# Optimization of Effective Throughput in NOMA-Based Cognitive UAV Short-Packet Communication
## 1 Introduction  
### Background and Related Works  
With the development of 6G communication technology, UAV communication is becoming a hot research topic [1]. In ultra-reliable and low-latency communication (URLLC) scenarios, stable line-of-sight (LoS) communication can be obtained using UAV communication [2]. In addition, UAVs can rapidly change location and be deployed on demand [3] for emergency communication scenarios. However, they also face several challenges, one of which is spectrum scarcity. Due to the development of communication technologies and the increase in communication users [4; 5; 6], the problem of spectrum resource scarcity has become more severe. To solve this challenge, the concept of spectrum sharing is proposed and cognitive radio (CR) technology is created [7]. In addition, non-orthogonal multiple access (NOMA) techniques can also improve spectrum utilization efficiency [8]. By using cognitive radio technology, the state of the primary user (PU) can be sensed by the UAV and when the state of the PU is idle, the UAV uses the spectrum of the PU for communication [9]. In [10], the authors investigated the effect of the UAV's sensing radius on the performance of the communication system under circular and straight trajectories. In [11], the sensing time and the transmitting power of the UAV were jointly optimized to improve the energy efficiency of the system. In [12], a cognitive UAV mobile relay network based on energy harvesting was studied and power control algorithms were proposed to maximize the throughput of the system. In [13], UAV cognitive communication systems in overlay mode and hybrid mode were investigated separately. Specifically, the energy and spectral efficiency of the system were improved by optimizing the system parameters. In [14], multiple PUs were considered in UAV cognitive communication systems. The results show that the trajectory of the UAV has an impact on the system transmission rate and the existence of an optimal trajectory. Successive interference cancellation (SIC) is used in NOMA communications, which allows the receiver to process information on the same time/frequency carrier [15]. This provides an efficient way for UAVs to serve users with different types of service needs with limited spectrum resources. Until now, many studies have been conducted on the application of NOMA to UAVs. In [16], the height of the UAV was optimized to ensure the fairness of the NOMA-based UAV communication system under the single-user rate limit. In [17], the authors derived the outage probability of the NOMA-based UAV communication system under the Rician channel model and analyzed the effect of the parameters on the system. In [18], the NOMA-UAV transmitted data from the base station to multiple ground users and the authors considered jointly optimizing the location and transmission power of the UAV to minimize its total power consumption. In [19], a UAV was used as a relay node for emergency communication employing NOMA techniques while considering fair transmission for ground users. In [20], a scenario of data collection by NOMA-based UAV was considered. The UAV flew in a linear trajectory and the authors took the time efficiency of the data collection as the optimization objective. As an important component of 6G wireless technology, UAVs need to provide URLLC, which typically uses short-packet communication (SPC) to reduce physical-layer transmission delays [21]. In [22], Professor [PERSON] investigated the mathematical relationship between the transmission rate and relevant parameters in short-packet communication under additive Gaussian white noise (AWGN) channels. In contrast to long-packet communication, where the packets are shorter, the transmission rate of the packets was shown to be smaller than the Shannon capacity and the decoding error probability should be considered [23; 24; 25; 26].