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Điện thoại di động mạng lưới Radio P14
Mobile Satellite Communication∗ In principle communications satellites provide the same connectivity as terrestrial (wireless and wireline) networks. The advantages of satellites, such as fast wide-area coverage, flexible transmission parameters and cost independence due to distance, are compared with the disadvantages, such as restricted channel capacity because of the frequencies available, orbital positions, need for line-of-sight connectivity and high initial investment besides relatively long signal propagation times. As a result, only certain application areas have been developed for satellites in the past. ...
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GSM and UMTS (P11)
Before the specification of a protocol can be started, it is necessary first to determine the two entities that are exchanging the information. This in turn requires a description of the overall system in terms of entities, such as mobile stations, terminals attached to mobile stations, radio
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GSM and UMTS (P12)
From Analogue Car Telephone to Digital Pocket Phone CEPT took a very much forward looking decision when it decided to create, as early as 1982, the GSM Group with the mandate to define a second generation harmonised cellular system in Europe. At that time, the true market potential for mobile systems was not known. Also many technologies, which became key to the GSM radio design, were just emerging. This is true particularly of cellular networking, digital signal processing and real-time computing...
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GSM and UMTS (P13)
Since its conception in 1988 the Subscriber Identity Module (SIM) has undergone continuous development extending its technical and functional capabilities. Initially, it was defined as a security module to authenticate the user to the network providing, at the same time, some very limited amount of memory for network and private user data. In those days, smart cards were still in their infancy. The technological and market requirements of GSM, its need for a global solution and its growing market power shaped the face of the SIM and changed the world of the smart card....
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GSM and UMTS (P14)
All voice codecs include speech coding (source coding), channel coding (error protection and bad frame detection), concealment of erroneous or lost frames (bad frame handling), Voice Activity Detection (VAD), and a low bit rate source controlled mode for coding background noise. The codecs operate either in the GSM full-rate traffic channel at the gross bit rate of 22.8 kbit/s (FR, EFR, AMR-WB), or in the half-rate channel at the gross bit rate of 11.4 kbit/s (HR), or in both (AMR). AMR and AMR-WB have also been...
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GSM and UMTS (P15)
Security was perceived by some in the first days of GSM as an unnecessary expense. Certainly, initially, all involved considered protection of user data from eavesdropping as more important than authentication of the user, though some questioned whether the perceived complexity of introducing encryption over the radio interface was justified. However, as fraud losses from cloning of analogue phones rocketed in the US and the UK, as the Dutch PTT withdrew all its NMT phones so a form of authentication could be added, and as the Germans introduced simple authentication on its C-Netz system, it became apparent that authentication of...
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GSM and UMTS (P16)
The Mandate by CEPT and the First Action Plan of 1982 The mandate given to the Technical Committee GSM by CEPT in mid-1982 requested the ‘‘harmonisation of a public mobile communication system in the 900 MHz band’’. 2 This decision took place during the very hot promotion phase for ISDN. Therefore it is remarkable to note that GSM was not defined as a ‘‘mobile ISDN’’. Instead the decision leaves the nature of the GSM open, but requests the study of the interconnection with ISDN. ...
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GSM and UMTS (P17)
In this chapter we aim to explain the principles and evolutions of the testing and type approval of the GSM Mobile Equipment (ME). After having recalled the context at the end of the 1980s (paragraph 17.2), we outline the technical background (paragraph 17.3) and we explain the first step of the type approval, i.e. the ‘‘interim type approval’’(paragraph 17.4). Then we describe the TBR regime (paragraph 17.5) and how it evolved to cope with phase 2 (paragraph 17.6) and phase 21 (paragraph 17.7)....
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GSM and UMTS (P18)
What is O&M? Operation and Maintenance (O&M) of telecommunications networks comprises the following functions: Alarm handling and fault management: Indications of malfunctions or outages of any network component are transferred back to the O&M system. The O&M technician can then remotely interact with the network component in question and try to repair the problem. Configuration management: Parameters necessary for network configuration such as frequency plans, next-neighbour relationships or handover algorithms are sent from the O&M centre to all network elements....
