1,720,966 research outputs found
A new interference aware on demand routing protocol for vehicular networks
No full textVehicular communication systems represent one of the most desirable technologies when the safety, efficiency and comfort of everyday road travel need to be improved. The main advantage is the absence of an infrastructure, typical of centralized networks, that makes them very scalable and adequate for highly-variable network topologies. On the other hand, communication protocols become very complex and, sometimes, signaling overhead may waste bandwidth availability. Vehicular Ad-hoc NETworks (VANETs) are able to provide wireless networking capability in situations where no fixed infrastructure exists and the communication among nodes can be either direct or made via relaying nodes, as in the classical ad-hoc networks. In order to relieve the effects of the co-channel interference perceived by mobile nodes, transmission channels are switched on a basis of a periodical Signal-to-Interference Ratio (SIR) evaluation. The attention is focused on the routing level of VANET and we propose an interference aware routing scheme for multi-radio vehicular networks, wherein each node is equipped with a multi-channel radio interface. A new metric is also proposed, based on the maximization of the average SIR level of the connection between source and destination. Our solution has been integrated with the AODV routing protocol to design an enhanced Signal-to-Interference- Ratio-AODV (SIR-AODV). NS-2 has been used for implementing and testing the proposed idea, and significant performance enhancements were obtained, in terms of throughput, packet delivery and, obviously, interference. © 2011 Society for Modeling & Simu
A new Markovian approach for dynamic bandwidth allocation in wireless networks
No full textIn wireless networking, users mobility has a heavy impact on QoS parameters and the existing architectures for real-time services with motionless hosts become inadequate for QoS management. In particular Doppler shift and multipath fading introduce some degradations in wireless transmissions. For these reasons, the management of real-time flows and handover events (in terms of bandwidth guarantee and service continuity) when the system is dealing with Mobility Independent Predictive (MIP) services is mandatory, if QoS constraints need to be satisfied. In order to offer a soft QoS increasing the total system utilization, a bandwidth reallocation algorithm has been considered for dynamic resource adaptation, based on wireless channel modeling, in order to take into account the degradations related to the channel state conditions. The main idea of this proposal is the utilization of a pre-reservation phase in the admission control through a Markovian approach, in order to predict the amount of bandwidth needed by a mobile host during its movements among active and passive cells. The performance evaluation of the proposed idea has been made in terms of total admitted/dropped MIP flows, assigned bandwidth and system utilization. © 2012 IEEE
A Predictive Cross-Layered Interference Management in a Multichannel MAC with Reactive Routing in VANET
No full textVehicular ad hoc networks (VANETs) represent a particular mobile technology that permits communication between vehicles, offering security and comfort. Nowadays, distributed mobile wireless computing is becoming a very important communication paradigm, due to its flexibility to adapt to different mobile applications. In this work, an interference aware metric is proposed in order to reduce the level of interference between each pair of nodes at the MAC and routing layer. In particular, this metric with a prediction algorithm is proposed to work in a cross-layered MAC and an on-demand routing scheme in multi-radio vehicular networks, wherein each node is equipped with two multi-channel radio interfaces. The proposed metric is based on the maximization of the average signal-to-interference ratio (SIR) level of the connection between source and destination. In order to relieve the effects of the co-channel interference perceived by mobile nodes, transmission channels are switched on a basis of a periodical SIR evaluation. Our solution has been integrated with an on-demand routing scheme but it can be applied to other routing strategies. Three on-demand interference aware routing schemes integrating IEEE 802.11p Multi-channel MAC have been tested to assess the benefits of the novel metric applied to a vehicular context. NS-3 has been used for implementing and testing the proposed idea, and significant performance improvements were obtained: in particular, the proposed policy has resulted in an enhancement of network performance in terms of throughput and packet delivery ratio
A new channel assignment scheme for interference-aware routing in vehicular networks
No full textMobile computing and vehicular communications are becoming a very important paradigm for wireless communications, mainly because of their ability to adapt to different mobile applications. In this paper, we propose a new scheme for reducing the interference level during mobile transmissions in the VehiculAr inter-NETworking (VANET) environment, taking the advantage of the multi-channel nature of IEEE802.11p standard. In order to relieve the effects of the cochannel interference perceived by mobile nodes, transmission channels are switched on a basis of a periodical Signal-to- Interference Ratio (SIR) evaluation. The attention is focused on the routing level of VANET and we propose an interference aware routing scheme for multi-radio vehicular networks, wherein each node is equipped with a multi-channel radio interface. A new metric is also proposed, based on the maximization of the average SIR level of the connection between source and destination. Our solution has been integrated with the AODV routing protocol to design an enhanced Signal-to- Interference-Ratio-AODV (SIR-AODV). NS-2 has been used for implementing and testing the proposed idea, and significant performance enhancements were obtained, in terms of throughput, packet delivery and, obviously, interference. ©2011 IEEE © 2011 IEEE
Pattern prediction in infrastructured wireless networks: Directional vs temporal statistical approach
No full textThe main desire of end-users of a telecommunication system is to take advantage of satisfactory services, in terms of Quality of Service (QoS), especially when they pay for a required needing. Unfortunately, when hosts are moving into an infrastructured network, it is very important to mitigate hand-over effects, which may cause heavy flow degradations or disruptions. In this paper, we are interested in investigating how the continuity of services can be guaranteed in QoS networks, by the analysis of users mobility from two different points of view: the first based on a directional modeling of users mobility, the second based on a time-based modeling of Cell Permanence Time (CPT). After a hand-over event, bandwidth availability should always be granted for those users who need to take benefits from QoS networks: the only way to face this issue is represented by the employment of a mobility prediction scheme, in order to know 'how and when' users move among infrastructured coverage areas. Based on a large number of experiments, the proposed schemes are then compared, in order to observe what are the benefits of the considered policies and when it is preferred to use each of them. © 2013 IEEE
Modeling the Prediction of the Effect of the Molecular Weight Distribution of Polymer Products
No full textVehicular networking and channel modeling: A new Markovian approach
No full textVehicular networking is rapidly growing in the last years, due to its ability of enhancing users everyday-life, in terms of comfort, security and QoS. New services are being implemented and the research activity on the topic is embracing different OSI layers, like the network and application ones. Many efforts have been also given at the PHY layer. In this paper we focus our attention on a new approach for modeling the wireless channel of VANETs communications. In the literature many channel models have been proposed, 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 IEEE802.11p channel model based on Discrete Time Markov Chain (DTMC) modeling, useful in every simulation context. The proposed model is called Markovian Vehicular Channel Model (MVCM) and it is based on the concept of Packet Error Rate (PER) discretization: we do not consider the performance analysis at the bit level, but we derive the proposed model by computing the PER, associated to different observation times. The effectiveness of the proposed idea has been evaluated through a deep campaign of simulations
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
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