OVSF-CDMA Code Assignment in Wireless Ad Hoc Networks

  • Authors:

  • Peng-Jun Wan;Xiang-Yang Li;Ophir Frieder

  • Affiliations:

  • Illinois Institute of Technology, Department of Computer Science, 60616, Chicago, IL, USA;Illinois Institute of Technology, Department of Computer Science, 60616, Chicago, IL, USA;Illinois Institute of Technology, Department of Computer Science, 60616, Chicago, IL, USA

  • Venue:
  • Algorithmica
  • Year:
  • 2007

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Abstract

Orthogonal Variable Spreading Factor (OVSF) CDMA code consists of an infinite number of codewords with variable rates, in contrast to the conventional orthogonal fixed-spreading-factor CDMA code. Thus, it provides a means of supporting of variable rate data service at low hardware cost. However, assigning OVSF-CDMA codes to wireless ad hoc nodes posts a new challenge since not every pair of OVSF-CDMA codewords are orthogonal to each other. In an OVSF-CDMA wireless ad hoc network, a code assignment has to be conflict-free, i.e., two nodes can be assigned the same codeword or two non-orthogonal codewords if and only if their transmission will not interfere with each other. The throughput (resp., bottleneck) of a code assignment is the sum (resp., minimum) of the rates of the assigned codewords. The max-throughput (resp., max-bottleneck) conflict-free code assignment problem seeks a conflict-free code assignment which achieves the maximum throughput (resp., bottleneck). In this paper, we present several efficient methods for conflict-free code assignment in OVSF-CDMA wireless ad hoc networks. Each method is proved to be either a constant-approximation for max-throughput conflict-free code assignment problem, or a constant-approximation for max-bottleneck conflict-free code assignment problem, or constant-approximations for both problems simultaneously.