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GSM and UMTS (P19)
The Permanent Nucleus in the CEPT Environment Bernard Mallinder 1 ´ During late 1985 the CEPT Groupe Special Mobile (GSM) decided that in the interest of maintaining speed and quality in the development of the technical recommendations, a central support function was required. The mandate for this unit was agreed in early 1986 and the ‘‘Permanent Nucleus’’ (PN) of the GSM was created. The approach and mandate of the unit built on the successful experience that the CEPT had had in the rapid development of specifications for both satellite and ISDN services....
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GSM and UMTS (P20)
SMG 2 has always treated its working methods using a pragmatic approach. Working methods were discussed and agreed when problems arose or in anticipation of problems, and were adapted when practical experiences were made.
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GSM and UMTS (P21)
The Contribution of the GSM Association to the Building of GSM and UMTS Section 1: Cooperation of the Operators from the Agreement of the GSM MoU to the Opening of Service in 1991/1992 Renzo Failli 1 21.1.1 The Main Objectives of the MoU Group in the First Period of its Activity and its Organization The MoU group had its first meeting on 14 October 1987, shortly after the signature of the MoU by the mobile operators of 13 European Countries: Federal Republic of Germany (FRG), France, Belgium, Denmark, Ireland, Finland, Italy, Norway, Netherlands, Portugal, Sweden, UK and Spain...
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GSM and UMTS (P22)
GSM and UMTS Acceptance in the World Section 1: Global Acceptance of GSM Friedhelm Hillebrand 1 22.1.1 Introduction Nobody amongst the early key players expected that GSM would become a global success. There was even deep concern whether it would become a success in all Western European countries. The GSM MoU signed in September 1987 2 differentiated between commitments for CEPT countries and the rest of the world:
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GSM and UMTS (P23)
GSM’s Success Factors Friedhelm Hillebrand 1 23.1 Acceptance in Europe, the First Step The first big step was the success and acceptance in all European countries. GSM was certainly the right product at the right time. There were countries like France and Germany who needed capacity in the early 1990s. Other countries like the UK, Italy, the Nordic countries had high capacity analogue systems. They were attracted by superior GSM features like small hand-held terminals as well as superior services like international roaming, SMS and data services. Also the high security, capacity and quality played an important role....
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Sổ tay của các mạng không dây và điện toán di động P1
Mobility is the most important feature of a wireless cellular communication system. Usually, continuous service is achieved by supporting handoff (or handover) from one cell to another. Handoff is the process of changing the channel (frequency, time slot, spreading code, or combination of them) associated with the current connection while a call is in progress. It is often initiated either by crossing a cell boundary or by a deterioration in quality of the signal in the current channel.
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Sổ tay của các mạng không dây và điện toán di động P2
It has been known for over one hundred years that radio can be used to keep in touch with people on the move. However, wireless communications using radio were not popular until Bell Laboratories developed the cellular concept to reuse the radio frequency in the 1960s and 1970s [31]. In the past decade, cellular communications have experienced an explosive growth due to recent technological advances in cellular networks and cellular telephone manufacturing.
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Sổ tay của các mạng không dây và điện toán di động P3
The tremendous growth of the mobile users’ population coupled with the bandwidth requirements of new cellular services is in contrast to the limited spectrum resources that have been allocated for mobile communications. The objective of channel allocation is to assign a required number of channels to each cell such that efficient frequency spectrum utilization is provided and interference effects are minimized.
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Sổ tay của các mạng không dây và điện toán di động P4
In a cellular network, there are ongoing requests for communication links from mobiles in each cell to the base stations responsible for the cell. In FDMA or TDMA networks, the available spectrum is divided into narrow frequency channels, and each communication request is served by the assignment of a frequency channel. Spectrum is a scarce resource, and careful assignment of channels to calls is critical to being able to maximize the number of users in the network.
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Sổ tay của các mạng không dây và điện toán di động P5
Due to rapid growth in the use of wireless communication services and the corresponding scarcity and high cost of radio spectrum bandwidth, it has become increasingly important for cellular network operators to maximize spectrum efficiency. Such efficiency can be achieved by optimal frequency reuse, i.e., the simultaneous use of the same part of the radio spectrum by communication links in different locations of the network.
