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Showing papers by "Richard H. Middleton published in 2019"


Journal ArticleDOI
TL;DR: Stability analysis based on integral quadratic constraint theory is applied to characterize the global stability of the controller, and it is stressed that the proposed controller does not require internode time synchronization.
Abstract: Automatic control using ultrareliable and low latency communication is one of the potential applications of the new fifth-generation wireless systems. A remaining challenge is then to guarantee a low end-to-end delay with low jitter over combined internet and wireless interfaces that are packet switched and capacity optimized. The main novelty of this paper is to introduce stringent delay control to meet this challenge, over simultaneous multiple data paths. The proposed multiple-input-multiple-output (MIMO) cascade control system is nonlinear since the dwell times of the transmission node queues used as actuators cannot be negative. Stability analysis based on integral quadratic constraint theory is, therefore, applied to characterize the global stability of the controller. The practical performance is evaluated with experiments using product like test bed C++ code. It is stressed that the proposed controller does not require internode time synchronization.

28 citations


Journal ArticleDOI
TL;DR: A pricing mechanism that relies on non-cooperative heterogeneous loads knowledgeable of future energy consumption transferring minimal amounts of information to achieve peak demand response in a distributed fashion, whilst maintaining the privacy of the players is presented.
Abstract: Demand response technology offers the exciting potential to reduce peak energy demand, electricity infrastructure expenditure, and household electricity bills. In this paper, a pricing mechanism that relies on non-cooperative heterogeneous loads knowledgeable of future energy consumption—such as electric vehicles—transferring minimal amounts of information to achieve peak demand response in a distributed fashion, whilst maintaining the privacy of the players. The existence of a Nash equilibrium is proven, as well as convergence conditions proving uniqueness of a Nash equilibrium and the stability of an “Iterated Synchronous Best Response Algorithm.” The price of anarchy (PoA) is proven to approach 1 as the number of homogeneous players approaches infinity, indicating there is no advantage to cooperation for a large number of similar players. Finally, simulation results are presented which suggest that the PoA for a system with heterogeneous players is likely to be proportional to the spread of energy consumption constraints.

24 citations


Posted Content
TL;DR: A novel scheme for cell-free massive multiple-input multiple-output (CFmMIMO) networks to support any federated learning (FL) framework is proposed and a new algorithm is developed to solve the formulated problem with proven convergence to the neighbourhood of its stationary points.
Abstract: This paper proposes a novel scheme for cell-free massive multiple-input multiple-output (CFmMIMO) networks to support any federated learning (FL) framework. This scheme allows each instead of all the iterations of the FL framework to happen in a large-scale coherence time to guarantee a stable operation of an FL process. To show how to optimize the FL performance using this proposed scheme, we consider an existing FL framework as an example and target FL training time minimization for this framework. An optimization problem is then formulated to jointly optimize the local accuracy, transmit power, data rate, and users' processing frequency. This mixed-timescale stochastic nonconvex problem captures the complex interactions among the training time, and transmission and computation of training updates of one FL process. By employing the online successive convex approximation approach, we develop a new algorithm to solve the formulated problem with proven convergence to the neighbourhood of its stationary points. Our numerical results confirm that the presented joint design reduces the training time by up to $55\%$ over baseline approaches. They also show that CFmMIMO here requires the lowest training time for FL processes compared with cell-free time-division multiple access massive MIMO and collocated massive MIMO.

22 citations


Journal ArticleDOI
TL;DR: Simulation results show that a fully-equipped contractor who opportunistically exploits a relatively small proportion of the contracted farmers in most instances can outperform spot market-based contractors in terms of average profit achieved for each crop, and are in agreement with the existing literature that the contract farming scheme is not a cost-effective method for buyers with limited rice processing capacity.
Abstract: We would like to thank Michael Maes and the anonymous reviewers for their insightful and constructive feedback. The first author, H. K. Nguyen, would like to acknowledge support from an Australian Government Research Training Program scholarship to study a PhD degree in Computer Science at The University of Newcastle, Australia. R. Chiong is the corresponding author of this paper. The third author, M. Chica, is supported through the Ramon y Cajal program (RYC-2016-19800)

21 citations


Journal ArticleDOI
TL;DR: It is shown that consensus over expander families is fragile to a grounding of the network (resulting in leader-follower consensus), and that grounding may deteriorate system performance by orders of magnitude in large networks, or cause instability in high-order consensus.

