Defense Notices

State-of-the-art General-Purpose computing on Graphics Processing Unit (GPGPU) is facing severe power challenge due to the increasing number of cores placed on a chip with decreasing feature size. In order to hide the long latency operations, GPGPU employs the fine-grained multi-threading among numerous active threads, leading to the sizeable register files with massive power consumption. Exploring the optimal power savings in register files becomes the critical and first step towards the energy-efficient GPGPU design. The conventional method to reduce dynamic power consumption is the supply voltage scaling, and the inter-bank tunneling FETs (TFETs) are the promising candidates compared to CMOS for low voltage operations regarding to both leakage and performance. However, always executing at the low voltage (so that low frequency) will result in significant performance degradation. In this study, we propose the hybrid CMOS-TFET based register files. To optimize the register power consumption, we allocate TFET-based registers to threads whose execution progress can be delayed to some degree to avoid the memory contentions with other threads, and the CMOS-based registers are still used for threads requiring normal execution speed. Our experimental results show that the proposed technique achieves 30% energy (including both dynamic and leakage) reduction in register files with little performance degradation compared to the baseline case equipped with naive power optimization technique.

Radar instruments can be used to provide information on the internal and basal conditions of large and small ice masses. Radars operating in the lower part of the high frequency (HF) spectrum are required for sounding glaciers with large inclusions. Also, low-frequency sounders are useful for measuring thickness of fast-flowing glaciers in Greenland and Antarctica. This is due to the composition, attenuation, and backscattering from large pockets of water (inclusions) present in ice profile. 
To radio-echo sound (RES) glaciers while providing compatibility between lightweight/portability (mass and volume) with low power consumption, we have designed, built, tested and deployed a radar for sounding glaciers requiring the trade-offs between science requirements and performance. The attenuation factors for an electromagnetic (EM) wave traveling through ice such as the extinction coefficient (Ke), the target surface scattering due to the rms height and correlation length, and the external EM noise sources, have been estimated for the design of the radar. 
The HF radar used is a man-portable, dual-frequency radio-echo sounder, optimized to work in the lower half of the HF spectrum using electrically-small antennas (ESA). The radar is powered by 24 VDC provided by the use of batteries, solar panels or a portable generator capable of at least 50 W. 
On July 31, 2009, the HF sounder successfully collected ice thickness data when operated at 8.75 MHz and 14.2 MHz at Jakobshavn, Greenland glacier. The present work represents the first successful survey for ice thickness using a dual-frequency technique for enhancing range accuracy. Indeed, with a single frequency time of arrival (TOA) backscattered signal the ice thickness was estimated to be 957.1 m with an estimated accuracy of 22 m. By using a second frequency TOA and the phase information at the previously estimated range at both frequencies, the target range has been re-estimated to be 952.2 m with an estimated accuracy of 8.8 m.

Synchronization is a critical operation in digital communication systems which establishes and maintains an operational link between the transmitter and the receiver. As the advancement of digital modulation and coding schemes continues, the synchronization task becomes more and more challenging since the new standards require high-throughput functionality at low signal-to-noise ratios (SNRs). Consequently, well-established synchronization methods have to be revised and improved in order to meet the new requirements. In this research effort, we study the synchronization of continuous phase modulations (CPMs) in burst-mode communications which allow transmission of data packets to multiple users efficiently in terms of consumed power and bandwidth. Despite the attractive characteristics of CPM, its synchronization in burst-mode transmissions has not been studied well because it is a rather complex modulation with memory. In this work, we resort to data-aided techniques where a known training sequence is embedded in the burst to assist the synchronization algorithms. Therefore, the first phase of this effort is to derive the optimum training sequence for which the estimation error is minimized. The second phase consists of designing practical synchronization algorithms to resolve frequency offset, carrier phase and symbol timing ambiguities based on the observed training sequence. Finally, a hardware implementation is proposed in order to test the theoretical results in a real-world environment.

Power line communication (PLC) has received steady interest over recent decades because of its economic use of existing power lines, and is one of the communication technologies envisaged for Smart Grid (SG) applications. However, since the power lines are not initially designed for data communication, the power line medium exhibits unique challanges for data communication. In particular for broadband (BB) PLC, the PLC channel shows linear periodically time varying (LPTV) behavior synchronous to the AC mains cycle, due to the time varying impedances of electrical devices that are connected to the power grid. In this research proposal, we focus on BB PLC LPTV channels, and investigate two major aspects for an orthogonal frequency division multiplexing (OFDM) system. First, we investigate the problem of optimal bit and power allocation, in order to increase throughput and improve energy e?ciency. We also provide reduced complexity mechanisms for the proposed bit loading scheme. This part constitutes the initial phase of our research. Second, we plan to tackle the problem of channel estimation for BB PLC LPTV channels and try to come up with low overhead and reduced complexity solutions, which is part of our future work that is in progress.

Healthcare information is growing exponentially and is made more available to public. However, not all health-related information on the Internet is scientific, accurate and objective. The trustworthiness of the web information can be hardly discriminated due to the fast and augmentative properties of the Internet. Most search engines provide relevant pages to given keywords, but the results might contain unreliable or biased information. Consequently, a significant challenge associated with the information explosion is to ensure effective use of information. One way to improve the search results is by accurately identifying more trustworthy data. Surprisingly, although trustworthiness of sources is essential for a great number of daily users, not much work has been done for healthcare information sources by far. In this work, we propose a new method, HealthTrust, a new approach to automatically assess the trustworthiness of online healthcare information providers. The goal of the HealthTrust is to generalize and formalize the observations to develop a computational model that integrates topology-based and opinion-based approaches for credibility assessment of websites containing healthcare related information.

