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.
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The work of Peng-Jun Wan and Xiang-Yang Li is partially supported by NSF CCR-0311174.
The preliminary version of the paper first appeared in ACM DIAL M-POMC 2004, workshop of ACM MobiCom 2004.
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Wan, PJ., Li, XY. & Frieder, O. OVSF-CDMA Code Assignment in Wireless Ad Hoc Networks. Algorithmica 49, 264–285 (2007). https://doi.org/10.1007/s00453-007-9094-6
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DOI: https://doi.org/10.1007/s00453-007-9094-6