Dieter Fiems

Dieter Fiems
Ghent University | UGhent · Department of Telecommunications and Information

32.33
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177
Research items
7,101
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899
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Research Experience
Jan 2006 - Dec 2012
Universiteit Gent
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Projects (2)
Project
Awareness is increasing that small-scale farming practices must be tailored to location-specific needs to achieve higher productivity and minimize risks to the environment. Precision agriculture (PA) is introduced to enable the farmers to know what amount of fertilizers, pesticide, seed and other inputs should be applied in their farming systems. One of the proficient tools in the PA technological package is wireless sensor networks (WSNs) that can offer farmers real-time field data from sensors distributed in the field. The application of WSN is understood as an effective way for utilizing resources and enhancing crop productivity. Although WSNs in agriculture is showing progress, it is often seen as a far-fetched idea for small-scale farmers in developing countries. Agricultural cooperatives could be used to facilitate the adoption of WSNs amongst small-scale farmers by collective marketing and improving accessibility to WSNs, providing knowledge, resources and support services. Fatemeh’s ongoing research aims at analyzing the role cooperatives could play in facilitating the adoption of WSNs amongst small-scale farmers.
Research
Research items (177)
Article
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 are...
Article
Depending on the application level quality requirements, packets on the Internet can broadly be classified into two classes: Streaming (S) and Elastic (E). Streaming packets require low delays, but can tolerate packet losses without degrading the user level performance. Elastic traffic has less stringent delay demands, but its performance is very s...
Article
We propose a Markovian queueing model for computing travel times at a macroscopic scale during rush hour. The service rates of the queueing model are state-dependent, reflecting the speed/density relation of the fundamental diagram of traffic flow. In the fluid limit, the dynamics of the transient queue size and travel time processes are governed b...
Conference Paper
We consider the problem of evaluating and constructing appointment schedules for patients in a health-care facility where a single physician treats patients in consecutive order, as is common for general practitioners, clinics and for outpatients in hospitals. Specifically, given a fixed-length session during which a physician sees K patients, each...
Article
Full-text available
Interest in underwater wireless sensor networks (UWSNs) based on acoustic communication has rapidly grown over the last decade. In this field, the design of energy-efficient communication protocols is a crucial task as battery replacement may be unfeasible in practical scenarios. While routing protocols play a pivotal role in determining the effici...
Article
We study the optimal data collection rate in a hybrid wireless sensor network where sensor data is collected by mobile sinks. In such networks, there is a trade-off between the cost of data collection and the timeliness of the data. We further assume that the sensor node under study harvests its energy from its environment. Such energy harvesting s...
Article
This paper studies a discrete-time single-server queueing system with correlated arrivals. Arrivals at the queue stem from a number of active sessions, each generating a packet in a slot with a fixed probability q. Since an exact queueing analysis is not feasible for q ≠ 1, we rely on Taylor-series expansions of the joint probability generating fun...
Article
Exploiting the differences in supported transmission rates between mobile users, opportunistic scheduling promises a substantial increase of the aggregate throughput of wireless networks. In this paper, we present a Markov model to study the trade-off between fairness and wireless efficiency of opportunistic scheduling at an access point which serv...
Article
Full-text available
We consider the discrete-time G/GI/1 queueing system with multiple exhaustive vacations. By a transform approach, we obtain an expression for the probability generating function of the waiting time of customers in such a system. We then show that the results can be used to assess the performance of G/GI/1 queueing systems with server breakdowns as...
Article
We consider the problem of appointment scheduling in the presence of unpunctual patients. To address this problem, many studies combine simulation with some heuristic search method. Such optimization techniques usually involve a huge number of repeated schedule evaluations which makes the simulation run-time an important factor. In this paper, we p...
Article
In their exposé on the past, present and perspective of the analysis of polling systems, professors Borst and Boxma give a first-hand account on the advancement of this particular research field. As any good historical account, the paper highlights some of the key turning points in the advancement of our current understanding of the dynamics of pol...
Article
We propose an analytical model that accurately captures the service advertisement and access mechanisms in IEEE 1609.4/IEEE 802.11p multi-channel vehicular networks where road-side units announce non-safety services to passing vehicles on a dedicated channel. For a drive-thru scenario, we calculate various performance measures including the service...
Chapter
Full-text available
In the last decade, Underwater Wireless Sensor Networks (UWSNs) have been widely studied because of their peculiar aspects that distinguish them from common wireless terrestrial networks. In fact, most UWSNs use acoustic instead of radio-frequency based communications, and nodes are subject to high mobility caused by water currents. As a consequenc...
