Coupled queues with customer impatience

Motivated by assembly processes, we consider a Markovian queueing system with multiple coupled queues and customer impatience. Coupling means that departures from all constituent queues are synchronised and that service is interrupted whenever any of the queues is empty and only resumes when all queues are non-empty again. Even under Markovian assumptions, the state space grows exponentially with the number of queues involved. To cope with this inherent state space explosion problem, we investigate performance by means of two numerical approximation techniques based on series expansions, as well as by deriving the fluid limit. In addition, we provide closed-form expressions for the first terms in the series expansion of the mean queue content for the symmetric coupled queueing system. By an extensive set of numerical experiments, we show that the approximation methods complement each other, each one being accurate in a particular subset of the parameter space. (C) 2017 Elsevier B.V. All rights reserved

A Taylor Series Approach for Service-Coupled Queueing Systems with Intermediate Load

This paper investigates the performance of a queueing model with multiple finite queues and a single server. Departures from the queues are synchronised or coupled which means that a service completion leads to a departure in every queue and that service is temporarily interrupted whenever any of the queues is empty. We focus on the numerical analysis of this queueing model in a Markovian setting: the arrivals in the different queues constitute Poisson processes and the service times are exponentially distributed. Taking into account the state space explosion problem associated with multidimensional Markov processes, we calculate the terms in the series expansion in the service rate of the stationary distribution of the Markov chain as well as various performance measures when the system is (i) overloaded and (ii) under intermediate load. Our numerical results reveal that, by calculating the series expansions of performance measures around a few service rates, we get accurate estimates of various performance measures once the load is above 40% to 50%

Vertically and Horizontally Mounted Wind Mills : Wind Energy Production in Tampere University of Applied Sciences

The purpose of this thesis was to gather information about vertical and horizontal wind mills and to complete a research on wind power production by wind mills which were installed in Tampere University of Applied Sciences. The horizontally mounted wind mill Windspot 3.5 and vertically mounted wind mill Cypress were installed in summer 2011 but they started functioning and supplying energy only during 2012. In the theoretical part of this thesis wind speed and wind power production is discussed, various factors which could influence wind mills or energy extraction are also analyzed. In particular technical characteristics and power production of Windspot 3.5 and Cypress was taken into consideration. The data which was used in this study (wind speed, temperature, humidity) was collected from Tampere-Pirkkalan lentoasema and on-the-spot measurements were performed by Davis Vantage Pro 2 weather station. The total power production was calculated for April 2012 for horizontally mounted wind mill because performance of vertically mounted wind mill was not stable and therefore reliable enough for the research, however analysis of historical background of wind conditions includes data from 1980 till 2011. As a result of the research efficiency of Windspot 3.5 within wind conditions during April 2012 was calculated. The final value was 2.6 % which means that conditions allow us to extract a certain amount wind energy but this wind mill has extracted only 2,6% of it. Since the average performance of a wind mill goes up to 20%, this result is not positive. Further research is required to improve those results, since amount of produced energy with horizontal wind mill is not enough even for its own maintenance. In this thesis such measures as replacement and weather conditions analysis are suggested. However, it was figured out that replacement of wind mills is quite complicated issue due to heli-copter routes and restrictions coming with that. Taking this issue into consideration, a conclusion that these wind turbines should be used mainly for study purpose rather than reliable energy supply was made. Although, author of the thesis sees a possibility of improving turbines performance by concentrating on Finnish weather conditions and it influence on power production by these particular wind turbines

Air pollution and air cleaning equipment in buildings

The subject of this thesis work is air pollution and air cleaners in building. Clean air has big significance for human health because different pollutions can cause allergy and disease. The quality of indoor air affects health and effective working. The aim of this thesis is to present methods and devices for cleaning the air

Internet provisioning in VANETs : performance modeling of drive-thru scenarios

Drive-thru-Internet is a scenario in cooperative intelligent transportation systems (C-ITSs), where a road-side unit (RSU) provides multimedia services to vehicles that pass by. Performance of the drive-thru-Internet depends on various factors, including data traffic intensity, vehicle traffic density, and radio-link quality within the coverage area of the RSU, and must be evaluated at the stage of system design in order to fulfill the quality-of-service requirements of the customers in C-ITS. In this paper, we present an analytical framework that models downlink traffic in a drive-thru-Internet scenario by means of a multidimensional Markov process: the packet arrivals in the RSU buffer constitute Poisson processes and the transmission times are exponentially distributed. Taking into account the state space explosion problem associated with multidimensional Markov processes, we use iterative perturbation techniques to calculate the stationary distribution of the Markov chain. Our numerical results reveal that the proposed approach yields accurate estimates of various performance metrics, such as the mean queue content and the mean packet delay for a wide range of workloads

An Analytical Performance Evaluation Tool for Wireless Access Points with Opportunistic Scheduling

International audienceThis paper introduces a performance analysis tool for a wireless access point which serves multiple mobile nodes. The wireless channel conditions vary over time and the opportunistic scheduler in the access point can account for the channel conditions as well as for the number of backlogged packets for the different mobile nodes. The tool is designed to allow for fast and accurate calculations of the main performance measures of the system. The calculation method is based on a Maclaurin series expansion of the stationary solution of the Markov process that describes the channel conditions and the queue contents for the different mobile nodes. The Maclaurin series expansion only requires the inversion of sparse block triangular matrices, which is considerably faster than directly calculating the stationary solution. The tool provides a user interface for defining the network and channel parameters and can be easily used for assessing the efficiency of opportunistic schedulers, or for optimizing system parameters and scheduling policies of such schedulers