Abstract
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 parameter 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 nonlinear amplification at the SDR on multisine waveforms. Our experiments suggest that when the direct current (dc) input power at the transmitter is constant, high peak-to-average power ratio (PAPR) multisines 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 with 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 modulation (QAM), yield better end-to-end efficiency than multisines. Moreover, the end-to-end efficiency of PSK and QAM signals is invariant to 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.
Highlights
T HE fifth generation (5G) of mobile communications is expected to network trillions of sensors into the so-calledManuscript received November 16, 2019; revised June 18, 2020 and September 11, 2020; accepted November 30, 2020
2) We show that with a fixed PiDn C and the resistive loads in the orders of a few hundred ohms, ordinary communication signals such as phase-shift keying (PSK) and quadrature amplitude modulation (QAM) are more suitable for RF wireless power transfer (WPT) than the co-phased multisine waveforms with high peak-to-average power ratio (PAPR) that are tailored for energy harvesting (EH) only
The constellation analysis of quadrature phase-shift keying (QPSK)-modulated signal reveals that the gradual increase of error vector magnitude (EVM) beyond 2 Mbps bit rate is due to the impact of carrier frequency offset (CFO) which occurs over clusters of samples, while the rapid increase in the saturation region of operation can be attributed to the wideband noise that creeps in
Summary
T HE fifth generation (5G) of mobile communications is expected to network trillions of sensors into the so-called. This paper is an expanded version from the IEEE MTT-S International Microwave Symposium (IMS 2019), Boston, MA, USA, June 2-7, 2019. Color versions of one or more of the figures in this article are available online at https://ieeexplore.ieee.org. Internet-of-Things (IoT); such an extreme-scale deployment would certainly require equipping the sensors with replenishable energy sources. Far-field radiofrequency (RF) wireless power transfer (WPT) is being studied as a possible solution to these challenges [2]. It would allow powering sensors on demand, and supercapacitors could suffice for temporary energy storage, averting sensors from becoming hazardous waste after their working life
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