  In this paper, we study power-efficient resource allocation for multicarrier
non-orthogonal multiple access (MC-NOMA) systems. The resource allocation
algorithm design is formulated as a non-convex optimization problem which
jointly designs the power allocation, rate allocation, user scheduling, and
successive interference cancellation (SIC) decoding policy for minimizing the
total transmit power. The proposed framework takes into account the
imperfection of channel state information at transmitter (CSIT) and quality of
service (QoS) requirements of users. To facilitate the design of optimal SIC
decoding policy on each subcarrier, we define a channel-to-noise ratio outage
threshold. Subsequently, the considered non-convex optimization problem is
recast as a generalized linear multiplicative programming problem, for which a
globally optimal solution is obtained via employing the branch-and-bound
approach. The optimal resource allocation policy serves as a system performance
benchmark due to its high computational complexity. To strike a balance between
system performance and computational complexity, we propose a suboptimal
iterative resource allocation algorithm based on difference of convex
programming. Simulation results demonstrate that the suboptimal scheme achieves
a close-to-optimal performance. Also, both proposed schemes provide significant
transmit power savings than that of conventional orthogonal multiple access
(OMA) schemes.
