Analytical Model For Performance Evaluation Research Articles

Study on a piezohydraulic pump for linear actuators

To obtain high flowrate and pressure, a piezostack pump with stiffened chamber diaphragm (consisting of a membrane and rigid disk) was presented and studied. An analytical model for performance evaluation is established based on the theory of plate and shells. The effect of chamber diaphragm parameters on flowrate, pressure and output energy coefficient, and that of external load on flowrate and output energy coefficient were analyzed. Considering the influence of the diaphragm stiffness on dynamic–response performance of the piezostack actuator, the design method was introduced. Analysis results show that all of the flowrate, backpressure and output energy coefficient increase with the decreasing of membrane thickness. There is an optimal radius ratio (rigid-disk radius to membrane radius) for flowrate and pressure to achieve peak value, which decreases with the raising of the membrane thickness. On the other hand, output energy coefficient, which decreases with the increasing of radius ratio, achieves peak when force ratio (external load to blocked force of piezostack) is 0.5. At stiffness match and optimal load, maximal output energy coefficient is independent of membrane thickness, and flowrate decreases with the increasing of membrane thickness. To examine analytical results, a check-valve piezostack pump was fabricated and tested. The experiment results show that the flowrate can be enhanced with optimizing rigid disk.

An analytical model for performance evaluation of multimedia applications over EDCA in an IEEE 802.11e WLAN

We extend the modeling heuristic of (Harsha et al. 2006. In IEEE IWQoS '06, pp 178 --- 187) to evaluate the performance of an IEEE 802.11e infrastructure network carrying packet telephone calls, streaming video sessions and TCP controlled file downloads, using Enhanced Distributed Channel Access (EDCA). We identify the time boundaries of activities on the channel (called channel slot boundaries) and derive a Markov Renewal Process of the contending nodes on these epochs. This is achieved by the use of attempt probabilities of the contending nodes as those obtained from the saturation fixed point analysis of (Ramaiyan et al. 2005. In Proceedings ACM Sigmetrics, '05. Journal version accepted for publication in IEEE TON). Regenerative analysis on this MRP yields the desired steady state performance measures. We then use the MRP model to develop an effective bandwidth approach for obtaining a bound on the size of the buffer required at the video queue of the AP, such that the streaming video packet loss probability is kept to less than 1%. The results obtained match well with simulations using the network simulator, ns-2. We find that, with the default IEEE 802.11e EDCA parameters for access categories AC 1, AC 2 and AC 3, the voice call capacity decreases if even one streaming video session and one TCP file download are initiated by some wireless station. Subsequently, reducing the voice calls increases the video downlink stream throughput by 0.38 Mbps and file download capacity by 0.14 Mbps, for every voice call (for the 11 Mbps PHY). We find that a buffer size of 75KB is sufficient to ensure that the video packet loss probability at the QAP is within 1%.

IEEE 802.11 goodput analysis for mixed real-time and data traffic for home networks

Increasingly, wireless networks are being used to provide connection services for devices running applications with very different quality of service requirements. Although this issue has been addressed by the IEEE 802.11e standard, the fact is that most networks deployed in home/office environments nowadays use IEEE 802.11a/b/g standard devices. Unfortunately, administrators often do not set configuration parameters of network devices to maximize resources performance, thus providing poor quality of service. In this paper, two IEEE 802.11a/b/g analytical performance evaluation models for mixed traffic Ad Hoc and infrastructure WLANs are presented, assuming that some network devices are executing single applications, like VoIP, videoIP or network browsing. In our analysis, network devices are grouped according to the expected traffic pattern of the applications they are running. Then, global and individual group goodput are calculated assuming a congested network. Based upon the outcome of this analysis for different settings of the device configuration parameters, it is shown that the performance of a standard home/office IEEE 802.11 wireless network can be significantly improved by choosing appropriate values of these parameters.

