# Maximization of Average Achievable Rate for NOMA-UAV Dual-User Communication System Assisted by RIS
## 1 Introduction
The goal is to enhance the frequency resource efficiency of the system, assuming imperfect continuous interference cancellation. In [14], the author focuses on a RIS-assisted multi-UAV network scenario. The research goal is to minimize the system's total power expenditure while ensuring the minimum data rate threshold for users and the smallest safe spacing between drones. The joint optimal configuration problem is solved using the SCA algorithm and maximum ratio transmission technique. In [15], a UAV-RIS cooperative mobile edge computing framework is developed, and a dedicated NOMA-based task offloading protocol is introduced. The UAV performsboth relay and computing functions, enabling ground users to offload tasks to remote access points via RIS. In [16], the author thoroughly investigates the UAV communication scenario assisted by RIS. The research focuses on maximizing the total data throughput of all participants by collaboratively refining the RIS beamforming weight vector, the drone's spatial flight trajectory, and the energy distribution strategy. Within a downlink NOMA-UAV network, a UAV equipped with a single antenna is connected to a pair of users, each with a single antenna, with the assistance of RIS. The incoming signal is reconfigured via RIS and then forwarded to the users. The issue of enhancing total throughput in RIS-aided NOMA-based UAV communication systems is addressed, and a practical, efficient algorithm is proposed to obtain a suboptimal solution to the original problem [17]. In [18], this work investigates the synergistic optimization of a multi-RIS-assisted satellite-UAV-terrestrial integrated network and reshapes the transmission path in UAVs equipped with RIS to account for obstacles and dynamic environments. For the RIS-UAV hybrid optimization framework, ref. [19] proposes broadcasting data to ground devices using the NOMA protocol and maximizing the total rate of the vehicular network framework under the constraints of rate, battery, and coordination. In [20], the author investigates the RIS-assisted UAV-NOMA data collection network, where RIS enhances channel controllability, reduces interference, and adapts to UAV dual-mode switching scenarios. In [21], the NOMA network with a single UAV and RIS is studied. For scenarios involving a temporary base station and two users, the full-path outage probability and time-averaged channel capacity under the Nakagami-m channel are evaluated, with selection combining and maximum ratio combining techniques applied. The performance of both perfect and imperfect NOMA schemes based on SIC is analyzed. In [22], this paper investigates the NOMA millimeter-wave network in multi-UAV base station and distributed RIS scenarios, jointly optimizing beamforming, phase shifts, power, and three-dimensional layout to maximize system energy efficiency under imperfect SIC. In [23], the author investigates the optimization of power-utilization efficiency in the uplink NOMA system. The UAV equipped with RIS for anti-eavesdropping is used to jointly optimize power, coefficients, and three-dimensional layout, subject to rate and safe flight constraints. Additionally, in the high-frequency band, the channels of RIS and UAV are often sparse, meaning most propagation paths cannot effectively transmit signals, making the modeling of channel sparsity particularly important. In [24], the author propose a sparse adaptive channel estimation approach with a dynamic-threshold mechanism. By focusing exclusively on the columns of the measurement matrix that are above the threshold, this approach effectively minimizes computational complexity and subsequently decreases the number of required inner-product calculations. The comparison of related literature is shown in Table 1.  
The RIS-assisted NOMA-UAV scheme has garnered increasing attention in the context above. In this paper, the NOMA communication mode is introduced for the RIS-assisted UAV, with the number of users increased to two.