Doctor of Philosophy

dissertationLow-cost wireless embedded systems can make radio channel measurements for the purposes of radio localization, synchronization, and breathing monitoring. Most of those systems measure the radio channel via the received signal strength indicator (RSSI), which is widely available on inexpensive radio transceivers. However, the use of standard RSSI imposes multiple limitations on the accuracy and reliability of such systems; moreover, higher accuracy is only accessible with very high-cost systems, both in bandwidth and device costs. On the other hand, wireless devices also rely on synchronized notion of time to coordinate tasks (transmit, receive, sleep, etc.), especially in time-based localization systems. Existing solutions use multiple message exchanges to estimate time offset and clock skew, which further increases channel utilization. In this dissertation, the design of the systems that use RSSI for device-free localization, device-based localization, and breathing monitoring applications are evaluated. Next, the design and evaluation of novel wireless embedded systems are introduced to enable more fine-grained radio signal measurements to the application. I design and study the effect of increasing the resolution of RSSI beyond the typical 1 dB step size, which is the current standard, with a couple of example applications: breathing monitoring and gesture recognition. Lastly, the Stitch architecture is then proposed to allow the frequency and time synchronization of multiple nodes' clocks. The prototype platform, Chronos, implements radio frequency synchronization (RFS), which accesses complex baseband samples from a low-power low-cost narrowband radio, estimates the carrier frequency offset, and iteratively drives the difference between two nodes' main local oscillators (LO) to less than 3 parts per billion (ppb). An optimized time synchronization and ranging protocols (EffToF) is designed and implemented to achieve the same timing accuracy as the state-of-the-art but with 59% less utilization of the UWB channel. Based on this dissertation, I could foresee Stitch and RFS further improving the robustness of communications infrastructure to GPS jamming, allow exploration of applications such as distributed beamforming and MIMO, and enable new highly-synchronous wireless sensing and actuation systems

Signal Processing for Caching Networks and Non-volatile Memories

The recent information explosion has created a pressing need for faster and more reliable data storage and transmission schemes. This thesis focuses on two systems: caching networks and non-volatile storage systems. It proposes network protocols to improve the efficiency of information delivery and signal processing schemes to reduce errors at the physical layer as well. This thesis first investigates caching and delivery strategies for content delivery networks. Caching has been investigated as a useful technique to reduce the network burden by prefetching some contents during o˙-peak hours. Coded caching [1] proposed by Maddah-Ali and Niesen is the foundation of our algorithms and it has been shown to be a useful technique which can reduce peak traffic rates by encoding transmissions so that different users can extract different information from the same packet. Content delivery networks store information distributed across multiple servers, so as to balance the load and avoid unrecoverable losses in case of node or disk failures. On one hand, distributed storage limits the capability of combining content from different servers into a single message, causing performance losses in coded caching schemes. But, on the other hand, the inherent redundancy existing in distributed storage systems can be used to improve the performance of those schemes through parallelism. This thesis proposes a scheme combining distributed storage of the content in multiple servers and an efficient coded caching algorithm for delivery to the users. This scheme is shown to reduce the peak transmission rate below that of state-of-the-art algorithms

