The Study Of The Spreading Spectrum Address Code In WCDMA Communication System

WCDMA is one of the three major technique standards in 3G. Orthogonal variable spreading factors (OVSF) is used as channel address codes in WCDMA system. Meanwhile, truncated Gold codes are used as base-station address code and user address code.The correlation and balance characteristics and the truncated length of truncated Gold sequence have direct impact on the capacity of multi-addressing and some other aspects in CDMA system such as carrier leakage, synchronous detection probability and capture time. Therefore, it is important that a series of methods for generating truncated Gold sequence and the capability of truncated Gold sequence are studied. A series of methods and software programmes for generating truncated Gold sequence are brought forward in this paper, the correlation and balance characteristics of different truncated proportion Gold sequence have been analysed through the simulation of truncated Gold sequence performance, involve with before and after truncated, different period of sequence and different truncated length. Finally the relevant valuable conclusions are given based on the analysis results.The variable length words of OVSF could suffice the differet velocity of multimedia services, and its orthogonality words also reduces the mutual interference between channels. Not all OVSF code words have orthogonality, allotable code words is limited at the same time. Therefore, in order to improve the utilization of bandwidth resources, it's necessary to allot limited OVSF codes rationally, equitably and efficiently. Hence, dynamic allocation algorithm of OVSF code is becoming a hot issue of the current study.In this paper, the rule of allocation and the structure of OVSF are introduced, OVSF code dynamic allocation strategy is analyzed. As a new type of OVSF code allocation and release strategy, Parity-correlation method have been brought out and demonstrated, which is based on comprehensive analysis in a variety of dynamic allocation method. Software programmes of OVSF code allocation, release and defragmentation based on left most-fragment method and Parity-correlation method, which have been developed and implemented OVSF code dynamic allocation, release and defragmentation, and the large number of simulation data have been compared and analyzed. The results of simulation shows that Parity-correlation method could implemented OVSF codes allocation, release and defragmentation correctly, which has efficient allocation of code resources and it is a simple and efficient dynamic allocation algorithm.