1,146 research outputs found
Design of Feedback Controls Supporting TCP Based on the State–Space Approach
This paper investigates how to design feedback controls supporting transmission control protocol (TCP) based on the state-space approach for the linearized system of the well-known additive increase multiplicative decrease (AIMD) dynamic model. We formulate the feedback control design problem as state-space models without assuming its structure in advance. Thereby, we get three results that have not been observed by previous studies on the congestion control problem. 1) In order to fully support TCP, we need a proportional-derivative (PD)-type state-feedback control structure in terms of queue length (or RTT: round trip time). This backs up the conjecture in the networking literature that the AQM RED is not enough to control TCP dynamic behavior, where RED can be classified as a P-type AQM (or as an output feedback control for the linearized AIMD model). 2) In order to fully support TCP in the presence of delays, we derive delay-dependent feedback control structures to compensate for delays explicitly under the assumption that RTT, capacity and number of sources are known, where all existing AQMs including RED, REM/PI and AVQ are delay-independent controls. 3) In an attempt to interpret different AQM structures in a unified manner rather than to compare them via simulations, we propose a PID-type mathematical framework using integral control action. As a performance index to measure the deviation of the closed-loop system from an equilibrium point, we use a linear quadratic (LQ) cost of the transients of state and control variables such as queue length, aggregate rate, jitter in the aggregate rate, and congestion measure. Stabilizing gains of the feedback control structures are obtained minimizing the LQ cost. Then, we discuss the impact of the control structure on performance using the PID-type mathematical framework. All results are extended to the case of multiple links and heterogeneous delays
Generalized receding horizon control scheme for constrained linear discrete-time systems
In this paper, we propose a generalized stabilizing receding horizon control (RHC) scheme for input/state constrained linear discrete-time systems, which includes existing ones, and is much more flexible and profitable in terms of feasibility & computation. The control scheme is based on a time-varying horizon cost function with time-varying terminal weighting matrices, which can easily be implemented via linear matrix inequality (LMI) optimization. We discuss modified schemes of the proposed one, which are better than the proposed general scheme in terms of feasibility or computation. Through various simulation examples, we illustrate the proposed results
Disturbance Attenuation for Constrained Discrete-Time Systems via Receding Horizon Controls
In this note, we propose new receding horizon H/sub /spl infin// control (RHHC) schemes for linear input-constrained discrete time-invariant systems with disturbances. The proposed control schemes are based on the dynamic game problem of a finite-horizon cost function with a fixed finite terminal weighting matrix and a one-horizon cost function with time-varying finite terminal weighting matrices, respectively. We show that the resulting RHHCs guarantee closed-loop stability in the absence of disturbances and H/sub /spl infin// norm bound for 2-norm bounded disturbances. We also show that the proposed schemes can easily be implemented via linear matrix inequality optimization. We illustrate the effectiveness of the proposed schemes through simulations
Faster is More Different: Mean-Field Dynamics of Innovation Diffusion
Based on a recent model of paradigm shifts by Bornholdt et al., we studied
mean-field opinion dynamics in an infinite population where an infinite number
of ideas compete simultaneously with their values publicly known. We found that
a highly innovative society is not characterized by heavy concentration in
highly valued ideas: Rather, ideas are more broadly distributed in a more
innovative society with faster progress, provided that the rate of adoption is
constant, which suggests a positive correlation between innovation and
technological disparity. Furthermore, the distribution is generally skewed in
such a way that the fraction of innovators is substantially smaller than has
been believed in conventional innovation-diffusion theory based on normality.
Thus, the typical adoption pattern is predicted to be asymmetric with slow
saturation in the ideal situation, which is compared with empirical data sets.Comment: 11 pages, 4 figure
Percolation on hyperbolic lattices
The percolation transitions on hyperbolic lattices are investigated
numerically using finite-size scaling methods. The existence of two distinct
percolation thresholds is verified. At the lower threshold, an unbounded
cluster appears and reaches from the middle to the boundary. This transition is
of the same type and has the same finite-size scaling properties as the
corresponding transition for the Cayley tree. At the upper threshold, on the
other hand, a single unbounded cluster forms which overwhelms all the others
and occupies a finite fraction of the volume as well as of the boundary
connections. The finite-size scaling properties for this upper threshold are
different from those of the Cayley tree and two of the critical exponents are
obtained. The results suggest that the percolation transition for the
hyperbolic lattices forms a universality class of its own.Comment: 17 pages, 18 figures, to appear in Phys. Rev.
Anomalous response in the vicinity of spontaneous symmetry breaking
We propose a mechanism to induce negative AC permittivity in the vicinity of
a ferroelectric phase transition involved with spontaneous symmetry breaking.
This mechanism makes use of responses at low frequency, yielding a high gain
and a large phase delay, when the system jumps over the free-energy barrier
with the aid of external fields. We illustrate the mechanism by analytically
studying spin models with the Glauber-typed dynamics under periodic
perturbations. Then, we show that the scenario is supported by numerical
simulations of mean-field as well as two-dimensional spin systems.Comment: 6 pages, 5 figure
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