10913965
A study of time warp rollback mechanisms
The Time Warp “optimistic” approach is one of the most important parallel simulation protocols. Time Warp synchronizes processes via rollback. The original rollback mechanism called lazy cancellation has aroused great interest. This paper studies these rollback mechanisms. The general tradeoffs between aggressive and lazy cancellation are discussed, and by a conservitive-optimal simulation is defined for comparitive purposes. Within the framework of aggressive cancellation, we offer some observations and analyze the rollback behavior of tandom systems. The lazy cancellation mechanism iss examined using a metric called the sensitivity of output message. Both aggressive and lazy cancellation are shown to work well for a process with a small simulated load intensity. Finally, an analytical model is given to analyze message preemtion, an important factor that affects the performance of rollback mechanisms. Results indicate that message preemtion has a significant effect on performance when (1) the processor is highly utilized, (2) the execution times of messages have high varience, and (3) rollbacks occur frequently.
16744149
Performance Analysis for Dual Band PCS Networks
In a dual band personal communications services (PCS) network, heavy traffic areas are covered by microcells which overlay macrocells. In such a network, microcells and macrocells utilize different frequency bands. We propose an analytic model to study the performance of a dual band PCS architecture. Our model assumes that a PCS subscriber has a general residence time distribution in a microcell and the macrocell residence time distribution is derived from the microcell residence time distribution. An iterative algorithm is used to compute the overflow traffic from a microcell to its overlaid macrocell. Then, the call incompletion probability is computed by a macrocell model based on the overflow traffic. Our study indicates that the variance of the microcell residence time distribution and the number of microcells covered by a macrocell have significant effects on the call incompletion probability.
5110930
A comparison study of the two-tier and the single-tier personal communications services systems
A two-tier PCS system integrates the high tier PCS system and the low tier PCS systems into a single system to provide the advantages of both tiers. Such a system is expected to provide better service (more available and more cost effective to the users) at the expense of the extra tier switching management. We compare the performance of the two-tier PCS system and the single low tier system in two aspects: the registration traffic and the service availability. Because of the tier management, the two-tier system generates more registration traffic than the single low tier system. Under the range of the input parameters in our study, we show that the two-tier system generates less than 10% extra registration traffic than the single low tier system in most cases and generates less than 20% registration traffic in the worst cases. It is clear that for the service availability, the two-tier system is better than the single one tier system. We also study the probability that a call is forced terminated in the single low tier system because the low tier becomes unavailable during the call (such a call can be continued in the two-tier system).
15619003
A Graphical User Interface Design for Network Simulation
Abstract This article describes a prototyping effort of a flexible graphical user interface (GUI) for a simulation tool called COPS. The GUI is designed to allow parameter setup for all modules in simulation model, and can be easily replaced by new GUIs implemented in different languages/graphical tools. This article provides design guidelines and implementation details of the flexible GUI.
2805042
A new random walk model for PCS networks
This paper proposes a new approach to simplify the two-dimensional random walk models capturing the movement of mobile users in personal communications services (PCS) networks. Analytical models are proposed for the new random walks. For a PCS network with hexagonal configuration, our approach reduces the states of the two-dimensional random walk from (3n/sup 2/+3n-5) to n(n+1)/2, where n is the layers of a cluster. For a mesh configuration, our approach reduces the states from (2n2-2n+1) to (n/sup 2/+2n+4)/4 if n is even and to (n/sup 2/+2n+5)/4 if n is odd. Simulation experiments are conducted to validate the analytical models. The results indicate that the errors between the analytical and simulation models are within 1%. Three applications (i.e., microcell/macrocell configuration, distance-based location update, and GPRS mobility management for data routing) are used to show how our new model can be used to investigate the performance of PCS networks.
22500122
Performance of hot billing mobile prepaid service
Abstract Prepaid service has become an important mobile application with rapid growth for subscription rate in the recent years. Implementation of prepaid service may generate large network traffic that significantly affects the performance of a mobile network. This paper studies the hot billing solution for prepaid service. We investigate how the amount of prepaid credit and the frequency of call detail record (CDR) transmissions affect network signaling and potential bad debt that a service provider may bear. Our study suggests that a prepaid service provider should encourage customers to buy large prepaid credits by giving them discounts. Furthermore, based on call traffic, an optimal CDR transmission frequency can be found by using our modeling technique.
11056764
Integrating multi-agent negotiation to resolve constraints in fulfilling supply chain orders
Abstract As the order fulfillment process (OFP) in supply chains shifts to outsourcing paradigm, the OFP performance relies on the coordination among supply chain partners to reach executable and effective plans. The coordination of OFP among supply chain partners can be viewed as a distributed constraint satisfaction problem (DCSP). This study adds the multi-agent negotiation mechanism to enhance the existing methods to solve the DCSP, and then evaluates the integrated system’s performance through experimentation on the OFP in the context of the metal industry. The experimental results show that the integrated system outperforms the existing distributed constraint satisfaction algorithms in various demand patterns.
