GPS 通信系统外文文献 英文文献.docx

《GPS 通信系统外文文献 英文文献.docx》由会员分享，可在线阅读，更多相关《GPS 通信系统外文文献 英文文献.docx（25页珍藏版）》请在淘文阁 - 分享文档赚钱的网站上搜索。

1、附录A译文全球移动通信系统移动系统跨越世界性成功标志是越来越朝着个人化、方便化方向发展。在商业活动中， 人们必须使用移动电话，以便无论何时何地都能实现电话的功能。在快速的个人生活中， 移动电话已成为一种必须，而不仅仅是为了方便。不像固定通信系统那样，很大程度上依靠技术和通信标准，移动通信系统随着个人通 信系统的革命而发生变化。对移动通信系统而言，要获得调整后的武夫，有三个关键因素，即价格、电话的大小 和重量以及网络的花费和质量。如果上述因素实现有困难，特别是前两个，那么市场的发 展将严格受限。固定电话的服务是全球的，相互联系的范围从同轴电缆到光纤，以及人造卫星。世界 通信标准是不同的，但随着普

2、通接口以及对接口转化，相互之间的联系能发生改变。随着 漫游的创建，需要一个复杂的网络工作系统，这对于移动通信而言是一个非常复杂的问题。 因此，移动通信的通信标准问题比固定通信系统标准问题更关键，此外，在移动通信领域 无线电频谱分配问题也非常使人烦恼。移动通信系统是最初工作在频带为450MHz模拟方式（现在仍然有），后来随着数字 式GSM发展,工作在频带为900 MHz,之后随着个人通信系统的发展,工作的频带为1800 MHz。移动通信系统的历史可分为几代。第一代为美国的先进移动电话系统（AMPS）,欧 洲大部分的全通路通信系统（TACS）,以及北欧的移动电话系统（NMTS）,这些都是模拟 系统

3、。第二代由第一个非常标准的计划支配这个计划由欧洲特殊移动通信系统委员会 （GSM）制定，这个设计作为全球移动通信系统。GSM系统基于蜂窝通信原理，其最早作为一个概念由美国贝尔实验室的工程师们提 出，这一思想出自于增加网络容量的需要以及解决网络堵塞的问题。在人口稠密地区运 行的广播式移动网络系统会由于很少的几个用户同时呼叫而引起堵塞。蜂窝系统的功能在 于允许频率复用。蜂窝的概念由两个特征定义，即频率复用和小区分裂。频率复用的区域相隔非常远， 不会产生同一通道的干扰问题。这允许传递同时呼叫，超过了理论上的频谱容量。当需要 一个小区的通信量到达最大，小区分裂是必须的，那么这个小区被分为一个更小的小区

4、。 蜂窝系统的小区通常被描绘成六角形，一组七个、九个或十二个。附录B外文文献GSM (Global System for Mobile Communication)The success of mobile systems across the world is a sign that communication is moving towards a more personalized, convenient system. People who have to use a mobile phone on business soon begin to realize that the abi

5、lity to phone any time, any place in ones personal life rapidly becomes a necessity, not a convenience.The speed and rapidity with which the personal communications revolution takes place is, unlike fixed transmission systems, highly dependent on technology and communication standards.For mobile the

6、 three key elements to achiexdng sendee take-up are the cost, the size and the weight of the phone, and the cost and quality of the link. If any of these are wrong, especially the first two, then market growth is liable to be severely restricted.The fixed telephone service is global and the intercon

7、nection varies from coaxial cable to optical fiber and satellite. The national standards are different, but with common interfaces and interface conversion, interconnection can take place. For mobile the problem is far more complex, with the need to roam creating a need for complex, networks and sys

8、tems. Thus in mobile the question of standards is far more crucial to success than fixed systems. In addition, there is also the vexed question of spectrum allocation in the mobile area.Mobile systems originally operated in analogue mode (and still do) in the 450 MHz band moving later to 900 MHz wit

9、h digital GSM and then to 1800 MHz with personal communications systems. The history to mobility can split into generations. The first generation systems were the advanced mobile phone systems (AMPS) in the US, total access communication systems (TACS) in most of Europe and Nordic mobile telephone s

10、ystem (NMTS); which were all analogue systems. The second generation is very much dominated by the standard first set out in Europe by the group special mobile (GSM) committee, which was designed as a global mobile communication system.The GSM system is based on a cellular communication principle wh

11、ich was first proposed as a concept in the 1940s by Bell System engineers in the US. The idea came out of the need to increase network capacity and got round the fact that broadcast mobile networks, operating in densely populated areas, could be jammed by a very small number of simultaneous calls. T

