Papers by Maurits de Graaf
A Generic Processor Temperature Estimation Method
2019 25th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC)
Most modern mobile embedded devices have the ability to increase their computational power typica... more Most modern mobile embedded devices have the ability to increase their computational power typically at the cost of increased heat dissipation. This may result in temperatures above the design limit, especially if active cooling is inapplicable. Thus, it is necessary to consider processor temperature while scheduling tasks. This means estimating the change in temperature due to changed workload is crucial for high performance mobile embedded devices. To address this challenge, we first introduce a model to estimate the temperature and classify the system dependent model parameters. Then, to determine these parameters, we develop a new method, which can be applied on any mobile embedded device. The only requirement for our new method is learning the device characteristics by processing a certain task while recording the temperature with built-in sensors. Our results show that our method can achieve high accuracy within a short testing period.
Memorandum / Department of Applied Mathematics, Sep 27, 2011
Mobile wireless networks need to maximize their network lifetime (defined as the time until the f... more Mobile wireless networks need to maximize their network lifetime (defined as the time until the first node runs out of energy). In the broadcast network lifetime problem, all nodes are sending broadcast traffic, and one asks for an assignment of transmit powers to nodes, and for sets of relay nodes so that the network lifetime is maximized. The selection of a dynamic relay set consisting of a single node (the 'master'), can be regarded as a special case, providing lower bounds to the optimal lifetime in the general setting. This paper provides a first analysis of a 'dynamic master selection' algorithm.
T.J.M. Coenen
An upper bound on multi-hop multi-channel wireless network performance
Civil/Military cooperation is vital when addressing civil emergencies. In order to most efficient... more Civil/Military cooperation is vital when addressing civil emergencies. In order to most efficiently enable such cooperations, it is important to ensure easy and secure information exchange. This paper describes an approach to enable such information exchange using a robust MILS kernel, using a content-based security approach to allow each organisation to remain in control of their own data. Furthermore, we demonstrate the approach by combining a military standard Command and Control (C2) system with a civilian system, where specific information can be securely and easily transmitted between the parties.
Random Structures & Algorithms, 2018
We present an average case analysis of the minimum spanning tree heuristic for the power assignme... more We present an average case analysis of the minimum spanning tree heuristic for the power assignment problem. The worst-case approximation ratio of this heuristic is 2. We show that in Euclidean d-dimensional space, when the vertex set consists of a set of i.i.d. uniform random independent, identically distributed random variables in [0, 1] d , and the distance power gradient equals the dimension d, the minimum spanning tree-based power assignment converges completely to a constant depending only on d. KEYWORDS ad-hoc networks; analysis of algorithms; approximation algorithms; average case analysis; point processes; power assignment; range assignment 1 INTRODUCTION Ad hoc wireless networks have received significant attention in recent years due to their potential applications in battlefield, emergency disaster relief, and other scenarios (see for example [14, 19, 21]). In an ad hoc wireless network, a communications session is achieved either through single-hop transmission or by relaying through intermediate nodes. The topology of a multihop wireless network is given by the set of communication links between node pairs. It may depend on uncontrollable factors such as node mobility, interference, as well as on controllable parameters such as transmit power. In this paper, we assume an idealized propagation model, where omnidirectional antennas are used. We consider the This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Energy-efficient data collection in wireless sensor networks with time constraints
Performance Evaluation, 2016
We consider the problem of retrieving a reliable estimate of an attribute from a wireless sensor ... more We consider the problem of retrieving a reliable estimate of an attribute from a wireless sensor network within a fixed time window and with minimum energy consumption for the sensors. The sensors are located in the plane according to some random spatial process. They perform energy harvesting and follow an asleep/awake cycle. A sink, at a random location in the plane, requests measurements from the awake sensors in order to retrieve an estimate of an attribute. The sink has to collect a sufficient number of measurements within a fixed time window. Moreover, the sink aims to minimize the energy that the sensors use to transmit their measurements. We determine a closed-form expression for the expected energy consumption of the sensors when measurements are retrieved according to a Greedy schedule. We also provide an upper bound on the maximum expected distance over which a sensor transmits under this Greedy schedule. Furthermore, we formulate a Markov Decision Process (MDP) to determine a sensor transmission schedule with general time constraints. We also develop a heuristic that schedules the sensors for transmission. We compare numerically the performance of the MDP schedule with the heuristic and with an offline, optimal schedule, where the asleep/awake state of the sensors is assumed to be known ahead of time. We show that the energy consumption under the MDP schedule converges to the energy of the offline schedule as the size of the time window for measurement collection increases. We also show that the heuristic performs close to the MDP schedule in terms of energy consumption.
