Có 40+ tài liệu thuộc chủ đề "TRUYỀN THÔNG DI ĐỘNG"
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Dominating-Set-Based Routing in Ad Hoc Wireless Networks. 20.1 INTRODUCTION. Note that gateway hosts form a dominating set [14] of the corresponding wireless net- work. A subset of the vertices of a graph is a dominating set if every vertex not in the sub- set is adjacent to at least one vertex in the subset. Moreover, this dominating set should be...
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21.1 INTRODUCTION. Mobile ad hoc networks consist of wireless hosts that communicate with each other in the absence of a fixed infrastructure. Thus, routes between two hosts in a network may consist of hops through other hosts in the network. The task of finding and maintaining routes in the network is nontriv- ial since host mobility causes frequent unpredictable topological...
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22.1 INTRODUCTION. One of the major advantages of LEO satellites (as opposed to geostationary—GEO—satellites) is that they are closer to the Earth’s surface. Second, the footprint of each satellite moves continuously, implying a high mobility of the whole network, in contrast with other cellular systems.. 22.2 TOPOLOGIES. All such factors determine the topology of the network, as shown in this...
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In the case of IP, for example, the datagram is not guaranteed to arrive intact at all members of the destination group or in the same order relative to other datagrams [1].. The multicast service is critical in applications characterized by the close collaboration of teams (e.g., rescue patrols, mil- itary battalions, scientists, etc.) with requirements for audio and video...
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Broadcasting is one of the fundamental tasks in network communication. Its goal is to transmit a message from one node of the network, called the source, to all other nodes.. Every node can reach a given subset of other nodes, de- pending on the power of its transmitter and on the topographic characteristics of the sur- rounding region.. Nodes of...
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The mobile node uses two IP ad- dresses: a fixed home address and a care-of address that changes at each new point of at- tachment.. Packets destined to a mobile node are routed first to their home network—a network identified by the network prefix of the mo- bile node’s (permanent) home address. At the home network, the mobile node’s home...
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26.1 INTRODUCTION. The field of mobile computing is the result of the merger of these advances in computing and communication with the aim of providing a seamless and ubiquitous com- puting environment for mobile users. In mobile computing, however, these problems become more difficult to solve, mainly because of the narrow bandwidth of the wireless communication channels, the relatively short...
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27.1 INTRODUCTION. In this chapter, we review the main characteristics of applications of pervasive comput- ing in Section 27.2, discuss the architecture of pervasive computing software in Section 27.3, and review key open protocols in Section 27.4.. 27.2 PERVASIVE COMPUTING APPLICATIONS. Context awareness translates to adaptation of the behavior of an application as a func- tion of its current environment....
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28.1 INTRODUCTION. Another major factor that presents a real opportunity for data networking in indoor environments is the massive growth and usage of the Inter- net. These users might need to send data files to each other, run some local applications or use any of the existing internet-based applications available on wired terminals located within their range. Some of the...
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Multiple Access Protocols for Mobile Communications: GPRS, UMTS and Beyond Alex Brand, Hamid Aghvami Copyright 2002 John Wiley &. This book focuses on issues related to multiple access for cellular mobile communications, with a specific interest in access arbitration through multiple access protocols situated at the lower sub-layer of the second OSI layer, namely the medium access control (MAC)...
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The basic principles of cellular communications were explained in the introductory chapter, and terms such as cluster size and reuse efficiency introduced. In the following, some more considerations on the advantages and limitations of the cellular concept will be made before reviewing first generation (1G) and second generation (2G) cellular communication systems. The emergence of the Internet witnessed in the...
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MULTIPLE ACCESS IN. Multiple access protocols. These can be associated with the first or physical layer in the OSI reference model. For instance, in the case of pure ALOHA, the physical layer is a broadband broadcast channel, which per se does not provide any particular means for multiple access. With the exception of Prasad, one could argue that those authors...
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Release 1997 had a quite fundamental impact on the air interface, due to the introduction of GPRS. 4.1.4 Approach to the Description of the GSM Air Interface. We first describe in Section 4.2 the physical channels available, in OSI terms thus physical layer issues, and then in Section 4.3 the logical channels and how they are mapped onto these physical...
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She does not have to worry about the details of implementation of the next lower layer, but must only be aware of the services it provides. As we want to investigate the performance of multiple access protocols, we are inter- ested in the MAC sub-layer, which will make use of the services provided by the physical layer. We must therefore...
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The PRMA protocol extended for operation on a hybrid CDMA/TDMA air interface is defined in the following. With a few exceptions, this is the only term which will be used in the following. ‘MD PRMA’ does not specify which multiple access scheme is being used, the focus will be on CDMA/TDMA in the next few chapters. In the context of...
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MD PRMA WITH LOAD-BASED ACCESS CONTROL. With access control, the overall packet-loss probability P loss is composed of the packet-dropping ratio P drop. To assess the benefits of load-based access control through so-called channel access functions (CAFs), several benchmarks are introduced. The analysis is expanded to underpin some of the comments made in the introductory chapter of this book on...
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MD PRMA ON CODE-TIME-SLOTS. This chapter is concerned with MD PRMA on perfect-collision code-time-slot channels.. In the first case, the CDMA feature is relinquished, and MD PRMA degenerates to pure PRMA. In the second case, the TDMA feature is relinquished. The performances of pure PRMA, MD PRMA and RCMA will be compared, all with the same number of resource units...
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This last of the three chapters dealing exclusively with MD PRMA-related research results finally treats scenarios that are not limited to voice traffic only. To assess the performance of the prioritised Bayesian broadcast algorithm proposed in the following, a simulation study for different mixtures of voice and data traffic is conducted, where the latter consists either of Web traffic, email...
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The main focus is on the mechanisms that are available for packet access on UTRA FDD and UTRA TDD air interfaces, as provided by release 1999 of the 3GPP specifications. Figure 10.1 The UTRAN architecture. For more information on the radio interface protocol architecture, the reader is referred to 3GPP technical specification . Figure 10.2 Protocol architecture on the radio...
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This concluding chapter provides first an introduction to some of the planned release 5 enhancements to UMTS and the GPRS/EDGE RAN (GERAN). The system would have to be able to deliver IP-based multimedia services efficiently, requiring also enhancements to the air interface. One of the main benefits provided by IP technology is the service flexibility, as already identified in Section...