Thomas Yang

Nonlinear Time Series: Computations and Applications 2012

1 School of Information Science & Technology, East China Normal University, Shanghai 200241, China 2 Department of Mathematics, University of Rome “La Sapienza”, Piazzale Aldo Moro 2, 00185 Rome, Italy 3 Department of Mathematics, University of Salerno, Via Ponte Don Melillo, 84084 Fisciano, Italy 4 Faculty of Engineering, Multimedia University, 63100 Cyberjaya, Selanger, Malaysia 5 College of Computer Science, Chongqing University, Chongqing 400044, China 6 Department of Electrical, Computer, Software, & Systems Engineering, Embry-Riddle Aeronautical University, Daytona Beach, FL 32114, USA

A gradient-based optimum block adaptation ICA technique for interference suppression in highly dynamic communication channels

The fast fixed-point independent component analysis (ICA) algorithm has been widely used in various applications because of its fast convergence and superior performance. However, in a highly dynamic environment, real-time adaptation is necessary to track the variations of the mixing matrix. In this scenario, the gradient-based online learning algorithm performs better, but its convergence is slow, and depends on a proper choice of convergence factor. This paper develops a gradient-based optimum block adaptive ICA algorithm (OBA/ICA) that combines the advantages of the two algorithms. Simulation results for telecommunication applications indicate that the resulting performance is superior under time-varying conditions, which is particularly useful in mobile communications.

Feasibility study of IEEE 802.15.4 for aerospace wireless sensor networks

Wireless communications has been a reliable data link means in many aerospace applications, including critical ones. The major concern for using wireless links for aerospace sensors is the feasibility of their in the aerospace setting; i.e., whether wireless links will negatively affect the overall reliability and safety of the aircrafts. In a previous paper, we studied the feasibility issue and concluded that with appropriate choice of wireless communication schemes and parameters, the wireless links can have reasonable immunity to interferences, low interference to other on-board wireless systems, and good security performance. In this paper, we consider the feasibility of adapting an existing technology, IEEE 802.15.4, to implement the wireless links for aerospace sensors, with focuses on immunity to interferences and data security. We conclude that a wireless network based on IEEE 802.15.4-compatible devices is appropriate for non-critical aerospace applications, at least from building a demo systems point of view.

Communication schemes for aerospace wireless sensors

Wireless communications has been a preferred and reliable data transmission means in many aerospace applications, including flight-critical ones. The aerospace industry should consider replacing some aerial-vehicle sensor wiring with wireless communications; the related sensors are referred to as aerospace wireless sensors (AWSs). This replacement can lower the weight of aerial-vehicle wiring and thus lead to increased payload capacity. It can also improve the overall safety of aerial vehicles via reducing wiring problems, ease the design of aerial-vehicle structures for running wiring, and lower the sensor installation and maintenance cost. The major concern for using AWSs is whether they will negatively affect the overall reliability and safety of the aerial vehicles. In this paper, the feasibility of using AWSs is discussed. In particular, the employment of wireless communication schemes is studied in terms of immunity to jamming signals, interference to other on-board wireless systems, simultaneous data transmission from multiple AWSs, and low detectability to unintended parties. We recommend using the code-division multiple-access (CDMA) scheme and demonstrate its feasibility in terms of communication performance.

Optimum block adaptive algorithm for gradient based independent component analysis(OBA/ICA) for time varying wireless channels

The fixed-point Independent Component Analysis (ICA) algorithm is widely used because of its fast convergence under static conditions. However, in a highly dynamic environment, it lacks the ability to adapt to the time variation of the mixing matrix. This paper develops an Optimum Block Adaptation ICA algorithm (OBA/ICA) that is capable of tracking time variation. Simulation results for mobile telecommunication applications indicate that the resulting performance, particularly with respect to convergence properties, is superior to Fast-ICA under dynamic channel conditions.

Optimal block adaptive I/Q mismatch compensation based on circularity

Wireless systems frequently employ I/Q modulation techniques to achieve spectral efficiency for high data rate applications. However, the main drawback of I/Q downconversion is the amplitude and phase imbalances between the analog components in the I and Q branches of the receiver. The resulting I/Q mismatch is unavoidable for practical quadrature receivers and can be frequency-dependent in nature. In this paper, a novel Optimal Block Adaptive algorithm based on the circularity property is presented for frequency-dependent I/Q imbalance compensation. The proposed technique, called OBA-C, is based on the assumption that the received baseband signal deviates from circularity in the presence of I/Q mismatch. OBA-C uses the complex Taylor series expansion to optimally update the adaptive filter coefficients at each iteration, until the circularity of the received signal is restored. Simulation results confirm the remarkable improvement in I/Q mismatch compensation and convergence speed of the proposed technique as compared to another recently proposed circularity based method.

