High-performance switching architectures for optical networks

The need for high bandwidth, due to the explosion of new multi\-media-oriented IP-based services, as well as increasing broadband access requirements is leading to the need of flexible and highly reconfigurable optical networks. While transmission bandwidth does not represent a limit due to the huge bandwidth provided by optical fibers and Dense Wavelength Division Multiplexing (DWDM) technology, the electronic switching nodes in the core of the network represent the bottleneck in terms of speed and capacity for the overall network. For this reason DWDM technology must be exploited not only for data transport but also for switching operations. In this Ph.D. thesis solutions for photonic packet switches, a flexible alternative with respect to circuit-switched optical networks are proposed. In particular solutions based on devices and components that are expected to mature in the near future are proposed, with the aim to limit the employment of complex components. The work presented here is the result of part of the research activities performed by the Networks Research Group at the Department of Electronics, Computer Science and Systems (DEIS) of the University of Bologna, Italy. In particular, the work on optical packet switching has been carried on within three relevant research projects: the e-Photon/ONe and e-Photon/ONe+ projects, funded by the European Union in the Sixth Framework Programme, and the national project OSATE funded by the Italian Ministry of Education, University and Scientific Research. The rest of the work is organized as follows. Chapter 1 gives a brief introduction to network context and contention resolution in photonic packet switches. Chapter 2 presents different strategies for contention resolution in wavelength domain. Chapter 3 illustrates a possible implementation of one of the schemes proposed in chapter 2. Then, chapter 4 presents multi-fiber switches, which employ jointly wavelength and space domains to solve contention. Chapter 5 shows buffered switches, to solve contention in time domain besides wavelength domain. Finally chapter 6 presents a cost model to compare different switch architectures in terms of cost.

Dynamic power management: from portable devices to high performance computing

Electronic applications are nowadays converging under the umbrella of the cloud computing vision. The future ecosystem of information and communication technology is going to integrate clouds of portable clients and embedded devices exchanging information, through the internet layer, with processing clusters of servers, data-centers and high performance computing systems. Even thus the whole society is waiting to embrace this revolution, there is a backside of the story. Portable devices require battery to work far from the power plugs and their storage capacity does not scale as the increasing power requirement does. At the other end processing clusters, such as data-centers and server farms, are build upon the integration of thousands multiprocessors. For each of them during the last decade the technology scaling has produced a dramatic increase in power density with significant spatial and temporal variability. This leads to power and temperature hot-spots, which may cause non-uniform ageing and accelerated chip failure. Nonetheless all the heat removed from the silicon translates in high cooling costs. Moreover trend in ICT carbon footprint shows that run-time power consumption of the all spectrum of devices accounts for a significant slice of entire world carbon emissions. This thesis work embrace the full ICT ecosystem and dynamic power consumption concerns by describing a set of new and promising system levels resource management techniques to reduce the power consumption and related issues for two corner cases: Mobile Devices and High Performance Computing.

Heterogeneous Multi-core Architectures for High Performance Computing

This thesis deals with heterogeneous architectures in standard workstations. Heterogeneous architectures represent an appealing alternative to traditional supercomputers because they are based on commodity components fabricated in large quantities. Hence their price-performance ratio is unparalleled in the world of high performance computing (HPC). In particular, different aspects related to the performance and consumption of heterogeneous architectures have been explored. The thesis initially focuses on an efficient implementation of a parallel application, where the execution time is dominated by an high number of floating point instructions. Then the thesis touches the central problem of efficient management of power peaks in heterogeneous computing systems. Finally it discusses a memory-bounded problem, where the execution time is dominated by the memory latency. Specifically, the following main contributions have been carried out: A novel framework for the design and analysis of solar field for Central Receiver Systems (CRS) has been developed. The implementation based on desktop workstation equipped with multiple Graphics Processing Units (GPUs) is motivated by the need to have an accurate and fast simulation environment for studying mirror imperfection and non-planar geometries. Secondly, a power-aware scheduling algorithm on heterogeneous CPU-GPU architectures, based on an efficient distribution of the computing workload to the resources, has been realized. The scheduler manages the resources of several computing nodes with a view to reducing the peak power. The two main contributions of this work follow: the approach reduces the supply cost due to high peak power whilst having negligible impact on the parallelism of computational nodes. from another point of view the developed model allows designer to increase the number of cores without increasing the capacity of the power supply unit. Finally, an implementation for efficient graph exploration on reconfigurable architectures is presented. The purpose is to accelerate graph exploration, reducing the number of random memory accesses.

Analysis and design of high performance multiphase electric drives for vehicle and aircraft applications

The first part of this thesis has focused on the construction of a twelve-phase asynchronous machine for More Electric Aircraft (MEA) applications. In fact, the aerospace world has found in electrification the way to improve the efficiency, reliability and maintainability of an aircraft. This idea leads to the aircraft a new management and distribution of electrical services. In this way is possible to remove or to reduce the hydraulic, mechanical and pneumatic systems inside the aircraft. The second part of this dissertation is dedicated on the enhancement of the control range of matrix converters (MCs) operating with non-unity input power factor and, at the same time, on the reduction of the switching power losses. The analysis leads to the determination in closed form of a modulation strategy that features a control range, in terms of output voltage and input power factor, that is greater than that of the traditional strategies under the same operating conditions, and a reduction in the switching power losses.