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Sổ tay của các mạng không dây và điện toán di động P6
The rapid technological advances and innovations of the past few decades have pushed wireless communication from concept to reality. Advances in chip design have dramatically reduced the size and energy requirements of wireless devices, increasing their portability and convenience. These advances and innovations, combined with the freedom of movement, are among the driving forces behind the vast popularity of wireless communication.
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Sổ tay của các mạng không dây và điện toán di động P7
Currently, users identify wireless networks with first- and second-generation cellular telephony networks. Although voice and short messaging have driven the success of these networks so far, data and more sophisticated applications are emerging as the future driving forces for the extensive deployment of new wireless technologies. In this chapter, we will consider future wireless technologies that will provide support to different types of traffic including legacy voice applications, Internet data traffic, and sophisticated multimedia applications...
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Sổ tay của các mạng không dây và điện toán di động P8
Recent years have witnessed a tremendous growth in the wireless networking industry. The growing use of wireless networks has brought the issue of providing fair wireless channel arbitration among contending flows to the forefront. Fairness among users implies that the allocated channel bandwidth is in proportion to the “weights” of the users.
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Sổ tay của các mạng không dây và điện toán di động P9
In recent years, wireless and mobile communications have seen explosive growth both in terms of the number of services provided and the types of technologies that have become available. Indeed, cellular telephony, radio paging, cellular data, and even rudimentary multimedia services have become commonplace and the demand for enhanced capabilities will continue to grow into the foreseeable future [6, 12, 43, 46].
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Sổ tay của các mạng không dây và điện toán di động P10
A radio network (RN, for short) is a distributed system with no central arbiter, consisting of n radio transceivers, henceforth referred to as stations. In a single-channel RN, the stations communicate over a unique radio frequency channel known to all the stations. A RN is said to be single-hop when all the stations are within transmission range of each other.
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Sổ tay của các mạng không dây và điện toán di động P11
We have been witnessing in the past few years the rapid growth of wireless data applications in the commercial market thanks to the advent of wireless devices, wireless highspeed networks, and supporting software technologies. We envisage that in the near future, a large number of mobile users carrying portable devices (e.g., palmtops, laptops, PDAs, WAP phones, etc.) will be able to access a variety of information from anywhere and at any time.
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Sổ tay của các mạng không dây và điện toán di động P12
It is expected that in many countries digital broadcasting systems will mostly replace current FM radio and television technology in the course of the next one or two decades. The digital media not only offer superior image and audio quality and interesting new types of multimedia data services “on the air,” but also have the potential to employ the scarce resource of broadcast frequencies much more efficiently.
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Sổ tay của các mạng không dây và điện toán di động P13
The Internet has undergone a spectacular change over the last 10 years in terms of its size and composition. At the heart of this transformation has been the evolution of increasingly better wireless networking technologies, which in turn has fostered growth in the number of mobile Internet users (and vice versa). Industry market studies forecast an installed base of about 100 million portable computers by the year 2004, in addition to around 30 million hand-held devices and a further 100 million “smart phones.”...
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Sổ tay của các mạng không dây và điện toán di động P14
The fusion of computer and telecommunication technologies has heralded the age of information superhighway over wireline and wireless networks. Mobile cellular communication systems and wireless networking technologies are growing at an ever-faster rate, and this is likely to continue in the foreseeable future. Wireless technology is presently being used to link portable computer equipment to corporate distributed computing and other sources of necessary information.
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Sổ tay của các mạng không dây và điện toán di động P15
Future information technology will be mainly based on wireless technology [49, 50, 56]. Traditional cellular and mobile networks are still, in some sense, limited by their need for infrastructure (i.e., base stations, routers). For mobile ad hoc networks, this final limitation is eliminated. Ad hoc networks are key to the evolution of wireless networks [48]. Ad hoc networks are typically composed of equal nodes that communicate over wireless links without any central control.
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Sổ tay của các mạng không dây và điện toán di động P16
Wireless multihop networks, also known as packet radio networks and ad hoc networks, hold great promise for providing easy to use mobile services for many applications, especially military and disaster relief communications. Such networks can provide robust communication, be rapidly deployed, and respond quickly in dynamic environments. However, effectively deploying and utilizing such networks poses many technical challenges. One such challenge is to make effective use of the limited channel bandwidth....
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