Backscatter Communications Using Harmonic Transponders

Backscatter communications is a collection of approaches, all which endeavor to increase the connectivity between devices using little to no additional power. In this work, we propose that harmonic transponders can be leveraged for this goal. These passive, nonlinear devices backscatter, nominally, the second harmonic of the incident signal, which eliminates self interference. Furthermore, the device's nonlinearity implies that weaker arriving multipath components are backscattered less effectively that stronger, e.g., line-of-sight, components, thereby, also mitigating multipath effects. In this work, we demonstrate, using a software defined radio (SDR) platform, that a bistatic communication link, leveraging a harmonic transponder as the passive repeater, can be established. Both binary and quadrature phase shift keying (BPSK and QPSK, respectively) are demonstrated and are shown to achieve an EVM of ~20%, when the power at the transponder is at least -20 dBm.