Continuous-time adaptive delay system

We have developed a direction-selective system that has a row of pixels with photodiodes as the front-end. The output of each photodiode is converted to a digital signal, which is then fed to an adaptive-delay block within each pixel. The adaptive block adjusts an internal delay such that the delay matches the phase offset between the rising edges of this digital signal and the corresponding digital signal from the neighboring pixel. The system does this delay matching by using a dynamic current source to adapt the bias voltage that controls the delay. The adaptive-delay block is similar to a digital charge-pump phase-lock loop (PLL). It differs from conventional PLL's however, both in its compact size and its lack of a system clock. It also has a fast pull-in time during the locking of the signal. Since our application does not require low jitter, we have not introduced a phase offset in the comparator as is typically done in PLLs. The transistors here are operated In subthreshold. A stability analysis of the feedback system leads to simple stability and convergence constraints. Experimental results from circuits fabricated in 2 μm CMOS technology show that the circuit can lock over 5 decades of frequency

Continuous-time adaptive delay system

We have developed an adaptive delay system that adjusts the delay of a delay element so that it matches the temporal disparity between the onset of two input signals. The delay is controlled either by an external bias voltage, or by an intrinsic signal derived from an adaptive block. The operation of the adaptive delay system is similar to that of a charge-pump phase-lock loop, with an extended lock-in range of more than 5 decades. Standard CMOS transistors are used in their subthreshold region. Experimental results from circuits fabricated in 2 μm CMOS technology are in agreement with the analysi

Analytical evaluation of adaptive-modulation-based opportunistic cognitive radio in Nakagami-m fading channels

The performance of adaptive modulation for cognitive radio with opportunistic access is analyzed by considering the effects of spectrum sensing, primary user (PU) traffic, and time delay for Nakagami- m fading channels. Both the adaptive continuous rate scheme and the adaptive discrete rate scheme are considered. Numerical examples are presented to quantify the effects of spectrum sensing, PU traffic, and time delay for different system parameters

Optimal adaptive control of time-delay dynamical systems with known and uncertain dynamics

Delays are found in many industrial pneumatic and hydraulic systems, and as a result, the performance of the overall closed-loop system deteriorates unless they are explicitly accounted. It is also possible that the dynamics of such systems are uncertain. On the other hand, optimal control of time-delay systems in the presence of known and uncertain dynamics by using state and output feedback is of paramount importance. Therefore, in this research, a suite of novel optimal adaptive control (OAC) techniques are undertaken for linear and nonlinear continuous time-delay systems in the presence of uncertain system dynamics using state and/or output feedback. First, the optimal regulation of linear continuous-time systems with state and input delays by utilizing a quadratic cost function over infinite horizon is addressed using state and output feedback. Next, the optimal adaptive regulation is extended to uncertain linear continuous-time systems under a mild assumption that the bounds on system matrices are known. Subsequently, the event-triggered optimal adaptive regulation of partially unknown linear continuous time systems with state-delay is addressed by using integral reinforcement learning (IRL). It is demonstrated that the optimal control policy renders asymptotic stability of the closed-loop system provided the linear time-delayed system is controllable and observable. The proposed event-triggered approach relaxed the need for continuous availability of state vector and proven to be zeno-free. Finally, the OAC using IRL neural network based control of uncertain nonlinear time-delay systems with input and state delays is investigated. An identifier is proposed for nonlinear time-delay systems to approximate the system dynamics and relax the need for the control coefficient matrix in generating the control policy. Lyapunov analysis is utilized to design the optimal adaptive controller, derive parameter/weight tuning law and verify stability of the closed-loop system”--Abstract, page iv

Synchronization between variable time delayed systems and cryptography

In this letter we consider a prototype model which is described as an autonomous continuous time delayed differential equation with just one variable. The chaos has been investigated with variable delay time and the synchronization phenomenon is examined both numerically and analytically using the Krasovskii-Lyapunov functions. We have applied adaptive coupling law for synchronization,where the coupling equation also contains delay with modulated time. We also studied the effect of cryptography for this coupled system and the message extraction procedure is illustrated with the help of simulated results.Comment: 9 pages,3 figures. Submitted to EP

System Identification of Heat-Transfer Process of Frequency Induction Furnace for Melting Copper Based on Particle Swarm Algorithm

An adaptive evolutionary strategy in standard particle swarm optimization is introduced. Adaptive evolution particle swarm optimization is constructed to improve the capacity of global search. A method based on adaptive evolution particle swarm optimization for identification of continuous system with time delay is proposed. The basic idea is that the identification of continuous system with time delay is converted to an optimization of continuous nonlinear function. The adaptive evolution particle swarm optimization is utilized to find an optimal solution of continuous nonlinear function. Convergence conditions are given by the convergence analysis based on discrete time linear dynamic system theory. Numerical simulation results show that the proposed method is effective for a general continuous system with time delay and the system of heat-transfer process of frequency induction furnace for melting copper

Adaptive Time-delay Estimated Sliding Mode Control for a Bias Momentum Satellite with Two Reaction Wheels

An adaptive sliding mode control to stabilize the attitude of a bias momentum satellite with a time delay via two wheels is proposed. Stabilizing the attitude of a rigid body via two control torques is an under-actuated control problem, and belongs to the class of systems that are controllable but cannot be asymptotically stabilized via continuous state feed-back because Brockett\u27s necessary condition is not satisfied. The adaptive method combined with the sliding mode control estimates the time delay contained in the system by sensing the difference between the attitude predicted and the measured one at each sampling time and compensates for the time delay by predicting the current state using the past measured attitude and angular velocity. Provided that external disturbances and modeling uncertainties in the satellite moments of inertia are absent, the validity of the proposed adaptive time delay estimated sliding mode control for attitude control of a bias momentum satellite is verified through numerical simulations