Richard A. Raines

Computer-aided breast cancer detection and diagnosis of masses using difference of Gaussians and derivative-based feature saliency

A new model-based vision (MBV) algorithm is developed to find regions of interest (ROIs) corresponding to masses in digitized mammograms and to classify the masses as malignant/benign. The MBV algorithm is comprised of 5 modules to structurally identify suspicious ROIs, eliminate false positives, and classify the remaining as malignant or benign. The focus of attention module uses a difference of Gaussians (DoG) filter to highlight suspicious regions in the mammogram. The index module uses tests to reduce the number of nonmalignant regions from 8.39 to 2.36 per full breast image. Size, shape, contrast, and Laws texture features are used to develop the prediction modules mass models. Derivative-based feature saliency techniques are used to determine the best features for classification. Nine features are chosen to define the malignant/benign models. The feature extraction module obtains these features from all suspicious ROIs. The matching module classifies the regions using a multilayer perceptron neural network architecture to obtain an overall classification accuracy of 100% for the segmented malignant masses with a false-positive rate of 1.8 per full breast image. This system has a sensitivity of 92% for locating malignant ROIs. The database contains 272 images (12 b, 100 /spl mu/m) with 36 malignant and 53 benign mass images. The results demonstrate that the MBV approach provides a structured order of integrating complex stages into a system for radiologists.

An operational and performance overview of the IRIDIUM low earth orbit satellite system

Today, both the military and commercial sectors are placing an increased emphasis on global communications. This has prompted the development of several low earth orbit satellite systems that promise worldwide connectivity and real-time voice communications. This article provides a tutorial overview of the IRIDIUM low earth orbit satellite system and performance results obtained via simulation. First, it presents an overview of key IRIDIUM design parameters and features. Then, it examines the issues associated with routing in a dynamic network topology, focusing on network management and routing algorithm selection. Finally, it presents the results of the simulation and demonstrates that the IRIDIUM system is a robust system capable of meeting published specifications.

An overview of the IRIDIUM (R) low Earth orbit (LEO) satellite system

This paper provides a tutorial overview of the IRIDIUM(R) low earth orbit (LEO) satellite system. Section I contains an introduction to the IRIDIUM(R) network as well as the system specifications. Section II discusses the satellite constellation design, orbital parameters, and horizontal pointing angles between satellites. Section III introduces the idea of time dependent connectivity in a mobile network, and analyzes the cycle of network connectivity for IRIDIUM(R). Section IV discusses the IRIDIUM(R) Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) schemes and uses these to calculate the overall system capacity. Section V examines the call processing procedure to include user location and call set up. Finally, Section VI analyzes the network performance in terms of end-to-end delay and hop count.

Using Attack and Protection Trees to Analyze Threats and Defenses to Homeland Security

Attacks against computer networks are a serious threat and occur quite often. Currently there are methods using attack trees that can be used to model how these attacks may occur. We have extended this concept to a new tree structure called a protection tree as a tool for decision makers to allocate limited resources towards the appropriate defenses against a specified attack. Protection trees ensure these limited resources are used in a manner to achieve the highest probability of success in stopping an attack. Protection trees are produced systematically by first developing an attack tree, computing metrics for each node of an attack, and then developing a corresponding protection tree with similar metrics. Eventually, libraries of attacks and available protections can be used to automate the process of developing the trees. An example attack and protection tree is used to notionally show how an organization such as the department of homeland security can allocate resources to protect their computer networks from being compromised. Decision makers in the organization can use the resultant protection tree to determine where to allocate limited resources for the best protection of their network

Evolution of the air interface of cellular communications systems toward 4G realization

Early cellular networks used analog frequency modulation for voice communication and frequency division multiple access to accommodate multiple users. Despite their utility, these networks were often unstable and provided poor quality. Over the past 25 years, robust coding, modulation, and multiple access schemes have contributed greatly to improved, ubiquitous cellular service. This survey chronicles the coding, modulation, and multiple access developments within the evolutional framework of cellular communication systems which spans early first generation (1G) to future fourth generation (4G) systems. EVOLUTION OF THE AIR INTERFACE OF CELLULAR COMMUNICATIONS SYSTEMS TOWARD 4G REALIZATION 1ST QUARTER 2006, VOLUME 8, NO. 1 www.comsoc.org/pubs/surveys 1553-877X The views expressed in this article are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the U.S. Government.

