Coded slotted aloha with multipacket reception over block fading channels (for satellite networks)

Random access (RA) protocols are normally used in a satellite networks for initial terminal access and are particularly effective since no coordination is required. On the other hand, contention resolution diversity slotted Aloha (CRDSA), irregular repetition slotted Aloha (IRSA) and coded slotted Aloha (CSA) has shown to be more efficient than classic RA schemes as slotted Aloha, and can be exploited also when short packets transmissions are done over a shared medium. In particular, they relies on burst repetition and on successive interference cancellation (SIC) applied at the receiver. The SIC process can be well described using a bipartite graph representation and exploiting tools used for analyze iterative decoding. The scope of my Master Thesis has been to described the performance of such RA protocols when the Rayleigh fading is taken into account. In this context, each user has the ability to correctly decode a packet also in presence of collision and when SIC is considered this may result in multi-packet reception. Analysis of the SIC procedure under Rayleigh fading has been analytically derived for the asymptotic case (infinite frame length), helping the analysis of both throughput and packet loss rates. An upper bound of the achievable performance has been analytically obtained. It can be show that in particular channel conditions the throughput of the system can be greater than one packets per slot which is the theoretical limit of the Collision Channel case.

Determining the roles of dendritic cells and ICAM-1 in the transpresentation of IL-15 to CD8 T cells

The maintenance and generation of memory CD8 T cells is dependent on the cytokine IL-15. IL-15 is delivered by a novel mechanism termed transpresentation: IL-15 is presented by a cell expressing IL-15Ralpha to the CD8 T cell which responds via IL-2Rbeta/gammac. The identity of what cells transpresent IL-15 to support the survival and homeostatic proliferation of memory CD8 T cells is unknown. Using a transgenic mouse model that limits IL-15 transpresentation to DCs, I have demonstrated that DCs transpresent IL-15 to CD8 T cells. DCs transpresent IL-15 to CD8 T cells during the contraction of an immune response and also drive homeostatic proliferation of memory CD8 T cells. Additionally, I identified a role for ICAM-1 in promoting homeostatic proliferation. Wt memory CD8 T cells displayed impaired homeostatic proliferation in ICAM-1-/- hosts but not in models of acute IL-15-driven proliferation. In this way, the role of ICAM-1 in IL-15 transpresentation resembles the role for ICAM-1 in antigenpresentation: where antigen or IL-15 is limited, adhesion molecules are important for generating maximal responses. In vitro cultures between CD8 T cells and bone marrowdifferentiated DCs (BMDC) activated with a TLR agonist established a model of proliferation and signaling in CD8 T cells that was dependent on IL-15 transpresentation and required ICAM-1 expression by BMDCs. Regarding the expression of IL-15, I demonstrated that in normal mice it is undetectable without stimulation but is elevated in lymphopenic mice, suggesting a role for T cells in regulating IL-15 expression. Overall, these studies have identified many novel aspects of the interaction between DCs and CD8 T cells that were previously unknown. The study of adhesion molecules in IL-15 transpresentation describes a novel role for these well-known adhesion molecules and it will be interesting for future studies to further characterize this relationship for other IL-15-dependent cell types.

Determining the roles of dendritic cells and ICAM-1 in the transpresentation of IL-15 to CD8 T cells

The maintenance and generation of memory CD8 T cells is dependent on the cytokine IL-15. IL-15 is delivered by a novel mechanism termed transpresentation: IL-15 is presented by a cell expressing IL-15Ralpha to the CD8 T cell which responds via IL-2Rbeta/gammac. The identity of what cells transpresent IL-15 to support the survival and homeostatic proliferation of memory CD8 T cells is unknown. Using a transgenic mouse model that limits IL-15 transpresentation to DCs, I have demonstrated that DCs transpresent IL-15 to CD8 T cells. DCs transpresent IL-15 to CD8 T cells during the contraction of an immune response and also drive homeostatic proliferation of memory CD8 T cells. Additionally, I identified a role for ICAM-1 in promoting homeostatic proliferation. Wt memory CD8 T cells displayed impaired homeostatic proliferation in ICAM-1-/- hosts but not in models of acute IL-15-driven proliferation. In this way, the role of ICAM-1 in IL-15 transpresentation resembles the role for ICAM-1 in antigenpresentation: where antigen or IL-15 is limited, adhesion molecules are important for generating maximal responses. In vitro cultures between CD8 T cells and bone marrowdifferentiated DCs (BMDC) activated with a TLR agonist established a model of proliferation and signaling in CD8 T cells that was dependent on IL-15 transpresentation and required ICAM-1 expression by BMDCs. Regarding the expression of IL-15, I demonstrated that in normal mice it is undetectable without stimulation but is elevated in lymphopenic mice, suggesting a role for T cells in regulating IL-15 expression. Overall, these studies have identified many novel aspects of the interaction between DCs and CD8 T cells that were previously unknown. The study of adhesion molecules in IL-15 transpresentation describes a novel role for these well-known adhesion molecules and it will be interesting for future studies to further characterize this relationship for other IL-15-dependent cell types.

