Third generation mobile communication systems promise a greater data rate and new services to the mobile subscribers. 3G systems support up to 2 Mbps of data rate to a fixed subscriber and 144 Kbps of data rate to a fully mobile subscriber. Code Division Multiple Access (CDMA) is the air interface access scheme widely used in all the 3G communication systems. This access scheme has many inherent advantages m terms of noise immunity, security, coherent combining of multi path signals etc. But all these advantages come at the expense of higher complexity of the receivers. The receivers form the major portion of the processing involved in a base station. The heart of any CDMA receiver is the RAKE. The RAKE receiver separates the different multi-paths received by the antenna by using the properties of the Pseudo Random sequences. The phase and strength of each of these path signals is measured and are used by the coherent combiner, which de-rotates all the signals to a single reference and coherently combines them In general the Base station receivers make use of the top three multi-path signals ranked in terms of their signal energy Hence four RAKE fingers, each catering to single multi-path are needed for receiving a single code channel (3 for coherent combining and one for scanning). One such channel receiver requires a processing power of 860 MIPS (Mega Instructions Per Second). Some of the CDMA standards support up to 90 code channels at the same time. This means that the total processing power required at the base station is about 80 GIPS. This much of processing power will require large number of high end DSPs, which will be a very costly solution. In the current base station architectures these blocks are implemented using ASICs, which are specific to a particular standard and also the algorithms used for the different operations are fixed at the design time itself. This solution is not flexible and is not amenable for SDR (Software defined Radio) architectures for the Base stations. This thesis proposes a Co-Processor solution, which can be attached to a generic DSP or any other processor. The processor can control the Co-Processor by programming its parameter registers using memory mapped register accesses. This co-processor implements only those blocks, which are compute intensive. This co-processor performs all chip-rate processing functions involved m a RAKE receiver. All the symbol-rate functions are implemented through software in the processor. This provides more choices m selecting the algorithms for timing recovery and scanning. The algorithms can be changed through software even after the base station is installed in the field. All the inputs and outputs of the Co-Processor are passed through dual port RAMs with independent read and write clocks. This allows the Co-Processor and the processor to be running on two independent clocks. This memory scheme also increases the throughput as the reads and writes to these memories can happen simultaneously. This thesis introduces a concept of incorporating programmable PN/Gold code generators as part of the Co-Processor, which significantly reduces the amount of memory required to store the Scrambling and Spreading codes. The polynomial lengths as well as the polynomials of the code generator are programmable. The input signal memory has a bus width equal to 4 times the bus width of the IQ signal bus width (4 * 24 = 96 bits) towards the Co-Processor to meet the huge data bandwidth requirement. This memory is arranged as word interleaved memory banks. This can supply one word per memory bank on each clock cycle as long as the accessed words fall in different memory banks. The number of banks is chosen as more than twice that of the number of Correlators/ Rake fingers. This gives more flexibility in choosing the address offsets to different Correlator inputs. This flexibility allows one to use different timing recovery schemes since the number of allowable address offsets for different Correlators is more. The overall complexity of the solution is comparatively less with respect to the generic DSP based solution and much easier to modify for a different standard, when compared to the rigid ASIC based solution. The proposed solution is significantly different from the conventional way of designing the Base station with fixed ASICs and it clearly outweighs the solutions based on conventional approach in terms of flexibility, design complexity, design time and cost.

