19 research outputs found

    Feed-forward technique to measure the reflection coefficient under CW high-power signals

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    ©2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper describes a measurement setup to obtain the reflection coefficient response over the frequency of a given device when this is subjected to a single-tone high-power (HP) signal. The proposed system is based on a feed-forward technique to cancel the reflected HP signal before reaching the vector network analyzer. This allows measuring the effects of the HP interfering signal into the device's low-power frequency response. This technique does not require either power-calibrated standards or complex calibration techniques. Experiments in several devices are also reported to validate the suitability of this technique.Peer ReviewedPostprint (author's final draft

    Sistemas eficientes de transmissão de energia sem-fios e identificação por radiofrequência

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    Doutoramento em Engenharia EletrotécnicaIn the IoT context, where billions of connected objects are expected to be ubiquitously deployed worldwide, the frequent battery maintenance of ubiquitous wireless nodes is undesirable or even impossible. In these scenarios, passive-backscatter radios will certainly play a crucial role due to their low cost, low complexity and battery-free operation. However, as passive-backscatter devices are chiefly limited by the WPT link, its efficiency optimization has been a major research concern over the years, gaining even more emphasis in the IoT context. Wireless power transfer has traditionally been carried out using CW signals, and the efficiency improvement has commonly been achieved through circuit design optimization. This thesis explores a fundamentally different approach, in which the optimization is focused on the powering waveforms, rather than the circuits. It is demonstrated through theoretical analysis, simulations and measurements that, given their greater ability to overcome the built-in voltage of rectifying devices, high PAPR multi-sine (MS) signals are capable of more efficiently exciting energy harvesting circuits when compared to CWs. By using optimal MS signals to excite rectifying devices, remarkable RF-DC conversion efficiency gains of up to 15 dB with respect to CW signals were obtained. In order to show the effectiveness of this approach to improve the communication range of passive-backscatter systems, a MS front-end was integrated in a commercial RFID reader and a significant range extension of 25% was observed. Furthermore, a software-defined radio RFID reader, compliant with ISO18000-6C standard and with MS capability, was constructed from scratch. By interrogating passive RFID transponders with MS waveforms, a transponder sensitivity improvement higher than 3 dB was obtained for optimal MS signals. Since the amplification and transmission of high PAPR signals is critical, this work also proposes efficient MS transmitting architectures based on space power combining techniques. This thesis also addresses other not less important issues, namely self-jamming in passive RFID readers, which is the second limiting factor of passive-backscatter systems. A suitable self-jamming suppression scheme was first used for CW signals and then extended to MS signals, yielding a CW isolation up to 50 dB and a MS isolation up 60 dB. Finally, a battery-less remote control system was developed and integrated in a commercial TV device with the purpose of demonstrating a practical application of wireless power transfer and passive-backscatter concepts. This allowed battery-free control of four basic functionalities of the TV (CH+,CH-,VOL+,VOL-).No contexto da internet das coisas (IoT), onde são esperados bilhões de objetos conectados espalhados pelo planeta de forma ubíqua, torna-se impraticável uma frequente manutenção e troca de baterias dos dispositivos sem fios ubíquos. Nestes cenários, os sistemas radio backscatter passivos terão um papel preponderante dado o seu baixo custo, baixa complexidade e não necessidade de baterias nos nós móveis. Uma vez que a transmissão de energia sem fios é o principal aspeto limitativo nestes sistemas, a sua otimização tem sido um tema central de investigação, ganhando ainda mais ênfase no contexto IoT. Tradicionalmente, a transferência de energia sem-fios é feita através de sinais CW e a maximização da eficiência é conseguida através da otimização dos circuitos recetores. Neste trabalho explora-se uma abordagem fundamentalmente diferente, em que a otimização foca-se nas formas de onda em vez dos circuitos. Demonstra-se, teoricamente e através de simulações e medidas que, devido à sua maior capacidade em superar a barreira de potencial intrínseca dos dispositivos retificadores, os sinais multi-seno (MS) de elevado PAPR são capazes de excitar os circuitos de colheita de energia de forma mais eficiente quando comparados com o sinal CW tradicional. Usando sinais MS ótimos em circuitos retificadores, foram verificadas experimentalmente melhorias de eficiência de conversão RF-DC notáveis de até 15 dB relativamente ao sinal CW. A fim de mostrar a eficácia desta abordagem na melhoria da distância de comunicação de sistemas backscatter passivos, integrou-se um front-end MS num leitor RFID comercial e observou-se um aumento significativo de 25% na distância de leitura. Além disso, desenvolveu-se de raiz um leitor RFID baseado em software rádio, compatível com o protocolo ISO18000-6C e capaz de gerar sinais MS, com os quais interrogou-se transponders passivos, obtendo-se ganhos de sensibilidade dos transponders maiores que 3 dB. Uma vez que a amplificação de sinais de elevado PAPR é uma operação crítica, propôs-se também novas arquiteturas eficientes de transmissão baseadas na combinação de sinais em espaço livre. Esta tese aborda também outros aspetos não menos importantes, como o self-jamming em leitores RFID passivos, tido como o segundo fator limitativo neste tipo de sistemas. Estudou-se técnicas de cancelamento de self-jamming CW e estendeu-se o conceito a sinais MS, tendo-se obtido isolamentos entre o transmissor e o recetor de até 50 dB no primeiro caso e de até 60 dB no segundo. Finalmente, com o objetivo de demonstrar uma aplicação prática dos conceitos de transmissão de energia sem fios e comunicação backscatter, desenvolveu-se um sistema de controlo remoto sem pilhas, cujo protótipo foi integrado num televisor comercial a fim de controlar quatro funcionalidades básicas (CH+,CH-,VOL+,VOL-)

