Leverage the Duty Ratio of Frequency-Shift Wave to Design a Novel Amplitude Modulation for Backscatter Communications

The demand for ultra-low-power wireless connectivity motivates the study of backscatter communication technology. There are already some related products on the market based on excitation signals from commercial radios. However, their modulation techniques, which are the key to backscatter communications, mainly focus on the phase or frequency domain while amplitude modulation is largely ignored. Most research works either deploy one finely tuned RF impedance port for every needed reflection state or connect a nonlinear device to antenna and tune the reflection amplitude by adjusting its biasing voltage, where the former is too complex and the latter is unstable under variable incident signal power, limiting the backscatter applications. For this reason, we introduce AMscatter to leverage the duty ratio of the frequency-shift wave (FS-wave) to design a novel amplitude modulation. Both theoretical analysis and experimental results show that the reflection amplitude approximates a sinusoidal function of the duty ratio. This method requires only two fixed RF impedances, making AMscatter simple and stable. Moreover, we show how to use AMscatter to design quadrature amplitude modulation (QAM) and pulse shaping to improve backscatter communication performance. Extensive experimental results show that the throughput can be as high as 3.9 Mbps, the supported operational range can reach 20 m with 16-QAM modulation, and the out-of-band interference can be suppressed by 15 dB without negatively affecting the communication performance through our pulse shaping.