| 1. |
- Terelius, Håkan, 1987-, et al.
(författare)
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An efficiency measure for road transportation networks with application to two case studies
- 2015
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Ingår i: 2015 IEEE 54th Annual Conference on Decision and Control (CDC). - : IEEE conference proceedings. ; , s. 5149-5155
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Konferensbidrag (refereegranskat)abstract
- Enabling efficient transportation is a major challenge for large cities, as the transportation need is increasing, while the environmental impact has to be minimized.In this paper, we define an efficiency measure that shows how much of the current transportation mileage that is really necessary to meet all the transportation assignments.We show that the efficiency measure can be computed efficiently as a minimum cost flow, and we apply it on two case studies. The first case demonstrate the efficiency measure on a freight transportation system, and the second case computes the measure for a large real-world data set from the New York City taxis.
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| 2. |
- Terelius, Håkan, 1987-
(författare)
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Consensus Algorithms in Dynamical Network Systems
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dynamical network systems are complex interconnected systems describing many real world problems. The current trend is to connect more and more systems together, and at the same time requiring continuous availability. To this end, it is crucial to understand the dynamic behaviors of networked systems.This thesis makes three contributions in this area.First, we study the important problem of gathering data that are distributed among the nodes in a network. Two specific tasks are considered: to estimate the size of the network, and to aggregate the distribution of local measurements generated by the nodes. We consider a framework where the nodes require anonymity, and restricted computational resources. We propose probabilistic algorithms with low resource requirements, that quickly generate arbitrarily accurate estimates. For dynamical networks, we improve the accuracy through a regularization term which captures the trade-off between the gathered data and a-priori assumptions on the dynamics.In the second part of this thesis, we consider a dynamical network system where one node is misbehaving due to a failure. We specifically seek robustness conditions that guarantee that the entire network system is still functional. The nodes' dynamics is governed by consensus updates, and we present thresholds on the interaction strengths that determines if the system will reach consensus, or if the system will diverge.Finally, a P2P network is utilized to improve a live-streaming media application. In particular, we study how an overlay network, constructed from simple preference functions, can be used to build efficient topologies that reduce both network latency and interruptions. We present necessary and sufficient convergence conditions, as well as convergence speed estimates, and demonstrate the improvements for a real P2P video streaming application.
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| 3. |
- Terelius, Håkan, 1987-, et al.
(författare)
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Consensus Control for Multi-agent Systems with a Faulty Node
- 2013
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Ingår i: 4th IFAC Workshop on Distributed Estimation and Control in Networked Systems. - : IFAC Papers Online. - 9783902823557 ; , s. 425-432
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Konferensbidrag (refereegranskat)abstract
- This paper studies consensus control for a multi-agent system with a faulty node. The node dynamics follow a continuous-time consensus protocol with negative feedback from the relative state of the neighbors, where the faulty node is instead using positive feedback from the state. Conditions for reaching consensus are established, and a fault threshold is introduced. Numerical examples investigate how the fault threshold determines the system behavior.
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| 4. |
- Terelius, Håkan, et al.
(författare)
-
Converging an Overlay Network to a Gradient Topology
- 2011
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Konferensbidrag (refereegranskat)abstract
- In this paper, we investigate the topology convergence problem for the gossip-based Gradient overlay network. In an overlay network where each node has a local utility value, a Gradient overlay network is characterized by the properties that each node has a set of neighbors containing higher utility values, such that paths of increasing utilities emerge in the network topology. The Gradient overlay network is built using gossiping and a preference function that samples from nodes using a uniform random peer sampling service. We analyze it using tools from matrix analysis, and we prove both the necessary and sufficient conditions for convergence to a complete gradient structure, as well as estimating the convergence time. Finally, we show in simulations the potential of the Gradient overlay, by building a more efficient live-streaming peer-to-peer (P2P) system than one built using uniform random peer sampling.
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| 5. |
- Terelius, Håkan, et al.
(författare)
-
Decentralized Multi-Agent Optimization via Dual Decomposition
- 2011
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Konferensbidrag (refereegranskat)abstract
- We study a distributed multi-agent optimization problem of minimizing the sum of convex objective functions. A new decentralized optimization algorithm is introduced, based on dual decomposition, together with the subgradient method for finding the optimal solution. The iterative algorithm is implemented on a multi-hop network and is designed to handle communication delays.The convergence of the algorithm is proved for communication networks with bounded delays. An explicit bound, which depends on the communication delays, on the convergence rate is given.A numerical comparison with a decentralized primal algorithm shows that the dual algorithm converges faster, and with less communication.
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| 6. |
- Terelius, Håkan, et al.
(författare)
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Distributed size estimation of dynamic anonymous networks
- 2012
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Ingår i: 2012 IEEE 51st Annual Conference on Decision and Control (CDC). - : IEEE conference proceedings. - 9781467320641 ; , s. 5221-5227
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Konferensbidrag (refereegranskat)abstract
- We consider the problem of estimating the size of dynamic anonymous networks, motivated by network maintenance. The proposed algorithm is based on max-consensus information exchange protocols, and extends a previous algorithm for static anonymous networks. A regularization term is accounting for a-priori assumptions on the smoothness of the estimate, and we specifically consider quadratic regularization terms since they lead to closed-form solutions and intuitive design laws. We derive an explicit estimation scheme for a particular peer-to-peer service network, starting from its statistical model. To validate the accuracy of the algorithm, we perform numerical experiments and show how the algorithm can be implemented using finite precision arithmetics as well as small communication burdens
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| 7. |
- Terelius, Håkan, 1987-, et al.
