751 research outputs found
A dynamic approach to rebalancing bike-sharing systems
Bike-sharing services are flourishing in Smart Cities worldwide. They provide a low-cost and environment-friendly transportation alternative and help reduce traffic congestion. However, these new services are still under development, and several challenges need to be solved. A major problem is the management of rebalancing trucks in order to ensure that bikes and stalls in the docking stations are always available when needed, despite the fluctuations in the service demand. In this work, we propose a dynamic rebalancing strategy that exploits historical data to predict the network conditions and promptly act in case of necessity. We use Birth-Death Processes to model the stations' occupancy and decide when to redistribute bikes, and graph theory to select the rebalancing path and the stations involved. We validate the proposed framework on the data provided by New York City's bike-sharing system. The numerical simulations show that a dynamic strategy able to adapt to the fluctuating nature of the network outperforms rebalancing schemes based on a static schedule
A Study of Path Selection Algorithms for Mobile Video Streaming QoE
This thesis discusses the problem of path selection for video streaming over 4G mobile networks; its final goal is to devise path selection strategies and test them with a pre-existing network simulator. The objective of path selection algorithms is to optimize both the use of network resources and the Quality of Experience of end users, quantified by various objective metrics. We will propose several path selection algorithms for LTE video transmission, testing them with a simulationope
Galectin genes: regulation of expression.
In this review we have summarized the more recent studies on the expression of mammalian galectins. One interesting observation that can be made is that in most of microarrays and/or differential display analysis performed in recent years one or more galectins have been picked up. From a critical evaluation of the pertinent studies the main conclusion that can be drawn is that, although it is not yet clear whether the 14 galectins identified so far have functions in common, a striking common feature of all galectins is the strong modulation of their expression during development, differentiation stages and under different physiological or pathological conditions. This suggests that the expression of different galectins is finely tuned and possibly coordinated. In spite of these observations it is rather unexpected that very few studies have been performed on the molecular mechanisms governing the activity of galectin genes
A QUIC Implementation for ns-3
Quick UDP Internet Connections (QUIC) is a recently proposed transport
protocol, currently being standardized by the Internet Engineering Task Force
(IETF). It aims at overcoming some of the shortcomings of TCP, while
maintaining the logic related to flow and congestion control, retransmissions
and acknowledgments. It supports multiplexing of multiple application layer
streams in the same connection, a more refined selective acknowledgment scheme,
and low-latency connection establishment. It also integrates cryptographic
functionalities in the protocol design. Moreover, QUIC is deployed at the
application layer, and encapsulates its packets in UDP datagrams. Given the
widespread interest in the new QUIC features, we believe that it is important
to provide to the networking community an implementation in a controllable and
isolated environment, i.e., a network simulator such as ns-3, in which it is
possible to test QUIC's performance and understand design choices and possible
limitations. Therefore, in this paper we present a native implementation of
QUIC for ns-3, describing the features we implemented, the main assumptions and
differences with respect to the QUIC Internet Drafts, and a set of examples.Comment: 8 pages, 4 figures. Please cite it as A. De Biasio, F. Chiariotti, M.
