1,055 research outputs found
Waveforms and End-to-End Efficiency in RF Wireless Power Transfer Using Digital Radio Transmitter
We study radio-frequency (RF) wireless power transfer (WPT) using a digital
radio transmitter for applications where alternative analog transmit circuits
are impractical. An important paramter for assessing the viability of an RF WPT
system is its end-to-end efficiency. In this regard, we present a prototype
test-bed comprising a software-defined radio (SDR) transmitter and an energy
harvesting receiver with a low resistive load; employing an SDR makes our
research meaningful for simultaneous wireless information and power transfer
(SWIPT). We analyze the effect of clipping and non-linear amplification at the
SDR on multisine waveforms. Our experiments suggest that when the DC input
power at the transmitter is constant, high peak-to-average power ratio (PAPR)
multisine are unsuitable for RF WPT over a flat-fading channel, due to their
low average radiated power. The results indicate that the end-to-end efficiency
is positively correlated to the average RF power of the waveform, and that it
reduces with increasing PAPR. Consequently, digital modulations such as
phase-shift keying (PSK) and quadrature amplitude modeulation (QAM) yield
better end-to-end efficiency than multisines. Moreover, the end-to-end
efficiency of PSK and QAM signals is invariant of the transmission bit rate. An
in-depth analysis of the end-to-end efficiency of WPT reveals that the
transmitter efficiency is lower than the receiver efficiency. Furthermore, we
study the impact of a reflecting surface on the end-to-end efficiency of WPT,
and assess the transmission quality of the information signals by evaluating
their error vector magnitude (EVM) for SWIPT. Overall, the experimental
observations of end-to-end efficiency and EVM suggest that, while employing an
SDR transmitter with fixed DC input power, a baseband quadrature PSK signal is
most suitable for SWIPT at large, among PSK and QAM signals.Comment: Accepted for publication in IEEE Transactions on Microwave Theory and
Technique
Waveform Design for Wireless Power Transfer with Power Amplifier and Energy Harvester Non-Linearities
Waveform optimization has shown its great potential to boost the performance
of far-field wireless power transfer (WPT). Current research has optimized
transmit waveform, adaptive to channel state information (CSI), to maximize the
harvested power in WPT while accounting for energy harvester (EH)'s
non-linearity. However, the existing transmit waveform design disregards the
non-linear high power amplifiers (HPA) at the transmitter. Driven by this, this
paper optimizes the multi-carrier waveform at the input of HPA to maximize the
harvested DC power considering both HPA's and EH's non-linearities. Two
optimization models are formulated based on whether the frequencies of the
multi-carrier waveform are concentrated within the transmit pass band or not.
Analysis and simulations show that, while EH's non-linearity boosts the power
harvesting performance, HPA's non-linearity degrades the harvested power.
Hence, the optimal waveform shifts from multi-carrier that exploits EH's
non-linearity to single-carrier that reduces HPA's detrimental non-linear
distortion as the operational regime of WPT becomes more sensitive to HPA's
non-linearity and less sensitive to EH's non-linearity (and inversely).
Simultaneously, operating towards HPA's non-linear regime by increasing the
input signal power benefits the harvested power since HPA's DC power supply is
better exploited, whereas the end-to-end power transfer efficiency (PTE) might
decrease because of the increasing non-linear degradation. Throughout the
simulations, the proposed waveforms show significant gain over those not
accounting for HPA's non-linearity, especially in frequency-flat channels. We
also compare the two proposed waveforms and show that the severity of HPA's
non-linearity dictates which of the two proposed waveforms is more beneficial.Comment: 13 pages, 11 figures, submitted for potential publicatio
Wideband Waveforming for Integrated Data and Energy Transfer: Creating Extra Gain Beyond Multiple Antennas and Multiple Carriers
When wideband signals propagate in a rich-scatterer environment, we obtain abundant resolvable multiple transmission paths to form a number of virtual antennas. Therefore, substantial spatial gain can be attained by carefully waveforming in all these resolvable transmission paths without additional antennas. This resultant spatial gain is then exploited for improving the performance of integrated-data-and-energy-transfer (IDET) from a single transmitter to multiple receivers. We aim to maximise the downlink fair-throughput and sum-throughput, while satisfying the energy harvesting requirements by jointly optimising the waveformers at the transmitter and the power splitters at the receivers. A low-complexity fractional-programming (FP) based alternating algorithm is proposed to solve these non-convex optimisation problems. The non-convex wireless energy transfer (WET) constraints are transformed to be convex with a modified quadratic transform (MQT) method. As a result, the stationary points for both the fair-throughput and the sum-throughput maximisation problems are obtained. The numerical results demonstrate the advantage of our proposed algorithm over a minimum-mean-square-error (MMSE) scheme, a zero-forcing (ZF) scheme and a time-reversal (TR) scheme. Simulation results show that the wireless data transfer (WDT) performance of our scheme outperforms the single-input-single-output orthogonal-frequency-division-multiple-access (SISO-OFDMA) when the output direct current (DC) power requirement is high. When we have a practical individual subcarrier power constraint, the WDT performance of our scheme outperforms multiple-input-single-output orthogonal-frequency-division-multiplex-access (MISO-OFDMA)
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