1,721,007 research outputs found
Interference Aware-based Ad-Hoc on Demand Distance Vector (IA-AODV) ultra wideband system routing protocol
No full textUltra wideband (UWB) systems are communication systems based on a baseband impulsive transmission that has recently excited interest both in the commercial and academic fields. Physical layer aspects and MAC protocols have been intensively investigated in the recent years leading, in some cases, to important and definitive results. However, many questions relating to the UWB network layer are still open. The aim of this paper is to investigate the network layer of the UWB system: for this purpose a new routing protocol called Interference Aware-based Ad-Hoc On Demand Distance Vector (IA-AODV) and based on the interference concept has been proposed. In particular, two distinct metrics are explained in detail: the first one is based on the concept of global interference perceived by each node; the second one is based on the concept of link interference perceived by a node on a wireless path to a generic neighbor. Finally, a comparative analysis between our protocol and Ad-Hoc On Demand Distance Vector (AODV) protocol are carried out in order to show the soundness of our proposal. © 2011 Elsevier B.V. All rights reserved
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
Variations on the Author
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
BER regression analysis of DS-UWB based WPAN
No full textUltra-Wideband (UWB) radio is a viable candidate for short-range multiple access communications in dense multipath environments. This paper analyzes the efficiency of Direct Sequence - UWB physical layer standard proposal in a indoor environment with fixed transmitters and receiver positions. The performance evaluation is carried out using the UWB channel model provided by the IEEE 802.15 channel modelling subcommittee to model the dense multipath indoor environment typical of the UWB system. DS-UWB architecture has been implemented using a Matlab Simulink tool and simulation results are evaluated in terms of Bit Error Rate (BER) vs. transmitter-receiver distance and noise power spectral density. Moreover, a polynomial regression analysis is carried out on simulation results in order to obtain a closed formula to describe, for different scenarios, the BER as a function of data rates, noise Power Spectral Density (PSD) and distance between the transmitter and receiver. © 2007 IEEE
Time and distance dependent DS-SS UWB channel modelling: BER and per evaluation
No full textThe low cost of devices and the possibility of achieving higher data rates without increasing transmitter power make Ultra-Wideband (UWB) radio a viable candidate for short-range multiple access communications in dense multipath environments. This paper analyses the efficiency of the Direct Sequence - Spread Spectrum (DS-SS) physical layer standard proposal in an indoor environment with fixed transmitters and receiver positions. The modelling and the performance evaluation of a new channel model, where impulse response is also distance-dependent, are outlined. Moreover, the performance evaluation of an ideal Minimum Mean Square Error (MMSE) receiver is exploited in terms of distance, noise and data rates dependence. Packet Error Rate (PER) analysis has been carried out by using a polynomial regression technique, through the Matlab tool, on simulation results. Simulation results are evaluated in terms of Bit Error Rate (BER) and PER vs. transmitter-receiver distance. © 2006 IEEE
A new DVB-RCS satellite channel model based on Discrete Time Markov Chain and Quality Degree
No full textDVB-RCS is an open satellite communications standard allowing a bi-directional communication via satellite. These characteristics certainly promoted its enormous diffusion in the commercial area and the academic research interest. In this context, it is very important to test DVB-RCS systems using an efficient satellite channel model. In the literature many channel models have been carried out, but most of them work at the bit level or they investigate only some aspects of channel interaction. In this work we provide a high level satellite channel model based on Discrete Time Markov Chain (DTMC) modeling, useful in every simulation context. Our model, called Quality Degree-DTMC (QD-DTMC), is based on the concept of Quality Degree (QD) of a given observation windows: the idea is not to analyze a single packet, but fixing an observation window and evaluating the QD of the link, computing the Packet Error Rate (PER) associated to the specific window. The effectiveness of the proposed idea has been evaluated through a deep campaign of simulations. © 2013 IEEE
Performance evaluation of the packet error rate of DS-SS physical layer in UWB networks
No full textThe low cost of devices and the possibility of achieving higher data rates without increasing transmitter power make Ultra- Wideband (UWB) radio a viable candidate for short-range multiple access communications in dense multipath environments. This paper analyses the efficiency in terms of PER of Direct Sequence - Spread Spectrum (DS-SS) physical layer standard proposal in an indoor environment with fixed transmitters and receiver positions. The modelling and the performance evaluation of a new channel model, where impulse response is also distance-dependent, are outlined. Simulation results are evaluated in terms PER vs transmitter-receiver distance and number of users
Per analysis and performance evaluation of DS-SS uwb networks
No full textThe low cost of devices and the possibility of achieving higher data rates without increasing transmitter power make Ultra-Wideband (UWB) radio a viable candidate for shortrange multiple access communications in dense multipath environments. This paper analyses the efficiency of the Direct Sequence - Spread Spectrum (DS-SS) physical layer standard proposal in an indoor environment with fixed transmitters and receiver positions. The modelling and the performance evaluation of a new channel model, where impulse response is also distance-dependent, are outlined. Packet Error Rate (PER) analysis has been carried out by using a polynomial regression technique, through the Matlab tool, on simulation results obtaining an expression for the PER as function of distance and packet length. Simulation results are evaluated in terms of PER vs transmitter-receiver distance. © 2006 IEEE
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