Queueing Systems, 2017
We present a tandem network of queues 0,. .. , s − 1. Customers arrive at queue 0 according to a ... more We present a tandem network of queues 0,. .. , s − 1. Customers arrive at queue 0 according to a Poisson process with rate λ. There are s independent batch service processes at exponential rates μ 0 ,. .. , μ s−1. Service process i, i = 0,. .. , s−1, at rate μ i is such that all customers of all queues 0,. .. , i simultaneously receive service and move to the next queue. We show that this system has a geometric product-form steady-state distribution. Moreover, we determine the service allocation that minimizes the waiting time in the system and state conditions to approximate such optimal allocations. Our model is motivated by applications in wireless sensor networks, where s observations from different sensors are collected for data fusion. We demonstrate that both optimal centralized and decentralized sensor scheduling can be modeled by our queueing model by choosing the values of μ i appropriately. We quantify the performance gap between the centralized and decentralized schedules for arbitrarily large sensor networks.
Ad Hoc Networks, 2016
We consider an ad-hoc network of wireless sensors that harvest energy from the environment and br... more We consider an ad-hoc network of wireless sensors that harvest energy from the environment and broadcasts measurements independently, at random, provided sufficient energy is available. Clients arriving at the network are interested in retrieving measurements from an arbitrary set of sensors of some fixed size s. We show that the sensors broadcast measurements according to a phase-type distribution. We determine the probability distribution of the time needed for a client to retrieve s sensor measurements. We provide a closed-form expression for the retrieval time of s sensor measurements for an asymptotically large capacity of the sensor battery or the rate at which energy is harvested. We also analyze numerically the retrieval time of s sensor measurements under various assumptions regarding the battery capacity of the sensors, the energy harvesting and consumption processes. The results provide a lower bound for the energy storage capacity of the sensors for which the retrieval time of measurements is below a targeted level. It is also shown that the ratio between the energy harvesting rate and the broadcasting rate significantly influences the retrieval time of measurements, whereas deploying sensors with large batteries does not significantly reduce the retrieval time of measurements. Numerical experiments also indicate that our theoretical
An Average Case Analysis of the Minimum Spanning
ABSTRACT
Lecture Notes in Computer Science, 2007
Given a placement of wireless nodes in space and a traffic demand between pairs of nodes, can the... more Given a placement of wireless nodes in space and a traffic demand between pairs of nodes, can these traffic demands be supported by the resulting network? A key issue for answering this question is wireless interference between neighbouring nodes including self interference along multi-hop paths. This paper presents a generic model for sustainable network load in a multi-hop wireless network under interference constraints, and recasts this model into a multicommodity flow problem with interference constraints. Using Farkas' Lemma, we obtain a necessary and sufficient condition for feasibility of this multicommodity flow problem, leading to a tight upper bound on network throughput. Our results are illustrated by examples.
Lecture Notes in Computer Science, 2009
In large-scale distributed applications, a loosely-coupled event-based style of communication as ... more In large-scale distributed applications, a loosely-coupled event-based style of communication as in publish/subcribe systems eases the integration of autonomous, heterogeneous components. In a publish/subscribe system, content based routingwhere routing is based on the content of the messages-is an alternative to addressbased delivery. In this paper we compare the efficiency of two content-based routing algorithms: the flooding scheme and the more sophisticated identity-based routing scheme. Our analytical approach is based on continuous time Markov Chains and extends the steady state approach by Jaeger and Mühl [8] to systems with time-fluctuating parameters. We obtain explicit closed form solutions for the timedependent distribution of the number of active clients, taking into account the use of advertisements and roaming clients. The results allow us to investigate, for example, the switching point between optimality of flooding and identity-based routing.
Linear Algebra and its Applications, 1995
Let C 1 , .•. , Ck and c;, ... , C~ be dosed curves on a compact surface S. We characterize (in t... more Let C 1 , .•. , Ck and c;, ... , C~ be dosed curves on a compact surface S. We characterize (in terms of counting crossings) when there exists a permutation 7T of {l, ... , k} such that C~(il is freely homotopic to C; or C;-1 , for each i = l, ... , k.
AEU - International Journal of Electronics and Communications, 2015
A trade-off between two QoS requirements of wireless sensor networks: query waiting time and vali... more A trade-off between two QoS requirements of wireless sensor networks: query waiting time and validity (age) of the data feeding the queries, is investigated. We propose a Continuous Time Markov Decision Process with a drift that trades-off between the two QoS requirements by assigning incoming queries to the wireless sensor network or to the database. To compute an optimal assignment policy, we argue, by means of non-standard uniformization, a discrete time Markov decision process, stochastically equivalent to the initial continuous process. We determine an optimal query assignment policy for the discrete time process by means of dynamic programming. Next, we assess numerically the performance of the optimal policy and show that it outperforms in terms of average assignment costs three other heuristics, commonly used in practice. Lastly, the optimality of the our model is confirmed also in the case of real query traffic, where our proposed policy achieves significant cost savings compared to the heuristics.