13768633
Software Defined Radio - A High Performance Embedded Challenge
Wireless communication is one of the most computationally demanding workloads. It is performed by mobile terminals (“cell phones”) and must be accomplished by a small battery powered system. An important goal of the wireless industry is to develop hardware platforms that can support multiple protocols implemented in software (software defined radio) to support seamless end-user service over a variety of wireless networks. An equally important goal is to provide higher and higher data rates. This paper focuses on a study of the wideband code division multiple access protocol, which is one of the dominant third generation wireless standards. We have chosen it as a representative protocol. We provide a detailed analysis of computation and processing requirements of the core algorithms along with the interactions between the components. The goal of this paper is to describe the computational characteristics of this protocol to the computer architecture community, and to provide a high-level analysis of the architectural implications to illustrate one of the protocols that would need to be accommodated in a programmable platform for software defined radio. The computation demands and power limitations of approximately 60 Gops and 100~300 mW, place extremely challenging goals on such a system. Several of the key features of wideband code division multiple access protocol that can be exploited in the architecture include high degrees of vector and task parallelism, small memory footprints for both data and instructions, limited need for complex arithmetic functions such as multiplication, and a highly variable processing load that provides the opportunity to dynamically scale voltage and frequency.
16396963
Performance-driven interconnection optimization for microarchitecture synthesis
This paper addresses the interconnection synthesis problem in microarchitecture-level designs. With emphasis on the speed of data movement operations, we propose algorithms that take into consideration the effect of each data-transfer-to-bus binding on the data transfer delay time. The delay time is calculated as a function of both data source load and data carrier (bus) load. By balancing loads among hardware components, the data transfer delay time (hence the total execution time) is shortened. We consider two types of problems: resource-constrained binding and performance-constrained binding. Two integer linear programming (ILP) formulations are derived to optimally solve the problems. In order to speed up the computation, a bipartite weighted matching method for the resource-constrained binding and a greedy merging method for the performance-constrained binding are also proposed. Both the ILP formulation generators and the heuristics have been programmed. Experimental results indicate that the proposed algorithms are indeed very effective in optimizing the performance aspect of the interconnection design. >
16924532
Expansion of layouts of complete binary trees into grids
Let Th be the complete binary tree of height h. Let M be the infinite grid graph with vertex set Z2, where two vertices (x1, y1) and (x2, y2) of M are adjacent if and only if |x1-x2| + |y1-y2|= 1. Suppose that T is a tree which is a subdivision of Th and is also isomorphic to a subgraph of M. Motivated by issues in optimal VLSI design, we show that the point expansion ratio n(T)/n(Th) = n(T)/(2h+1 - 1) is bounded below by 1.122 for h sufficiently large. That is, we give bounds on how many vertices of degree 2 must be inserted along the edges of Th in order that the resulting tree can be laid out in the grid. Concerning the constructive end of VLSI design, suppose that T is a tree which is a subdivision of Th and is also isomorphic to a subgraph of the n × n grid graph. Define the expansion ratio of such a layout to be n2/n(Th)=n2/(2h+1 - 1). We show constructively that the minimum possible expansion ratio over all layouts of Th is bounded above by 1.4656 for sufficiently large h. That is, we give efficient layouts of complete binary trees into square grids, making improvements upon the previous work of others. We also give bounds for the point expansion and expansion problems for layouts of Th into extended grids, i.e. grids with added diagonals.
14636806
Channel density reduction by routing over the cells
We propose a new approach for reducing the density of a channel by routing some nets (or subnets) over the cells (i.e., outside the channel). Previous research assumed that the more nets being routed over the cells the greater the reduction in the channel density. We show that only the removal of critical nets contributes to the re- duction in the channel density. We divide channel into zones where each zone has a zone density and the removal of any net from a zone will reduce its density by one. In order to reduce the channel density, only certain critical zones need to have their nets routed over the cells. A bipartite graph is used to represent the relationship between nets and zones. The problem is transformed into a constrained covering problem and formulated as an integer linear programming problem. In comparison with previous research, our approach reduces more channel densities while using fewer tracks over the cells. For Deutsch's difficult khannel, a previous aiiproach needs 15 tracks over the cells to reduce the channel density by 3 while we need only 5 tracks to achieve the same result . Index Terms-Over-the-cell routing, channel density reduction, stan- dard-cell layout, VLSI routing, integer linear programming.