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Poster abstract: Practical Limits of WiFi Time-of-Flight Echo Techniques
Get PDFTime-of-flight echo techniques have been proposed to estimate the distance between a local and a target station over regular WiFi radio devices. Their current main shortcoming is that they are affected by severe noise components at both stations. Our aim in this work is to quantify the noise level introduced by the target in order to derive practical limits of the ranging accuracy achievable using off-the-shelf devices. For this purpose, we develop a low-noise experimental platform which allows us to measure the echo-reply delay with very high accuracy. Our preliminary results with two popular chipsets from different manufacturers show that the median echo-reply delay at the target is never equal to the nominal SIFS value, and it deviates by approximately 10-20 ns over time, suggesting a practical ranging accuracy limit of 3 m.TRUEpu
A Model for Throughput Prediction for Mobile Users
Get PDFIn this paper we propose a stochastic model to predict user throughput in mobile networks. In particular, the model accounts for uncertainty such as random phenomena (e.g., fast fading) or inexact information (e.g., user location) to derive the statistical distribution of the user throughput. Such a model is highly useful for aiding scheduling and resource allocation decisions. In addition, we provide a taxonomy of prediction techniques to investigate error sources and the main characteristics of prediction accuracy.
Finally, we show the versatility of the model by analyzing LTE user throughput for the case where knowledge of either the user's actual position or the congestion level in the cell is inexact.TRUEpu
The Fair Distribution of Power to Electric Vehicles: An Alternative to Pricing
No full texthttp://dx.doi.org/10.1109/SmartGridComm.2014.7007727As the popularity of electric vehicles increases, the demand for more power can increase more rapidly than our ability to install additional generating capacity. In the long term we expect that the supply and demand will become balanced. However, in the interim the rate at which electric vehicles can be deployed will depend on our ability to charge these vehicles without inconveniencing their owners. In this paper, we investigate using fairness mechanisms to distribute power to electric vehicles on a smart grid. We assume that during peak demand there is insufficient power to charge all the vehicles simultaneously. In each five minute interval of time we select a subset of the vehicles to charge, based upon information about the vehicles. We evaluate the selection mechanisms using published data on the current demand for electric power as a function of time of day, current driving habits for commuting, and the current rates at which electric vehicles can be charged on home outlets. We found that conventional selection strategies, such as first-come-first-served or round robin, may delay a significant fraction of the vehicles by more than two hours, even when the total available power over the course of a day is two or three times the power required by the vehicles. However, a selection mechanism that minimizes the maximum delay can reduce the delays to a few minutes, even when the capacity available for charging electric vehicles exceeds their requirements by as little as 5%.TRUEpu
SDN-based Mobility Management in a Dense Small Cells scenario
No full textThe proposed SDN-based Mobility Management solution uses OpenFlow 1.3 as Southbound API and RYU as Network Controller. The Network Controller it is responsible to store the users’ mobility sessions and to configure properly the anchors. By the access network’s point of view, any OpenFlow-enabled node can play the role of anchor. Unlike classical protocol such as GPT and PMIPv6, our solution does not involve any tunnelling mechanism. This can be done by having an IP-based access network where the internal routing is independently driven by MPLS or 802.1Q VLANs. Our implementation deals only the case where the whole access network is Ethernet-based. The internal routing is thus performed using 802.1Q VLANs. As a use case to show the benefits of our SDN-based solution, the MN run multiple flows and a different anchor is selected for each flow. The anchor selection is based on the characteristics of the flows. Furthermore, we cover the use case of network reconfiguration, namely the case when a branch of the network is switched-off for energy saving purpose. In case of anchors placed in the switched-off branch, that have been already assigned and are still active, we show the anchor reassignment mechanism where new anchors are selected in the active branch of the network.FALSEpu
Asymptotic Competitive Analysis of Task Scheduling Algorithms on a Fault-Prone Machine
Get PDFReliable task execution in systems with machines that are prone to unpredictable crashes and restarts is challenging and of high importance. However, not much work exists on the worst case analysis of such systems. In this work, we analyze the fault-tolerant properties of four popular scheduling algorithms, Longest In System, Shortest In System, Largest Processing Time and Shortest Processing Time, under worst case scenarios on a fault-prone machine. We define three metrics for the evaluation and comparison of their competitive performance in the long run, namely, completed cost, pending cost and latency. We also investigate the effect of resource augmentation by increasing the speed of the machine. Finally, we compare their behavior for different speed intervals concluding that each of them behaves better than the rest under different circumstances and none is clearly the best.TRUEpu