Computación celular con membranas: un estudio de modelos de cómputo bioinspirados

Los resultados presentados en la memoria de esta tesis doctoral se enmarcan en la denominada computación celular con membranas una nueva rama de investigación dentro de la computación natural creada por Gh. Paun en 1998, de ahí que habitualmente reciba el nombre de sistemas P. Este nuevo modelo de cómputo distribuido está inspirado en la estructura y funcionamiento de la célula. El objetivo de esta tesis ha sido analizar el poder y la eficiencia computacional de estos sistemas de computación celular. En concreto, se han analizado dos tipos de sistemas P: por un lado los sistemas P de neuronas de impulsos, y por otro los sistemas P con proteínas en las membranas. Para el primer tipo, los resultados obtenidos demuestran que es posible que estos sistemas mantengan su universalidad aunque muchas de sus características se limiten o incluso se eliminen. Para el segundo tipo, se analiza la eficiencia computacional y se demuestra que son capaces de resolver problemas de la clase de complejidad ESPACIO-P (PSPACE) en tiempo polinómico. Análisis del poder computacional: Los sistemas P de neuronas de impulsos (en adelante SN P, acrónimo procedente del inglés «Spiking Neural P Systems») son sistemas inspirados en el funcionamiento neuronal y en la forma en la que los impulsos se propagan por las redes sinápticas. Los SN P bio-inpirados poseen un numeroso abanico de características que ha cen que dichos sistemas sean universales y por tanto equivalentes, en poder computacional, a una máquina de Turing. Estos sistemas son potentes a nivel computacional, pero tal y como se definen incorporan numerosas características, quizás demasiadas. En (Ibarra et al. 2007) se demostró que en estos sistemas sus funcionalidades podrían ser limitadas sin comprometer su universalidad. Los resultados presentados en esta memoria son continuistas con la línea de trabajo de (Ibarra et al. 2007) y aportan nuevas formas normales. Esto es, nuevas variantes simplificadas de los sistemas SN P con un conjunto mínimo de funcionalidades pero que mantienen su poder computacional universal. Análisis de la eficiencia computacional: En esta tesis se ha estudiado la eficiencia computacional de los denominados sistemas P con proteínas en las membranas. Se muestra que este modelo de cómputo es equivalente a las máquinas de acceso aleatorio paralelas (PRAM) o a las máquinas de Turing alterantes ya que se demuestra que un sistema P con proteínas, es capaz de resolver un problema ESPACIOP-Completo como el QSAT(problema de satisfacibilidad de fórmulas lógicas cuantificado) en tiempo polinómico. Esta variante de sistemas P con proteínas es muy eficiente gracias al poder de las proteínas a la hora de catalizar los procesos de comunicación intercelulares. ABSTRACT The results presented at this thesis belong to membrane computing a new research branch inside of Natural computing. This new branch was created by Gh. Paun on 1998, hence usually receives the name of P Systems. This new distributed computing model is inspired on structure and functioning of cell. The aim of this thesis is to analyze the efficiency and computational power of these computational cellular systems. Specifically there have been analyzed two different classes of P systems. On the one hand it has been analyzed the Neural Spiking P Systems, and on the other hand it has been analyzed the P systems with proteins on membranes. For the first class it is shown that it is possible to reduce or restrict the characteristics of these kind of systems without loss of computational power. For the second class it is analyzed the computational efficiency solving on polynomial time PSACE problems. Computational Power Analysis: The spiking neural P systems (SN P in short) are systems inspired by the way of neural cells operate sending spikes through the synaptic networks. The bio-inspired SN Ps possess a large range of features that make these systems to be universal and therefore equivalent in computational power to a Turing machine. Such systems are computationally powerful, but by definition they incorporate a lot of features, perhaps too much. In (Ibarra et al. in 2007) it was shown that their functionality may be limited without compromising its universality. The results presented herein continue the (Ibarra et al. 2007) line of work providing new formal forms. That is, new SN P simplified variants with a minimum set of functionalities but keeping the universal computational power. Computational Efficiency Analisys: In this thesis we study the computational efficiency of P systems with proteins on membranes. We show that this computational model is equivalent to parallel random access machine (PRAM) or alternating Turing machine because, we show P Systems with proteins can solve a PSPACE-Complete problem as QSAT (Quantified Propositional Satisfiability Problem) on polynomial time. This variant of P Systems with proteins is very efficient thanks to computational power of proteins to catalyze inter-cellular communication processes.