Article
In this paper, we study a discrete-time queueing system with one server and two classes of customers. Customers enter the system according to a general independent arrival process. The classes of consecutive customers, however, are correlated in a Markovian way. The system uses a “global FCFS” service discipline, i.e., all arriving customers are ac...
Article
We study optimal data collection in energy harvesting sensor networks. The sensed data-stream constitutes a sequence of stationary ergodic random variables and, assuming that timely data is valued more, the value of the data is discounted over time such that frequent collection is required to avoid a loss in value. However, unlimited data collectio...
Conference Paper
Full-text available
In the last decade, Underwater Wireless Sensor Networks (UWSNs) have been widely studied because of their peculiar aspects that distinguish them from common wireless terrestrial networks. In fact, most UWSNs use acoustic instead of radio-frequency based communications, and nodes are subject to high mobility caused by water currents. As a consequenc...
Article
We study the optimal transmission policy of a sensor node in an energy-harvesting wireless sensor network. We consider a hybrid wireless sensor network in which a mobile sink is used to collect data. Taking cues from recent works on the value of information (VoI), we posit that the optimal policy maximises the VoI that can be sent for the node to t...
Article
Full-text available
This paper considers a network of infinite-server queues with the special feature that, triggered by specific events, the network population vector may undergo a linear transformation (a `multiplicative transition'). For this model we characterize the joint probability generating function in terms of a system of partial differential equations; this...
Article
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 assu...
Article
Full-text available
We consider a retrial queueing model for random access protocols arising in local area networks such as carrier sense multiple access networks. In our model, one channel is shared among multiple nodes. Each node accesses the channel according to a Poison process and the holding time of the channel is exponentially distributed. Blocked users join th...
Conference Paper
We focus on the numerical analysis of a coupled queueing system with Poisson arrivals and exponentially distributed service times. Such a system consists of multiple queues served by a single server. Service is synchronised meaning that there is a departure from every queue upon service completion and there is no service whenever one of the queues...
Article
We assess appointment scheduling strategies for outpatient services. To this end, we consider a fixed-length consultation session in which K patients have to be scheduled at predefined appointment times, but who may not be punctual. Their effective arrival time deviates from their appointment time by a stochastic unpunctuality time. We assume gener...
Article
In Cognitive Radio Networks (CRNs), spectrum sensing is performed by secondary (unlicensed) users to utilize transmission opportunities, so-called white spaces or spectrum holes, in the primary (licensed) frequency bands. Secondary users (SUs) perform sensing upon arrival to find an idle channel for transmission as well as during transmission to av...
Article
Battery lifetime is a key impediment to long-lasting low power sensor nodes and networks thereof. Energy harvesting—conversion of ambient energy into electrical energy—has emerged as a viable alternative to battery power. Indeed, the harvested energy mitigates the dependency on battery power and can be used to transmit data. However, unfair data de...
Article
We analyze the delay experienced in a discrete-time priority queue with a train-arrival process. An infinite user population is considered. Each user occasionally sends packets in the form of trains: a variable number of fixed-length packets is generated and these packets arrive to the queue at the rate of one packet per slot. This is an adequate a...
Article
Full-text available
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 analy...
Conference Paper
We consider a Markovian single-server retrial queueing system. Customers in orbit retry after an exponentially distributed amount of time, the retrial rate depending on the number of times the customer has retried before. Moreover, the number of retrials by a single customer is bounded by K, customers abandoning after the kth retrial with probabili...
Conference Paper
Full-text available
This 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 design...
Conference Paper
In hybrid energy harvesting sensor networks, there is a trade-off between the cost of data collection by a wireless sink and the timeliness of the collected data. The trade-off further depends on the energy harvesting capability of the sensor nodes as sensors cannot transmit data if they do not have sufficient energy. In this paper, we propose an a...
Chapter
Buffer overflow in intermediate network routers is the prime cause of packet loss in wired communication networks. Packet loss is usually quantified by the packet loss ratio , the fraction of packets that are lost in a buffer. While this measure captures part of the loss performance of the buffer, we show that it is insufficient to quantify the eff...
Article
In optical packet/burst switching, fibre-loop optical buffers provide a compact and effective means of contention resolution. In case of a fixed packet length, the involved loop length is typically chosen matched (equal to the packet length), and the loops are arranged in parallel, constituting a single-stage buffer. In this contribution, we invest...