17 citations


Journal ArticleDOI
30 May 2019
TL;DR: A new closed-loop structure for mechanical systems with dissipation, controlled via energy shaping is proposed, which generalizes the well-established potential energy shaping technique by introducing a kinetic-potential function which has both configuration and momentum states as arguments.
Abstract: In this letter, we propose a new closed-loop structure for mechanical systems with dissipation, controlled via energy shaping. The structure generalizes the well-established potential energy shaping technique by introducing a kinetic-potential function which has both configuration and momentum states as arguments. As a consequence of this generalization, dissipation terms are able to be added to the configuration coordinates of the system, resulting in both exponential stability and input-to-state stability (ISS) properties of the closed-loop. The developments are applied to the tracking problem where it is shown that the scheme is ISS with respect to friction modelling error.

14 citations


Journal ArticleDOI
TL;DR: The scope of this article is to discuss and motivate recognition of the need for delay alignment in general.
Abstract: In a new radio (NR) communication system, low latency and limited jitter are critical to support new use cases exploiting haptic feedback and other closed-loop feedback control applications. Therefore, mechanisms for delay control and delay alignment are important. The simplest approaches to mitigating delay jitter, using buffering techniques, come at the price of memory and increased delay. More recently, techniques using feedback of delays experienced have shown great promise for improved performance with low overhead. The scope of this article is to discuss and motivate recognition of the need for delay alignment in general.

7 citations


Proceedings ArticleDOI
10 Jun 2019
TL;DR: This work uses agent-based modeling (ABM) to study the dynamics of migration flows across provinces and cities in the Mekong Delta, Vietnam, anditivity analysis carried out helps to further understand the impact of critical factors on the final migration decision.
Abstract: Migration is one of the many responses humans and societies make to ongoing demographic, economic, societal and environmental changes. In this work, we use agent-based modeling (ABM) to study the dynamics of migration flows across provinces and cities in the Mekong Delta, Vietnam. The strength of ABM is that it allows a bottom-up approach that focuses on how individuals make decisions in a complex system comprising various factors. Outputs of our agent-based model are automatically calibrated with actual data using a genetic algorithm. This automated calibration yields some significant improvement in the results, with all observed net- and out-migration data captured within the 95% confidence interval. Sensitivity analysis carried out helps to further understand the impact of critical factors on the final migration decision.

6 citations


Posted Content
TL;DR: In this paper, the authors investigate the performance of linear consensus algorithms subject to a scaling of the underlying network size and show that consensus over expander families is fragile to a grounding of the network (resulting in leader-follower consensus), which may deteriorate system performance by orders of magnitude in large networks, or cause instability in high-order consensus.
Abstract: We investigate the performance of linear consensus algorithms subject to a scaling of the underlying network size. Specifically, we model networked systems with $n^{\text{th}}$ order integrator dynamics over families of undirected, weighted graphs with bounded nodal degrees. In such networks, the algebraic connectivity affects convergence rates, sensitivity, and, for high-order consensus ($n \ge 3$), stability properties. This connectivity scales unfavorably in network size, except in expander families, where consensus performs well regardless of network size. We show, however, that consensus over expander families is fragile to a grounding of the network (resulting in leader-follower consensus). We show that grounding may deteriorate system performance by orders of magnitude in large networks, or cause instability in high-order consensus. Our results, which we illustrate through simulations, also point to a fundamental limitation to the scalability of consensus networks with leaders, which does not apply to leaderless networks.

Proceedings ArticleDOI
01 Aug 2019
TL;DR: To study robust local stability of a controller design based on feedback linearisation applied to a wind turbine with a permanent magnet synchronous generator, an analysis of the eigenvalues of the small signal model is employed.
Abstract: The objective of this paper is to assess parameter robustness of a controller design based on feedback linearisation applied to a wind turbine with a permanent magnet synchronous generator (PMSG). To study robust local stability, we employ an analysis of the eigenvalues of the small signal model. Some controller parameters are deduced based on measured system variables. It is therefore of interest to know bounds on measurement errors that are guaranteed to preserve local stability. Finally, simulations of a 2MW direct drive PMSG wind turbine system illustrate the effectiveness of the method.

Journal ArticleDOI
TL;DR: A novel algorithm for sparse reconstruction that relies on the recently proposed stepwise Tikhonov regularization (STIR) method to implement forward selection procedures such as Orthogonal least squares, orthogonal matching pursuit, and STIR.
Abstract: This letter describes a novel algorithm for sparse reconstruction. The method uses offline computations to reduce the computational burden of online execution. The approach relies on the recently proposed stepwise Tikhonov regularization (STIR) method to implement forward selection procedures such as orthogonal least squares (OLS), orthogonal matching pursuit (OMP), and STIR. Numerical simulations show the efficacy of the proposed approach, which is competitive against state-of-the-art implementation of OLS and OMP.