A Unified NOMA Framework in Beam-Hopping Satellite Communication Systems

This article investigates the application of a unified nonorthogonal multiple access framework in beam hopping (U-NOMA-BH)-based satellite communication systems. More specifically, the proposed U-NOMA-BH framework can be applied to code-domain NOMA-based BH (CD-NOMA-BH) and power-domain NOMA-based BH (PD-NOMA-BH) systems. To satisfy dynamic-uneven traffic demands, we formulate the optimization problem to minimize the square of discrete difference by jointly optimizing power allocation, carrier assignment, and beam scheduling. The nonconvexity of the objective function and the constraint condition is solved through Dinkelbach's transform and variable relaxation. As a further development, the closed-form and asymptotic expressions of outage probability are derived for the CD/PD-NOMA-BH systems. Based on approximated results, the diversity orders of a pair of users are obtained in detail. In addition, the system throughput of the U-NOMA-BH is discussed in a delay-limited transmission mode. Numerical results verify that: 1) the gap between traffic requests of the CD/PD-NOMA-BH systems appears to be more closely compared with orthogonal multiple access-based BH (OMA-BH); 2) the CD-NOMA-BH system is capable of providing the enhanced traffic request and capacity provision; and 3) the outage behaviors of the CD/PD-NOMA-BH are better than that of OMA-BH.