Improving Admission Control Policies in Database Management Systems, Using Data Mining Techniques

In multiuser multiple‐input multiple‐output/orthogonal frequency‐division multiplexing (MIMO/OFDM) systems, the EigenValue Decomposition (EVD) method was proposed to construct a number of parallel spatial channels. The beamforming technique which only exploits the spatial subchannel related to the largest eigenvalue is usually adopted in many papers to deal with adaptive resource allocation. Although these previous studies could maximise the received signal‐to‐noise ratio (SNR), they could not get the maximum system throughput. In this paper, all the spatial subchannel are investigated. With the goal of maximising the overall system throughput, we derive a simple effective criterion of subcarrier allocation and introduce an adaptive resource allocation algorithm. The proposed algorithm could get higher system throughput especially at high SNR, that is the spectral efficiency is improved about 3 bit/s/Hz at 14 dB. At the same time, in order to decrease the computational complexity, a time‐frequency blockwise loading design is suggested. In practical channel with partial channel state information (CSI), a modified algorithm based on mean feedback model is proposed. The simulation results show that under imperfect CSI, the modified algorithm could achieve optimum system throughput while guaranteeing prescribed error performance. On the other hand, in comparison to perfect CSI, the system throughput decreases. Copyright © 2008 John Wiley & Sons, Ltd.

One of the most important qualities of a database management system running on a small system is its ability to provide data independence. A relational database management system provides data independence through its use of tables for data storage. Use of a standard operating system means that a database management system can be run on a wide variety of systems, allowing data to be transported not only between small systems but between small and large systems.Assuming that a database management system provides data independence, what other features are needed? A comparison of the features provided by two such database management systems and how easy they are to use would be helpful in answering this question. This paper presents a comparison of UNIFY and Intel Database Management System (iDB). Both are relational, multi-user systems that run under the UNIX operating system.

The Web Map Server Implementation Specification (WMS), originally developed and published by the Open Geospatial Consortium, was finally adopted by ISO as an international standard. According to this standard maps are presented either in picture formats or formats. While the pictorial (visual) representation uses raster formats, graphic element formats include Scalable Vector Graphics (SVG) or Web Computer Graphics Metafile (WebCGM) format. In this paper a framework for supporting Web Map Services using SVG will be presented. Geo-data, converted to SVG, is stored in a database management system, retrieved by the WMS server upon user request and transferred - optionally compressed - through the Internet. Finally it is visualized in Web browsers on desktop computes or mobile devices, natively or using plug-ins extending the browser's functionality. Besides supporting the WMS request GetCapabilities, GetMap and GetFeatureInfo requests, additional formats and extensions have been included in this framework. The development proves that open, XML-based standards in combination with modern programming languages and integrated development environments allow rapid implementation of recommendations and standards in geo-informatics.

Phase masks coronagraphs can be seen as linear systems that spatially redistribute, in the pupil plane, the energy collected by the telescope. Most of the on-axis light must ideally be rejected outside the aperture to be blocked with a Lyot stop, while almost all off-axis light must go through it. The unobstructed circular apertures of off-axis telescopes make this possible but all major telescopes are however on-axis and the performance of these coronagraphs is dramatically reduced by the central obstruction. Their performance can be restored by using an additional optimally designed apodizer that changes the amplitude in the first pupil plane so that the on-axis light is rejected outside the obstructed aperture of the telescope. The numerical optimization model is built by maximizing the apodizer's transmission while setting constraints on the extremum values of the electric field that the Lyot stop does not block. The coronagraphic image is compared to what a non-apodized phase mask coronagraph provides and an analysis is made of the trade-offs that exist between the apodizer transmission and the Lyot stop properties. The existence of a solution and the mask transmission depend on the aperture and the Lyot stop geometries, and on the constraints that are set on the on-axis attenuation. The system throughput is a concave function of the Lyot stop transmission. In the case of a VLT-like aperture, apodizers with a transmission of 0.16 to 0.92 associated with a four-quadrant phase mask provide contrast as low as a few 1e-10 at 1 lambda/D from the star. The system's maximum throughput is 0.64, for an apodizer with an 0.88 transmission and a Lyot stop with a 0.69 transmission. Optimizing apodizers for a vortex phase mask requires computation times much longer than in the previous case, and no result is presented for this mask.