Advanced lithium and lithium-ion rechargeable batteries for automotive applications

The worldwide demand for a clean and low-fuel-consuming transport promotes the development of safe, high energy and power electrochemical storage and conversion systems. Lithium-ion batteries (LIBs) are considered today the best technology for this application as demonstrated by the recent interest of automotive industry in hybrid (HEV) and electric vehicles (EV) based on LIBs. This thesis work, starting from the synthesis and characterization of electrode materials and the use of non-conventional electrolytes, demonstrates that LIBs with novel and safe electrolytes and electrode materials meet the targets of specific energy and power established by U.S.A. Department of Energy (DOE) for automotive application in HEV and EV. In chapter 2 is reported the origin of all chemicals used, the description of the instruments used for synthesis and chemical-physical characterizations, the electrodes preparation, the batteries configuration and the electrochemical characterization procedure of electrodes and batteries. Since the electrolyte is the main critical point of a battery, in particular in large- format modules, in chapter 3 we focused on the characterization of innovative and safe electrolytes based on ionic liquids (characterized by high boiling/decomposition points, thermal and electrochemical stability and appreciable conductivity) and mixtures of ionic liquid with conventional electrolyte. In chapter 4 is discussed the microwave accelerated sol–gel synthesis of the carbon- coated lithium iron phosphate (LiFePO 4 -C), an excellent cathode material for LIBs thanks to its intrinsic safety and tolerance to abusive conditions, which showed excellent electrochemical performance in terms of specific capacity and stability. In chapter 5 are presented the chemical-physical and electrochemical characterizations of graphite and titanium-based anode materials in different electrolytes. We also characterized a new anodic material, amorphous SnCo alloy, synthetized with a nanowire morphology that showed to strongly enhance the electrochemical stability of the material during galvanostatic full charge/discharge cycling. Finally, in chapter 6, are reported different types of batteries, assembled using the LiFePO 4 -C cathode material, different anode materials and electrolytes, characterized by deep galvanostatic charge/discharge cycles at different C-rates and by test procedures of the DOE protocol for evaluating pulse power capability and available energy. First, we tested a battery with the innovative cathode material LiFePO 4 -C and conventional graphite anode and carbonate-based electrolyte (EC DMC LiPF 6 1M) that demonstrated to surpass easily the target for power-assist HEV application. Given that the big concern of conventional lithium-ion batteries is the flammability of highly volatile organic carbonate- based electrolytes, we made safe batteries with electrolytes based on ionic liquid (IL). In order to use graphite anode in IL electrolyte we added to the IL 10% w/w of vinylene carbonate (VC) that produces a stable SEI (solid electrolyte interphase) and prevents the graphite exfoliation phenomenon. Then we assembled batteries with LiFePO 4 -C cathode, graphite anode and PYR 14 TFSI 0.4m LiTFSI with 10% w/w of VC that overcame the DOE targets for HEV application and were stable for over 275 cycles. We also assembled and characterized ―high safety‖ batteries with electrolytes based on pure IL, PYR 14 TFSI with 0.4m LiTFSI as lithium salt, and on mixture of this IL and standard electrolyte (PYR 14 TFSI 50% w/w and EC DMC LiPF 6 50% w/w), using titanium-based anodes (TiO 2 and Li 4 Ti 5 O 12 ) that are commonly considered safer than graphite in abusive conditions. The batteries bearing the pure ionic liquid did not satisfy the targets for HEV application, but the batteries with Li 4 Ti 5 O 12 anode and 50-50 mixture electrolyte were able to surpass the targets. We also assembled and characterized a lithium battery (with lithium metal anode) with a polymeric electrolyte based on poly-ethilenoxide (PEO 20 – LiCF 3 SO 3 +10%ZrO 2 ), which satisfied the targets for EV application and showed a very impressive cycling stability. In conclusion, we developed three lithium-ion batteries of different chemistries that demonstrated to be suitable for application in power-assist hybrid vehicles: graphite/EC DMC LiPF 6 /LiFePO 4 -C, graphite/PYR 14 TFSI 0.4m LiTFSI with 10% VC/LiFePO 4 -C and Li 4 T i5 O 12 /PYR 14 TFSI 50%-EC DMC LiPF 6 50%/LiFePO 4 -C. We also demonstrated that an all solid-state polymer lithium battery as Li/PEO 20 –LiCF 3 SO 3 +10%ZrO 2 /LiFePO 4 -C is suitable for application on electric vehicles. Furthermore we developed a promising anodic material alternative to the graphite, based on SnCo amorphous alloy.

Variability-tolerant High-reliability Multicore Platforms

Next generation electronic devices have to guarantee high performance while being less power-consuming and highly reliable for several application domains ranging from the entertainment to the business. In this context, multicore platforms have proven the most efficient design choice but new challenges have to be faced. The ever-increasing miniaturization of the components produces unexpected variations on technological parameters and wear-out characterized by soft and hard errors. Even though hardware techniques, which lend themselves to be applied at design time, have been studied with the objective to mitigate these effects, they are not sufficient; thus software adaptive techniques are necessary. In this thesis we focus on multicore task allocation strategies to minimize the energy consumption while meeting performance constraints. We firstly devise a technique based on an Integer Linear Problem formulation which provides the optimal solution but cannot be applied on-line since the algorithm it needs is time-demanding; then we propose a sub-optimal technique based on two steps which can be applied on-line. We demonstrate the effectiveness of the latter solution through an exhaustive comparison against the optimal solution, state-of-the-art policies, and variability-agnostic task allocations by running multimedia applications on the virtual prototype of a next generation industrial multicore platform. We also face the problem of the performance and lifetime degradation. We firstly focus on embedded multicore platforms and propose an idleness distribution policy that increases core expected lifetimes by duty cycling their activity; then, we investigate the use of micro thermoelectrical coolers in general-purpose multicore processors to control the temperature of the cores at runtime with the objective of meeting lifetime constraints without performance loss.