Papers by Jan-Kees van Ommeren
Ad hoc network routing protocols may fail to operate in the absence of an end-to-end connection f... more Ad hoc network routing protocols may fail to operate in the absence of an end-to-end connection from source to destination. This deficiency can be resolved by so-called opportunistic networking which exploits the mobility of the nodes by letting them operate as relays according to the storecarry-and-forward paradigm. However, the efficiency of this approach will depend to a large extent on the contact and inter-contact times of node pairs. In this work, we analyze the delay performance of a small opportunistic network by considering a tandem queueing system. We present an exact packet-level analysis by applying ideas from the polling literature. Due to the state-space expansion, this analysis cannot efficiently be applied for all model parameter settings. For this reason, an analytical approximation is constructed and its excellent performance has extensively been validated. Numerical results on the mean end-to-end delay show that the inter-contact time distribution impacts this metric only through its first two moments. Finally, we study delay optimization under power control.
In this paper, we present a new method to evaluate the performance of a network of intersections.... more In this paper, we present a new method to evaluate the performance of a network of intersections. We apply this method to a tandem of intersections. Using this simple example, we show difference between fixed and semi-actuated control. Our method takes the random nature of the traffic and the impact of offsets on the delays into account.
OR Spectrum, 2017
In this paper, we consider the integrated planning of resources in a service maintenance logistic... more In this paper, we consider the integrated planning of resources in a service maintenance logistics system in which spare parts supply and service engineers deployment are considered simultaneously. The objective is to determine close-tooptimal stock levels as well as the number of service engineers that minimize the total average costs under a maximum total average waiting time constraint. When a failure occurs, a spare part and a service engineer are requested for the repair call. In case of a stock-out at spare parts inventory, the repair call will be satisfied entirely via an emergency channel with a fast replenishment time but at a high cost. However, if the requested spare part is in stock, the backlogging policy is followed for engineers. We model the problem as a queueing network. An exact method and two approximations for the evaluation of a given policy are presented. We exploit evaluation methods in a greedy heuristic procedure to optimize this integrated planning. In a numerical study, we show that for problems with more than five types of spare parts it is preferable to use approximate evaluations as they become significantly faster than exact evaluation.
In this paper we present a new method on how to compute the expectation and distribution of the q... more In this paper we present a new method on how to compute the expectation and distribution of the queue length for a particular class of systems. We apply this method and prove its time-efficiency for models in road traffic such as the fixed-cycle traffic light (FCTL) model and for the bulkservice queue model. We give several generalizations of the FCTL queue, which model right-turns, disruptions of the traffic and uncertainty in departure times. We also consider different ways of green time allocation, which are based on either minimizing the maximum expected delay per vehicle or minimizing the total expected queue length. We compare these methods to proportional allocation.
The growing urbanization concentrated in large cities poses enormous challenges to the society. T... more The growing urbanization concentrated in large cities poses enormous challenges to the society. The efficient use of available infrastructure and sound mobility and logistics planning and control frameworks are among the main challenges. This proposal focuses on logistics and mobility, and seeks to reconcile economic, social and ecological objectives. That is: transport and logistics should be maximally efficient, with minimum delay and limited adverse environmental effects (carbon and particle emission, noise). In particular, we focus on the use of massively available planning and floating-car data in addition to data from roadside equipment, to enable dynamic control of both freight and passenger flows. In addition, we will extend existing mathematical models for road traffic so as to jointly study interacting bottlenecks while capturing the essential characteristics of road traffic dynamics. In an urban setting, optimal control for smooth traffic flow requires an integrated appro...
In this paper, we present an open queuing network modeling approach to estimate performance measu... more In this paper, we present an open queuing network modeling approach to estimate performance measures of a cellular manufacturing layout. It is assumed a layout and production data for a planning period of specified length are available. The production data takes into account, processing and handling set-up times as well as transfer and process batch size information of multiple products that flow through the system. It is assumed that two sets of discrete material handling devices are used for material transfer. The first set, of which there is a copy in each cell, is used for intra-cell transfer and the second for inter-cell transfer. Experimental results are provided to demonstrate the effectiveness of this approach.
Crisis situations require fast regain of control. Wireless ad-hoc networks will enable emergency ... more Crisis situations require fast regain of control. Wireless ad-hoc networks will enable emergency services to act upon the actual status of the situation by retrieving and exchanging detailed up-to-date information. Deployment of highbandwidth, robust, self-organising ad-hoc ...
Transportation Research Part B: Methodological
Many queueing systems are analysed using the probability-generating- function (pgf) technique. Th... more Many queueing systems are analysed using the probability-generating- function (pgf) technique. This approach often leads to expressions in terms of the (complex) roots of a certain equation. In this paper, we show that it is not necessary to compute the roots in order to evaluate these expressions. We focus on a certain class of pgfs with a rational form and represent it explicitly using symmetric functions of the roots. These functions can be computed using contour integrals. We also study when the mean of the random variable corresponding to the considered pgf is an additive function of the roots. In this case, it may be found using one contour integral, which is more reliable than the root-finding approach. We give a necessary and sufficient condition for an additive mean. For example, the mean is an additive function when the numerator of the pgf has a polynomial-like structure of a certain degree, which means that the pgf can be represented in a special product form. We also gi...
