IMDEA Networks Institute Digital Repository
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A Disjoint Frame Topology-Independent TDMA MAC Policy for Safety Applications in Vehicular Networks
Get PDFMedium access control (MAC) is a challenging problem in vehicular environments due to a constantly changing topology due to vehicle’s mobility and stringent delay requirements, especially for safety-related applications (e.g., for vehicular-to-vehicular communication). Consequently, topology-independent TDMA MAC policies that guarantee a number of successful transmissions per frame independently of the underlying topology, can be regarded as a suitable choice for the particular vehicular environment. One such policy (TiMAC) is revisited and considered in this paper for a vehicular environment and is also extended to one that considers disjoint frames depending on the vehicle’s direction of movement (d-TiMAC). Both TiMAC and d-TiMAC are evaluated against VeMAC – a well-established TDMA MAC protocol in the area of vehicular networks – based on simulations. It is observed that throughput under the considered TiMAC policy is close to that induced by VeMAC, whereas the number of retransmissions is reduced leading to a smaller time delay. Furthermore, the proposed d-TiMAC appears to achieve a higher throughput than VeMAC, and an even lower number of retransmissions (when compared to TiMAC), suggesting that d-TiMAC yields an even smaller time delay. Eventually, this observation is also supported when d-TiMAC is compared against TiMAC showing a further reduced number of retransmissions.pu
I want to be a scientist
No full textIn this talk, IMDEA Networks research engineer Rafael García has explained to a group of 50 sixth degree students at a public primary school what is the day by day of a researcher. With the help of a collection of videos recorded by the own researchers of the Institute, Rafael has explained how we are progressing in areas like device to device communications, visible light communications, millimeter waves, and the future 5G. Moreover, the videos included some advices and and a detailed explanation of the steps required to become a scientist where, as professor Antonio Fernández explains, the motivation and personal goals play a critical role.FALSEpu
Data Fusion for Hybrid and Autonomous Time-of-Flight Positioning
Get PDFExisting mobile devices such as smartphones rely on a multi-radio access technology (RAT) architecture to provide pervasive location information in various environmental contexts as the user is moving. Yet, existing architectures consider the different localization technologies as monolithic entities and choose the final navigation position from the RAT that is expected to provide the highest accuracy. In contrast, we propose to fuse timing range measurements of diverse radio technologies in order to circumvent the limitations of the individual radio access technologies. We take a first step in this direction and propose to fuse timing measurements of satellite navigation system and WiFi networks. We introduce different novel methods such as a data fuser, an estimator of WiFi ToF distance and a geometrical-statistical approach to best fuse the set of timing ranging measurements in presence of a rich set of measurements. Experimental results show that our solution allows the mobile device to efficiently self-position itself in diverse challenging scenarios.TRUEpu
DenseVLC: A Cell-Free Massive MIMO System with Distributed LEDs
Get PDFLED luminaries are now deployed densely in indoor areas to provide uniform illumination. Visible Light Communication (VLC) can also benefit from this dense LED infrastructure. In this paper, we propose DenseVLC, a cell-free massive MIMO system enabled by densely distributed LEDs, that forms different beamspots to serve multiple receivers simultaneously. Given a power budget for communication, DenseVLC can optimize the system throughput by properly assigning the power budget among the distributed LEDs. We formulate an optimization problem to derive the optimal policy for the power allocation. Our insights from the optimal policies allow us to simplify DenseVLC’s system design and propose a heuristic algorithm that can reduce the complexity by 99.96%. Besides, we propose a novel synchronization method using nonline-of-sight VLC to synchronize all the transmitters that will form a beamspot to serve the same receiver. We implement DenseVLC with off-the-shelf devices, solve practical challenges in the system design, and evaluate it with extensive and realistic experiments in a system of 36 transmitters and 4 receivers in an area of 3 m × 3 m. Our results show that DenseVLC can improve the average system throughput by 45%, or improve the average power efficiency by 2.3 times, while maintaining the requirement for uniform illumination.TRUEpu
Design and Analysis of 5G Scenarios with simmer: An R Package for Fast DES Prototyping
Get PDFSimulation frameworks are important tools for the analysis and design of communication networks and protocols, but they can be extremely costly and/or complex (for the case of very specialized tools), or too naive and lacking proper features and support (for the case of ad-hoc tools). In this article, we present an analysis of three 5G scenarios using simmer, a recent R package for discrete-event simulation that sits between the above two paradigms. As our results show, it provides a simple yet very powerful syntax, supporting the efficient simulation of relatively complex scenarios at a low implementation cost.pu
Performance Evaluation of a Proposed On-Demand Recharging Policy in Wireless Sensor Networks
No full textTRUEpu
Experimental Performance Evaluation of WebRTC Video Services over Mobile Networks
Get PDFWith the rapid growing market for smartphones, and user’s confidence for immediate access to high-quality multimedia content, the delivery of video over wireless networks has become a big challenge. WebRTC is a new and evolving standard that has been developed specifically to meet this
demand and enable a high-quality experience for mobile users
of real time communication services. However, little systematic experimental studies have been carried out so far to assess the service experienced by users in a realistic mobile setting. In this work, we describe measurements collected from a WebRTC implementation operated from real mobile nodes within the pan-European MONROE platform. Using data from application and network, in different wireless environments, we experimentally investigate and compare the performance of WebRTC for static and mobile cellular users of several networks across Europe.TRUEpu
Enabling Multi-Mission Interoperable UAS Using Data-Centric Communications
