abstract: It is commonly known that High Performance Computing (HPC) systems are most frequently used by multiple users for batch job, parallel computations. Less well known, however, are the numerous HPC systems servicing data so sensitive that administrators enforce either a) sequential job processing - only one job at a time on the entire system, or b) physical separation - devoting an entire HPC system to a single project until recommissioned. The driving forces behind this type of security are numerous but share the common origin of data so sensitive that measures above and beyond industry standard are used to ensure information security. This paper presents a network security solution that provides information security above and beyond industry standard, yet still enabling multi-user computations on the system. This paper's main contribution is a mechanism designed to enforce high level time division multiplexing of network access (Time Division Multiple Access, or TDMA) according to security groups. By dividing network access into time windows, interactions between applications over the network can be prevented in an easily verifiable way. / Dissertation/Thesis / M.S. Computer Science 2013

In the design of the third generation of multi-media wireless networks, we are primarily concerned with the greatly varying information source rates, the quality requirements of various traffic types, the characteristics of the wireless environment, as well as the complexity and cost. Code Division Multiple Access (CDMA) cellular system is one of the most important candidates for supporting the future universal communications services. The objective of this research is to improve the capacity and the quality of service (QOS), as well as to reduce the complexity of cellular CDMA with integrated services, through improving or optimizing the design of system level operations. To facilitate the system performance and capacity evaluation, the multi-cell multi-user interference is analyzed through a new approach. The area averaged probability density function (PDF) of interference power from one active user is evaluated. The Gamma distribution is proposed for modelling the area averaged PDF of the interference power. An efficient method for evaluating system performance is developed. Differing from the Gaussian approximation, this method is very effective and accurate for both a large number and a small number of users. In this research, differing from the distance membership determination, the statistical effect of handoff is considered. The effects of soft handoff operation on multi-cell multi-user interference are analyzed. Membership statistics which are determined by soft handoff are investigated. A simple binomial model is proposed for modelling the distribution of the number of users belonging to a base station. Considering the call arrival statistics, user membership statistics and a finite number of channels available at a base station, we evaluate the call blocking/dropping rate. The minimum number of channels required at a base-station, which ensures a specified quality of service at a given capacity requirement, is determined. System capacity is further evaluated considering both outage probability limited by interference and call blocking/dropping rate limited by finite number of channels. A pilot assisted channel allocation method is proposed to minimize the number of channels required at a base station. Based on the analysis of a CDMA cellular system with a single traffic type, the design issues in developing a multi-media wireless networks are further discussed. The capacity of a CDMA cellular system with high quality requirements and mixed stream and packet types of traffic is assessed. The impact of the choice of a line rate (bit transmission rate through channel) on the system capacity is investigated. It is also shown that the power allocated to different types of traffic can be optimized to achieve maximum capacity. The optimum power allocation suggests that the power assignments to different traffic types are mainly determined by their quality requirements. / Graduate

Orientador: Leonardo de Souza Mendes / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-04T09:20:09Z (GMT). No. of bitstreams: 1 Inocencio_AnaCarolinaGondim_M.pdf: 3226003 bytes, checksum: 6f0c024fb30ddcc6324cf74855f034f9 (MD5) Previous issue date: 2004 / Resumo: Este projeto de pesquisa desenvolveu um modelo de simulação sobre o ambiente Hydragyrum, baseado no padrão CDMA 2000. Para isto foi necessário estudar este padrão e os protocolos necessários para se desenvolver um modelo de rede, onde o comportamento deste padrão pudesse ser verificado. Foram criados cenários de simulação que possibilitassem a coleta de resultados, bem como que permitisse comprovar a validade do modelo desenvolvido. Ao longo das implementações realizadas, foi possível verificar como deve ser conduzido o estudo de alguma tecnologia, ou mesmo um padrão, para que deste possam ser abstraídas variáveis relevantes aos resultados que se pretende alcançar. Os resultados obtidos foram apresentados em forma de gráfico e demonstraram como o modelo se comporta. Para isto foram analisadas variações do atraso, throughput, atraso e taxa de perda. O modelo implementado servirá como base para futuros projetos de simulação que objetivem o desenvolvimento de modelos baseados em um ambiente sem fio / Abstract: In this research project it was developed a simulation model to the Hydragyrum environment, based on the standard CDMA 2000. For the development, it was necessary to study the standard and the protocols necessary to develop a network model, where the behavior of the standard could be verified. Simulation scenarios have been created to make possible the collection of results to prove the validity of the developed model. Along the implementations that were carried out, it was possible to verify how the study of some technology must be conducted so that one could abstract relevant variables from the results that one intends to obtain. The results were presented in graphical form and they demonstrate what is the model/behaviour. This was achieved throught the analysis of delay variations, throught, end-to-end delay out pecket loss ratio. The implemented model can be bases for future simulations that aim the development of models based on a wireless environment / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

