Steve F. Russell

Design of FIR filters with complex desired frequency response using a generalized Remez algorithm

Complex approximation with a generalized Remez algorithm is used to design FIR digital filters with nonconjugate symmetric frequency responses. The minimax criterion is used and the Chebychev approximation is posed as a linear optimization problem. The primal problem is converted to its dual and is solved using an efficient, quadratically convergent algorithm developed by Tang. Optimal Chebychev real-coefficient FIR filters with group delay smaller than half the filter length can be designed with slightly better magnitude responses compared to linear-phase filters. Linear-phase filters can also be designed when the group delay is specified to be half the filter length. Most importantly, the design method is capable of producing filters with complex coefficients that approximate nonconjugate symmetric frequency responses. >

A statistical indoor localization method for supporting location-based access control

Location awareness is critical for supporting location-based access control (LBAC). The challenge is how to determine locations accurately and efficiently in indoor environments. Existing solutions based on WLAN signal strength either cannot provide high accuracy, or are too complicated to accommodate to different indoor environments. In this paper, we propose a statistical indoor localization method for supporting location-based access control. First, in an offline training phase, we fit a locally weighted regression and smoothing scatterplots (LOESS) model on the signal strength received at different training locations, and build a radio map that contains the distribution of signal strength. Then, in an online estimation phase, we determine the locations of unknown points using maximum likelihood estimation (MLE) based on the measured signal strength and the stored distribution. In addition, we provide a 95% confidence interval to our estimation using a Bootstrapping module. Compared with other approaches, our method is simpler, more systematic and more accurate. Experimental results show that the estimation error of our method is less than 2m. Hence, it can better support LBAC applications than others.

Short Paper: A Signal Fingerprinting Paradigm for General Physical Layer and Sensor Network Security and Assurance

In this paper, we present a new paradigm for security in conventional networks that has dramatic implications for improving their physical layer network security. We call this paradigm, Detecting Intrusions at Layer ONe (DILON). DILON’s enabling hypothesis is that the inherent variability in the construction of digital devices leads to significant variability in their analog signaling. This is true not only for different device models but even for nearly identical devices of the same manufacturing lot. The idea is that by oversampling digital signals to make analog measurements that constitute “voiceprints” of network devices. These form a profile that can be used for detecting MAC address spoofing, reconfiguration of network topologies, and in the long term possibly predict the failure of network devices. This paper discusses historic references and how digital networks enable new approaches as well as a number of applications.

Physical-Layer Identification of Wired Ethernet Devices

This work sets forth a systematic approach for the investigation and utilization of the signal characteristics of digital devices for use in a security context. A methodology, built upon an optimal detector, the matched filter, is proposed that allows for the reliable identification and tracking of wired Ethernet cards by use of their hardware signaling characteristics. The matched filter is found to be sensitive enough to differentiate between devices using only a single Ethernet frame; an adaptive thresholding strategy employing prediction intervals is used to cope with the stochastic nature of the signals. To demonstrate the validity of the methodology, and to determine which portions of the signal are useful for identification purposes, experiments were performed on three different models of 10/100 Ethernet cards, totaling 27 devices in all. In selecting the cards, an effort was made to maximize intramodel similarity and thus present a worst-case scenario. While the primary focus of the work is network-based authentication, forensic applications are also considered. By using data collected from the same devices at different times, it is shown that some models of cards can be reidentified even after a month has elapsed since they were last seen.

Design of FIR Hilbert transformers and differentiators in the complex domain

This paper presents a method for the design of FIR Hilbert transformers and differentiators in the complex domain. The method can be used to obtain conjugate-symmetric designs with smaller group delay compared to linear-phase designs. Non-conjugate symmetric Hilbert transformers are also designed. This paper is an extension of our previous work, which presented the algorithm for the design of standard frequency selective filters. The minimax criterion is used and the Chebychev approximation is posed as a linear optimization problem. The primal problem is converted to its dual and is solved using an efficient quadratically convergent algorithm developed by Tang (1988). When a constant group delay is specified, the filter designs have almost linear phase in the passbands. When the specified group delay is half the filter length, the algorithm results in exactly linear-phase designs.

