We are in the midst of a major paradigm shift in how we manage the radio spectrum. This paradigm shift in spectrum management from exclusive access to shared access is necessitated by the growth of wireless services and the demand pressure imposed on limited spectrum resources under legacy management regimes. The primary constraint in any spectrum sharing regime is that the incumbent users (IUs) of the spectrum need to be protected from harmful interference caused due to transmissions from secondary users (SUs). Unfortunately, legacy techniques rely on inadequately flexible and overly conservative methods for prescribing interference protection that result in inefficient utilization of the shared spectrum. In this dissertation, we first propose an analytical approach for characterizing the aggregate interference experienced by the IU when it shares the spectrum with multiple SUs. Proper characterization of aggregate interference helps in defining incumbent protection boundaries, a.k.a. Exclusion Zones (EZs), that are neither overly aggressive to endanger the IU protection requirement, nor overly conservative to limit spectrum utilization efficiency. In particular, our proposed approach addresses the two main limitations of existing methods that use terrain based propagation models for estimating the aggregate interference. First, terrain-based propagation models are computationally intensive and data-hungry making them unsuitable for large real-time spectrum sharing applications such as the spectrum access system (SAS). Second, terrain based propagation models require accurate geo-locations of SUs which might not always be available, such as when SUs are mobile, or when their locations are obfuscated for location privacy concerns. Our second contribution in this dissertation is the novel concept of Multi-tiered Incumbent Protection Zones (MIPZ) that can be used to prescribe interference protection to the IUs. Based on the aforementioned analytical tool for characterizing the aggregate interference, we facilitate a framework that can be used to replace the legacy notion of static and overly conservative EZs with multi-tiered dynamic EZs. MIPZ is fundamentally different from legacy EZs in that it dynamically adjusts the IU's protection boundary based on the radio environment, network dynamics, and the IU interference protection requirement. Our extensive simulation results show that MIPZ can be used to improve the overall spectrum utilization while ensuring sufficient protection to the IUs. As our third contribution, we investigate the operational security (OPSEC) issue raised by the emergence of new spectrum access technologies and spectrum utilization paradigms. For instance, although the use of geolocation databases (GDB) is a practical approach for enabling efficient spectrum sharing, it raises a potentially serious OPSEC problem, especially when some of the IUs are federal government entities, including military users. We show that malicious queriers can readily infer the locations of the IUs even if the database's responses to the queries do not directly reveal such information. To address this issue, we propose a perturbation-based optimal obfuscation strategy that can be implemented by the GDB to preserve the location privacy of IUs. The proposed obfuscation strategy is optimal in the sense that it maximizes IUs' location privacy while ensuring that the expected degradation in the SUs' performance due to obfuscated responses does not exceed a threshold. In summary, this dissertation focuses on investigating techniques that improve the utilization efficiency of the shared spectrum while ensuring adequate protection to the IUs from SU induced interference as well as from potential OPSEC threats. We believe that this study facilitates the regulators and other stakeholders a better understanding of mechanisms that enable improved spectrum utilization efficiency and minimize the associated OPSEC threats, and hence, helps in wider adoption of dynamic spectrum sharing. / Ph. D.

