Assignment of OVSF codes in wideband CDMA

Abstract

In Wideband Code Division Multiple Access, Channelization codes are used to preserve the orthogonality between physical channels, in order to increasing system capacity. The Orthogonal Variable Spreading Factor (OVSF) codes are used as the channelization codes in this system. In WCDMA, it is possible to provide multi-rate service by employing the OVSF codes, which can be generated in the form of tree structure. This scheme is known as OVSF-CDMA. One important limitation of OVSF-CDMA is that the system must maintain the orthogonality among the assigned codes. The maintenance of the orthogonality among the assigned OVSF codes causes the code blocking problem. Efficient channelization code management, result in high efficiency of code utilization and increasing system capacity. This research compares the performance of OVSF code assignment schemes, in terms of code blocking probability and number of required code reassignment. © 2008 Springer-Verlag.