An Algorithmic View on OVSF Code Assignment

OrthogonalVariableSpreadingFactor(OVSF)codesareusedinUMTStosharetheradiospectrum among several connections of possibly different bandwidth requirements. The combinatorial core of the OVSF code assignment problem is to assign some nodes of a complete binary tree of height h (the code tree) to n simultaneous connections, such that no two assigned nodes (codes) are on the same root-to-leaf path. A connection that uses a 2−d fraction of the total bandwidth requires some code at depth d in the tree, but this code assignment is allowed to change over time. Requests for connections that would exceed the total available bandwidth are rejected. We consider the one-step code assignment problem: Given an assignment, move the minimum number of codes to serve a new request. Minn and Siu propose the so-called DCA algorithm to solve the problem optimally. In contrast, we show that DCA does not always return an optimal solution, and that the problem is NP-hard. We give an exact nO(h)-time algorithm,...

• Type: Conference
• Year: 2004
• Where: STACS
• Authors: Thomas Erlebach, Riko Jacob, Matús Mihalák, Marc Nunkesser, Gábor Szabó, Peter Widmayer
• Keywords: Code Assignment Problem, One-step Code Assignment, OVSF Code Assignment, STACS 2004, Theoretical Computer Science