OVSF code assignment strategies with minimal fragmentations for WCDMA systems
This paper handles the internal and external fragmentation problems of WCDMA systems using Orthogonal Variable Spreading Factor (OVSF) codes. Internal fragmentation occurs when the allocated data Fate is larger than what is requested, while external fragmentation Occurs when the OVSF code tree is too fragmented to support a call even if there is sufficient capacity remaining in the code tree. The key factor in solving these two problems is the OVSF code assignment strategy. Most works in the literature do not consider the time-varying and location-depenclent channel conditions. In this paper, we formulate the fragmentation problem as a multiple knapsack problem where each OVSF code is considered as a knapsack. We propose single-code, time-shared strategies that consider channel conclitions while solving these fragmentation problems. Simulation results verify that our strategies efficiently use the precious Wireless bandwidth. (c) 2008 Elsevier B.V. All rights reserved.
ovsf wcdma mobile computing personal communication services wireless communication 3g