A Constant-Competitive Algorithm for Online OVSF Code Assignment

  • Authors:

  • F. Y. L. Chin;H. F. Ting;Y. Zhang

  • Affiliations:

  • The University of Hong Kong, Department of Computer Science, Pokfulam road, Hong Kong, Hong Kong;The University of Hong Kong, Department of Computer Science, Pokfulam road, Hong Kong, Hong Kong;The University of Hong Kong, Department of Computer Science, Pokfulam road, Hong Kong, Hong Kong

  • Venue:
  • Algorithmica - Special Issue: Algorithms and Computation; Guest Editor: Takeshi Tokuyama
  • Year:
  • 2010

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Abstract

Orthogonal Variable Spreading Factor (OVSF) code assignment is a fundamental problem in Wideband Code-Division Multiple-Access (W-CDMA) systems, which plays an important role in third generation mobile communications. In the OVSF problem, codes must be assigned to incoming call requests with different data rate requirements, in such a way that they are mutually orthogonal with respect to an OVSF code tree. An OVSF code tree is a complete binary tree in which each node represents a code associated with the combined bandwidths of its two children. To be mutually orthogonal, each leaf-to-root path must contain at most one assigned code. In this paper, we focus on the online version of the OVSF code assignment problem and give a 10-competitive algorithm (where the cost is measured by the total number of assignments and reassignments used). Our algorithm improves the previous O(h)-competitive result, where h is the height of the code tree, and also another recent constant-competitive result, where the competitive ratio is only constant under amortized analysis and the constant is not determined. We also improve the lower bound of the problem from 3/2 to 5/3.