Although D2D communications have been extensively investigated in the literature, relatively few works have focused on understanding the capacity of direct links in a real setup. In this paper, we propose an empirical characterization of the currently available high-speed D2D technologies in Android, namelyWi-Fi P2P andGoogle Nearby. To this end, we developed a custom Android application calledOcat which interacts with the available D2D APIs and measures the link's goodput. From the experimental campaign, we derive several useful observations. Concerning communication capacity, the goodput between Android devices ranges between 320~Mbits/s when nodes are within 20 meters of each other and 0.1~Mbits/s when the distance grows to 300 meters. Based on the experimental measurements, we propose a model of the upper-bound goodput as a function of the distance between two devices. Using the wireless signal strength as a link measurement, we combine it with the two-ray ground-reflection model to infer the goodput and obtain a good fit for the characterization of D2D links between Android devices. Our findings provide a reality check in regards to actual direct data-exchange capabilities of Android devices and can help assess system performance of D2D applications.

Assessing the performance of opportunistic networks requires a subtle understanding of both contact and intercontact patterns. While the analysis of intercontacts has attracted significant attention from the research community, surprisingly only a few works have focused on explaining what happens during a contact. In this paper, we perform an in-depth analysis of contacts using both empirical measurements and reference models. We make several observations that allow us to better capture the adaptive nature of device-to-device (D2D)links. In particular, in the case of Wi-Fi 5, we show that a slight modification of the nominal modulation scheme is enough to achieve an accurate characterization of opportunistic contacts for some categories of propagation models. As a consequence, we confirm previous observations that the evaluation of protocols and algorithms for D2D networks based on links of fixed rate may lead to inaccurate results. We finally propose a tool that extends mobility traces with plausible values of per-link capacity.

Mobile data traffic is set to triple in three years from now according to Cisco. This trend is a real challenge for operators since wireless capacity is bounded.

This work relies on previous studies that aims at emphasizing the benefit to use Network Coding when one considers a multiple source-destination traffic pattern. This is the case of video transmission between rescue teams on an incident area. The goal of this study is to reduce bandwidth requirements, limited in the case of wireless networks but highly required for the proper functioning of the whole system. In this document, we present the architecture of TenDoc, a software that has been first designed to support any application and that has been adapted especially, here, for the video diffusion case. We also describe a use case scenario to be demonstrated.

One of the challenging features of the TVWS for public safety operation is its variation across space and time. More specifically the available channels are not contiguous and vary from one location to another. In addition the white space available in a given location can vary with time if one or more of the TV band primary users start/stop operation. Public Safety Situation Aware services are a main concern when one strives to provide a standard overview of an incident. This standard overview aims at providing intervention information as refreshed as possible to facilitate Incident Commander/Unified Command (e.g. in the case of an European cooperative intervention that involves different Operations Center). Within this study, we propose to investigate how this service can be supported in a Cognitive Radio Network context by considering the unpredictable availability of spectrum resources. We present a Random Network Coding based technique and evaluate the performance assessment of this technique under Cognitive Radio Network assumptions. We show that even for a very restrictive radio resource access, Public Safety Situation Aware services can be fully supported without interfering with a existing primary user activity.

In this paper, we investigate the ability of using Delay Tolerant Networking (DTN) in Public Safety networks, where bandwidth and storage are constrained. We formalize the problem as a Wardrop equilibrium over a time-discretized graph. Driven by our findings, we propose RECOR, a centralized REsource-Constrained ORacle-based DTN routing mechanism, which spreads the demand across multiple store-carry forward paths to satisfy the node storage and link transport constraints observed in intervention situations. By applying the proposed mechanism to real Bluetooth-based DTN traces, we show that the transmission bottleneck can be compensated, but only up to a certain extent, by increasing storage capacity and delay. We also analyze the benefit of strategies that provide more resources to highly connected nodes (e.g. ambulances and firetrucks) which can then feed incentives and policies for DTN network engineering. Finally, the idea presented here is general and suggests the necessity of trace-driven simulation and specific modeling tools for appropriate design of future DTN resource management policies.

During this last decade, mesh networks have experienced strong growth due to their ability to provide an additional and complementary support for existing infrastructure communication systems. In such a network, routers are supposed to be fixed for short (e.g. public safety deployment) or long (e.g. network operator extension) period. This relative stability of infrastructure makes proactive routing protocols appropriate. One of the well known proactive routing protocols is OLSR (Optimized Link State Routing), which routing decisions are based on exchanges of topology information using all-to-all flooding of local information in order for each router to build a global knowledge of the topology. This study first goal is to improve the performance of topology information flooding in OLSR by introducing network coding techniques, which leads to a decrease of signaling overhead.

