Fundamental Design Tradeoffs Research Articles

Mean-square convergent continuous state estimation of randomly switched linear systems with unobservable subsystems and stochastic output noises

This paper studies mean-square (MS) convergent observers for estimating continuous states of randomly switched linear systems (RSLSs) with unobservable subsystems that are subject to stochastic output observation noises. When subsystems are unobservable and switching sequences are random, the classical Kalman–Bucy filters that are applied to observable sub-states are shown to be potentially divergent. It is also shown that unless the switching interval T can be selected to be sufficiently small from the outset, MS convergence may never be achieved, regardless of how the observers for the subsystems are designed. The critical threshold Tmax on T is derived for MS convergent observers to be achievable. Under the condition T<Tmax, this paper introduces design algorithms for subsystem observers to generate a globally MS convergent observer for the entire continuous state. A fundamental design tradeoff between convergence speeds and steady-state estimation errors is analyzed. This paper extends our recent new framework and algorithms for strong convergent observer design in RSLSs by including observation noises, considering multi-output systems, establishing new algorithms for MS convergence, and developing design tradeoff analysis. Examples and a practical case study are presented to illustrate the design procedures, main convergence properties, and error analysis.

Experimental assessment of a linear actuator driven by magnetorheological clutches for automotive active suspensions.

The main functions of automotive suspensions are to improve passenger comfort as well as vehicle dynamic performance. Simultaneously satisfying these functions is not possible because they require opposing suspension adjustments. This fundamental design trade-off can be solved with an active suspension system providing real-time modifications of the suspension behavior and vehicle attitude corrections. However, current active suspension actuator technologies have yet to reach a wide-spread commercial adoption due to excessive costs and performance limitations. This paper presents a design study assessing the potential of magnetorheological clutch actuators for automotive active suspension applications. An experimentally validated dynamic model is used to derive meaningful design requirements. An actuator design is proposed and built using a motor to feed counter-rotating MR clutches to provide upward and downward forces. Experimental characterization shows that all intended design requirements are met, and that the actuator can output a peak force of ±5300 N, a peak linear speed of ±1.9 m/s and a blocked-output force bandwidth of 92 Hz. When compared to other relevant technologies, the MR approach simultaneously shows both better force density and speeds (bandwidth) while adding minimal costs and weight. Results from this experimental assessment suggest that MR slippage actuation is promising for automotive active suspensions.

Communication Aspects of the Integration of Wireless IoT Devices with Distributed Ledger Technology

The pervasive need to safely share and store information between devices calls for the replacement of centralized trust architectures with decentralized ones. DLTs are seen as the most promising enabler of decentralized trust, but they still lack technological maturity, and their successful adoption depends on the understanding of the fundamental design trade-offs and their reflection in the actual technical design. This work focuses on the challenges and potential solutions for an effective integration of DLTs in the context of the Internet of Things (IoT). We first introduce the landscape of IoT applications and discuss the limitations and opportunities offered by DLTs. Then we review the technical challenges encountered in the integration of resource-constrained devices with distributed trust networks. We describe the common traits of lightweight synchronization protocols, and propose a novel classification rooted in the IoT perspective. We identify the need for receiving ledger information at the endpoint devices, implying a two-way data exchange that contrasts with the conventional uplink-oriented communication technologies intended for IoT systems.

Engineering Translational Resource Allocation Controllers: Mechanistic Models, Design Guidelines, and Potential Biological Implementations.

The use of orthogonal ribosomes in combination with dynamic resource allocation controllers is a promising approach for relieving the negative effects of cellular resource limitations on the modularity of synthetic gene circuits. Here, we develop a detailed mechanistic model of gene expression and resource allocation, which when simplified to a tractable level of complexity, allows the rational design of translational resource allocation controllers. Analysis of this model reveals a fundamental design trade-off: that reducing coupling acts to decrease gene expression. Through a sensitivity analysis of the experimentally tunable controller parameters, we identify how each controller design parameter affects the overall closed-loop behavior of the system, leading to a detailed set of design guidelines for optimally managing this trade-off. On the basis of our designs, we evaluated a number of alternative potential experimental implementations of the proposed system using commonly available biological components. Finally, we show that the controller is capable of dynamically allocating ribosomes as needed to restore modularity in a number of more complex synthetic circuits, such as the repressilator, and activation cascades composed of multiple interacting modules.