Article
We study the dynamics of opinion propagation in a medium-sized population with low population turnover. Opinion spreading is modelled by a Markovian non-standard Susceptible-Infected-Recovered (SIR) epidemic model with stochastic arrivals, departures, infections and recoveries. The system performance is evaluated by two complementary approaches: a...
Book
This book constitutes the refereed proceedings of the 13th European Workshop on Computer Performance Engineering, EPEW 2016, held in Chios, Greece, in October 2016. The 14 papers presented together with 2 invited talks in this volume were carefully reviewed and selected from 25 submissions. The papers presented at the workshop reflect the diversit...
Conference Paper
This paper investigates the performance of opportunistic schedulers in wireless networks. A base station communicates over fading channels with multiple mobile nodes, each experiencing varying and not necessarily identical wireless channel conditions. An opportunistic scheduler optimises performance by accounting for both buffer size as well as cha...
Conference Paper
Full-text available
Epidemics of a biological and technological nature pervade modern life. For centuries, scientific research focused on biological epidemics, with simple compartmental epidemiological models emerging as the dominant explanatory paradigm. Yet there has been limited translation of this effort to explain internet-based spreading phenomena. Indeed, singl...
Conference Paper
Full-text available
In optical packet/burst switching, fibre-loop optical buffers provide a compact and effective means of contention resolution. In case of fixed packet length, the involved loop length is typically chosen matched (equal to the packet length), and the loops are arranged in parallel, constituting a single-stage buffer. In this contribution , we investi...
Article
We consider the problem of evaluating and constructing appointment schedules for patients in a health care facility where a single physician treats patients in a consecutive manner, as is common for general practitioners, clinics and for outpatients in hospitals. Specifically, given a fixed-length session during which a physician sees K patients, e...
Article
Full-text available
Queueing models can be used to model and analyze the performance of various subsystems in telecommunication networks; for instance, to estimate the packet loss and packet delay in network routers. Since time is usually synchronized, discrete-time models come natural. We start this paper with a review of suitable discrete-time queueing models for co...
Conference Paper
Epidemic modelling is fundamental to our understanding of biological, social and technological spreading phenomena. As conceptual frameworks for epidemiology advance, it is important they are able to elucidate empirically-observed dynamic feedback phenomena involving interactions amongst pathogenic agents in the form of syndemic and counter-syndemi...
Conference Paper
An efficient numerical evaluation technique is presented for families of finite Markov chains indexed by a parameter e, that possess a monotonicity property for the chain at e=0. The monotonicity allows for retrieving the series expansion of the steady state solution in e=0 in O(NM) operations, where N is the size of the state space and M is the nu...
Article
Motivated by kitting processes in assembly systems, we consider a Markovian queueing system with KK paired finite-capacity buffers. Pairing means that departures from the buffers are synchronised and that service is interrupted if any of the buffers is empty. To cope with the inherent state-space explosion problem, we propose an approximate numeric...
Conference Paper
This paper investigates a finite capacity queueing system in a Markovian setting with power control and various flavours of processor sharing policies like generalised and discriminatory processor sharing. Allowing for multiple customer classes, the Markovian description of the system at hand obviously suffers from the state space explosion problem...
Article
Full-text available
Nowadays, customers request more variation in a company’s product assortment leading to an increased amount of parts moving around on the shop floor. To cope with this tendency, a kitting process can be implemented. Kitting is the operation of collecting the necessary parts for a given end product in a specific container, called a kit, prior to arr...
Article
Full-text available
This paper studies a power control game over a collision channel. Each player has an energy state and balances energy conservation and transmission success. When opting for higher transmission power, the chances of a successful transmission in the presence of interference increases at the cost of a larger drop in energy. We study this dynamic game...
Article
We investigate Markov-modulated stochastic recursive equations. This class includes multi-type branching processes with immigration as well as linear stochastic equations. Conditions are established for the existence of a stationary solution and expressions for the first two moments of this solution are found. Furthermore, the transient characteris...
Article
Full-text available
Social networks can have asymmetric relationships. In the online social network Twitter, a follower receives tweets from a followed person but the followed person is not obliged to subscribe to the channel of the follower. Thus, it is natural to consider the dissemination of information in directed networks. In this work we use the mean-field appro...
Conference Paper
Full-text available
In this work, we propose a new model for the dynamics of single opinion propagation at a size-limited location with a low population turnover. This means that a maximum number of individuals can be supported by the location and that the allowed individuals have a long sojourn time before leaving the location. The individuals can have either no opin...