Get PDFWe claim the strong potential of data-centric communications in Unmanned Aircraft Systems (UAS), as a suitable paradigm to enhance collaborative operations via efficient information sharing, as well as to build systems supporting flexible mission objectives. In particular, this paper analyzes the primary contributions to data dissemination in UAS that can be given by the Data Distribution Service (DDS) open standard, as a solid and industry-mature data-centric technology. Our study is not restricted to traditional UAS where a set of Unmanned Aerial Vehicles (UAVs) transmit data to the ground station that controls them. Instead, we contemplate flexible UAS deployments with multiple UAV units of different sizes and capacities, which are interconnected to form an aerial communication network, enabling the provision of value-added services over a delimited geographical area. In addition, the paper outlines an approach to address the issues inherent to the utilization of network-level multicast, a baseline technology in DDS, in the considered UAS deployments. We complete our analysis with a practical experience aiming at validating the feasibility and the advantages of using DDS in a multi-UAV deployment scenario. For this purpose, we use a UAS testbed built up by heterogeneous hardware equipment, including a number of interconnected micro aerial vehicles, carrying single board computers as payload, as well as real equipment from a tactical UAS from the Spanish Ministry of Defense.pu
Design and Performance of Resource Allocation Mechanisms for Network Slicing
Get PDFNext generation wireless networks are expected to handle an exponential increase in demand for capacity generated by a collection of tenants and/or services with heterogeneous requirements. Multi-tenant network sharing, enabled through virtualization and network slicing, offers the opportunity to reduce operational and deployment costs, and the challenge of managing resource allocations among multiple tenants serving possibly mobile diverse customers. When designing shared radio resource allocation mechanisms, it is as important to provide tenants with customization and isolation guarantees, as it is to achieve high resource utilization and to do so via low complexity and easy to implement algorithms. This thesis is devoted to the design and analysis of resource allocation mechanisms that meet these objectives.
We propose a sharing model in which tenants are assigned a share/budget of a pool of network resources. This share is then redistributed in the form of weights amongst users, which in turn drive dynamic resource allocations which are partially able to adapt to the traffic demands on, and requirements of, different slices customer populations. We propose and analyze two approaches for redistributing slices’ share among customers which we classify into their associated (i) cooperative, and (ii) competitive resource allocations.
In the cooperative resource allocation setting, a pre-established policy is
proposed, in which resources are eventually assigned in proportion to the slice’s share and the relative number of active users in currently has at a resource. This is shown to be socially optimal in a particular setting and simple to implement, with statistical multiplexing gains that increase with the number of tenants and the size of the resource pool. These gains stem from the ability of the scheme to adapt to dynamic loads leading to an up to 50% network capacity savings with respect to static allocations. We further improve these gains by presenting a framework that combines resource allocation and wireless user association which uses limited computational, information, and handoff overheads. However, using our cooperative scheme over a large pool of resources restricts the degree to which a slice can differentiate its customers’ performance at a per resource level. Thus, we study how this trade-off affects the network utility and propose a mechanism to determine an optimal partition the resources into a collection of self-managed pools under cooperative
resource allocations.
Our competitive resource allocation approach enables tenants to reap the
performance benefits of sharing while retaining the ability to customize their own users’ allocations. This setting results in a network slicing game in which each tenant reacts to the user allocations of the others so as to maximize its own customers’ utility. We show that, under appropriate conditions, the game associated with such strategic behavior converges to a Nash equilibrium. At the Nash equilibrium, a tenant always achieves the same, or better, utility than it could achieve under a static partitioning of resources, hence providing the same level of inter-slice protection as static resource partitioning. The network utility of the equilibrium allocations is shown to be, under mild conditions, close to the socially optimal ones. The competitive resource allocation framework is complemented with a study on admission control policies that enable tenants to ensure minimum rate guarantees to their users. Our analysis and extensive simulation results confirm that our framework provides a comprehensive practical solution towards multi-tenant network slicing. We also discuss how our theoretical results fill a gap in the general resource allocation literature for strategic players.Electrical and Computer EngineeringThe University of Texas at Austin, Austin, Texas, USApu
Examining COPPA Compliance at Scale
No full textWe present a scalable dynamic analysis framework that allows for the automatic evaluation of the privacy behaviors of Android apps. We use our system to analyze mobile apps' compliance with the Children's Online Privacy Protection Act (COPPA), one of the few stringent privacy laws in the U.S. Based on our automated analysis of 5,855 of the most popular free children's apps, we found that a majority are potentially in violation of COPPA, mainly due to their use of third-party SDKs. While many of these SDKs offer configuration options to respect COPPA by disabling tracking and behavioral advertising, our data suggest that a majority of apps either do not make use of these options or incorrectly propagate them across mediation SDKs. Worse, we observed that 19% of children's apps collect identifiers or other personally identifiable information (PII) via SDKs whose terms of service outright prohibit their use in child-directed apps. Finally, we show that efforts by Google to limit tracking through the use of a resettable advertising ID have had little success: of the 3,454 apps that share the resettable ID with
advertisers, 66% transmit other, non-resettable, persistent identifiers as well, negating any intended privacy-preserving properties of the advertising ID.TRUEpu