Showing papers by "Jie Chen published in 2016"
TL;DR: This paper proposes fully distributed consensus algorithms over a general directed graph when there exist, respectively, absolute velocity damping and relative velocity damped and shows that one proposed algorithm also works for consensus of agents with intrinsic Lipschitz nonlinear dynamics.
Abstract: In this paper, we study the consensus problem for second-order multi-agent systems with heterogeneous unknown inertias and control gains under a general directed graph. Unlike the existing consensus algorithms for second-order multi-agent systems in which all agents are assumed to have common unit inertias or share common control gains, we allow the inertias and the control gains to be heterogeneous and time-varying for each agent. We propose fully distributed consensus algorithms over a general directed graph when there exist, respectively, absolute velocity damping and relative velocity damping. Novel integral-type Lyapunov functions are proposed to study the consensus convergence. Moreover, the adaptive $\sigma$ - modification schemes for the gain adaptation are proposed, which renders smaller control gains and thus requires smaller amplitude on the control input without sacrificing consensus convergence. Furthermore, we show that one proposed algorithm also works for consensus of agents with intrinsic Lipschitz nonlinear dynamics. The control gains are varying and updated by distributed adaptive laws. As a result, the proposed algorithms require no global information and thus can be implemented in a fully distributed manner.
315 citations
TL;DR: Novel distributed adaptive output feedback protocols to achieve leader-follower consensus for any directed graph containing a directed spanning tree with the leader as the root are presented.
121 citations
TL;DR: It is shown that the AWN channel power constraint imposes fundamental limits on the system's stabilizability and tracking performance, which depend on the unstable poles and nonminimum phase zeros of the system.
Abstract: In this paper, we study the limitations in stabilization and tracking of multi-input, multi-output (MIMO) networked feedback systems. We adopt a parallel additive white noise (AWN) model for MIMO communication channels, and consider as our performance measure the mean square error for a system's output to track in the mean square sense a random reference signal with finite power. We derive necessary and sufficient conditions for the system to be mean square stabilizable and obtain analytical expressions of the optimal performance achievable by linear time-invariant (LTI) controllers subject to channel input power constraint. We show that the AWN channel power constraint imposes fundamental limits on the system's stabilizability and tracking performance, which depend on the unstable poles and nonminimum phase zeros of the system. In particular, for MIMO systems, these limits are seen to be dependent on the directions of the unstable poles and nonminimum phase zeros, and especially in how these directions are aligned with noise power distribution; in order to achieve the optimal tracking performance, the channel input power must be allocated to individual channels in ways accounting for pole/zero directions, a scheme that departs from the Shannon's classical “water-filling” strategy. Channel scalings are investigated as a means of realigning pole/zero directions and redistributing the channel power, which are found to be capable of improving fundamentally a system's stabilizability and tracking performance.
28 citations
TL;DR: An azimuth spatial variation removing method based on the principle of nonlinear CS is proposed to equalize the Doppler rates of the targets located at the same range cell, which can extend the depth-of-azimuth-focus (DOAF) and improve processing efficiency.
Abstract: To process squinted sliding-spotlight synthetic aperture radar data, the azimuth preprocessing step based on the linear range walk correction (LRWC) and derotation operations is implemented to eliminate the effect of 2-D spectrum skew and azimuth spectral aliasing. However, two key issues arise from the azimuth preprocessing. First, the traditional chirp scaling (CS) kernel is not suitable for data focusing because the property of the 2-D spectrum is changed significantly; second, the spatial variation of the targets' Doppler rates along the azimuth direction due to the LRWC operation limits the depth-of-azimuth-focus (DOAF) seriously. In this letter, a modified accurate CS kernel is derived to realize range compensation. Then, an azimuth spatial variation removing method based on the principle of nonlinear CS is proposed to equalize the Doppler rates of the targets located at the same range cell, which can extend the DOAF and improve processing efficiency. Finally, a novel imaging algorithm is proposed, with its effectiveness demonstrated by simulation results.
23 citations
06 Jul 2016
TL;DR: The robust consensus problem of a network of general discrete-time linear agents coordinating through unreliable communication channels is studied, which unveils the fundamental limitation posed by the synchronizability factor, the topological entropy of the agents, and the mean square channel capacity.
