6721869
A Performance Study of Deployment Factors in Wireless Mesh Networks
We present a measurement-parameterized performance study of deployment factors in wireless mesh networks using three performance metrics: client coverage area, backhaul tier connectivity, and fair mesh capacity. For each metric, we identify and study topology factors and architectural features which strongly influence mesh performance via an extensive set of Monte Carlo simulations capturing realistic physical layer behavior. Our findings include: (i) A random topology is unsuitable for a large-scale mesh deployment due to doubled node density requirements, yet a moderate level of perturbations from ideal grid placement has a minor impact on performance. (ii) Multiple backhaul radios per mesh node is a cost-effective deployment strategy as it leads to mesh deployments costing 50% less than with a single-radio architecture, (iii) Dividing access and backhaul connections onto two separate radios does not use the second radio efficiently as it only improves fair mesh capacity 40% to 80% for most users. This is in contrast to using the second radio to move half the user population to a new network operated on the second radio. This work adds to the understanding of mesh deployment factors and their general impact on performance, providing further insight into practical mesh deployments.
12209685
Measurement driven deployment of a two-tier urban mesh access network
Multihop wireless mesh networks can provide Internet access over a wide area with minimal infrastructure expenditure. In this work, we present a measurement driven deployment strategy and a data-driven model to study the impact of design and topology decisions on network-wide performance and cost. We perform extensive measurements in a two-tier urban scenario to characterize the propagation environment and correlate received signal strength with application layer throughput. We find that well-known estimates for pathloss produce either heavily overprovisioned networks resulting in an order of magnitude increase in cost for high pathloss estimates or completely disconnected networks for low pathloss estimates. Modeling throughput with wireless interface manufacturer specifications similarly results in severely underprovisioned networks. Further, we measure competing, multihop flow traffic matrices to empirically define achievable throughputs of fully backlogged, rate limited, and web-emulated traffic. We find that while fully backlogged flows produce starving nodes, rate-controlling flows to a fixed value yields fairness and high aggregate throughput. Likewise, transmission gaps occurring in statistically multiplexed web traffic, even under high offered load, remove starvation and yield high performance. In comparison, we find that well-known noncompeting flow models for mesh networks over-estimate network-wide throughput by a factor of 2. Finally, our placement study shows that a regular grid topology achieves up to 50 percent greater throughput than random node placement.
6898048
Supporting manufacturing with simulation: model design, development, and deployment
In this paper, we identify and discuss the features we believe are key to the successful use of simulation as a manufacturing support tool. The discussion begins with three sample projects drawn from the authors' industrial and consulting experiences. Using these projects as motivation, we discuss the ideal project lifecycle model design, development, and deployment. For model design, we emphasize the importance of a clear and consistent specification, articulated in a written document. This specification should identify project customers, goals, and deliverables. We next review a range of model development options, stressing the existence of many non-simulation alternatives. We also discuss methods for model verification and validation. Finally, we consider the difficulties of model deployment, including simulation output analysis, data maintenance, and model integration. We close with several suggestions on how best to present simulation results to a management audience.
5441653
Integrating targeted cycle-time reduction into the capital planning process
This paper describes the development and application of an integrated static capacity and dynamic simulation analysis methodology for purchasing equipment capacity. The goal of the study is to address targeted cycle time objectives in a start up recording head wafer manufacturing facility at Seagate Technology, Minneapolis, MN. The short product cycle time, coupled with the competitive nature of the disc drive industry, has made cycle time reduction one of the most important objectives of production capacity planning. This paper describes an equipment procurement strategy in which static capacity analysis is used to identify an initial equipment set with a low slack capacity variable on each tool group. Simulation analysis is then used to identify the critical tool groups that contribute to cycle time delays. The Seagate Industrial Engineering team used the simulation analysis tool Factory Explorer(R) from Wright, Williams and Kelly to perform the cycle time reduction analysis. This targeted approach is compared to the traditional static capacity planning approach of globally applying reserve capacity buffers of 20% or more to achieve the same cycle time reduction goal. Overall, the targeted approach has proven to be efficient in terms of minimizing capital equipment expenditures and also effective on the factory floor.
10379830
Extended Query Answering Using Integrity Rules
The conventional use of databases is commonly restricted to the retrieval of factual data in the form of tuples or records. However most databases also contain metadata in the form of integrity rules which can provide a rich source of additional information not normally available to the user. Integrity rules define what data values and relationships may exist within the database and so their interrogation can provide answers as to whether a certain database state is possible. Our paper describes how this may be achieved and specifies a formal approach to implementing such an enquiry system.
15957762
Sensor networks and grid middleware for laboratory monitoring
By combining automatic environment sensing and experimental data collection with broker based messaging middleware, a system has been produced far the real-time monitoring of experiments whilst away from the lab. Changes in the laboratory environment are encapsulated as simple messages, which are published using an MQTT compliant broker. Clients subscribe to the MQTT stream, and perform a data transform on the messages; this may be to produce a user display or to change the format of the message for republishing. For example, an MQTT client written for the Java MIDP platform can be run on a smart-phone with a GPRS Internet connection, freeing us from the constraints of the network. We present an overview of the technologies used, and how these are helping chemists make the best use of their time
6479052
Data Analysis for Query Processing
Data analysis is needed in connection with query processing, to produce data summary information in the form of rules or assertions that allow semantic query optimisation or direct query answering without consulting the data itself. The goal of an intelligent analyser in this context is to produce robust rules, stable in the presence of data changes, which allow easy rule maintenance as data changes, and provide rapid query reformulation, refutation or answering. It must also limit the rule set to rules useful for query processing.