Fundamentals of metasurface lasers based on resonant dark states

Recently, our group proposed a metamaterial laser design based on explicitly coupled dark resonant states in low-loss dielectrics, which conceptually separates the gain-coupled resonant photonic state responsible for macroscopic stimulated emission from the coupling to specific free-space propagating modes, allowing independent adjustment of the lasing state and its coherent radiation output. Due to this functionality, it is now possible to make lasers that can overcome the trade-off between system dimensions and $Q$ factor, especially for surface emitting lasers with deeply subwavelength thickness. Here, we give a detailed discussion of the key functionality and benefits of this design, such as radiation damping tunability, directionality, subwavelength integration, and simple layer-by-layer fabrication. We examine in detail the fundamental design tradeoffs that establish the principle of operation and must be taken into account and give guidance for realistic implementations.

Why Will Computing Power Need Particular Attention in Future Wireless Devices?

In this tutorial particular attention is given to the computing power in the physical layer of wireless devices, which are energy and power limited. Communication uses the power in the analog radio frequency parts and computation uses power in the signal processing and other tasks required during communication, both in the transmitter and in the receiver. Example applications include sensor networks and mobile devices in ultra-dense small cell networks where the link distances are below about 10 m, and the computing power is larger than the communication power. The computation-communication tradeoff means that if one of the powers is increased, the other one must be decreased, otherwise the total power increases. Energy efficiency is a challenging multidisciplinary topic, and the consequences of the interrelated fundamental limits are not well understood. According to Edholm?s prediction, the link bit rates are increasing exponentially each year, which implies that there must be a corresponding exponential trend in improving energy efficiency, defined as number of bits per energy unit, both in computation and communication. It is well known that for communications, due to noise, the Shannon limit forms the fundamental limit for the received energy per bit, but in computation there is a similar limit called Landauer limit for the switching energy of a transistor. Near the two fundamental limits the energy efficiency cannot be improved any more exponentially. Our main contribution is to elaborate the connections between the various technology predictions, different fundamental limits and possible design trade-offs. Specifically, we show that because of the aforementioned fundamental limits, the exponential trends in bit rates cannot continue without a compensating exponential trend in energy efficiency. We also revisit the concept of crossover distance and derive it from the fundamental limits to give some further system-level insight on the energy consumption bottlenecks.

A fundamental control limitation for linear positive systems with application to Type 1 diabetes treatment

This paper presents a fundamental design trade-off applicable to a class of linear positive systems. The result connects the maximum and minimum output response peaks due to a disturbance for all feasible inputs. A core consequence of the result is that, when the disturbance pulse response peaks faster than the input pulse response, then attempts to minimise the maximum peak response to the disturbance are necessarily accompanied by unavoidable undershoot at a later time. The result has potential application in many areas. For example, it provides a defensible benchmark for comparison of all possible insulin treatment strategies for Type 1 diabetes patients. This includes any control strategy implemented in the context of an Artificial Pancreas (AP). The lack of such a benchmark has been a deficiency in the existing AP literature.

OC3 Hywind 부유식 풍력발전기 플랫폼의 유체력 계산 및 운동해석

In this study, the analyzed turbine is a 5MW upwind-type wind turbine. This conceptual model was made to compare the results of the numerical analysis program in the IEA Annex23 Subtask2 OC3 project. The numerical analysis program used in this study is FAST developed by NREL and AQWA of ANSYS. Motion characteristics, such as RAO, average motion, significant motion and average amplitude of 1/10 highest motion were obtained through the numerical analysis. The results of the numerical analysis were compared with the results of other numerical analyses and the experimental results, and all the results agreed with one another. The results will help resolve the fundamental design trade-offs between basic floating system concepts.

On the Capacity Region of Cognitive Multiple Access over White Space Channels

Opportunistically sharing the white spaces, or the temporarily unoccupied spectrum licensed to the primary user (PU), is a practical way to improve the spectrum utilization. In this paper, we consider the fundamental problem of rate regions achievable for multiple secondary users (SUs) which send their information to a common receiver over such a white space channel. In particular, the PU activities are treated as on/off side information, which can be obtained causally or non-causally by the SUs. The system is then modeled as a multi-switch channel and its achievable rate regions are characterized in some scenarios. Explicit forms of outer and inner bounds of the rate regions are derived by assuming additional side information, and they are shown to be tight in some special cases. An optimal rate and power allocation scheme that maximizes the sum rate is also proposed. The numerical results reveal the impacts of side information, channel correlation and PU activity on the achievable rates, and also verify the effectiveness of our rate and power allocation scheme. Our work may shed some light on the fundamental limit and design tradeoffs in practical cognitive radio systems.

