Demultiplexing techniques of 320 Gb/s OTDM-DQPSK signals: A comparison by simulation
2010 IEEE International Conference on Communication Systems, 2010
ABSTRACT We present the demultiplexing and demodulation of 320 Gb/s OTDM-DQPSK signals using eith... more ABSTRACT We present the demultiplexing and demodulation of 320 Gb/s OTDM-DQPSK signals using either 'conventional', i.e. demultiplexing then detection, or coherent detections with the local oscillator operating in pulsed sequence. A continuous-wave local oscillator (LO) can be replaced by a short-pulse laser source in a homodyne coherent receiver enabling us simultaneously demultiplex and detect the multiplexed channels of the ultra-high speed OTDM phase modulated signals. Simulated results also indicate at least 5 dB improvement of the receiver sensitivity over the conventional technique by the pulsed LO coherent receiver.
Active Multi-Bound Soliton Lasers: Generation of Dual to Sextuple States
Optical Fiber Communication Conference and National Fiber Optic Engineers Conference, 2009
We present the generation of multi-bound solitons of 2nd to 6th order states in a phase-modulatio... more We present the generation of multi-bound solitons of 2nd to 6th order states in a phase-modulation mode-locked fiber ring cavity. Temporal distribution and optical spectra confirm the differential phase states between adjacent solitons.
Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, 2009
We report novel low bit rate non-line-of-sight optical free space communication over 200 km emplo... more We report novel low bit rate non-line-of-sight optical free space communication over 200 km employing forward scattering from clouds with 134 dB link loss and mid-path scatter gain of 10 dBi.
Generation of high order multi-bound solitons and propagation in optical fibers
Optics Communications, 2009
We demonstrate experimental generation of multi-bound solitons of up to sextuple in an active FM ... more We demonstrate experimental generation of multi-bound solitons of up to sextuple in an active FM mode-locked fiber ring laser operating under power saturation in the locking state. The ring laser consists of two booster optical amplifiers operating in saturation regime, an ...
In this paper, we present a modeling error driven adaptive controller for control of a robot with... more In this paper, we present a modeling error driven adaptive controller for control of a robot with unknown dynamics. In general, modeling error is not used since the ideal parameters are not known. However, using a feedback linearization approach we show that the modeling ...
In the presence of large uncertainties, a control system needs to be able to adapt rapidly to reg... more In the presence of large uncertainties, a control system needs to be able to adapt rapidly to regain performance. Fast adaptation is referred to the implementation of adaptive control with a large adaptive gain to reduce the tracking error rapidly. However, a large adaptive gain can lead to high-frequency oscillations which can adversely affect robustness of an adaptive control law. A new adaptive control modification is presented that can achieve robust adaptation with a large adaptive gain without incurring high-frequency oscillations as with the standard model-reference adaptive control. The modification is based on the minimization of the L 2 norm of the tracking error, which is formulated as an optimal control problem. The optimality condition is used to derive the modification using the gradient method. The optimal control modification results in a stable adaptation and allows a large adaptive gain to be used for better tracking while providing sufficient stability robustness. Simulations were conducted for a damaged generic transport aircraft with both standard adaptive control and the adaptive optimal control modification technique. The results demonstrate the effectiveness of the proposed modification in tracking a reference model while maintaining a sufficient time delay margin.
This paper presents a recent study of a damaged generic transport model as part of a NASA researc... more This paper presents a recent study of a damaged generic transport model as part of a NASA research project to investigate adaptive control methods for stability recovery of damaged aircraft operating in offnominal flight conditions under damage and or failures. Aerodynamic modeling of damage effects is performed using an aerodynamic code to assess changes in the stability and control derivatives of a generic transport aircraft. Certain types of damage such as damage to one of the wings or horizontal stabilizers can cause the aircraft to become asymmetric, thus resulting in a coupling between the longitudinal and lateral motions. Flight dynamics for a general asymmetric aircraft is derived to account for changes in the center of gravity that can compromise the stability of the damaged aircraft. An iterative trim analysis for the translational motion is developed to refine the trim procedure by accounting for the effects of the control surface deflection. A hybrid direct-indirect neural network, adaptive flight control is proposed as an adaptive law for stabilizing the rotational motion of the damaged aircraft. The indirect adaptation is designed to estimate the plant dynamics of the damaged aircraft in conjunction with the direct adaptation that computes the control augmentation. Two approaches are presented: 1) an adaptive law derived from the Lyapunov stability theory to ensure that the signals are bounded, and 2) a recursive least-square method for parameter identification. A hardware-inthe-loop simulation is conducted and demonstrates the effectiveness of the direct neural network adaptive flight control in the stability recovery of the damaged aircraft. A preliminary simulation of the hybrid adaptive flight control has been performed and initial data have shown the effectiveness of the proposed hybrid approach. Future work will include further investigations and high-fidelity simulations of the proposed hybrid adaptive flight control approach.