Beim Entwurf großer Netzwerke der Automation ermöglichen Methoden der Leistungsbewertung den Test und die Dimensionierung eines Netzwerkes bereits vor der Inbetriebnahme und erlauben damit einen effizienten, qualitätsorientierten Entwurf. Es ist jedoch sehr wissensintensiv und aufwendig, entsprechende Analyse- oder Simulations-Modelle aufzustellen und die Ergebnisse auszuwerten, weshalb die Methoden in der Praxis der Automation selten verwendet werden. Viel vertrauter sind dem Entwerfer hingegen die speziellen Software-Tools, mit denen in der Automation Netzwerke entworfen werden. Auf Basis der Datenbanken dieser Tools werden in dieser Arbeit verschieden Verfahren zur automatischen Systemmodellierung, Verkehrsmodellierung, Leistungsbewertung und Fehlerdiagnose zu einem Control Network Performance Engineering kombiniert, welches die Qualitätsbewertung und -beratung nahtlos und ohne Mehraufwand in den Netzwerkentwurf integriert. (Die Dissertation wurde veröffentlicht im Jörg Vogt Verlag, Voglerstr. 20, 01277 Dresden, Internet: http://www.vogtverlag.de/, email: info@vogtverlag.de, ISBN 978-3-938860-10-6) / During the design of large automation networks, performance analysis methods can be used for testing and dimensioning the network before implementation and are essential for an efficient and reliable design process. However, setting up the necessary analytical or simulative models is time-consuming, requires in-depth knowledge, and is therefore often not applicable in practice. The network designers are much more used to the design tools used to develop automation networks. Based on these tools' databases various methods for automated system and traffic modeling, performance analysis and diagnoses are combined in the control network performance engineering that seamlessly integrates quality analysis and consulting into network design without requiring additional effort. (This manuscript is also available - in the form of a book - from Jörg Vogt Verlag, Voglerstr. 20, 01277 Dresden, Germany world-wide web address: http://www.vogtverlag.de/, electronic-mail address: info@vogtverlag.de, ISBN 978-3-938860-10-6 )

Road accidents represent a serious social problem and are one of the leading causes of human death and disability on a global scale. To reduce the risk and severity of a road accident, a variety of new safety applications can be realized through wireless communications among vehicles driving nearby each other, or among vehicles and especially deployed road side units (RSUs), a technology known as a vehicular ad hoc network (VANET). Most of the VANET-enabled safety applications are based on broadcasting of safety messages by vehicles or RSUs, either periodically or in case of an unexpected event, such as a hard brake or dangerous road condition detection. Each broadcast safety message should be successfully delivered to the surrounding vehicles and RSUs without any excess delay, which is one of the main functions of a medium access control (MAC) protocol proposed for VANETs. This thesis presents VeMAC, a new multichannel time division multiple access (TDMA) protocol specifically designed to support the high priority safety applications in a VANET scenario. The ability of the VeMAC protocol to deliver periodic and event-driven safety messages in VANETs is demonstrated by a detailed delivery delay analysis, including queueing and service delays, for both types of safety messages. As well, computer simulations are conducted by using MATLAB, the network simulator ns-2, and the microscopic vehicle traffic simulator VISSIM, in order to evaluate the performance of the VeMAC protocol, in comparison with the IEEE 802.11p standard and the ADHOC MAC protocol (another TDMA protocol proposed for ad hoc networks). A real city scenario is simulated and different performance metrics are evaluated, including the network goodput, protocol overhead, channel utilization, protocol fairness, probability of a transmission collision, and safety message delivery delay. It is shown that the VeMAC protocol considerably outperforms the existing MAC schemes, which have significant limitations in supporting VANET safety applications. In addition to enhancing road safety, in-vehicle Internet access is one of the main applications of VANETs, which aims at providing the vehicle passengers with a low-cost access to the Internet via on-road gateways. This thesis presents a new strategy for deploying Internet gateways on the roads, in order to minimize the total cost of gateway deployment, while ensuring that a vehicle can connect to an Internet gateway (using multihop communications) with a probability greater than a specified threshold. This cost minimization problem is formulated by using binary integer programming, and applied for optimal gateway placement in a real city scenario. To the best of our knowledge, no previous strategy for gateway deployment has considered the probability of multihop connectivity among the vehicles and the deployed gateways. In order to allow a vehicle to discover the existence of an Internet gateway and to communicate with the gateway via multihops, a novel data packet routing scheme is proposed based on the VeMAC protocol. The performance of this cross-layer design is evaluated for a multichannel VANET in a highway scenario, mainly in terms of the end-to-end packet delivery delay. The packet queueing at each relay vehicle is considered in the end-to-end delay analysis, and numerical results are presented to study the effect of various parameters, such as the vehicle density and the packet arrival rate, on the performance metrics. The proposed VeMAC protocol is a promising candidate for MAC in VANETs, which can realize many advanced safety applications to enhance the public safety standards and improve the safety level of drivers/passengers and pedestrians on roads. On the other hand, the proposed gateway placement strategy and packet routing scheme represent a strong step toward providing reliable and ubiquitous in-vehicle Internet connectivity.