Complex Adaptive ICA Employing the Conjugate Gradient Technique for Signal Separation in Time-Varying Flat Fading Channels

The conjugate gradient method is a prominent technique for solving systems of linear equations and unconstrained optimization problems, including adaptive filtering. Since it is an iterative method, it can be particularly applied to solve sparse systems which are too large to be handled by direct methods. The main advantage of the conjugate gradient method is that it employs orthogonal search directions with optimal steps along each direction to arrive at the solution. As a result, it has a much faster convergence speed than the steepest descent method, which often takes steps in the same direction as earlier steps. Furthermore, it has lower computational complexity than Newton’s iteration approach. This unique tradeoff between convergence speed and computational complexity gives the conjugate gradient method desirable properties for application in numerous mathematical optimization problems. In this paper, the conjugate gradient principle is applied to complex adaptive independent component analysis (ICA) for maximization of the kurtosis function, to achieve separation of complex-valued signals. The proposed technique is called the complex block conjugate independent component analysis (CBC-ICA) algorithm. The CBC-ICA derives independent conjugate gradient search directions for the real and imaginary components of the complex coefficients of the adaptive system employed for signal separation. In addition, along each conjugate direction an optimal update is generated separately for the real and imaginary components using the Taylor series approximation. Simulation results confirm that in dynamic flat fading channel conditions, the CBC-ICA demonstrates excellent convergence speed and accuracy, even for large processing block sizes.

Dual-EKF-Based Real-Time Celestial Navigation for Lunar Rover

A key requirement of lunar rover autonomous navigation is to acquire state information accurately in real-time during its motion and set up a gradual parameter-based nonlinear kinematics model for the rover. In this paper, we propose a dual-extended-Kalman-filter- (dual-EKF-) based real-time celestial navigation (RCN) method. The proposed method considers the rover position and velocity on the lunar surface as the system parameters and establishes a constant velocity (CV) model. In addition, the attitude quaternion is considered as the system state, and the quaternion differential equation is established as the state equation, which incorporates the output of angular rate gyroscope. Therefore, the measurement equation can be established with sun direction vector from the sun sensor and speed observation from the speedometer. The gyro continuous output ensures the algorithm real-time operation. Finally, we use the dual-EKF method to solve the system equations. Simulation results show that the proposed method can acquire the rover position and heading information in real time and greatly improve the navigation accuracy. Our method overcomes the disadvantage of the cumulative error in inertial navigation.

Blind source separation-based multi-user detection for multi-antenna QAM receivers with I/Q imbalances

This paper presents a blind multi-user detection technique for multi-antenna quadrature amplitude modulation (QAM) receivers with Inphase/Quadrature phase (I/Q) imbalances. The estimation of multiple users in the presence of I/Q imbalances is performed by Blind Source Separation (BSS) methods. While the complex-valued signal model for multi-antenna QAM receivers does not lend itself to BSS due to the effect of I/Q imbalances, reformulating the signal model to a real-valued equivalent form enables the application of BSS. The proposed method enables multiple users to share the same bandwidth simultaneously in different geographical locations, and avoids the need for the knowledge of the channel state information. In addition, despite of the presence of I/Q imbalances in all receiver branches, the number of antenna required in the receiver is equal to the number of users. Computer simulations are conducted using the popular Fast-ICA (Independent Component Analysis) algorithm, and the simulation results confirmed the effectiveness of the proposed technique.

Intercarrier interference mitigation and multi-user detection employing adaptive ICA for MIMO-OFDM systems in time variant channels

Orthogonal Frequency Division Multiplexing (OFDM) is a widely applied scheme in modern wireless communication systems that effectively operate in frequency selective fading channels. The combination of OFDM and the Multiple-Input-Multiple-Output (MIMO) technique represents a promising candidate for future broadband wireless systems. This paper addresses the InterCarrier Interference (ICI) issue in multi-user MIMO-OFDM systems operating in time-varying frequency selective channel environments. ICI, which is caused by Carrier Frequency Offset (CFO) between local oscillators in the transmitter and the receiver, can lead to severe system performance degradation. In our proposed method, a recently presented Independent Component Analysis (ICA) technique called Complex Optimum Block Adaptive ICA (Complex OBA-ICA) is employed to recover user signals in the presence of ICI and channel induced mixing. Simulation results indicate that the new technique significantly reduces Inter Symbol Interference (ISI) in multi-user MIMO-OFDM systems in dynamic channel environments.