An OVSF code tree partition policy for WCDMA systems based on the multi-code approach
Huei-Wen Ferng, Hao-Lun Chin, David Shiung, Ying-Tsung Chen · 2006
Abstract — Orthogonal variable spreading factor (OVSF) codes for wide-band CDMA (WCDMA) systems have been proposed in the third generation (3G) mobile communications ’ standard to support services of variable rates. To assign OVSF codes, there are single-code and multi-code approaches. In this paper, the multi-code placement and replacement issue is addressed. We propose a tree partition policy for managing the OVSF code tree to reduce code fragments and the number of code reassignments. Besides, we adjust the multi-code rate according to a unit-based method, which is capable of decreasing the number of code fragments because fewer low-rate codes are utilized. Through extensive simulations, it turns out that the tree partition policy and the unit-based multi-code method jointly perform better than the left-most and crowded-first schemes. I.