Gary J. Saulnier

Bio: Gary J. Saulnier is an academic researcher from Rensselaer Polytechnic Institute. The author has contributed to research in topics: Spread spectrum & Electrical impedance tomography. The author has an hindex of 37, co-authored 217 publications receiving 4389 citations. Previous affiliations of Gary J. Saulnier include Martin Marietta Materials, Inc. & General Electric.

ACT3: a high-speed, high-precision electrical impedance tomograph

Abstract: Presents the design, implementation, and performance of Rensselaer's third-generation adaptive current tomograph, ACT3. This system uses 32 current sources and 32 phase-sensitive voltmeters to make a 32-electrode system that is capable of applying arbitrary spatial patterns of current. The instrumentation provides 16 b precision on both the current values and the real and reactive voltage readings and can collect the data for a single image in 133 ms. Additionally, the instrument is able to automatically calibrate its voltmeters and current sources and adjust the current source output impedance under computer control. The major system components are discussed in detail and performance results are given. Images obtained using stationary agar targets and a moving pendulum in a phantom as well as in vivo resistivity profiles showing human respiration are shown. >

Ultrasonic Through-Wall Communication (UTWC) System

Abstract: Apparatus for communicating information across a solid wall has one or two outside ultrasonic transducers coupled to an outside surface of the wall and connected to a carrier generator for sending an ultrasonic carrier signal into the wall and for receiving an output information signal from the wall. One or two inside ultrasonic transducers are coupled to an inside surface of the wall and one of them introduces the output information signal into the wall. When there are two inside transducers inside the wall, one receives the carrier signal and the second transmits the carrier after it is modulated by the output information from the sensor. When there is one inside transducer, the output information from the sensor is transmitted by changing the reflected or returned signal from the inside transducer. A power harvesting circuit inside the wall harvests power from the carrier signal and uses it to power the sensor.

Current source design for electrical impedance tomography.

Abstract: Questions regarding the feasibility of using electrical impedance tomography (EIT) to detect breast cancer may be answered by building a sufficiently precise multiple frequency EIT instrument. Current sources are desirable for this application, yet no current source designs have been reported that have the required precision at the multiple frequencies needed. We have designed an EIT current source using an enhanced Howland topology in parallel with a generalized impedance converter (GIC). This combination allows for nearly independent adjustment of output resistance and output capacitance, resulting in simulated output impedances in excess of 2 GΩ between 100 Hz and 1 MHz. In this paper, the theoretical operation of this current source is explained, and experimental results demonstrate the feasibility of creating a high precision, multiple frequency, capacitance compensated current source for EIT applications.

Electrical impedance tomography

Abstract: Electrical impedance tomography (EIT) is an imaging modality that estimates the electrical properties at the interior of an object from measurements made on its surface. Typically, currents are injected into the object through electrodes placed on its surface, and the resulting electrode voltages are measured. An appropriate set of current patterns, with each pattern specifying the value of the current for each electrode, is applied to the object, and a reconstruction algorithm uses knowledge of the applied current patterns and the measured electrode voltages to solve the inverse problem, computing the electrical conductivity and permittivity distributions in the object. This article focuses on the type of EIT called adaptive current tomography (ACT) in which currents are applied simultaneously to all the electrodes. A number of current patterns are applied, where each pattern defines the current for each electrode, and the subsequent electrode voltages are measured to generate the data required for image reconstruction. A ring of electrodes may be placed in a single plane around the object, to define a two-dimensional problem, or in several layers of such rings, to define a three-dimensional problem. The reconstruction problem is described and two algorithms are discussed, a one-step, two-dimensional (2-D) Newton-Raphson algorithm and a one-step, full three-dimensional (3-D) reconstructor. Results from experimental data are presented which illustrate the performance of the algorithms.

General ICI self-cancellation scheme for OFDM systems

Abstract: One of the challenges in designing orthogonal frequency-division multiplexing (OFDM) systems is their inherent sensitivity to any frequency shift in the signal. A frequency offset between the local oscillators at the transmitter and receiver causes a single frequency shift in the signal, while a time-varying channel can cause a spread of frequency shifts known as the Doppler spread. Frequency shifts ruin the orthogonality of OFDM subcarriers and cause intercarrier interference (ICI); therefore, quickly diminishing the performance of the system. ICI self-cancellation schemes have been proposed to reduce the sensitivity of OFDM systems to frequency shifts. These schemes use signal processing and frequency domain coding to reduce the amount of ICI generated as a result of frequency shifts, with little additional computational complexity. These methods can be used as an alternative to the fine frequency-offset estimation methods to battle oscillator frequency offset or simply be used as an ICI mitigation technique when the system is operating over time-varying channels. We propose a general ICI self-cancellation scheme that can be implemented through windowing at the transmitter and receiver. We show that the previously proposed self-cancellation schemes are equivalent to special cases of this method. Through theoretical analysis of the signal-to-interference ratio and bit-error rate and the use of Monte Carlo simulations, we demonstrate that the proposed system considerably outperforms the existing systems in the presence of frequency offset or time variations in the channel. We consider both coherent and noncoherent systems.

On the capacity of a cellular CDMA system

Abstract: It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

Wavelet Methods for Time Series Analysis

Abstract: 1. Introduction to wavelets 2. Review of Fourier theory and filters 3. Orthonormal transforms of time series 4. The discrete wavelet transform 5. The maximal overlap discrete wavelet transform 6. The discrete wavelet packet transform 7. Random variables and stochastic processes 8. The wavelet variance 9. Analysis and synthesis of long memory processes 10. Wavelet-based signal estimation 11. Wavelet analysis of finite energy signals Appendix. Answers to embedded exercises References Author index Subject index.

Electrical Impedance Tomography

Abstract: t. This paper surveys some of the work our group has done in electrical impedance tomography.

MMSE interference suppression for direct-sequence spread-spectrum CDMA

Abstract: We consider interference suppression for direct-sequence spread-spectrum code-division multiple-access (CDMA) systems using the minimum mean squared error (MMSE) performance criterion. The conventional matched filter receiver suffers from the near-far problem, and requires strict power control (typically involving feedback from receiver to transmitter) for acceptable performance. Multiuser detection schemes previously proposed mitigate the near-far problem, but are complex and require explicit knowledge or estimates of the interference parameters. In this paper, we present and analyze several new MMSE interference suppression schemes, which have the advantage of being near-far resistant (to varying degrees, depending on their complexity), and can be implemented adaptively when interference parameters are unknown and/or time-varying, Numerical results are provided that show that these schemes offer significant performance gains relative to the matched filter receiver. We conclude that MMSE detectors can alleviate the need for stringent power control. In CDMA systems, and may be a practical alternative to the matched filter receiver. >