Wireless local area networks are currently evolving to support adequate degrees of service differentiation. Work is in progress to define an enhanced version of the IEEE 802.11 distributed coordination function, which is capable of supporting quality of service for multimedia traffic at the medium access control layer. In this paper, we aim at gaining insight into one mechanism to differentiate among traffic categories, i.e., differentiating the minimum contention window sizes according to the priority of different traffic categories. The contribution of this paper is the analysis of the optimal operation point where maximum throughput can be achieved. Through the analysis, we answer some fundamental questions about the existence and uniqueness of the optimal operation point, about the maximum system throughput, about the existence of simple rules to decide if the system operates under the optimal state or not, and about procedures to lead the system to the optimal operation point. The other contribution is the proposal of a simple adaptive scheme that makes the system operate under the optimal operation point and, at the same time, achieve target service differentiation between different traffic flows. The results that are obtained in this paper are relevant to both theoretical research and implementations of real systems

Workload adaptation is a performance management process in which an autonomic database management system (DBMS) efficiently makes use of its resources by filtering or controlling the workload presented to it in order to meet its Service Level Objectives (SLOs). This paper presents a framework and a prototype implementation of a query scheduler that performs workload adaptation in a DBMS. The system manages multiple classes of queries to meet their performance goals by allocating DBMS resources through admission control in the presence of workload fluctuation. The resource allocation plan is derived by maximizing the objective function that encapsulates the performance goals of all classes and their importance to the business. A first-principle performance model is used to predict the performance under the new resource allocation plan. Experiments with IBM® DB2® Universal Database#8482; are conducted to show the effectiveness of the framework.

Cognitive radio networks (CRNs) allow unlicensed users to opportunistically access the licensed spectrum without causing disruptive interference to the primary users (PUs). One of the main challenges in CRNs is the ability to detect PU transmissions. Recent works have suggested the use of secondary user (SU) cooperation over individual sensing to improve sensing accuracy. In this paper, we consider a CRN consisting of multiple PUs and SUs to study the problem of maximizing the total expected system throughput. First, we study the sensing decision problem for maximizing the system throughput subject to a constraint on the PU throughput, and we design a Bayesian decision rule-based algorithm. The problem is shown to be strongly NP-hard and solved via a greedy algorithm with time complexity O([(N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> )/(log <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> [1/(1-ε)])]), where N is the total number of SUs. The algorithm achieves a throughput strictly greater than 1/2(1-ε) of the optimal solution and results in a small constraint violation that goes to zero with ε. We then investigate the more general problem with constraints on both PU throughput and the sensing time overhead, which limits the number of SUs that can participate in cooperative sensing. We illustrate the efficacy of the performance of our algorithms and provide sensitivity analysis via a numerical investigation.

For multi-transmission rate environments, access point (AP) connection methods have been proposed for maximizing system throughput, which is the throughput of an entire system, on the basis of the cooperative behavior of users. These methods derive optimal positions for the cooperative behavior of users, which means that new users move to improve the system throughput when connecting to an AP. Typically, the arrival of two or more new users causes signal interference for other users. Specifically, traditional methods have not considered interference and the number of allowable mobile positions is so large that it is difficult to find the optimal position to maximize system throughput. In this paper, we propose an AP connection method that maximizes system throughput by considering interference between users, with a potential game model. This game can find at least one optimal user position. Moreover, numerical analyses show the effectiveness of our method.

A model for a code division multiple access (CDMA) packet radio network in which users are organized, by geography or some other criteria, into multiple clusters or cells, is presented. Each cell contains a base station through which all user communications occur. Inter-cell connectivity is provided by a backbone network of the base stations. In this network, downlink (base station-to-user) transmissions suffer from head-of-line blocking. Taking this into account, the maximum system throughput is found. Tight upper bounds for the maximum system throughput are also found using a much simpler analysis. >

The Multimedia Cable Networks Systems (MCNS) Data Over Cable Service Interface Specifications (DOCSIS) is established as the primary cable network data communications standard. The head-end scheduling algorithm is not defined within the standard but it is the key function for providing the required performance capability. Computer simulation, using the Common Simulation Framework (CSF) 12 version of the CableLabs DOCSIS 1.0 computer model, has been used to predict the upstream system throughput and mean access delay. A prioritised first come first served scheduling algorithm has been considered to provide a baseline reference set of performance statistics against which other algorithms can be compared. The simulations, with theoretical confirmation, have shown that the maximum sustainable system throughput is 1965 kbps for a channel capacity of 2560 kbps and a packet size of 1500 octets, whereas for packet size of 100 octets the maximum sustainable throughput is only 1550 kbps. The mean access delay is found to vary between 10-900 ms depending on the offered load and assuming that the offered load does not exceed the capacity of the channel. Excess offered load causes service starvation according to the assigned priority.

