This paper investigates a semi-grant-free (SGF) access scheme for satellite communication systems, where one earth station (ES) and many mobile terminals (MTs) desire to access the satellite network simultaneously via uplink non-orthogonal multiple access (NOMA). We first propose two NOMA assisted SGF transmission schemes according to the availability of different channel state information (CSI). When perfect CSI is available, the satellite broadcasts an instantaneous access threshold to all MTs to enable dynamic power control (DPC), thus guaranteeing the quality of service of the ES. Otherwise, with the introduction of a statistical access threshold, a novel DPC with probability constraint is proposed to fulfill a satisfactory transmission. Next, we propose a new probability density function to characterize the shadowed-Rician distribution with estimation error, with which closed-form system throughput expressions under the proposed schemes are derived. Finally, computer simulations validate the effectiveness and superiority of our analysis and reveal the impact of CSI errors on the system performance.

This paper investigates a semi-grant-free (SGF) based transmission strategy to provide a flexible connectivity for various kinds of users in an integrated satellite-aerial-terrestrial network (ISATN). Herein, a high-altitude platform (HAP) termed as a grant-based user (GBU), which serves multiple mobile terminals (MTs) through space division multiple access (SDMA), wants to access a satellite network with multiple earth stations (ESs) termed as grant-free users (GFUs) simultaneously via non-orthogonal multiple access (NOMA) assisted SGF. To this end, we first propose two SGF-based uplink transmission schemes for both perfect channel state information (CSI) and imperfect CSI cases. When perfect CSI is available, a zero-forcing based beamforming (BF) scheme is used in HAP network while an adaptive transmit power allocation (ATPA) approach is adopted for SGF transmission. When only imperfect CSI is available, BF scheme employing the derived channel correlation matrix of HAP-MT link is proposed to achieve SDMA, and a novel ATPA strategy with rate probability constraint is proposed to guarantee quality-of-service of the GBU. Next, we derive the closed-form throughput expressions to evaluate the performance of the considered ISATN with the proposed two SGF-based schemes. Finally, computer simulations are conducted to validate the theoretical performance analysis and show the superiority of the proposed schemes over the related works. Moreover, our numerical results not only demonstrate a satisfactory performance of the proposed SGF-based scheme using imperfect CSI, but also reveal the impact of CSI errors on the system performance.

This paper proposes a novel bi-directional non-orthogonal multiple access (NOMA)-based cooperative underlay satellite-terrestrial network (CUSTN), in which two secondary satellite users can serve as a potential relay for each user, thus gaining higher cooperative diversity order (DO). We analyze the exact and asymptotic outage probabilities (OPs) of both users under a multi-antenna setup and a practical residual hardware impairment (RHI) consideration. Numerical results are provided to validate the analysis, reveal the impacts of key parameters on the system performance, and demonstrate the advantages of our proposed scheme over other benchmarks.

In this paper, we investigate the outage performance of an uplink (UL) non-orthogonal multiple access (NOMA)-based hybrid satellite-terrestrial relay network (HSTRN), in which two users communicate with the satellite through a decode-and-forward (DF) relay due to the lack of direct link. To provide a comprehensive yet hitherto unexplored outage analysis framework, we consider a more generalized channel model, i.e., the terrestrial and satellite links, respectively, undergo$\alpha -\mu $and$\kappa -\mu $shadowed fadings. Under fixed power allocation (FPA) for both multiple access phase and relaying phase, we firstly study three successive interference cancellation (SIC) decoding schemes, of which the first two are refined from existing schemes, while the third one, named asextended SIC (ESIC), is proposed in this paper to satisfy the quality of service (QoS) decoding criterion, which is shown to offer better performances for both users as compared to the former two SIC schemes. We also propose a novel dynamic power allocation (DPA) scheme for the multiple access phase, termed asenhanced DPA (EDPA), to overcome both users’ error floor (EF) issue yet provide better user fairness than the conventional DPA in the literature. We then analyze the exact and asymptotic outage performance for three SIC and theEDPAschemes under the generalized channel setting. It is shown that both the proposedESICandEDPAcan circumvent the EF issue and moreover, each has its own advantage in terms of the diversity order (DO). Our results also reveal that there exists a trade-off betweenESICandEDPA, since the former requires a premise on users’ targets rates to overcome the EF and once this premise is satisfied, no DO degradation will occur, while the latter does not entail such a premise but may face potential DO degradation. Finally, we present numerical results to verify the theoretical analysis, manifest the impacts of key parameters on the system performance, and demonstrate the advantages of our proposed network over other benchmarks.

This paper investigates the outage performance of a novel two-user non-orthogonal multiple access (NOMA)-based hybrid satellite-terrestrial relay network (HSTRN), where one user has direct link to the satellite (termed as direct-link user), while the other user needs to seek the help of the direct-link user or a dedicated relay to acquire its desired signal. An adaptive switch-and-stay combining relaying (ASSCR) scheme is proposed for boosting the system performance without excessive use of relaying resources of the network. Exact and asymptotic expressions of the outage probabilities (OPs) of both users are derived under the fixed-gain (FG) amplify-and-forward (AF) protocol. Finally, numerical results are presented to verify the theoretical analysis, manifest the impacts of key parameters on the system performance, and demonstrate the advantages of our proposed network over other benchmarks.

In this paper, the outage performance of nonorthogonal multiple access (NOMA) based coordinated direct and relay transmission (CDRT) system is analyzed. Exact and asymptotic outage probabilities of both cell-center user (CCU) and celledge user (CEU) are derived. Our analysis is conducted based on the independent but not identically distributed (i.n.i.d) Nakagami-m fading model and the fixed-gain amplify-and-forward relaying protocol, and hence the result is applicable to general relay-aided communications, where only statistical channel state information is available. Monte Carlo simulation results are provided to verify the accuracy of the derived analytical expressions with comparison to conventional orthogonal multiple access (OMA) counterpart as well as the decode-and-forward NOMA-based CDRT, demonstrating the superiority of the proposed scheme.