Protection ellipsoids for stability analysis of feedforward neural-net controllers
International Symposium on Neural Networks, 2009
In this paper, we consider a feedforward neural network for the control of a class of multi-input... more In this paper, we consider a feedforward neural network for the control of a class of multi-input, multi-output nonlinear systems. While feedforward neural networks offer a simple and appealing approach to enhance the trajectory tracking performance of the closed loop system, stability analysis is often more difficult than the conventional implementation of a neural network embedded within the feedback path.
SNAC convergence and use in adaptive autopilot design
2009 International Joint Conference on Neural Networks, 2009
Abstract In this paper, approximate dynamic programming (ADP) based design tools are developed fo... more Abstract In this paper, approximate dynamic programming (ADP) based design tools are developed for adaptive control of aircraft control under nominal and damaged conditions. Nominal control of the system is computed with a single network adaptive critic (SNAC) ...
Robustness quantification of recurrent neural network using unscented transform
Neurocomputing, 2010
Artificial recurrent neural network has been proved to be a valuable tool in modeling nonlinear d... more Artificial recurrent neural network has been proved to be a valuable tool in modeling nonlinear dynamical systems. Robustness study of recurrent neural network is critical to its successful implementation. The goal of robustness study is to reduce the sensitivity of modeling capability to parametric uncertainties or make the network fault tolerant. In this study, an uncertainty propagation analysis is performed
AIAA Guidance, Navigation, and Control Conference, 2009
This paper addresses the problem of controlling a nonlinear plant with a slow actuator using sing... more This paper addresses the problem of controlling a nonlinear plant with a slow actuator using singular perturbation method. For the known plant-actuator cascaded system the proposed scheme achieves tracking of a given reference model with considerably less control demand than would otherwise result when using conventional design techniques. This is the consequence of excluding the small parameter from the actuator dynamics via time scale separation. The resulting tracking error is within the order of this small parameter. For the unknown system the adaptive counterpart is developed based on the prediction model, which is driven towards the reference model by the control design. It is proven that the prediction model tracks the reference model with an error proportional to the small parameter, while the prediction error converges to zero. The resulting closed-loop system with all prediction models and adaptive laws remains stable. The benefits of the approach are demonstrated in simulation studies and compared to conventional control approaches.
Parameter Estimation for a Hybrid Adaptive Flight Controller
AIAA Infotech@Aerospace Conference, 2009
This paper expands on the hybrid control architecture developed at the NASA Ames Research Center ... more This paper expands on the hybrid control architecture developed at the NASA Ames Research Center by addressing issues related to indirect adaptation using the recursive least squares (RLS) algorithm. Specifically, the hybrid control architecture is an adaptive flight controller that features both direct and indirect adaptation techniques. This paper will focus almost exclusively on the modifications necessary to achieve quality
AIAA Guidance, Navigation, and Control Conference, 2009
The paper presents an adaptive control technique for a damaged large transport aircraft subject t... more The paper presents an adaptive control technique for a damaged large transport aircraft subject to unknown atmospheric disturbances such as wind gust or turbulence. It is assumed that the damage results in vertical tail loss with no rudder authority, which is replaced with a differential thrust input. The proposed technique uses the adaptive prediction based control design in conjunction with the time scale separation principle, based on the singular perturbation theory. The application of later is necessitated by the fact that the engine response to a throttle command is substantially slow that the angular rate dynamics of the aircraft. It is shown that this control technique guarantees the stability of the closed-loop system and the tracking of a given reference model. The simulation example shows the benefits of the approach.
