An OOK Chirp Spread Spectrum Backscatter Communication System for Wireless Power Transfer Applications

In this work, a general-purpose wireless energy receiving unit with improved backscatter (BS) communications capabilities assisted by far-field wireless power transfer (WPT) techniques is proposed. The unit employs an auxiliary RF-to-dc converter circuit which is used to simultaneously power and tune a low-power voltage controlled oscillator (VCO). By doing so, a relation between its frequency of oscillation and the instantaneous available RF input power is established. It is shown that by adding a small amplitude modulation to the wireless power carrier, the device can generate a linear frequency modulated signal which is used to provide low-power and long-range ON-OFF keying (OOK) chirp spread spectrum (CSS) BS communications. Experimental validation in real scenarios is provided, showing its superiority against the well-known conventional BS amplitude shift-keying (ASK) modulation scheme. Moreover, contrary to other designs, it is demonstrated that the proposed design does not need a dedicated processing unit to generate the required baseband signals, allowing to save power and complexity.