1,720,986 research outputs found
Qos in hybrid WiFi and DVB-RCS networks
No full textNowadays there is an increasing need of broadband communications anytime, anywhere for users requiring multimedia services with quality of service support. This paper deals with the integration of GEO satellite networks and terrestrial wireless networks. Our interest is for a DVB-RCS GEO system integrated with a WiFi terrestrial segment based on the IEEE 802.11b and e standards. Such a scenario is particularly relevant for the provision of multimedia interactive services in emergency areas. In this paper, we focus on a satellite DAMA strategy with related MAC buffer sizing, on the support of FTP and VoIP traffic flows, and on the traffic mapping with the WiFi segment. An ns-2-based simulation tool has been developed that permits to achieve a fine understanding on TCP-MAC interactions in terms of frame and buffer sizes. Finally, referring to the Skyplex DVB-RCS payload on board of HotBird 6 GEO satellite, simulation results have permitted to show the good utilization of resources with the considered DAMA strategy for FTP traffic flows
Resource management in hybrid DVB-RCS and WiFi networks
No full textSatellite networks are an attractive solution to provide broadband communication services anytime, anywhere with quality of service support. The aim of this paper is to study the integration of GEO satellite networks, DVB-RCS-based, with WiFi networks. This is particularly important in emergency scenarios where reliable satellite networks could be integrated with WiFi systems for local mobility support. In this paper, a combined-dynamic resource management scheme, CRA & A/VBDC, is investigated for the satellite segment to support VoIP and FTP elephant connections. A corresponding QoS differentiation is considered in the WiFi segment, based on the IEEE 802.11e standard; in particular, a suitable traffic class mapping is proposed for an efficient interconnection of the DVB-RCS segment with the WiFi one. The obtained results prove the efficiency achieved by the proposed dynamic approach as the number of terminals increases, the good performance obtained with Scalable TCP and the importance of the proposed traffic mapping in the WiFi segment
A survey on mobile satellite systems
No full textSatellite systems represent a significant solution to provide communication services to mobile users in under-populated regions, in emergency areas, on planes, trains, and ships. In all these cases, satellite systems have unique capabilities in terms of robustness, wide area coverage, and broadcast/multicast capabilities. This paper surveys current mobile satellite networks and services from different standpoints, encompassing research issues, recent standardization advances (e.g. mobile extension for DVB-S2/-RCS, DVB-SH) and some operational systems (e.g. Globalstar, Inmarsat BGAN, Iridium, and Thuraya). The last part of this paper is devoted to qualitative and quantitative comparisons of the different mobile satellite systems to understand their characteristics in terms of services, capacity, resource utilization efficiency, and user mobility degree
QoS support in hybrid WiFi and DVB-S networks
No full textThe aim of this paper is to investigate QoS in a hybrid satellite-WiFi network and to study mapping issues in the interconnection of these two segments. We have considered both a DVB-RCS-based satellite network and a wireless system based on IEEE 802.11e. Both TCP-based and UDP-based traffic flows are considered. In the satellite network, a dynamic bandwidth allocation scheme is used that is managed by a network control center: differentiated QoS support is guaranteed by the use of separate queues at the Gateway for distinct traffic classes. An ns-2-based simulator has been implemented to study the hybrid scenario. We have been able to show the impact of both different traffic mapping solutions in the interconnection of the network segment and different channel condition on the TCP performance
A comparison framework for MSSs
No full textSatellite networks can provide the possibility to access communication services on wide areas of the earth; this characteristic coupled with the support of user mobility allows satellite networks having unique features well suited for different scenarios, like: land mobile, aeronautical, maritime, transports, rescue and disaster relief. Mobile satellite networks, however, entail crucial technological challenges, such as: link budget, antenna technologies for both the satellite and the mobile terminal, and efficient utilization of the radio spectrum. This paper investigates these aspects and provides an analytical framework that can be used to evaluate the characteristics of satellite networks in the design phase as well as for their operational phase. In particular, quantitative comparisons are presented here for different systems in terms of supported user density, bandwidth efficiency, and mobility aspects
A mobile satellite systems frame work for network centric applications
No full textCommercial Satellite Communications (SATCOM) provide a range of set-vices to network centric military applications. In addition to fixed satellite systems, a wide range of mobile satellite systems are suitable to support mobile services to emergency applications and communications on the move. The unique capabilities such as robustness, wide area covet-age and broadcast/multicast capabilities make SATCOM a preferred choice for worldwide war fighter communication services. In this paper we survey current mobile satellite networks and services, encompassing recent standardization efforts and currently available and planned systems characteristics. An efficiency comparison is also presented to emphasize the impact different design parameters in selecting a GEO or LEO based system architecture
Non-standardized languages and the Romance grammaticalization cline
No full textNessun abstract pubblicat
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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