Over the last few years, wireless cellular communications has experienced rapid growth in the demand for provision of high data rate wireless multimedia services. This fact motivates the need to find ways to improve the spectrum efficiency of wireless communication systems. Smart or adaptive antennas have emerged as a promising technology to enhance the spectrum efficiency of present and future wireless communications systems by exploiting the spatial domain. The aim of this thesis is to investigate smart antenna applications for Direct Sequence Code Division Multiple Access (DS-CDMA) systems. CDMA is chosen as the platform for this thesis work since it has been adopted as the air-interface technology by the Third Generation (3G) wireless communication systems. The main role of smart antennas is to mitigate Multiple Access Interference (MAI) by beamforming (i.e. spatial filtering) operation. Therefore, irrespective of a particular wireless communication system, it is important to consider whether a chosen array configuration will enable optimal performance. In this thesis an initial assessment is carried out considering linear and circular array of dipoles, that can be part of a base station antenna system. A unified and systematic approach is proposed to analyse and compare the interference rejection capabilities of the two array configurations in terms of the Signal to Interference Ratio (SIR) at the array output. The theoretical framework is then extended to include the effect of mutual coupling, which is modelled using both analytical and simulation methods. Results show that when the performance is averaged over all angles of arrival and mutual coupling is negligible, linear arrays show similar performance as circular arrays. Thus in the remaining part of this thesis, only linear arrays are considered. In order to properly evaluate the performance of smart antenna systems, a realistic channel model is required that takes into account both temporal and spatial propagation characteristics of the wireless channel. In this regard, a novel parameterized physical channel model is proposed in this thesis. The new model incorporates parameters such as user mobility, azimuth angle of arrival, angle spread and Doppler frequency, which have critical influence on the performance of smart antennas. A mathematical formulation of the channel model is presented and the proposed model is implemented in software using Matlab. The statistics of the simulated channels are analysed and compared with theory to confirm that the proposed model can accurately simulate Rayleigh and Rician fading characteristics. To assist system planners in the design and deployment of smart antennas, it is important to develop robust analytical tools to assess the impact of smart antennas on cellular systems. In this thesis an analytical model is presented for evaluating the Bit Error Rate (BER) of a DS-CDMA system employing an array antenna operating in Rayleigh and Rician fading environments. The DS-CDMA system is assumed to employ noncoherent M-ary orthogonal modulation, which is relevant to IS-95 CDMA and cdma2000. Using the analytical model, an expression of the Signal to Interference plus Noise Ratio (SINR) at the output of the smart antenna receiver is derived, which allows the BER to be evaluated using a closed-form expression. The proposed model is shown to provide good agreement with the (computationally intensive) Monte Carlo simulation results and can be used to rapidly calculate the system performance for suburban and urban fading environments. In addition to MAI, the performance of CDMA systems is limited by fast fading. In this context, a hybrid scheme of beamforming and diversity called Hierarchical Beamforming (HBF) is investigated in this thesis to jointly combat MAI and fading. The main idea behind HBF is to divide the antenna elements into widely separated groups to form subbeamforming arrays. The performance of a hierarchical beamforming receiver, applied to an IS-95 CDMA system, is compared with smart antenna (conventional beamforming) receiver and the effect of varying the system and channel parameters is studied. The simulation results show that the performance of hierarchical beamforming is sensitive to the operating conditions, especially the value of the azimuth angle spread. The work presented in this thesis has been published in part in several journals and refereed conference papers, which reflects the originality and significance of the thesis contributions.