Estudo microscópico local dos efeitos magneto, eletro e elastocalóricos

Determining and acting on thermo-physical properties at the nanoscale is essential for understanding/managing heat distribution in micro/nanostructured materials and miniaturized devices. Adequate thermal nano-characterization techniques are required to control device thermal behavior and address thermal issues deterrent to their desired performance. In this context, Scanning Thermal Microscopy (SThM) is a high spatial resolution probing and acting technique based on Atomic Force Microscopy (AFM) using a nano-probe as thermometer and resistive heater. Enabling direct observation and mapping of thermal properties, it is becoming a powerful tool in several fields, from material science to device thermal management. The mechanisms driving heat transfer at the nano/microscopic-scale are essential for device development and optimization, particularly when using first-order phase transition materials exhibiting coupled structural and ferrocaloric effects, as Ni-Mn-Ga, BaTiO3 and Ni-Ti (magnetocaloric, electrocaloric, elastocaloric), researched for multifunctional actuating, sensing and solid-state heat-management technologies (cooling) applications. This work aims to raise the understanding of the interplay of these effects by local probing of thermal properties, combined with magnetic, structural, and electric studies: - local thermomagnetic, thermoelectric and thermoelastic phenomena by scanning thermal microscopy (SThM) and microscopic-infrared-thermography - local actuation by heating performed by SThM-tip to evaluate thermal conductivity, phase change contrast and map sample dynamic inhomogeneities. - time-dependence of local thermal phenomena correlated with thermal diffusion processes across phase transformations for Ni-Mn-Ga, BaTiO3 and Ni-Ti. - local probing of “thermal return-point-memory” and avalanche effects on Ni-Mn- Ga films produced by temperature cycling. One of our most significant results consisted in finding that locally inducing the structural transformation in Ni-Mn-Ga thin films results in much wider martensitic transformation temperatures (TM) intervals than for overall structural transformation inducing, within a same micrometric area of the material. We also observed large differences in the behavior of the magnetocaloric effect in bulk Co-doped Ni-Mn-Ga on heating and cooling, at the microscopic scale, in the vicinity of the structural transformation. Mapping of the contribution of each microscopic area of the sample to the effect was achieved.Determinar e atuar nas propriedades termofísicas à nanoescala é essencial para compreender/gerir a distribuição térmica de calor em materiais e dispositivos miniaturizados. Técnicas de nanocaracterização térmica são necessárias para analisar e controlar o comportamento térmico de dispositivos, evitando prejuízos à performance desejada. Neste contexto, a microscopia de varrimento térmico (SThM) é uma técnica de sondagem e atuação de elevada resolução espacial baseada na microscopia de força atómica (AFM), utilizando uma nano-sonda como termómetro e elemento resistivo de aquecimento. Permitindo a observação direta e o mapeamento de propriedades térmicas, esta é uma ferramenta poderosa em várias áreas, desde a ciência de materiais até à gestão térmica em dispositivos. Os mecanismos responsáveis pela transferência de calor à nano/microescala são essenciais para desenvolver e otimizar dispositivos, particularmente aquando da utilização de materiais que sofrem transições de fase de primeira ordem, que exibem efeitos ferrocalóricos (magnetocalórico, eletrocalórico e elastocalórico) e estruturais acoplados, tais como o Ni-Mn-Ga, o BaTiO3 e o Ni-Ti, investigados para aplicações de atuação, deteção e tecnologias de gestão térmica em estado sólido (arrefecimento). Este trabalho pretende aumentar a compreensão da interação destes efeitos através da sondagem local das propriedades térmicas, combinada com estudos magnéticos, eletricos e estruturais: - fenómenos termomagnéticos, termoeletricos e termoelasticos locais por microscópio de varrimento térmico (SThM) e termografia de infravermelhos. - atuação local por aquecimento levada a cabo pela sonda SThM para avaliar condutividade térmica, contraste de mudança de fase e mapeamento de inomogeneidades dinâmicas de amostras. - dependência temporal de fenómenos térmicos locais correlacionados com processos de difusão térmica através de transformações de fase para o Ni-Mn- Ga, o BaTiO3 e o Ni-Ti. - sondagem local de “memória de ponto de retorno térmica” e efeitos de avalanche em filmes de Ni-Mn-Ga provocados por ciclagens térmicas. Um dos resultados mais significativos consistiu na constatação de que a indução local da transformação estrutural em filmes finos de Ni-Mn-Ga resulta em intervalos muito mais alargados de temperaturas de transformação martensítica do que no caso de indução global da transformação estrutural, numa mesma área microscópica do material. Observámos ainda grandes diferenças no comportamento do efeito magnetocalórico no Ni-Mn-Ga dopado com Co, em aquecimento e arrefecimento, à escala microscópica, na vizinhança da transformação estrutural. Foi realizado com sucesso o mapeamento da contribuição para o efeito de cada área microscópica da amostra.Programa Doutoral em Engenharia Físic

A Scalable Flash-Based Hardware Architecture for the Hierarchical Temporal Memory Spatial Pooler

Hierarchical temporal memory (HTM) is a biomimetic machine learning algorithm focused upon modeling the structural and algorithmic properties of the neocortex. It is comprised of two components, realizing pattern recognition of spatial and temporal data, respectively. HTM research has gained momentum in recent years, leading to both hardware and software exploration of its algorithmic formulation. Previous work on HTM has centered on addressing performance concerns; however, the memory-bound operation of HTM presents significant challenges to scalability. In this work, a scalable flash-based storage processor unit, Flash-HTM (FHTM), is presented along with a detailed analysis of its potential scalability. FHTM leverages SSD flash technology to implement the HTM cortical learning algorithm spatial pooler. The ability for FHTM to scale with increasing model complexity is addressed with respect to design footprint, memory organization, and power efficiency. Additionally, a mathematical model of the hardware is evaluated against the MNIST dataset, yielding 91.98% classification accuracy. A fully custom layout is developed to validate the design in a TSMC 180nm process. The area and power footprints of the spatial pooler are 30.538mm2 and 5.171mW, respectively. Storage processor units have the potential to be viable platforms to support implementations of HTM at scale

Energy-efficient architectures for chip-scale networks and memory systems using silicon-photonics technology

