18483873
Modeling Frequently Accessed Wireless Data With Weak Consistency
To reduce the response times of wireless data access in a mobile network, caches are utilized in wireless handheld devices. If the original data entry has been updated, the cached data in the handheld device becomes stale. Thus, a mechanism is required to predict when the cached copy will expire. This paper studies a weakly consistent data access mechanism that computes the time-to-live (TTL) interval to predict the expiration time. We propose an analytic model to investigate this TTL-based algorithm for frequently accessed data. The analytic model is validated against simulation experiments. Our study quantitatively indicates how the TTL-based algorithm reduces the wireless communication cost by increasing the probability of stale accesses. Depending on the requirements of the application, appropriate parameter values can be selected based on the guidelines provided in this paper.
16848330
A flexible graphical user interface for performance modeling
We identify three goals for the graphical user interface (GUI) of a network simulation environment: user friendliness, model re-usability, and application extensibility. We address the user friendliness issue by proposing a simple yet efficient approach to setup parameters for the simulation models. We address the application extensibility issue by a two-layer GUI architecture. The two layers are loosely-coupled, and the first layer can be easily replaced (without affecting the other components of the simulation environment). We address the model re-usability issue by subnetworks. Unlike most existing simulation packages where subnetwork is simply a method to group the nodes, the subnetwork construct in our approach is an integral part of the simulation environment (i.e., all operations for a basic node also apply to a subnetwork). The port concept is used to explicitly define the I/O relationship between a subnetwork and the outside world. Parameter dialog boxes are used to set up the parameters for a subnetwork conveniently. Finally, a simple stack mechanism is proposed to measure subnetwork-wide output statistics.<<ETX>>
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).
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.
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.
18540245
Array allocation taking into account SDRAM characteristics
Multimedia, image processing and other signal processing applications often involve data stored in large arrays. Due to chip area limitation, arrays are typically assigned to off-chip memories, such as DRAM. This being the case, we try to optimize off-chip memory accesses to improve performance. We take the characteristics of the current mainstream SDRAM memory into account. We propose an algorithm to allocate arrays to different banks to increase the probability of utilizing SDRAM's multi-bank characteristic. Experimental results show significant improvement over traditional approaches.
27186635
Register minimization beyond sharing among variables
Traditionally, it is assumed that every variable in the input HDL (hardware description language) behavioral description needs to be held in a register; a register can be shared by multiple variables if they have mutually disjointed lifetime intervals. This approach has been shown effective for signal-flow-like computations such as various DSP algorithms. However, the same is not true for the synthesis of control-dominated circuits, which usually have variables of different bit-width as well as very long lifetime. To go beyond register minimization by lifetime-analysis-based sharing, we propose holding some variables in the state registers, some signal nets, some unclocked sequential networks or a combination of above. We identify the conditions in which the substitution is feasible. We have implemented the proposed method in a software program called VReg. Experimental results have demonstrated that VReg minimizes the number of registers more effectively than the lifetime-analysis-based approach does. Better register area minimization also generally leads to faster designs.
6310496
Middleware based data replication providing snapshot isolation
Many cluster based replication solutions have been proposed providing scalability and fault-tolerance. Many of these solutions perform replica control in a middleware on top of the database replicas. In such a setting concurrency control is a challenge and is often performed on a table basis. Additionally, some systems put severe requirements on transaction programs (e.g., to declare all objects to be accessed in advance). This paper addresses these issues and presents a middleware-based replication scheme which provides the popular snapshot isolation level at the same tuple-level granularity as database systems like PostgreSQL and Oracle, without any need to declare transaction properties in advance. Both read-only and update transactions can be executed at any replica while providing data consistency at all times. Our approach provides what we call "1-copy-snapshot-isolation" as long as the underlying database replicas provide snapshot isolation. We have implemented our approach as a replicated middleware on top of PostgreSQL replicas. By providing a standard JDBC interface, the middleware is completely transparent to the client program. Fault-tolerance is provided by automatically reconnecting clients in case of crashes. Our middleware shows good performance in terms of response times and scalability.
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.
30062933
LiB: a CMOS cell compiler
An automatic layout generation system, called LiB, for the small-scale integrated (SSI) cells used in CMOS VLSI design, is presented. LiB takes a transistor-level circuit schematic in SPICE format and outputs a mask layout in CIF. The layout style is a modification of that proposed by T. Uehara, and W. M. van Cleemput (IEEE Trans. Comput., vol.C-30, no.5, p.305-12, 1981). An optimal transistor chaining algorithm has been developed to derive a transistor placement with a minimum number of diffusion separations. To meet the cell height constraint, large transistors are folded into multiple columns algorithmically. The whole cell is divided into five routing regions. Two are on the diffusion island and the others are rectilinear-shaped routing channels. A graph-theoretic method for selecting nets (subnets) for routing on the diffusion island is proposed. A global routing algorithm has been developed to assign the remaining nets to the three rectilinear channels. For the detailed routing SILK, a simulated evolution router, is employed. LiB can be used as a cell library builder or as a subsystem of a random logic module generator. Users can alternate LiB's layout using a symbolic editor. >