The demand for real-time e-commerce data services has been increasing recently. In many e-commerce applications, it is essential to process user requests within their deadlines, i.e., before the market status changes, using fresh data reflecting the current market status. However, current data services are poor at processing user requests in a timely manner using fresh data. To address this problem, we present a differentiated real-time data service framework for e-commerce applications. User requests are classified into several service classes according to their importance, and they receive differentiated real-time performance guarantees in terms of deadline miss ratio. At the same time, a certain data freshness is guaranteed for all transactions that commit within their deadlines. A feedback-based approach is applied to differentiate the deadline miss ratio among service classes. Admission control and adaptable update schemes are applied to manage potential overload. A simulation study, which reflects the e-commerce data semantics, shows that our approach can achieve a significant performance improvement compared to baseline approaches. Our approach can support the specified per-class deadline miss ratios maintaining the required data freshness even in the presence of unpredictable workloads and data access patterns, whereas baseline approaches fail.

A request distribution method for clustered VOD servers considering buffer sharing effects

Recent research has shown that the cooperative diversity can efficiently combat the fading effects caused by the hostile wireless channels just as the multiple-input multiple-output (MIMO) antenna systems do. Besides, due to the inherent cost and size constraints by many small area wireless networks, e.g. wireless ad hoc networks and wireless sensor networks, in such environments, it would be almost impossible to deploy the antenna array in a mobile node. However, cooperative diversity can provide an economical and viable solution by sharing each mobile node’s single-antenna with others to form a virtual antenna array, while it still can maintain significant performance gains similar to MIMO systems. Meanwhile, the adaptive modulation is a proven technique which can significantly increase the spectral efficiency when perfect channel estimation can be achieved, and many wireless standards have adopted it as an implementation option. It also has been shown that combining these two techniques can greatly raise the system efficiency. Nevertheless, in the multiple nodes cooperative communication networks, the randomness of demodulation process at each relay node makes the task of correctly selecting the forwarding relay nodes very complicated. In view of this problem, a novel adaptive node selection algorithm is proposed for the destination node to effectively select the forwarding relay nodes to help the source node transfer the signals. In this paper, the decode-and-forward (DF) protocol is employed as the cooperative diversity signaling, and the constant-power variable-rate M-ary phase shift keying (M-PSK) is adopted as the adaptive modulation scheme. At the destination node, the maximal-ratio-combining (MRC) method is used to combine all of the signals from diversity branches with the main path transmitted directly from the source node. Because of the random phenomenon of the demodulation process, the outage requirement is used as the baseline in the first stage of the proposed node selection algorithm to choose the maximal transmission rate. Hence the maximal overall system throughput in terms of rate can be achieved. In the meantime, the first candidate forwarding sets of the relay nodes which collectively meet the required outage probability are also been chosen. Then in the second stage, we can further refine the number of the relay nodes among the first candidate forwarding sets by using the following criterion — maximum average rate per node. It will screen out the first candidate sets with the minimum number of the relay nodes. If only one candidate set is left at the end of the second stage, it will be the end of the proposed algorithm. However, if the result of the screening still has more than one set, then the final election among the second candidate sets would be the one which can give the minimum outage probability. In the simulation results, our proposed node selection algorithm can even further improve the spectral efficiency while the deleteriously fading effect induced by the wireless channels can also be effectively removed.

In this paper, we propose a distributed contention resolution algorithm for multi-packet reception slotted ALOHA systems, which is based on backlog estimation. In the algorithm, a base station broadcasts a binary-valued collision indicator and the identifications of the packets successfully received, when some of packets simultaneously transmitted collide. Then, mobile terminals (MTs) estimate the expected number of MTs involved in the collision given the number of packets successfully transmitted and the collision indicator. Based on this estimation, MTs construct the backlog information and choose their retransmission probability in order to maximize the system throughput. In simulations, the proposed algorithm shows 67% throughput efficiency against the maximum achievable system throughput. The stability of the algorithm is evaluated by examining negative drift from simulation.

A new distance learning system, integrating a top-down design support system and a multi-user/multi-test-bed remote laboratory system for digital circuit hardware design and implementation course, is realized. The proposed system employs the hardware description language (VerilogHDL) for the design database and FPGAs for design implementation test-beds. Students using this remote laboratory system at remote sites can perform actual hardware experiments in parallel. It realized a remote multi-user time-sharing hardware experiment system. It has achieved seamless remotes and actual hardware laboratories, which resolve conflicts among users, when many users request the same services at the same time. The top-down design support system guides students to complete projects. The course material database is organized in the form of a design-module-cell hierarchy tree, where each design-module-cell contains a sample circuit design, described in VerilogHDL. The use of XNIL wrapped VerilogHDL descriptions and specially extended XNIL vocabularies contributed to share designed modules among students and teachers as well across the Internet via the Web. The prototype of the distance learning system, integrating both the digital circuit design support system using top-down approach and the multi-user remote laboratory system for running experiment of digital circuit, has been developed. It has achieved an effective and efficient distance learning system.