295636
Agent-Based Forwarding Strategies for Reducing Location Management Cost in Mobile Networks
An important issue in location management for dealing with user mobility in wireless networks is to reduce the cost associated with location updates and searches. The former operation occurs when a mobile user moves to a new location registration area and the network is being informed of the mobile user's current location; the latter operation occurs when there is a call for the mobile user and the network must deliver the call to the mobile user. In this paper, we propose and analyze a class of new agent-based forwarding schemes with the objective to reduce the location management cost in mobile wireless networks. We develop analytical models to compare the performance of the proposed schemes with existing location management schemes to demonstrate their feasibility and also to reveal conditions under which our proposed schemes are superior to existing ones. Our proposed schemes are particularly suitable for mobile networks with switches which can cover a large number of location registration areas.
2862791
A data delivery strategy in ubiquitous computing systems
Browsing Web pages through wireless devices will become more and more popular in the near future. However, accessing a large chunk of Web data incurs a great amount of access latency while a mobile user migrates across cells. This paper investigates this problem and proposes an effective way of delivering such data to a mobile user in a ubiquitous computing system. Our data delivery (/spl Dscr//sup 2/) strategy is based on the dynamic programming skill needed to pre-assign the user-requested data on the possible cells to be visited in order to reduce the access latency. We first design an encoding method for the cells and then derive the properties of the encoding scheme. These properties are then used in our algorithm to deliver the data. Finally, experiments are conducted to demonstrate the feasibility and efficiency of the proposed method.
31930663
Minimization of resource consumption for multidatabase query optimization
Due to the autonomy of individual databases, a multidatabase system (MDBS) has no control over the task execution within each database system. This complicates the issue of query optimization in a MDBS. Past researchers tackled this problem mainly by regenerating the cost model of each participating database systems. However a completely autonomous participating database system does nor own the information (data) as well as the mechanism (software) for converting data of one database to another to resolve the data type conflict problems that can occur in any MDBS environment. In addition, unpredictable factors that can drastically deviate the accuracy of a regenerated cost model (in the past research) come into play at unknown time. This confines the processing of an intersite operation (such as a join over two relations of different databases) to the MDBS only. The participating database systems will not be able to share the workload of the MDBS under this circumstance. Hence, minimizing the consumption of system resources of the MDBS is an urgent problem. The authors propose three scheduling algorithms that are used in the MDBS to reduce the processing cost of a multidatabase query. A major difference between the strategies and the past methods is that ours do not require the knowledge of the cost models of the participating databases.
9253270
Query Optimization in Multidatabase Systems Considering Schema Conflicts
In a multidatabase system, the participating databases are autonomous. The schemas of these databases may be different in various ways, while the same information is represented. A global query issued against the global database needs to be translated to a proper form before it can be executed in a local database. Since data requested by a query (or a part of a query) is sometimes available in multiple sites, the site (database) that processes the query with the least cost is the desired query processing site. The authors study the effect of differences in schemas on the cost of query processing in a multidatabase environment. They first classify schema conflicts to different types. For each type of conflict, they show how much more or less complex a translated query can become in comparison with the originally user-issued global query. Based on this observation, they propose an analytical method that considers the conflicts between local databases and finds the database(s) that renders the least execution cost in processing a global query. This research introduces a new level of query optimization (termed the schema-level optimization) in multidatabase environments. The results provide a new dimension of enhancement for the capability of a query optimizer in multidatabase systems.
18796888
Design and Performance Evaluation of Broadcast Algorithms for Time-Constrained Data Retrieval
We refer "time-constrained services" to those requests that have to be replied to within a certain client-expected time duration. If the answer cannot reach the client within this expected time, the value of the information may seriously degrade or even become useless. On-demand channels may not be able to handle all time-constrained services without degrading the performance. How to handle these services in broadcast channels becomes crucial to balance the load of wireless systems. In this paper, we study this problem and find the minimum number of broadcast channels required for such a task. Also, we propose solutions for this problem when the available channels are insufficient. Our performance result reveals that only a moderate number of channels is required to promote these time-constrained services
20308502
Object signatures for supporting efficient navigation in object-oriented databases
Most methods that have been proposed to improve query processing in object-oriented databases are designed for the aggregation hierarchy. Although the structure of the generalization hierarchy is similar to the aggregation hierarchy, techniques developed for the aggregation hierarchy cannot fully use the characteristics of the generalization hierarchy to improve performance. We devise a new object signature for the generalization hierarchy. The object signature consists of two parts: a reference signature and a structure signature. The former can be used to eliminate objects that do not match the nested predicates specified in the query, and the latter can be used to eliminate objects that do not belong to the target classes. We propose some processing methods using the object signatures for queries that involve generalization hierarchies. In addition, we define cost models of the object signature and then compare the performance of the traditional query processing method with the object signature method. The results show that using the object signatures can effectively reduce the number of disk accesses in a query.