Characteristic Mode Based Tradeoff Analysis of Antenna-Chassis Interactions for Multiple Antenna Terminals

The design of multiple antennas in compact mobile terminals is a significant challenge, due to both practical and fundamental design tradeoffs. In this paper, fundamental antenna design tradeoffs of multiple antenna terminals are presented in the framework of characteristic mode analysis. In particular, interactions between the antenna elements and the characteristic modes and their impact on design tradeoffs are investigated in both theory and simulations. The results reveal that the characteristic modes play an important role in determining the optimal placement of antennas for low mutual coupling. Moreover, the ability of antenna elements to localize the excitation currents on the chassis can significantly influence the final performance. To demonstrate the effectiveness of the proposed approach, a dual-band, dual-antenna terminal is designed to provide an isolation of over 10 dB for the 900 MHz band without additional matching or decoupling structures. A tradeoff analysis of bandwidth, efficiency, effective diversity gain and capacity is performed over different antenna locations. Finally, three fabricated prototypes verify the simulation results for representative cases.

Design Drivers of Energy-Efficient Transport Aircraft

The fuel energy consumption of subsonic air transportation is examined. The focus is on identification and quantification of fundamental engineering design tradeoffs which drive the design of subsonic tube and wing transport aircraft. The sensitivities of energy efficiency to recent and forecast technology developments are also examined. Background and Motivation Early development of the modern jet transport, starting with the DeHavilland Comet and Boeing 707 in the 1950’s, was strongly driven by range requirements. With the imperatives of rising fuel costs and increased environmental concerns, more recent developments have focused on fuel economy and also on noise. Of the three main drivers of fuel economy — aerodynamics, structures, and propulsion — the latter has seen the largest improvements, not surprisingly because in the 1950’s turbojet and turbofan engines were a very young technology. As engine technology maturation has now reached the levels of the other disciplines, further improvements will have to come from all technologies. The recent and ongoing NASA Aeronautics research, 1 in particular the N+1,2,3 programs 2 target a wide range of aerodynamic, structural, and propulsion technologies towards this goal.

PRIME: Peer-to-Peer Receiver-Driven Mesh-Based Streaming

The success of file swarming mechanisms such as BitTorrent has motivated a new approach for scalable streaming of live content that we call <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mesh-based</i> Peer-to-Peer (P2P) streaming. In this approach, participating end-systems (or peers) form a randomly connected mesh and incorporate swarming content delivery to stream live content. Despite the growing popularity of this approach, neither the fundamental design tradeoffs nor the basic performance bottlenecks in mesh-based P2P streaming are well understood. In this paper, we follow a performance-driven approach to design PRIME, a scalable mesh-based P2P streaming mechanism for live content. The main design goal of PRIME is to minimize two performance bottlenecks, namely bandwidth bottleneck and content bottleneck. We show that the global pattern of delivery for each segment of live content should consist of a diffusion phase which is followed by a swarming phase. This leads to effective utilization of available resources to accommodate scalability and also minimizes content bottleneck. Using packet level simulations, we carefully examine the impact of overlay connectivity, packet scheduling scheme at individual peers and source behavior on the overall performance of the system. Our results reveal fundamental design tradeoffs of mesh-based P2P streaming for live content.

Incremental tensor analysis

How do we find patterns in author-keyword associations, evolving over time? Or in data cubes (tensors), with product-branchcustomer sales information? And more generally, how to summarize high-order data cubes (tensors)? How to incrementally update these patterns over time? Matrix decompositions, like principal component analysis (PCA) and variants, are invaluable tools for mining, dimensionality reduction, feature selection, rule identification in numerous settings like streaming data, text, graphs, social networks, and many more settings. However, they have only two orders (i.e., matrices, like author and keyword in the previous example). We propose to envision such higher-order data as tensors, and tap the vast literature on the topic. However, these methods do not necessarily scale up, let alone operate on semi-infinite streams. Thus, we introduce a general framework, incremental tensor analysis (ITA), which efficiently computes a compact summary for high-order and high-dimensional data, and also reveals the hidden correlations. Three variants of ITA are presented: (1) dynamic tensor analysis (DTA); (2) streaming tensor analysis (STA); and (3) window-based tensor analysis (WTA). In paricular, we explore several fundamental design trade-offs such as space efficiency, computational cost, approximation accuracy, time dependency, and model complexity. We implement all our methods and apply them in several real settings, such as network anomaly detection, multiway latent semantic indexing on citation networks, and correlation study on sensor measurements. Our empirical studies show that the proposed methods are fast and accurate and that they find interesting patterns and outliers on the real datasets.

