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Dejemeppe C.,ICTEAM | Devolder O.,N SIDE | Lecomte V.,ICTEAM | Schaus P.,ICTEAM
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2016

Response to electricity price fluctuations becomes increasingly important for industries with high energy demands. Consumer tissue manufacturing (toilet paper, kitchen rolls, facial tissues) is such an industry. Its production process is flexible enough to leverage partial planning reorganization allowing to reduce electricity consumption. The idea is to shift the production of the tissues (rolls) requiring more energy when electricity prices (forecasts) are lower. As production plans are subject to many constraints, not every reorganization is possible. An important constraint is the order book that translates into hard production deadlines. A Constraint Programming (CP) model to enforce the due dates can be encoded with p Global Cardinality Constraints (GCC); one for each of the p prefixes of the production variable array. This decomposition into separate GCC’s hinders propagation and should rather be modeled using the global nested gcc constraint introduced by Zanarini and Pesant. Unfortunately it is well known that the GAC propagation does not always pay off in practice for cardinality constraints when compared to lighter Forward-Checking (FWC) algorithms. We introduce a preprocessing step to tighten the cardinality bounds of the GCC’s potentially strengthening the pruning of the individual FWC filterings.We further improve the FWC propagation procedure with a global algorithm reducing the amortized computation cost to O(log(p)) instead of O(p). We describe an energy cost-aware CP model for tissue manufacturing production planning including the nested gcc. Our experiments on real historical data illustrates the scalability of the approach using a Large Neighborhood Search (LNS). © Springer International Publishing Switzerland 2016.

Hoang N.H.,Ho Chi Minh City University of Technology | Mai T.P.,Ho Chi Minh City University of Technology | Dochain D.,ICTEAM
IFAC-PapersOnLine | Year: 2015

This paper further explores the link between irreversible thermodynamics and system theory, and its use for port-based modeling for reaction systems. More specifically we show here that a pseudo Hamiltonian representation with R(x) > 0 can be obtained by considering the Brayton-Moser formulation via a unified potential function that verifies a thermodynamic evolution criterion. As a consequence, it gives additional degrees of freedom (i.e. to construct alternate pseudo Hamiltonian models with new passive outputs) usable for further studies on the control design. A representative example of irreversible processes via the non isothermal continuous stirred tank reactor model is used to illustrate the theoretical developments. © 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

El Soussi M.,ICTEAM | Zaidi A.,University of Marne-la-Vallée | Vandendorpe L.,ICTEAM
IEEE International Conference on Communications | Year: 2012

We1 consider a multiple access relay channel (MARC), in which a relay, based on the recently proposed compute-and-forward protocol, helps two transmitters to communicate with a common destination. The relay decodes a linear combination of the received symbols instead of the individual symbols then forwards the new symbol to the destination. The destination recovers two linear equations from the decoded signals. The two equations relate the transmitted symbols with integer coefficients at different computational rates. We propose an iterative algorithm to optimize the integer coefficients and the power allocation at the transmitters alternatively, so that the sum-rate is maximized. In each iteration, the integer coefficients are updated by solving a mixed-integer quadratic programming (MIQP) problem with quadratic constraints, while the power allocation is updated by solving a series of geometric programs using a successive convex approximation method. The simulation results show that the compute-and-forward strategy and the proposed optimization method can offer substantial gain over the standard amplify-and-forward and decode-and-forward protocols for this model. © 2012 IEEE.

Aguilar-Garnica E.,Autonomous University of Guadalajara | Garcia-Sandoval J.P.,University of Guadalajara | Dochain D.,ICTEAM
Journal of Process Control | Year: 2016

This paper is concerned with the monitoring of a biodiesel production process, more specifically with the monitoring of the esterification of grease trap wastes, a low quality feedstock for biodiesel production typically characterized by its high content of Free Fatty Acids (FFAs). The esterification takes place in a jacketed Continuous Stirred Tank Reactor (CSTR). A reset observer is designed and applied in order to provide on-line estimation of the concentration of FFAs from temperature measurements within the CSTR. In addition, the proposed reset observer is compared to two other observers (classical fuzzy observer and extended Kalman filter). According to a multiple range test conducted for analyzing the estimation error, the monitoring task for the process under study has been better fulfilled by the reset observer which is able to update the estimation results every instant when the measurements were available. © 2016 Elsevier Ltd. All rights reserved.

Gay S.,ICTEAM | Hartert R.,ICTEAM | Schaus P.,ICTEAM
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2015

Cumulative is an essential constraint in the CP framework, and is present in scheduling and packing applications. The lightest filtering for the cumulative constraint is time-tabling. It has been improved several times over the last decade. The best known theoretical time complexity for time-table is O(n log n)introduced by Ouellet and Quimper. We show a new algorithm able to run in O(n), by relying on range min query algorithms. This approach is more of theoretical rather than practical interest, because of the generally larger number of iterations needed to reach the fixed point. On the practical side, the recent synchronized sweep algorithm of Letort et al, with a time-complexity of O(n2), requires fewer iterations to reach the fix-point and is considered as the most scalable approach. Unfortunately this algorithm is not trivial to implement. In this work we present a O(n2) simple two step alternative approach: first building the mandatory profile, then updating all the bounds of the activities. Our experimental results show that our algorithm outperforms synchronized sweep and the time-tabling implementations of other open-source solvers on large scale scheduling instances, sometimes significantly. © Springer International Publishing Switzerland 2015.

