1,720,968 research outputs found
A Competitive Scheduling Problem and its Relevance to UMTS Channel Assignment
No full textThis article investigates a two-user competitive scheduling problem. The problem arises in a Universal Mobile Telecommunication System (UMTS) developed within the European IST project FUTURE: given two mobile terminals, one wants to maximize the on-time data packets transmitted to one user, while guaranteeing a certain amount of on-time data packets to the other. We show that the problem is NP-hard, despite peculiar properties of data and solutions. We propose a fast Lagrangian heuristic able to cope with a severe real-time requirement, and compare it to a greedy-like heuristic on a set of practical instances
Sorting Common Operations to Minimize the Number of Tardy Jobs
No full textWe study an operation scheduling problem where a finite set of jobs with due dates must be completed by one machine: each job is completed as soon as a specific subset of unit operations is done. Distinct jobs may share operations, and when an operation is done, it is done for all the jobs that share it. The goal is to schedule operations so that the (weighted) number of tardy jobs is minimized. We reformulate the problem as maximum stable set problem on a special graph and study its structure. Valid inequalities and optimality cuts are derived, separated and tested in a computational experience that identifies some features of hard instances and the potential contribution of the addition, at root, of various cut classes
Optimum channel allocation in OFDMA multi-cell systems
No full textThis paper addresses the problem of allocating users to radio resources (i.e., sub-carriers) in the downlink of an OFDMA cellular system. We consider a classical multi-cellular environment with a realistic interference model and a margin adaptive approach, i.e., we aim at minimizing total transmission power while maintaining a certain given rate for each user. We discuss computational complexity issues of the resulting model and present a heuristic approach that finds optima under suitable conditions, or "reasonably good" solutions in the general case. Computational experiences show that, in a comparison with a commercial state-of-the-art optimization solver, our algorithm is quite effective in terms of both infeasibilities and transmitted powers and extremely efficient in terms of CPU times
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Optimal power control in OFDMA cellular networks
No full textThis article addresses the problem of allocating users to radio resources in the downlink of an OFDMA cellular system. We consider a classical multicellular environment with a realistic interference model and a margin adaptive approach, i.e., we aim at minimizing total transmission power while maintaining a certain given rate for each user. We discuss computational complexity issues of the resulting model and present a heuristic approach that finds optima under suitable conditions or reasonably good solutions in the general case. Computational experiments show the effectiveness of the proposed heuristic in a comparison with both a commercial state-of-the-art optimization solver and other approaches from the literature. Copyright © 2011 Wiley Periodicals, Inc
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