## 1 Introduction
### Related Work  
Regarding developing applications of satellite communication systems, there was considerable attention paid to the research community since these systems are widely implemented in the field of broadcasting and navigation for their larger coverage in serving terrestrial devices [11; 12]. Since obstacles exist in the link from terrestrial users to satellite and it limits the transmission of the line of sight (LoS). As a result, the masking effect occurs in such systems as the main impairment. In recent technical literature, the HSTRN has been extensively investigated. For example, in [13; 14; 15], amplify-and-forward (AF) relaying is employed to enhance the performance of HSTRN. In contrast, HSTRN was considered in relaying mode using the decode-and-forward (DF) as in [16; 17]. The HSTRN was studied in a system model that combines the beamforming technique and AF transmission mode [18]. The author in [19] studied an overlay cognitive hybrid satellite-terrestrial network allowing a primary satellite source-receiver pair and a secondary transmitter-receiver pair can operate under impact of practical hardware impairments (HIs). The DF-based secure 3D mobile unmanned aerial vehicle (UAV) relaying was investigated in the scenario of satellite-terrestrial networks [20]. In this case, probability of non-zero secrecy capacity (PNZSC) and secrecy outage probability (SOP) are presented. In the context of all network nodes are subjected to hardware impairments, a multi-relay selection (MRS) scheme is studied to improve the outage performance of the HSTRN [21].  
Recently, to improve spectral efficiency NOMA was introduced as one promising architecture for multiple access applied in future fifth-generation (5G) wireless networks [22]. By permitting multiple users to be served by same resource (the same time, frequency or code domain), the improved spectral efficiency and user fairness are provided in NOMA, which is different compared with traditional orthogonal multiple access (OMA) In particular, the transmitter experiences superposing signal from multiple users while successive interference cancellation (SIC) is implemented at the receivers which are required to separate the mixture signals in the power domain [23]. Specifically, in [24], a cooperativenetwork and NOMA are employed to form the NOMA (C-NOMA) scheme and then this scheme is facilitated in NOMA-based cellular network with multiple users. In their system, relays are adopted to assist the users with weak channel conditions while users with strong channel conditions acted as such relay. In [25], ergodic capacity and outage probability were determined to measure the quality of NOMA transmission in a cellular system.  
However, a limited energy situation exists in the relay node in this C-NOMA. It is hard to replace the battery and/or there is no power line. The energy from the surrounding environments can be reused to address this problem, i.e., via an energy harvesting technique. Regarding radio frequency (RF) energy harvesting [26], stable energy supply can be achieved and such an energy harvesting scheme has been widely studied in cooperative networks in which relay harvests the energy from the radio-frequency signals [27; 28]. An HSTRN using the NOMA scheme was proposed [29], in which a user with better channel condition is adopted as a relay node and forwarded the information to other users. The satellite in the downlink is considered in the scenario in which a relay node is employed to retransmit the NOMA signal from the satellite [30]. To validate the effectiveness of the proposed system model, and the closed-form outage probability expressions are derived. However, works [29; 30] mainly conducted performance evaluation based on a fixed power source at the relay, without considering energy harvesting strategy in a scenario where relay can harvest energy from the satellite directly.