Frequency-Domain SWIPT and Modulation Classification: Design and Experimental Validation

Simultaneous wireless information and power transfer (SWIPT) constitutes an emerging paradigm that prolongs the lifetime of energy-constrained devices, such as wireless sensors and Internet-of-Things (IoT) nodes. Its frequency-domain (FD) variant enables energy harvesting (EH) by using (low-power) local oscillators/mixers. In this paper, a novel FD-SWIPT waveform design that minimizes the multitone interference induced to the information signal by the energy signal, thus eliminating the need for using receive filters to this end, is described. The inherent interference suppression of the proposed strategy allows also for applying modulation classification (MC). This functionality is highly desirable in contemporary networks, where the access points utilize adaptive transmission. In this context, we analytically derive the average error probability of the proposed waveform over a Rayleigh fading channel for various modulation schemes under non-zero interference and frequency synchronization errors. Furthermore, we optimize the power of the energy tones, such that the signal-to-interference-ratio at the information signal is maximized subject to the EH and transmission power constraints. In addition, we investigate the coexistence of SWIPT with blind MC under this framework. Numerical simulation results reveal that the proposed approach substantially increases both the data rate and the harvested power in comparison to the conventional power-splitting method at the cost of a negligibly higher error probability. Also, they indicate that the employed MC scheme achieves a high success rate even in the low signal-to-noise-ratio regime. The proposed concept is validated experimentally in a realistic indoor environment by using a testbed based on software-defined radio units.