Dynamic Traffic Grooming in Optical Networks with Wavelength Conversion

Traffic grooming in wavelength division multiplexing (WDM) optical networks refers to routing and aggregating low-rate client traffic onto wavelength granularity lightpaths. When client traffic randomly arrives/departs, it is called dynamic traffic grooming. This paper focuses on dynamic traffic grooming when the optical network has sparse wavelength conversion, and aims to examine the impact of wavelength conversion and converter placement on dynamic traffic grooming. We have developed both an analytical model for performance evaluation, and an adaptive traffic load-based (ATL) heuristic algorithm for converter placement, accompanied with a discussion of various converter placement heuristics. Numerical results indicate that the ATL heuristic can obtain similar performance as the greedy heuristic with lower computation complexity.

Performance goals for the laboratory testing of antithrombin, protein C and protein S

To achieve a reliable analytical quality for both monitoring and diagnostic testing, laboratories need to fulfil the widely accepted analytical performance goals based on the biological variation of the analytes of testing. Not only is the short-term analytical performance, which regularly is assessed by internal quality control procedures, of importance, but also the long-term analytical performance. To assess the long-term analytical performance, data obtained from an external quality assessment programme can be used. In this study we have used the evaluation model designed by the ECAT Foundation for the assessment of the longterm analytical performance, including imprecision, bias and total analytical error. The model was applied to the data from 136 different laboratories for the assay of antithrombin (activity), protein C (activity and antigen) and protein S (activity, total and free antigen). The imprecision (median; range), reflected by the long-term analytical coefficient of variation (LCV (A) ), was the lowest for antithrombin (7.6%; 2.6 - 43.8%) and the highest for protein S activity (17.2%; 4.3 - 88.6%). For bias and total error the same pattern was observed (antithrombin: 3.8%; 0.3 - 17.1% and 9.1%; 3.4 - 34.3%, respectively; protein S activity: 12.8%; 3.1 - 34.8% and 24.5%; 9.9 - 87.0%, respectively). For the majority of the laboratories (70 - 85%) the imprecision contributes considerably more to the total error than the bias. However the effect of the bias on the analytical quality is not negligible. Assays for antithrombin, protein C and protein S are mainly used for diagnostic testing. About 70 - 100% of the laboratories can fulfil the desirable performance goal for imprecision. The desirable performance goal for bias was reached by 50 - 95% of the laboratories. In all cases the highest numbers of laboratories fulfilling performance goals was obtained for the protein C variables. To improve the analytical quality in assays of antithrombin, protein C and protein S it is highly recommended that primarily imprecision (non-systematic failures) be suppressed. However the effect of the bias (systematic failures) on the analytical quality should not be neglected. A useful tool for determining the imprecision (LCV (A) ) and bias is the long-term analytical performance evaluation model as used by the ECAT Foundation.

Modeling of Segmented Peltier Cooling with Discrete and Continuous Concentration Function

Commercialization of Peltier coolers has progressed during last years and special efforts have been undertaken to enhance the efficiency of thermoelectric (TE) devices. Along with the continued search for advanced TE materials, the concept of FGM offers a strategy of gradual improvement of device performance. In reality a functional gradient in a TE material means a related spatial variation of all TE properties – Seebeck coefficient, electrical, and thermal conductivity – whereas the most relevant effect is linked to the gradient of the Seebeck coefficient. Due to the spatial dependence of the Seebeck coefficient, Peltier heat is absorbed or released inside the TE element under current flow (distributed Peltier effect) which can be exploited to shape the internal temperature profile in a desired manner. Starting from the first principles of thermoelectricity, a differential equation governing the coupling of thermal and electrical transport is derived within the frame of a one-dimensional model. It is shown that this approach can be also used to model multi-segment Peltier cooling devices. Temperature profiles T(x) have been calculated for a segmented TE element within the framework of a constant parameters theory. The work presents an analytical model for performance evaluation of multiply-segmented Peltier elements. The problem is treated in a one-dimensional approach for a p-type stack containing N segments of different properties. Assuming constant TE material properties in each of the segments, the differential equation of TE transports has been solved to obtain the temperature profile T(x) in each segment. With the material properties values in each segment representing volume average values this model gives an excellent approximation also for continuously graded elements. The boundary conditions of the TE problem set-up, as conservation of heat at any intermediate junction between the segments, and fixed temperature at the cold and hot end of the element, lead to a linear equation system, which can be easily solved by means of standard methods. From the solution, all desired performance parameters can be deduced. Based on realistic material data exemplary calculations are presented for stacked and continuously graded elements. To demonstrate the developed numerical algorithm, gradients of the Seebeck coefficient are mainly considered. Calculations have been performed for N = 2, 5, 10, and continuous gradients. As target parameters, the C.O.P. and the cooling power have been calculated as functions of the electric current. As well, the minimum temperature of the cold side has been determined for various shape of the Seebeck gradient. It is shown that the TE FGM effect can be almost completely utilized already by a stack of two to five homogeneous segments. The results allow for giving an estimation on the order of magnitude of performance improvement of both discontinuously and continuously graded Peltier cooling devices. The model calculation was implemented with the software tool MATHEMATICA. The code provides an easy to handle convenient instrument for performance estimation of non-homogeneous Peltier pellets. Technological studies for controlled fabrication of those pellets are underway.

