Ralph Thomas Hoctor

Delay-hopped transmitted-reference RF communications

Previously, the authors have invented and experimented with a new radio communications scheme called delay-hopped transmitted-reference (DHTR) radio. This technique can function either as an impulse radio, or can employ a more traditional spread-spectrum carrier such as broadband noise. The DHTR method is well-suited to short-range transmissions in a high multipath environment, and, in contrast to time-modulated impulse radio, is easy to synchronize at the receiver. Finally, DHTR receivers and transmitters are not highly complex, and can be implemented in a cost-effective way.

Super-resolution image synthesis using projections onto convex sets in the frequency domain

In this report we propose a frequency domain POCS algorithm for the canonical problem of super-resolution (SR) image synthesis. Unlike previous frequency domain SR algorithms, this approach is structured to accommodate rotations of the source relative to the imaging device, which we believe to help in producing a well-conditioned image synthesis problem. Generally, frequency domain methods have been used when component images were related by subpixel shifts only, because rotations of a sampled image do not correspond to a simple operation in the frequency domain.

Delay hopped transmitted reference experimental results

This paper describes the experimental hardware design and implementation for a delay hopped transmitted reference communication system. The hardware is designed to generate the delay hopped transmitted reference signal for a number of experimental conditions. It can be used either in an ultra wideband pulse mode, ultra wideband noise mode, or in a narrowband mode. We use the experimental hardware setup to conduct link experiments with a delay hopped transmitted reference communication system. Experiments were conducted in an indoor multipath environment to test the viability of delay hopped transmitted reference for short-range indoor communications. The experimental results presented demonstrate that this modulation format is capable of transmitting data short range indoors without line of sight transmission path with minimal transmitted RF power.

Array signal processing for local arterial pulse wave velocity measurement using ultrasound

A new signal processing approach to estimation of local arterial pulse wave velocity (PWV) in superficial arterial segments using long-axis ultrasound measurements is proposed. The method is designed to be resistant to estimation bias due to pulse wave reflections. It is evaluated using a laboratory test tank, and it appears to estimate local PWV with less bias than previously accepted methods, and with similar estimation variance to those methods

Multiple access capacity in multipath channels of delay-hopped transmitted-reference UWB

The multiple access capacity of delay-hopped transmitted-reference (DHTR) ultra-wideband radio [R.T. Hoctor et al., May 2002, N. Vanstralen et al., May 2002] is investigated through analysis and simulation. The factor that limits the multiple access capacity of DHTR is the degree of multipath in the transmission channel.

Signal processing for ultrasound-based arterial pulse wave velocity estimation

In this paper we propose a new signal processing approach for estimating arterial pulse wave velocity (PWV) in a uniform arterial segment based on ultrasound measurements. The new approach compensates for whatever pulse wave reflections are present in the observation. We show that the long-axis PWV estimation problem with reflections is similar to that of direction-of-arrival (DOA) estimation for two far-field, narrowband, coherent sources. A high-SNR simulation is performed to compare the performance of the new method to that of three existing methods in the presence of reflections. A limited amount of in vivo data is processed and the resulting estimates, although superior to those obtained from existing methods, are seen to be noisy. Finally, further research directions are outlined.

A physical layer for the CAN bus using modulated PLC

In this paper, we describe a physical layer for the CAN bus using PLC. Our application is a low-data-rate sensor network used to monitor railroad crossing warning systems.

Communications and Control--A Natural Linkage for SWARM

We present a simple distributed concept that appears to insinuate SWARM behavior in a collection of mobile platforms. The control is based on the inter-mobile platform communication links’ signal-to-noise ratio. This double use of communications is a natural linkage for SWARM behavior.

Array signal processing approaches to ultrasound-based arterial pulse wave velocity estimation

Assessment of the arterial pulse wave velocity (PWV) has long been an area of interest in physiology, and ultrasound has long been used to provide measurements for such assessments. Recently, new signal processing approaches for ultrasound data have emerged. However, these methods suffer from inaccuracies due to pulse wave reflections, which are always present and can strongly bias the PWV estimates away from the true velocity. Recently the authors (Hoctor et al. (2004)) showed that pulse wave velocity estimation from several ultrasound measurements taken along a short uniform arterial segment is equivalent to the broadband directional of arrival problem with coherent multipath found in radar and sonar. This tutorial paper reviews the physiological and ultrasound-systems aspects of the PWV estimation problem, and examines its relationship to the direction-of-arrival estimation problem. The paper also demonstrates why nonlinear, high-resolution methods are needed and outlines the application of several such estimators to the problem.

Non-invasive hemodynamic state monitoring using ultrasound

Hemodynamic monitoring provides vital information for diagnosing and treating patients in acute clinical settings. A method is investigated to non-invasively monitor changes in the hemodynamic state. The approach utilizes short-axis ultrasound color flow imaging and processing methods to produce simultaneous waveforms for the arterial area and flow. Beat-to-beat measurements of the mean area, peak volumetric flow rate, and heart rate are extracted, and the distribution of these parameters is used to define the hemodynamic state. Changes in the hemodynamic state are detected by calculating a distance between new measurements and the current hemodynamic state, and then comparing this distance to an adaptive threshold. The distribution was modeled as a multivariate normal distribution characterized by a mean vector and a covariance matrix, and the Mahalanobis distance was used as the distance metric. The threshold level was adapted to produce a constant probability of false positives based on the current distribution. The method was evaluated by observing pharmacologically induced changes in the hemodynamic state during an in vivo animal experiment. The ultrasound-based measurements provided sufficient accuracy to discriminate between the hemodynamic states before, during and after infusion of a vasodilator. The ability to detect an acute change in the hemodynamic state was demonstrated in the transient period at the start of the infusion.