1,721,018 research outputs found
A General Methodology and Key Metrics For Scatternet Formation in Bluetooth
No full textTo fully exploit the capabilities of Bluetooth for the deployment of wireless ad-hoc networks, the scatternet concept has been proposed. A scatternet is constituted by an overlapping of simple structures named piconets, each composed of up to eight devices sharing the same radio channel. A scatternet may present different topological configurations, depending on the number of composing piconets, the role of the involved devices and the configuration of the links. This paper presents a general methodology for the scatternet formation and proposes metrics that can be used to evaluate a the scatternet performance. Several numerical examples are presented and discussed, highlighting the impact of metric selection on the scatternet performance
MIMO underwater acoustic communications over time-varying channels: from theory to practice
Full text linkDespite more than 70% of our planet surface is covered by water, today the underwater world can still be considered largely unknown.
Rivers, lakes, seas and oceans have always been a fundamental resource for human life development, but at the same time they have often represented natural obstacles very hard to surmount.
The most impressive example is probably given by the ocean, whose vastness severely limited geographical explorations and discoveries for tens of centuries.
Anyway, the growing curiosity about what happens below the water surface has gradually led man to immerse in this unknown environment, trying to overcome its inaccessibility and figure out its secrets.
Underwater investigation and exploring have been increasingly supported by technology, advanced over time for different purposes (military, commercial, scientific).
In this regard, providing a communication link between remote users has been recognized as one of the main issues to be addressed.
The first significant solutions derived from the radio-frequency world, subject of study since the 19th century.
Unfortunately both wired and wireless RF inspired signal propagation strategies were not evaluated as successful.
The former ones, since considering the deployment of meters (up to kilometers) of cable in depth, were too costly and difficult, while the latter ones did not offer good performance in terms of communication range due to signal attenuation.
An alternative way, examined with particular interest from the beginning of the 20th century, has been that one offered by acoustics.
Actually, the study of sound and its propagation through different media has been an intriguing topic since the Old World Age, hence the attempt of messaging underwater has seemed to be a great opportunity to convey theoretical principles in a real application.
In addition, not only humans but also marine animals use acoustic waves to communicate, even over several kilometers distances as demonstrated by whales.
So, since already existing in nature, acoustic communications have been considered as potentially successful, furthermore representing an effective trade-off between feasibility and performance, especially if compared to the other electromagnetic signals-based methods.
Communication over RF channels has been extensively investigated so as to become a mature technology.
The thorough knowledge about OSI (Open Systems Interconnection) model physical layer issues has allowed the researchers attention to be drawn to the upper layers.
Following this direction, the recent advances in technology in this field have been accomplished mainly due to novelties in networks managing rather than to enhancements in the signal propagation study.
Moving to acoustics, unfortunately this approach results to be failing if applied in the underwater scenario, as the major challenges rise indeed from physics matters.
The underwater environment is varied and variable, so understanding the mechanisms that govern the propagation of sound in water is a key element for the design of a well-performing communication system.
In this sense, the physical layer has therefore regained the centrality that has been diminished in other contexts.
The underwater acoustic communications can be adopted in a wide range of applications.
The best-known are coastal monitoring, target detection, AUVs (Autonomous Underwater Vehicles) remote control, tsunami alarm, environmental data collection and transmission.
Those ones are very specific activities, so the devices to be employed must sometimes meet very strict requirements.
In this regard, the solutions commercially available provide good performance (that are paid in terms of high costs).
On the other hand, the fact that hardware and software are usually copyrighted leads to have a closed system.
Having reconfigurable devices is instead an opportunity to match the technology with the environment features and variations, especially in real-time applications.
Recently, the need to overcome these constraints has encouraged the debate about underwater technology challenges.
The work by Demirors et al. [1] reports an interesting discussion about the implementation of software-defined underwater acoustic networks (UWANs), highlighting how this solution can provide enhancements in terms of software portability, computational capacity, energy efficiency and real-time reconfigurability.
Furthermore, the authors propose the architecture of a software-defined acoustic modem and evaluate its performance and capabilities with tank and lake experiments.
Considering the comments outlined above, the following dissertation deals with the design of an acoustic communication system.
The preliminary theoretical analysis regarding physical layer concerns, such as signal propagation and channel behavior, represents the starting point from which several proposals regarding the implementation of UWANs are introduced.
In particular the context of Multiple-Input Multiple-Output (MIMO) communications is investigated, presenting several solutions about transmission schemes and receiver implementation.
Furthermore, concerning UWANs management, some strategies for access and error control, established at the data link layer level, are detailed.
It is worth highlighting that the goal of this contribution is not to present a disjointed discussion about the topics just listed.
The objective is instead to propose practical solutions developed hand in hand with theory, making choices firstly by looking at what nature allows
A MAC protocol for Delay-Bounded applications in Wireless Sensor Networks
No full textThe problem of scheduling packet transmissions
for data gathering in wireless sensor networks is
studied in this paper. A scenario is considered where
different sources contemporarily sense an event and signal
the acquired information to a sink. Energy-latency tradeoffs
for data gathering in sensor networks are explored
by means of Integer Linear Programming Formulations.
The objective of the optimization problems defined is to
find minimum latency and minimum energy optimal data
delivery trees, which are defined as aggregates of flows
from multiple sources to a single receiver.
A new distributed MAC protocol explicitly designed for
Delay-Bounded Applications in Wireless Sensor Networks
(DB-MAC) is also introduced. The primary objective of
DB-MAC is to minimize the latency for delay bounded applications.