Over the last few years, wireless cellular communications has experienced rapid growth in the demand for provision of high data rate wireless multimedia services. This fact motivates the need to find ways to improve the spectrum efficiency of wireless communication systems. Smart or adaptive antennas have emerged as a promising technology to enhance the spectrum efficiency of present and future wireless communications systems by exploiting the spatial domain. The aim of this thesis is to investigate smart antenna applications for Direct Sequence Code Division Multiple Access (DS-CDMA) systems. CDMA is chosen as the platform for this thesis work since it has been adopted as the air-interface technology by the Third Generation (3G) wireless communication systems. The main role of smart antennas is to mitigate Multiple Access Interference (MAI) by beamforming (i.e. spatial filtering) operation. Therefore, irrespective of a particular wireless communication system, it is important to consider whether a chosen array configuration will enable optimal performance. In this thesis an initial assessment is carried out considering linear and circular array of dipoles, that can be part of a base station antenna system. A unified and systematic approach is proposed to analyse and compare the interference rejection capabilities of the two array configurations in terms of the Signal to Interference Ratio (SIR) at the array output. The theoretical framework is then extended to include the effect of mutual coupling, which is modelled using both analytical and simulation methods. Results show that when the performance is averaged over all angles of arrival and mutual coupling is negligible, linear arrays show similar performance as circular arrays. Thus in the remaining part of this thesis, only linear arrays are considered. In order to properly evaluate the performance of smart antenna systems, a realistic channel model is required that takes into account both temporal and spatial propagation characteristics of the wireless channel. In this regard, a novel parameterized physical channel model is proposed in this thesis. The new model incorporates parameters such as user mobility, azimuth angle of arrival, angle spread and Doppler frequency, which have critical influence on the performance of smart antennas. A mathematical formulation of the channel model is presented and the proposed model is implemented in software using Matlab. The statistics of the simulated channels are analysed and compared with theory to confirm that the proposed model can accurately simulate Rayleigh and Rician fading characteristics. To assist system planners in the design and deployment of smart antennas, it is important to develop robust analytical tools to assess the impact of smart antennas on cellular systems. In this thesis an analytical model is presented for evaluating the Bit Error Rate (BER) of a DS-CDMA system employing an array antenna operating in Rayleigh and Rician fading environments. The DS-CDMA system is assumed to employ noncoherent M-ary orthogonal modulation, which is relevant to IS-95 CDMA and cdma2000. Using the analytical model, an expression of the Signal to Interference plus Noise Ratio (SINR) at the output of the smart antenna receiver is derived, which allows the BER to be evaluated using a closed-form expression. The proposed model is shown to provide good agreement with the (computationally intensive) Monte Carlo simulation results and can be used to rapidly calculate the system performance for suburban and urban fading environments. In addition to MAI, the performance of CDMA systems is limited by fast fading. In this context, a hybrid scheme of beamforming and diversity called Hierarchical Beamforming (HBF) is investigated in this thesis to jointly combat MAI and fading. The main idea behind HBF is to divide the antenna elements into widely separated groups to form subbeamforming arrays. The performance of a hierarchical beamforming receiver, applied to an IS-95 CDMA system, is compared with smart antenna (conventional beamforming) receiver and the effect of varying the system and channel parameters is studied. The simulation results show that the performance of hierarchical beamforming is sensitive to the operating conditions, especially the value of the azimuth angle spread. The work presented in this thesis has been published in part in several journals and refereed conference papers, which reflects the originality and significance of the thesis contributions.