Performance simulation of a transform domain communication system for multiple access applications

A previously proposed interference-avoiding transform domain communication system (TDCS) is shown capable of operating successfully in a multiple access environment (MAE). The TDCS uses phase coding (mapping) generated from a linear feedback shift register (LFSR) configured to output a maximal-length binary pseudorandom sequence (m-sequence). Quasi-orthogonal basis functions (BFs) are used in a code division multiple access (CDMA) scheme to provide private communication channels to independent user pairs in the MAE. An existing single channel TDCS model is augmented to simulate MAE interference effects on bit error performance (P/sub B/) The proposed TDCS system is simulated using MATLAB for system capacities up to eight channels and E/sub b//N/sub 0/ values ranging from 0 to 9 dB. Simulated MAE TDCS bit error performance closely approximates estimated results; the error for eight channels has a mean value less than 1.7/spl times/10/sup -3/ and a standard deviation less than 1.3/spl times/10/sup -3/. The analysis of acquisition-related performance metrics and bit error performance through computer simulation provides a good measure of TDCS operational capabilities in a MAE.

Initial acquisition performance of a transform domain communication system: modeling and simulation results

Initial acquisition performance of a transform domain communication system (TDCS) is characterized via modeling and simulation (M&S). A TDCS with interference suppression capability differs from typical spread spectrum systems in two primary ways. 1) spectrally crowded regions are avoided via adaptive spectral notching, and 2) no carrier modulation is employed. Thus, minimal signal structure exists for synchronization purposes. Initial TDCS acquisition performance is investigated for various synchronization codewards and several acquisition methods, e.g., direct time correlation (DTC) and Germans technique, using both peak and threshold detection techniques. IMATLAB(R) simulation results indicate that a TDCS can achieve a high probability of detection (P/sub d/>0.9) for relatively low input signal-to-noise ratios (SNRs), as low as -23 dB for peak detection and -21 dB for threshold detection. Extensive computer simulations and subsequent analysis indicates that a TDCS can adequately acquire and accurately align a locally generated reference waveform with the received noise-like TDCS signal.

Communication Waveform Design Using an Adaptive Spectrally Modulated, Spectrally Encoded (SMSE) Framework

Fourth-generation (4G) communication systems will likely support multiple capabilities while providing universal, high-speed access. One potential enabler for these capabilities is software-defined radio (SDR). When controlled by cognitive radio (CR) principles, the required waveform diversity is achieved through a synergistic union called CR-based SDR. This paper introduces a general framework for analyzing, characterizing, and implementing spectrally modulated, spectrally encoded (SMSE) signals within CR-based SDR architectures. Given orthogonal frequency division multiplexing (OFDM) is one 4G candidate signal, OFDM-based signals are collectively classified as SMSE since data modulation and encoding are applied in the spectral domain. The proposed framework provides analytic commonality and unification of multiple SMSE signals. Framework applicability and flexibility is demonstrated for candidate 4G signals by: 1) showing that resultant analytic expressions are consistent with published results and 2) presenting representative modeling and simulation results to reinforce practical utility

Cryptanalysis of an elliptic curve cryptosystem for wireless sensor networks

We present a brute-force attack on an elliptic curve cryptosystem implemented on UC Berkleys TinyOS operating system for Wireless Sensor Networks (WSNs). The attack exploits the short period of the Pseudorandom Number Generator (PRNG) used by the cryptosystem to generate private keys. In order to define failure in the event a brute-force attack takes too long to execute, we create a metric that relates the duty cycle of the mote to the compromise rate and the period of the key generation algorithm. Experimental results show that roughly 50% of the motes address space leads to a private key compromise in 25 min on average. Furthermore, approximately 32% of the mote address space leads to a compromise in 17 min on average, 11% in 6 min and the remaining 7% in 2 min or less. We examine two alternatives to the PRNG our own design modified from a published algorithm and the new PRNG distributed with the beta release of TinyOS 2.0. Our design executes 12.47 times faster than the other alternative and requires 50 CPU cycles more than the original PRNG. In addition, our design is 6.3 times smaller than the other alternative and requires 106 additional bytes of memory. The period of our PRNG is uniform for all mote addresses and requires 6.6 years on average for a key compromise with the attack presented in this paper.

Packetized voice transmission using RT-MAC, a wireless real-time medium access control protocol

RT-MAC is a simple, elegant, and robust medium access control (MAC) protocol for use in transmitting real-time data in point-to-point ad hoc wireless local area networks (WLANs). Our enhancement of IEEE 802.11, real-time MAC (RT-MAC), dramatically reduces missed deadlines and packet collisions while increasing throughput by selectively discarding packets and sharing station state information. For example, RT-MAC is able to successfully transmit 40 2-way voice conversations in addition to a normalized offered load of 80%. IEEE 802.11 is only able to transmit 10 2-way conversations under the same conditions. In another instance, RT-MAC reduced packet collisions from 50% to less than 15% while increasing throughput by more than 50%. Herein we extend our previous performance analysis of RT-MAC to include integrated voice-data transmission. Stations using RT-MAC are interoperable with stations using IEEE 802.11 and show a significant performance improvement even when a minority of stations in the network employ RT-MAC.