Demultiplexing techniques of 320 Gb/s OTDM-DQPSK signals: A comparison by simulation
2010 IEEE International Conference on Communication Systems, 2010
ABSTRACT We present the demultiplexing and demodulation of 320 Gb/s OTDM-DQPSK signals using eith... more ABSTRACT We present the demultiplexing and demodulation of 320 Gb/s OTDM-DQPSK signals using either 'conventional', i.e. demultiplexing then detection, or coherent detections with the local oscillator operating in pulsed sequence. A continuous-wave local oscillator (LO) can be replaced by a short-pulse laser source in a homodyne coherent receiver enabling us simultaneously demultiplex and detect the multiplexed channels of the ultra-high speed OTDM phase modulated signals. Simulated results also indicate at least 5 dB improvement of the receiver sensitivity over the conventional technique by the pulsed LO coherent receiver.
Active Multi-Bound Soliton Lasers: Generation of Dual to Sextuple States
Optical Fiber Communication Conference and National Fiber Optic Engineers Conference, 2009
We present the generation of multi-bound solitons of 2nd to 6th order states in a phase-modulatio... more We present the generation of multi-bound solitons of 2nd to 6th order states in a phase-modulation mode-locked fiber ring cavity. Temporal distribution and optical spectra confirm the differential phase states between adjacent solitons.
Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, 2009
We report novel low bit rate non-line-of-sight optical free space communication over 200 km emplo... more We report novel low bit rate non-line-of-sight optical free space communication over 200 km employing forward scattering from clouds with 134 dB link loss and mid-path scatter gain of 10 dBi.
Generation of high order multi-bound solitons and propagation in optical fibers
Optics Communications, 2009
We demonstrate experimental generation of multi-bound solitons of up to sextuple in an active FM ... more We demonstrate experimental generation of multi-bound solitons of up to sextuple in an active FM mode-locked fiber ring laser operating under power saturation in the locking state. The ring laser consists of two booster optical amplifiers operating in saturation regime, an ...
In this paper, we present a modeling error driven adaptive controller for control of a robot with... more In this paper, we present a modeling error driven adaptive controller for control of a robot with unknown dynamics. In general, modeling error is not used since the ideal parameters are not known. However, using a feedback linearization approach we show that the modeling ...
In the presence of large uncertainties, a control system needs to be able to adapt rapidly to reg... more In the presence of large uncertainties, a control system needs to be able to adapt rapidly to regain performance. Fast adaptation is referred to the implementation of adaptive control with a large adaptive gain to reduce the tracking error rapidly. However, a large adaptive gain can lead to high-frequency oscillations which can adversely affect robustness of an adaptive control law. A new adaptive control modification is presented that can achieve robust adaptation with a large adaptive gain without incurring high-frequency oscillations as with the standard model-reference adaptive control. The modification is based on the minimization of the L 2 norm of the tracking error, which is formulated as an optimal control problem. The optimality condition is used to derive the modification using the gradient method. The optimal control modification results in a stable adaptation and allows a large adaptive gain to be used for better tracking while providing sufficient stability robustness. Simulations were conducted for a damaged generic transport aircraft with both standard adaptive control and the adaptive optimal control modification technique. The results demonstrate the effectiveness of the proposed modification in tracking a reference model while maintaining a sufficient time delay margin.
This paper presents a recent study of a damaged generic transport model as part of a NASA researc... more This paper presents a recent study of a damaged generic transport model as part of a NASA research project to investigate adaptive control methods for stability recovery of damaged aircraft operating in offnominal flight conditions under damage and or failures. Aerodynamic modeling of damage effects is performed using an aerodynamic code to assess changes in the stability and control derivatives of a generic transport aircraft. Certain types of damage such as damage to one of the wings or horizontal stabilizers can cause the aircraft to become asymmetric, thus resulting in a coupling between the longitudinal and lateral motions. Flight dynamics for a general asymmetric aircraft is derived to account for changes in the center of gravity that can compromise the stability of the damaged aircraft. An iterative trim analysis for the translational motion is developed to refine the trim procedure by accounting for the effects of the control surface deflection. A hybrid direct-indirect neural network, adaptive flight control is proposed as an adaptive law for stabilizing the rotational motion of the damaged aircraft. The indirect adaptation is designed to estimate the plant dynamics of the damaged aircraft in conjunction with the direct adaptation that computes the control augmentation. Two approaches are presented: 1) an adaptive law derived from the Lyapunov stability theory to ensure that the signals are bounded, and 2) a recursive least-square method for parameter identification. A hardware-inthe-loop simulation is conducted and demonstrates the effectiveness of the direct neural network adaptive flight control in the stability recovery of the damaged aircraft. A preliminary simulation of the hybrid adaptive flight control has been performed and initial data have shown the effectiveness of the proposed hybrid approach. Future work will include further investigations and high-fidelity simulations of the proposed hybrid adaptive flight control approach.
