Signal Waveform Impact on Efficiency of Low Power Harvesting Devices in WSN

The paper is devoted to the study of the impact of different multi-tone signals on the efficiency of low power harvesting devices in wireless sensor networks (WSN). Moreover, the impact of the load resistance on harvesting device performance is examined. For the current experimental study a low power RF harvesting device, consisting of a classic voltage doubler circuit for RF-DC conversion and a DC-DC converter based on Texas Instruments manufactured chip BQ25504, is used. Single-tone and 8-64 multi-tone signals with high and low peak-to-average power ratio (PAPR) levels are employed as signal waveforms. A software defined radio (SDR) USRP B210 and a PC with MATLAB/Simulink software are used for generation and RF transmission of different waveforms in an unlicensed sub-gigahertz ISM band. To generate low PAPR signals, Zadoff-Chu sequences and an IFFT operation are employed, but for high PAPR signal generation subcarriers with the same amplitude are summed together in phase. To evaluate the efficiency of RF-DC conversion of the low power harvesting device, the voltage at the input and output of the classic voltage doubler circuit is measured. For the performance estimation of the harvesting device the average output power of the DC-DC power converter is also measured.