Improved Techniques for Video Compression and Communication

Thesis (Ph.D.)--University of Washington, 2016-06

Efficiency improvements to the Groupe Special Mobile (GSM) digital mobile radio system

Groupe Spécial Mobile (GSM) has been developed as the pan-European second generation of digital mobile systems. GSM operates in the 900 MHz frequency band and employs digital technology instead of the analogue technology of its predecessors. Digital technology enables the GSM system to operate in much smaller zones in comparison with the analogue systems. The GSM system will offer greater roaming facilities to its subscribers, extended throughout the countries that have installed the system. The GSM system could be seen as a further enhancement to European integration. GSM has adopted a contention-based protocol for multipoint-to-point transmission. In particular, the slotted-ALOHA medium access protocol is used to coordinate the transmission of the channel request messages between the scattered mobile stations. Collision still happens when more than one mobile station having the same random reference number attempts to transmit on the same time-slot. In this research, a modified version of this protocol has been developed in order to reduce the number of collisions and hence increase the random access channel throughput compared to the existing protocol. The performance evaluation of the protocol has been carried out using simulation methods. Due to the growing demand for mobile radio telephony as well as for data services, optimal usage of the scarce availability radio spectrum is becoming increasingly important. In this research, a protocol has been developed whereby the number of transmitted information packets over the GSM system is increased without any additional increase of the allocated radio spectrum. Simulation results are presented to show the improvements achieved by the proposed protocol. Cellular mobile radio networks commonly respond to an increase in the service demand by using smaller coverage areas. As a result, the volume of the signalling exchanges increases. In this research, a proposal for interconnecting the various entitles of the mobile radio network over the future broadband networks based on the IEEE 802.6 Metropolitan Area Network (MAN) is outlined. Simulation results are presented to show the benefits achieved by interconnecting these entities over the broadband Networks.

Performance modelling and analysis of multiple coexisting IEEE 802.15.4 wireless sensor networks

With the features of low-power and flexible networking capabilities IEEE 802.15.4 has been widely regarded as one strong candidate of communication technologies for wireless sensor networks (WSNs). It is expected that with an increasing number of deployments of 802.15.4 based WSNs, multiple WSNs could coexist with full or partial overlap in residential or enterprise areas. As WSNs are usually deployed without coordination, the communication could meet significant degradation with the 802.15.4 channel access scheme, which has a large impact on system performance. In this thesis we are motivated to investigate the effectiveness of 802.15.4 networks supporting WSN applications with various environments, especially when hidden terminals are presented due to the uncoordinated coexistence problem. Both analytical models and system level simulators are developed to analyse the performance of the random access scheme specified by IEEE 802.15.4 medium access control (MAC) standard for several network scenarios. The first part of the thesis investigates the effectiveness of single 802.15.4 network supporting WSN applications. A Markov chain based analytic model is applied to model the MAC behaviour of IEEE 802.15.4 standard and a discrete event simulator is also developed to analyse the performance and verify the proposed analytical model. It is observed that 802.15.4 networks could sufficiently support most WSN applications with its various functionalities. After the investigation of single network, the uncoordinated coexistence problem of multiple 802.15.4 networks deployed with communication range fully or partially overlapped are investigated in the next part of the thesis. Both nonsleep and sleep modes are investigated with different channel conditions by analytic and simulation methods to obtain the comprehensive performance evaluation. It is found that the uncoordinated coexistence problem can significantly degrade the performance of 802.15.4 networks, which is unlikely to satisfy the QoS requirements for many WSN applications. The proposed analytic model is validated by simulations which could be used to obtain the optimal parameter setting before WSNs deployments to eliminate the interference risks.

