The 4th generation of communication networks (4G) seems limited and unable to satisfy the growing networks’ performances demands of new intended communication services such as the internet-of-things (IoTs). The 5th generation of communication networks (5G) has therefore been envisaged to fill the gap. The non-orthogonal multiple access (NOMA) technology and the satellite communication have been identified as key enabling technologies for the achievement of 5G networks. There are many ongoing NOMA related works for 5G; however, the few existing reviews mostly discuss works that apply NOMA to terrestrial networks. This paper therefore, gives a comprehensive and up-to-date review of existing works applying NOMA to satellite communication networks. More precisely, it presents studies that have either designed or do performance analysis of NOMA-based multibeam satellitesystems (MBSSs) or integrated satellite-terrestrial networks (ISTNs). The surveys presented showed that the application of NOMA to satellite communications for 5G is starting to gain considerable interest. Most of the current PD-NOMA design works attempt to maximize the system capacity (sum-rate), and most of the current PD-NOMA performance analysis works demonstrate the superiority of NOMA over OMA through Ergodic Capacity and Outage probability estimations. The surveys also showed that this field is still quite opened for research, with issues such as user-fairness maximization, satellite capacity improvement, ground-surface moving beams (for LEOs and MEOs satellites) and multiple gateways combination … etc. remaining prospective research areas to be explored.
Non‐Orthogonal Multiple‐Access (NOMA)‐based Multibeam Satellite Networks (MBSNs) are intended for 5G implementation, and 5G networks set the requirement for both high system capacity as well as high system reliability to all users, which is achieved via high system's fairness. The NOMA network requires a user grouping algorithm (UGA), and most existing UGAs for 2‐users NOMA‐MBSNs, favor the system's capacity maximization with little regard to the system's fairness. Thus, this paper proposes a UGA that maximizes the fairness of 2‐users NOMA‐MBSNs. The algorithm seeks to group 2M users into M‐pairs satisfying three requirements, (i) a minimum channel‐gain margin; (ii) high channel‐correlation coefficients; and (iii) there is high fairness amongst the resulting pairs, in term of their respective channel‐correlation coefficients, to increase the users' fairness of the system. To achieve this, the 2M users are split into two sets of M‐far and M‐near users based on users' channel gains for pairing far and near users with high channel‐correlation coefficients. It will turn it into a maximization Bipartite Matching problem (BPMP) of channel‐correlation coefficients. The BPMP is addressed by means of the Hungarian Method (HM) to ensure high fairness amongst resulting pairs regarding their channel‐correlation coefficients. The proposed UGA demonstrates superior fairness compared to existing UGAs.
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