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移动通信已经历了两代的发展,第一代移动通信系统是模拟蜂窝移动通信,使用频分多址接入方式(以TACS、AMPS制为代表),使用900MHz频段,其业务单一(提供区域性的话音业务),频率利用率低,用户容量有限,不能实现国际漫游。第二代移动通信系统使用数字调制技术,采用TDMA/FDMA或CDMA/FDMA混合方式接入。它比第一代移动通信系统有明显的优势,但随着全球信息传输范围的越来越广泛,人们希望在任意时间、任意地点,为任何人提供话音、图像、数据的多媒体业务,显然第二代移动通信已不能满足公众的需要,因而以提供全球多媒体
Mobile communication has gone through two generations of development. The first generation of mobile communication system is analog cellular mobile communication, which uses frequency division multiple access (represented by TACS and AMPS systems), uses 900MHz band and has a single service (providing area Sexual voice service), low frequency utilization, limited user capacity, can not achieve international roaming. The second generation of mobile communication system uses digital modulation technology, using TDMA / FDMA or CDMA / FDMA hybrid access. It has obvious advantages over the first-generation mobile communication system. However, as the scope of global information transmission becomes more and more widespread, people want multimedia services that provide voice, image and data to anyone at anytime, anywhere. Obviously, The second generation of mobile communications has been unable to meet the needs of the public, so as to provide global multimedia