[pt] O desempenho de protocolos de múltiplos acesso em redes de dados, no que diz respeito a parâmetros como vazão, retardado e probabilidade de rejeição de pacotes, representa um dos fatores primordiais na comparação entre diversos tipos de sistemas propostos, no sentido de se buscar uma otimização do uso do canal de transmissão. Tendo em vista a dificuldade de se fazer um modelo analítico que represente bem os protocolos existentes, utilizam-se, normalmente, formulações simplificadas para o cálculo dos parâmetros desejados, ou recorre-se a um modelo de simulação, que necessita de maior tempo de computação pra obtenção dos resultados. Com o objetivo de se obter uma análise mais precisa dos protocolos de múltiplo acesso utilizados em redes de dados foram desenvolvidos modelos a partir de um método proposto por S.M.Meerkov e J.T.Lim. estes modelos consideram estações com buffers transmitindo mensagens que possuem um ou mais pacotes em canais com retardo, utilizando a distribuição de probabilidades do tamanho destas mensagens. É proposta também a retirada da hipótese simplificadora usualmente feita em análises envolvendo o protocolo ALOHA- Segmentado, de que a primeira transmissão de cada pacote é também feita com retardo. Esta metodologia é novamente aplicada para modelar um protocolo híbrido, que combina transmissões utilizando o modo S- ALOHA e um modo de reserva. São apresentados, também, modelos e resultados de simulação para validação dos modelos analíticos propostos. / [en] The performance of multiple access protocols in data networks, whit respect to parameters like throughput, delay and probability of packet rejection, is one of the major factor when comparing different types of proposed systems during an optimization process of the transmission channel. Due to difficulties in developing an analitical model that can make a good representation of the existing protocols, usally simprified formulations are used to evauate the desired parameters, or instead, simulations models are created, requiting more time of CPU to obtain the results. Having the objective of obtaing a more precise analitical tool for evaluating the multiple access protocols used in data networks models have been developed, based on the method proposed by S.M.Meerkov and J.T.Lim. these models consider stations having buffers and transmitting messages with one or more packets through delay channels, according to the distribuition of probabilities of the size of these messages. It is also proposed a model which do not present the hypothesis ususally used to simplify the Slotted-ALOHA (S-ALOHA) protocol, with respect to the need of having a delayed first transmission of a packet. The reffered combines transmittions in S-ALOHA mode and in a reervation mode. Simulation models and results are also used for validation of the proposed analitical models.