Improving storage performance through layout optimizations

Disk drives are the bottleneck in the processing of large amounts of data used in almost all common applications. File systems attempt to reduce this by storing data sequentially on the disk drives, thereby reducing the access latencies. Although this strategy is useful when data is retrieved sequentially, the access patterns in real world workloads is not necessarily sequential and this mismatch results in storage I/O performance degradation. This thesis demonstrates that one way to improve the storage performance is to reorganize data on disk drives in the same way in which it is mostly accessed. We identify two classes of accesses: static, where access patterns do not change over the lifetime of the data and dynamic, where access patterns frequently change over short durations of time, and propose, implement and evaluate layout strategies for each of these. Our strategies are implemented in a way that they can be seamlessly integrated or removed from the system as desired. We evaluate our layout strategies for static policies using tree-structured XML data where accesses to the storage device are mostly of two kinds—parent-to-child or child-to-sibling. Our results show that for a specific class of deep-focused queries, the existing file system layout policy performs better by 5–54X. For the non-deep-focused queries, our native layout mechanism shows an improvement of 3–127X. To improve performance of the dynamic access patterns, we implement a self-optimizing storage system that performs rearranges popular block accesses on a dedicated partition based on the observed workload characteristics. Our evaluation shows an improvement of over 80% in the disk busy times over a range of workloads. These results show that applying the knowledge of data access patterns for allocation decisions can substantially improve the I/O performance.

Improving Storage Performance Through Layout Optimizations

Disk drives are the bottleneck in the processing of large amounts of data used in almost all common applications. File systems attempt to reduce this by storing data sequentially on the disk drives, thereby reducing the access latencies. Although this strategy is useful when data is retrieved sequentially, the access patterns in real world workloads is not necessarily sequential and this mismatch results in storage I/O performance degradation. This thesis demonstrates that one way to improve the storage performance is to reorganize data on disk drives in the same way in which it is mostly accessed. We identify two classes of accesses: static, where access patterns do not change over the lifetime of the data and dynamic, where access patterns frequently change over short durations of time, and propose, implement and evaluate layout strategies for each of these. Our strategies are implemented in a way that they can be seamlessly integrated or removed from the system as desired. We evaluate our layout strategies for static policies using tree-structured XML data where accesses to the storage device are mostly of two kinds - parent-tochild or child-to-sibling. Our results show that for a specific class of deep-focused queries, the existing file system layout policy performs better by 5-54X. For the non-deep-focused queries, our native layout mechanism shows an improvement of 3-127X. To improve performance of the dynamic access patterns, we implement a self-optimizing storage system that performs rearranges popular block accesses on a dedicated partition based on the observed workload characteristics. Our evaluation shows an improvement of over 80% in the disk busy times over a range of workloads. These results show that applying the knowledge of data access patterns for allocation decisions can substantially improve the I/O performance.

Estudo da densidade de corrente crítica para reversão da magnetização de nanoelementos ferromagnéticos

The discovery that a spin-polarized current is capable of exerting a torque in a ferromagnetic material, through spin transfer, might provide the development of new technological devices that store information via the direction of magnetization. The reduction of current density to revert the magnetization is a primary issue to potential applications on non volatile random access memories (MRAM). We report a theorical study of the dipolar and shape effects on the critical current density for reversal of magnetization, via spin transfer torque (STT), on ferromagnetic nanoelements. The nanostructured system consists on a reference layer, in which the current will be spin-polarized, and a free layer of magnetization reversal. We observed considerable changes on the critical current density as a function of the element’s reversion layer thickness (t = 1.0 nm, 1.5 nm, 2.0 nm e 2.5 nm) and geometry (circular and elliptical), the material kind of the system free layer (Iron and Permalloy) and according to the orientation of the magnetization and the spin polarization with the major axis. We show that the critical current density may be reduced about 50% by reducing the Fe free layer thickness and around 75% when we change the saturation magnetization of circular nanoelements with 2.5 nm of thickness. We still observed a reduction as much as 90% on the current density of reversion for thin nanoelements magnetized along the minor axis direction, using in-plane spin polarization parallel to the magnetization.