Polese, A. Zanella, M. Zorzi, "A QUIC Implementation for ns-3", Proceedings
of the Workshop on ns-3 (WNS3 '19), Firenze, Italy, 201
Quality-Aware Broadcasting Strategies for Position Estimation in VANETs
The dissemination of vehicle position data all over the network is a
fundamental task in Vehicular Ad Hoc Network (VANET) operations, as
applications often need to know the position of other vehicles over a large
area. In such cases, inter-vehicular communications should be exploited to
satisfy application requirements, although congestion control mechanisms are
required to minimize the packet collision probability. In this work, we face
the issue of achieving accurate vehicle position estimation and prediction in a
VANET scenario. State of the art solutions to the problem try to broadcast the
positioning information periodically, so that vehicles can ensure that the
information their neighbors have about them is never older than the
inter-transmission period. However, the rate of decay of the information is not
deterministic in complex urban scenarios: the movements and maneuvers of
vehicles can often be erratic and unpredictable, making old positioning
information inaccurate or downright misleading. To address this problem, we
propose to use the Quality of Information (QoI) as the decision factor for
broadcasting. We implement a threshold-based strategy to distribute position
information whenever the positioning error passes a reference value, thereby
shifting the objective of the network to limiting the actual positioning error
and guaranteeing quality across the VANET. The threshold-based strategy can
reduce the network load by avoiding the transmission of redundant messages, as
well as improving the overall positioning accuracy by more than 20% in
realistic urban scenarios.Comment: 8 pages, 7 figures, 2 tables, accepted for presentation at European
Wireless 201
Tuning of the functional beamforming resolution for wind tunnel measurements
Conventional Frequency Domain Beamforming (CB) is characterised by the frequency
dependency of the mainlobe width and by the presence of sidelobes that limit its dynamic
range. Functional Beamforming (FB) has been introduced with the aim to overcome these
limitations, narrowing the mainlobe and reducing the sidelobe levels. This paper introduces
a strategy to obtain a beamformer with a target mainlobe width that is constant over a
desired frequency range. The idea is to properly adjust the Functional Beamforming order
ν, frequency by frequency, to preserve the mainlobe width. A tuning procedure of the
order ν is presented and applied to a typical wind tunnel setup. A detailed analysis of the
dependency “order ν versus frequency” is discussed and a general formula describing this
dependency is provided. Finally, the effectiveness of the proposed approach is shown both
on simulated and experimental test case
Hidden Markov Model-Based Encoding for Time-Correlated IoT Sources
As the use of Internet of Things (IoT) devices for monitoring purposes
becomes ubiquitous, the efficiency of sensor communication is a major issue for
the modern Internet. Channel coding is less efficient for extremely short
packets, and traditional techniques that rely on source compression require
extensive signaling or pre-existing knowledge of the source dynamics. In this
work, we propose an encoding and decoding scheme that learns source dynamics
online using a Hidden Markov Model (HMM), puncturing a short packet code to
outperform existing compression-based approaches. Our approach shows
significant performance improvements for sources that are highly correlated in
time, with no additional complexity on the sender side.Comment: Preprint version of the paper published in IEEE Communications
Letter
On the Role of Preemption for Timing Metrics in Coded Multipath Communication
Recent trends in communication networks have focused on Quality of Service
(QoS) requirements expressed through timing metrics such as latency or Age of
Information (AoI). A possible way to achieve this is coded multipath
communication: redundancy is added to a block of information through a robust
packet-level code, transmitting across multiple independent channels to reduce
the impact of blockages or rate fluctuation. The number of these links can grow
significantly over traditional two-path schemes: in these scenarios, the
optimization of the timing metrics is non-trivial, and latency and AoI might
require different settings. In particular, packet preemption is often the
optimal solution to optimize AoI in uncoded communication, but can
significantly reduce the reliability of individual blocks. In this work, we
model the multipath communication as a fork-join D/M/(K,N)/L queue, where K
blocks of information are encoded into N>K redundant blocks. We derive the
latency and Peak AoI (PAoI) distributions for different values of the queue
size L. Our results show that preemption is not always the optimal choice, as
dropping a late packet on one path might affect the reliability of the whole
block, and that minimizing the PAoI leads to poor latency performance.Comment: Submitted for publication to the IEEE Transactions on Communication
Lifetime Maximization of an Internet of Things (IoT) Network based on Graph Signal Processing
The lifetime of an Internet of Things (IoT) system consisting of battery-powered devices can be increased by minimizing the number of transmissions per device while not excessively deteriorating the correctness of the overall IoT monitoring. We propose a graph signal processing based algorithm for partitioning the sensor nodes into disjoint sampling sets. The sets can be sampled on a round-robin basis and each one contains enough information to reconstruct the entire signal within an acceptable error bound. Simulations on different models of graphs, based on graph theory and on real-world applications, show that our proposal consistently outperforms state-of-the-art sampling schemes, with no additional computational burden
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