Protection ellipsoids for stability analysis of feedforward neural-net controllers
International Symposium on Neural Networks, 2009
In this paper, we consider a feedforward neural network for the control of a class of multi-input... more In this paper, we consider a feedforward neural network for the control of a class of multi-input, multi-output nonlinear systems. While feedforward neural networks offer a simple and appealing approach to enhance the trajectory tracking performance of the closed loop system, stability analysis is often more difficult than the conventional implementation of a neural network embedded within the feedback path.
SNAC convergence and use in adaptive autopilot design
2009 International Joint Conference on Neural Networks, 2009
Abstract In this paper, approximate dynamic programming (ADP) based design tools are developed fo... more Abstract In this paper, approximate dynamic programming (ADP) based design tools are developed for adaptive control of aircraft control under nominal and damaged conditions. Nominal control of the system is computed with a single network adaptive critic (SNAC) ...
Robustness quantification of recurrent neural network using unscented transform
Neurocomputing, 2010
Artificial recurrent neural network has been proved to be a valuable tool in modeling nonlinear d... more Artificial recurrent neural network has been proved to be a valuable tool in modeling nonlinear dynamical systems. Robustness study of recurrent neural network is critical to its successful implementation. The goal of robustness study is to reduce the sensitivity of modeling capability to parametric uncertainties or make the network fault tolerant. In this study, an uncertainty propagation analysis is performed
AIAA Guidance, Navigation, and Control Conference, 2009
This paper addresses the problem of controlling a nonlinear plant with a slow actuator using sing... more This paper addresses the problem of controlling a nonlinear plant with a slow actuator using singular perturbation method. For the known plant-actuator cascaded system the proposed scheme achieves tracking of a given reference model with considerably less control demand than would otherwise result when using conventional design techniques. This is the consequence of excluding the small parameter from the actuator dynamics via time scale separation. The resulting tracking error is within the order of this small parameter. For the unknown system the adaptive counterpart is developed based on the prediction model, which is driven towards the reference model by the control design. It is proven that the prediction model tracks the reference model with an error proportional to the small parameter, while the prediction error converges to zero. The resulting closed-loop system with all prediction models and adaptive laws remains stable. The benefits of the approach are demonstrated in simulation studies and compared to conventional control approaches.
Parameter Estimation for a Hybrid Adaptive Flight Controller
AIAA Infotech@Aerospace Conference, 2009
This paper expands on the hybrid control architecture developed at the NASA Ames Research Center ... more This paper expands on the hybrid control architecture developed at the NASA Ames Research Center by addressing issues related to indirect adaptation using the recursive least squares (RLS) algorithm. Specifically, the hybrid control architecture is an adaptive flight controller that features both direct and indirect adaptation techniques. This paper will focus almost exclusively on the modifications necessary to achieve quality
AIAA Guidance, Navigation, and Control Conference, 2009
The paper presents an adaptive control technique for a damaged large transport aircraft subject t... more The paper presents an adaptive control technique for a damaged large transport aircraft subject to unknown atmospheric disturbances such as wind gust or turbulence. It is assumed that the damage results in vertical tail loss with no rudder authority, which is replaced with a differential thrust input. The proposed technique uses the adaptive prediction based control design in conjunction with the time scale separation principle, based on the singular perturbation theory. The application of later is necessitated by the fact that the engine response to a throttle command is substantially slow that the angular rate dynamics of the aircraft. It is shown that this control technique guarantees the stability of the closed-loop system and the tracking of a given reference model. The simulation example shows the benefits of the approach.
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