  Non-Orthogonal Multiple Access (NOMA) and Fog Radio Access Networks (FRAN)
are promising candidates within the 5G and beyond systems. This work examines
the benefit of adopting NOMA in an FRAN architecture with constrained capacity
fronthaul. The paper proposes methods for optimizing joint scheduling and power
adaptation in the downlink of a NOMA-based FRAN with multiple resource blocks
(RB). We consider a mixed-integer optimization problem which maximizes a
network-wide rate-based utility function subject to fronthaul-capacity
constraints, so as to determine i) the user-to-RB assignment, ii) the allocated
power to each RB, and iii) the power split levels of the NOMA users in each RB.
The paper proposes a feasible decoupled solution for such non-convex
optimization problem using a three-step hybrid centralized/distributed
approach. The proposed solution complies with FRAN operation that aims to
partially shift the network control to the FAPs, so as to overcome delays due
to fronthaul rate constraints. The paper proposes and compares two distinct
methods for solving the assignment problem, namely the Hungarian method, and
the Multiple Choice Knapsack method. The power allocation and the NOMA power
split optimization, on the other hand, are solved using the alternating
direction method of multipliers (ADMM). Simulations results illustrate the
advantages of the proposed methods compared to different baseline schemes
including the conventional Orthogonal Multiple Access (OMA), for different
utility functions and different network environments.