[Truncated abstract] This thesis develops a scheduled protocol (time division multiple access, TDMA) called flexible-schedule-based TDMA Protocol (FlexiTP), to address the problem of providing end-to-end guarantees on data delivery, whilst also respecting severe resource constraints of wireless sensor networks. FlexiTP achieves this balance through a distributed, synchronised, and loose slot structure in which sensor nodes can build, modify, or extend their schedules based on their local information. In FlexiTP, it is not necessary to predetermine the number of slots required for a network. FlexiTP's local repair scheme allows nodes to adjust their schedules dynamically and autonomously to recover from node and communication faults. Hence, it maintains a reliable and selforganising multihop network. Most sensor network protocols designed for data gathering applications implicitly assume a periodic rate of data collection from all nodes in the network to the base station. However, nodes may want to report their data more rapidly or slowly depending on the significance and importance of their data to the end-user. The problem is that traditional TDMA-based protocols are not flexible to changes in traffic patterns because of their rigid slot structure schemes. This thesis aims to solve this problem by developing an ondemand TDMA slot transfer method that leverages the flexible-slot structure algorithm of FlexiTP to transfer time slots from one part of the network to another part. ... While these communication patterns are sufficient for monitoring applications, individual sensor nodes may need to send their data to multiple destination nodes across the network in order to execute a distributed cooperative-function based on their local environment. This peer-to-peer communication pattern makes sensor networks more reactive to triggers from the environment. This thesis attempts to solve the problem of lack of peer-to-peer communication in the design of a TDMA-driven protocol by extending the idea of on-demand TDMA slot transfer method to allow each sensor node in the network to claim extra time slots to communicate with any other nodes (peers) in the network, without going through the base station. Nodes in the network may have different priorities of data because of event-triggering sensor readings or various types of sensor readings (e.g., light, temperature, and humidity) they provide. When nodes with high priority packets increase the frequency of their data collections, the network bandwidth may be dominated by these nodes. It is desirable to allow nodes with low priority packets to aggregate their packets and so enabling these nodes to send their data to the base station under the current available network bandwidth. This thesis proposes an on-demand data aggregation algorithm that enables sensor nodes to perform an in-network-aggregation based on their current sensing requirements and network capacity constraints. In summary, this thesis describes the design, implementation, and evaluation of protocols for wireless sensor networks that focus on achieving energy-efficiency, provisioning performance assurances, and supporting reactivity and adaptability in constantly changing environment.

Abstract In the current LTE-Advanced system, decode-and-forward (DF) is leveraged for cooperative relaying, where the erroneously decoded sequences are discarded at the relay, resulting in a waste of resources. The reason lies in that the erroneously decoded sequence can provide a certain amount of useful information about the source at the destination. Therefore, we develop a new relaying scheme, called lossy DF (also known as lossy forward (LF)), where the relay always forwards the decoded sequence to the destination. Beneficial from the always-forward principle, it has been verified that LF relaying outperforms DF relaying in terms of outage probability, ε-outage achievable rate, frame error rate (FER), and communication coverage. Three exemplifying network scenarios are studied in this thesis: the one-way multiple-input multiple-output (MIMO) relay network, the multiple access relay channel (MARC), and the general multi-source multi-relay network. We derive the outage probability of the one-way MIMO relay networks under the assumption that the orthogonal space-time block code (OSTBC) is implemented at the transmitter side for each