[pt] Com o objetivo de prover acesso global ao mundo da informação, as comunicações via satélite desempenham um papel fundamental, possibilitando o acesso de serviços de faixa larga em áreas onde a infra-estrutura terrestre não permite. Este trabalho apresenta uma caracterização destas aplicações potenciais para redes ATM via satélite, descrevendo os problemas e as limitações que ainda precisam ser superados, assim como as soluções que já foram sugeridas. Entre estes problemas, está o desenvolvimento de protocolos de múltiplo acesso que possibilitem a utilização eficiente do segmento espacial e, ao mesmo tempo, garanta a qualidade do serviço. Os protocolos de múltiplo acesso tradicionais não são adequados para redes com múltiplos serviços, como se espera num ambiente de faixa larga, visto que foram desenvolvidos para redes com um determinado tipo de aplicação. Desta forma, é necessário realizar uma adaptação destas técnicas convencionais, para esta nova realidade, pois através de protocolos de múltiplos acesso eficiente, será possível obter ganhos consideráveis nos recursos de segmento espacial, cada vez mais escassos e, conseqüentemente, caros. Para verificar em mais detalhes este problema, descreveremos três protocolos propostos para múltiplo acesso em redes ATM via satélite, todas eles baseados na técnica de método de acesso por divisão do tempo (ADTMA). O desempenho destes protocolos é analisado, através de simulação, comparando-se as vantagens e desvantagens de cada um. / [en] In order to provide global Access to the world of information, the satellite communications play a key rolo, making possible the Access of broadband services to areas where the terrestrial infrastructure doesn´t allow. This work shows a characterization of the potencials applications to the satellite ATM networks, making a description of the problems and limitations that need to be overcome, as well as the solutions that have been suggested. Among thesse problems, we have the development of multiple access protocols that allow an efficient utilization of space segment and, at same time, guarantee the quality of service. The traditionals multiples access protocols are not well suitable to multiple service networks, as we hope in a broadband environment, since they were created to networks with a specific application. So, it´s necessary to make an adaptation in these conventionals technics to this new reality, because through efficients multiple access protocols, will be possible to have considerable gains in space segment`s resources, more and more rare and, consequantly, expensive. To verify in more details this problem, we describe three protocols suggested to provide multiple access in satellite ATM networks, all of them based on the technic of time division multiple access (TDMA). The performance analysis of these protocols is done, through simulations, confronting the advantages and disadvantages of each one.

[pt] É considerado um protocolo de múltiplo acesso de alocação híbrida e adaptativa, que pode ser utilizado em redes VSAt. Neste protocolo as transmissão são feitas em um canal S-Aloha ou em um canal TDMA de alocação por reserva. As estações remotas dispõem de buffer para armazenamento de mensagens. O desempenho do protocolo é avaliado em termos da vazão e do retardo médio, através da técnica de Análise do Ponto de Equilíbrio (EPA). A estabilidade do protocolo é também examinada. É feita uma comparação deste protocolo com um protocolo S-Aloha, ambos ocupando igual largura de faixa de freqüências. Variações do protocolo básico, considerando o canal TDMA de alocação por reserva com largura de faixa menor que a alocada para o canal S- Aloha são também analisadas. Outra variação importante abordada é aquela na qual W canais S-Aloha com grupos de equações remotas operando separando em cada um deles se servem de um único canal TDMA de alocação por reserva. Para esta variação são indicadas as modificações nas equações obtidas para o protocolo básico que permitem escrever as expressões da vazão e do retardo médio. Resultados numéricos da vazão e do retardo médio para os diversos protocolos são apresentados. / [en] A multiple acess protocol, which can be used in a VSAT network, with an adaptive and hybrid assignment is considered. In this protocol the transmission can be done in either an S-Aloha channel or in a demand assignment TDMA channel. The remote stations have finite buffer capacity to store arriving messages. The performance is evaluated in terms of throughput and expected delay, by means of the so called Equilibrium Point Analysis (EPA). Stability of the protocol is also examined. A comparison between this protocol and an S-Aloha one, both with the same bandwidth, is also carried out. Variations of the basic protocol considering the demand assignment TDMA channel with a smaller bandwidth than that one of the S- Aloha channel are also considered. Another important variation examined is the one in which W S-Aloha channels serve W separate groups of remote stations and all share a demand assignment TDMA channel. For this variation, modification in the equilibrium equations obtained for the basic protocol as well as for expression of throughput and expected delay are indicated. Numerical results of throughput and expect delay for the several protocols are given.

