

In this paper, we investigate two approaches to handle UMTS traffic classes at the AAL2 and ATM layer over the Iub and Iur interfaces in the UMTS Terrestrial Radio Access Network (UTRAN). The first method is proposed to improve the (AAL2-) CPS scheduler by introducing the notion of traffic priority. The second method consists of multiplexing each UMTS traffic class into separate ATM connections with specific QoS. We present some simulation results on ATM/AAL2 performance to evaluate the two methods in terms of mean transmit delays, bounds of transmit delay and bandwidth efficiency.

We investigate a downlink channel assignment scheme for multipoint communications and we propose a new simulcast-based dynamic channel assignment policy for both unicast and multicast connections in LEO satellite networks. In order to reduce co-channel interference power and to avoid intersymbol interference problem, our policy is combined with a power control algorithm. Performance evaluations show that our policy compared to other policies achieve bandwidth optimization and improves the quality of service since it reduces call blocking probabilities for both unicast and multicast connections.

This paper generalizes the classical Jacobaeus (1950) method for evaluating the call blocking probabilities in multistage interconnection networks in the context of ATM type traffic. The aim of this generalization is twofold, first the results are extended to capture the heterogeneous, multirate and multiclass nature of the traffic; second it takes into account a path hunting algorithm inside the interconnection network. Sequential routing is chosen. The kernel of the method is computing occupancy probabilities of interstage links. An aggregation method is used for this computation. The accuracy of the method is shown by comparing with simulation. In addition to call blocking evaluation, the method may easily be extended to include other hunting algorithms.