Algorithmic aspects of capacity in wireless networks

This paper considers two inter-related questions: (i) Given a wireless ad-hoc network and a collection of source-destination pairs {( s i ,t i )}, what is the maximum throughput capacity of the network, i.e. the rate at which data from the sources to their corresponding destinations can be transferred in the network? (ii) Can network protocols be designed that jointly route the packets and schedule transmissions at rates close to the maximum throughput capacity? Much of the earlier work focused on random instances and proved analytical lower and upper bounds on the maximum throughput capacity. Here, in contrast, we consider arbitrary wireless networks. Further, we study the algorithmic aspects of the above questions: the goal is to design provably good algorithms for arbitrary instances. We develop analytical performance evaluation models and distributed algorithms for routing and scheduling which incorporate fairness, energy and dilation (path-length) requirements and provide a unified framework for utilizing the network close to its maximum throughput capacity.Motivated by certain popular wireless protocols used in practice, we also explore "shortest-path like" path selection strategies which maximize the network throughput. The theoretical results naturally suggest an interesting class of congestion aware link metrics which can be directly plugged into several existing routing protocols such as AODV, DSR, etc. We complement the theoretical analysis with extensive simulations. The results indicate that routes obtained using our congestion aware link metrics consistently yield higher throughput than hop-count based shortest path metrics.

Performance modeling and analysis of integrated logistic chains: An analytic framework

This paper is geared toward developing a network of inventory-queue models for the performance modeling and analysis of an integrated logistic network. An inventory-queue is a queueing model that incorporates an inventory replenishment policy for a store, which is a basic modeling element for an integrated logistic network. To achieve this objective, first, this paper presents an analytical modeling framework for integrated logistic chains, in which the interdependencies between model components are captured. Second, a network of inventory-queue models for performance analysis of an integrated logistic network with inventory control at all sites is developed. Then this paper extends the previous work done on the supply network model with base-stock control and service requirements. Instead of one-for-one base stock policy, batch-ordering policy and lot-sizing problems are considered. In practice, the assumption of uncapacitated production is often not true, therefore, GI x /G/1 queueing analysis is used to replace the M x /G/∞ queue based method. To include lot-sizing issue in the analysis of stores, a fixed-batch target-level production authorization mechanism is employed to explicitly obtain performance measures of the logistic chain queueing model. The validity of the proposed model is illustrated by comparing the results from the analytical performance evaluation model and those obtained from the simulation study.

Inventory planning of supply chains by linking production authorization strategy to queueing models

A methodology for supply chain inventory analysis and optimization is presented by linking production authorization (PA) strategy to queueing models. For modelling issue, an integrated framework is provided. This framework regards a supply chain as a network of stores, which are considered as single-stage manufacturing facilities. The interdependencies between supply chain components can be captured by this framework. For analysis issue, first, a queueing model that incorporates production authorization strategy is developed for each store. Second, a network of inventory-queue models for entire supply network with inventory control at all stores is developed. Furthermore, an optimization model is introduced to improve the performance of the entire supply chain. This paper extends the previous work on the supply network model with base-stock control and service requirements. Instead of one-for-one base stock policy, batch-ordering policy and lot-sizing problems are considered. To determine the replenishment lead times of items at the stores, a fixed-batch target-level production authorization mechanism is employed to explicitly obtain performance measures of the supply chain queueing model. The validity of the proposed model is illustrated by comparing the results from the analytical performance evaluation model and those obtained from the simulation study.

