  In this paper, facilitated via the flexible software defined structure of the
radio access units in 5G, we propose a novel dynamic multiple access technology
selection among orthogonal multiple access (OMA) and non-orthogonal multiple
access (NOMA) techniques for each subcarrier. For this setup, we formulate a
joint resource allocation problem where a new set of access technology
selection parameters along with power and subcarrier are allocated for each
user based on each user's channel state information. Here, we define a novel
utility function taking into account the rate and costs of access technologies.
This cost reflects both the complexity of performing successive interference
cancellation and the complexity incurred to guarantee a desired bit error rate.
This utility function can inherently demonstrate the trade-off between OMA and
NOMA. Due to non-convexity of our proposed resource allocation problem, we
resort to successive convex approximation where a two-step iterative algorithm
is applied in which a problem of the first step, called access technology
selection, is transformed into a linear integer programming problem, and the
nonconvex problem of the second step, referred to power allocation problem, is
solved via the difference-of-convex-functions (DC) programming. Moreover, the
closed-form solution for power allocation in the second step is derived. For
diverse network performance criteria such as rate, simulation results show that
the proposed new dynamic access technology selection outperforms
single-technology OMA or NOMA multiple access solutions.
