Waveform Optimization for Large-Scale Multi-Antenna Multi-Sine Wireless Power Transfer

Wireless power transfer (WPT) is expected to be a technology reshaping the landscape of low-power applications such as the Internet of Things, machine-to-machine communications and radio frequency identification networks. Although there has been some progress towards multi-antenna multi-sine WPT design, the large-scale design of WPT, reminiscent of massive multiple-input multiple-output (MIMO) in communications, remains an open problem. Considering the nonlinear rectifier model, a multiuser waveform optimization algorithm is derived based on successive convex approximation (SCA). A lower-complexity algorithm is derived based on asymptotic analysis and sequential approximation (SA). It is shown that the difference between the average output voltage achieved by the two algorithms can be negligible provided the number of antennas is large enough. The performance gain of the nonlinear model based design over the linear model based design can be large, in the presence of a large number of tones.Comment: To appear in the 17th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2016

Wirelessly Powered Backscatter Communications: Waveform Design and SNR-Energy Tradeoff

This paper shows that wirelessly powered backscatter communications is subject to a fundamental tradeoff between the harvested energy at the tag and the reliability of the backscatter communication, measured in terms of SNR at the reader. Assuming the RF transmit signal is a multisine waveform adaptive to the channel state information, we derive a systematic approach to optimize the transmit waveform weights (amplitudes and phases) in order to enlarge as much as possible the SNRenergy region. Performance evaluations confirm the significant benefits of using multiple frequency components in the adaptive transmit multisine waveform to exploit the nonlinearity of the rectifier and a frequency diversity gain.Comment: submitted for publicatio

Large-Scale Multi-Antenna Multi-Sine Wireless Power Transfer

Wireless Power Transfer (WPT) is expected to be a technology reshaping the landscape of low-power applications such as the Internet of Things, Radio Frequency identification (RFID) networks, etc. Although there has been some progress towards multi-antenna multi-sine WPT design, the large-scale design of WPT, reminiscent of massive MIMO in communications, remains an open challenge. In this paper, we derive efficient multiuser algorithms based on a generalizable optimization framework, in order to design transmit sinewaves that maximize the weighted-sum/minimum rectenna output DC voltage. The study highlights the significant effect of the nonlinearity introduced by the rectification process on the design of waveforms in multiuser systems. Interestingly, in the single-user case, the optimal spatial domain beamforming, obtained prior to the frequency domain power allocation optimization, turns out to be Maximum Ratio Transmission (MRT). In contrast, in the general weighted sum criterion maximization problem, the spatial domain beamforming optimization and the frequency domain power allocation optimization are coupled. Assuming channel hardening, low-complexity algorithms are proposed based on asymptotic analysis, to maximize the two criteria. The structure of the asymptotically optimal spatial domain precoder can be found prior to the optimization. The performance of the proposed algorithms is evaluated. Numerical results confirm the inefficiency of the linear model-based design for the single and multi-user scenarios. It is also shown that as nonlinear model-based designs, the proposed algorithms can benefit from an increasing number of sinewaves.Comment: Accepted to IEEE Transactions on Signal Processin

Metodologia de excitação para identificação de parâmetros dinâmicos de selos anulares

The choice of the excitation signal is an important step in any identification procedure of rotating machinery. There are applications where the total experiment time, as well as the shaft displacement are boundary conditions which have to be taken into account before performing the test. Thus, the excitation signal used in the actuator must be such that there is an adequate distribution of the energy applied into the system, complying the aforementioned restrictions. In this thesis, a comparisson between the dynamic parameters of annular seals and bearings obtained using several excitation signals is made. Modified multisine signals produced by means of iterative algorithms, which reduce their crest factor and therefore improve the input Signal-to-noise ratio, are also included in this work. Two small-scale test rigs with electromagnetic actuators, developed in the Acoustics and Vibration Laboratory of the Federal University of Rio de Janeiro, were used to perform the experimental tests. It can be observed from the obtained results a noteworthy reduction of the variances when modified multisine signals are used, if compared with the traditional swept or white noise signalsA escolha do sinal de excitação desempenha um papel importante em qualquer procedimento de identificação de parâmetros em máquinas rotativas. Existem aplicações cujo tempo total de experimento, como também o deslocamento do eixo permitido são condições que devem ser levadas em conta na preparação dos ensaios. Portanto, o sinal de excitação aplicado no atuador deve ser de tal maneira que haja uma adequada distribuição da energia aplicada no sistema, respeitando as limitações anteriormente mencionadas. Nesta tese é apresentada uma comparação entre os coeficientes equivalentes de selos anulares e mancais obtidos mediante distintos sinais de excitação, incluindo sinais multitônicos modificados, construídos a partir de algoritmos iterativos que reduzem o fator de crista do sinal, e que permitem aumentar a razão sinal-ruído nas medições, diminuindo as incertezas dos coeficientes obtidos nos ensaios. Para isso, duas bancadas de pequeno porte, desenvolvidas no Laboratório de Acústica e Vibrações da UFRJ, cuja excitação é aplicada por meio de atuadores eletromagnéticos, foram empregadas para realizar os respectivos ensaios. A partir dos resultados obtidos nessas bancadas, é possível observar a redução das variâncias dos coeficientes quando sinais multitônicos modificados são empregados, se comparado com as obtidas usando sinais tipo varredura em frequência ou ruído branco