PERFORMANCE ANALYSIS OF AN ASSEMBLY STATION WITH INPUT FROM MULTIPLE FABRICATION LINES

We develop analytical models for performance evaluation of Fabrication/Assembly (F/A) systems. We consider an F/A system that consists of an assembly station with input from K fabrication lines. Each fabrication line consists of one or more fabrication stations. The system is closed with a fixed number of items circulating between each fabrication line and the assembly station. We present algorithms to estimate the throughput and mean queue lengths of such systems with exponential processing times. We then extend our approach to analyze F/A systems with general processing time distributions. Numerical comparisons with simulations demonstrate the accuracy of our approach.

Modeling recirculating conveyors with blocking

Recirculating conveyors provide both a delivery mechanism and a buffer for queueing behavior. Although these systems are commonly found in flexible manufacturing systems and assembly systems, accurate analytical models for performance evaluation have not been available. We present a new analytical model for such systems that provides virtually the same information as obtained from simulation models. This model uses processing times and travel times having an exponential distribution and allows for blocking and recirculation of loads and can be extended to large conveying systems with multiple servers.

An analytical model for performance evaluation of parallel interference cancellers in CDMA systems

In multistage parallel interference cancellation, the tentative decisions for different users at each stage are mutually correlated, and they are also correlated with Gaussian noise. By taking the correlations into consideration and employing Price's theorem, an analytical model is proposed to refine the variance evaluation of the final decision variable. It is shown that the refined variance is very close to that obtained by simulation and can improve the accuracy in bit error rate evaluation.

Teletraffic issues in mobile communication network planning

In this paper we present an overview of the application of teletraffic methods for the planning of mobile communication networks. It is shown that there is a necessity for an accurate description of the spatial traffic in order to perform a demand based planning. To accomplish this task, a new traffic demand characterization concept based on a pattern of discretized demand nodes is presented. The spatial traffic distribution also plays an important role when designing networks according to new emerging standards like UMTS. Here, novel analytical models for performance evaluation are required, whether for the examination of the interference limited system capacity or the impacts of variable bit rate voice coding on the transportation over the interconnecting fixed network structure. It is also shown that a spatial characterization of the demand facilitates the application of discrete algorithms for locating base stations.

Queuing analysis of shared-buffer switches with control scheme under bursty traffic

Shared-buffer switches have many advantages such as relatively low cell loss rate and good buffer utilization, and they are increasingly favoured in recent VLSI switch designs for ATM. However, their performance degrades dramatically under nonuniform traffic due to the monopolization of the buffer by some favoured cells. To overcome this, restricted types of sharing and hot-spot pushout (HSPO) have been proposed, and the latter has been shown by simulation to perform better in all situations. In this paper we develop an analytical model for performance evaluation of a shared-buffer asynchronous transfer mode (ATM) switch with HSPO under bursty traffic. This analytical model is an improved version of the first model ever developed for this purpose. We balance the relative queues to approximate the effects of pushout, while keeping only four state-variables, and our model gives a good agreement with simulation, for calculating throughput and cell loss.

Very high capacity WDM coherent transmission systems

An analytical performance evaluation model is presented for very high capacity WDM amplified systems. Results are presented regarding phase modulated coherent systems. The results indicate that these systems are worthy of consideration for links in the higher level of the digital transport network.

Approximate analytical performance models for automatic assembly systems with statistical process control and automated inspection

Analytical methods for modeling manufacturing systems have emerged as promising performance evaluation techniques. Some analytical tools have been developed for the performance evaluation of automatic assembly systems (AASs), which form an important class of manufacturing systems. In some AASs there is a strong interaction between statistical process control of the assembly process and the dynamics of the assembly system. This paper presents an analytical performance evaluation model where this interaction has been integrated with the system dynamics. The analytical tool models the splitting and merging of the flow of the assemblies among the main and repair loops of the assembly system in addition to the dynamics of the main system. The model is a general one that can be used to model AASs with several automatic inspection stations and counter-flow repair loops. For the statistical process control, Dodge CSP-1 plans, which have wide application for continuous production, are chosen. AASs with a single automatic inspection station and counter-flow repair loop with various system parameters are discussed as examples. The ability of the proposed analytical model to accurately predict the performance of the AASs is demonstrated. The system throughput as a function of process quality is analyzed.