European Journal of Operational Research, 2022
Abstract In this paper, we study an inventory model for an omnichannel retailer, that is, a retai... more Abstract In this paper, we study an inventory model for an omnichannel retailer, that is, a retailer that sells items both via brick-and-mortar stores and online. Online items are delivered from a warehouse, which also replenishes the stores. When the inventory in a store drops below a certain level, the retailer offers customers a discount for purchasing online. In this way, the retailer can save items for customers who need the item immediately and thus avoid lost sales. For this model, we propose an approximation method for calculating the average inventory costs for one store and one warehouse and an optimization procedure for the case of more stores. Using extensive numerical experiments, we show that the approximations are very close to the performance measured via simulation. Finally, we show that by adopting the discounts policy proposed in this paper, the retailer can reduce its total cost, on average, by 8.5% compared to the no-discounts policy.
Maritime Economics & Logistics, 2022
We consider approximation of the performance of random walks in the quarter-plane. The approximat... more We consider approximation of the performance of random walks in the quarter-plane. The approximation is in terms of a random walk with a product-form stationary distribution, which is obtained by perturbing the transition probabilities along the boundaries of the state space. A Markov reward approach is used to bound the approximation error. The main contribution of the work is the formulation of a linear program that provides the approximation error. 1
Introduction The methods of intensification and diversification are indispensable in successful m... more Introduction The methods of intensification and diversification are indispensable in successful meta heuristics for local search. Intensification corresponds in some sense to local optimisation; the neighbourhood of a solution is searched intensively for solutions which are better or have better opportunities. On the other hand, diversification tries to escape from (relatively small) neighbourhoods to solutions which might lead to better final results. A heuristic that is well aware of the intensification versus diversification problems, is the Variable Neighbourhood Search (VNS), see [2]. In this method, more than one neighbourhood structure is considered. After finishing intensification with respect to one neighbourhood, the heuristic diversifies to another neighbourhood. In this way one hopes to escape from poor local optima. In this work we introduce a model to predict the quality of a neighbourhood. We use this model to identify `bad' neighbourhoods and avoid searching the...
ABSTRACT www.math.utwente.nl/publications
A distributed storage approach is proposed to access data reliably and to cope with node failures... more A distributed storage approach is proposed to access data reliably and to cope with node failures in wireless sensor networks. This approach is based on random linear network coding in combination with a scheduling algorithm based on backpressure. Upper bounds are provided on the maximum rate at which data can be reliably stored. Moreover, it is shown that the backpressure algorithm allows to operate the network in a decentralized fashion for any rate below this maximum.
Integrated Resources Planning: A Continuous Approach by Karisa Laras Widyadari Maintenance logist... more Integrated Resources Planning: A Continuous Approach by Karisa Laras Widyadari Maintenance logistics is an important area that has been receiving wide attention in scientific literature. Efficient maintenance and logistics can help improve industry’s and business’ efficiency. In this problem, high availability of resources (spare parts and service engineers) are needed to facilitate corrective maintenance. However, these resources call for high investments since these resources are mostly expensive. This leads to an interest in efficient cost savings; minimizing the cost while still maintaining to meet the resources availability requirement. Therefore, an optimal resource availability in the maintenance logistics is needed. In this master thesis assignment, a service logistics system that involves both spare parts and highly skilled engineers is considered. Highly skilled engineers are considered expensive assets, thus it is necessary to optimally plan the engineers availability. Th...
Green waves in urban settings are seen to be beneficial both for the drivers and the environment ... more Green waves in urban settings are seen to be beneficial both for the drivers and the environment because they lower delays and reduce pollution. To obtain these benefits, it is important to determine the optimal network parameters, e.g., green splits and offsets, that yield the desired traffic behaviour. We consider two possibilities for network optimization. The first one is minimising the average lost time per vehicle; the second one is maximizing the green wave efficiency. We compare the results with the MAXBAND algorithm, which is used at the design stage of arterial traffic light settings to facilitate green waves. Using our optimisation method, the average delay per vehicle can be reduced by up to 10% and more vehicles can encounter a green wave compared to the MAXBAND approach. The reduction of the average delay for the main stream reaches 20%.
We investigate the decoding delay performance of a communication network in which a single source... more We investigate the decoding delay performance of a communication network in which a single source is transmitting data packets to a single receiver via multiple routers. Network coding is applied to all data packets at the source at each transmission opportunity. Receiver receives network coded packets from routers and decodes them. We define the delay as the time between arrival of a data packet at the source and decoding of all the packets served in the busy period of the source queue starting from the arrival of that data packet. We show that the delay can be expressed in closed-form.
Queueing Systems, 2019
Polling systems are systems consisting of multiple queues served by a single server. In this pape... more Polling systems are systems consisting of multiple queues served by a single server. In this paper, we analyze polling systems with a server that is self-ruling, i.e., the server can decide to leave a queue, independent of the queue length and the number of served customers, or stay longer at a queue even if there is no customer waiting in the queue. The server decides during a service whether this is the last service of the visit and to leave the queue afterward, or it is a regular service followed, possibly, by other services. The characteristics of the last service may be different from the other services. For these polling systems, we derive a relation between the joint probability generating functions of the number of customers at the start of a server visit and, respectively, at the end of a server visit. We use these key relations to derive the joint probability generating function of the number of customers and the Laplace transform of the workload in the queues at an arbitr...
Lecture Notes in Computer Science, 2014
We consider a P H/P H/1 queue in which a threshold policy determines the stage of the system. The... more We consider a P H/P H/1 queue in which a threshold policy determines the stage of the system. The arrival and service processes follow a Phase-Type (P H) distribution depending on the stage of the system. Each stage has both a lower and an upper threshold at which the stage of the system changes, and a new stage is chosen according to a prescribed distribution. This P H/P H/1 multi-threshold queue is modelled as a Level Dependent Quasi-Birth-and-Death process. An efficient algorithm is presented to obtain the stationary queue length vectors using Matrix Analytic methods.
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Papers by Jan-Kees van Ommeren