Impact of Software-Defined Radio Transmitter on the Efficiency of RF Wireless Power Transfer

In this paper, we experimentally examine the impact of a digital radio transmitter on radio-frequency (RF) wireless power transfer (WPT). The test-bed for this purpose consists of a software-defined radio (SDR) transmitter, an external power amplifier (PA), a variable attenuator to emulate the high losses in wireless propagation, and an RF energy harvesting receiver. The test-bed facilitates determining the transmitter efficiency and overall DC-DC efficiency of different test waveforms for RF WPT. We assess the performance of multisine signals as well as an information-bearing quadrature phase-shift keying (QPSK) signal for RF WPT, under different channel conditions, by determining the transmitter, DC-DC and receiver efficiency. The experiments reveal that high peak-to-average power ratio constraints the maximum RF output power for multisine signals. Even with similar input average power, single sinusoid RF waveforms yield the highest DC-DC and receiver efficiency. Moreover, a QPSK signal with transmit filtering provides good efficiency for WPT and seems to be a waveform suitable for simultaneous wireless information and power transfer applications.