[pt] Este trabalho propõe e analisa uma versão de um protocolo híbrido de acesso aleatório com notificação, desenvolvido para redes VSAT ( Very Small Aperture Terminal) onde se busca uma combinação do baixo tempo de resposta de protocolos do tipo RA-TDMA (Random Access-Time Division Multiple Access) . No protocolo aqui estudado as transmissões são feitas em uma primeira tentativa através de um esquema RA-TDMA e no caso de ocorrência de colisão, os pacotes envolvidos são retransmitidos através de um esquema DA-TDMA. As notificações de transmissões são feitas pelas estações VSAT, através de um canal de sinalização, onde é atribuído a cada uma delas um segmento de tempo, aqui referido como slot de tempo, de posição fixa dentro de cada quadro. O desempenho do protocolo é analisado utilizando a técnica de Análise no Ponto de Equilíbrio (EPA), sendo considerados como medida de desempenho os parâmetros retardo médio de mensagem, vazão e taxa de rejeição de pacotes. São consideradas mensagens de um pacote e mensagens de tamanho variável. Comparações com outros protocolos contendo buffer ou não, também analisados utilizando a técnica EPA, são realizadas. Resultados de simulação encontrados na literatura de dois outros protocolos são também apresentados. / [en] A version of a random access with notification, multiple access protocol developed for VSAT networks is considered. This hybrid protocol combines the low response delay of RA- TDMA contention protocols with the efficiency and stability of DA-TDMA type protocols. In the considered protocol a message generated by a VSAT station is transmitted, in a first attempt, using a RA-TDMA type of scheme. If a collision occurs in this first transmission of the message the collided packets are retransmitted through a Demand Assignment (DA)-TDMA type of access. When a remote station transmits its message in a RA-TDMA contention mode it notifies the central hub using a separate TDMA channel in which a fixed position time slot is reserved to each station within a frame. The performance of the protocol is evaluated in terms of throughput, expected delay and packet rejection rate by means of the so called Equiilibrium Point Analysis (EPA). Single and multi-packet messages, with a random number of packets, are considered in the performance analysis. Comparisons with other hybrid protocols, which were also evaluated in the literature by means of the EPA technique or through simulation results, are presented.

Abstract The present dissertation deals with initial synchronization in Code Division Multiple Access (CDMA) networks. In the first part of this thesis an extensive and up-to-date review of the literature is presented. The basic theory of code acquisition as well as different techniques and structures used to achieve the initial synchronization are discussed. A survey of the most common theoretical approaches allowing performance characterization of the acquisition process is included. The effect of noise, interference, carrier Doppler, multipath propagation, fading and data modulation on system performance are reviewed. Advanced code acquisition approaches exploiting interference suppression techniques and multiple antennas are also described. A summary of the results obtained within the area of code acquisition in CDMA networks is also embraced by this thesis. The distinctive assumption is to consider the actual variable effect of multiple access interference on the delay-domain search process, instead of the usual constant approximation. Three directions of research are followed. Models for code acquisition in quasi-synchronous and asynchronous CDMA networks are first developed and analysed. Closed-form expressions for the main performance figures of the acquisition process are derived and analysed. Results show a strong dependence of the mean acquisition time with the nature of the multiple access interference. In the second area of research the previous results are extended to consider code acquisition with a multi-branch (Rake) receiver in a multipath channel. A generic model for Rake receiver code acquisition is considered and developed, in which the synchronization takes place in two phases. The first detected path is allocated to the first finger during the initial synchronization phase, whereas the remaining fingers are successively allocated to other available paths in the postinitial synchronization phase. Performance measures for this acquisition process are also derived and analysed. Finally, based on the use of an antenna array and beamforming techniques, conventional delay-domain code acquisition is extended to the angular domain, resulting in a two-dimensional (delay-angle) search. This technique is found to be feasible, outperforming the synchronization approach exploiting a single-antenna. It is found that there exists an optimal number of antennas that minimises the mean acquisition time. Two-dimensional code acquisition is studied in a variety of scenarios, including single and multipath channels, fixed and fading channels, and with uniform and nonuniform spatial distributions of interference. Different two-dimensional search strategies are studied. A clear dependence of acquisition performance with the search strategy and the particular distribution of interference is pointed out. The performance of two-dimensional code acquisition is found to be seriously deteriorated by the presence of spatially nonuniform interference. Schemes based on search strategy and adaptive detector structures are considered and analysed to combat the performance degradation in the mentioned case. A comparative study of code acquisition exploiting multiple antennas is also presented.

