Hybrid Backscatter and Underlay Transmissions in RF-Powered Cognitive Radio Networks

The radio frequency (RF)-powered cognitive radio network (CRN) has been introduced with the harvest-then-transmit (HTT) protocol. Here, wireless nodes harvest energy from the ambient signal and transmit data through sharing communication channels with primary users. The transmission efficiency of the HTT protocol, however, depends on the primary channel condition, which varies over time. On the other hand, backscatter communication (BSC) can be integrated into the RF-powered communication to circumvent limitations of the HTT protocol. Therefore, efficient combination of both communication modes is crucial to achieve the highest throughput for the secondary system while respecting regulation constraints of the primary system. In this paper, the Stackelberg game approach is employed to study the interaction between a primary transmitter (PT) and multiple secondary transmitters (STs) who are interested in maximizing their own utilities. Specifically, the PT imposes prices charged to the STs based on the level of interference emitted by the STs during their HTT data transmission mode. Given the prices, the STs optimize the time fractions in the BSC and HTT modes to maximize their utilities. We apply the backward induction method to analyze the game and prove the uniqueness of the Nash equilibrium (NE) for the underlying game. Extensive numerical results confirm the efficacy of our proposed framework in balancing the utilities achieved by the players. They also show that our proposed design framework outperforms other baseline approaches.