Coolstreaming: Design, Theory, and Practice

Peer-to-peer (P2P) technology has found much success in applications like file distributions and VoIP yet, its adoption in live video streaming remains as an elusive goal. Our recent success in Coolstreaming system brings promises in this direction; however, it also reveals that there exist many practical engineering problems in real live streaming systems over the Internet. Our focus in this paper is on a nonoptimal real working system, in which we illustrate a set of existing practical problems and how they could be handled. We believe this is essential in providing the basic understanding of P2P streaming systems. This paper uses a set of real traces and attempts to develop some theoretical basis to demonstrate that a random peer partnership selection with a hybrid pull-push scheme has the potentially to scale. Specifically, first, we describe the fundamental system design tradeoffs and key changes in the design of a Coolstreaming system including substreaming, buffer management, scheduling and the adopt of a hybrid pull-push mechanism over the original pull-based content delivery approach; second, we examine the overlay topology and its convergence; third, using a combination of real traces and analysis, we quantitatively provide the insights on how the buffering technique resolves the problems associated with dynamics and heterogeneity; fourth, we show how substream and path diversity can help to alleviate the impact from congestion and churns; fifth, we discuss the system scalability and limitations.

Modeling and analysis of dynamic coscheduling in parallel and distributed environments

Scheduling in large-scale parallel systems has been and continues to be an important and challenging research problem. Several key factors, including the increasing use of off-the-shelf clusters of workstations to build such parallel systems, have resulted in the emergence of a new class of scheduling strategies, broadly referred to as dynamic coscheduling. Unfortunately, the size of both the design and performance spaces of these emerging scheduling strategies is quite large, due in part to the numerous dynamic interactions among the different components of the parallel computing environment as well as the wide range of applications and systems that can comprise the parallel environment. This in turn makes it difficult to fully explore the benefits and limitations of the various proposed dynamic coscheduling approaches for large-scale systems solely with the use of simulation and/or experimentation.To gain a better understanding of the fundamental properties of different dynamic coscheduling methods, we formulate a general mathematical model of this class of scheduling strategies within a unified framework that allows us to investigate a wide range of parallel environments. We derive a matrix-analytic analysis based on a stochastic decomposition and a fixed-point iteration. A large number of numerical experiments are performed in part to examine the accuracy of our approach. These numerical results are in excellent agreement with detailed simulation results. Our mathematical model and analysis is then used to explore several fundamental design and performance tradeoffs associated with the class of dynamic coscheduling policies across a broad spectrum of parallel computing environments.

Realising personal satcom antennas

The worldwide interest in personal mobile satellite communications using constellations of low-orbiting satellites highlights the handset antenna as a component that has a critical effect on the overall system viability. The antenna design is, however, influenced by many factors and the purpose of this overview is to identify key design aspects, their interrelation and prospects for optimisation. Fundamental engineering design issues, difficulties and trade-offs are considered first, followed by a note of research and an outline appraisal of the power budget that should be achievable. The antenna requirements are application dependent and the future customer base is conjectured upon together with suggestions for alleviating the stringent antenna design constraints.

Fundamental design tradeoffs in filtering, prediction, and smoothing

This paper examines fundamental design tradeoffs that apply to all linear filtering, prediction, and smoothing problems. We introduce sensitivity functions that quantify filter performance, and we show that their frequency response satisfies constraints imposed by unstable poles and nonminimum phase zeros of the system. The constraints allow one to determine, a priori, whether or not a desired filter performance is attainable and how different arrangements of the measurement system influence the achievable performance.

GaAs Schottky barrier varactor diodes for submillimeter wavelength power generation

AbstractThere is interest in the development of heterodyne receivers for submillimeter wavelengths, particularly for space‐based remote sensing of the Earth's upper atmosphere. These receivers require solid‐state local oscillator sources. This article considers the fundamental design tradeoff that limits the cutoff frequency of varactor diodes. Recent results demonstrate a maximum cutoff frequency of 5 THz. and significant power to frequencies as high as 640 GHz.