Abstract Conventional versions of linear multiuser detectors (MUD) are not feasible in the wideband code division multiple access (WCDMA) downlink due to the use of long scrambling sequences. As an alternative, linear channel equalizers restore the orthogonality of the spreading sequences lost in frequency-selective channels, thus, suppressing multiple access interference (MAI) in the WCDMA downlink. In this thesis, linear channel equalizers in WCDMA terminals are studied. The purpose of the thesis is to develop novel receivers that provide performance enhancement over conventional rake receivers with an acceptable increase in complexity, and to validate their performance under WCDMA downlink conditions. Although the WCDMA standard is emphasized as the candidate system, the receivers presented are suitable for any synchronous direct sequence code division multiple access downlink employing coherent data detection and orthogonal user or channel separation. Two adaptive channel equalizers are developed based on the constrained minimum output energy (MOE) criterion and sample matrix inversion method. An existing equalizer based on the matrix inversion lemma is also developed further to become a prefilter-rake equalizer. Performance analysis is carried out for equalizers trained using a common pilot channel and for the channel response constrained MOE (CR-MOE) and sample matrix inversion (SMI) based equalizers developed in the thesis. The linear minimum mean square error (LMMSE) channel equalizer, which assumes a random scrambling sequence, is shown to approximate the performance of the LMMSE MUD. The adaptive CR-MOE, SMI-based, and prefilter-rake equalizers are observed to attain performance close to that of an approximate LMMSE channel equalizer. The equalizers considered are also shown to be suitable for implementation with fixed-point arithmetic. The SMI-based equalizer is shown to provide good performance and to require an acceptable increase in complexity. It is also well suited for symbol rate equalization after despreading, which allows for computationally efficient receiver designs for low data rate terminals. Hence, the SMI-based equalizer is a suitable receiver candidate for both high and low data rate terminals. Adaptive equalizers are considered in conjunction with forward error correction (FEC) coding, soft handover, transmit diversity and high speed downlink packet access (HSDPA). The adaptive equalizers are shown to provide significant performance gains over the rake receiver in frequency selective channels. The performance gains provided by one antenna equalizers are noted to decrease near the edges of a cell, whereas the equalizers with two receive antennas achieve significant performance improvements also with soft handover. The performance gains of one or two antenna equalizers are shown to be marginal in conjunction with transmit antenna diversity. Otherwise the equalizers are observed to attain good signal-to-noise-plus-interference ratio performance. Therefore, they are also suitable receiver candidates for HSDPA.

[pt] Neste trabalho é feito um estudo sobre o desempenho de protocolos de múltiplo acesso adaptativos utilizados em redes via satélite. Inicialmente é apresentado um histórico destes protocolos de múltiplo acesso, descrevendo-se seus fundamentos e incluindo os principais protocolos utilizados atualmente. Em seguida, o protocolo denominado DVB-RCS é descrito e analisado em detalhe e sua aplicação é avaliada em uma rede interativa via satélite utilizando o simulador de redes Opnet. O modelo simulado é o de uma rede VSAT constituída de um grande número de estações terrenas, um satélite e uma estação Hub. São considerados vários tipos de tráfego: tráfego CBR, para transmissão de voz, tráfego VBR para vídeo e UBR para tráfego HTTP e transmissão de dados em geral. Os modelos de tráfego utilizados se basearam na modelagem tradicional de fontes on-off e, no caso de tráfego HTTP, o modelo foi o mesmo adotado para avaliação do sistema UMTS (Universal Mobile Telecommunications System). Para cenários correspondentes a diferentes composições de tráfego, é avaliada a vazão média e o atraso na reserva de recursos, procurando-se determinar critérios para dimensionamento da rede, como a composição de tráfego adequada a cada situação. / [en] In this work, we study the performance of adaptive multiple access protocols used in satellite networks. Firstly a survey of such protocols is presented, describing their basic characteristics and including the main protocols used nowadays. Then, the protocol DVB-RCS is described and analyzed in detail and its applications to an interactive satellite network is evaluated using the Opnet network simulator. The simulated model is the one of a VSAT network with a large number of earth stations, a satellite and a Hub station. Several types of traffic source are considered: CBR traffic for voice transmission, VBR traffic for video stream transmission and UBR traffic for HTTP traffic and general data transmission. The traffic models are based on traditional on-off source and, for HTTP, the model is the one adopted for evaluation of the UMTS (Universal Mobile Telecommunications System). For scenarios corresponding to different traffic compositions, the average throughput and resource reservation delay, seeking to design criteria for the network, e.g. the most appropriate traffic composition for each situation.