Joint User Association, Power Allocation and Beamforming for NOMA-Based Integrated Satellite-Terrestrial Networks  
[PERSON]  
1 State Grid Economic and Technological Research Institute Co., Ltd., 102209 Beijing, China; 1  
[PERSON]  
1 State Grid Economic and Technological Research Institute Co., Ltd., 102209 Beijing, China; 1  
[PERSON]  
1 State Grid Economic and Technological Research Institute Co., Ltd., 102209 Beijing, China; 1  
[PERSON]  
1 State Grid Economic and Technological Research Institute Co., Ltd., 102209 Beijing, China; 1  
[PERSON]  
1 State Grid Economic and Technological Research Institute Co., Ltd., 102209 Beijing, China; 1  
[PERSON]  
2 Information Materials and Intelligent Sensing Laboratory of Anhui Province, Anhui University, 1  
Hefei 230601, China; 1  
[PERSON]  
2 Information Materials and Intelligent Sensing Laboratory of Anhui Province, Anhui University, 1  
Hefei 230601, China; 1  
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and outage constraints of satellite communications. In [8], the authors studied hybrid beamforming, user scheduling, and power allocation optimization in ISTN with the purpose of improving system sum rate and energy efficiency. The authors in [9] considered an uplink communication model consisting of a single satellite, a single terrestrial station, and multiple ground users. In this model, the BS serves as a satellite-terrestrial relay, bridging users and the satellite. The sum rate was maximized by optimizing user grouping and transmit power of users. Although elaborate resource allocation design can mitigate interference effectively, with the surge in user numbers, the congestion of spectrum resources has seriously degraded the communication rate in ISTNs. Recently, non-orthogonal multiple access (NOMA) technology has presented an effective solution to promote spectrum efficiency. In a NOMA system, multiple UEs can share the same spectrum resource, with interference being effectively mitigated by the adoption of successive interference cancellation (SIC) technology at the receiver [10; 11]. NOMA has been widely investigated in terrestrial networks. Ref. [12] investigated a sum rate maximization problem in a movable antenna-enabled uplink NOMA system. The author proposed a successive convex approximation-based algorithm to jointly optimize the movable antennas' positions, the decoding order, and the power control. The authors in [13] formulated a joint power allocation and channel assignment problem for uplink NOMA-based wireless communication networks. In order to solve the problem, a methodology that integrates convex optimization and machine learning techniques was proposed. In [14], a resource allocation problem for the coexistence of enhanced mobile broadband (eMBB) and ultra-reliable low-latency communication (URLLC) traffic scheduling was investigated; the sum rate of all eMBB users was maximized while maintaining the minimum data rate requirement of each eMBB user. Research reveals that NOMA offers significant performance advantages compared with the traditional orthogonal multiple access (OMA) schemes. The integration of NOMA into ISTNs to enhance communication performance and resource utilization tends to be an inevitable trend. Considering applying NOMA technology to terrestrial networks, [1] and [15] investigated downlink ISTNs. The authors in [15] studied user association, user pairing, subchannel allocation, and power allocation algorithms.