Soussi M.E.,ICTEAM | Zaidi A.,University of Marne-la-Vallée | Vandendorpe L.,ICTEAM
Proceedings of the International Symposium on Wireless Communication Systems | Year: 2011

In this work 1, we study a multiaccess relay channel (MARC). The system consists of two transmitters communicating with a destination with the help of a half-duplex relay. We extend and adapt the recently proposed lattice-based compute-and-forward coding scheme to the model we study. This coding scheme can be seen as a form of some network-coding that is implemented at the relay through modulo-reduction. In this scheme, the destination decodes two linear equations with integer coefficients that relate the transmitted symbols at different computational rates. First, we discuss the design criteria, and derive the allowed computation rate. Then, we optimally allocate the different parameters by solving a series of geometric programs using successive convex approximation methods. The analysis shows that our coding scheme can offer substantial gain over the standard amplify-and-forward and decode-and-forward for this model. We illustrate our results through some numerical examples. © 2011 IEEE.

Brante G.,Federal Technological University of Paraná | Souza R.D.,Federal Technological University of Paraná | Vandendorpe L.,ICTEAM
IEEE Wireless Communications and Networking Conference, WCNC | Year: 2012

We analyze the energy efficiency of reactive and proactive relay selection algorithms under the incremental decode-and-forward protocol. By taking into account the consumption of the RF circuitry, the transmit power, and a nonlinear model for the battery, we show that a large number of available relays can actually compromise the energy efficiency of the system. Our results show that, depending on the source to destination distance, it may be preferable to consider only a small subset of nodes and select the relay among these nodes. © 2012 IEEE.

Paasch C.,ICTEAM | Ferlin S.,Simula Research Laboratory | Alay O.,Simula Research Laboratory | Bonaventure O.,ICTEAM
CSWS 2014 - Proceedings of the ACM SIGCOMM 2014 Workshop on Capacity Sharing Workshop | Year: 2014

Today many end hosts are equipped with multiple interfaces. These interfaces can be utilized simultaneously by multipath protocols to pool resources of the links in an efficient way while also providing resilience to eventual link failures. However how to schedule the data segments over multiple links is a challenging problem, and highly influences the performance of multipath protocols. In this paper, we focus on different schedulers for Multipath TCP. We first design and implement a generic modular scheduler framework that enables testing of different schedulers for Multipath TCP. We then use this framework to do an in-depth analysis of different schedulers by running emulated and real-world experiments on a testbed. We consider bulk data transfer as well as application limited traffic and identify metrics to quantify the scheduler's performance. Our results shed light on how scheduling decisions can help to improve multipath transfer. © 2014 ACM.

Gay S.,ICTEAM | Hartert R.,ICTEAM | Schaus P.,ICTEAM
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2015

Scheduling has been a successful domain of application for constraint programming since its beginnings. The cumulative constraint – which enforces the usage of a limited resource by several tasks – is one of the core components that are surely responsible of this success. Unfortunately, ensuring bound-consistency for the cumulative constraint is already NP-Hard. Therefore, several relaxations were proposed to reduce domains in polynomial time such as Time-Tabling, Edge- Finding, Energetic Reasoning, and Not-First-Not-Last. Recently, Vilim introduced the Time-Table Edge-Finding reasoning which strengthens Edge-Finding by considering the time-table of the resource. We pursue the idea of exploiting the time-table to detect disjunctive pairs of tasks dynamically during the search. This new type of filtering – which we call time-table disjunctive reasoning – is not dominated by existing filtering rules. We propose a simple algorithm that implements this filtering rule with a O(n2) time complexity (where n is the number of tasks) without relying on complex data structures. Our results on well known benchmarks highlight that using this new algorithm can substantially improve the solving process for some instances and only adds a marginally low computation overhead for the other ones. © Springer International Publishing Switzerland 2015.

Soussi M.E.,ICTEAM | Zaidi A.,University of Marne-la-Vallée | Vandendorpe L.,ICTEAM
IEEE International Conference on Communications | Year: 2013

We study a system in which two sources communicate with a destination with the help of a half-duplex relay. We consider a decoding strategy, based on the compute-and-forward strategy, in which the destination decodes two integer-valued linear combinations that relate the transmitted codewords. In this strategy, the relay compresses its observation using Wyner-Ziv compression and then forwards it to the destination. The destination appropriately combines what it gets from the direct transmission and the relay. Then, using this combination, it computes two integer-valued linear combinations. We discuss the encoding/decoding strategy, and evaluate the achievable sum-rate. Next, we consider the problem of allocating the powers and selecting the integer-valued coefficients of the recovered linear combinations in order to maximize the sum-rate. For the model under consideration, the optimization problem is NP hard. We propose an iterative algorithm to solve this problem using coordinate descent method. The results are illustrated through some numerical examples. © 2013 IEEE.

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