At present, there are three most representative 3G technical standards in the world, namely TD-SCDMA, WCDMA and CDMA2000. Among them, TD-SCDMA belongs to time division duplex (TDD) mode, which is a 3G technical standard proposed by China. WCDMA and CDMA2000 belong to frequency division duplex (FDD) mode.
Internationally, the standardization of TD-SCDMA, WCDMA and CDMA2000 is mainly undertaken by 3GPP and 3GPP2, two third generation mobile communication partners. Among them, TD-SCDMA and WCDMA are specifically standardized by 3GPP; While CDMA2000 is specially standardized by 3GPP2.
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The third generation mobile communication system is still a regional communication system based on different terrestrial standards. Although its transmission rate is 7.2Mb/ s under the mature WCDMA standard, it is far from this value due to various restrictions of resources and wireless environment in commercial networks. It still can't meet the requirements of many multimedia communications and can't support communications with high speed requirements.
The supply of multi-rate services with dynamic range is insufficient. Moreover, at present, there is no unified standard for the core network supported by the air interfaces of the three commercial standards, so it is difficult to provide multi-rate services with various QoS and performance. Seamless roaming between different frequency bands and different business environments cannot be truly realized.
For different business environments with different frequency bands, mobile terminals need to be configured with different software and hardware modules, and 3G mobile terminals cannot realize different configurations of this business environment. It is these limitations that exist in 3G systems, so various companies and institutions have begun to study LTE.
Composition of People's Network -3G Technology and Standards
Baidu Encyclopedia -3G