12、he power of the cellular system was that it allowed frequency reuse.The cellular concept is defined by two features, frequency reuse and cell splitting. Frequency reuse comes into play by using radio channels on the same frequency in coverage areas that are far enough apart not to cause co-channel i

13、nterference. This allows handling of simultaneous calls that exceed the theoretical spectral capacity. Cell splitting is necessaty when the traffic demand on a cell has reached the maximum and the cell is then divided into a micro-cellular system. The shape of cell in a cellular system is always dep

14、icted as a hexagon and the cluster size can be seven, nine or twelve.The GSM system requires a number of functions to be created for a fully operational mobile system.The cell coverage area is controlled by a base station which is itself made up of two elements. The first element is the transmission

15、 system which communicates out to the mobile and also receives information from it to set up and maintain calls when actually in operation. The baseStation transceiver (BST) is controlled by the base station controller( BSC ), which communicates with the mobile switching center( MSC)-the essential l

16、ink to the local public switched telephone network(PSTN), and to the subscriber data which is stored in registers within the system. The subscriber registers allow the GSM system to check a subscriber who requests the use of the network, allow access and then set up the charging function, etc.The GS

17、M system was allocated part of the 900 MHz band at the 1978 World Administration Conference (WAC), the actual bands being 890 to 915 MHz for the uplink transmission and 935 to 960 MHz for the downlink. The access method is time division multiple access (TDMA).The GSM system operates in a burst trans

18、mission mode with 124 radio channels in the 900 MHz band, and these bursts can carry different types of information. The first type of information is speech, which is coded at 6.5 kb/s or 13 kb/s. The second type is data, which can be sent at 3.6 kb/s, 6 kb/s or 12.6 kb/s. There two forms of transmi

19、ssion are the useful parts of the transmission, but have to be supported by overhead information which is sent in control channels (CCH).The use of digital radio transmission and the advanced handover algorithms between radio cells in GSM network allows for significantly better frequency usage than

20、in analogue cellular systems, thus increasing the number of subscribers that can be served. Since GSM provides a common standard, cellular subscribers will also be able to use their telephones over the entire GSM service area. Roaming is fully automatic between and within all countries covered by GS

21、M system. In addition to international roaming, GSM provides new services, such as high-speed data communication, facsimile and short message service. The GSM technical specifications are designed to work in concert with other standards, e.g. ISDN. Inter-working between the standards is in this way

22、assured. In the long term perspective cellular systems, using a digital technology will become the universal method of telecommunication.The third generation mobile communication system currently being developed in Europe is intended to integrate all the different sendees of the second generation sy

23、stems and cover a much wider range of broadband sendees (voice, data, video, multimedia) consistent and compatible with technology developments taking place within the fixed telecommunication networks.Radio ReceiverA modern radio receiver , whose input signals to this radio are amplitude-modulated r

24、adio waves. The basic electronic circuits include: antenna, tuner, mixer, local oscillator, IF amplifier, audio detector, AF amplifier, loudspeaker, and power supply.Any antenna system capable of radiating electrical energy is also able to abstract energy from a passing radio wave. Since every wave

25、passing the receiving antenna includes its own voltage in the antenna conductor, it is necessary that the receiving equipment be capable of separating the desired signal from the unwanted signals that are also inducing voltages in the antenna. This separation is made on the basis of the difference i

26、n frequency between transmitting stations and is carried out by the use of resonant circuits, which can be made to discriminate very strongly in favor of a particular frequency. It has already been pointed that, by making antenna circuit resonant to a particular frequency, the energy abstracted from

27、 radio waves of that frequency will be much greater than the energy from waves of other frequencies; this alone gives a certain amount of separation between signals. Still greater selective action can be obtained by the use of additional suitably adjusted resonant circuits located somewhere in the r

28、eceiver in such a way as to reject all but the desired signal. The ability to discriminate between radio waves of different frequencies is called selectivity and the process of adjusting circuits to resonance with the frequency of a desired signal is spoken of as tuning.Although intelligible radio s

29、ignals have been received from the stations thousands of miles distant, using only the energy abstracted from the radio wave by the receiving antenna much more satisfactory to the radio-frequency currents before detection, in which case it is called radio-frequency amplification or it may be applied

30、 to the rectified currents after detection, in which case it is called audio-frequency amplification. The use of amplification makes possible the satisfactory reception of signals from waves that would otherwise be too weak to give an audible response.The process by which the signal being transmitte

