Online OVSF Code Assignment with Resource Augmentation

  • Authors:

  • Francis Y. Chin;Yong Zhang;Hong Zhu

  • Affiliations:

  • Department of Computer Science, The University of Hong Kong, Hong Kong;Department of Computer Science, The University of Hong Kong, Hong Kong;Institute of Theoretical Computing, East China Normal University, China

  • Venue:
  • AAIM '07 Proceedings of the 3rd international conference on Algorithmic Aspects in Information and Management
  • Year:
  • 2007

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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 play an important role in third generation mobile communications. In the OVSF problem, codes must be assigned to incoming code 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, in the often-studied context of the single cell as well as in the more general context of the whole multi-cell cellular network (for which there are no known results). With the help of 1/8 and 11/8 extra bandwidth resources, we are able to give a 5-competitive algorithm in the single cell and the multi-cell context respectively, which means that the competitive ratio is a constant and not a function of the height of the OVSF tree and thereby improving upon past results.