Today's supercomputers and cloud systems run many data-centric applications such as machine learning, graph algorithms, and cognitive processing, which have large data footprints and complex data access patterns. With computational capacity of large-scale systems projected to rise up to 50GFLOPS/W, the target energy-per-bit budget for data movement is expected to reach as low as 0.1pJ/bit, assuming 200bits/FLOP for data transfers. This tight energy budget impacts the design of both chip-scale networks and main memory systems. Conventional electrical links used in chip-scale networks (0.5-3pJ/bit) and DRAM systems used in main memory (>30pJ/bit) fail to provide sustained performance at low energy budgets. This thesis builds on the promising research on silicon-photonic technology to design system architectures and system management policies for chip-scale networks and main memory systems. The adoption of silicon-photonic links as chip-scale networks, however, is hampered by the high sensitivity of optical devices towards thermal and process variations. These device sensitivities result in high power overheads at high-speed communications. Moreover, applications differ in their resource utilization, resulting in application-specific thermal profiles and bandwidth needs. Similarly, optically-controlled memory systems designed using conventional electrical-based architectures require additional circuitry for electrical-to-optical and optical-to-electrical conversions within memory. These conversions increase the energy and latency per memory access. Due to these issues, chip-scale networks and memory systems designed using silicon-photonics technology leave much of their benefits underutilized. This thesis argues for the need to rearchitect memory systems and redesign network management policies such that they are aware of the application variability and the underlying device characteristics of silicon-photonic technology. We claim that such a cross-layer design enables a high-throughput and energy-efficient unified silicon-photonic link and main memory system. This thesis undertakes the cross-layer design with silicon-photonic technology in two fronts. First, we study the varying network bandwidth requirements across different applications and also within a given application. To address this variability, we develop bandwidth allocation policies that account for application needs and device sensitivities to ensure power-efficient operation of silicon-photonic links. Second, we design a novel architecture of an optically-controlled main memory system that is directly interfaced with silicon-photonic links using a novel read and write access protocol. Such a system ensures low-energy and high-throughput access from the processor to a high-density memory. To further address the diversity in application memory characteristics, we explore heterogeneous memory systems with multiple memory modules that provide varied power-performance benefits. We design a memory management policy for such systems that allocates pages at the granularity of memory objects within an application

LWF Gender Justice Policy: Tool for ongoing reformation of Lutheran theology on women in the Malagasy Lutheran Church (MLC)

God created human beings in his image. Unfortunately, the fallen humanity broken its original relationship to God, destroyed its rapport to each other and failed to take care of the creation. However, the salvation work of Christ in the cross only restored the human dignity and restored these damaged connections. Thus, the new children of God testimony the renewal work of Christ, by continuing Christ’s salvation work through respecting God and valuing each other. The Lutheran World Federation (LWF) Gender Justice Policy (GJP) is a tool to accompany its member churches to respect the equality of women and men. As a communion of churches in the Lutheran tradition, the LWF take for granted the "sola scriptura" as "norma normans" and the "solus Christus" as "hermeneutical key”. With the diverse interpretations of Martin Luther and his follower’s theology on women, the LWF conducted a critical study of biblical texts to re-affirm the equality of all human beings. It is using the contextual approach as a tool to interpret and implement in its churches different contexts the ten principles and the methodologies of its policy. Offered as a tool to advocate and encourage equal participation of men and women, both in the church and in the society, the LWF GJP was translated in many local languages. The Malagasy Lutheran Church (MLC) is in its final process of translation and publication of the document. Right interpretation of the biblical foundations of equality of human beings and correct use of the hermeneutical tools for the implementations are provided by this paper. They result from the study of the LWF GJP document. The implementation is improved by the learning from the effective employment of the GJP in the other LWF member churches.publishedVersio

Building Bridges for Women Through Service-Learning: Bringing Students and Communities Together To Combat Domestic Violence in Honduras

This thesis defines service-learning and domestic violence, while describing how bringing students and communities together through service-learning courses can build and has already built bridges for victims of violence against women. Collaboration is essential in the quest to raise awareness about domestic violence through education. This thesis will demonstrate through data and photojournalism this collaboration between students of SPA/MLC Service-Learning Classes of UMaine from 2006 through to and including 2011. As the themes in this thesis develop the reader will also begin to question what lies just beyond our borders and behind closed doors for women of the twenty-first century. There are two compelling quotes that say in a few words what this thesis is all about. Isaac Newton stated, “We build too many walls and not enough bridges.” We (women) are often lost in society behind those walls, living in the shadows of forceful and oblivious patriarchal societies and communities. In order for these women to take a stand and feel empowered to demand equality, say nothing about their human rights, the entire community needs education: education of the what and why and when of violence against women, and then the how and where and who of combatting such violence against women. First we have to ask ourselves: What is violence against women? Why does violence against women happen? When do acts of violence against women occur? And then, we need to follow-up with: How can violence against women be prevented or greatly reduced? Where do we go from here? Where do we start? Who needs to take responsibility and who needs to step up and lead the society and communities toward equality for women and intolerance for violence against women? Violence against women is being perpetrated each and every day, but building bridges through education is a fundamental and vital component in combating this societal malaise. As Ralph Ellison points out, “Education is all a matter of building bridges.” “We build too many walls and not enough bridges.” Isaac Newton “Education is all a matter of building bridges.” Ralph Elliso

Fault-tolerant computer study

A set of building block circuits is described which can be used with commercially available microprocessors and memories to implement fault tolerant distributed computer systems. Each building block circuit is intended for VLSI implementation as a single chip. Several building blocks and associated processor and memory chips form a self checking computer module with self contained input output and interfaces to redundant communications buses. Fault tolerance is achieved by connecting self checking computer modules into a redundant network in which backup buses and computer modules are provided to circumvent failures. The requirements and design methodology which led to the definition of the building block circuits are discussed