Conference Papers

Minimum cost constrained input-output and control configuration co-design problem: A structural systems approach

Pequito S., Kar S., Pappas G.J.

Proceedings of the American Control Conference

2015

Abstract:

In this paper, we study the minimal cost constrained input-output (I/O) and control configuration co-design problem. Given a linear time-invariant plant, where a collection of possible inputs and outputs is known a priori, we aim to determine the collection of inputs, outputs and communication among them incurring in the minimum cost, such that desired control performance, measured in terms of arbitrary pole-placement capability of the closed-loop system, is ensured. We show that this problem is NP-hard in general (in the size of the state space). However, the subclass of problems, in which the dynamic matrix is irreducible, is shown to be polynomially solvable and the corresponding algorithm is presented. In addition, under the same assumption, the same algorithm can be used to solve the minimal cost constrained I/O selection problem, and the minimal cost control configuration selection problem, individually. In order to illustrate the main results of this paper, some simulations are also provided.

Minimum cost input-output and control configuration selection: A structural systems approach

Pequito S., Kar S., Aguiar A.P.

Proceedings of the IEEE Conference on Decision and Control

2013

Abstract:

In this paper we provide solutions to two different (but related) design problems involving large-scale linear dynamical systems: 1) the optimal input/output structural design ensuring structural controllability/observability and incurring in the minimal cost under generic assumptions; and 2) the optimal structural control configuration design for decentralized control, i.e., the sparsest information pattern or the minimal communication between outputs and inputs, such that the closed-loop system has no structurally fixed modes and incurring in the minimal cost under the assumption that the communication devices have the same cost. We show that the proposed solution can be implemented efficiently, i.e., using an algorithm with polynomial time complexity in the number of the state variables. We illustrate the obtained results with an example.

Minimum cost input/output design for large-scale linear structural systems

Pequito S., Kar S., Aguiar A.P.

Automatica

2016

Abstract:

In this paper, we provide optimal solutions to two different (but related) input/output design problems involving large-scale linear dynamical systems, where the cost associated to each directly actuated/measured state variable can take different values, but is independent of the input/output performing the task. Under these conditions, we first aim to determine and characterize the input/output placement that incurs in the minimum cost while ensuring that the resulting placement achieves structural controllability/observability. Further, we address a constrained variant of the above problem, in which we seek to determine the minimum cost placement configuration, among all possible input/output placement configurations that ensures structural controllability/observability, with the lowest number of directly actuated/measured state variables. We develop new graph-theoretical characterizations of cost-constrained input selections for structural controllability and properties that enable us to address both problems by reduction to a weighted maximum matching problem — efficiently addressed by algorithms with polynomial time complexity (in the number of state variables). Finally, we illustrate the obtained results with an example.

Minimum number of information gatherers to ensure full observability of a dynamic social network: A structural systems approach

Pequito S., Kar S., Aguiar A.P.

2014 IEEE Global Conference on Signal and Information Processing, GlobalSIP 2014

2014

Abstract:

This paper studies the problem of identifying the minimum number of entities (agents), referred to as information gatherers, that are able to infer all the states in a dynamical social network. The information gatherers can be, for instance, service providers and the remaining agents the clients, each comprising several dynamic states associated with the services and personal information. The problem of identifying the minimum number of information gatherers can constitute a way to create coalitions to oversee the entire state of the system, and consequently the behavior of the agents in the social network. The dynamical social network is assumed to be modelled as a linear time-invariant system, and we will make use of the structural systems concept, i.e., by considering only the sparsity pattern (location of zeroes/non-zeroes) of the system coupling matrix. As a consequence, the design guarantees derived hold for almost all numerical parametric realizations of the system. In this paper, we show that this problem is NP-hard: in addition, we provide a reduction of the coalition problem to a minimum set covering problem that, in practice, leads to efficient (polynomial complexity) approximation schemes for solving the coalition problem with guaranteed optimality gaps. Finally, an example is provided which illustrates the analytical findings.

Minimum robust sensor placement for large scale linear time-invariant systems: A structured systems approach

Liu X., Pequito S., Kar S., Mo Y., Sinopoli B., Aguiar A.P.

IFAC Proceedings Volumes (IFAC-PapersOnline)

2013

Abstract:

The paper addresses the problem of robust sensor placement for large scale linear time-invariant systems. Two different concepts of robustness are analyzed: 1) the robustness with respect to one sensor failure, and 2) the robustness with respect to one link failure. We show that both aforementioned problems can be posed as certain set cover problems, a classical problem for which many solutions exist. In addition we formulate and partially solve the minimum robust sensor placement, a much harder problem. By relating robust sensor placement to spanning trees associated with the dynamical system structure, readily computable upper and lower bounds are provided on the size of such robust placement configurations. Finally, some illustrative examples are presented.

Mining parallel corpora from Sina Weibo and Twitter

Ling W., Marujo L., Dyer C., Black A.W., Trancoso I.

