【資料名稱】：principle1

【資料作者】：普天

【資料日期】：2008.01.02

【資料語言】：中文

【資料格式】：DOC

【資料目錄和簡介】：

As one of the 3G RAT (Radio Access Technology) international standards, standardization of TD-SCDMA has been speeding up in China ,more and more major suppliers of telecom industry are jointly developing it energetically because of its technical advantages and strong support from Chinese government .
Using Time Division Multiple Access (TDMA) , the sub-frame is transmitted repetitively on a radio carrier. This sub-frame is subdivided into several time slots, where different time slots are assigned to different users accessing the radio carrier.In addition ,traffic from one user can occupy one or more time slots. With the Time Division Duplex (TDD) principle uplink traffic and downlink traffic are transmitted in the same frame in different time slots.
The capability of adapting the uplink/downlink symmetry/asymmetry according to data loadwithin a single frequency band increases the overall capacity of the air interface. Therefore the TDD operation is ideal for asymmetric as well as symmetric services.

In contrast, the FDD (Frequency Division Duplex) scheme users different frequency bands for uplinkand downlink .With asymmetric loads, portions of the spectrum are occupied but not used for data transfer . Due to the FDD characteristics there is even no way of utilizing these idle resources for any other communication means.
In the TDD mode,for strongly asymmetric services, where for example more data is transported from Node B to the terminal (as during internet access), more time slots are used for downlink than for uplink. If symmetric services are required, where the same amount of data is transmitted in both directions (e.g. telephony), the frame is symmetrically split between uplink and downlink.