OVSF code assignment strategies with minimal fragmentations for WCDMA systems

Authors:
Chih-Min Chao
Affiliations:
Department of Computer Science and Engineering, National Taiwan Ocean University, 2, Pei-Ning Road, Keelung, Taiwan 20224, Taiwan, ROC
Venue:
Computer Networks: The International Journal of Computer and Telecommunications Networking
Year:
2008

Citing 9
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Reducing internal and external fragmentations of OVSF codes in WCDMA systems with multiple codes

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Abstract

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 rate 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-dependent 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 conditions while solving these fragmentation problems. Simulation results verify that our strategies efficiently use the precious wireless bandwidth.