[pt] A tecnologia do rádio cognitivo tem sido pesquisada para utilização mais eficiente do espectro, pois permite o aproveitamento de faixas de frequência subutilizadas. Dispositivos rádio cognitivos que operam na banda de frequência da TV digital são conhecidos como White Space Devices (WSD) e utilizam canais livres sob a condição de não provocar interferência acima do limite estabelecido pelo órgão regulador. A autoridade reguladora do Reino Unido, Office of Communication (Ofcom), publicou, em fevereiro de 2015, a primeira regulação européia permitindo a operação de sistemas WSD na banda da TV digital através do suporte de sistemas de banco de dados geolocalizados. O regulamento Ofcom define uma metodologia para calcular a potência de transmissão máxima de um WSD através de um método de entrada única (single-entry) da interferência intersistema máxima. Devido a isso, a interferência agregada de WSDs co-canais que operam na mesma região pode ultrapassar a interferência intersistema máxima. Além deste problema, verifica-se que a metodologia Ofcom não define a interferência intersistema máxima pelo mesmo critério da interferência intrasistema como foi definida pelo planejamento do sistema primário de TV. Esta tese desenvolve uma nova metodologia de cálculo da potência de transmissão dos WSDs que soluciona os problemas identificados na metodologia Ofcom. A metodologia proposta garante a proteção do receptor de TV digital através de uma abordagem de múltiplas entradas da interferência dos WSDs e, adicionalmente, aumenta a capacidade do sistema WSD quando comparada à metodologia Ofcom. / [en] The technology of cognitive radio has been researched for more efficient use of spectrum, since it allows the use of under-utilized frequency bands. Cognitive radio devices operating in the digital TV frequency band are known as White Space Devices (WSD) and use free channels under the condition of not causing interference above the limit set by the regulator. The UK regulatory authority, Office of Communication (Ofcom), published in February 2015, the first European regulation allowing WSD systems in the digital TV band through the support of geo-database systems. The Ofcom regulation defines a methodology to calculate the maximum WSD transmission power through a single-entry method for the maximum intersystem interference. Due to this, the aggregate interference of cochannel WSDs operating in the same region may exceed this maximum intersystem interference. In addition to this problem, it is verified that the Ofcom methodology does not define maximum intersystem interference by the same criterion of intrasystem interference as was defined by the primary TV system planning. This thesis develops a new methodology for calculating the transmission power of WSDs that solves the problems identified in the Ofcom methodology. The proposed methodology guarantees the protection of the digital TV receiver through a multiple-entry approach of the WSDs interference and, additionally, increases the WSD system capacity when compared to the Ofcom methodology.

[pt] Neste trabalho, limites para a densidade de fluxo de potência equivalente produzida pelos lances de descida de sistemas de satélites nãogeoestacionários (não-GEO), operando na faixa de 3,7-4,2 GHz, são analisados. Estes limites visam proteger os receptores do Serviço Fixo por Satélite (FSS) das interferências produzidas por sistemas de satélites não geoestacionários, quando ambos operam na faixa de frequências considerada. A analise destes limites foi motivada pela Resolução 157 da Conferência Mundial de Radiocomunicações de 2015 (WRC-15), que ressalta a necessidade de estudos envolvendo aspectos técnicos e operacionais relativos à operação de sistemas não-GEO operando na faixa de frequências de 3,7 - 4,2 GHz de modo a permitir que esses sistemas possam operar nestas faixas de frequências assegurando, ao mesmo tempo, que os serviços primários existentes, entre eles o FSS, continuem protegidos. A importância do assunto fez com que este tópico fosse incluído na agenda da WRC-19. No trabalho, é inicialmente desenvolvida uma metodologia para a determinação de máscaras limitantes para a densidade de fluxo de potência equivalente produzida pelos lances de descida (epfd(descida)) de sistemas de satélites não-GEO. Esta metodologia foi utilizada na obtenção de duas máscaras baseadas, respectivamente, nos critérios de proteção das recomendações ITU-R S.1323 e ITU-R F.1495. Uma análise comparativa das máscaras de epfd(descida) obtidas foi feita considerando-se cinco constelações de satélites não-GEO do tipo Walker Delta, escolhidas adequadamente para cobrir um amplo conjunto de possibilidades. A análise utilizou, como base, o comportamento estatístico das margens associadas a cada uma das máscaras de epfd(descida) propostas. / [en] In this work, the limits for the equivalent power-flux density produced by the down-links of non-geostationary satellite systems (non-GSO), operating in the 3,7-4,2 GHz band are analyzed. These limits aim the protection of Fixed-Satellite Service (FSS) receivers, from the interferences produced by non-geostationary satellite systems, operating in the same frequency band. The analysis of these limits was motivated by Resolution 157 of the 2015 World Radiocommunication Conference (WRC-15), that recognized the need for studies on technical and operational aspects related to the operation of non-GSO systems operating in the 3,7-4,2 GHz frequency band, so that these systems can adequately operate in these frequency band while ensuring, at the same time, that the existing primary services, among them the FSS, remain protected. Due to its importance the topic was included in the agenda of the WRC-19. In this work, a methodology for the determination of limiting masks for the equivalent power-flux density generated by the down-links (epfd(down)) of non-GSO satellite systems is initially developed. This methodology was used to obtain two mask based, respectively, on the protection criteria of the ITU-R S.1323 and ITU-R F.1495 recommendations. A comparative analysis of the two obtained epfd(down) masks was made considering five Walker Delta type non-GSO satellite constellation, appropriately chosen to cover a wide set of possibilities. The analysis used, as a basis, the statistic behavior of the margins associated to each of the proposed epfd(down) masks.

