Packing Resizable Items with Application to Video Delivery over Wireless Networks

Abstract

Motivated by fundamental optimization problems in video delivery over wireless networks, we consider the following problem of packing resizable items (PRI). Given is a bin of capacity B > 0, and a set I of items. Each item j ∈ I is of size s _j  > 0. A packed item must stay in the bin for a fixed time interval. To accommodate more items in the bin, each item j can be compressed to a size p _j  ∈ [0,s _j ) for at most a fraction q _j  ∈ [0,1) of the packing interval. The goal is to pack in the bin, for the given time interval, a subset of items of maximum cardinality. PRI is strongly NP-hard already for highly restricted instances.

Our main result is an approximation algorithm that packs, for any instance I of PRI, at least $\frac{2}{3}OPT(I) -3$ items, where OPT(I) is the number of items packed in an optimal solution. Our algorithm yields better ratio for instances in which the maximum compression time of an item is $q_{max} \in (0, \frac 1 2)$. For subclasses of instances arising in realistic scenarios, we give an algorithm that packs at least OPT(I) − 2 items. Finally, we show that a non-trivial subclass of instances admits an asymptotic fully polynomial time approximation scheme (AFPTAS).

Work partially supported by the Technion V.P.R. Fund, by Smoler Research Fund, and by the Ministry of Trade and Industry MAGNET program through the NEGEV Consortium ( www.negev-initiative.org ).