Outage Analysis for Cooperative Ambient Backscatter Systems

The outage probability of three symbiotic radio paradigms, namely, commensal, parasitic, and competitive schemes, are studied in a cooperative ambient backscatter system, where each scheme resorts to a different cooperative spectrum-sharing mechanism and a different system parameters setup for the primary and backscatter communications. For each scheme, the optimal reflection coefficient or the optimal primary transmit power are derived and closed-form expressions of outage probability are then developed for both primary and backscatter systems. Also, asymptotic outage behavior is characterized in the high transmit signal-To-noise ratio (SNR) regime. Our analysis shows that for the backscatter system, both parasitic and competitive schemes achieve the same outage probability which is irrelevant to the backscatter channels, whereas the commensal scheme can attain exactly the same asymptotic outage performance with the other two schemes at high transmit SNR. In addition, as the SNR threshold of the backscatter system approaches to zero, the three schemes can achieve the same outage performance for the backscatter system. Finally, the theoretical results are validated via Monte-Carlo simulations.