Article
This paper considers the process of spreading rumours in Euclidean space. The rumour (or epidemic) process under study includes (i) a discrete-time stochastic arrival process of new spatially distributed rumours and (ii) a stochastic process of linear transformations of the current rumours which allows for modelling mobility as well as dispersion o...
Conference Paper
Full-text available
In the highly competitive environment in which companies operate today, it is crucial that the supporting processes such as inventory management are as efficient as possible. In particular, a trade-off between inventory costs and service levels needs to be assessed. In this paper, we determine an optimal batch ordering policy accounting for both de...
Conference Paper
Full-text available
We assess appointment scheduling for outpatients in a hospital. A physician sees K patients during a fixed-length session. Each patient has been given an appointment time during the session in advance. Our evaluation approach aims at obtaining accurate predictions at a very low computational cost for the waiting times of the patients and the idle t...
Article
There is a considerable interest nowadays in improving energy efficiency of wireless telecommunications. The sleep-mode mechanism in WiMAX (IEEE 802.16) and the discontinuous reception (DRX) mechanism of LTE are prime examples of energy saving measures. Recently, Samsung proposed some modifications on the sleep-mode mechanism, scheduled to appear i...
Conference Paper
This paper addresses the effects of power saving mechanisms on cooperation in wireless networks. Cooperation by relaying data of other wireless nodes is crucial in (next-generation) wireless networks as it can greatly attribute to ensuring connectivity, reliability, performance, etc. As power saving relies on sleep mode, turning off the communicati...
Article
In this contribution we investigate discrete-time queueing systems with vacations. A framework is constructed that allows for studying numerous different vacation systems, including a.o. classical vacation systems like the exhaustive and limited vacation systems as well as queueing systems with service interruptions. Using a probability generating...
Article
Full-text available
We consider a single-server queueing system. The arrival process is modelled as a Poisson process while the service times of the consecutive customers constitute a sequence of autoregressive random variables. Our interest into autoregressive service times comes from the need to capture temporal correlation of the channel conditions on wireless netw...
Conference Paper
Infinite capacity queues are often used as approximation for their finite real-world counterparts as they are mathematically tractable. It is generally known that tail probabilities of low-priority system content in a two-class priority queue with infinite capacity for customers of both priority classes can be non-exponential, even if the interarri...
Book
This book constitutes the refereed proceedings of the 6th International Workshop on Multiple Access Communications, MACOM 2013, held in Vilnius, Lithuania, in December 2013. The 16 full papers presented were carefully reviewed and selected from various submissions. They describe the latest advancements in the field of multiple access communications...
Article
Full-text available
We investigate a gated polling system with semi-linear feedback and Markovian routing. We thereby relax the classical independence assumption on the walking times; the walking times constitute a sequence of stationary ergodic random variables. It is shown that the dynamics of this polling system can be described by semi-linear stochastic recursive...
Conference Paper
Full-text available
Battery lifetime is a key impediment to long-lasting low power sensor nodes. Energy or power harvesting mitigates the ependency on battery power, by converting ambient energy into electrical energy. This energy can then be used by the device for data collection and transmission. This paper proposes and analyses a queueing model to assess performanc...
Article
This letter investigates a single-server discrete-time queuing system with single-slot service times. For a broad class of arrival processes, a closed-form expression for the mean queue content in steady state is obtained. Apart from being stationary-ergodic, the arrival process adheres to a regeneration property when there are no arrivals in a slo...
Article
Short battery life being a major impediment to a more widespread use of wireless devices, industry standards like WiMAX and 3GPP Long Term Evolution (LTE) embed power saving mechanisms in their protocol stack. Trading in network delay performance for extended battery life, these mechanisms require a careful balance to optimize overall network perfo...
Conference Paper
Full-text available
This paper investigates the performance of different hybrid push-pull systems with a decoupling inventory at the semi-finished prod-ucts and reordering thresholds. Raw materials are 'pushed' into the semi-finished product inventory and customers 'pull' products by placing or-ders. Furthermore, production of semi-finished products starts when the in...
Conference Paper
Recent years have seen a considerable increase of attention devoted to Poisson’s equation for Markov chains, which now has attained a central place in Markov chain theory, due to the extensive list of areas where Poisson’s equation pops up: perturbation analysis, Markov decision processes, limit theorems of Markov chains, etc. all find natural expr...
