Wireless spectrum is a limited resource that must be used efficiently. It is also a broadcast medium, hence, additional procedures are required to maintain communication over the wireless spectrum private. In this thesis, we investigate three key issues related to efficient use and privacy of wireless spectrum use. First, we propose GAVEL, a truthful short-term auction mechanism that enables efficient use of the wireless spectrum through the licensed shared access model. Second, we propose CPRecycle, an improved Orthogonal Frequency Division Multiplexing (OFDM) receiver that retrieves useful information from the cyclic prefix for interference mitigation thus improving spectral efficiency. Third and finally, we propose WiFi Glass, an attack vector on home WiFi networks to infer private information about home occupants. First we consider, spectrum auctions. Existing short-term spectrum auctions do not satisfy all the features required for a heterogeneous spectrum market. We discover that this is due to the underlying auction format, the sealed bid auction. We propose GAVEL, a truthful auction mechanism, that is based on the ascending bid auction format, that avoids the pitfalls of existing auction mechanisms that are based on the sealed bid auction format. Using extensive simulations we observe that GAVEL can achieve better performance than existing mechanisms. Second, we study the use of cyclic prefix in Orthogonal Frequency Division Multiplexing. The cyclic prefix does contain useful information in the presence of interference. We discover that while the signal of interest is redundant in the cyclic prefix, the interference component varies significantly. We use this insight to design CPRecycle, an improved OFDM receiver that is capable of using the information in the cyclic prefix to mitigate various types of interference. It improves spectral efficiency by decoding packets in the presence of interference. CPRecycle require changes to the OFDM receiver and can be deployed in most networks today. Finally, home WiFi networks are considered private when encryption is enabled using WPA2. However, experiments conducted in real homes, show that the wireless activity on the home network can be used to infer occupancy and activity states such as sleeping and watching television. With this insight, we propose WiFi Glass, an attack vector that can be used to infer occupancy and activity states (limited to three activity classes), using only the passively sniffed WiFi signal from the home environment. Evaluation with real data shows that in most of the cases, only about 15 minutes of sniffed WiFi signal is required to infer private information, highlighting the need for countermeasures.

[pt] Nesta dissertação é proposto um novo método para a avaliação da eficiência de uso do espectro a ser aplicado para os sistemas de telecomunicações pontoárea, incluindo radiodifusão, e ponto-a-ponto. A definição proposta para o índice de eficiência é baseada nos aspectos técnicos, mas outros aspectos que podem influenciar na determinação da eficiência dos sistemas de telecomunicações, como os econômicos, sociais, políticos e estratégicos também são discutidos. O método é testado com dados reais de sistemas disponibilizados pela Anatel e no sítio dos prestadores de serviços de telecomunicações no Brasil. É muito importante avaliar a eficiência dos sistemas de telecomunicações, pois sendo o espectro de radiofreqüências um recurso limitado, pela tecnologia e capacidade de gerenciamento, a introdução de novos serviços de telecomunicações somente será possível com a substituição, pela realocação ou extinção, de determinadas aplicações menos eficientes. Apesar da regulamentação nacional e internacional constantemente referir-se à importância do uso eficiente das faixas de freqüências, não existe um método harmonizado de avaliação, o que impede a verificação deste aspecto pelos órgãos reguladores. As novas tecnologias e as oportunidades de desenvolvimento social que elas proporcionam demonstram a necessidade da boa gerência do espectro de radiofreqüências e de que cada uma de suas porções seja utilizada de forma eficiente e adequada a cada tipo de aplicação. / [en] In this work a new method for the assessment of the spectrum use efficiency is proposed to be applied to point-area, including broadcasting, and point-to-point telecommunications systems. The proposed definition of the efficiency index is based in technical aspects, but other subjects that affect the determination of a telecommunications system efficiency, as economics, social, political and strategic issues are also discussed. The method is tested with data of real systems available from the Brazilian Regulatory Agency (Anatel) and at the telecommunications service providers web sites. It is very important to assess the telecommunications systems efficiency, because being the radio spectrum a scarce resource, limited by technology and management capacity, the introduction of new telecommunications services will only be possible by replacement, refarming or suppression of some less efficient applications. Despite national and international regulations usually refers to the importance of efficient use of the frequency bands, there is no harmonized assessment method to be applied and verified by the regulators. The new technologies and the opportunities for social development provided by them, bring to the light the need for a good radio spectrum management and how each part of it must be used efficiently and assigned properly for each type of application or telecommunications service.