A computationally efficient correlator for pseudo-random correlation systems

Pseudo-random correlation systems find their application in many engineering fields like, communications, nondestructive testing, medical imaging, and geophysics. The heart of such systems is a correlator, which performs the crosscorrelation between the received signal and a reference waveform. A new method of DSP-based correlator implementation is discussed. It exploits the structural characteristics of pseudo-random waveforms and performs the crosscorrelation of any digitized waveform with a reference pseudo-random waveform, in a manner, much more efficient in terms of the processing speed and hardware requirements. This new method can be applied for baseband or bandpass waveforms, and it can handle a wide range of modulation schemes and signaling structures. In order to achieve greater resolution of the calculated correlation function, it is possible to compute the correlation function for the lag values in fraction of the basic chip interval.

Implementation of Self-Noise Suppression Techniques for Ultrasonic Correlation Systems

Pseudo-random signal correlation techniques can improve the flaw detection capability of ultrasonic NDE systems. While the correlation-based systems provide significant improvement in the signal-to-noise ratio compared to pulsed systems, their performance is limited by the so-called “self-noise” of the system. Self-noise is a result of imperfect autocorrelation characteristics of the excitation signal. Last year, we suggested some techniques for improving the flaw detection capability of continuous-mode ultrasonic NDE systems [1]. These systems use a continuously transmitted coded waveform as an excitation signal, and the received signal is processed through a correlation filter. This year, we present another new approach and demonstrate performance results and the practicability of each approach.

Bipolar active inductor realizability limits, distortion, and bias considerations

Active inductors for MMICs offer an interesting alternative to passive implementations when the rf currents are below the threshold levels needed to maintain low distortion. This paper examines the limits of realizability for a MMIC inductor circuit that utilizes two bipolar junction transistors in a common collector-common emitter configuration to gyrate the base-emitter capacitance of the common emitter stage to form a synthetic inductor. The inductance range, Q-factor, distortion, dc bias points, and dc power consumption for the circuit are considered. Governing equations and graphs describing circuit performance are presented. The results show that the goals of higher Q, lower distortion, and good DC power utilization are not conflicting in terms of the biasing of the transistors.

Choice of Coded Waveform and Correlation Filter for Self-Noise Suppression in Ultrasonic Correlation Systems

Various ultrasonic correlation systems have been suggested in the past [1–5] in order to improve the flaw detection capability of ultrasonic NDE systems. These systems use a coded waveform for transmission, and the received signal is processed through a correlation filter. Although, these systems provide considerable improvement in the flaw detection capability, their performance is limited by what is called “self-noise” of the system. This paper discusses the self-noise limitation of conventional ultrasonic correlation systems and presents various approaches for self-noise suppression. Theoretically predicted performance has been verified using detailed computer simulations. Finally, comparison of the performance and practicability of each approach is discussed.

Application of Spread-Spectrum Ultrasonic Evaluation to Concrete Structures

Spread-Spectrum Ultrasonic Evaluation (SSUE) is an emerging technology for the global testing of structures and materials [1]. It incorporates the correlation properties of pseudo-random signals into ultrasonic NDE using spread-spectrum technology. The SSUE instrument records the ultrasonic correlation signature that is representation of the aggregate acoustic state of the test sample. The measured ultrasonic correlation signature is used for the detection of changes in the acoustic state of the test object. One major advantage of the SSUE technique is that it provides a global inspection of the material or structure without scanning. Some examples of unique SSUE applications are when; 1) the test object is of complex geometry or too large for scanning or, 2) the test material is a highly attenuative material such as concrete, wood, or composites. This paper reports the progress in applying the SSUE technique to concrete. The aim of the reported research is to study the propagation of the spread-spectrum signal in concrete structures of various sizes and determine the sensitivity of the SSUE correlation signature to changes in the various acoustic properties of the concrete object. A comparison of the SSUE technique with conventional ultrasonic NDE techniques for concrete testing is done and advantages of this technique for standard concrete inspection methods are discussed.