IoT Communications With $M$ -PSK Modulated Ambient Backscatter: Algorithm, Analysis, and Implementation

Ambient backscatter (AB), making use of both energy harvesting and backscattering, has recently become a promising solution to communications among low-power devices and demonstrates its potential application in the Internet of Things. Existing AB systems adopt two-state amplitude shift keying or phase shift keying (PSK), where data are transmitted at the rate of one bit per symbol period. To increase the data rate, we investigate the high-order modulation where ${M}$ -PSK is employed for backscattering. We derive the optimal multilevel energy detector and compute the closed-form symbol error rate. To show the realizability of the proposed design, we build a 4PSK-AB hardware prototype, in which the selection of load impedance is discussed with the aid of phasor diagram illustration. The hardware prototype can achieve the date rate of 20 kb/s. Besides, higher date rate is achievable for 98.7% of the time compared with binary AB communications, and the mean number of distinguishable symbols is 3.66.