High-speed multimedia data transmission is a sign$-cant feature in the third-generation mobile communication systems. Wideband CDMA is widely studied and accepted as the transmission scheme over the air. The single-code and multi-code transmission schemes over the CDMA were also investigated by many researchers. OVSF codes were proposed by the 3GPP as the forward channelization codes to the IMT-2000, the property the OVSF code tree and the code manipulations are important in achieving the high spectral eflciency, which is also the key issue of resource management.This paper proposed an efficient and fast channelization code assignment scheme (FEX scheme), by utilizing the code exchange and garbage collection technique, to reduce the blocking rate of the system. The simulations demonstrated the efectiveness of this scheme by comparing to an "ideal system". The results also revealed the importance of the code exchange and multi-code property to greatly reduce the blocking rate of the system.

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High data-rate and variable data-rate services are important features in the third-generation mobile communication systems. Intemational Mobile Telecommunication-2000 (IMT-2000 in the Intemational Telecommunication Union (ITU) [I] sets up the air interface objectives to support wideband data services as high as 2Mb/s for limited coverage and mobility, and 144Kb/s to 384Kb/s for full coverage and mobility, with the same quality as in fixed telecommunication network [2]. Direct sequence code division multiple access (DS-CDMA) is widely investigated [3,4] and accepted as the wireless access technique of IMT-2000 for its

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