Department of Computer Science | Institute of Theoretical Computer Science | CADMO

Theory of Combinatorial Algorithms

Prof. Emo Welzl and Prof. Bernd Gärtner

Mittagsseminar (in cooperation with M. Ghaffari, A. Steger and B. Sudakov)

Mittagsseminar Talk Information

Date and Time: Friday, March 19, 2004, 12:15 pm

Duration: This information is not available in the database

Location: This information is not available in the database

Speaker: Marc Nunkesser

An algorithmic view on OVSF code assignment

Recently UMTS has received a lot of attention, and raised new algorithmic problems. In this talk I focus on a specific aspect of its multiple access method DS-CDMA (Direct Sequence Code Division Multiple Access) that turns out to be of algorithmic interest. The DS-CDMA method makes it possible for all users in one cell to share the bandwidth by assigning them Orthogonal Variable Spreading Factor (OVSF-) codes. This assignment is straight-forward, as long as only a few users request such codes. In cells with many users new code requests can make code reassignments necessary. Algorithms that aim at minimizing the number of such necessary reassignments are presented. It is shown that existing algorithms for the underlying code assignment (CA-) problem are erroneous, and that its offline version is NP-complete. Finally, I will argue that the online-version of the CA-problem is the most natural one.

(Joint work with T. Erlebach, R. Jacob, M. Mihalak, G. Szabo, P. Widmayer)

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