1,720,980 research outputs found
MAC principles for an Ultra Wide Band wireless access
No full textThe Ultra Wide Band (UWB) radio is becoming a promising field for the design of digital communications systems of new conception. This technique, mainly based on the Impulse Radio paradigm, offers great flexibility and enormous potentiality in view of a broadband wireless access. This paper presents the main principles for the development of a multi-access scheme based on the UWB. The principles for the definition of a distributed medium access control for mobile computing applications are described as well as the detailed functional model involved in the capacity-sharing procedures
Joint channel and traffic adaptive packet scheduling over multiaccess radio interfaces
No full textIn the third generation wireless access systems the objective of integrating service classes with different QoS requirements introduces efficient and fair capacity sharing Issues. In this paper we present a general packet scheduling, called CHAOS (Channel Adaptive Open Scheduling) whose objectives are to be adaptive to traffic and so fair with respect to different users, to be adaptive to channel quality in order to improve the radio resources utilization, to use simple algorithms to realize the previous two goals. One key point in the definition of such a scheduling is the knowledge of the channel state: in fact on the basis of the adopted channel model a prediction criteria must be identified
An interference-controlled admission control scheme for QoS support in distributed UWB networks
No full textPower controlled RRC (Radio Resource Control) is
becoming the most attractive paradigm to provide efficient
and flexible access for future wireless communications,
both in public cellular systems and in local area ones. We
aim at investigating how the design of an interferencecontrolled
RRC protocol leads to an efficient support of
traffic requiring Quality of Service (QoS). This work has
been developed in the framework of the European IST
whyless.com project where the Ultra Wide Band (UWB)
radio technology is used to supply an Open Mobile Access
Network. Radio resource management is performed in a
distributed fashion with cooperation among the network
entities, exploiting the UWB characteristics. We propose
an RRC approach based on margins on the desired QoS
and we compare this approach with other proposals
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Distributed radio resource sharing with Ultra Wide Band radio
No full textUltra Wide Band technology is rapidly maturing for multiple access communication purposes. By referring to Impulse Radio realization and to the classic link analysis of multicode time-hopping UWB multiple access schemes we focus on distributed algorithms to share the radio resource capacity in an ad-hoc type of network, handling both best effort and QoS requesting traffic flows. A practical solution is shown to exist and a preliminary performance evaluation is presented, showing the benefit brought about by admission control rules
MAC layer: resource sharing principles and algorithms
No full text"This document aims at laying out a modelling framework and a quantitative approach to the
resource sharing issue in an UWB air interface, where the main issues are: i) multiplexing of best
effort traffic with reservation based traffic with QoS (in terms of delay); ii) distributed algorithms.
Therefore, we assume that traffic offered to the UWB air interface (MAC layer) falls into two
categories: i) Reservation Based (RB) traffic; ii) Best Effort (BE) traffic.
The RB traffic serves those services requiring some guarantees as to throughput (hence transfer
delay). As seen by the MAC entities, the terminal to be addressed (among those that are
“connected”, i.e. reachable) and the bit rate of the MAC layer communication to be set up are given
as input, while the decision variables are the power levels to be used under the constraints on the
maximum transmittable average power and the communication quality (BER).
The BE traffic offers a transfer resource that adapts itself to the available bandwidth at a given
time and in a given point in space. The aim here is to achieve the maximum possible overall
throughput, possibly with fairness constraints, but no guarantees are offered as to achievable
throughput and transfer delay.
The resource sharing among the UWB terminodes requires both signalling and local
measurements.
The rest of the document is structured as follows.
Section 2 summarizes with some detail the derivation of the bit error probability for the UWB air
interface under the fundamental hypothesis of ideal channel with Gaussian additive noise (AWGN
channel). Moreover, unsynchronised randomly coded time hopping sequences are assumed for the
co-existing communications.
Section 3 lays down the principles of the resource sharing starting out from the expression of the
SNR and of the BER derived in the previous Section. A theoretical framework is assessed, and hints
are given as to how a distributed algorithm can exploit the theoretical results.
Section 4 presents a distributed algorithm based on the approach outlined in the previous
Section, by specifying signalling flows for RB and BE traffic.
Section 5 reports the analysis of the proposed algorithms based on simulations
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Radio resource optimization in an UWB wireless access
No full textThe Ultra Wide Band (UWB) radio is a promising technology for wireless digital communications. In this paper we present the main principles for the radio resource sharing in UWB. We describe both the theoretical approach and the practical one and we address the procedures of a MAC protocol for the support of Dynamic Bandwidth service class and Reserved one
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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