Energy consumption is also reduced by means of
a path aggregation mechanism that improves path sharing.
Simulation results show that DB-MAC reduces the latency
up to 70% with respect to a CSMA/CA MAC protocol, with
up to 60% less transmissions. The performance of DBMAC
is shown to be closer than CSMA/CA to the optimal values
of latency and energy consumption
SHAPER: a self-healing algorithm producing multi-hop bluetooth scatternets
No full textThis paper deals with scatternet formation in Bluetooth.
A scatternet is an ad hoc network of Bluetooth devices.
Some works in the literature rely on the single-hop hypothesis,
i.e., all devices are in radio visibility of each other. Other works
refer to the more likely circumstance that devices are scattered
in an area where some of them can not directly communicate.
A challenging issue in this latter scenario (often referred to as
multi-hop) is the design of a formation algorithm that: i) operates
in a distributed way; ii) dynamically adapts the topology to the
mobility of devices; iii) forms a scatternet with given topological
properties. In this paper a distributed algorithm for scatternet
formation that gives rise to a tree-like structure is introduced.
The algorithm is shown to present three key properties that make
it innovative with respect to the literature in the field: i) it is fully
distributed and asynchronous; ii) it can be applied in a multi-hop
environment; iii) it operates in order to dynamically adapt the
topology to nodes’ mobility and failures. The key steps and rules
of the algorithm are described and performance results obtained
by simulation are discussed
Optimized Scatternet Topologies for Personal Area Networking in Dynamic Environments
No full textIn a scenario where different radio technologies
cooperate to provide access to the Internet and advanced wireless
services to mobile and nomadic users, Bluetooth is considered an
enabling technology for the Personal Area Networking segment.
To this aim, Bluetooth devices should be able to set-up a wireless
multi-hop network with given topological characteristics and with
limited formation delay. In this work SHAPER, a distributed
algorithm for tree scatternet formation, is enhanced to work
in a dynamic environment where devices enter and leave the
Personal Area Network and require a fast interconnection with
an optimized topology. We define a procedure (called SHAPEROPT)
that produces a meshed topology applying a Distributed
Scatternet Optimization Algorithm (DSOA) on the network built
by SHAPER. Nodes are shown to be able to easily join or
leave the scatternet at any time, without compromising the long
term connectivity. Benefits brought by DSOA are shown by
performance analysis, while the delay for network set-up and
reconfiguration in dynamic environments is shown to be within
acceptable bounds
Understanding Optimal Data Gathering in the Energy and Latency Domains of a Wireless Sensor Network
No full textThe problem of optimal data gathering in wireless sensor networks (WSNs) is addressed by means of optimization techniques. The goal of this work is to lay the foundations to develop algorithms and techniques that minimize the data gathering latency and at the same time balance the energy consumption among the nodes, so as to maximize the network lifetime. Following an incremental-complexity approach, several mathematical programming problems are proposed with focus on different network performance metrics. First, the static routing problem is formulated for large and dense WSNs. Optimal data-gathering trees are analyzed and the effects of several sensor capabilities and constraints are discussed, e.g., radio power constraints, energy consumption model, and data aggregation functionalities. Then, dynamic re-routing and scheduling are considered. An accurate network model is proposed that captures the tradeoff between the data gathering latency and the energy consumption, by modeling the interactions among the routing, medium access control and physical layers.For each problem, extensive simulation results are provided. The proposed models provide a deeper insight into the problem of timely and energy efficient data gathering. Useful guidelines for the design of efficient WSNs are derived and discussed
Understanding optimal data gathering in the energy and latency domains of a wireless sensor network
No full textThe problem of optimal data gathering in wireless sensor networks (WSNs) is addressed by means of optimization techniques. The goal of this work is to lay the foundations to develop algorithms and techniques that minimize the data gathering latency and at the same time balance the energy consumption among the nodes, so as to maximize the network lifetime. Following an incremental-complexity approach, several mathematical programming problems are proposed with focus on different network performance metrics. First, the static routing problem is formulated for large and dense WSNs. Optimal data-gathering trees are analyzed and the effects of several sensor capabilities and constraints are discussed, e.g., radio power constraints, energy consumption model, and data aggregation functionalities. Then, dynamic re-routing and scheduling are considered. An accurate network model is proposed that captures the tradeoff between the data gathering latency and the energy consumption, by modeling the interactions among the routing, medium access control and physical layers. For each problem, extensive simulation results are provided. The proposed models provide a deeper insight into the problem of timely and energy efficient data gathering. Useful guidelines for the design of efficient WSNs are derived and discussed. (c) 2006 Elsevier B.V. All rights reserved
Locally Optimal Scatternet Topologies for Bluetooth Ad Hoc Networks
No full textBluetooth is a promising technology for personal/local area wireless communications. A Bluetooth scatternet is composed of overlapping piconets, each with a low number of devices sharing the same radio channel. This paper discusses the scatternet formation issue by analyzing topological characteristics of the scatternet formed. A matrix-based representation of the network topology is used to define metrics that are applied to evaluate the key cost parameters and the scatternet performance. Numerical examples are presented and discussed, highlighting the impact of metric selection on scatternet performance. Then, a distributed algorithm for scatternet topology optimization is introduced, that supports the formation of a "locally optimal" scatternet based on a selected metric. Numerical results obtained by adopting this distributed approach to optimize the network topology are shown to be close to the global optimum
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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