individual transmission. Interestingly, we find that the diversity order of the OSTBC based one-way MIMO relay network can be interpreted and formulated by the well-known max-flow min-cut theorem, which is widely utilized to calculate the network capacity. For the MARC, non-orthogonal transmission is introduced to further improve the network throughput compared to its orthogonal counterpart. The region for lossless recovery of both sources is formulated by the theorem of multiple access channel (MAC) with a helper, which combines the Slepian-Wolf rate region and the MAC capacity region. Since the region for lossless recovery is obtained via sufficient condition, the derived outage probability can be regarded as a theoretical upper bound. We also conduct the performance evaluation by exploiting different accumulator (ACC) aided turbo codes at the transmitter side, exclusive or (XOR) based multi-user complete decoding at the relay, and iterative joint decoding (JD) at the destination. For the general multi-source multi-relay network, we focus on the investigation the end-to-end outage probability. The performance improvement of LF over DF is verified through theoretical analyses and numerical results in terms of outage probability. / Tiivistelmä Tämän päivän LTE-A-tiedonsiirtojärjestelmissä hyödynnetään dekoodaa-ja-välitä (decode-and-forward, DF) menetelmää yhteistoiminnalliseen tiedon edelleenlähetykseen (relaying) siten, että virheellisesti vastaanotetut sekvenssit hylätään välittimessä (relay). Tämä on resurssien hukkaamista, sillä virheellisissäkin viesteissä on informaatiota, jota voidaan hyödyntää vastaanottimessa. Tässä väitöskirjassa tutkitaan uutta häviöllistä DF-menetelmää, johon viitataan nimellä häviöllinen välitys (lossy forward, LF). Menetelmässä välitin lähettää informaation aina eteenpäin olipa siinä virheitä tai ei. Sen etuna verrattuna perinteiseen DF-menetelmään, on parantunut luotettavuus metriikoilla jossa mitataan vastaanoton todennäköisyyttä ja verkon peittoaluetta. Väitöskirjassa tarkastellaan LF-menetelmää kolmessa eri verkkotopologiassa jotka ovat yksisuuntainen monitulo-monilähtövälitinverkko (multiple-input multiple-output, MIMO), moniliityntävälitinkanava (multiple access relay channel, MARC), sekä yleinen moniläheinen monivälitinverkko. Työssä johdetaan matemaattinen esitys estotilan todennäköisyydelle (outage probability) yksisuuntaisessa MIMO-välitinverkossa olettaen ortogonaalisen tila-aika lohkokoodin (orthogonal space-time block code, OSTBC) käyttö. Estotilan todennäköisyys esitetään käyttäen toisteastta (diversity order), joka saadaan johdettua tunnetusta max-flow min-cut lauseesta, jota puolestaan käytetään yleisesti erilaisten verkkojen kapasiteettien laskentaan. MARC-topologiassa hyödynnetään ei-ortogonaalista lähetystä verkon datavirran kasvattamiseen. Häviöttömän lähetyksen informaatioteoreettinen kapasiteettialue saadaan johdettua MAC-auttajan kanssa. Lähestymistavassa Slepian-Wolf- sekä MAC-kapasiteettialueet yhdistyvät. Alueelle, jossa kahden lähteen lähetysnopeudet ovat sellaiset, että vastaanotto on häviötöntä, annetaan riittävä ehto, jolloin johdettu estotilan todennäköisyys on teoreettinen yläraja. Suorituskykyä evaluoidaan myös tietokonesimulaatioilla, joissa käytetään erilaisia akkumulaattoriavusteisia turbokoodeja lähettimessä, ehdoton tai (exclusive or, XOR) pohjaista monen käyttäjän dekoodausta välittimessä sekä iteratiivista yhteisdekoodausta vastaanottimessa. Yleisessä monilähteisessä monivälitinverkossa keskitytään alkuperäisen lähetyksen estotilatodennäköisyyteen. Teoreettinen analyysi sekä simulaatiot osoittavat, että LF:n estotilan todennäköisyys on pienempi kuin DF:n.

Orientador: Jaime Portugheis / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-17T00:51:09Z (GMT). No. of bitstreams: 1 Sharma_Manish_D.pdf: 1122815 bytes, checksum: ac184067a2eeb2f29617e0a5da608708 (MD5) Previous issue date: 2010 / Resumo: O objetivo deste trabalho é analisar o desempenho da recepção e detecção conjunta e iterativa para canais de acesso múltiplo. A análise se concentrou em torno de um canal ruidoso com N frequências compartilhado por T usuários. Encontramos valores para a capacidade do canal para detecção conjunta e individual. Embora a eficiência espectral do sistema seja relativamente baixa, a combinação deste fator com uma grande faixa de frequências permite altas taxas de transmissão