信息科学与电子工程专业英语 lecture06.pptVIP

* Second generation systems were introduced in the early 1990’s, and all use digital technology. This provided an increase in the user capacity of around three times. This was achieved by compressing the voice waveforms before transmission. 第二代系统出现于二十世纪90年代初，全部使用数字技术，使容量增加了三倍左右，这是通过发送前将话音波形压缩而实现的。 Unit 6-2 第三代无线网络 —— 电信系统的发展（Evolution of telecommunication systems ） * Third generation systems are an extension on the complexity of second generation systems and are expected to be introduced after the year 2000. The system capacity is expected to be increased to over ten times original first generation systems. This is going to be achieved by using complex multiplex access techniques such as Code Division Multiplex Access (CDMA), or an extension of TDMA, and by improving flexibility of services available. 第三代系统是在复杂性方面对第二代系统的扩展，预计将于2000年以后推出。系统容量预计将扩大到原来第一代系统的10倍以上。这将通过使用复杂的多址技术如码分多址（CDMA）或者TDMA的一种扩展技术，以及改进已有业务的灵活性来实现。 Unit 6-2 第三代无线网络 —— 电信系统的发展（Evolution of telecommunication systems ） * Table 6.1 and Table 6.2 show some of the major cellular mobile phone standards in North America and Europe. Figure 6.3 shows the evolution of current services and networks to the aim of combining them into a unified third generation network. 表6.1和表6.2列出了北美和欧洲的一些主要蜂窝式移动电话标准。图6.1给出现有业务和网络向融入一个统一的第三代网络这一目标的发展情况。 Unit 6-2 第三代无线网络 —— 电信系统的发展（Evolution of telecommunication systems ） Analog Cellular Radio Paging Digital Cellular Private Radio PCNs Mobile satellite Cordless Telephony Third Generation Wireless Network * Many currently separate systems and services such as radio paging, cordless telephony, satellite phones, private radio systems for companies, etc., will be combined so that all these services will be provided by third generation telecommunications systems.3 当今许多分离的系统和业务例如无线电寻呼、无绳电话、卫星电话、公司的私人电话系统等将互相结合，由第三代电信系统来提供。 Unit 6-2 第三代无线网络 —— 电信系统的发展（Evolution of telecommunication systems ） * Table 6.1 Major mobile standards in North America Cellular System Year of Introduction T