Information Theory and Reliable Communication

Array processing involves manipulation of signals induced on various antenna elements. Its capabilities of steering nulls to reduce cochannel interferences and pointing independent beams toward various mobiles, as well as its ability to provide estimates of directions of radiating sources, make it attractive to a mobile communications system designer. Array processing is expected to play an important role in fulfilling the increased demands of various mobile communications services. Part I of this paper showed how an array could be utilized in different configurations to improve the performance of mobile communications systems, with references to various studies where feasibility of apt array system for mobile communications is considered. This paper provides a comprehensive and detailed treatment of different beam-forming schemes, adaptive algorithms to adjust the required weighting on antennas, direction-of-arrival estimation methods-including their performance comparison-and effects of errors on the performance of an array system, as well as schemes to alleviate them. This paper brings together almost all aspects of array signal processing.

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Application of antenna arrays to mobile communications. II. Beam-forming and direction-of-arrival considerations

Sphere Packings, Lattices and Groups

Tremor was suppressed by test stimulation of the thalamic ventralis intermedius (VIM) nucleus at high frequency (130 Hz) during stereotaxy in nonanesthetized patients suffering from Parkinson's disease or essential tremor. Ventralis intermedius stimulation has since been used by the authors over the last 8 years as a treatment in 117 patients with movement disorders (80 cases of Parkinson's disease, 20 cases of essential tremor, and 17 cases of various dyskinesias and dystonias including four multiple sclerosis). Chronic electrodes were stereotactically implanted in the VIM and connected to a programmable stimulator. Results depend on the indication. In Parkinson's disease patients, tremor, but not bradykinesia and rigidity, was selectively suppressed for as long as 8 years. Administration of L-Dopa was decreased by more than 30% in 40 Parkinson's disease patients. In essential tremor patients, results were satisfactory but deteriorated with time in 18.5% of cases, mainly for patients who presented an action component of their but deteriorated with time in 18.5% of cases, mainly for patients who presented an action component of their tremor. In other types of dyskinesias (except multiple sclerosis), results were much less favorable. Fifty-nine patients underwent bilateral implantation and 14 other patients received implantation contralateral to a previous thalamotomy. Thirty-seven patients (31.6%) experienced minor side effects, which were always well tolerated and immediately reversible. Three secondary scalp infections led to temporary removal of the implanted material. There was no permanent morbidity. This tremor suppression effect could be due to the inhibition or jamming of a retroactive loop. Chronic VIM stimulation, which is reversible, adaptable, and well tolerated even by patients undergoing bilateral surgery (74 of 117 patients) and by elderly patients, should replace thalamotomy in the regular surgical treatment of parkinsonian and essential tremors.

Chronic electrical stimulation of the ventralis intermedius nucleus of the thalamus as a treatment of movement disorders

The paper describes the method of determining direction and frequency content of the brain activity flow. The method was formulated in the framework of the AR model. The transfer function matrix was found for multichannel EEG process. Elements of this matrix, properly normalized, appeared to be good estimators of the propagation direction and spectral properties of the investigated signals. Simulation experiments have shown that the estimator proposed by us unequivocally reveals the direction of the signal flow and is able to distinguish between direct and indirect transfer of information. The method was applied to the signals recorded in the brain structures of the experimental animals and also to the human normal and epileptic EEG. The sensitivity of the method and its usefulness in the neurological and clinical applications was demonstrated.

A new method of the description of the information flow in the brain structures

One of the challenges in MRI-controlled hyperthermia cancer treatment for localized tumor is that the tissue properties are dynamic and difficult to measure. Therefore, tuning the optimal gains for a constant gain controller can be challenging. In this paper, a new multi-input single-output adaptive controller strategy is proposed to address these problems. The inputs to the controller block are the frequency, rotation rate, and applied power level of an interstitial applicator, and the output is the boundary temperature during treatment. The time-varying gains of the new controller are updated over time using Lyapunov-based stability analysis. The robustness of the new controller to changes in the parameters of the tissue is investigated and compared to a constant gain controller through simulation studies. Simulations take into account changes in tissue properties and other conditions that may be encountered in a practical clinical situation. Finally, the effectiveness of the proposed controller is validated through an experimental study.

A Self-Tuning Adaptive Controller for 3-D Image-Guided Ultrasound Cancer Therapy

The coefficients of the optimal steady-state k -step ahead predictor for a scalar ARMAX process in general depend on k . It is shown that a simple formula completely characterizes all these coefficients. This extends previous results on the characterization of ARMA predictors.

A simple formula for optimal ARMAX predictors

In this report, results on observable canonical forms for time-varying systems are extended to treat classes of bilinear systems whose structural properties guarantee that certain observability properties hold, regardless of the choice of input signal. The resulting canonical forms lead naturally to equivalent models which exhibit linearity with respect to (possibly unknown) system parameters, and which can therefore be used for online identification and adaptive observer design. This paper explicitly parametrizes selected classes of models, in both continuous and discrete time, and discusses the requirements for observer design and identification.

Parametrization and identification of bilinear systems

The estimation and control of linear stochastic systems with delays in the state, control, and observations are studied. First, the infinite time deterministic optimal control problem with quadratic cost is examined. Using an appropriate notion of stabilizability and detectability, the optimal control law is obtained, and the closed loop system is shown to be L2-stable. Next, the stochastic filtering problem is studied. Under suitable assumptions of detectability and stabilizability, the filter gains are shown to converge, and the optimal stationary filter is shown to be L2-stable. Finally, by putting together the optimal control and filtering results, a stable constant stochastic control law is obtained for the linear-quadratic-Gaussian problem.

A stability theory for the linear-quadratic-Gaussian problem for systems with delays in the state, control, and observations

This paper proposes a secure semi-fragile authentication watermarking algorithm for natural images by embedding two complementary watermarks for content change analysis. Two authenticator watermarks are generated and embedded in different regions of the images: one for detecting malicious modifications and the other for estimating the degree of the changes. The proposed scheme is able to distinguish common content-preserving changes from malicious content-changing modifications. Simulations on real images demonstrate the effectiveness of the authentication watermarking scheme.

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Raymond H. Kwong

Papers

A Self-Tuning Adaptive Controller for 3-D Image-Guided Ultrasound Cancer Therapy

A simple formula for optimal ARMAX predictors

Parametrization and identification of bilinear systems

A stability theory for the linear-quadratic-Gaussian problem for systems with delays in the state, control, and observations

Secure semi-fragilewatermarking for image authentication