com baixa relação sinal ruído. O receptor foi modelado como um grafo de fatores e foi analisado através de curvas EXIT, que também são utilizadas para otimizar os códigos corretores de erro dos usuários. Propomos alguns sistemas baseados nesta técnica e simulamos a sua probabilidade de erro de bit. Os resultados indicam que é possível transmitir informação com taxas próximas da capacidade do canal. Tanto o grafo do receptor como as análises subsequentes podem ser aplicadas para outros canais de acesso múltiplo, especialmente para sistemas com N símbolos de transmissão ortogonais. / Abstract: The aim of this work is to analyze the performance of iterative joint reception and detection for multi-user channels. The analysis is centered around an N-frequency MFSK noisy channel shared by T users. Channel capacity values are obtained for joint and single user detection. Although the system's spectral efficiency is low, high rates at low signal to noise ratio are achievable by using a wide-bandwidth channel. The receiver is modeled as a factor graph and analyzed by its EXIT charts, which were also used to analyze the users' error correcting codes. Some systems are proposed and simulated to obtain the bit error probability. Results indicate that it is possible to transmit information with rates close to channel capacity. The proposed receiver and the performed analysis can be applied to other types of multiple access channels, in particular for systems with N orthogonal transmission symbols. / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

Neste trabalho propomos e analisamos algoritmos de alocação dinâmica de banda para rede óptica passiva (PON) de acesso padrão GPON (Gigabit PON). Estes algoritmos utilizam dados oriundos de SLA (service level agreement) para gerenciar a alocação de banda e classificar em 4 contêineres de tráfego (T-CONT) o tráfego gerado em 16 ONUs (optical network unit). Na transmissão upstream é utilizada a técnica de multiplexação por divisão de tempo (TDM) para gerenciar o acesso ao meio, evitando colisões. O primeiro algoritmo proposto aloca banda garantida para as ONUs e distribui a banda não utilizada de acordo com critério baseado em três SLAs. A taxa de bit upstream é 1,25 Gbps e o desempenho do algoritmo é analisado com base na variação do atraso de pacotes em função do tráfego gerado nas ONUs. O segundo algoritmo proposto utiliza ponderação de tráfego. Neste, analisamos o comportamento dos atrasos e a quantidade de banda solicitada e atendida por ONU quando as bandas garantida e extra são alteradas. Por fim, acrescentamos em nossa implementação um intervalo para o processamento do algoritmo de alocação dinâmica de banda (DBA) e resposta do hardware relacionado ao ciclo de interrogação. Então, analisamos o atraso de pacotes quando variamos o intervalo de processamento do DBA. Ao final, propomos uma solução preliminar para minimizar estes atrasos. Os resultados obtidos por meio de simulação computacional mostram a versatilidade dos algoritmos. / In this work we propose and analyze the performance of dynamic bandwidth allocation algorithms for optical passive networks (PON) in GPON standard (Gigabit PON). These algorithms use data from SLA (service level agreement) to manage bandwidth allocation and classify in 4 traffic containers (T-CONT) the traffic generated by 16 ONUs (optical network unit). In the upstream transmission the time division multiplexing (TDM) technique is used to manage the medium access, avoiding collisions. The first proposed algorithm allocates guaranteed bandwidth for the ONUs and distributes the bandwidth not used according to the criteria based on three SLAs. The upstream bit rate is 1.25 Gbps and the algorithm performance is analyzed based on the packets delay variation versus the traffic generated by ONUs. The second proposed algorithm uses weighted traffic. In this, we analyze the delay performance and the required bandwidth for each ONU and how much it is served when the guaranteed and extra bandwidth are changed. Finally, we added in our implementation an interval for the processing of the dynamic bandwidth allocation algorithm (DBA) and response of the hardware related to the interrogation cycle. In the end, we propose a preliminary solution to minimize these delays. The results obtained by means of computational simulation show the versatility of the algorithms.

