Thad B. Welch

The effects of the human body on UWB signal propagation in an indoor environment

Ultra-wideband (UWB) communication systems are investigated for their ability to operate in dense multipath environments. While a great deal of time and effort has been spent characterizing both the indoor and outdoor UWB channels, the effects of human body interaction with a close proximity UWB antenna remains unexplored. Measurements of a commercially available UWB antenna performance in an anechoic chamber and in various indoor multipath environments were conducted. Comparisons of these measurement results indicate that while the human body creates a deep null (23.6 dB) in a light multipath environment, this null is drastically reduced (6.8 dB) in a dense multipath environment.

Use of one-dimensional iris signatures to rank iris pattern similarities

A one-dimensional approach to iris recognition is presented. It is translation-, rotation-, illumination-, and scale-invariant. Traditional iris recognition systems typically use a two-dimensional iris signature that requires circular rotation for pattern matching. The new approach uses the Du measure as a matching mechanism, and generates a set of the most probable matches (ranks) instead of only the best match. Since the method generates one-dimensional signatures that are rotation-invariant, the system could work with eyes that are tilted. Moreover, the system will work with less of the iris than commercial systems, and thus could enable partial-iris recognition. In addition, this system is more tolerant of noise. Finally, this method is simple to implement, and its computational complexity is relatively low.

A new approach to iris pattern recognition

An iris identification algorithm is proposed based on adaptive thresholding. The iris images are processed fully in the spatial domain using the distinct features (patterns) of the iris. A simple adaptive thresholding method is used to segment these patterns from the rest of an iris image. This method could possibly be utilized for partial iris recognition since it relaxes the requirement of using a majority of the iris to produce an iris template to compare with the database. In addition, the simple thresholding scheme can improve the computational efficiency of the algorithm. Preliminary results have shown that the method is very effective. However, further testing and improvements are envisioned.

A multidisciplinary approach to biometrics

Biometrics is an emerging field of technology using unique and measurable physical, biological, or behavioral characteristics that can be processed to identify a person. It is a multidisciplinary subject that integrates engineering, statistics, mathematics, computing, psychology, and policy. The need for biometrics can be found in governments, in the military, and in commercial applications. The Electrical Engineering Department at the U.S. Naval Academy, Annapolis, MD, has introduced a biometric signal processing course for senior-level undergraduate students and has developed a biometrics lab to support this course. In this paper, the authors present the course content, the newly developed biometric signal processing lab, and the interactive learning process of the biometric course. They discuss some of the challenges that were encountered in implementing the course and how they were overcome. They also provide some feedback from the course assessment.

A one-dimensional approach for iris identification

A novel approach to iris recognition is proposed in this paper. It differs from traditional iris recognition systems in that it generates a one-dimensional iris signature that is translation, rotation, illumination and scale invariant. The Du Measurement was used as a matching mechanism, and this approach generates the most probable matches instead of only the best match. The merit of this method is that it allows users to enroll with or to identify poor quality iris images that would be rejected by other methods. In this way, the users could potentially identify an iris image by another level of analysis. Another merit of this approach is that this method could potentially improve iris identification efficiency. In our approach, the system only needs to store a one-dimensional signal, and in the matching process, no circular rotation is needed. This means that the matching speed could be much faster.

Shipboard radio frequency propagation measurements for wireless networks

This paper discusses several in-hull RF propagation studies on board one decommissioned and several active naval ships in the 0.8 - 2.5 GHz range. During these tests, it was repeatedly demonstrated that radio signals propagate from one compartment to another even when the watertight doors (hatches) are shut and sealed. In fact, signals have been received across several bulkheads. Results indicate approximately 20 dB of attenuation is associated with transmission through a bulkhead/watertight door. It has also been found that the wireless channel aboard naval vessels does not show good correspondence with a Rician channel. Finite element modeling of a shipboard compartment has been performed and supports the hypothesis that rubber door gaskets and other non-conductive structures may be the source of bulkhead penetration/leakage. For comparison, ultra-wideband channel measurements within the hull of a ship have also been taken. These measurements are used to characterize the propagation within a single compartment as well as through a sealed bulkhead/watertight door.

Very near ground radio frequency propagation measurements and analysis for military applications

We analyze, using a 2-ray model, the effects associated with placing a man-portable radio transceiver very near the ground (3-28 cm). A significant decrease in signal strength occurs when a soldier drops from the crouched position to the prone position. As much as a 16.8 dB decrease in signal strength was observed. This effect is more pronounced at short ranges, even without obstructions in the signal path. The Rician k factor generally decreases as the antenna height is lowered. The assumed 2-ray propagation model is only appropriate when the Rician k factor is much greater than zero.

winDSK: a Windows-based DSP demonstration and debugging program

Today there is a global need for engineers who are DSP literate. An obvious solution for supplying this need is to educate new engineers. To help educate the next generation of DSP engineers, several powerful and highly versatile DSP boards designed for educational use are offered. The problem with most of these systems is that they lack user-friendly software to demonstrate the capabilities of the DSP boards. Some of the software shipped with these devices has a very steep learning curve, while other packages are still DOS or command line based. Most of todays students are hesitant to approach these impediments to learning without significant motivation. To allow a students first hardware based DSP experience to be a positive one, software tools must be provided that are affordable, easy to install, attention getting, Windows based, and feature rich. This paper discusses winDSK, an object-oriented application program that meets these requirements.

A systematic model for teaching DSP

While many DSP topics are difficult for undergraduates to internalize, appropriate demonstrations and laboratory experiences have been shown to be very helpful. This paper describes a highly successful pedagogical model the authors have developed which includes theory, demos, lab exercises, and real-time DSP experience using MATLAB and the Texas Instruments C6711 digital signal processing starter kit.

Very near ground RF propagation measurements for wireless systems

Using a forward control channel of two different base stations as the signal source, we measure the effects associated with placing a cellular/PCS handheld transceiver very near the ground. A significant decrease in signal strength occurs when a system user drops from a standing to a lying position. As much as a 10.9 dB decrease in signal strength can result. This effect occurs with either a weak or strong specular signal component. Additionally, when a strong specular signal component, the shadowing caused by the system users head is small compared to the variations caused by antenna elevation.