31、d is reproduced from the radio-frequency currents present at the receiver is called detection, or sometimes demodulation. Where the intelligence is transmitted by varying the amplitude of the radiated wave, detection is accomplished by rectifying the radio frequency current. The rectified current th

32、us produced varies in accordance with the signal originally modulated on the wave radiated at the transmitter and so reproduces the desired signal. Thus, when the modulated wave is rectified, the resulting current is seen to have an average value that varies in accordance with the amplitude of the o

33、riginal signal.Receiver circuit are made up a of a number of stages. A stage is a single transistor connected to components which provide operating voltages and currents and also signal voltages and currents. Each stage has its input circuit from which the signal comes in and it output circuit from

34、which the signal, usually amplified, goes out. When one stage follows another, the output circuit of the first feeds the signal to the circuit of the second. And so the signal s amplified, stage by stage, until it strong enough to operate the loudspeaker.Mobile CommunicationCordless Telephone System

35、sCordless telephone systems are full duplex communication systems that use radio to connect a portable handset to a dedicated base station, which is then connected to a dedicated telephone line with a specific telephone number on the public switched telephone network (PSTN). In first generation cord

36、less telephone systems (manufactured in the 1980s) , the portable unit communicates only to the dedicated base unit and only over distances of a few tens of meters.Early cordless telephones operate solely as extension telephones to a transceiver connected to a subscriber line on the PSTN and are pri

37、marily for in-home use.Second generation cordless telephones have recently been introduced which allow subscribers to use their handsets at many outdoor locations within urban centers such as London or Hong Kong. Modern cordless telephones are sometimes combined with paging receivers so that a subsc

38、riber may first be paged and then respond to the page using the cordless telephone. Cordless telephone systems provide the user with limited range and mobility, as it is usually not possible to maintain a call if the user travels outside the range of the base station. Typical second generation base

39、stations provide coverage ranges up to a few hundred meters.Cellular Telephone SystemsA cellular telephone system provides a wireless connection to the PSTN for any user location within the radio range of the system. Cellular systems accommodate a large number of users over a large geographic area,

40、within a limited frequency spectrum. Cellular radio systems provide high quality service that is often comparable to that of the landline telephone systems. High capacity is achieved by limiting the coverage of each base station transmitter to a small geographic area called a cell so that the same r

41、adio channels may be reused by another base station located some distance away. A sophisticated switching technique called a handoff enables a call to proceed uninterrupted when the user moves from one cell to another.A basic cellular system consists of mobile station, base stations and a mobile swi

42、tching center (MSC). The Mobile Switching Center is sometimes called a mobile telephone switching office (MTSO), since it is responsible for connecting all mobiles to the PSTN in a cellular system. Each mobile communication via radio with one of the base stations and may be handed-off to any number

43、of base stations throughout the duration of a call. The mobile station contains a transceiver, an antenna, and control circuitry, and may be mounted in a vehicle or used as a portable hand-held unit. The base stations consist of several transmitters and receivers which simultaneously handle full dup

44、lex communications and generally have towers which support several transmitting and receiving antennas. The base station serves as a bridge between all mobile users in the cell and connects the simultaneous mobile calls via telephone lines or microwave links to the MSC. The MSC coordinates the activ

45、ities of all of the base stations and connects the entire cellular system to the PSTN. A typical MSC handless 100 ooo cellular subscribers and 5000 simultaneous conversations at a time, and accommodates all billing and system maintenance functions, as well. In large cities, several MSCs are used by

46、a single carrier.Why GPS and How It Works?Whafs GPS?Navigation and positioning are crucial to so many activities and yet the process has always been quite cumbersome. Over the years all kinds of technologies have tried to simplify the task, but every one has had some disadvantage. Finally, the U.S.

47、Department of Defense (DoD) decided that the military had to have a super precise form of worldwide positioning. And fortunately they had the kind of money. It took to build something really good. The result is the Global Positioning System, a system thats changed navigation forever.The Global Posit

48、ioning System (GPS) is a worldwide radio-navigation system formed from a constellation of 24 satellites and their ground station. GPS uses these“man-made stars” as reference points to calculate positions accurate to a matter of meters. In fact, with advanced forms of GPS you can make measurements to

49、 better than a centimeter. In a sense its like giving every square meter on the planet a unique address.GPS receivers have been miniaturized to just a few integrated circuits and so are becoming very economical. And that makes the technology accessible to virtually everyone. These days GPS is finding us way into cars, boats, planes, construction equipment, movie making gear, farm machinery, even laptop computers. Soon GPS will become almost as basic as the telephone. Indeed it just may become a universal utili