We analyze the dynamics of a mobility data set collected in a pipelined disruption-tolerant network (DTN), a particular class of intermittently-connected wireless networks characterized by a 1-D topology. First, we collected and investigated traces of contact times among thousands of participants of a rollerblading tour in Paris. The data set shows extreme dynamics in the mobility pattern of a large number of nodes. Most strikingly, fluctuations in the motion of the rollerbladers cause a typical accordion phenomenon—the topology expands and shrinks with time, thus influencing connection times and opportunities between participants. Second, we show through an analytical model that the accordion phenomenon, through the variation of the average node degree, has a major impact on the performance of epidemic dissemination. Finally, we test epidemic dissemination and other existing forwarding schemes on our traces, and conclude that routing should adapt to the varying, though predictable, nature of the network. To this end, we propose DA-SW (Density-Aware Spray-and-Wait), a measurement-oriented variant of the spray-and-wait algorithm that tunes, in a dynamic fashion, the number of a message copies to be disseminated in the network. The particularity of DA-SW is that it relies on a set of abaci that represents the three phases of the accordion phenomenon: aggregation, expansion, and stabilization. We show that DA-SW leads to performance results that are close to the best case (obtained with an oracle).

We analyze the dynamics of a mobility dataset collected in a pipelined disruption-tolerant network (DTN), a particular class of intermittently-connected wireless networks characterized by a one-dimensional topology. First, we collected and investigated traces of contact times among a thousand participants of a rollerblading tour in Paris. The dataset shows extreme dynamics in the mobility pattern of a large number of nodes. Most strikingly, fluctuations in the motion of the rollerbladers cause a typical accordion phenomenon - the topology expands and shrinks with time, thus influencing connection times and opportunities between participants. Second, we show through an analytical model that the accordion phenomenon, through the variation of the average node degree, has a major impact on the performance of epidemic dissemination. Finally, we test epidemic dissemination and other existing forwarding schemes on our traces, and argue that routing should adapt to the varying, though predictable, nature of the network. To this end, we propose DA-SW (density-aware spray-and-wait), a measurement-oriented variant of the spray-and-wait algorithm that tunes, in a dynamic fashion, the number of a message copies disseminated in the network. We show that DA-SW leads to performance results that are close to the best case (obtained with an oracle).

The proliferation of mobile computing devices and local wireless networks has promoted a growing interest in location-aware systems. The problem with existing positioning techniques is that they are designed to position dimensionless objects. Such an assumption may lead to practical inconsistencies, as objects might overlap in the resulting coordinate system. Moreover, it is usual to neglect the effects of an object volume and its physical characteristics on signal propagation. In the scenario considered throughout this paper (positioning containers in a harbor), such characteristics can be finely estimated. We propose VAPS, a volume-aware positioning system that takes advantage of the waveguide effect generated by containers. Although VAPS is specific to the harbor scenario, its principles can be extended and adapted to other situations. VAPS maps discrete RSSI levels into hop-counts and relies on realistic propagation models to obtain near-perfect positioning at a very low control overhead. Our results demonstrate that, in scenarios where the assumptions made by traditional approaches fail, the new considerations of VAPS do make a difference.

We investigate performance bounds of P2P systems by application of the law of bandwidth conservation. This approach is quite general and allows us to consider various sharing systems such as fixed-rate streaming, VoD-type streaming, and elastic file sharing. Starting from a general law of bandwidth conservation, we consider several specific cases that apply to various P2P systems. For dynamic systems with a stationary arrival process, we show that simple seeding policies result in regimes where the download rates are arbitrarily fast. We consider a case with equal download rate among all peers as well as cases where the download rate is a function of upload rates, inspired by BitTorrent's tit-for-tat policy. In particular, we show that the sustainable proportion of free-riders is closely related to the tit-for-tat parameter.

In this paper, we explore the impact of reference node, or "landmark", placement on the accuracy of the coordinate systems built using topology-based localization techniques. Such techniques employ landmarks to which each node computes its hop-count distance. A node's coordinates is given by the hop-count distance to all landmarks. To our knowledge, our paper is the first to study the impact of landmark placement on the accuracy of the resulting coordinate system. We show that placing landmarks on the periphery of the topology yields more accurate coordinate systems when compared to placing landmarks in the interior of the topology. Nevertheless, our simulation results also show that, in general, if enough landmarks are used, random landmark placement yields comparative performance to placing landmarks on the boundary randomly or equally spaced. This is an important result since boundary placement (especially at equal distances) may turn out to be infeasible and/or prohibitively expensive (in terms of power consumption as well as processing and communication overhead). This is also the first study to consider not only uniform, synthetic topologies, but also, non-uniform topologies resembling more concrete deployments.

In age-based routing protocols, nodes forward data toward a position which is an estimation of the destination's coordinates. The fresher the estimation, the higher the probability to reach the destination. In such a class of solutions, it is fundamental that accurate estimations of nodes' positions be disseminated throughout the network in order for the forwarding algorithm to converge in a reasonable time and with as few hops as possible. In general, dissemination is done following uniform distributions. In this paper, we argue that coordinate dissemination should rely on measured parameters (thus adaptive to the network conditions), such as the mobility of a node. We investigate the impact of node locality on the performance of dissemination algorithms and propose a new algorithm that adjusts the dissemination level of a node's coordinates based on the displacements of the node. Through extensive simulations, we show that our proposal leads to both faster discovery and significant reduction of the overhead when compared to flat solutions.