(författare)
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Fast distributed estimation of empirical mass functions over anonymous networks
- 2013
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Ingår i: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC). - : IEEE conference proceedings. - 9781467357173 ; , s. 6771-6777
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Konferensbidrag (refereegranskat)abstract
- The aggregation and estimation of values over networks is fundamental for distributed applications, such as wireless sensor networks. Estimating the average, minimal and maximal values has already been extensively studied in the literature. In this paper, we focus on estimating empirical distributions of values in a network with anonymous agents. In particular, we compare two different estimation strategies in terms of their convergence speed, accuracy and communication costs. The first strategy is deterministic and based on the average consensus protocol, while the second strategy is probabilistic and based on the max consensus protocol.
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| 8. |
- Terelius, Håkan, 1987-, et al.
(författare)
-
On the optimal location of distribution centers for a one-dimensional transportation system
- 2016
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Ingår i: 2016 IEEE 55th Conference on Decision and Control, CDC 2016. - : IEEE. - 9781509018376 ; , s. 2574-2580
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Konferensbidrag (refereegranskat)abstract
- Transportation service providers are pressurized to enable real-time logistics planning from a constantly changing demand. This paper focus on a real-time transportation service provider operating along a one-dimensional highway. Transportation assignments arrive following a Poisson process, and the transportation service provider is operating on this road system with a fleet of vehicles, trying to minimize the expected delivery time. Specifically, the optimal locations for idle vehicles, and the optimal locations for construction of distribution centers are considered. The strategies are evaluated with numerical simulations along a Swedish highway system.
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| 9. |
- Terelius, Håkan, 1987-
(författare)
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Optimization and Control in Dynamical Network Systems
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dynamical network systems are complex interconnected systems useful to describe many real world problems. The advances in information technology has led the current trend towards connecting more and more systems, creating "intelligent" systems, where the intelligence originates in the scale and complexity of the network. With the growing scale of networked systems comes also higher demands on performance and continuous availability and this creates the need for optimization and control of network systems. This thesis makes four important contributions in this area.In the first contribution, we consider a collaborative road freight transportation system. An efficiency measure for the road utilization in collaborative transportation scenarios is introduced, which evaluates the performance of collaboration strategies in comparison to an optimal central planner. The efficiency measure is used to study a freight transport simulation in Germany and taxi trips using real data from New York City. This is followed by a study of the optimal idling locations for trucks, and the optimal locations for distribution centers. These locations are then exploited in a simulation of a realistic collaborative freight transport system.The second contribution studies the important problem of gathering data that are distributed among the nodes in an anonymous network, i.e., a network where the nodes are not endowed with unique identifies. Two specific tasks are considered: to estimate the size of the network, and to aggregate the distribution of local measurements generated by the nodes. We consider a framework where the nodes require anonymity and have restricted computational resources. We propose probabilistic algorithms with low resource requirements, that quickly generate arbitrarily accurate estimates. For dynamical networks, we improve the accuracy through a regularization term which captures the trade-off between the reliability of the gathered data and a-priori assumptions for the dynamics.In the third contribution, a peer-to-peer network is utilized to improve a live-streaming media application. In particular, we study how an overlay network, constructed from simple preference functions, can be used to build efficient topologies that reduce both network latency and interruptions. We present necessary and sufficient convergence conditions, as well as convergence rate estimates, and demonstrate the improvements for a real peer-to-peer video streaming application.The final contribution is a distributed optimization algorithm. We consider a distributed multi-agent optimization problem of minimizing the sum of convex objective functions. A decentralized optimization algorithm is introduced, based on dual decomposition, together with the subgradient method for finding the optimal solution. The convergence rate is analyzed for different step size rules, constant and time-varying communication delays, and noisy communication channels.
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| 10. |
- Terelius, Håkan, 1987-, et al.
(författare)
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Peer-to-Peer Gradient Topologies in Networks With Churn
- 2018
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Ingår i: IEEE Transactions on Control of Network Systems. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2325-5870. ; 5:4, s. 2085-2095
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the network topology convergence in a peer-to-peer (P2P) network system, where the goal of the system is to maximize live-streaming performance. The P2P system constructs a gradient overlay topology, characterized by a directed graph, where each node prefers neighbors containing higher utility values such that paths of increasing utilities emerge in the network topology. The gradient overlay network is built using gossiping and a preference function that samples nodes from a uniform random peer sampling service. Conditions for convergence to a gradient topology is derived, including the expected convergence time, and a threshold on the churn rate is provided for a gradient topology to emerge. Finally, a live-streaming video distribution experiment illustrates the benefits of constructing and utilizing the gradient topology for information dissemination in P2P systems.
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