Performance evaluation of orthogonal variable-spreading-factor code assignment schemes in W-CDMA

This paper compares the performance of the orthogonal-variable-spreading-factor (OVSF) code assignment among three proposed schemes so far, i.e., the conventional OVSF-code assignment scheme (CONV), the dynamic OVSF-code assignment scheme (DCA), and region division assignment scheme (RDA). In OVSF-CDMA, the maintenance of orthogonality among the assigned OVSF codes causes the code blocking problem which increases the high blocking rate for high-rate requests. DCA is aimed at eliminating the code blocking problem in order to reduce the high blocking rate for high-rate requests, whereas RDA has been proposed to mitigate the code blocking problem in order to efficiently provide services for all supported rates. The computer simulation results show that the blocking probability of RDA is lower than that of DCA under heavy traffic conditions. The simulation results also show that the calculation time of DCA is significantly larger than that of RDA. Furthermore, RDA is shown to be able to simultaneously handle many more voice sources than DCA.