Abstract
This paper completely eliminates the external and internal fragmentation of OVSF codes at the forward link in 3G WCDMA system. Only assigning a single OVSF code for each user is more preferable than assigning multiple OVSF codes for each user. Since it is an evolution from second-generation wireless CDMA system such as IS-95 and costs less in hardware design and complexity. However, OVSF-CDMA (with single code) has two severe constraints: code blocking (due to fragmenting OVSF code tree by scattered codes) and coarsely quantized data rates (due to that allocated rates are larger than guaranteed rates). To resolve the phenomenon of code blocking (external fragmentation), we contrives two innovative region division algorithms (DRDA, VRDA). Both of the two algorithms entirely eradicate the above external fragmentation, i.e., guarantee no code blocking, and provide flexible region size for rapidly altering arrival rates distribution, without losing fairness. Additionally, VRDA is the first mechanism that not only optimizes the number of OVSF codes that must be reassigned to support a new call but also takes the posterior potential code blocking possibility into account in long-term circumstances. On the other hand, to resolve the phenomenon of coarsely quantized data rates (internal fragmentation), we introduce the concept of group and share codes between group members. Our simulation results demonstrate that V-RDA performs more superiorly, in reducing income/spectrum loss, and number of reassignments, than previously proposed schemes, such as DCA, RDA, CONV, perform. Conclusively, combining VRDA and sharing codes mechanism, i.e., VRDA+, optimizes the bandwidth utilization of allocated/guaranteed rates.