13953434
A design of multi‐layered location registration areas in microcellular systems
Multi‐layered location registration areas are considered to minimize the control signals at boundary cells in the microcellular systems. The decision of multi‐layered location registration (LR) areas is formulated as an integer programming problem by examining the regional subscriber densities, traffic flows and call arrival rates. By relaxing the constraints of forward and reverse control channels the problem is decomposed into a number of subproblems each of which corresponds to a layer. Each subproblem is solved via a modified graph partitioning algorithm. Feasible LR areas are obtained by considering the two relaxed constraints. Computational experiments are performed in a system with 80 microcells to investigate the performance of the proposed multi‐layer scheme. The simulation results indicate that the two‐layer scheme generally outperforms the one‐layer and three‐layer methods in view of control signals.
2097119
Coordinated search and track by multiple phased array radars
This paper addresses the search and track coordination problems of multiple shipboard radars. The proposed approach first exploits the physical characteristics of a single phased array radar to improve its effective capacity. Its effective capacity is abstracted by a closed-form equation called a schedulability envelope. Using the schedulability envelope for each radar, we deal with search and track coordination as a relative-load-balancing problem in a multiresource environment. The simulation results show that the proposed approach significantly improves the overall capacity of a multiship multiradar system.
2177844
Design, performance analysis, and implementation of a super-scalar video-on-demand system
Despite the availability of video-on-demand (VoD) services in a number of cities around the world, large-scale deployment of VoD services in a metropolitan area is still economically impractical. This study presents a novel super-scalar architecture for building very large-scale and efficient VoD systems. The proposed architecture combines the use of static multicast, dynamic multicast, and intelligent client-side caching to vastly reduce server and network resource requirement. Moreover, in sharp contrast to conventional VoD systems where the system cost increases at least linearly with the system scale, the proposed architecture becomes more efficient as the system scales up and can ultimately be scaled up to serve any number of users while still keeping the startup latency short. This paper presents this new architecture, proposes methods to support interactive playback controls without the need for additional server or client resources, and derives an approximate performance model to relate the startup latency with other system parameters. The performance model is validated using simulation and the architecture is evaluated under various system settings. Lastly, a system implementation is presented and benchmarking results obtained to further verify the architecture, the performance model, and the simulation results.
13302890
An Efficient and Scalable Management of Ontology
OWL is a recommended language for publishing and sharing ontologies on the Semantic Web. To manage the ontologies, several OWL data management systems have been proposed. However, the existing systems have limitations of the scalability and the reasoning. In this paper, we propose an OWL data management system, ONTOMS, which stores OWL data into class based relations, performs complete inverseOf, symmetric, and transitive reasoning for instances, and efficiently evaluates OWL-QL queries against ontologies in a relational database.
19284732
Smart sinks: real-world opportunities for context-aware interaction
Can implicit interaction with a computer easily drive useful interface improvements in physical world settings? This paper presents a case study presenting multiple such context-aware interaction improvements in a sink. We have identified opportunities where automated interfaces at the sink have positive consequences for safety, hygiene and ecology. The danger of scalding oneself with hot water is confronted by transforming the water into a graphical user interface and using image understanding to dispense the proper temperature of water. Audio-visual feedback at the sink can motivate users to conserve water. Used in combination with an RFID reader, the sink can serve as an effective means of verifying hand-washing compliance for clean environments. Finally, automatic actuation of the sink's height based on the user and task can prevent burns and ergonomic injuries. This project demonstrates that the integration of digital interaction in a hostile environment can facilitate and improve our daily rituals.