Computational Linguistics

2016

Abstract:

Microblogs such as Twitter, Facebook, and Sina Weibo (China’s equivalent of Twitter) are a remarkable linguistic resource. In contrast to content from edited genres such as newswire, microblogs contain discussions of virtually every topic by numerous individuals in different languages and dialects and in different styles. In this work, we show that some microblog users post “self-translated” messages targeting audiences who speak different languages, either by writing the same message in multiple languages or by retweeting translations of their original posts in a second language. We introduce a method for finding and extracting this naturally occurring parallel data. Identifying the parallel content requires solving an alignment problem, and we give an optimally efficient dynamic programming algorithm for this. Using our method, we extract nearly 3M Chinese–English parallel segments from Sina Weibo using a targeted crawl of Weibo users who post in multiple languages. Additionally, from a random sample of Twitter, we obtain substantial amounts of parallel data in multiple language pairs. Evaluation is performed by assessing the accuracy of our extraction approach relative to a manual annotation as well as in terms of utility as training data for a Chinese–English machine translation system. Relative to traditional parallel data resources, the automatically extracted parallel data yield substantial translation quality improvements in translating microblog text and modest improvements in translating edited news content.

Modeling students self-studies behaviors

Mota P., Melo F.S., Coheur L.

Proceedings of the International Joint Conference on Autonomous Agents and Multiagent Systems, AAMAS

2015

Abstract:

In this work we propose a decision-theoretic approach to Intelligent Tutoring Systems (ITSs) that seeks to alleviate the need for extensive development and hand-tuning in the design of such systems. Given a set of available learning materials, our approach enables the ITS to track the students’ difficulties and provide the right material at the right time. We model the learning process as a Partially Observable Markov Decision Process (POMDP), where the hidden information corresponds to the student’s familiarity with each of the topics to be learned. The student’s progress is monitored from his/her performance in different test exercises and, depending on this performance, the ITS actively determines which type of materials should be provided to the student. We deploy our proposed approach in a learning scenario and compare the ability of our system to model the students’ self-study behaviors of the learning materials. Our initial results show that such behaviors are not trivial to model and that our proposed POMDP approach better matched the observed student behaviors in comparison with a baseline teaching policy that corresponds to a fix set of actions hand-designed by a human expert.

Modeling vehicle-to-vehicle line of sight channels and its impact on application-layer performance

Boban M., Viriyasitavat W., Tonguz O.

VANET 2013 - Proceedings of the 10th ACM International Workshop on VehiculAr Inter-NETworking, Systems, and Applications

2013

Abstract:

We analyze the properties of line of sight (LOS) channels in vehicle-to-vehicle (V2V) communication. We use V2V measurements performed in open space, suburban, and urban environments. By separating LOS from non-LOS data, we show that a two-ray ground reflection path loss model with effective reflection coefficient range fits the LOS channels better than the frequently used free space path loss model. Two-ray model is a better fit not only in open space, but also in suburban and urban environments. We investigate the impact of using the modified two-ray model on the application-level performance metrics: packet delivery rate, throughput, latency, and jitter. Our results show that considerable differences arise in application performance when using the modified two-ray and free space models.

MOTH- Mobility-induced Outages in THz: A Beyond 5G (B5G) application

Singh R., Sicker D., Huq K.

Preprint. To appear in IEEE CCNC 2020.

2019

Abstract:

5G will enable the growing demand for Internet of Things (IoT), high-resolution video streaming, and low latency wireless services. Demand for such services is expected to growth rapid, which will require a search for Beyond 5G technological advancements in wireless communi- cations. Part of these advancements is the need for additional spectrum, namely moving toward the terahertz (THz) range. To compensate for the high path loss in THz, narrow beamwidths are used to improve antenna gains. However, with narrow beamwidths, even minor fluctuations in device location (such as through body movement) can cause frequent link failures due to beam misalignment. In this paper, we provide a solution to these small-scale indoor movement that result in mobility-induced outages. Like a moth randomly flutters about, Mobilityinduced Outages in THz (MOTH) can be ephemeral in nature and hard to avoid. To deal with MOTH we propose two methods to predict these outage scenarios: (i) Align-AfterFailure (AAF), which predicts based on fixed time margins, and (ii) Align-Before-Failure (ABF), which learns the time margins through user mobility patterns. In this paper, two different online classifiers were used to train the ABF model to predicate if a mobility-induced outage is going to occur; thereby, significantly reducing the time spent in outage scenarios. Simulation results demonstrate a relationship between optimal beamwidth and human mobility patterns. Additionally, to cater to a future with dense deployment of Wireless Personal Area Network (WPAN), it is necessary that we have efficient deployment of resources (e.g., THz-APs). One solution is to maximize the user coverage for a single AP, which might be dependent on multiple parameters. We identify these parameters and observe their tradeoffs for improving user coverage through a single THz-AP.