Performance Evaluation of Unslotted Random Access Packet CDMA Channels

This paper presents an analytical performance evaluation model for a class of unslotted random access packet CDMA (code division multiple access) channels. In the system considered, many interactive terminals asynchronously transmit (uncoded) spread spectrum modulated variable length data packets on a shared wideband channel. Since unslotted operation at the physical level precludes the application of controlled multiaccess procedures, reliable link level operation is achieved using an ALOHA-Iike procedure in which incorrectly received packets are retransmitted with random delay. In view of the resulting traffic dependent packet success probability, Rich a packet CDMA (or “spread ALOHA”) channel may be expected to exhibit throughput and stability properties qualitatively similar to those of narrowband ALOHA. A flow equilibrium based analytical model for performance evaluation is presented and used to illustrate both throughput-delay and stability characteristics for an example random code direct sequence (DS) unslotted CDMA system. It is shown that a typical uncoded packet DS-CDMA channel achieves a maximum bandwidth normalized throughput (utilization) in the region of 0.15–0.2, and is thus competitive with narrowband ALOHA carrying similar data traffic. Stability issues for finite-population channels are also addressed, leading to the conclusion that relatively long average retransmission delays may often be required to prevent bistable behaviour unless adaptive policies are nsed.

Optimization problems and solution methods in the design of data distribution

The design of data distribution requires solving interrelated optimization problems, concerning data fragmentation and allocation, operations optimization and allocation, and the evaluation of system's performance for given data and operation allocations. Each problem can be solved with several different solution methods; thus, designing data distribution is a very difficult task. In this paper, we characterize each problem and the interactions between them, presenting a general framework for the design of data distribution. We present an entity-relationship schema of the design data dictionary, which stores all information useful during the design, and we use the data dictionary to specify the input and output data for each design problem. We then discuss how the design problems interact. Finally, we present an integrated toolset for the vertical partitioning of relations, which uses different solution methods, called DIVIDE and CONQUER. DIVIDE has a simple analytic model for performance evaluation, while CONQUER uses a detailed cost model. The complexity of methods and experimental results are presented.

Efficient mapping and implementation of matrix algorithms on a hypercube

It is well known that parallelism by itself does not lead to higher speeds. This study shows how to put parallelism to best use, that is, how to find an optimal balance between communication and computation overheads for two parallel matrix algorithms. The problem graph for matrix algorithms analyzed in this paper is a two-dimensional grid (toroidal mesh) which is mapped onto a hypercube topology. To perform matrix operations on a hypercube, a matrix is partitioned into several submatrices which are stored and manipulated in the nodes. We seek to find an optimal matrix partitioning to minimize overall execution time. The NCUBE parallel machine is used for experimental performance evaluation. For matrix multiplication, we derive an exact analytical model to determine the optimal partitioning size and perform its experimental verification on the NCUBE parallel processor. For a parallel Gaussian elimination known as the balanced algorithm, we present performance measurements and an approximate analytical model for performance evaluation. Our analyses show that the optimal submatrix size is typically small and does not depend on the original matrix size.

Stability, Throughput, and Delay of Asynchronous Selective Reject ALOHA

An analytical performance evaluation model is presented for selective reject (SREJ) ALOHA, a recently proposed high-capacity protocol for unslotted channels with high propagation delay. SREJALOHA approaches the theoretical asynchronous multiaccess throughput limit of 0.368 for fixed or variable length message traffic, using subpacketization of messages in conjunction with a selective reject retransmission policy. A finite user flow equilibrium-based model for SREJ-ALOHA with variable length messages is derived and used to characterize stability, throughput, and delay. Particular attention is given to the development of a stability analysis methodology for unslotted ALOHA-type protocols with variable length transmissions. Numerical results based on a satellite channel example are presented to demonstrate the significant performance advantages offered by SREJ-ALOHA, even after accounting for realistic subpacket overheads.