HyCloud: A system for device-to-device content distribution controlled by the cloud
Get PDFThe exponential growing demand of mobile Internet data traffic requires a rethinking of current infrastructures and calls for innovative approaches that provide online-streaming of content to interested subscribed mobile users. We introduce a mobile system called HyCloud for device-to-device content distribution. HyCloud delivers the content from a cloud backend, and it can reduce the total amount of data transferred through the cellular network by exploiting the similarity of interests among multiple mobile users. Our preliminary real-life experiment with video streaming with a simple content scheduler shows that the system can save in average 24% (and up to 38%) of data downloaded by the cellular connection.TRUEpu
Tangled: Analysis of AS-level Interconnection in LAC region
No full textDue to its importance, the Internet topology at the Autonomous System(AS) level has been attracting much attention from the research community for over a decade. Internet connectivity is increasingly recognized as a fundamental lever for development, triggering socio-economic progress in the society as a whole. Rich local interconnections between the ASes within a region make up a reliable Internet environment, which further helps to foster the Internet business in the region by promoting innovation and empowering local Internet entities to grow.
We propose an empirical study of the topological organization of the Internet ecosystem in Latin America and the Caribbean (LAC).
While basic connectivity to the global Internet exists throughout the region, the availability and quality of the infrastructure varies widely between different countries or even between different geographical areas within the same country. Using BGP routing data and information about the business relationship between ASes active in the region, we build the graph of Internet connectivity at the country level. We identify how many international ASes operate locally, connecting the local network to other countries within the region and to the global Internet. Based on this information, we analyze how prone a country is to disconnection, both as a consequence of government censorship or external attacks on the local Internet ecosystem. Next, we characterize Internet performance in LAC and observe very high latency between different countries and, sometimes, even within the same country. We observe that a large fraction of paths interconnecting different destinations circuit through the US, and quantify the fraction of destinations in the LAC region that are possibly affected by this phenomenon.FALSEpu
Do Optional Activities Matter in Virtual Learning Environments?
Get PDFVirtual Learning Environments (VLEs) provide students with activi-ties to improve their learning (e.g., reading texts, watching videos or solving exercises). But VLEs usually also provide optional activities (e.g., changing an avatar profile or setting goals). Some of these have a connection with the learn-ing process, but are not directly devoted to learning concepts (e.g., setting goals). Few works have dealt with the use of optional activities and the relation-ships between these activities and other metrics in VLEs. This paper analyzes the use of optional activities at different levels in a specific case study with 291 students from three courses (physics, chemistry and mathematics) using the Khan Academy platform. The level of use of the different types of optional ac-tivities is analyzed and compared to that of learning activities. In addition, the relationship between the usage of optional activities and different student be-haviors and learning metrics is presented.TRUEpu
A Survey on Device-to-Device Communication in Cellular Networks
Get PDFDevice-to-Device (D2D) communication was initially proposed in cellular networks as a new paradigm to enhance network performance. The emergence of new applications such as content distribution and location-aware advertisement introduced new use-cases for D2D communications in cellular networks. The initial studies showed that D2D communication has advantages such as increased spectral efficiency and reduced communication delay. However, this communication mode introduces complications in terms of interference control overhead and protocols that are still open research problems. The feasibility of D2D communications in LTE-A is being studied by academia, industry, and the standardization bodies. To date, there are more than 100 papers available on D2D communications in cellular networks and, there is no survey on this field. In this article, we provide a taxonomy based on the D2D communicating spectrum and review the available literature extensively under the proposed taxonomy. Moreover, we provide new insights into the over-explored and under-explored areas which lead us to identify open research problems of D2D communication in cellular networks.pu