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2025-02-24 00:58 本頁面
【文章內(nèi)容簡(jiǎn)介】 rt between the SGSN and GGSN. This allows data services such as or web browsing on the mobile device,with users being charged based on volume of data rather than time connected. The dominant standard for delivery of 3G works and services is the Universal Mobile Telemunications System, or UMTS. The first deployment of UMTS is the Release ’99 architecture, shown below in Figure 3. In this work, the major change is in the radio access work (RAN) with the introduction of CDMA technology for the air interface, and ATM as a transport in the transmission part. These changes have been introduced principally to support the transport of voice, video and data services on the same work. The core work remains relatively unchanged, with primarily software upgrades. However, the IP protocol pushes further into the work with the RNC now municating with the 3G SGSN using IP. The next evolution step is the Release 4 architecture, Figure 4. Here, the GSM core is replaced with an IP work infrastructure based around Voice over IP technology. The MSC evolves into two separate ponents: a Media Gateway (MGW) and an MSC Server (MSS). This essentially breaks apart the roles of connection and connection control. An MSS can handle multiple MGWs, making the work more scaleable. Since there are now a number of IP clouds in the 3G work, it makes sense to merge these together into one IP or IP/ATM backbone (it is likely both options will be available to operators.) This extends IP right across the whole work, all the way to the is referred to as the AllIP work, or the Release 5 architecture, as shown in Figure 5. The HLR/VLR/EIR are generalised and referred to as the HLR Subsystem(HSS). Now the last remnants of traditional telemunications switching are removed, leaving a work operating pletely on the IP protocol, and generalised for the transport of many service types. Realtime services are supported through the introduction of a new work domain, the IP Multimedia Subsystem (IMS). Currently the 3GPP are working on Release 6, which purports to cover all aspects not addressed in frozen releases. Some call UMTS Release 6 4G and it includes such issues as interworking of hot spot radio access technologies such as wireless LAN. UMTS FDD and TDD Like any CDMA system, UMTS needs a wide frequency band in which to operate to effectively spread signals. The defining characteristic of the system is the chip rate, where a chip is the width of one symbol of the CDMA code. UMTS uses a chip rate of of 5MHz wide. Since this is wider than the needed for the existing cdmaOne system, the UMTS air interface is termed ‘wideband’ CDMA. There are actually two radio technologies under the UMTS umbrella: UMTS FDD and TDD. FDD stands for Frequency Division Duplex, and like GSM, separates traffic in the uplink and downlink by placing them at different frequency channels. Therefore an operator must have a pair of frequencies allocated to allow them to run a work, hence the term ‘paired spectrum’. TDD or Time Division Duplex requires only one frequency channel, and uplink and downlink traffic are separated by sending them at different times. The ITUT spectrum usage, as shown in Figure 6, for FDD is 1920 980MHz for uplink traffic, and 21102170MHz for downlink. The minimum allocation an operator needs is two paired 5MHz channels, one for uplink and one for downlink, at a separation of 190MHz. However, to provide prehensive coverage and services, it is
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