Resource Allocation for Double IRSs Assisted Wireless Powered NOMA Networks

We consider an intelligent reflecting surface (IRS)-aided wireless-powered non-orthogonal multiple access (NOMA) network, in which double IRSs are adopted to boost the communication between the transmitter and receiver. We split the overall process into two phases: i) downlink wireless energy transmission (WET) in the first phase and ii) uplink wireless information transmission (WIT) in the second phase. Compared with the existing works, the double IRSs scheme is considered due to obstacles or deep shadowing between the transmitter and receiver. Specifically, we propose a scheme to maximize the sum rate by jointly optimizing the time allocation and phase shift matrices in these two phases. The optimization problem is non-trivial because of the coupling of multiple variables and the constraint of phase shift. An alternative optimization algorithm is adopted to surmount the objective step by step. The WET phase shift matrices are first obtained under given WIT phase shift matrices, and then vice versa. Numerical analysis proves the validity of the proposed scheme in increasing the sum rate and the effectiveness of double IRSs.