《通信英语LESSON09章节》由会员分享，可在线阅读，更多相关《通信英语LESSON09章节（79页珍藏版）》请在金锄头文库上搜索。
1、Unit 9,Cellular Mobile Telephone System,Contents,Revision Pre-reading Activities While-reading Activities New words and phrases Text organization Text and translation Post-reading Activities Further Development of the Theme-related Specialized Knowledge Assignments,Revision,上节课主要学习了第8单元关于paging syst
2、em的知识。 Please tell me the important new words related to paging system and whats the main idea of the text.,Pre-reading Activities,传统的移动电话系统有那些缺点？ 理想的移动电话系统有什么特点？ 本次课将给大家讲cellular mobile telephone system有关方面的知识。,While-reading Activities / New words and phrases,Deploy v. use something effectively e.g
3、. deploy ones arguments, resources etc. mobile adj. that can move or be moved easily and quickly from place to place; mobility n. conventional adj. following what is traditional or customary,While-reading Activities / New words and phrases,allocation n. 配给， 分配， 拔出 allocate v. allocate something to s
4、omebody or something: assign something to somebody or something for a special purpose e.g. He allocated tasks to each of us.,While-reading Activities / New words and phrases,Approach v. come near or nearer to somebody or something in space or time 在时间或空间上靠近 e.g. The time is approaching when we must
5、think about buying a new house. n. 接近； 方法 vicinity n. in the vicinity of something : in the surrounding district; in the neighborhood e.g. There isnt a good school in the vicinity. Radius n 半径 diameter n. 直径,While-reading Activities / Text organization,Step 1:Ask students to preview the text for sev
6、eral minutes. Step 2:Let students discuss the communication approaches in the past and nowadays. Step 3:Analyze the language points in the text.,Text and translation,Cellular Mobile Telephone System(1),Text and translation,One of many reasons for developing a cellular mobile telephone system and dep
7、loying it in many cities is the operational limitations of conventional mobile telephone systems: limited service capability, poor service performance, and inefficient frequency spectrum utilization.,Text and translation,A major problem facing the radio communication industry is the limitation of th
8、e available radio frequency spectrum（2）. In setting allocation policy, the Federal Communications Commission (FCC) seeks systems which need minimal bandwidth but provide high usage and consumer satisfaction(3).,Text and translation,The ideal mobile telephone system would operate within a limited ass
9、igned frequency band and would serve an almost unlimited number of users in unlimited areas. Three major approaches to achieve the ideal are:,Text and translation,1. Single-sideband (SSB), which divides the allocated frequency band into maximum numbers of channels; 2. Cellular, which reuses the allo
10、cated frequency band in different geographic locations; 3. Spread spectrum, frequency-hopped, which generates many codes over a wide frequency band(4).,Text and translation,In 1971, the computer industry entered a new era. Microprocessors and minicomputers are now used for controlling many complicat
11、ed features and functions with less power and size than was previously possible.,Text and translation,Large-scale integrated (LSI) circuit technology reduced the size of mobile transceivers so that they easily fit the standard automobile(5). These achievements were a few of the requirements for deve
12、loping advanced mobile phone systems and encouraging engineers to pursue this direction(6).,Text and translation,Another factor was the price reduction of the mobile telephone unit. LSI technology and mass production contribute to reduced cost so that in the near future an average-income family shou
13、ld be able to afford a mobile telephone unit.,Text and translation,On Jan. 4, 1979, the FCC authorized Illinois Bell Telephone Co. to conduct a developmental cellular system in the Chicago area and make a limited commercial offering of its cellular service to the public. In addition(7), American Rad
14、io Telephone Service Inc. was authorized to operate a cellular system in the Washington, D. C. (8)-Baltimore, Md., area. These first systems showed the technological feasibility of cellular service.,Text and translation,Why 800 MHz(9)? The FCCs decision to choose 800 MHz was made because of severe s
15、pectrum limitations at lower frequency bands. FM broadcasting services operate in the vicinity of 100 MHz. The television broadcasting service starts at 41 MHz and extends up to 960 MHz.,Text and translation,Air-to-ground systems use 118 to 136 MHz; military aircraft use 225 to 400 MHz. The maritime
16、 mobile service is located in the vicinity of 160 MHz(10). Also fixedstation services are allocated portions of the 30 to 100 MHz band. Therefore, it was hard for the FCC to allocate a spectrum in the lower portions of the 30 to 400 MHz band since the services of this band had become so crowded.,Text and translation,On the other hand, mobile radio transmission cannot be applied at 10 GHz or above because severe propagation path loss, multipath fading, and rain activity make the medium i