Conference Paper
Full-text available
This paper considers a discrete-time queueing system with one server and two classes of customers. All arriving customers are ac-commodated in one queue, and are served in a First-Come-First-Served order, regardless of their classes. The total numbers of arrivals during consecutive time slots are i.i.d. random variables with arbitrary distri-bution...
Conference Paper
Branching processes can describe the dynamics of various queueing systems, peer-to-peer systems, delay tolerant networks, etc. In this paper we study the basic stochastic recursion of multitype branching processes, but in two non-standard contexts. First, we consider this recursion in the max-plus algebra where branching corresponds to finding the...
Conference Paper
Full-text available
We consider a Delay/Disruption Tolerant Network under two-hop routing. Our objective is to estimate and track the degree of spread of a message/file in the network. Indeed, having such real-time information is critical for on-line control of routing and energy expenditure. It also benefits the multi-casting application. With exponential inter-meeti...
Conference Paper
Full-text available
In this paper, we study a power control game over a collision channel. Each player has an energy state. When choosing a higher transmission power, the chances of a successful transmission (in the presence of other interference) increases at the cost of a larger decrease in the energy state of the battery. A central feature in these games is that of...
Article
Full-text available
We propose an algorithm for multivariate Markovian characterisation of H.264/SVC scalable video traces at the sub-GoP (Group of Pictures) level. A genetic algorithm yields Markov models with limited state space that accurately capture temporal and inter-layer correlation. Key to our approach is the covariance-based fitness function. In comparison w...
Article
Full-text available
We perform a discrete-time analysis of customer delay in a buffer with batch arrivals. The delay of the kth customer that enters the FIFO buffer is characterized under the assumption that the numbers of arrivals per slot are independent and identically distributed. By using supplementary variables and generating functions, z-transforms of the trans...
Article
In this paper, we study a power control game over a collision channel. Each player has an energy state. When choosing a higher transmission power, the chance of a successful transmission (in the presence of other interference) increases at the cost of a larger decrease in the energy state of the battery. We study this dynamic game when restricting...
Conference Paper
Cooperation is crucial in (next-generation) wireless networks as it can greatly attribute to ensuring connectivity, reliability, performance, … Relaying looks promising in a wide variety of network types (cellular, ad-hoc on-demand), each using a certain protocol. Energy efficiency constitutes another key aspect of such networks, as battery power i...
Article
Full-text available
Addressing the bandwidth inefficiency problem of current IP over DWDM backbone switching, Optical Packet/Burst Switching (OPS/OBS) pro-vide viable solutions, capitalizing on statistical multiplexing gain, through packet-oriented scheduling. To resolve packet/burst contention, the involved photonic switches contain wavelength converters and fiber de...
Conference Paper
We propose an efficient numerical scheme for the evaluation of large-scale Markov chains, under the condition that their generator matrix reduces to a triangular matrix when a certain rate is sent to zero. A numerical algorithm is presented which calculates the first N coefficients of the MacLaurin series expansion of the steady-state probability v...
Conference Paper
We propose an efficient numerical scheme for the evaluation of large-scale Markov chains, under the condition that their generator matrix reduces to a triangular matrix when a certain rate is sent to zero. A numerical algorithm is presented which calculates the first N coefficients of the MacLaurin series expansion of the steady-state probability v...
Article
In a Make-to-Order system, products are only manufactured when orders are placed. As this may lead to overly long delivery times, a stock of semi-finished products can be installed to reduce production time: the so-called decoupling stock. As performance of the decoupling stock is critical to the overall performance and cost of the production syste...
Article
Full-text available
For many queueing systems, the server is not continuously available. Service interruptions may result from repair times after server failures, planned maintenance periods or periods during which customers from other queues are being served. These service interruptions cause an overall performance degradation which is most striking when interruption...
Article
This contribution presents the first stability analysis of multiwavelength queueing systems. Results are obtained for a wide class of implementable scheduling disciplines referred to as delay-oriented disciplines, a class to which for example join the shortest queue belongs. Scheduling is applied as contention resolution in optical switches accommo...
Article
Full-text available
As input traffic at various nodes in packet switched telecommunication networks typically exhibits considerable cor-relation, there is a continuing interest in queuing systems with correlated arrivals. The class of M/G/∞ arrival models can account for various types of arrival correlation, has a two-level structure which is appealing in the context...
Article
Full-text available
We consider a single-server discrete-time queueing system with N sources, where each source is modelled as a correlated Markovian customer arrival process, and the customer service times are generally distributed. We focus on the analysis of the number of customers in the queue, the amount of work in the queue, and the customer delay. For each of t...