The desire to hide communications has been around for a very long time. This includes hiding the existence of the transmission and the location of the sender. The existence of wireless networks offers another medium for these covert communications. 
With many devices and networks competing for the limited spectrum, new technologies and methods are constantly sought after to increase spectral efficiency and broaden use to more devices and their bandwidth hungry applications. Orthogonal Frequency Division Multiplexing (OFDM) increases spectral efficiency when compared to Frequency Division Multiplexing (FDM). Adaptive modulation and coding (AMC), hybrid auto-repeat-request (HARQ), and opportunistic scheduling allows the system the ability to adapt to the changing environment and maintain performance. These technologies are utilized in fourth generation (4G) wireless networks such as Long Term Evolution Advanced (LITE-Advanced) and WiMAX. 
This research proposes to hide a covert communications network within the RF environment of these packet based networks. We anticipate the existence of the aforementioned technologies to allow the non-covert network to adjust to the existence of the covert network. In other words, the wireless networks will view the covert network as a minor change in the RF environment. This research will also seek to measure the effect of the covert networks on the non-covert networks performance.

Web-based applications have become predominant in commercial software for all businesses, such as e-commerce, health care, government, and academia. There is a critical demand for effective and inexpensive functional testing methodologies for such applications to ensure their quality and reliability. The existing testing methodologies are insufficient to address the testing challenges raised by the increasing complexity of Web applications, including the use of multi-tier architectures, heterogeneous execution environments, dynamic contents, and frequent requirement changes. This research aims to address the above challenges by developing an extensible gray-box model-based testing (GMT) approach. 

The GMT defines a set of models that capture the dependencies of testing artifacts from a multi-tier architectural perspective. The models include Web conceptual model (WCM), Web object relation model (WORM), Web data to logic integration model (WDLIM), Web presentation to logic integration model (WPLIM), and Web system integration model (WSIM). The WORM, in the form of object relation diagrams, is used for the test case generation in intra-tier unit testing. The WLDIM and WPLIM are employed for gray-box integration testing across tiers. The WSIM, in the forms of system dependency graphs or UML sequence diagrams, is constructed for test path selection in black-box system testing phase. 

The GMT is capable of incorporating architectural styles beyond the traditional 3-tier Web applications. Extensions are developed to capture the component dependencies in elementary Web services, composite workflows, and Ajax-based rich Internet applications. A comprehensive empirical study is conducted to validate the GMT. Sixteen medium-scale projects from industrial context are selected as the subject applications. For each subject, 173 measurable attributes are collected. Formal analysis on the experiment data is performed and GMT is empirically evaluated against a well-known benchmark method to compare testing coverage effectiveness and testing performance. 

This research makes several important contributions to the software testing research community and demonstrates that the GMT effectively addresses the difficulty of analyzing multi-tier Web applications. The empirical results verify that the GMT is highly suitable in detecting functional defects in Web applications, particularly those from inter-tier integration. The fault seeding database and its experimental data establish a baseline for future empirical studies.

A hallmark of functional programming languages is their support for the algebraic manipulation of programs. While such techniques lend themselves to mechanization, they are usually employed by hand, requiring considerable expertise, but offering a high assurance of the correctness of the result. Library writers are especially likely to use these techniques in order to implement optimizations which are either deemed too narrowly applicable to be worth implementing in a general language compiler, or may only represent an optimization in certain specific contexts. Such domain-specific optimizations can be incredibly effective however, offering complexity-changing improvement. In many instances, they are accomplished by changing the data structures over which the computation operates. 

We propose a framework for mechanizing the worker/wrapper transformation, which can express a large number of these domain-specific optimizations that depend on changing data structures. As a significant case study, we propose to recast the Stream Fusion transformation as an instance of worker/wrapper, using it to motivate the capabilities of our framework. We also propose extensions to Stream Fusion to allow it to optimize higher-order stream combinators. The resulting framework should lower the effort required to mechanize such transformations, leading to increased correctness and reuse. Additionally, the extended Stream Fusion transformation will offer practical performance improvements to a wide range of programs.

This work presents the design and development of a genetic algorithm to generate long range transmit codes with low autocorrelation side lobes for radar. The genetic algorithm described in this work has a parallel processing design and has been used to generate codes with multiple constellations for various code lengths with low estimated error of a target profile.

As the World Wide Web continues to evolve as the preferred choice for information access it is critical that its utility to the user remains. Latency as a result of network congestion, bandwidth availability, server processing delays, embedded objects, and transmission delays and errors can impact the utility of the web browser application. To improve the overall user experience the application needs to not only provide feedback to the end user about the latency of links that are available but to also provide them decision controls in the retrieval of the web content. This thesis presents a background and related work relating to latency and web optimization techniques to reduce this latency and then introduce an improvement to the "latency aware" Mozilla Firefox extension which was originally developed by Sterbenz et. al., in 2002. This these describes the architecture and prototype implementation, followed with an analysis of its effectiveness to predict latency and future work.