Plataforma para projeto de sistemas de rádio definidos por software

Mestrado em Engenharia Electrónica e TelecomunicaçõesEste trabalho tem como objetivos o projeto e a realização de uma plataforma para desenvolvimento de sistemas baseados em tecnologia Software Defined Radio (SDR). Num sistema SDR todas as tarefas de um rádio (ou pelo menos banda base e eventualmente Frequência Intermédia), anteriormente efetuadas por hardware especifico num contexto analógico, são efetuadas no domínio digital por software ou hardware reconfigurável. Esta característica confere a este tipo de rádio uma maior simplicidade, em termos de hardware bem como maior flexibilidade, pois o mesmo dispositivo pode executar diferentes funções apenas alterando o seu firmware/software. Existem diferentes abordagens relativas ao uso desta tecnologia, quer ao nível da arquitetura usada (varia consoante a frequência onde ocorre a digitalização do sinal), quer relativas á topologia de utilização (controlada por hardware reconfigurável, rotinas de software ou ambos). A motivação deste trabalho resulta na necessidade de concepção de uma plataforma para fins académicos baseada num hardware reprogramável, Field Programmable Gate Array (FPGA), de baixo custo, flexível, com interfaces de comunicação digitais e analógicas e que faculte a possibilidade de ser usada em diferentes topologias de utilização. Efetuada a especificação e o estudo necessário ao projeto bem como a escolha apropriada de componentes, conseguiu-se uma plataforma baseada num módulo FPGA contendo um dispositivo Xilinx, da família Spartan-6, bem como outro hardware relevante. A comunicação com outros dispositivos é assegurada por interfaces USB e gigabit Ethernet. A plataforma concebida está também equipada com interfaces analógicas (conversores AD/DA) bem como algumas interfaces de integração com o utilizador consistindo em switches e LEDs. Em suma foi projetada e desenhada uma plataforma aberta e flexível, que pode ser usada com todas as ferramentas de desenvolvimento, programação e depuração, com fácil acesso a todos os sinais relevantes potenciando a sua utilização para efeitos de ensino e investigação em SDR.The main objective of this dissertation relies on projecting and designing a platform suitable for Software De ned Radio (SDR) system development. On an SDR system all, or at least base band and maybe Intermediate Frequency (IF) radio functions, before handled by analog speci c hardware, are now performed on the digital domain by software or an recon gurable hardware device. This feature provides to this type of radios a major simplicity regarding hardware as well as another exibility level since, through a rmware/software upgrade, the same equipment can perform di erent functions. There are some approaches related to the used of this technology, either regarding architecture implementation (they di er in which frequency the digitalization occurs) or utilization topologies (an SDR device can be controlled by a recon gurable hardware, software routines or both). This project's motivation results from the need of designing a exible, low-cost platform, to be used on academic purposes, in which the central component would be a recon gurable hardware, a Field Programmable Gate Array (FPGA). It must provide both analog and digital interfaces so that can be used on various utilization scenarios. Accomplished all the necessary study, design and hardware selection the result is a platform based on an FPGA module, containing an Xilinx device from the Spartan-6 family as well as other relevant hardware. The interaction with other devices is ensured by both gigabit Ethernet and 2.0 Universal Serial Bus (USB) connections. The platform also features analog interfaces (AD/DA converters) as well as some digital end-user interfaces performed by switches and Light Emiter Diodes (LED)s. Concluding, it was built an open and exible platform in which can be use with all provided development, programming and debugging tools and all the relevant signals have easy access enhancing its use for teaching and researching on SDR technology

Localization technique based on dual-frequency doppler ranging estimation

Positioning awareness plays an important role in modern applications such as internet of thing (IoT) and intelligent transportation system (ITS). One of the commonly used positioning techniques is trilateration as it estimates the location of a blind device or node by using the distance from several other devices or anchor nodes. The ranging technique used to obtain distance information is a crucial step to provide high accuracy in location estimation. Dual-frequency Doppler radar (DFDR) ranging technique has been widely used in radars and radio frequency identification (RFID) applications. In radar application, this technique requires a closed-loop communication link to estimate distance and has not been exploited in single radio frequency transmission. In this thesis, a ranging technique not requiring a closedloop communication link named one-way forward communication link dual-frequency Doppler (DFD) ranging technique is introduced. The performances of the DFD distance estimation were analysed using simulations and experimental measurements. In the DFD experiment, the anchor node transmitted two different frequencies with a certain frequency separation. The blind node captured the received signal, and the phase difference was extracted and unwrapped using offline processing system. The phase difference between the two received signals was used for DFD ranging estimation before being applied to locate the position of the blind node through trilateration method. Software defined radio (SDR) platform using GNU radio and universal software radio peripheral (USRP) was used to develop the localization system. The experimental results showed that DFD ranging technique can deliver up to 84% distance estimation improvement in comparison to conventional receive signal strength (RSS) ranging technique. In conclusion, the proposed DFD ranging technique is a promising positioning solution for future applications such as IoT and ITS

Spectrum sensing algorithms and software-defined radio implementation for cognitive radio system

The scarcity of spectral resources in wireless communications, due to a fixed frequency allocation policy, is a strong limitation to the increasing demand for higher data rates. However, measurements showed that a large part of frequency channels are underutilized or almost unoccupied. The cognitive radio paradigm arises as a tempting solution to the spectral congestion problem. A cognitive radio must be able to identify transmission opportunities in unused channels and to avoid generating harmful interference with the licensed primary users. Its key enabling technology is the spectrum sensing unit, whose ultimate goal consists in providing an indication whether a primary transmission is taking place in the observed channel. Such indication is determined as the result of a binary hypothesis testing experiment wherein null hypothesis (alternate hypothesis) corresponds to the absence (presence) of the primary signal. The first parts of this thesis describes the spectrum sensing problem and presents some of the best performing detection techniques. Energy Detection and multi-antenna Eigenvalue-Based Detection algorithms are considered. Important aspects are taken into account, like the impact of noise estimation or the effect of primary user traffic. The performance of each detector is assessed in terms of false alarm probability and detection probability. In most experimental research, cognitive radio techniques are deployed in software-defined radio systems, radio transceivers that allow operating parameters (like modulation type, bandwidth, output power, etc.) to be set or altered by software.In the second part of the thesis, we introduce the software-defined radio concept. Then, we focus on the implementation of Energy Detection and Eigenvalue-Based Detection algorithms: first, the used software platform, GNU Radio, is described, secondly, the implementation of a parallel energy detector and a multi-antenna eigenbased detector is illustrated and details on the used methodologies are given. Finally, we present the deployed experimental cognitive testbeds and the used radio peripherals. The obtained algorithmic results along with the software-defined radio implementation may offer a set of tools able to create a realistic cognitive radio system with real-time spectrum sensing capabilities