36399349
Optimal (N, T)-policy for M/G/1 system with cost structures
Abstract In this paper, the optimal (N,T)-policy for M/G/1 system with cost structure is studied. The system operates only intermittently. It is shut down when no customers are present. A fixed set-up cost of K>0 is incurred each time the system is reopened. Also, a holding cost of h>0 per unit time is incurred for each customer present. The (N,T)-policy studied for this system is as follows: the system reactivates as soon as N customers are present or the waiting time of the leading customer reaches a predefined time T (see A.S. Alfa, I. Frigui, Eur. J. Oper. Res. 88 (1996) 599-613; Y.N. Doganata, in: E. Arikan (Ed.), Communication, Control, and Signal Processing, 1990, pp. 1663–1669). Later on, as a comparison, the start of the timer count is relaxed as follows: the system reactivates as soon as N customers are present or the time units after the end of the last busy period reaches a predefined time T. For both cases, the explicit optimal policy (N*,T*) for minimizing the long-run average cost per unit time are obtained. As extreme cases, we include the simple optimal policies for N-and T-polices. Several counter-intuitive results are obtained about the optimal T-policies for both types of models.
18146611
A channel allocation model with preemptive priority for integrated voice/data mobile networks
This paper presents an analytical model of channel allocations with preemptive priority to study the handoff performance for integrated voice/data mobile networks. By analyzing the system as a quasi-birth-and-death process, we obtain the steady state probabilities and some interesting performance measures, such as new voice (new data) blocking probability, handoff voice (handoff data) dropping probability, the channel utilization, and the busy period time in the cell. From the analysis and numerical results, we can conclude that our scheme can provide complete service differentiation and different QoS guarantee for different traffic classes, and get pretty good channel utilization by appropriate threshold parameter design. The performance measures obtained in the paper are very useful in evaluating the needed resource of future wireless mobile networks.
16667492
Special issue: modeling and performance evaluation of radio resource QoS for next-generation wireless and mobile networks
A rotary regenerative heat exchanger wherein radial plates are connected to radial plate pins which engage a pair of core plates disposed about a rotor shaft and which permit axial, radial, and rotational movement.
6504334
Modeling and analysis of hierarchical cellular networks with bidirectional overflow and take-back strategies under generally distributed cell residence times
The rapid growth of wireless services and mobile users drives a great interest in cellular networks with a hierarchical structure. Hierarchical cellular networks (HCNs) can provide high system capacity, efficient channel utilization and inherent load-balancing capability. In this paper, we develop an analytical model and a performance analysis method for a two-layer HCN with bidirectional overflow and take-back strategies. Mobile users are divided into two classes. The call requests (including new and handoff calls) of fast and slow users are preferably assigned to the macrolayer and microlayer, respectively. A call from a fast user or slow user can overflow to its non-preferable layer if there is no channel available. The successful overflow call can be taken back to its preferable layer if a channel becomes available. Since the commonly used exponentially distributed assumption for cell residence time and then the channel occupancy time does not hold for emerging mobile networks, we model various cell residence times by general distributions to adapt to more flexible mobility environments. The channel occupancy times are derived in terms of the Laplace transforms of various cell residence times. The handoff rates, overflow rates and take-back rates of each layer are also derived in terms of the new call arrival rates and related probabilities. The stationary probabilities (and then the performance measures) are determined on the basis of the theory of multi-dimensional loss systems.
13091278
Dynamics of local search heuristics for the traveling salesman problem
This paper experimentally investigates the dynamical behavior of a search process in a local heuristic search system for a combinatorial optimization problem. Or-opt heuristic algorithm is chosen as the study subject, and the well-known traveling salesman problem (TSP) serves as a problem testbed. This study constructs the search trajectory by using the time-delay method, evaluates the dynamics of the local search system by estimating the correlation dimension for the search trajectory, and illustrates the transition of the local search process from high-dimensional stochastic to low dimensional chaotic behavior.
16400135
Adaptive grid-based document layout
Grid-based page designs are ubiquitous in commercially printed publications, such as newspapers and magazines. Yet, to date, no one has invented a good way to easily and automatically adapt such designs to arbitrarily-sized electronic displays. The difficulty of generalizing grid-based designs explains the generally inferior nature of on-screen layouts when compared to their printed counterparts, and is arguably one of the greatest remaining impediments to creating on-line reading experiences that rival those of ink on paper. In this work, we present a new approach to adaptive grid-based document layout, which attempts to bridge this gap. In our approach, an adaptive layout style is encoded as a set of grid-based templates that know how to adapt to a range of page sizes and other viewing conditions. These templates include various types of layout elements (such as text, figures, etc.) and define, through constraint-based relationships, just how these elements are to be laid out together as a function of both the properties of the content itself, such as a figure's size and aspect ratio, and the properties of the viewing conditions under which the content is being displayed. We describe an XML-based representation for our templates and content, which maintains a clean separation between the two. We also describe the various parts of our research prototype system: a layout engine for formatting the page; a paginator for determining a globally optimal allocation of content amongst the pages, as well as an optimal pairing of templates with content; and a graphical user interface for interactively creating adaptive templates. We also provide numerous examples demonstrating the capabilities of this prototype, including this paper, itself, which has been laid out with our system.
206817675
Independence numbers of graphs and generators of ideals
This article investigates the generators of certain homogeneous ideals which are associated with graphs with bounded independence numbers. These ideals first appeared in the theory oft-designs. The main theorem suggests a new approach to the Clique Problem which isNP-complete. This theorem has a more general form in commutative algebra dealing with ideals associated with unions of linear varieties. This general theorem is stated in the article; a corollary to it generalizes Turán’s theorem on the maximum graphs with a prescribed clique number.
9445959
Guiding real-world SAT solving with dynamic hypergraph separator decomposition
The general solution of satisfiability problems is NP-complete. Although state-of-the-art SAT solvers can efficiently obtain the solutions of many real-world instances, there are still a large number of real-world SAT families which cannot be solved in reasonable time. Much effort has been spent to take advantage of the internal structure of SAT instances. Existing decomposition techniques are based on preprocessing the static structure of the original problem. We present a dynamic decomposition method based on hypergraph separators. Integrating the separator decomposition into the variable ordering of a modern SAT solver leads to speedups on large real-world satisfiability problems. Compared with a static decomposition based variable ordering, such as Dtree (Huang and Darwiche, 2003), our approach does not need time to construct the full tree decomposition, which sometimes needs more time than the solving process itself. Our primary focus is to achieve speedups on large real-world satisfiability problems. Our results show that the new solver often outperforms both regular zChaff and zChaff integrated with Dtree decomposition. The dynamic separator decomposition shows promise in that it significantly decreases the number of decisions for some real-world problems.
2986954
EXIT chart analysis of turbo-BLAST receivers in Rayleigh fading channels
Turbo-BLAST is an advanced space-time layered architecture developed to approach the capacity limit of multiple-input multiple-output (MIMO) systems. Various multiuser detection (MUD) techniques have been explored in conjunction with turbo-BLAST to combat cochannel interference (CCI) and improve significantly the performance of MIMO systems in a multicell structure (Dai, H. et al., IEEE Trans. Wireless Commun.. vol.3. p.442-53, 2004). We study the extrinsic information transfer (EXIT) functions of several such turbo-BLAST receivers. We show that the EXIT functions, which work primarily for AWGN channels, are not accurate in giving quantitative performance estimates in a fading environment. A method that copes with this problem and yields reasonably accurate estimates of convergence rate and bit-error-rate is proposed. The performance of different turbo-BLAST receivers is compared in both single-cell and multicell scenarios.