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在３Ｇ系统中,ＣＤＭＡ系统成为了最具竞争力、最具发展前景的无线多址技术。虽然ＣＤＭＡ扩频技术可以采用直接序列扩频(ＤＳ)、跳频(ＦＨ)、跳时(ＴＨ)以及它们的组合等,但在移动通信中一般选用直接序列扩频,它构成了我们常说的ＤＳ－ＣＤＭＡ系统。３Ｇ系统结构如图１所示,它的核心网是在ＧＳＭ系统的核心网ＧＳＭ—ＭＡＰ和ＡＭＰＳ、ＩＳ—９５的核心网ＡＮＳＩ—４１的基础上发展而来的,其空中接口和相应的２Ｇ系统后向兼容。它的３种工作模式为:单载波频分双工、多载波频分双工和时分双工方式。
In 3G system, CDMA system has become the most competitive and most promising wireless multiple access technology. Although CDMA spread spectrum technology can use direct sequence spread spectrum (DS), frequency hopping (FH), time hopping (TH) and their combinations, etc., but in mobile communications generally choose direct sequence spread spectrum, which constitutes what we often say DS-CDMA system. The structure of 3G system is shown as in Fig. 1, its core network is developed on the basis of GSM-MAP and AMPS of GSM system core network, ANSI-41 of key network of IS-95, its air interface and corresponding 2G System backward compatible. Its 3 kinds of work patterns are: Single-carrier frequency division duplexing, multi-carrier frequency division duplexing and time division duplexing.