Este trabalho faz uma extensa e detalhada análise de sistemas ópticos coerentes baseados na tecnologia de acesso múltiplo por divisão de código, com ênfase naqueles em que o processo de codificação do sinal óptico é realizado por meio de deslocamentos de fase no domínio espectral (SPECTS-OCDMA). Apesar de ser um estudo numérico, esforços são concentrados na tentativa de aproximar estes cenários simulados aos cenários mais realistas, implementados em laboratórios. Nesse contexto, levando em consideração o impacto dos efeitos dispersivos e nãolineares da fibra óptica em sistemas SPECTS-OCDMA, são modelados diversos dispositivos que constituem o sistema de recepção do sinal óptico (nonlinear optical loop mirror e nonlinear thresholder), e mostradas suas influências no desempenho do sistema. Isso permite identificar o exato grau de interferência que cada código de uma determinada família de códigos causa nos outros códigos da mesma família. Esta análise é diferente de tudo previamente reportado para os sistemas OCDMA, porque até então sempre se supôs que todos os códigos de uma mesma família têm o mesmo desempenho. Também é demonstrado que uma escolha ótima do conjunto de códigos reduz consideravelmente a taxa de erro de bit (BER). Os conjuntos ótimos de códigos são obtidos em termos do padrão de interferência causado por todos os códigos no usuário de interesse. Isso permite mostrar que o uso de conjuntos ótimos de códigos não só melhora o desempenho geral do sistema em termos de BER, mas também elimina a quebra de ortogonalidade (nunca levada em consideração em análises anteriores de sistemas OCDMA) devido à diafonia (crosstalk). Este aspecto também é resolvido com detalhes neste trabalho uma vez que ele compromete seriamente a segurança do sistema contra espiões (intencionais e não intencionais). Ainda visando a modelagem de dispositivos voltados para sistemas ópticos coerentes, também foi investigado neste trabalho a evolução de pulsos ultracurtos e de alta potência (com fase modulada no domínio espectral) em fibras altamente não-lineares. Esse fenômeno conhecido por geração de luz supercontínua é caracterizado por um forte alargamento espectral induzido por efeitos não-lineares no meio óptico, e que encontra uma grande variedade de aplicações, como tomografia por coerência óptica, espectroscopia e metrologia de frequência. Entretanto, o ajuste do espectro obtido após a propagação para uma dessas aplicações requer uma escolha correta da fibra óptica e da fonte de pulsos ultracurtos utilizados. Uma vez que esses parâmetros estão definidos, fica muito difícil conseguir um ajuste fino do espectro obtido. Dessa forma, a vantagem da utilização de pulsos modulados é a possibilidade de se realizar uma sintonia fina do espectro obtido para uma aplicação desejada. Além disso, essa técnica permite a geração de pentes de frequências ópticos (optical frequency combs) sintonizáveis. / In this work we perform a comprehensive analysis of a spectral phase-encoded time spreading optical code division multiple access (SPECTS-OCDMA) system. Despite being a numerical study, efforts were concentrated on the investigation of more realistic scenarios using as much information as possible from implemented test-beds in laboratories. In this context, after take into account the impact of dispersive and nonlinear effects of optical fiber in SPECTS-OCDMA systems, some devices of the optical signal reception subsystem are modeled (nonlinear optical loop mirror and nonlinear thresholder), and their influences on system performance are shown. This allowed for the first time in the OCDMA literature the identification of the exact degree of interference that each code of a particular family of codes causes on other codes of the same family. This analysis considerably advances the common sense adopted in the literature in which all codes of the same family perform equally. It is demonstrated that an adequate (optimal) choice of codes can reduce considerably the bit error rate (BER). The optimal code-sets are obtained in terms of the interference pattern caused by every code on the code of interest. Furthermore, it is shown that the use of optimal code-sets not only improves the overall system performance in terms of BER, but also eliminates the orthogonality failure (never accounted for in previous OCDMA analysis) due to crosstalk. This issue is also addressed in details in this work since it seriously compromises the security of the system against (intentional or unintentional) eavesdroppers. Still aiming at modeling devices for coherent optical systems, it is investigated the evolution of ultrashort high-power pulses (spectrally phase modulated) in high nonlinear fibers. This phenomenon known as supercontinuum generation is characterized by strong spectral broadening induced by nonlinear effects in optical medium, and finds a wide range of applications such as optical coherence tomography, spectroscopy and frequency metrology. However, tailoring the supercontinuum (SC) spectra to a specific application requires the correct choice of the optical fiber and the ultrashort pulse source. Once these parameters are defined, it becomes very difficult to achieve a fine tune of the generated spectra. Therefore, an alternative is to phase modulate the input pulse to adjust the generated spectra to a specific application. Also, we show that this technique allow us to generate tunable optical frequency combs simply by adjusting the modulation parameters.