Abstract: In this paper, we study the robust consensus problem of a network of general discrete-time linear agents coordinating through unreliable communication channels. Two neighboring agents exchange information via a communication channel, which is modeled in this paper as an ideal transmission system subject to a multiplicative stochastic uncertainty. This uncertain channel model includes the commonly studied logarithmic quantizers and the stochastic packet dropout as special cases. For multi-agent systems with undirected connected graphs and stochastic uncertain communication channels, we derive a sufficient condition to guarantee robust consensus in the mean square sense, which unveils the fundamental limitation posed by the synchronizability factor, the topological entropy of the agents, and the mean square channel capacity. The consensus protocol based on uncertain relative state information is then designed, using the modified algebraic Riccati equation. We also consider the case where the agents are perturbed by uncertainties in the input channels. The relations between the uncertain input and communication channel models are discussed.
18 citations
10 Jul 2016
TL;DR: This paper provides a C-Band UAV SAR combining with linear modulated quasi continuous wave technique as well as integrated radar and communication design for multi-rotor UAV's requirements.
Abstract: State of the art UAV technology shows its advantage in both civil and military applications, and it is required to meet the needs for payloads special designed for UAVs. However, electric powered multi-rotor UAV provides limited power and more sensitive to the payloads mass. Linear frequency modulated quasi continuous wave SAR leads to small and efficiency radar system which meets multi-rotor UAV's requirements. This paper provides a C-Band UAV SAR combining with linear modulated quasi continuous wave technique as well as integrated radar and communication design. Experiments will be taken to verify the usage of UAV SAR in typical SAR working mode and GMTI ability.
11 citations
27 Dec 2016
TL;DR: Using a fully distributed control protocol, it is found that sign consensus can be achieved without requiring the graph to have an eventually positive adjacency matrix.
Abstract: This paper aims at solving the sign-consensus problem of linear multi-agents system, i.e., the signs of all agents' states achieve consensus. The communication network is modeled by a signed directed graph, where both cooperative and competitive interactions coexist among the agents. Each individual agent is assumed to access only the local information, and a fully distributed control protocol is proposed. Using this control protocol, we find that sign consensus can be achieved without requiring the graph to have an eventually positive adjacency matrix.
3 citations
01 Jun 2016
TL;DR: It is shown that the robust consensus problem with undirected communication topologies is equivalent to the simultaneous H∞ control problem for a set of low-dimensional subsystems and a necessary condition for the existence of a protocol achieving robust consensus is derived.
Abstract: In this paper, we study the robust consensus problem for a group of linear discrete-time agents to coordinate over an uncertain communication network, which is to achieve consensus against transmission errors and noises. We model the network by communication links subject to deterministic uncertainties, which can be either an additive perturbation described by some unknown transfer function or a norm bounded uncertainty. We show that the robust consensus problem with undirected communication topologies is equivalent to the simultaneous control problem for a set of low-dimensional subsystems. We derive a necessary condition for the existence of a protocol achieving robust consensus. That is, the upper bound of the uncertainties is less than the inverse of the Mahler measure of the agents. Sufficient conditions in terms of linear matrix inequalities are further presented to design the robust consensus protocols.
2 citations
10 Jul 2016
TL;DR: A new algorithm for implementing the range Split-Spectrum is introduced, when one corregistration step is performed, and no resampling of the slave images is needed, and the performance of the method is studied on a couple of ALOS data.
Abstract: Ionospheric effect is considered to be one of the factors limiting the accuracy of deformation measurement acquired from interferometric SAR data. The correction of this error source was studied recently, and some new methods was developed and improved. One of these methods is the range Split-Spectrum. In this work, we introduce a new algorithm for implementing the method. An improvement is made, when one corregistration step is performed, and no resampling of the slave images is needed. The performance of the method is studied on a couple of ALOS data, the variation of the differential STEC on the interferogram, was determined as less than 0.5 TECU.
2 citations
TL;DR: In this article, the stabilization problem of linear time-invariant (LTI) continuous-time systems under stochastic multiplicative uncertainty and time-delay was studied.
2 citations
10 Jul 2016
TL;DR: A novel unification scheme for environmental remote sensing application focuses on the feedbacks between frontend and backend, where the frontend procedures should serve the backend application to get a better result.
