Adaptive Ambient Backscatter Communication Systems With MRC

Ambient backscatter (AmBack) communication, also called “modulation in the air,” has drawn growing interest by both academia and industry recently. In this paper, we investigate and analyze an AmBack system, where the user is equipped with an AmBack circuit at the transmitter and maximum ratio combing at the receiver. By harvesting power from the surrounding radio frequency source, the circuit operation and the signal backscattering can be supported. However, if there is not enough harvested power for the circuit operation, the signal backscattering will be suspended. Different from previous works on AmBack, an adaptive scheme is proposed to opportunistically exploit the residual or full user battery power for insufficient harvested power so that the signal backscattering is always available. However, there is no exact closed-form expression for the outage probability, and its approximation is obtained to facilitate our analysis. For comparison, the traditional non-adaptive scheme is also analyzed, and a closed-form expression for the outage probability is derived. In order to get more insight into both schemes, asymptotic outage performance is also derived when the number of receiver antennas/the noise power is sufficiently large/low. Simulation results demonstrate the tightness and the correctness of the derived outage probabilities, and show that the proposed adaptive scheme can significantly outperform the traditional non-adaptive scheme.