    Itsehäiriön analoginen RF-kumoaminen

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    In this thesis a novel RF-canceler for full-duplex operation is presented, designed and implemented. The canceler is built for the full-duplex research group which is currently collaborating with Intel labs. The original design is from Intel. Two revision of cancelers were built and measured. The obtained results prove the canceler design to be effective and it is self-adaptive. The obtained cancellation in self-adaptive mode is order of 30 dB when using 20 MHz wide signal. This design fares well against other designs presented in academia

    Feed-forward technique to measure S-parameters under jamming CW high power out-of-band signals

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    In recent years, high-power radio frequency (RF) devices have become increasingly common due in part, to the high-speed telecommunications industry. The evolution of mobile devices drives to the use of wireless applications which will require different work frequencies and therefore the implementation of new and miniaturized devices. Moreover, passive intermodulation requirements at high-power levels, power handling of transmitting filters, thermal stability behaviour of duplexers, interference blockers, etc. are some examples of the increasing interest in characterizing passive devices such when they are driven by high power signals. Nowadays, there exist devices that use the above-mentioned power requirements. For example, a radar protection circuit of jamming signals incorporating frequency-selective auto-limiting devices must keep the low-signal performance while dealing with high power signals. The high-power components used in these applications must be characterized for both linear and nonlinear operation. Therefore, complex calibration procedures must be done and the calibration standard must be able to handle the power without changing their parameters or alternatively, using previously characterized power standards. Feed-forward techniques have been shown very useful to measure passive intermodulation (PIM) without using narrowband filters. The objective in PIM measurements is cancelling the high-power tone before going into the spectrum analyzer. Since no filters are required, there are no restrictions between the separation of tones and the system is not-specific to a given narrowband bandwidth. This master thesis is focused in the study of the interference problem in high-power transmitted signals and out-of-band transmissions through the design of different feed-forward cancellation algorithms with the aim of measure and characterize high-power components as well as study the nonlinear behaviour caused by thermal effects of Bulk Acoustic Wave (BAW) resonators due to the use of high-power signals

    Physical Layer Techniques for High Frequency Wireline Broadband Systems

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    This thesis collects contributions to wireline and wireless communication systems with an emphasis on multiuser and multicarrier physical layer technology. To deliver increased capacity, modern wireline access systems such as G.fast extend the signal bandwidth up from tens to hundreds of MHz. This ambitious development revealed a number of unforeseen hurdles such as the impact of impedance changes in various forms. Impedance changes have a strong effect on the performance of multi-user crosstalk mitigation techniques such as vectoring. The first part of the thesis presents papers covering the identification of one of these problems, a model describing why it occurs and a method to mitigate its effects, improving line stability for G.fast systems.A second part of the thesis deals with the effects of temperature changes on wireline channels. When a vectored (MIMO) wireline system is initialized, channel estimates need to be obtained. This thesis presents contributions on the feasibility of re-using channel coefficients to speed up the vectoring startup procedures, even after the correct coefficients have changed, e.g., due to temperature changes. We also present extensive measurement results showing the effects of temperature changes on copper channels using a temperature chamber and British cables. The last part of the thesis presents three papers on the convergence of physical layer technologies, more specifically the deployment of OFDM-based radio systems using twisted pairs in different ways. In one proposed scenario, the idea of using the access copper lines to deploy small cells inside users' homes is explored. The feasibility of the concept, the design of radio-heads and a practical scheme for crosstalk mitigation are presented in three contributions
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