Improving minimum rate predictors algorithm for compression of volumetric medical images

Medical imaging technologies are experiencing a growth in terms of usage and image resolution, namely in diagnostics systems that require a large set of images, like CT or MRI. Furthermore, legal restrictions impose that these scans must be archived for several years. These facts led to the increase of storage costs in medical image databases and institutions. Thus, a demand for more efficient compression tools, used for archiving and communication, is arising. Currently, the DICOM standard, that makes recommendations for medical communications and imaging compression, recommends lossless encoders such as JPEG, RLE, JPEG-LS and JPEG2000. However, none of these encoders include inter-slice prediction in their algorithms. This dissertation presents the research work on medical image compression, using the MRP encoder. MRP is one of the most efficient lossless image compression algorithm. Several processing techniques are proposed to adapt the input medical images to the encoder characteristics. Two of these techniques, namely changing the alignment of slices for compression and a pixel-wise difference predictor, increased the compression efficiency of MRP, by up to 27.9%. Inter-slice prediction support was also added to MRP, using uni and bi-directional techniques. Also, the pixel-wise difference predictor was added to the algorithm. Overall, the compression efficiency of MRP was improved by 46.1%. Thus, these techniques allow for compression ratio savings of 57.1%, compared to DICOM encoders, and 33.2%, compared to HEVC RExt Random Access. This makes MRP the most efficient of the encoders under study.

Stability of scheduled multi-access communication over quasi-static flat fading channels with random coding and independent decoding

The stability of scheduled multiaccess communication with random coding and independent decoding of messages is investigated. The number of messages that may be scheduled for simultaneous transmission is limited to a given maximum value, and the channels from transmitters to receiver are quasistatic, flat, and have independent fades. Requests for message transmissions are assumed to arrive according to an i.i.d. arrival process. Then, we show the following: (1) in the limit of large message alphabet size, the stability region has an interference limited information-theoretic capacity interpretation, (2) state-independent scheduling policies achieve this asymptotic stability region, and (3) in the asymptotic limit corresponding to immediate access, the stability region for non-idling scheduling policies is shown to be identical irrespective of received signal powers.

Variable Granularity Access Tracking Scheme for Improving the Performance of Software Transactional Memory

Software transactional memory (STM) has been proposed as a promising programming paradigm for shared memory multi-threaded programs as an alternative to conventional lock based synchronization primitives. Typical STM implementations employ a conflict detection scheme, which works with uniform access granularity, tracking shared data accesses either at word/cache line or at object level. It is well known that a single fixed access tracking granularity cannot meet the conflicting goals of reducing false conflicts without impacting concurrency adversely. A fine grained granularity while improving concurrency can have an adverse impact on performance due to lock aliasing, lock validation overheads, and additional cache pressure. On the other hand, a coarse grained granularity can impact performance due to reduced concurrency. Thus, in general, a fixed or uniform granularity access tracking (UGAT) scheme is application-unaware and rarely matches the access patterns of individual application or parts of an application, leading to sub-optimal performance for different parts of the application(s). In order to mitigate the disadvantages associated with UGAT scheme, we propose a Variable Granularity Access Tracking (VGAT) scheme in this paper. We propose a compiler based approach wherein the compiler uses inter-procedural whole program static analysis to select the access tracking granularity for different shared data structures of the application based on the application's data access pattern. We describe our prototype VGAT scheme, using TL2 as our STM implementation. Our experimental results reveal that VGAT-STM scheme can improve the application performance of STAMP benchmarks from 1.87% to up to 21.2%.

A static magnetic memory /

"November 20, 1953"

Memory of past random wave conditions in submarine groundwater discharge

Submarine groundwater discharge (SGD) is an integral part of the hydrological cycle and represents an important aspect of land-ocean interactions. We used a numerical model to simulate flow and salt transport in a nearshore groundwater aquifer under varying wave conditions based on yearlong random wave data sets, including storm surge events. The results showed significant flow asymmetry with rapid response of influxes and retarded response of effluxes across the seabed to the irregular wave conditions. While a storm surge immediately intensified seawater influx to the aquifer, the subsequent return of intruded seawater to the sea, as part of an increased SGD, was gradual. Using functional data analysis, we revealed and quantified retarded, cumulative effects of past wave conditions on SGD including the fresh groundwater and recirculating seawater discharge components. The retardation was characterized well by a gamma distribution function regardless of wave conditions. The relationships between discharge rates and wave parameters were quantifiable by a regression model in a functional form independent of the actual irregular wave conditions. This statistical model provides a useful method for analyzing and predicting SGD from nearshore unconfined aquifers affected by random waves