Outage Capacity Analysis for Ambient Backscatter Communication Systems

Ambient backscatter communication (AmBC) has become a promising technology to the Internet of Things $(IoT)$ due to its low cost and high energy-efficiency. Since the AmBC shares the same frequency band with the conventional system, they can be considered as a spectrum sharing system. In this paper, we first focus on the minimization of the secondary $(i.e.,$ AmBC) system’s outage probability by optimizing the power allocation strategy with perfect channel state information (CSI). Then, a more practical scenario where the CSI is imperfect is considered. A new power allocation strategy is proposed by introducing a channel power protection gap to improve the robustness of the secondary system. Finally, extensive numerical results show that as such protection gap increases, the decrease of the additional outage probability slows down. Therefore, with a certain tolerance of the additional outage probability, the primary transmitter can save its transmit power by using a proper channel power protection gap.