Abstract: Aimed at the problems that SAR (Synthetic Aperture Radar) environment parameter inversion and data processing are lack of both overall design and synergy, this paper proposed a novel unification scheme for environmental remote sensing application. Compared to the reality that application follows data processing in the frontend, the performance of application is highlighted as the ultimate objective in the proposed scheme, where the frontend procedures should serve the backend application to get a better result. Frontend processing is divided into three parts: system design, imaging processing and post-processing procedure, while backend processing is categorized as image processing and environment parameter inversion. The concept of unification scheme focuses on the feedbacks between frontend and backend, and some demonstrations are also given in the following sections.
TL;DR: In this paper, the optimised limit for polarimetric calibration of fully polarised synthetic aperture radar systems is derived by establishing an error model as a function of cross-talk, channel imbalance and system noise.
Abstract: The optimised limit for polarimetric calibration of fully polarised synthetic aperture radar systems is derived by establishing an error model as a function of cross-talk, channel imbalance and system noise. Compared with noise equivalent sigma zero, the polarimetric error below the optimised limit is too small to affect the signal of cross-polarised channel. Thus, polarimetric calibration could be relaxed or even ignored in this case. With the backscatter model, optimised limits for cross-talk and channel imbalance at X, C and L-bands are presented. Moreover, when ignoring channel imbalance, the limit for cross-talk is given in a quantitative way. These results are very useful in practice, allowing significant reduction in calibration cost.
10 Jul 2016
TL;DR: This study proposed a novel method to analyze slick-free and oil covered sea surface backscattering in the special case of Deepwater Horizon (DWH) oil spill accident based on combination of tilted Bragg scattering and volume scattering components.
Abstract: This study proposed a novel method to analyze slick-free and oil covered sea surface backscattering in the special case of Deepwater Horizon (DWH) oil spill accident based on combination of tilted Bragg scattering and volume scattering components. The DWH accident represents a particular and challenging case due to the very large amount of leaked oil that came from the bottom of the ocean. The proposed scattering model consists of first estimate the large scale tilting angle of sea surface Bragg scattering mechanism and then of the retrieval, through its linear relationship with the relative dielectric constant, of oil-insea volume concentration. Finally, Bragg and volume scattering components can be estimated which provide useful information for a better understanding of i) the sea surface status and ii) the weak-damping properties the leaked oil due to purification/emulsification phenomena. The model is tested considering actual UAVSAR L-band fully-polarimetric SAR data.
10 Jul 2016
TL;DR: A phase high fidelity model of high precision interferometric SAR, SAR non-stationary backscattering characteristics and cognition, SAR three-dimensional electromagnetic scattering modeling and its scattering mechanism and SAR multi-parameters optimization information extraction is conducted.
Abstract: Although Synthetic Aperture Radar (SAR) can capture rich land cover information as a most important advanced technique in the field of international earth observation, the application effects still limited significantly. One of the reasons is that the study of SAR imaging processing, SAR image processing and SAR applications are usually conducted respectively, and the study on integrating the three processes is lacked. Focusing on the science problem, taking the typical natural distribution targets (surface deformation, sea ice classification) and man-made targets (building complex and collapsed buildings) as examples, some application studies oriented to SAR environmental parameters inversion are conducted, and the information integrated frames and methods are proposed.
01 Jun 2016
TL;DR: This paper extends the existing results to multi-input multi-output systems and derives upper bounds on a generalized notion called delay radius, showing that for a delay whose direction is orthogonal to that of an unstable pole, no limit is imposed by the pole, while if the delay direction is parallel to thatof a nonminimum phase zero, its allowable range is further restricted.
Abstract: The delay margin of a time-delay system constitutes the fundamental limit beyond which no single controller may exist to robustly stabilize an unstable delay plant for a range of delay values. For single-input single-output systems with a linear time-invariant controller, this margin is known to be finite, and bounds on the delay margin are available. This paper extends the existing results to multi-input multi-output systems. We derive upper bounds on a generalized notion called delay radius. Our results show that for a delay whose direction is orthogonal to that of an unstable pole, no limit is imposed by the pole, while if the delay direction is parallel to that of a nonminimum phase zero, its allowable range is further restricted.