Implementation of a High-Performance Assignment Scheme for Orthogonal Variable-Spreading-Factor Codes in WCDMA Networks

In WCDMA, channelization is achieved by assigning OVSF codes to different users. The codes in a Node-B are valuable and limited. Much research has been devoted to devising OVSF code-assignment strategies to support as many users as possible. A number of the strategies suffer from a “code-set fragmentation” problem, which increases the call blocking probability (CBP) on the Node-B. In order to resolve this issue some strategies have applied code-exchange and reassignment policies but increased the corresponding complexity. This paper proposes a Best-fit Least Recently Used (BLRU) code-assignment scheme without reassignment to approach an optimal method. Furthermore, we devise a revised version, Queue-assist BLRU (QBLRU), to improve system utilization and to obtain an even lower CBP than the optimal method does. Consequently, code-assignment simulation results present a QBLRU scheme that has a low CBP and the highest utilization, which is a high performance OVSF code-assignment scheme which should be useful for WCDMA networks.