Cette thèse a pour but de modéliser les réseaux de capteurs sans fil à faible débit (WSN) basés sur la technique ultra bande étroite. Ce réseau a déjà été déployée par la société SIGFOX et a déjà démontré sa très grande efficacité pour les applications pour l’Internet des objets (IoTs) grâce à sa capacité de communication point à point efficace en terme de puissance consommée, et de sa connectivité de longue portée. Cette étude donne quelques aperçus sur le passage à l’échelle de la technique de l’UNB pour un réseau multipoint à point pour une liaison montante. L’accès au canal spécifique qui est basé sur l’accès multiple par répartition aléatoire de fréquence et de temps (R-FTDMA) est introduit et analysé. En outre, l’impact de l’interférence due à l’absence de stratégie d’ordonnancement à la couche MAC est étudié et modélisé. Notre modèle simplifié nous permet non seulement de décrire la puissance d’interférence agrégée, mais aussi d’évaluer les performances du système d’un tel réseau en matière de taux d’erreur et de probabilité de coupure. De même, la géométrie stochastique est utilisée pour modéliser la distribution spatiale des noeuds afin d’étendre le modèle simplifié dans le canal réaliste où les dégradations de canal sont prises en compte. De plus, le mécanisme de retransmission est considéré pour ce réseau. Cette étude permet de d’identifier le nombre optimal de retransmissions. Le réseau peut être configuré avec un paramètre global unique. Et enfin, cette thèse met en évidence le fait que le réseau de l’UNB Random-FTDMA est très pertinent dans un réseau réaliste, en particulier pour les applications à faible débit, car il allége le coût élevé du réseau, le coût de la synchronisation globale, mais sans perte de performance. / This thesis aims at modeling the low-throughput wireless sensor networks (WSNs) based on ultra-narrow-band technology. Such wireless network is already been deployed by Sigfox company and has proved to be ultra-efficient for the Internet of things (IoTs) applications thanks to its ability of point-to-point communication in terms of power efficiency and long range connectivity. In particular, this thesis gives some insights on the scalability of UNB technology for a multi-point-to-point network in an uplink scenario. The multiple access schemes based on random time and frequency selection are introduced and analyzed. Furthermore, the interference impact due to the lack of scheduling strategy at the MAC layer is studied and modeled. Our simplified model using rectangular function allows us not only to describe the aggregate interference power but also evaluate the system performance of such network in terms of the bit-error-rate and outage probability. Besides, the geometry stochastic is used for spatial node distribution in order to extend the simplified model in the realistic channel communication where the channel impairments are taken into account. Besides, the retransmission mechanism is considered for such network. This study argues an optimal number of retransmission. The network can be configured with a unique global parameter. Last but not least, this thesis highlights the fact that the UNB network using Random-FTDMA schemes is very relevant in a realistic network, especially for low-throughput applications, because it bypasses the high network cost, the cost of global synchronization but without loss of performance.