Lecture Notes in Computer Science, 2014
A fundamental problem for wireless ad hoc networks is the assignment of suitable transmission pow... more A fundamental problem for wireless ad hoc networks is the assignment of suitable transmission powers to the wireless devices such that the resulting communication graph is connected. The goal is to minimize the total transmit power in order to maximize the lifetime of the network. Our aim is a probabilistic analysis of this power assignment problem. We prove complete convergence for arbitrary combinations of the dimension d and the distance-power gradient p. Furthermore, we prove that the expected approximation ratio of the simple spanning tree heuristic is strictly less than its worst-case ratio of 2. Our main technical novelties are twofold: First, we find a way to deal with the unbounded degree that the communication network induced by the optimal power assignment can have. Minimum spanning trees and traveling salesman tours, for which strong concentration results are known in Euclidean space, have bounded degree, which is heavily exploited in their analysis. Second, we apply a recent generalization of Azuma-Hoeffding's inequality to prove complete convergence for the case p ≥ d for both power assignments and minimum spanning trees (MSTs). As far as we are aware, complete convergence for p > d has not been proved yet for any Euclidean functional.
2014 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 2014
We consider the problem of data estimation in a sensor wireless network where sensors transmit th... more We consider the problem of data estimation in a sensor wireless network where sensors transmit their observations according to decentralized and centralized transmission schedules. A data collector is interested in achieving a data estimation using several sensor observations such that the variance of the estimation is below a targeted threshold. We analyze the waiting time for a collector to receive sufficient sensor observations. We show that, for sufficiently large sensor sets, the decentralized schedule results in a waiting time that is a constant factor approximation of the waiting time under the optimal centralized scheme .
2013 IEEE Global Conference on Signal and Information Processing, 2013
We consider wireless caches placed in the plane according to a homogeneous Poisson process. A dat... more We consider wireless caches placed in the plane according to a homogeneous Poisson process. A data file is stored at the caches, which have limited storage capabilities. Clients can contact the caches to retrieve the data. The caches store the data according to one of the two data allocation strategies: partitioning & coding. We consider the Pareto front of the expected deployment cost of the caches and the expected cost of a client retrieving the data from the caches. We show that there is a strong trade-off between the expected retrieval and the expected deployment cost under the partitioning and the coding strategies. We also show that under coding, it is optimal to deploy a high number of caches, each with low storage capacity.
Lecture Notes in Computer Science, 2011
The ARTEMIS CAMMI project aims at developing a joint-cognitive system to optimise human operator'... more The ARTEMIS CAMMI project aims at developing a joint-cognitive system to optimise human operator's performance under demanding labour conditions. The CAMMI domain applications concern avionics, automotive, and civil emergencies. In this paper we address the development of a jointcognitive system for firefighter commanders to optimise situational and team awareness by reducing the workload through mitigation strategies and an adaptive HMI. A general framework and a research methodology are presented to explore the possibilities of applying the CAMMI building blocks in the development of systems to support the handling of firefighter emergencies.
Aerial networking communication solutions using Micro Air Vehicle (MAV)
Unmanned/Unattended Sensors and Sensor Networks X, 2014
The application of a Micro Air Vehicle (MAV) for wireless networking is slowly gaining significan... more The application of a Micro Air Vehicle (MAV) for wireless networking is slowly gaining significance in the field of network robotics. Aerial transport of data requires efficient network protocols along with accurate positional adjustment of the MAV to minimize transaction times. In our proof of concept, we develop an Aerial networking protocol for data transfer using the technology of Disruption Tolerant Networks (DTN), a store-and-forward approach for environments that deals with disrupted connectivity. Our results show that close interaction between networking and flight behavior helps in efficient data exchange. Potential applications are in areas where network infrastructure is minimal or unavailable and distances may be large. For example, forwarding video recordings during search and rescue, agriculture, swarm communication, among several others. A practical implementation and validation, as described in this paper, presents the complex dynamics of wireless environments and poses new challenges that are not addressed in earlier work on this topic. Several tests are evaluated in a practical setup to display the networking MAV behavior during such an operation.
Journal of Combinatorial Theory, Series B, 1997
Let C 1 , .... c,, be a system or closed curves on a triangulizable surface S. The system is call... more Let C 1 , .... c,, be a system or closed curves on a triangulizable surface S. The system is called mi11i11wlly crossing if each curve C, has a minimal number of sell~ intersections among all curves c; freely homotopic to C, and if each pair C,, C, has a minimal numher of intersections among all curve pairs (•;, (•; fredy homotopic tu C,. C, respectively Ii, j = l, ... , k, i Ij). The system is called rl'gu/ur it each point tra1ersed at least twice by these curves is traversed exactly twice. •md forms a crnssing. We show that we can make any regular system minimally crossing by applying Rcidcmcistcr moves in such a way that at each move the number of crossings dllcS not increase. It implies a finite algorithm to make a given system or curves minimally crossing by Rciden1eister moves.
Journal of Combinatorial Theory, Series B, 1994
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Papers by Maurits de Graaf